US20090135754A1 - Interference management in a wireless communication system using overhead channel power control - Google Patents

Abstract

Interference that occurs during wireless communication may be managed by reducing the power level of an overhead channel during a call. A method, apparatus and medium of communication determine an optimized reduced power level for an overhead channel of an unplanned access point to an associated access terminal during a call therebetween. The overhead channel is transmitted according to the optimized reduced power level resulting in a decrease in interference as seen by neighboring unplanned access points.

Description

CLAIM OF PRIORITY UNDER 35 U.S.C. §119
• This application claims the benefit of and priority to commonly owned U.S. Provisional Patent Application No. 60/990,541, filed Nov. 27, 2007, and assigned Attorney Docket No. 080324P1; U.S. Provisional Patent Application No. 60/990,547, filed Nov. 27, 2007, and assigned Attorney Docket No. 080325P 1; U.S. Provisional Patent Application No. 60/990,459, filed Nov. 27, 2007, and assigned Attorney Docket No. 080301P1; U.S. Provisional Patent Application No. 60/990,513, filed Nov. 27, 2007, and assigned Attorney Docket No. 080330P1; U.S. Provisional Patent Application No. 60/990,564, filed Nov. 27, 2007, and assigned Attorney Docket No. 080323P1; and U.S. Provisional Patent Application No. 60/990,570, filed Nov. 27, 2007, and assigned Attorney Docket No. 08033 IP 1, the disclosure of each of which is hereby incorporated by reference herein.
CROSS-REFERENCE TO RELATED APPLICATION
• This application is related to concurrently filed and commonly owned:
• U.S. patent application Ser. No. ______, entitled “INTERFERENCE MANAGEMENT IN A WIRELESS COMMUNICATION SYSTEM USING BEAM AND NULL STEERING,” and assigned Attorney Docket No. 080324;
• U.S. patent application Ser. No. ______, entitled “INTERFERENCE MANAGEMENT IN A WIRELESS COMMUNICATION SYSTEM USING FREQUENCY SELECTIVE TRANSMISSION,” and assigned Attorney Docket No. 080301;
• U.S. patent application Ser. No. ______, entitled “INTERFERENCE MANAGEMENT IN A WIRELESS COMMUNICATION SYSTEM USING ADAPTIVE PATH LOSS ADJUSTMENT,” and assigned Attorney Docket No. 080330;
• U.S. patent application Ser. No. ______, entitled “INTERFACE MANAGEMENT IN A WIRELESS COMMUNICATION SYSTEM USING SUBFRAME TIME REUSE,” and assigned Attorney Docket No. 080323; and
• U.S. patent application Ser. No. ______, entitled “INTERFACE MANAGEMENT IN WIRELESS COMMUNICATION SYSTEM USING HYBRID TIME REUSE,” and assigned Attorney Docket No. 080331; the disclosure of each of which is hereby incorporated by reference herein.
BACKGROUND
• 1. Field
• This application relates generally to wireless communication and more specifically, but not exclusively, to improving communication performance.
• 2. Introduction
• Wireless communication systems are widely deployed to provide various types of communication (e.g., voice, data, multimedia services, etc.) to multiple users. As the demand for high-rate and multimedia data services rapidly grows, there lies a challenge to implement efficient and robust communication systems with enhanced performance.
• To supplement conventional mobile phone network base stations, small-coverage base stations may be deployed (e.g., installed in a user's home) to provide more robust indoor wireless coverage to mobile units. Such small-coverage base stations are generally known as access points, base stations, Home NodeBs, or femto cells. Typically, such small-coverage base stations are connected to the Internet and the mobile operator's network via a DSL router or a cable modem.
• Since radio frequency (“RF”) coverage of small-coverage base stations may not be optimized by the mobile operator and deployment of such base stations may be ad-hoc, RF interference issues may arise. Moreover, soft handover may not be supported for small-coverage base stations. Lastly a mobile station may not be allowed to communicate with the access point which has the best RF signal due to restricted association (i.e., closed subscriber group) requirement. Thus, there is a need for improved interference management for wireless networks.
SUMMARY
• The disclosure relates to managing interference through determination of an optimal power level for an overhead (i.e., control) channel for a call between an access point and an associated access terminal. By optimizing an overhead signal at a first access point, the total perceived interference at a neighboring access terminal is reduced. In one exemplary embodiment, a method of communication includes determining an optimized power level for an overhead channel of an unplanned access point to an associated access terminal during a call therebetween. When the optimized power level is determined, the overhead channel is transmitted from the unplanned access point at the optimized power level to an associated access terminal.
• In another exemplary embodiment, an apparatus for communication includes an interference controller configured to determine an optimized power level for an overhead channel of an unplanned access point to an associated access terminal during a call therebetween. When the optimized power level has been determined, a communication controller transmits the overhead channel from the unplanned access point at the optimized power level to the associated access terminal.
BRIEF DESCRIPTION OF THE DRAWINGS
• These and other sample aspects of the disclosure will be described in the detailed description and the appended claims that follow, and in the accompanying drawings, wherein:
• FIG. 1 is a simplified block diagram of several sample aspects of a communication system;
• FIG. 2 is a simplified block diagram illustrating several sample aspects of components in a sample communication system;
• FIG. 3 is a flowchart of several sample aspects of operations that may be performed to manage interference;
• FIG. 4 is a simplified diagram of a wireless communication system;
• FIG. 5A is a simplified diagram of a wireless communication system including femto nodes;
• FIG. 5B is a simplified diagram of a specific arrangement of femto nodes and access terminals illustrating negative geometries;
• FIG. 6 is a simplified diagram illustrating coverage areas for wireless communication;
• FIG. 7 is a flowchart of several sample aspects of operations that may be performed to manage interference through the use of beam and null steering;
• FIG. 8 is a flowchart of several sample aspects of operations that may be performed to manage interference through the use of optimized reduced power levels for an overhead channel;
• FIG. 9 is a flowchart of several sample aspects of operations that may be performed to manage interference through the use of optimized reduced power levels for an overhead channel;
• FIG. 10 is a flowchart of several aspects of operations that may be performed to manage interference through the use of frequency selective transmission to address jamming and negative geometries;
• FIGS. 11A-11B are flowcharts of several aspects of operations that may be performed to manage interference through the use of adaptive noise figure and path loss adjustment;
• FIG. 12 is a flowchart of several aspects of operations that may be performed to manage interference through the use of subframe time reuse techniques;
• FIG. 13 is a slot diagram illustrating time sharing among femto nodes that may be performed to manage interference through the use of hybrid time reuse techniques;
• FIG. 14 is a flowchart of several aspects of operations that may be performed to manage interference through the use of hybrid time reuse;
• FIG. 15 is a simplified block diagram of several sample aspects of communication components; and
• FIGS. 16-21 are simplified block diagrams of several sample aspects of apparatuses configured to manage interference as taught herein.
• In accordance with common practice the various features illustrated in the drawings may not be drawn to scale. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all of the components of a given apparatus (e.g., device) or method. Finally, like reference numerals may be used to denote like features throughout the specification and figures.
DETAILED DESCRIPTION
• Various aspects of the disclosure are described below. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative. Based on the teachings herein one skilled in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. Furthermore, an aspect may comprise at least one element of a claim.
• In some aspects the teachings herein may be employed in a network that includes macro scale coverage (e.g., a large area cellular network such as a 3G networks, typically referred to as a macro cell network) and smaller scale coverage (e.g., a residence-based or building-based network environment). As an access terminal (“AT”) moves through such a network, the access terminal may be served in certain locations by access nodes (“ANs”) that provide macro coverage while the access terminal may be served at other locations by access nodes that provide smaller scale coverage. In some aspects, the smaller coverage nodes may be used to provide incremental capacity growth, in-building coverage, and different services (e.g., for a more robust user experience). In the discussion herein, a node that provides coverage over a relatively large area may be referred to as a macro node. A node that provides coverage over a relatively small area (e.g., a residence) may be referred to as a femto node. A node that provides coverage over an area that is smaller than a macro area and larger than a femto area may be referred to as a pico node (e.g., providing coverage within a commercial building).
• A cell associated with a macro node, a femto node, or a pico node may be referred to as a macro cell, a femto cell, or a pico cell, respectively. In some implementations, each cell may be further associated with (e.g., divided into) one or more sectors.
• In various applications, other terminology may be used to reference a macro node, a femto node, or a pico node. For example, a macro node may be configured or referred to as an access node, base station, access point, eNodeB, macro cell, and so on. Also, a femto node may be configured or referred to as a Home NodeB, Home eNodeB, access point, base station, femto cell, and so on.
• FIG. 1 illustrates sample aspects of acommunication system100 where distributed nodes (e.g.,access points102,104, and106) provide wireless connectivity for other nodes (e.g.,access terminals108,110, and112) that may be installed in or that may roam throughout an associated geographical area. In some aspects, theaccess points102,104, and106 may communicate with one or more network nodes (e.g., a centralized network controller such as network node114) to facilitate wide area network connectivity.
• An access point such asaccess point104 may be restricted whereby only certain access terminals (e.g., access terminal110) are allowed to access the access point, or the access point may be restricted in some other manner. In such a case, a restricted access point and/or its associated access terminals (e.g., access terminal110) may interfere with other nodes in thesystem100 such as, for example, an unrestricted access point (e.g., macro access point102), its associated access terminals (e.g., access terminal108), another restricted access point (e.g., access point106), or its associated access terminals (e.g., access terminal112). For example, the closest access point to given access terminal may not be the serving access points for that access terminal. Consequently, transmissions by that access terminal may interfere with reception at the access terminal. As discussed herein, frequency reuse, frequency selective transmission, interference cancellation and smart antenna (e.g., beamforming and null steering) and other techniques may be employed to mitigate interference.
• Sample operations of a system such as thesystem100 will be discussed in more detail in conjunction with the flowchart ofFIG. 2. For convenience, the operations ofFIG. 2 (or any other operations discussed or taught herein) may be described as being performed by specific components (e.g., components of thesystem100 and/or components of asystem300 as shown inFIG. 3). It should be appreciated, however, that these operations may be performed by other types of components and may be performed using a different number of components. It also should be appreciated that one or more of the operations described herein may not be employed in a given implementation.
• For illustration purposes various aspects of the disclosure will be described in the context of a network node, an access point, and an access terminal that communicate with one another. It should be appreciated, however, that the teachings herein may be applicable to other types of apparatuses or apparatuses that are referred to using other terminology.
• FIG. 3 illustrates several sample components that may be incorporated into the network node114 (e.g., a radio network controller), theaccess point104, and theaccess terminal110 in accordance with the teachings herein. It should be appreciated that the components illustrated for a given one of these nodes also may be incorporated into other nodes in thesystem100.
• Thenetwork node114, theaccess point104, and theaccess terminal110 includetransceivers302,304, and306, respectively, for communicating with each other and with other nodes. Thetransceiver302 includes atransmitter308 for sending signals and areceiver310 for receiving signals. Thetransceiver304 includes atransmitter312 for transmitting signals and areceiver314 for receiving signals. Thetransceiver306 includes atransmitter316 for transmitting signals and areceiver318 for receiving signals.
• In a typical implementation, theaccess point104 communicates with theaccess terminal110 via one or more wireless communication links and theaccess point104 communicates with thenetwork node114 via a backhaul. It should be appreciated that wireless or non-wireless links may be employed between these nodes or other in various implementations. Hence, thetransceivers302,304, and306 may include wireless and/or non-wireless communication components.
• Thenetwork node114, theaccess point104, and theaccess terminal110 also include various other components that may be used in conjunction with interference management as taught herein. For example, thenetwork node114, theaccess point104, and theaccess terminal110 may includeinterference controllers320,322, and324, respectively, for mitigating interference and for providing other related functionality as taught herein. Theinterference controller320,322, and324 may include one or more components for performing specific types of interference management. Thenetwork node114, theaccess point104, and theaccess terminal110 may includecommunication controllers326,328, and330, respectively, for managing communications with other nodes and for providing other related functionality as taught herein. Thenetwork node114, theaccess point104, and theaccess terminal110 may include timingcontrollers332,334, and336, respectively, for managing communications with other nodes and for providing other related functionality as taught herein. The other components illustrated inFIG. 3 will be discussed in the disclosure that follows.
