WO2010147386A2 - Method for transmitting and receiving paging message in a wireless communication system including femtocell - Google Patents

Abstract

A method for transmitting and receiving a paging message in a wireless communication system including femtocells is disclosed. The paging message reception method includes receiving a paging message from a macro base station during a primary paging listening interval, moving to a coverage area of a femtocell base station accessible to the mobile station and selecting the femtocell base station, and receiving a paging message from the femtocell base station during a secondary paging listening interval.

Description

METHOD FOR TRANSMITTING AND RECEIVING PAGING MESSAGE IN A WIRELESS COMMUNICATION SYSTEM INCLUDING FEMTOCELL

The present invention relates to a wireless communication system, and more particularly, to a method for transmitting and receiving a paging message in a wireless communication system including femtocells.

Technologies concerning femtocell Base Stations (BSs) supporting indoors or shadowing areas that are not supported by macro cells have recently been proposed. A femtocell BS is an ultra small, low-power indoor BS and a femtocell is the coverage area of a femtocell BS. Although a femtocell is conceptually similar to a pico cell, a femtocell BS is an advanced BS relative to a pico cell BS, in terms of functionality.

A femtocell BS may be overlaid within a macro cell or not overlaid in an area beyond the coverage of a macro cell. A macro BS covering a femtocell is referred to as an overlay macro BS.

A Mobile Station (MS) connected to a macro BS may or may not perform handover to a femtocell area overlaid within a macro cell, when it passes through the femtocell area.

If the MS moves into a femtocell area that it is authorized to access, it performs handover to the femtocell BS. On the contrary, if the MS moves into a femtocell area that it is not authorized to access, it does not perform handover to the femtocell BS.

A description will now be made of idle mode of an MS and a paging group.

A broadband wireless access system supports idle mode to minimize the power consumption of MSs. Generally, idle mode is intended as a mechanism to allow an MS to become periodically available for downlink broadcast traffic messaging without requiring the MS to register to any particular BS as the MS moves in a radio link environment populated by multiple BSs.

The idle-mode MS does not need to perform a handover procedure during moving between BSs within the same paging zone. Therefore, the MS may save power that might otherwise be consumed to transmit uplink information for the handover procedure.

A paging zone is defined as an area covered by a paging group including a plurality of BSs and paging is a function of, upon generation of an incoming call, locating an MS for which the incoming call is intended (e.g. detecting a BS or a Mobile Switching Center (MSC) to which the MS belongs). The paging group is a logical group. The purpose of the paging group is to offer a contiguous coverage area in which the MS can be paged on a downlink if there is traffic targeted at it.

A paging group may include one or more BSs and one BS may be a member of one or more paging groups. Paging groups are defined in a management system. A paging group may use a paging group-action backbone message. A paging controller may use another backbone message, paging-announce, to manage a list of idle-mode MSs and initiate paging of an MS on all BSs belonging to a paging group.

When an MS requests transition to idle mode to a BS, the BS may transition the MS to the idle mode by transmitting its paging group Identifier (ID) to the MS.

The idle-mode MS may notify the paging controller of its location by location updating, when a location update timer expires, when the MS moves into another paging group area, or before power-off.

A conventional paging procedure will be described below.

Upon receipt of an incoming call or a packet for an idle-mode MS, a paging controller transmits a paging message to all BSs within a paging group and, upon receipt of the paging message, each BS broadcasts a Paging Advertisement (PAG-ADV) message to MSs managed by the BS. The idle-mode MS monitors the PAG-ADV message and determines whether to transition to normal mode or stay in the idle mode. That is, if the paging controller has paged the idle-mode MS, the MS enters the normal mode and communicate with its serving BS.

However, when a femtocell BS is within the coverage area of a macro BS, the paging offsets of the macro BS and the femtocell BS are conventionally identical. Therefore, the macro BS and the femtocell BS transmit paging messages at the same time, interfering with each other.

As described above, the conventional technology causes interference because a macro BS and a femtocell BS use an identical paging offset.

An object of the present invention devised to solve the problem lies on a method for receiving a paging message with reduced interference.

It will be appreciated by persons skilled in the art that the objects that could be achieved with the present invention are not limited to what has been particularly described hereinabove and the above and other objects that the present invention could achieve will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.

The object of the present invention can be achieved by providing a method for receiving a paging message at a mobile station in a wireless communication system including femtocells, including receiving a paging message from a macro base station during a primary paging listening interval, moving to a coverage area of a femtocell base station accessible to the mobile station and selecting the femtocell base station, and receiving a paging message from the femtocell base station during a secondary paging listening interval.

The method may further include receiving a Paging Group Identifier (PGID) information message from the femtocell base station during the primary paging listening interval, and monitoring the secondary paging listening interval, if a PGID of a paging group to which the mobile station belongs is not included in the PGID information message.