• For illustrations purposes, theinterference controller320 and322 are depicted as including several controller components. In practice, however, a given implementation may not employ all of these components. Here, a hybrid automatic repeat request (HARQ)controller component338 or340 may provide functionality relating to HARQ interlace operations as taught herein. Aprofile controller component342 or344 may provide functionality relating to transmit power profile or receive attenuation operations as taught herein. Atimeslot controller component346 or348 may provide functionality relating to timeslot portion operations as taught herein. Anantenna controller component350 or352 may provide functionality relating to smart antenna (e.g., beamforming and/or null steering) operations as taught herein. A receivenoise controller component354 or356 may provide functionality relating to adaptive noise figure and path loss adjustment operations as taught herein. A transmitpower controller component358 or360 may provide functionality relating to transmit power operations as taught herein. A timereuse controller component362 or364 may provide functionality relating to time reuse operations as taught herein.
• FIG. 2 illustrates how thenetwork node114, theaccess point104, and theaccess terminal110 may interact with one another to provide interference management (e.g., interference mitigation). In some aspects, these operations may be employed on an uplink and/or on a downlink to mitigate interference. In general, one or more the techniques described byFIG. 2 may be employed in the more specific implementations that are described in conjunction withFIGS. 7-14 below. Hence, for purposes of clarity, the descriptions of the more specific implementations may not describe these techniques again in detail.
• As represented byblock202, the network node114 (e.g., the interference controller320) may optionally define one or more interference management parameters for theaccess point104 and/or theaccess terminal110. Such parameters may take various forms. For example, in some implementations thenetwork node114 may define types of interference management information. Examples of such parameters will be described in more detail below in conjunction withFIGS. 7-14.
• In some aspects, the definition of interference parameters may involve determining how to allocate one or more resources. For example, the operations of block402 may involve defining how an allocated resource (e.g., a frequency spectrum, etc.) may be divided up for fractional reuse. In addition, the definition of fraction reuse parameters may involve determining how much of the allocated resource (e.g., how many HARQ interlaces, etc.) may be used by any one of a set of access points (e.g., restricted access points). The definition of fraction reuse parameters also may involve determining how much of the resource may be used by a set of access points (e.g., restricted access points).
• In some aspects, thenetwork node114 may define a parameter based on received information that indicates whether there may be interference on an uplink or a downlink and, if so, the extent of such interference. Such information may be received from various nodes in the system (e.g., access points and/or access terminals) and in various ways (e.g., over a backhaul, over-the-air, and so on).
• For example, in some cases one or more access points (e.g., the access point104) may monitor an uplink and/or a downlink and send an indication of interference detected on the uplink and/or downlink to the network node114 (e.g., on a repeated basis or upon request). As an example of the former case, theaccess point104 may calculate the signals strength of signals it receives from nearby access terminals that are not associated with (e.g., served by) the access point104 (e.g.,access terminals108 and112) and report this to thenetwork node114.
• In some cases, each of the access points in the system may generate a load indication when they are experiencing relatively high loading. Such an indication may take the form of, for example, a busy bit in 1xEV-DO, a relative grant channel (“RGCH”) in 3GPP, or some other suitable form. In a conventional scenario, an access point may send this information to its associated access terminal via a downlink. However, such information also may be sent to the network node114 (e.g., via the backhaul).
• In some cases, one or more access terminals (e.g., the access terminal110) may monitor downlink signals and provide information based on this monitoring. Theaccess terminal110 may send such information to the access point104 (e.g., which may forward the information to the network node114) or to the network node114 (via the access point104). Other access terminals in the system may send information to thenetwork node114 in a similar manner.
• In some cases, theaccess terminal110 may generate measurement reports (e.g., on repeated basis). In some aspects, such a measurement report may indicate which access points theaccess terminal110 is receiving signals from, a received signal strength indication associated with the signals from each access point (e.g., Ec/Io), the path loss to each of the access points, or some other suitable type of information. In some cases a measurement report may include information relating to any load indications theaccess terminal110 received via a downlink.
• Thenetwork node114 may then use the information from one or more measurement reports to determine whether theaccess point104 and/or theaccess terminal110 are relatively close to another node (e.g., another access point or access terminal). In addition, thenetwork node114 may use this information to determine whether any of these nodes interfere with any other one of these nodes. For example, thenetwork node114 may determine received signal strength at a node based on the transmit power of a node that transmitted the signals and the path loss between these nodes.
• In some cases, theaccess terminal110 may generate information that is indicative of the signal to noise ratio (e.g., signal and interference to noise ratio, SINR) on a downlink. Such information may comprise, for example a channel quality indication (“CQI”), a data rate control (“DRC”) indication, or some other suitable information. In some cases, this information may be sent to theaccess point104 and theaccess point104 may forward this information to thenetwork node114 for use in interference management operations. In some aspects, thenetwork node114 may use such information to determine whether there is interference on a downlink or to determine whether interference in the downlink is increasing or decreasing.
• As will be described in more detail below, in some cases the interference-related information may be used to determine how to mitigate interference. As one example, CQI or other suitable information may be received on a per-HARQ interlace basis whereby it may be determined which HARQ interlaces are associated with the lowest level of interference. A similar technique may be employed for other fractional reuse techniques.
• It should be appreciated that thenetwork node114 may define parameters in various other ways. For example, in some cases thenetwork node114 may randomly select one or more parameters.
• As represented byblock204, the network node114 (e.g., the communication controller326) sends the defined interference management parameters to theaccess point104. As will be discussed below, in some cases theaccess point104 uses these parameters and in some cases theaccess point104 forwards these parameters to theaccess terminal110.
• In some cases, thenetwork node114 may manage interference in the system by defining the interference management parameters to be used by two or more nodes (e.g., access points and/or access terminals) in the system. For example, in the case of a fractional reuse scheme, thenetwork node114 may send different (e.g., mutually exclusive) interference management parameters to neighboring access points (e.g., access points that are close enough to potentially interfere with one another). As a specific example, thenetwork node114 may assign a first HARQ interlace to theaccess point104 and assign a second HARQ interlace to theaccess point106. In this way, communication at one restricted access point may not substantially interfere with communication at the other restricted access point.
• As represented byblock206, the access point104 (e.g., the interference controller322) determines interference management parameters that it may use or that may send to theaccess terminal110. In cases where thenetwork node114 defines the interference management parameters for theaccess point104, this determination operation may simply involve receiving the specified parameters and/or retrieving the specified parameters (e.g., from a data memory).
• In some cases theaccess point104 determines the interference management parameters on its own. These parameters may be similar to the parameters discussed above in conjunction withblock202. In addition, in some cases these parameters may be determined in a similar manner as discussed above atblock202. For example, theaccess point104 may receive information (e.g., measurement reports, CQI, DRC) from theaccess terminal110. In addition, theaccess point104 may monitor an uplink and/or a downlink to determine the interference on such a link. Theaccess point104 also may randomly select a parameter.
• In some cases, theaccess point104 may cooperate with one or more other access points to determine an interference management parameter. For example, in some cases theaccess point104 may communicate with theaccess point106 to determine which parameters are being used by the access point106 (and thereby selects different parameters) or to negotiate the use of different (e.g., mutually exclusive) parameters. In some cases, theaccess point104 may determine whether it may interfere with another node (e.g., based on CQI feedback that indicates that another node is using a resource) and, if so, define its interference management parameters to mitigate such potential interference.
• As represented byblock208, the access point104 (e.g., the communication controller328) may send interference management parameters or other related information to theaccess terminal110. In some cases this information may relate to power control (e.g., specifies uplink transmit power).
• As represented byblocks210 and212, theaccess point104 may thus transmit to theaccess terminal110 on the downlink or theaccess terminal110 may transmit to theaccess point104 on the uplink. Here, theaccess point104 may use its interference management parameters to transmit on the downlink and/or receive on the uplink. Similarly, theaccess terminal110 may take these interference management parameters into account when receiving on the downlink or transmitting on the uplink.
• In some implementations the access terminal110 (e.g., the interference controller306) may define one or more interference management parameters. Such a parameter may be used by theaccess terminal110 and/or sent (e.g., by the communication controller330) to the access point104 (e.g., for use during uplink operations).
• FIG. 4 illustrates awireless communication system400, configured to support a number of users, in which the teachings herein may be implemented. Thesystem400 provides communication for multiple cells402, such as, for example,macro cells402A-402G, with each cell being serviced by a corresponding access node404 (e.g.,access nodes404A-404G). As shown inFIG. 4, access terminals406 (e.g.,access terminals406A-406L) may be dispersed at various locations throughout the system over time. Each access terminal406 may communicate with one or more access nodes404 on a downlink (DL) (also known as forward link (FL)) and/or an uplink (UL) (also known as a reverse link (RL)) at a given moment, depending upon whether the access terminal406 is active and whether it is in soft handoff, for example. Thewireless communication system400 may provide service over a large geographic region. For example,macro cells402A-402G may cover a few blocks in a neighborhood.
• As stated, a node or localized access point that provides coverage over a relatively small area (e.g., a residence) may be referred to as a femto node.FIG. 5A illustrates anexemplary communication system500 where one or more femto nodes are deployed within a network environment. Specifically, thesystem500 includes multiple femto nodes510 (e.g.,femto nodes510A and510B) installed in a relatively small scale network environment (e.g., in one or more user residences530). Each femto node510 may be coupled to a wide area network540 (e.g., the Internet) and a mobileoperator core network550 via a DSL router, a cable modem, a wireless link, or other connectivity means (not shown). As will be discussed below, each femto node510 may be configured to serve associated access terminals520 (e.g., access terminal520A) and, optionally, non-associated (alien) access terminals520 (e.g., access terminal520F). In other words, access to femto nodes510 may be restricted whereby a given access terminal520 may be served by a set of designated home femto node(s)510 but may not be served by any non-designated foreign (alien) femto nodes510 (e.g., a neighbor's femto node510).
• FIG. 5B illustrates a more detailed view of negative geometries of multiple femto nodes and access terminals within a network environment. Specifically, thefemto node510A andfemto node510B are respectively deployed in neighboringuser residence530A anduser residence530B.Access terminals520A-520C are permitted to associate and communicate withfemto node510A, but not withfemto node510B. Likewise,access terminal520D and access terminal520E are permitted to associate and communicate withfemto node510B, but not withfemto node510A.Access terminal520F and access terminal520G are not permitted to associate or communicate with eitherfemto node510A orfemto node510B.Access terminal520F and access terminal520G may be associated with a macro cell access node560 (FIG. 5A), or another femto node in another residence (not shown).
• In unplanned femto node510 deployments with restricted associations (i.e., an access point may not be allowed to associate with the “closest” femto node providing the most favorable signal quality), jamming and negative geometries can be common. Solutions to address these negative geometries will be further discussed below.
• FIG. 6 illustrates an example of acoverage map600 where several tracking areas602 (or routing areas or location areas) are defined, each of which includes several macro coverage areas604. Here, areas of coverage associated with trackingareas602A,602B, and602C are delineated by the wide lines and the macro coverage areas604 are represented by the hexagons. The tracking areas602 also include femto coverage areas606. In this example, each of the femto coverage areas606 (e.g.,femto coverage area606C) is depicted within a macro coverage area604 (e.g.,macro coverage area604B). It should be appreciated, however, that a femto coverage area606 may not lie entirely within a macro coverage area604. In practice, a large number of femto coverage areas606 may be defined with a given tracking area602 or macro coverage area604. Also, one or more pico coverage areas (not shown) may be defined within a given tracking area602 or macro coverage area604.
• Referring again toFIGS. 5A-5B, the owner of a femto node510 may subscribe to mobile service, such as, for example, 3G mobile service, offered through the mobileoperator core network550. In addition, an access terminal520 may be capable of operating both in macro environments and in smaller scale (e.g., residential) network environments. In other words, depending on the current location of the access terminal520, the access terminal520 may be served by anaccess node560 of the macro cellmobile network550 or by any one of a set of femto nodes510 (e.g., thefemto nodes510A and510B that reside within a corresponding user residence530). For example, when a subscriber is outside his home, he is served by a standard macro access node (e.g., node560) and when the subscriber is at home, he is served by a femto node (e.g.,node510A). Here, it should be appreciated that a femto node520 may be backward compatible with existing access terminals520.
• A femto node510 may be deployed on a single frequency or, in the alternative, on multiple frequencies. Depending on the particular configuration, the single frequency or one or more of the multiple frequencies may overlap with one or more frequencies used by a macro node (e.g., node560).
• In some aspects, an access terminal520 may be configured to connect to a preferred femto node (e.g., the home femto node of the associated access terminal520) whenever such connectivity is possible. For example, whenever the access terminal520 is within the user'sresidence530, it may be desired that the access terminal520 communicate only with the home femto node510.
• In some aspects, if the access terminal520 operates within the macrocellular network550 but is not residing on its most preferred network (e.g., as defined in a preferred roaming list), the access terminal520 may continue to search for the most preferred network (e.g., the home femto node510) using a Better System Reselection (“BSR”), which may involve a periodic scanning of available systems to determine whether better systems are currently available, and subsequent efforts to associate with such preferred systems. With the acquisition entry, the access terminal520 may limit the search for specific band and channel. For example, the search for the most preferred system may be repeated periodically. Upon discovery of a preferred femto node510, the access terminal520 selects the femto node510 for camping within its coverage area.
• A femto node may be restricted in some aspects. For example, a given femto node may only provide certain services to certain access terminals. In deployments with so-called restricted (or closed) association, a given access terminal may only be served by the macro cell mobile network and a defined set of femto nodes (e.g., the femto nodes510 that reside within the corresponding user residence530). In some implementations, a node may be restricted to not provide, for at least one node, at least one of: signaling, data access, registration, paging, or service.
• In some aspects, a restricted or foreign (alien) femto node (which may also be referred to as a Closed Subscriber Group Home NodeB) is one that provides service to a restricted provisioned set of access terminals. This set may be temporarily or permanently extended as necessary. In some aspects, a Closed Subscriber Group (“CSG”) may be defined as the set of access nodes (e.g., femto nodes) that share a common access control list of access terminals. A channel on which all femto nodes (or all restricted femto nodes) in a region operate may be referred to as a femto channel.
• Various relationships may thus exist between a given femto node and a given access terminal. For example, from the perspective of an access terminal, an open femto node may refer to a femto node with no restricted association. A restricted femto node may refer to a femto node that is restricted in some manner (e.g., restricted for association and/or registration). A home femto node may refer to a femto node on which the access terminal is authorized to access and operate on. A guest femto node may refer to a femto node on which an access terminal is temporarily authorized to access or operate on. A restricted or foreign (alien) femto node may refer to a femto node on which the access terminal is not authorized to access or operate on, except for perhaps emergency situations (e.g., 911 calls).
• From a restricted or foreign femto node perspective, an associated or home access terminal may refer to an access terminal that authorized to access the restricted femto node. A guest access terminal may refer to an access terminal with temporary access to the restricted femto node. A non-associated (alien) access terminal may refer to an access terminal that does not have permission to access the restricted femto node, except for perhaps emergency situations, for example, such as 911 calls (e.g., an access terminal that does not have the credentials or permission to register with the restricted femto node).
• For convenience, the disclosure herein describes various functionality in the context of a femto node. It should be appreciated, however, that a pico node may provide the same or similar functionality for a larger coverage area. For example, a pico node may be restricted, a home pico node may be defined for a given access terminal, and so on.
• A wireless multiple-access communication system may simultaneously support communication for multiple wireless access terminals. As mentioned above, each terminal may communicate with one or more base stations via transmissions on the downlink (forward link) and uplink (reverse link). The downlink refers to the communication link from the base stations to the terminals, and the uplink refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out system, a multiple-in-multiple-out (“MIMO”) system, or some other type of system.
• A MIMO system employs multiple (NT) transmit antennas and multiple (N_R) receive antennas for data transmission. A MIMO channel formed by the NT transmit and N_Rreceive antennas may be decomposed into N_Sindependent channels, which are also referred to as spatial channels, where N_S≦min{N_T, N_R}. Each of the N_Sindependent channels corresponds to a dimension. The MIMO system may provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
• A MIMO system may support time division duplex (“TDD”) and frequency division duplex (“FDD”). In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the downlink (forward link) channel from the uplink (reverse link) channel. This enables the access point to extract transmit beam-forming gain on the downlink when multiple antennas are available at the access point.
• As stated, in unplanned base station deployments with restricted association (i.e., a mobile station is not allowed to associate with the “closest” base station to which it has the strongest link), jamming and negative geometries can be common. In one exemplary embodiment spatially described in conjunction withFIG. 5B, thefemto node510A andfemto node510B are deployed in neighboring residences.Access terminals520A-520C are permitted to associate and communicate withfemto node510A, but not withfemto node510B. Likewise,access terminals520D-520E are permitted to associate and communicate withfemto node510B, but not withfemto node510A.Access terminals520F-520G are not permitted to associate or communicate with eitherfemto nodes510A-510B.Access terminals520F-520G may be associated with a macro cell access node560 (FIG. 5A), or another femto node in another residence (not shown). Accordingly, such negative geometries respecting access-permitted femto nodes and neighboring access terminals may result if various interfering or jamming conditions on the uplink and downlink.
• Uplink Jamming
• By way of example, let L_A3(dB) and L_A5(dB) be the path loss betweenfemto node510A and access terminal520C andaccess terminal520D, respectively. In particular, L_A3may be much larger than L_A5. Thus, whenaccess terminal520D transmits to itshome femto node510B, it causes excessive interference (or jamming) atfemto node510A, effectively blocking the reception ofaccess terminals520A-C atfemto node510A. In this uplink jamming situation, even ifaccess terminal520C transmits at its maximum Tx power P_3max, the received C/I for access terminal atfemto node510A may be characterized as:
• 
  C/I(AT520Catfemto node 510A)=P_3max−L_A3−(P₅−L_A5) (dB)
• In some exemplary embodiments, depending on the transmit power P₅, the C/I ofaccess terminal520C atfemto node510A may be a very large negative value due to the large value of L_A3. Such a configuration geometry is referred to as a highly negative uplink geometry.
• Downlink Jamming
• Similarly, in one exemplary embodiment, L_B5may be much larger than L_A5. This implies that whenfemto node510A transmits to access terminal520A, it may cause excessive interference (or jamming) ataccess terminal520D, effectively blocking the reception offemto node510B ataccess terminal520D. In this downlink jamming situation, the received C/I forfemto node510B ataccess terminal520D may be calculated as follows:
• 
  C/I(femtocellBatAT5)=P_B−L_B5−(P_A−L_A5) (dB)
• Again, the C/I offemto node510B ataccess terminal520D may be a very large negative value due to the large value of L_B5. Such a configuration geometry is referred to as a highly negative downlink geometry.
• A further practical consideration includes addressing negative geometries without necessitating modifications to the operation of deployed (legacy) access terminals. Therefore, it is desirable in the present exemplary embodiment to address interference mitigation from negative geometries through modification processes in a femto node rather than requiring modifications to access terminals. Accordingly, negative geometries at the uplink and downlink are desirably addressed according to an exemplary embodiment disclosed below.
• Referring now toFIG. 7 and with further reference toFIGS. 5A-5B, operations relating to the use of beam-steering and null-steering to address jamming and negative geometries will be described in more detail. The present exemplary embodiment uses methods and apparatus to prevent jamming and negative geometries using beamsteering and null steering in unplanned base station deployments with restricted access.
• In an exemplary femto node deployment scenario, nearby signals (desired or interference) may be Rician by nature which includes a strong directional component and flat fading across the frequency band (due to the small delay-spread and multiple reflected paths in indoor environments). Especially for jamming situations, sectorization may provide a desirable method for combating a strong Rician component of interference.
• As represented byblock702, a femto node510 continuously listens (i.e., receives according to the various receiver configurations describe herein) for transmissions from access terminals520. As represented byquery704, the femto node510 determines if an access probe (e.g., transmission) by an access terminal are directed to the femto node510. If the detected access probe of the access terminal is directed to the specific femto node510, then, as represented byblock706, no interference mitigation is necessary since the access terminal is an “associated” access terminal with the “home” femto node.
• As represented byquery708, femto node510 further compares a characteristic (e.g., power level) of the access probe for determining if the characteristic is of a sufficient threshold level to result in interference at the home femto node. When the access probe does not exceed an interference threshold, then, as represented byblock706, no interference mitigation is necessary since the characteristic of the access probe by the “home” femto node510 results in acceptable interference.
• As represented byblock710, when the home femto node510 receives a sufficiently strong (i.e., greater than an interference threshold) access probe or otherwise strong uplink transmission from the non-associated access terminal520, the home femto node510 applies beam-forming (i.e., directional transmission and reception) antennas to steer signals or lack of signals (e.g., nulls) toward the non-associated access terminal520 on the downlink and uplink.
• By way of example, beam-forming (i.e., beam-steering) may be performed using a sectorized or directional (e.g., switched beam) antenna configuration described herein for forming a transmission signal beam and/or null or a reception signal beam and/or null. Specifically, interference nulling may be provided on a received Radio Frequency (RF) signal thereby reducing problems such as front-end overload and A/D desensitization of the receiver which results from jamming femto nodes. Furthermore, sectorized or directional antenna configurations enable the downlink and uplink to maintain the same directional component for use in both link directions.
• As represented byblock712, downlink pilot and overhead transmissions, as well as traffic channel transmissions if any, are transmitted according to beam-forming such that minimal energy is directed towards a nearby non-associated access terminal. Steering a transmission signal away from a non-associated access terminal results in reduction in the negative geometry at the non-associated access terminal.
• As represented byblock714, a directional null is steered towards the nearby non-associated access terminal520 using the antenna configuration (e.g., sectorized antennas or null-steering with adaptive phased arrays) described herein. Therefore, when an associated access terminal520 attempts to communicate with the home femto node510, the associated access terminal's access probe, as well as other traffic (e.g., voice/data) communications is not jammed by the strong transmissions from the nearby non-associated access terminals having negative geometries.
• As an example, if the access point employs two separate antennas AP can monitor the AT access probe characteristics on both antennas. If it is determined that the strong uplink transmission from the non-associated access terminal at one of the antennas, AP can turn off transmit function (beam steering) and turn off receive function (null steering) on that antenna.
• As represented inquery716, periodically (e.g., once per second) the femto node510 eliminates the sectorization null in the receive direction to determine, as represented inblock702, if the strong undesired non-associated access terminal520 has moved or terminated its communication. If, as represented inquery704, the strong undesired signal has disappeared, the femto node510 can eliminate the sectorization null and continue operation with omni-directional transmit and receive, as represented inblock706. If the strong undesired signal is still present or has moved and exceeds the threshold as represented byblock708, the femto node510 can adjust the transmit and receive sectorization null steering, as represented inblock710, in the direction of the undesired non-associated access terminal520.
• The above-example with reference toFIG. 5B illustratesfemto node510A steering a receive and transmit sectorization null in the direction ofnon-associated access terminal520D as long asnon-associated access terminal520D was present and in an active call withfemto node510B. Whennon-associated access terminal520D is idle,femto node510A would revert back to operating with omnidirectional transmit and receive.
• During periods when the femto node is steering a sectorization null in a particular direction, if there are any associated access terminals520 in the same direction they would experience outage. Accordingly, an exemplary embodiment, the femto node510 steers the sectorization nulls (i) as long as the strong undesired non-associated access terminal520 is active, and (ii) only if the undesired transmission from the non-associated access terminal520 exceeds a high signal strength threshold at the receiver as determined at query408, signifying that access probes from desired associated access terminals would not be decodable at the femto node510. With reference to FIG.5B,it is noted thatfemto node510B would have no need to steer a sectorization null towardsnon-associated access terminal520A since the signal fromnon-associated access terminal520A is not very strong. Iffemto node510B steers such a sectorization null towardsnon-associated access terminal520A, the sectorization null would resulting an outage at desired associatedaccess terminal520E.
• As a general case of the described method if the AP can not determine the direction of the interference from the non-associated access terminal (e.g., very strong jamming that saturates the AP receiver) it can try different directions for beam steering and null steering to maximize the received signal quality from associated AT.
• Referring now toFIG. 8 and with further reference toFIGS. 5A-5B, operations relating to the use of optimization in transmit power on overhead channels to address jamming and negative geometries will be described in more detail. The present exemplary embodiment uses methods and apparatus to prevent jamming and negative geometries using optimized transmit power levels on overhead channels in unplanned base station deployments.