The mobile station may receive a preamble from the femtocell base station and select the femtocell base station according to a signal strength of the preamble.

The mobile station may receive a deregistration command message including information about the primary paging listening interval and the secondary paging listening interval from a base station.

In another aspect of the present invention, provided herein is a method for transmitting a paging message at a femtocell base station in a wireless communication system including femtocells, including transmitting to a mobile station a PGID information message including a PGID during a secondary paging listening interval, and transmitting a paging message to the mobile station during the secondary paging listening interval. The secondary paging listening interval is different from a primary paging listening interval during which a macro base station having the femtocell BS overlaid transmits a paging message to the mobile station.

A PGID information message that the femtocell base station broadcasts during the primary paging listening interval may not include the PGID.

The femtocell base station may transmit a preamble including a cell ID to the mobile station.

Embodiments of the present invention have the following effects.

As a macro BS and a femtocell BS transmit paging messages at different points of time, interference can be reduced.

It will be appreciated by persons skilled in the art that that the effects that could be achieved with the present invention are not limited to what has been particularly described hereinabove and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.

The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention.

In the drawings:

FIG. 1 is a diagram illustrating a signal flow for an idle mode transition and paging procedure of a Mobile Station (MS) in a wireless communication system according to an embodiment of the present invention.

FIG. 2 illustrates a method for receiving a paging message according to an embodiment of the present invention.

FIG. 3 illustrates paging offsets of a macro Base Station (BS) and a plurality of femtocell BSs.

FIG. 4(a) illustrates a case where an MS monitors a primary Paging Listening Interval (PLI).

FIG. 4(b) illustrates a case where an MS monitors a secondary PLI.

FIG. 5 illustrates a case where a femtocell BS and a macro BS transmit SuperFrame Headers (SFHs) at the same point of time.

FIG. 6 illustrates a case where a femtocell BS and a macro BS transmit SFHs at different points of time.

Now, the above and other aspects of the present invention will be described in detail through preferred embodiments with reference to the accompanying drawings so that the present invention can be easily understood and realized by those skilled in the art. Modifications to the preferred embodiment will be readily apparent to those of ordinary skill in the art, and the disclosure set forth herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention and the appended claims. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention. The same reference numbers will be used throughout this specification to refer to the same or like parts.

Through the specification, when it is said that some part "includes" a specific element, this means that the part may further include other elements, not excluding them, unless otherwise mentioned. The term "-er(or)", "module", "portion" or "part" is used to signify a unit of performing at least one function or operation. The unit can be realized in hardware, software, or in combination of both.

With reference to FIG. 1, a description will be made of an idle mode transition and paging procedure of a Mobile Station (MS) in a wireless communication system.

FIG. 1 is a diagram illustrating a signal flow for an idle mode transition and paging procedure of an MS in a wireless communication system according to an embodiment of the present invention.

Paging may be carried out on a paging group basis in idle mode. For example, an MS may be a member of one or more paging groups. In each paging group, upon receipt of an incoming call for an MS or upon receipt of a user packet directed to the MS from an external network, a Paging Controller (PC) pages the MS to locate it. For the paging, specifically, the PC may transmit a paging message to all Base Stations (BSs) within the paging group and, upon receipt of the paging message, each BS broadcasts a Mobile Paging Advertisement (MOB_PAG-ADV) message to MSs managed by the BS.

Referring to FIG. 1, an MS transmits a Deregistration Request (DREG-REQ) message to a serving BS to transition from normal mode to idle mode in step S110.

Upon receipt of the DREG-REQ message, the serving BS transmits BS information and MS information to a PC in step S120. Specifically, the MS information may be an Identifier (ID) or Medium Access Control (MAC) ID of the MS, and the BS information may be an ID of the serving BS.

The PC transmits PC information to the serving BS in step S130.

The serving BS transmits a Deregistration Command (DREG-CMD) message to the MS in response to the DREG-REQ message in step S140.

The DREG-CMD message may include information about a Paging Group ID (PGID), a primary paging offset, a secondary paging offset, a primary Paging Listening Interval (PLI), and a secondary PLI.

The PGID is an ID of a paging group that the BS allocates to the MS. The primary paging offset indicates a time at which the MS monitors a paging message from a macro BS of the paging group. The secondary paging offset indicates a time at which the MS monitors a paging message from a femtocell BS of the paging group. A PLI is a time period during which the MS monitors a paging message from the paging group.

Upon receipt of the DREG-CMD message, the MS enters the idle mode. The idle-mode MS may receive a paging message based on paging information received in the DREG-CMD message.