• Generally, the transmit power gain of overhead channels and total transmit power of a femto node are chosen based on the desired range of a femto node. In order to allow access terminals to acquire a femto node in a location where the access terminal is being jammed by a neighbor femto node that restricts association, the overhead channels (e.g., common control channels such as pilot, synch and broadcast/paging) may be time multiplexed. Various numbers of time scales and methods for time multiplexing are contemplated. Furthermore, the overhead channels may be turned on only periodically, for example at the slot cycle index of the associated access terminals, so that the associated access terminals may receive paging messages. In a further configuration, a femto node may not transmit any signal at all.
• However, during an active voice call or data transfer, there may be no idle periods that allow a neighbor femto node the opportunity to time multiplex the overhead channels jamming situations resulting from negative geometries. Accordingly, an exemplary embodiment describes a method for optimizing transmit power for overhead signals (e.g., pilot, synch and broadcast/paging channels) when there is an active call at a femto node and time multiplexing of overhead signals is not practical.
• For example in 1xRTT and WCDMA networks, overhead channel (e.g., pilot, page, sych. channels) gain settings are adjusted for certain performance based on geometry and coverage constraints. Furthermore, femto node deployments exhibit some significant differences when compared to macro cell access node deployments. Various differences include:
• • 1. Due to limited coverage size, maximum path loss values are much less in areas (e.g., cells) serviced by femto nodes compared to areas (e.g., cells) serviced by macro cell access nodes (e.g., 80 dB max path loss compared to 140 dB in a macrocellular deployment);
  • 2. The number of simultaneously active access terminals are fewer in cells serviced by femto nodes than in cells serviced by macro cell access nodes (e.g., 1-2 users compared to 20-40 users);
  • 3. As discussed above, due to the femto node restricted association requirements, negative geometries can be common for femto node deployments unlike for macro cell access node deployments.
• These differences can result in very different optimal power settings for overhead channels for femto nodes510. Since a femto node510 generally will have few to no active access terminals520, it would be desirable for the overhead channels to be maintained at a minimum power setting in order to minimize interference to neighboring cells serviced by femto nodes510 and cells serviced by macro cell access nodes560 (i.e., assuming co-channel operation). By way of example, one exemplary embodiment focuses on pilot channel optimization, however, the analysis can be applied to other overhead channels as well.
• In the exemplary embodiment, an optimal traffic-to-pilot (“T2P”) value for the case of a single voice call is determined as well as a default pilot power setting, Ecp_DEFAULT. When downlink (forward link) power control results in a modified ratio of traffic-to-pilot, the pilot power is adjusted so as to maintain the smallest value of total transmitted power and interference caused by the neighbor femto node.
• By way of example, anaccess terminal520A at the boundary ofhome femto node510A andneighbor femto node510B exhibits equal path loss to both femto nodes510 and theneighbor femto node520B is transmitting at full power thereby creating interference, Ior_max. In the present example, assuming thehome femto node510A is transmitting a pilot channel at a gain level, Ecp, then the pilot signal-to-noise ratio (SNR) can be written as: Ecp/Ior_max. According to the present exemplary embodiment, it is desirable to find the optimal Ecp setting that results in lowest total transmitted power from ahome femto node510A.
• As represented byblock802, the pilot channel gain level Ecp is initialized to Ecp_DEFAULT. Thus, a default value of Ecp (Ecp_DEFAULT) can be determined based on a reasonable load and path loss differential values expected in femto networks.
• As represented inblock804, a traffic call (e.g., voice call) is set up between thehome femto510A and anaccess terminal520A with the power used on traffic channel denoted as Ect. In one exemplary embodiment, the Ect value is determined by the downlink (forward link) power control, as represented byquery806. Downlink (forward link FL) power control is used to maintain the required quality of service (e.g., packet error rate, PER). Downlink (forward link FL) power controls may either designate a decrease in Ect as represented byblock808, an increase in Ect as represented byblock810, or no change in Ect.
• As represented inquery812, a determination of the packet error rate (PER) is used to identify adequate signal quality. Generally, if Ecp is very low, then channel estimation quality would degrade which will result in very large Ect. As Ecp increases, channel estimation will improve and the required Ect will go down. However, if Ecp is very large, then channel estimation quality will be higher than the required amount, which will not result any further reduction in Ect. Accordingly, when PER is inadequate, downlink (forward link FL) power control adjusts the Ect.
• Since the interference generated to other femto nodes needs to be minimized, it would be desirable to have the optimal Ecp value that results in the minimum (Ect+Ecp). As represented byblock814, Ecp_OPTIMALis determined where:
• ${\mathrm{Ecp}}_{\mathrm{OPTIMAL}}=\arg \underset{\mathrm{Ecp}}{\min }\left[\mathrm{Ecp}+f\left[\mathrm{Ecp}\right)\right]$
• • in other optimal Ecp value is found that minimizes total transmit power where Ect=f(Ecp)
  • (The function f(.) can be determined through offline simulations or tests.)
  • Then, as represented byblock816, the optimal Ect value is determined as:
• 
  Ect_OPTIMAL=f(Ecp_OPTIMAL).
• As represented byblock818, the T2P_OPTIMALis determined as:
• $T2P_{\mathrm{OPTIMAL}}=\frac{{\mathrm{Ect}}_{\mathrm{OPTIMAL}}}{{\mathrm{Ecp}}_{\mathrm{OPTIMAL}}}.$
• In another exemplary embodiment, simulations may be run to find the Ecp_OPTIMALand Ect_OPTIMALfor typical channel types expected in cells of femto nodes using, for example, flat fading models, either Rayleigh or Rician, with low Doppler that can be tracked by power control. These optimal values depend, in one exemplary embodiment, on the particular path loss differential of the access terminal to neighbor femto node and the interference power received from the neighbor femto node (e.g., if the mobile terminal has 3 dB less path loss to neighbor femto compared to home femto, then the optimal Ecp and Ect values would need to increased by 3 dB).
• On the other hand, in an alternate exemplary embodiment, if neighbor femto node is transmitting at half of Ior_max, then optimal Ecp and Ect values would need to be reduced by 3 dB. However, also note that it is not very practical to change Ecp values very frequently since it determines the handoff boundaries of the femto cell. Thus, as stated, a default value of Ecp (Ecp_DEFAULT) can be determined based on a reasonable load and path loss differential values expected in femto networks.
• Referring now toFIG. 9, to maintain optimal operation for cases with higher then expected load and path loss differential, in one exemplary embodiment, the following algorithm can be run for each of a plurality of calls occurring between a femto node and multiple associated access terminals.
• As represented byblock902, the pilot channel gain level Ecp is initialized to Ecp_DEFAULTfor analysis of each voice call. Thus, a default value of Ecp (Ecp_DEFAULT) can be determined based on a reasonable load and path loss differential values expected in femto networks.
• As represented inblock904, the process is repeated for each call set up between thehome femto510A and associated access terminals520 with the power used on traffic channel denoted as Ect. In one exemplary embodiment, the Ect value is determined by the downlink (forward link FL) power control, as represented byquery906. Downlink (forward link FL) power control is used to maintain the required quality of service (e.g., packet error rate, PER). Downlink (forward link FL) power controls may either designate a decrease in Ect as represented byblock908, an increase in Ect as represented byblock910, or no change in Ect.
• As represented inquery912, a determination of the packet error rate (PER) is used to identify adequate signal quality. Accordingly, when PER is inadequate, downlink (forward link FL) power control adjusts the Ect.
• As represented byblock918, the T2P_FILTERED(e.g., Ect_FILTERED/Ecp_FILTERED) is monitored during the call. The purpose of filtering T2P would be to eliminate small scale fluctuations from the T2P calculation. E.g., a moving average filter can be used to filter Ect and Ecp values to compute Ect_FILTEREDand Ecp_FILTEREDrespectively.
• As represented inquery920, a determination is made as to the value of T2P_FILTERED. If T2P_FILTERED>T2P_OPTIMAL+Δ₁, then as represented inblock922 Ecp is increased to
• 
  ECP=Ect_FILTERED/T2P_OPTIMAL.
• As represented inquery924, a determination is made as the value of T2P_FILTERED. If T2P_FILTERED<T2P_OPTIMAL−Δ₂, then as represented inblock926 Ecp is decreased to
• 
  Ecp=max[Ect_FILTERED/T2P_OPTIMAL,Ecp_DEFAULT].
• T2P_OPTIMALdepends on particular traffic configuration (rate, coding etc.). For example, if two users are performing voice calls with same rate vocoders, they would have same T2P_OPTIMAL. However if there is another user performing data transfer (e.g., 1xRTT data transfer at 153 kbps) it would require a different T2P_OPTIMAL. Once the T2P_OPTIMALis determined for given user (based on its traffic type), then the algorithm automatically adjusts Ecp. The above algorithm is specified for one user. If there are multiple users, then the algorithm may result in different Ecp values for each user. However, overhead channels are common to all users and we can only have one Ecp setting. Thus the algorithm could be generalized to a multiple users case. By way of example, an “optimal” Ecp_ifor each user (i=1, . . . ,N) in the system could be found as described above and then an actual Ecp could be decided as max(Ecp₁, . . . , Ecp_N). Another option could be to find the optimal Ecp such that total power transmitted as overhead and traffic to all users is minimized. This would mean a modification of the calculation ofbox814 to:
• ${\mathrm{Ecp}}_{\mathrm{OPTIMAL}}=\arg \underset{\mathrm{Ecp}}{\min }\left[\mathrm{Ecp}+f_1\left({\mathrm{Ecp}}_1\right)+\dots +f_N\left({\mathrm{Ecp}}_N\right)\right]$
• for users1 to N in the femtocell. The purpose of filtering T2P would be to eliminate small scale fluctuations from the T2P calculation. E.g., a moving average filter can be used to filter Ect and Ecp values to compute Ect_FILTEREDand Ecp_FILTEREDrespectively.
• The optimal T2P may be obtained through simulations and once the T2P is decided, power control adjust Ect (which is part of standard 3G operation) may be determined. Then the Ecp is adjusted to achieve/maintain optimal T2P. Specifically, two algorithms may run together: 1) the power control algorithm adjusting Ect and 2) the adjustment of Ecp described herein.
• In the above algorithm, AΔ₁and Δ₂are hystheresis parameters used to prevent fast fluctuations of Ecp. Furthermore, in order to prevent abrupt changes of Ecp equations above may be modified, in one exemplary embodiment, to let the Ecp correction to be performed more slowly. Lastly, other overhead channels (e.g., page, sych) can be adjusted based on the pilot power level (i.e., their relative power level with respect to pilot power level can be kept constant).
• Accordingly, exemplary embodiments have been described for reducing transmit power for overhead signals (e.g., pilot, synch and broadcast/paging channels) when there is an active call at a femto node by determining an optimal overhead signal power level. The exemplary embodiment has been disclosed by way of example using in the pilot channel as the exemplary channel, however, the analysis can be applied to other overhead channels as well.
• Referring now toFIG. 10 and with further reference toFIGS. 5A-5B, operations relating to the use of frequency selective transmission to address jamming and negative geometries will be described in more detail. As stated, due to unplanned deployment of femto nodes, the received SINR for an associated access terminal can become very low due to interference from a neighbor femto node transmission. This interference degrades control channel and traffic channel performance for the access terminal and may result in outages or decreased services. The exemplary embodiment disclosed herein addresses operations to improve the performance of an access terminal in a high interference area without the need to change legacy access terminals.
• Generally, the exemplary embodiment introduces intentional frequency selectivity in downlink transmissions by orthogonalizing the transmit waveform among neighboring femto nodes to minimize interference. As an example, each femto node510 selects transmit pulse shaping via channel sensing from available waveforms, for example, from three 3-tap channel waveforms, with each coefficient set from a given row of, for example, a 3×3 DFT matrix. In this case each for a given access point, the transmitted waveform would be filtered by a three tap FIR (in addition to normal baseband filtering) with filter impulse responses selected from one of the following three waveforms:
• 
  h₁[n]=δ[n]+δ[n−2]+δ[n−4]h₂[n]=δ[n]+e^j2π/3δ[n−2]+e^−j2π/3δ[n−4]=δ[n]+(−0.5+j0.866)·δ[n−2]+(−0.5−j0.866)·δ[n−4]h₃[n]=δ[n]+e^−j2π/3δ[n−2]e^j2π/3δ[n−4]==δ[n]+(−0.5−j0.866)·δ[n−2]+(−0.5+j0.866)·δ[n−4]
• where exp(jx)=cos(x)+j sin(x).
• An alternative choice is two impulse responses with coefficient from 2×2 DFT (N=2). The choice of transmit filter stays for a certain period, after which the femto node510 may make the selection again based on channel sensing.
• With initial reference toFIG. 10,FIG. 10 describes method for interference management in a wireless communication system transmit waveform selection. As represented byblock1002, a set of N transmit waveforms are allocated to femto nodes510 for use in downlink transmissions. In one exemplary embodiment, the channel waveforms may be formed from coefficients of an N-tap channel filter with each coefficient set being derived from a specific row in an N×N DFT matrix.
• As represented byblock1004, a femto node510 selects a default waveform upon initialization (e.g., power up) according to a defined selection process (e.g., randomization, randomly assigned by the network, etc.). The default waveform from the set of N transmit (downlink) waveforms. The default waveform is initially assigned as the preferred transmit waveform, TxWave_PREFERRED.
• As represented byquery1006, the femto node510 transmits on the downlink using the preferred transmit waveform when a call is initiated. Call setup with the associated access terminal520 occurs and includes channel quality indications (e.g., Channel Quality Indicator CQI, Data Rate Control DRC) determined by the access terminal520 and forwarded to the femto node510 on the uplink.
• As represented byquery1008, the femto node initiates a waveform testing cycle for a time period of T_test_waveform until all the possible waveforms have been tested. As represented byblock1010, the femto node510 communicates with the associated access terminal520 using the current waveform. The associated access terminal receives the downlink transmissions and generates a channel quality indication in response to the signal quality. The channel quality indication is forwarded in the uplink (reverse link) to the femto node510.