Upon receipt of an incoming call or packet for the idle-mode MS in step S150, the PC transmits a paging message to all BSs of the paging group of the MS in step S160. Upon receipt of the paging message, the BSs of the paging group broadcast a Paging Advertisement (PAG-ADV) message to their managed MSs in step S170. The MS checks the PAG-ADV message, enters normal mode, and communicates with the serving BS in step S180. Notably, the macro BS transmits a PAG-ADV message at the primary paging offset, whereas the femtocell BS transmits a PAG-ADV message at the secondary paging offset.

Now a method for receiving a paging message at an MS in the wireless communication system according to an embodiment of the present invention will be described below.

FIG. 2 illustrates a method for receiving a paging message according to an embodiment of the present invention and FIG. 3 illustrates paging offsets of a macro BS and a plurality of femtocell BSs. In FIGs. 2 and 3, third and fourth femtocell BSs (femtocell BS #3 and femtocell BS #4) are accessible to the MS, whereas a fifth femtocell BS (femtocell BS #5) is not accessible to the MS.Femtocell BS #3 andfemtocell BS #4 are members of Closed Subscriber Group (CSG) A andfemtocell BS #5 is a member of CSG B. Femtocell BSs in different CSGs use different paging offsets.

In accordance with an embodiment of the present invention, a macro BS transmits a PGID and a paging message during a primary PLI, and a femtocell BS transmits a PGID and a paging message during a secondary PLI. Accordingly, the MS monitors the primary PLI when it receives a service from the macro BS, and monitors the secondary PLI when it receives a service from the femtocell BS. FIG. 4(a) illustrates a case where an MS monitors a primary PLI and FIG. 4(b) illustrates a case where an MS monitors a secondary PLI.

Referring to FIGs. 2 and 3, when an idle-mode MS moves from a second macro BS (macro BS #2) to a first macro BS (macro BS #1) at time T₀, it receives a PAG-ADV message frommacro BS #1 during a primary PLI.

Then the MS moves to the coverage area offemtocell BS #3 at time T₁. The MS selects a cell based on the signal quality of a preamble received from the cell. If the MS moves to the coverage area of a femtocell BS, the Signal-to-Noise Ratio (SNR) of a preamble from a macro BS is decreased due to a preamble from the femtocell BS. Then the MS selects the femtocell BS that offers a strong preamble by cell selection. The MS may identify whether the selected BS is a femtocell BS or a macro BS, using the preamble received from the BS. The MS receives a SuperFrame Header (SFH) from the femtocell BS, identifies from a cell ID carried in the preamble whether the femtocell BS is accessible, and checks a BS ID (BSID) from the SFH.

The femtocell BS and the macro BS may transmit SFHs at the same point of time or at different points of time. FIG. 5 illustrates a case where a femtocell BS and a macro BS transmit SFHs at the same point of time and FIG. 6 illustrates a case where a femtocell BS and a macro BS transmit SFHs at different points of time.

As illustrated in FIGs. 5 and 6, the macro BS transmits an SFH after a Secondary Advanced Preamble (SA-Preamble) that precedes a Primary Advanced Preamble (PA-Preamble), whereas the femtocell BS may transmit an SFH simultaneously with the SFH of the macro BS as illustrated in FIG. 5 or after an SA-Preamble that follows a PA-Preamble as illustrated in FIG. 6.

The MS, which has selectedfemtocell BS #3, receives a PGID information message fromfemtocell BS #3 during the primary PLI. A BS includes a PGID only in a PGID information message transmitted during its PLI. Therefore, the PGID information message received fromfemtocell BS #3 during the primary PLI does not include a PGID of a paging group to which the MS belongs.

In the absence of the PGID of the paging group in the received PGID information message, the MS monitors a secondary PLI. If the PGID of the paging group is included in a PGID information message received fromfemtocell BS #3 during the secondary PLI, the MS receives a paging message during the secondary PLI.

When the MS moves to the coverage area offemtocell BS #4 at time T₂, it receives a PGID information message fromfemtocell BS #4 during the secondary PLI. As the received PGID information message includes the PGID of the paging group to which the MS belongs, the MS stays in the idle mode without performing a location update.

Subsequently, if the MS moves to the coverage area offemtocell BS #5 at time T₃, it selectsmacro BS #1 becausefemtocell BS #5 is not accessible to the MS. Thus, since a PGID information message received frommacro BS #1 during the secondary PLI does not include the PGID of the paging group to which the MS belongs, the MS monitors the primary PLI. In the presence of the PGID of the paging group to which the MS belongs in a PGID information message received frommacro BS #1 during the primary PLI, the MS receives a paging message during the primary PLI.

FIG. 15 is a block diagram of an MS (or Advanced MS (AMS)) and a BS (or Advanced BS (ABS)) for implementing the embodiments of the present invention, according to an embodiment of the present invention.

Referring to FIG. 7, each of the MS and the BS includes anantenna 700 or 710 for transmitting and receiving information, data, signals and/or messages, a Transmission (Tx)module 740 or 750 for transmitting a messages by controlling theantenna 700 or 710, a Reception (RX)module 760 or 770 for receiving a message by controlling theantenna 700 or 710, amemory 780 or 790 for storing information related to communication between the MS and the BS, and aprocessor 720 or 730 for controlling theTx module 740 or 750, theRx module 760 or 770, and thememory 780 or 790. The BS may be a femto BS or a macro BS.

Theantennas 700 and 710 externally transmit signals generated from theTX modules 740 and 750 or output received external Radio Frequency (RF) signals to theRX modules 760 and 770. When Multiple Input Multiple Output (MIMO) is supported, two or more antennas may be used.

Theprocessors 720 and 730 provide overall control to the MS and the BS. Particularly, theprocessors 720 and 730 may perform a control function for implementing the embodiments of the present invention, a variable MAC frame control function based on service characteristics and a propagation environment, a handover function, and an authentication and encryption function. Each of the processors 820 and 830 may further include an encryption module for encrypting various messages and a timer for controlling transmission and reception of various messages.

TheTx modules 740 and 750 may encode and modulate transmission signals and/or data scheduled by theprocessors 720 and 730 in a predetermined coding and modulation scheme and outputs the modulated signals and/or data to theantennas 700 and 710.

TheRx modules 760 and 770 may recover the original data by decoding and modulating RF signals received through theantennas 700 and 710 and thus may provide the original data to theprocessors 720 and 730.

Thememories 780 and 790 may store programs for processing and control operations of the processors 720 and 830 and temporarily store input/output data. For example, thememory 780 of the MS may temporarily store an uplink grant, system information, a Station ID (STID), a Flow ID (FID), action time information, resource allocation information, and frame offset information, which are received from the BS.

Also, each of the memories 880 and 890 may include at least one of a flash memory-type storage medium, a hard disc-type storage medium, a multimedia card micro-type storage medium, a card-type memory (e.g. an Secure Digital (SD) or extreme Digital (XS) memory), a Random Access Memory (RAM), a Read-Only Memory (ROM), an Electrically Erasable Programmable Read-Only Memory, a Programmable Read-Only Memory, a magnetic memory, a magnetic disc, and optical disk.

Various embodiments have been described in the best mode for carrying out the invention.

The present invention is applicable to a wireless communication system. More particularly, the present invention is applicable to a method for transmitting and receiving a paging message in a wireless communication system.

The embodiments of the present invention may be achieved by various means, for example, hardware, firmware, software, or a combination thereof. In a hardware configuration, the embodiments of the present invention may be achieved by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, etc.

In a firmware or software configuration, the method for transmitting and receiving a paging message in a wireless communication system according to the embodiments of the present invention may be implemented in the form of a module, a procedure, a function, etc. performing the above-described functions or operations. A software code may be stored in a memory unit and executed by a processor. The memory unit is located at the interior or exterior of the processor and may transmit and receive data to and from the processor via various known means.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

It is obvious to those skilled in the art that claims that are not explicitly cited in each other in the appended claims may be presented in combination as an exemplary embodiment of the present invention or included as a new claim by a subsequent amendment after the application is filed.

Claims (7)

1. A method for receiving a paging message at a mobile station in a wireless communication system including femtocells, the method comprising:

   receiving a paging message from a macro base station during a primary paging listening interval;

   moving to a coverage area of a femtocell base station accessible to the mobile station and selecting the femtocell base station; and

   receiving a paging message from the femtocell base station during a secondary paging listening interval.
2. The method according to claim 1, further comprising:

   receiving a Paging Group Identifier (PGID) information message from the femtocell base station during the primary paging listening interval; and

   monitoring the secondary paging listening interval, if a PGID of a paging group to which the mobile station belongs is not included in the PGID information message.
3. The method according to claim 1, wherein the selection comprises:

   receiving a preamble from the femtocell base station; and

   selecting the femtocell base station according to a signal strength of the preamble.
4. The method according to claim 1, further comprising receiving a deregistration command message including information about the primary paging listening interval and the secondary paging listening interval from a base station.
5. A method for transmitting a paging message at a femtocell base station in a wireless communication system including femtocells, the method comprising:

   transmitting to a mobile station a Paging Group Identifier (PGID) information message including a PGID during a secondary paging listening interval; and

   transmitting a paging message to the mobile station during the secondary paging listening interval,

   wherein the secondary paging listening interval is different from a primary paging listening interval during which a macro base station having the femtocell BS overlaid transmits a paging message to the mobile station.
6. The method according to claim 5, wherein a PGID information message that the femtocell base station broadcasts during the primary paging listening interval does not include the PGID.
7. The method according to claim 5, further comprising transmitting a preamble including a cell ID to the mobile station.

Images