• As represented byblock1012, the femto node monitors the uplink to determine the channel quality using the current waveform based on the received channel quality indication. The femto node510 may either form a table of waveforms and corresponding channel quality indications, or compare the current channel quality indication with any previous channel quality indications and retained an indication of the preferred waveform.
• As represented byblock1014, the waveform testing increments to the next allocated waveform for continued evaluation. The exemplary waveform selection process iterates until the possible waveforms have been engaged for transmission on the downlink and the corresponding channel quality indication has been received on the uplink. As represented byblock1016, the preferred waveform based upon channel quality determination is then selected as the preferred transmit waveform which provides the best channel quality in the presence of interference from negative geometries associated with deployments of other unplanned base station deployments.
• As represented byblock1018, the preferred waveform may be periodically updated based upon various factors including a specific time period, call termination, channel quality degradation threshold or other channel conditions know by those of ordinary skill in the art. Upon an update determination, processing returns to evaluate the channel quality of the various possible transmit waveforms.
• The present exemplary embodiment manages interference from strong neighboring interference energy due to orthogonality of the Fourier series on the dominant signal energy during convolution, at the expense of creating self-noise through ISI and thereby limiting performance at high geometry. Further gains could be achieved with the use of MMSE equalizer due to different frequency coloring of impulse responses for the desired and interference signals. This mechanism is feasible in a femto node configuration as the delay spread is significantly smaller than one chip interval.
• Referring now toFIGS. 11A-11B and with further reference toFIGS. 5A-5B, operations relating to the use of adaptive noise figure and path loss adjustment to address jamming and negative geometries will be described in more detail. The present exemplary embodiment uses methods and apparatus to prevent jamming and address jamming and negative geometries using adaptive noise figures and path loss adjustments.
• Generally, femto nodes are connected to the Internet540 and the mobileoperator core network550 via a wide band connection (e.g., DSL router or cable modem). Since the RF coverage of femto nodes510 is not manually optimized by the mobileoperator core network550 and deployment is generally ad hoc, serious RF interference issues may arise unless appropriate interference mitigation methods are utilized.
• In a macro cell network, access terminals520 and macrocell access nodes560 are designed to operate in a certain dynamic range. In cells formed by femto nodes510, a home femto node510 and an associated access terminal520 may be arbitrarily spatially nearby, thus creating very high signal levels beyond the sensitivity range of the respective receivers. On a downlink (forward link FL), such a configuration can saturate the receiver of associated access terminal and create degraded demodulation performance. On the reverse link, such a configuration can create very high noise rise (RoT), also known to create instability at the home femto node510. Thus maximum and minimum transmit power levels and receiver noise figure values need to be adjusted accordingly for home femto nodes510. This situation is illustrate inFIG. 5B with reference tohome femto node510A and associatedaccess terminal520A.
• Femto nodes510B can cause interference both on the uplink UL (reverse link RL)) and in the downlink DL (forward link FL) of cells serviced by macrocell access nodes560. For example afemto node510B installed, for example, near a window of aresidence530B can cause significant downlink DL interference to theaccess terminals520F outside the house (i.e., non-associated access terminal) that are not served by thefemto node510B. Also, on the uplink UL, the associated access terminals520 that are served by a specific home femto node510 can cause significant interference on the macrocell access nodes560.
• On the uplink UL,non-associated access terminals520F that are served by the macrocell access nodes560 can cause significant interference on thehome femto node510A.
• As stated, femto nodes510 can also create significant interference to each other due to unplanned deployment. For example innearby residences530, a femto node510 installed near a wall separating tworesidences530 can cause significant interference to a neighboring femto node510 in anadjacent residence530. In such a case, the strongest signal (in terms of RF signal strength) from a femto node510 to an access terminal520 may not necessarily be the associated access terminal's home femto node due to restricted association requirement described above. Such a scenario is illustrated inFIG. 5B where on the downlink DL,femto node510A may cause significant interference (e.g., low SINR) to access terminal520D. Also, on the uplink UL,non-associated access terminal520D may cause significant interference (e.g., high RoT) to foreign (alien)femto node510A.
• For example, on the uplink of CDMA wireless networks, system stability and load is usually determined by the metric: rise over thermal (RoT), also know as noise rise, at the femto node. Rise over thermal (RoT) indicates the ratio between the total power received from all sources at the femto node and the thermal noise:
• 
  RoT=(Ioc+Ior+No)/No,
• where
• • Ior: Total received power received at the femto node from all wireless devices for whom femto node is in their active set
  • Ioc: Total received power received at the femto node from all wireless devices for whom femto node is not in their active set
  • No: Variance of the thermal noise including the femto node noise figure (NF).
• For stable system operation on the uplink UL, RoT needs to be controlled. Typically, RoT is controlled to be around 5 dB and higher. High RoT values can cause significant performance degradation. For example, inFIG. 5B for the two neighboring cells formed byfemto nodes510A and510B, high RoT caused byaccess terminal520D atfemto node510A results in performance degradation for associatedaccess terminal520C. One specific interfering scenario occurs whenneighbor access terminal520D has bursty uplink UL traffic and exhibits overly high power levels (e.g., in close proximity) atfemto node510A. Accordingly, during high rate data uplink UL bursts fromaccess terminal520D, the RoT atfemto node510A goes above 20 dB. Furthermore, the uplink UL power control mechanism in CDMA systems (e.g., CDMA2000, WCDMA, 1xEV-DO) is design to combat this type of interference scenarios. However due to excessive variation in RoT, the mechanism may take some time forfemto node510A to power control associatedaccess terminal520C to overcome the interference caused bynon-associated access terminal520D. Meanwhile the signal-to-interference ratio (SIR) of associatedaccess terminal520C falls below required levels resulting in consecutive packet errors on the uplink UL from associatedaccess terminal520C tohome femto node510A.
• To minimize the sudden drop in SIR in the described scenario, one alternative could be to increase the power control step size on the uplink UL as conveyed fromhome femto node510A to associatedaccess terminal520C. However, there are usually upper limits on the power control step size imposed by the communication standards since other system degradations occur when a system operates at very high power control step size. Thus it is desirable to control the RoT level at the femto node510.
• In order to prevent an abrupt jump in RoT due to sudden increase in interference created by non-associated access terminals (e.g., interference created bynon-associated access terminal520D atfemto node510A), the noise figure NF can be increased or the received signal can be attenuated by adding some path loss (PL) component on the uplink UL. However, such an operation is performed at the femto node experiencing high levels of interference. For example, in the scenario shown inFIG. 5B, if bothfemto node510A andfemto node510B increase the noise figure NF or attenuation by the same amount, the result is larger uplink UL transmit power levels for bothaccess terminals520C andaccess terminal520D. As a result, the high RoT problem occurring atfemto node510A is not remedied.
• According to an exemplary embodiment, the femto node exhibiting high RoT,femto node510A in the present scenario, increases its noise figure NF or attenuation level while femto nodes not exhibiting high RoT,femto node510B in the present scenario, keep their noise figures NFs constant as long as they are not experiencing high levels of out-of-cell interference. Thus, a method is provided to adjust the noise figure NF or attenuation when there is high level of out-of-cell interference at a particular femto node. According to an exemplary embodiment for managing interference in a wireless communication system, RoT at a given time slot n can be expressed as:
• $\mathrm{RoT}\left(n\right)=\left[\mathrm{Ioc}\left(n\right)+\mathrm{Ior}\left(n\right)+\mathrm{No}\left(n\right)\right]/\mathrm{No}\left(n\right)$$\mathrm{Ior}\left(n\right)=\sum _{i\in \mathrm{InCell}}^{}{\mathrm{Ec}}_i\left(n\right)$
• where Ec_iis the total received energy per user i.
• With initial reference toFIGS. 11A-11B,FIGS. 11A-11B describe a method for interference management in a wireless communication system using adaptive noise figure and path loss adjustment to adaptively adjust path loss for controlling RoT. It is noted that the adjustment factor can be applied either to uplink UL attenuation or the noise figure NF of the femto node.
• As represented byquery1104, the operations described herein may occur periodically, such as upon the occurrence of a subsequent time slot n. By way of example, at every slot n, the femto node510 may perform the following method to provide interference management to a communication system. As represented byblock1104, various signals are measured and levels are computed. Specifically as represented byblock1106, a thermal noise figure: No(n) is measured at the femto node510. The thermal noise figure No(n) is the variance of the thermal noise including the femto node noise figure (F).
• As represented byblock1108, a total received signal strength Io(n) is measured. The total received signal strength Io(n) is the total received power received at the femto node from all wireless devices for whom femto node is in their active set and from all wireless devices for whom femto node is not in their active set. As represented byblock1112, the in-cell (associated access terminal) interference level Ior, which is the total received power received at the femto node from all wireless devices for whom femto node is in their active set, is computed. The computed in-cell interference level can be expressed as:
• $\mathrm{Ior}\left(n\right)=\sum _{i\in \mathrm{InCell}}^{}{\mathrm{Ec}}_i\left(n\right)$
• As represented byblock1110, a received pilot chip energy Ecp(n) to interference and noise Nt(n) ratio is measured from all wireless devices for whom the femto node is in their active set.
• As represented byblock1114, the out-of-cell (non-associated access terminal) interference level Ioc, which is the total received power received at the femto node from all wireless devices for whom femto node is not in their active set, is computed. The computed out-of-cell interference level can be expressed as:
• 
  Ioc(n)=Io(n)−Ior(n)−No(n)
• As represented byblock1116 the received out-of-cell interference level to the thermal noise figure No(n) ratio and maximum filtered received pilot chip energy Ecp(n) to interference plus noise Nt(n) ratio among in-cell access terminals are computed. As represented byblock1118, the access terminal signal-to-noise ratio measured as the received pilot chip energy Ecp(n) to interference and noise Nt(n) ratio for all in-cell access terminals are filtered, by way of example, according to infinite impulse response (IIR) filtering in the dB domain. The maximum filtered value among access terminals for whom the femto node is in their active set can be expressed as:
• $\max \stackrel{\_}{\left(\frac{\mathrm{Ecp}\left(n\right)}{\mathrm{Nt}\left(n\right)}\right)}=\underset{i\in \mathrm{in}\text{-}\mathrm{cell}\mathrm{access}\mathrm{terminals}}{\max }\left[\mathrm{filter}\left(\frac{{\mathrm{Ecp}}_i\left(n\right)}{{\mathrm{Nt}}_i\left(n\right)}\right)\right]$
• As represented byblock1120, the signal-to-noise ratio of the out-of-cell received interference level Ioc and the thermal noise figure No(n) are computed. The signal-to-noise ratio is also further filtered, by way of example, according to finite impulse response (FIR) filtering in the dB domain. The computed out-of-cell (non-associated access terminal) signal-to-noise ratio can be expressed as:
• $\stackrel{\_}{\left(\frac{\mathrm{Ioc}\left(n\right)}{\mathrm{No}\left(n\right)}\right)}=\mathrm{filter}\left(\frac{\mathrm{Ioc}\left(n\right)}{\mathrm{No}\left(n\right)}\right)$
• As represented byblock1122, the excessive received out-of-cell interference beyond the allowed (target) amount with which the communication system can reliably operate and the maximum excessive received pilot chip energy to interference and noise ratio among in-cell access terminals are determined. As represented byblock1124, the excess amount for received pilot chip energy to interference and noise ratio can be expressed as:
• $\mathrm{EcpNt\_excess}=\max \stackrel{\_}{\left(\frac{\mathrm{Ecp}\left(n\right)}{\mathrm{Nt}\left(n\right)}\right)}-\mathrm{EcpNt\_target}$
• with the above allowed threshold EcpNt_target having the units of dB.
• As represented byblock1126, the excess amount of the out-of-cell received interference level Ioc_excess can be expressed as:
• $\mathrm{Ioc\_excess}=\stackrel{\_}{\left(\frac{\mathrm{Ioc}\left(n\right)}{\mathrm{No}\left(n\right)}\right)}-\mathrm{Ioc\_target}$
• with the above allowed threshold Ioc_target having the units of dB.
• As represented inblock1128, an amount of additional path loss (PL_adjust) that needs to be applied is computed. As represented inblock1130, the candidate path loss adjustments are determined. The candidate adjustments can be expressed as:
• ${\mathrm{PL\_cand}}_1=\mathrm{Ior\_excess}$${\mathrm{PL\_cand}}_2=\{\begin{array}{cc}0,& 0\ge \mathrm{EcpNt\_excess}\\ \mathrm{EcpNtbased\_PL}\mathrm{\_step},& 0<\mathrm{EcpNt\_excess}\end{array}{\mathrm{PL\_cand}}_3=\mathrm{PL\_cand}\left(n-1\right)-\mathrm{PL\_step}\mathrm{\_down}\mathrm{PL\_cand}=\max \left({\mathrm{PL\_cand}}_1,{\mathrm{PL\_cand}}_2,{\mathrm{PL\_cand}}_3\right)$
• Regarding determining the candidate adjustment values, the candidate values may be based upon various characteristics or rules. By way of example, various points can be expressed as:
• • (1) PL_cand₁and PL_cand₂are designed to quickly adjust the PL based on high Ecp/Nt or Ioc values exceeding a high threshold.
  • (2) In case both Ecp/Nt and Ioc are below allowed limits, PL_cand₃is designed to slowly reduce (decay) PL such that it won't be unnecessarily high.
  • (3) If there is only one active user in the cell there maybe no reason to directly limit Ioc since RoT control mechanisms already can control the RoT level. So in the case when there is only one active user in the system, Ioc_target can be set to a very large value.
• As represented inblock1132, the appropriate path loss (PL_adjust) can be applied according to the upper and lower path loss PL adjustment limitations expressed as:

• 	If (PL_cand > PL_adjust—max )
  	PL_adjust(n) = PL_adjust—max
  	elseif (PL_cand > 0 )
  	PL_adjust(n) = PL_cand
  	elseif (PL_cand ≦ 0 )
  	PL_adjust(n) = 0

• As represented inblock1134, the uplink UL attenuation (or noise figure) is increased by PL_adjust(n). It is noted that in an actual implementation, hardware limitations may require quantization of PL_adjust(n) to the closest possible setting.
• Referring now toFIG. 12 and with further reference toFIGS. 5A-5B, operations relating to the use of subframe time reuse to address jamming and negative geometries will be described in more detail. The present exemplary embodiment uses methods and apparatus to prevent jamming and address jamming and negative geometries using subframe time reuse.
• In one exemplary embodiment, if an air interface permits time division multiplexing, transmissions can be scheduled in such a manner as to eliminate time periods with negative geometries. Thus,femto node510B may communicate with associatedaccess terminal520D during a period that femtonode510A is silent. Similarly, associatedaccess terminal520C may communicate withfemto node510A during a period wherenon-associated access terminal520D is scheduled byfemto node510A to be silent. Such methods of synchronization and scheduling approaches find application to systems that permit time division scheduling, such as 1xEVDO. By way of example, since the 1xEVDO control channels are time multiplexed, neighbor femto nodes510 can be organized to use time re-use of these control channels.
• However, as discussed next, this does not work with air interface technologies that do not permit operation with scheduling and time division multiplexing, for example, technologies that use CDM control channels, including, for example, 1xRTT, WCDMA and HSPA. Design details for sub-frame time reuse are described in detail in embodiments below.
• In one exemplary embodiment, sub-frame time reuse is applicable to technologies where hybrid time reuse cannot be applied. In many cellular technologies such as cdma2000 and WCDMA, the base station transmits a continuous pilot and other CDM control channels (e.g., synch, paging and broadcast, etc.) which the access terminals use for a variety of purposes, including initial scanning and acquisition, idle mode tracking and channel estimation. This continuous transmission of pilot and overhead channels from femto nodes may result in the above described downlink jamming, even when there is no active traffic at the jammer.
• In one exemplary embodiment, the first step is to address the outage situations when the desired femto node510 pilot and overhead channels (e.g., synch and paging) cannot be received at the access terminal520. By way of example, a cdma2000 frame is divided into sixteen power control groups (PCGs). To permit acquisition of the pilot signal, a fraction of the pilot and overhead channel transmission is gated off.
• With reference toFIG. 5B,femto node510A, transmitting to associatedaccess terminals520A-C, transmits such gated frames (i.e., during gated off periods no FL traffic is transmitted). Atnon-associated access terminal520D, the carrier-to-interference ratio, C/I, for transmissions fromfemto node510B improves dramatically during the period that femtonode510A is gated off, permitting acquisition of the pilot and synch channels fromfemto node510B ataccess terminal520D, in spite of the highly negative geometry ataccess terminal520D.
• In one exemplary embodiment, these gated on-off periods are scheduled to be non-overlapping. Thus,femto node510A andfemto node510B can use non-overlapping sub-frames (or power-control groups). In one exemplary embodiment, by gating off (i.e., not transmitting any FL traffic) a fraction ½, ⅔ or ¾ of the sub-frames, for example, a time division reuse pattern of 2, 3 or 4 may be created. If the pilot and overhead channels have sufficient redundancy, for pilot acquisition as well as decoding of the overhead channels, this would have an impact of 3-6 dB, for example, on the link budget of the pilot and overhead channels. However, this can be easily compensated by increasing the transmit power of the femto node510, since in the femto node510 deployment, the arrangements are not limited by transmit power.
• In addition to the pilot and overhead channels, the same gating method may also be applied to the voice or data channel transmissions. In one exemplary embodiment, the femto node510 gates a fraction of each frame transmission off. If, for example, the fraction (e.g., ½) that is turned off is lesser than the channel coding rate used for that transmission, for example, in cdma2000 forward link voice packet transmissions, a particular standard format (RC3) uses a rate ¼ convolutional code, the access terminal520 will be able to decode the packet, even though half of the packet transmission was gated off. To avoid the necessity of knowing these geometries and scheduling these non-overlapping gated off times, the following method is disclosed to prevent jamming and address jamming and negative geometries using subframe time reuse.
• With initial reference toFIG. 12,FIG. 12 describes an exemplary embodiment for interference management in a wireless communication system using subframe time reuse. As represented byblock1202, gating sequences (or patterns) are identified with each gating sequence gating-off, for example, either eleven of sixteen power control groups (PCGs) to obtain a reuse of 5/16, or eight of sixteen PCGs to obtain a reuse of 2.
• The gating sequence may be chosen in such a way as to minimize the cross-correlation between pairs of gating sequences from potentially interfering femto nodes510. As represented byblock1204, each femto node510 selects one of the gating sequences. Although the femto node510 may attempt to choose a gating sequence that is non-overlapping with neighbor femto nodes, general selection does not necessarily result in a non-overlapping arrangement. However, the exemplary embodiment provides a mechanism such that a non-overlapping gating sequence can be identified and selected.
• As represented byblock1206, an access terminal520 establishes an active connection with a femto node510. In response to establishing the connection, the access terminal520 provides a “fast” per-subframe downlink (forward link) power control feedback allowing the femto node5101 to select a desired non-overlapping gating sequence.
• Specifically and as represented inblock1208,femto node510B transmits a series of frames on, for example, a data/voice channel to theaccess terminal520D with all power control groups (PCGs) gated on. As represented byblock1210, since a potentially interferingneighbor femto node530A is already engaged in communication withaccess terminals520A-C using sub-frame gating techniques,access terminal520D will observe interference on a subset of the subframes in response to gated transmissions by interferingneighbor femto node510A. Furthermore,access terminal520D will also observe another subset of subframes where no interference fromneighbor femto node520A is observed whenneighbor femto node510A is gated off during that subset of subframes.
• During the subframes in whichfemto node510A is gated on, theaccess terminal520D will observe, for example, low Eb/No. As represented byblock1212, the downlink (forward link) power control feedback fromaccess terminal520D will indicate thatfemto node510B should increase the transmit power for specific subframes. Similarly, during the subframes that femtonode510A is gated off,access terminal520D will observe high Eb/No and the downlink (forward link) power control feedback fromaccess terminal520D will indicate thatfemto node510B should decrease the transmit power for specific subframes.
• As represented byblock1214, the sub-frame downlink (forward link) power control feedback provided byaccess terminal520D tofemto node510B indicates which sub-frames at transmitted by interferingneighbor femto node510A are gated on and which are gated off. Accordingly, such an indication allowsfemto node510B to select a gating sequence (pattern) that is non-overlapping (complementary) with the gating sequence (pattern) chosen and in use by interferingneighbor femto node510A. The exemplary embodiment finds application for the gating sequence (pattern) chosen by interfering neighboringfemto node510A.
• Depending on the implementation technology, other considerations may further determine the types of gating sequences (patterns) best suited for this sub-frame gating technique. Furthermore, since legacy access terminals are unaware of the gating being done on the downlink (forward link), other considerations may be applied to include choosing gating sequences (patterns) that intersperse shortened “off” periods between shortened “on” periods. Such a consideration may reduce impact on downlink (forward link) channel estimation and channel quality feedback estimation methods in use by the legacy access terminal. Thus, for example, in a case when eight sub-frames out of sixteen are gated off, there may be beneficial reasons for selecting alternating sub-frames to be gated off and gated on.
• In another exemplary embodiment, gating sequence selection may apply different considerations for deployments where neighbor femto nodes510 are not synchronized. Such considerations may exist, for example, when WCDMA femto nodes510 are not synchronized. In one exemplary embodiment of non-synchronized femto nodes510, instead of alternate on-off gated subframes, it may be beneficial to have all or many of the gated-off subframes be contiguous, as well as all or many of the gated-on subframes. For example, in the case of a WCDMA system with fifteen subframes over 10 ms, or thirty subframes over 20 ms, a beneficial method may be for each femto node510 to gate off nine contiguous of the fifteen subframes and gate on six contiguous subframes. Alternately, using a 20 ms frame, the femto node510 may gate off sixteen contiguous subframes and gate on fourteen contiguous subframes out of thirty subframes.
• In alternate exemplary embodiments, other methods to address this situation and improve downlink C/I involve femto nodes510 configured to gate-off pilot and overhead channel transmissions when there are no access terminals associated, and to turn on pilot and overhead channels periodically and/or at very low power only at times when associated access terminals520 are expected to be scanning for the femto node510.
• Referring now toFIGS. 13-14 and with further reference toFIGS. 5A-5B, operations relating to the use of hybrid time reuse to address jamming and negative geometries will be described in more detail. The present exemplary embodiment uses methods and apparatus to prevent jamming and address jamming and negative geometries using hybrid time reuse techniques.
• In an exemplary embodiment, if an air interface permits time division multiplexing (such as 1xEV-DO), then transmissions may be scheduled in such a manner as to eliminate time periods with negative geometries. Thus,femto node510B can communicate with associatedaccess terminal520D during a period whenfemto node510A is not transmitting. Similarly, associatedaccess terminal520C may communicate withfemto node510A during a period whereaccess terminal520D is scheduled byfemto node510B to not transmit.
• In an exemplary embodiment of a hybrid time reuse method, a downlink DL transmission is divided into three separate groups in time:
• • 1. Synchronous Control Channel (SCC) transmission period
  • 2. Limited HARQ Interlace Tx. Period
  • 3. Unlimited HARQ Interlace Tx. Period
• FIG. 13 illustrates an exemplary downlink DL timeline including three different time periods during each synchronous control channel (SCC) cycle period of 256 time slots. In one exemplary embodiment based on time sharing of the resources during “unlimited HARQ interlace,” there are three different femto channels defined. As described in more detail later, it is desired that neighboring femto nodes510 pick different femto channels so that they do not experience interference from other neighbor femto nodes510 (i.e., each femto node selects a primary femto channel different than the neighbor femto node510). If there is no interference from a neighbor femto node, multiple femto channels (in addition to the primary femto channel) can be used by one femto node510. Details of one exemplary embodiment of a hybrid time reuse operation is described below.
• With initial reference toFIG. 14,FIG. 14 describes a method for interference management in a wireless communication system using hybrid time reuse, in accordance with an exemplary embodiment. As represented byblock1402, at the initial power up or other synchronization of a femto node510, the femto node510 performs time synchronization with the macro cell network (e.g., macro cell access node560). As represented byblock1404, during time synchronization with the macrocell access node560, the femto node510 measures secondary synchronization channel (SCC) offsets (MSCCO) used by the macrocell access node560 and neighboring femto nodes510. Based on the measurement, the femto node510 identifies a preferred HARQ interlace with the least interference, as represented byblock1406. A preferred slot offset (PSO) is defined from the identified preferred HARQ interlace.
• As represented inblock1408, a primary femto channel is selected. By way of example, on exemplary selection process may follow the following algorithm:
• • If mod(PSO-MSCCO,4)=1 then Femto Chn.1 is picked as primary Femto Channel
  • If mod(PSO-MSCCO,4)=2 then Femto Chn.2 is picked as primary Femto Channel
  • If mod(PSO-MSCCO,4)=3 then Femto Chn.3 is picked as primary Femto Channel
  • where Chn1, Chn2 and Chn3 are described inFIG. 13.
• Once femto channels are determined, femto nodes510 may transmit traffic in the downlink (forward link). Transmissions by femto nodes510 are timed to reduce interference with macro cell transmissions and other femto node transmissions. A femto node transmission protocol for the various macro cell transmission periods, SCC transmission period, limited HARQ interlace transmission period, and unlimited HARQ interlace transmission period, are described below.
• As represented inblock1410 and with reference toFIG. 13, anSCC transmission period1302 is defined at the beginning of each SCC cycle1304 (e.g., 256 slots) to allow transmission of an SCC offset (e.g., first 32 slots of every SCC cycle). In one exemplary embodiment, two sub-periods1306,1308 are defined based on HARQ interlace: preferred slot offset and non-preferred slot offset.
• On HARQ interlace with the preferred slot offset (PSO), femto node510 transmits SCC information. This allows reliable transmission of control channel information and enables associated access terminals520 to hand-in and hand-out from femto node510. During HARQ interlaces on non preferred slot offsets, femto nodes510 do not transmit any downlink (forward link) traffic (DTX FL transmission) so that minimum interference is caused to neighbor macro cells and neighbor femto node SCC transmission. On these slot offsets, a fractional of downlink DL power is used for Pilot and MAC channels so that these channels can operate successfully.
• As represented inblock1412 and with reference toFIG. 13, during a limited HARQ interlace transmission period, the femto node510 is allowed to transmit downlink (forward link) traffic on the HARQ interlace of PSO and delay sensitive traffic is given absolute priority over best effort traffic. With reference toFIG. 13, limited HARQ interlace transmission period gives a transmission opportunity for each femto node so that delay sensitive traffic (such as VoIP etc.) does not suffer too excessive delay. In one example, during limited HARQ interlace transmission period, if requested DRC is null, then single user packet type of 38.4 kbps may be used. If DRC is null or erased, then compatible packet types such as single user packet (SUP) 38.4 kbps or multi user packet (MUP) of 256/512/1024 bits may be utilized (similar to DRC erasure mapping).
• In one exemplary embodiment, downlink (forward link) traffic may also be transmitted on HARQ interlace of MSCCO. In one embodiment, neighboring femto nodes510 may use this interlace as well (i.e., no protection against interference). During HARQ interlaces of other slot offsets, femto nodes do not transmit any downlink (forward link) traffic (time re-use) however a fraction of downlink (forward link) power can be allocated to pilot and MAC channels for successful operation of these channels.
• As represented inblock1414 and with reference toFIG. 13, during an unlimited HARQ interlace transmission period, the femto node510 is allowed to transmit downlink (forward link) traffic on all of the four HARQ interlaces. At the beginning of the period, downlink (forward link) transmit power can be ramped up slowly to let the access terminal rate predictor to ramp up. In one exemplary embodiment, to further increase the ramp-up of DRC values, DRC length of 1 slot should be used. Due to conservative predictor behavior, if null DRC is requested by the mobile at the beginning of unlimited HARQ interlace transmission period, femto node510 can transmit compatible packet types (multi use packet or 38.4 kbps single user packet). Also, femto node downlink (forward link) scheduler can keep track of previously requested DRC values and maintain DRC values from last transmission periods and HARQ early termination statistics to decide on what data rates can be decoded by access terminal520.
• The teachings herein may be incorporated into a node (e.g., a device) employing various components for communicating with at least one other node.FIG. 15 depicts several sample components that may be employed to facilitate communication between nodes. Specifically,FIG. 15 illustrates a wireless device1510 (e.g., an access point) and a wireless device1550 (e.g., an access terminal) of a MIMO system1500. At the device1510, traffic data for a number of data streams is provided from a data source1512 to atransmit (“TX”) data processor1514.
• In some aspects, each data stream is transmitted over a respective transmit antenna. The TX data processor1514 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.
• The coded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (i.e., symbol mapped) based on a particular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream may be determined by instructions performed by a processor1530. A data memory1532 may store program code, data, and other information used by the processor1530 or other components of the device1510.
• The modulation symbols for all data streams are then provided to a TX MIMO processor1520, which may further process the modulation symbols (e.g., for OFDM). The TX MIMO processor1520 then provides NT modulation symbol streams to NT transceivers (“XCVR”)1522A through1522T. In some aspects, the TX MIMO processor1520 applies beam-forming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.
• Each transceiver1522 receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. NT modulated signals from transceivers1522A through1522T are then transmitted from NT antennas1524A through1524T, respectively.
• At the device1550, the transmitted modulated signals are received by N_Rantennas1552A through1552R and the received signal from each antenna1552 is provided to a respective transceiver (“XCVR”)1554A through1554R. Each transceiver1554 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream.
• A receive (“RX”) data processor1560 then receives and processes the N_Rreceived symbol streams from N_Rtransceivers1554 based on a particular receiver processing technique to provide NT “detected” symbol streams. The RX data processor1560 then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by the RX data processor1560 is complementary to that performed by the TX MIMO processor1520 and the TX data processor1514 at the device1510.
• A processor1570 periodically determines which pre-coding matrix to use (discussed below). The processor1570 formulates a reverse link message comprising a matrix index portion and a rank value portion. A data memory1572 may store program code, data, and other information used by the processor1570 or other components of the device1550.
• The reverse link message may comprise various types of information regarding the communication link and/or the received data stream. The reverse link message is then processed by a TX data processor1538, which also receives traffic data for a number of data streams from a data source1536, modulated by a modulator1580, conditioned by the transceivers1554A through1554R, and transmitted back to the device1510.
• At the device1510, the modulated signals from the device1550 are received by the antennas1524, conditioned by the transceivers1522, demodulated by a demodulator (“DEMOD”)1540, and processed by a RX data processor1542 to extract the reverse link message transmitted by the device1550. The processor1530 then determines which pre-coding matrix to use for determining the beam-forming weights then processes the extracted message.
• FIG. 15 also illustrates that the communication components may include one or more components that perform interference control operations as taught herein. For example, an interference (“INTER.”) control component1590 may cooperate with the processor1530 and/or other components of the device1510 to send/receive signals to/from another device (e.g., device1550) as taught herein. Similarly, an interference control component1592 may cooperate with the processor1570 and/or other components of the device1550 to send/receive signals to/from another device (e.g., device1510). It should be appreciated that for each device1510 and1550 the functionality of two or more of the described components may be provided by a single component. For example, a single processing component may provide the functionality of the interference control component1590 and the processor1530 and a single processing component may provide the functionality of the interference control component1592 and the processor1570.
• The teachings herein may be incorporated into various types of communication systems and/or system components. In some aspects, the teachings herein may be employed in a multiple-access system capable of supporting communication with multiple users by sharing the available system resources (e.g., by specifying one or more of bandwidth, transmit power, coding, interleaving, and so on). For example, the teachings herein may be applied to any one or combinations of the following technologies: Code Division Multiple Access (“CDMA”) systems, Multiple-Carrier CDMA (“MCCDMA”), Wideband CDMA (“W-CDMA”), High-Speed Packet Access (“HSPA,” “HSPA+”) systems, Time Division Multiple Access (“TDMA”) systems, Frequency Division Multiple Access (“FDMA”) systems, Single-Carrier FDMA (“SC-FDMA”) systems, Orthogonal Frequency Division Multiple Access (“OFDMA”) systems, or other multiple access techniques. A wireless communication system employing the teachings herein may be designed to implement one or more standards, such as IS-95, cdma2000, IS-856, W-CDMA, TDSCDMA, and other standards. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (“UTRA)”, cdma2000, or some other technology. UTRA includes W-CDMA and Low Chip Rate (“LCR”). The cdma2000 technology covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (“GSM”). An OFDMA network may implement a radio technology such as Evolved UTRA (“E-UTRA”), IEEE 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (“UMTS”). The teachings herein may be implemented in a 3GPP Long Term Evolution (“LTE”) system, an Ultra-Mobile Broadband (“UMB”) system, and other types of systems. LTE is a release of UMTS that uses E-UTRA. Although certain aspects of the disclosure may be described using 3GPP terminology, it is to be understood that the teachings herein may be applied to 3GPP (Re199, Re15, Re16, Re17) technology, as well as 3GPP2 (1xRTT, 1xEV-DO Re10, RevA, RevB) technology and other technologies.
• The teachings herein may be incorporated into (e.g., implemented within or performed by) a variety of apparatuses (e.g., nodes). In some aspects, a node (e.g., a wireless node) implemented in accordance with the teachings herein may comprise an access point or an access terminal.
• For example, an access terminal may comprise, be implemented as, or known as user equipment, a subscriber station, a subscriber unit, a mobile station, a mobile, a mobile node, a remote station, a remote terminal, a user terminal, a user agent, a user device, or some other terminology. In some implementations an access terminal may comprise a cellular telephone, a cordless telephone, a session initiation protocol (“SIP”) phone, a wireless local loop (“WLL”) station, a personal digital assistant (“PDA”), a handheld device having wireless connection capability, or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smart phone), a computer (e.g., a laptop), a portable communication device, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music device, a video device, or a satellite radio), a global positioning system device, or any other suitable device that is configured to communicate via a wireless medium.
• An access point may comprise, be implemented as, or known as a NodeB, an eNodeB, a radio network controller (“RNC”), a base station (“BS”), a radio base station (“RBS”), a base station controller (“BSC”), a base transceiver station (“BTS”), a transceiver function (“TF”), a radio transceiver, a radio router, a basic service set (“BSS”), an extended service set (“ESS”), or some other similar terminology.
• In some aspects a node (e.g., an access point) may comprise an access node for a communication system. Such an access node may provide, for example, connectivity for or to a network (e.g., a wide area network such as the Internet or a cellular network) via a wired or wireless communication link to the network. Accordingly, an access node may enable another node (e.g., an access terminal) to access a network or some other functionality. In addition, it should be appreciated that one or both of the nodes may be portable or, in some cases, relatively non-portable.
• Also, it should be appreciated that a wireless node may be capable of transmitting and/or receiving information in a non-wireless manner (e.g., via a wired connection). Thus, a receiver and a transmitter as discussed herein may include appropriate communication interface components (e.g., electrical or optical interface components) to communicate via a non-wireless medium.
• A wireless node may communicate via one or more wireless communication links that are based on or otherwise support any suitable wireless communication technology. For example, in some aspects a wireless node may associate with a network. In some aspects the network may comprise a local area network or a wide area network. A wireless device may support or otherwise use one or more of a variety of wireless communication technologies, protocols, or standards such as those discussed herein (e.g., CDMA, TDMA, OFDM, OFDMA, WiMAX, Wi-Fi, and so on). Similarly, a wireless node may support or otherwise use one or more of a variety of corresponding modulation or multiplexing schemes. A wireless node may thus include appropriate components (e.g., air interfaces) to establish and communicate via one or more wireless communication links using the above or other wireless communication technologies. For example, a wireless node may comprise a wireless transceiver with associated transmitter and receiver components that may include various components (e.g., signal generators and signal processors) that facilitate communication over a wireless medium.
• The components described herein may be implemented in a variety of ways. Referring toFIGS. 16-21,apparatuses1600,1700,1800,1900,2000, and2100 are represented as a series of interrelated functional blocks. In some aspects the functionality of these blocks may be implemented as a processing system including one or more processor components. In some aspects the functionality of these blocks may be implemented using, for example, at least a portion of one or more integrated circuits (e.g., an ASIC). As discussed herein, an integrated circuit may include a processor, software, other related components, or some combination thereof. The functionality of these blocks also may be implemented in some other manner as taught herein.
• Theapparatuses1600,1700,1800,1900,2000, and2100 may include one or more modules that may perform one or more of the functions described above with regard to various figures. In some aspects, one or more components of theinterference controller320 or theinterference controller322 may provide functionality relating to, for example, a interference receiving/direction means1602, interference comparing/determining/updating means1606, overhead channel power means1702, transmit waveform means1802, channel quality means1806, interference determining means1902, path loss means1906, gating sequence means2002, reuse pattern means2102, and synchronization/offset/timing means2106. In some aspects, thecommunication controller326 or thecommunication controller328 may provide functionality relating to, for example, transceiving (transmitting/receiving) means1604,1704,1804,1904,2004, and2104.
• It should be understood that any reference to an element herein using a designation such as “first,” “second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations may be used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements may be employed there or that the first element must precede the second element in some manner. Also, unless stated otherwise a set of elements may comprise one or more elements.
• Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.
• Those of skill would further appreciate that any of the various illustrative logical blocks, modules, processors, means, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware (e.g., a digital implementation, an analog implementation, or a combination of the two, which may be designed using source coding or some other technique), various forms of program or design code incorporating instructions (which may be referred to herein, for convenience, as “software” or a “software module”), or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.
• The various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented within or performed by an integrated circuit (“IC”), an access terminal, or an access point. The IC may comprise a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, electrical components, optical components, mechanical components, or any combination thereof designed to perform the functions described herein, and may execute codes or instructions that reside within the IC, outside of the IC, or both. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
• It is understood that any specific order or hierarchy of steps in any disclosed process is an example of a sample approach. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.
• The functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. In summary, it should be appreciated that a computer-readable medium may be implemented in any suitable computer-program product.
• The previous description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the scope of the disclosure. Thus, the present disclosure is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (28)

1. A method of communication, comprising:

determining an optimized reduced power level for an overhead channel of an unplanned access point to an associated access terminal during a call therebetween; and

transmitting the overhead channel from the unplanned access point at the optimized reduced power level to the associated access terminal.

2. The method ofclaim 1, further comprising receiving forward link power control signals designating adjustments to a power level of a traffic channel associated with the overhead channel.

3. The method ofclaim 2, further comprising adjusting the power level of the traffic channel until an adequate error rate is determined.

4. The method ofclaim 3, further comprising determining a traffic-to-overhead channel ratio of the power level of the traffic channel over the power level of the overhead channel.

5. The method ofclaim 1, wherein the optimized reduced power level for the overhead channel is determined as

${\mathrm{Ecp}}_{\mathrm{OPTIMAL}}=\arg \underset{\mathrm{Ecp}}{\min }\left[\mathrm{Ecp}+f\left(\mathrm{Ecp}\right)\right]$$\mathrm{where}$$\mathrm{Ect}=f\left(\mathrm{Ecp}\right).$

6. The method ofclaim 1, wherein the overhead channel is one of a pilot channel, a synchronization channel, and a broadcast/paging channel.

7. The method ofclaim 1, further comprising:

repeating the determining an optimized reduced power level for each overhead channel of each of the plurality of calls from the unplanned access point with a respective plurality of associated access terminals; and

determining an overall optimized reduced power level from the plurality of calls.

8. An apparatus for communication, comprising:

an interference controller configured to determine an optimized reduced power level for an overhead channel of an unplanned access point to an associated access terminal during a call therebetween; and

a communication controller configured to transmit the overhead channel from the unplanned access point at the optimized reduced power level to the associated access terminal.

9. The apparatus ofclaim 8, wherein the communication controller is further configured to receive forward link power control signals designating adjustments to a power level of a traffic channel associated with the overhead channel.

10. The apparatus ofclaim 9, wherein the communication controller is further configured to adjust the power level of the traffic channel until an adequate error rate is determined.

11. The apparatus ofclaim 10, wherein the interference controller is further configured to determine a traffic-to-overhead channel ratio of the power level of the traffic channel over the power level of the overhead channel.

12. The apparatus ofclaim 8, wherein the optimized reduced power level for the overhead channel is determined as

${\mathrm{Ecp}}_{\mathrm{OPTIMAL}}=\arg \underset{\mathrm{Ecp}}{\min }\left[\mathrm{Ecp}+f\left(\mathrm{Ecp}\right)\right]$$\mathrm{where}$$\mathrm{Ect}=f\left(\mathrm{Ecp}\right).$

13. The apparatus ofclaim 8, wherein the overhead channel is one of a pilot channel, a synchronization channel, and a broadcast/paging channel.

14. The apparatus ofclaim 8, wherein the interference controller is further configured to repeat determining an optimized reduced power level for each overhead channel of each of the plurality of calls from the unplanned access point with a respective plurality of associated access terminals, and to determine an overall optimized reduced power level from the plurality of calls.

15. An apparatus for communication, comprising:

means for determining an optimized reduced power level for an overhead channel of an unplanned access point to an associated access terminal during a call therebetween; and

means for transmitting the overhead channel from the unplanned access point at the optimized reduced power level to the associated access terminal.

16. The apparatus ofclaim 15, further comprising means for receiving forward link power control signals designating adjustments to a power level of a traffic channel associated with the overhead channel.

17. The apparatus ofclaim 16, further comprising means for adjusting the power level of the traffic channel until an adequate error rate is determined.

18. The apparatus ofclaim 17, further comprising means for determining a traffic-to-overhead channel ratio of the power level of the traffic channel over the power level of the overhead channel.

19. The apparatus ofclaim 15, wherein the optimized reduced power level for the overhead channel is determined as

${\mathrm{Ecp}}_{\mathrm{OPTIMAL}}=\arg \underset{\mathrm{Ecp}}{\min }\left[\mathrm{Ecp}+f\left(\mathrm{Ecp}\right)\right]$$\mathrm{where}$$\mathrm{Ect}=f\left(\mathrm{Ecp}\right).$

20. The apparatus ofclaim 15, wherein the overhead channel is one of a pilot channel, a synchronization channel, and a broadcast/paging channel.

21. The apparatus ofclaim 15, further comprising:

means for repeating the determining an optimized reduced power level for each overhead channel of each of the plurality of calls from the unplanned access point with a respective plurality of associated access terminals; and

means for determining an overall optimized reduced power level from the plurality of calls.

22. A computer-program product, comprising:

computer-readable medium comprising codes for causing a computer to:

determine an optimized reduced power level for an overhead channel of an unplanned access point to an associated access terminal during a call therebetween; and

transmit the overhead channel from the unplanned access point at the optimized reduced power level to the associated access terminal.

23. The computer-program product ofclaim 22, further comprising codes for causing the computer to receive forward link power control signals designating adjustments to a power level of a traffic channel associated with the overhead channel.

24. The computer-program product ofclaim 23, further comprising codes for causing the computer to adjust the power level of the traffic channel until an adequate error rate is determined.

25. The computer-program product ofclaim 24, further comprising codes for causing the computer to determine a traffic-to-overhead channel ratio of the power level of the traffic channel over the power level of the overhead channel.

26. The computer-program product ofclaim 22, wherein the optimized reduced power level for the overhead channel is determined as

${\mathrm{Ecp}}_{\mathrm{OPTIMAL}}=\arg \underset{\mathrm{Ecp}}{\min }\left[\mathrm{Ecp}+f\left(\mathrm{Ecp}\right)\right]$$\mathrm{where}$$\mathrm{Ect}=f\left(\mathrm{Ecp}\right).$

27. The computer-program product ofclaim 22, wherein the overhead channel is one of a pilot channel, a synchronization channel, and a broadcast/paging channel.

28. The computer-program product ofclaim 22, further comprising codes for causing the computer to:

repeat the determining an optimized reduced power level for each overhead channel of each of the plurality of calls from the unplanned access point with a respective plurality of associated access terminals; and

determine an overall optimized reduced power level from the plurality of calls.

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