US20090257479A1 - Use of correlation combination to achieve channel detection - Google Patents
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- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
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Definitions
- CDMA modulationis a multi-user access transmission scheme in which signals from different users overlap both in frequency and in time. This is in contrast with Frequency Division Multiple Access (FDMA) in which user signals overlap in time, but are assigned unique frequencies, and Time Division Multiple Access (TDMA) in which user signals overlap in frequency, but are assigned unique time slots.
- FDMAFrequency Division Multiple Access
- TDMATime Division Multiple Access
- CDMA signalingis frequently used in cellular communication systems between a base station within a cell and a plurality of access units, e.g., wireless handsets, in the possession of users within the cell.
- the CDMA transmitted signal for each user that broadcasts from the user's access unitis spread over a wide bandwidth, which is greater than the initial user information bandwidth. Each user's signal is spread by a different spreading code to create a wideband spread.
- All of the spread wideband signals transmitted by the different usersare received at the base station and form a composite received signal.
- the receiver at the base stationdistinguishes different users by using a local copy (or local reference) of the spreading code, which is available to both the access units and the base station in the CDMA system. Such a process is called channelization.
- channelsare defined for a reverse link, i.e., when an access unit is transmitting to a base station in the system, using a code called a pseudorandom noise (PN) code.
- PNpseudorandom noise
- the receiver at the base stationdetects the desired signal from a particular user out of the composite signal by correlating the composite signal with the original PN code. All other signals having codes that do not match the code for the desired user code are rejected by the correlator.
- An exemplary CDMA reverse linkincludes a plurality of channels, e.g., access and traffic channels (or even more channel types depending on the design of the CDMA system).
- the traffic channelis used to transmit user data and voice, as well as signaling messages.
- the access channelis used on the reverse link to communicate control information to the base station. For example, when the access unit does not have a traffic channel assigned, the access channel is used to make call originations and to respond to pages and orders.
- the traffic channelsare principally used to communicate voice or data payload information but are also used for other functions.
- third generation (3G) systemsmultiple traffic channels may be assigned to each user, and the traffic channels may be encoded at different rates. This requires a receiver to configure a correlator for different data rates such that a single output is produced for a particular data rate. However, if multiple outputs and options are required, without a priori knowledge as to which channel is used, multiple codes must be searched, thus requiring multiple correlators. Such requirements contribute to the complexity and increase the cost of the receiver design.
- a wireless communications systemis particularly needed that provides a single correlator in the receiver which can be used to receive multiple channels.
- the present inventionrelates to use of combinations of correlation results to achieve detection of multiple coded signals at a receiver in a wireless communications system.
- One aspect of the inventionprovides a method of detecting coded signals wherein the code applied to the signal includes a lower rate code and a higher rate code.
- the lower rate codeis a nested or tiered code such that it comprises at least two repetitions or two sequences of the higher rate code.
- the received coded signalis correlated with the higher rate code using a single higher rate correlator to provide a higher rate code correlation result.
- the higher rate code correlation resultsare fed to two or more lower rate code correlators that combine multiple higher rate code correlation results, each using a different lower rate code, to provide corresponding lower rate code correlation results.
- the presence of at least one coded signalcan be determined from the lower rate code correlation results.
- the presence of one or another of two mutually exclusive coded signalscan be determined from the corresponding first and second lower rate code correlation results.
- the first and second lower rate code correlation resultsare compared with each other to determine the presence of either a first indication corresponding to the first lower rate code or a second indication corresponding to the second lower rate code.
- one of the two indicationscorresponds to a request by an access unit to enter an active mode in order to communicate a data payload from the access unit to a base station in a wireless communications system.
- the other indicationcorresponds to a notification by the access unit to the base station that the access unit desires to remain in a standby mode.
- N lower rate codesare used in the detection to provide M lower rate code correlation results.
- the presence of at least one coded signalcan be determined from the N lower rate code correlation results.
- the N lower rate codescan be selected from a set of M possible codes based on a priori system information.
- the system informationcan be used to limit the hypothesis outcomes, if any are known, such as the mutual exclusivity of the presence of coded signals.
- the set of M possible codesmay represent data or instructions relating to a set of nearby base stations that are candidates for possible cell handoff and N may represent the subset of the M nearby base stations that are identified as actual active candidates based on system criteria such as signal strength or signal-to-noise figure.
- the lower rate codesare preferably orthogonal to each other and can be Walsh codes, Gutleber codes, maximum length (M)-sequences, or PN-sequences.
- detection of the received coded signalis provided independent of the correlation method that is used.
- the detection methodcomprises correlating the received coded signal to provide N nested code correlation results and determining the presence of at least one coded signal from the N nested code correlation results.
- FIG. 1is a general diagram illustrating a wireless communication system.
- FIG. 2is a timing diagram illustrating heartbeat slot and link quality management (LQM) slot timing.
- LQMlink quality management
- FIG. 3is a diagram illustrating the relationship among tier 1 , tier 2 and tier 3 code sequences.
- FIG. 4is a diagram illustrating a selected set of codes in a tiered code structure.
- FIG. 5is a block diagram of channel encoding at a transmitter in the system of FIG. 1 .
- FIG. 6is a block diagram of channel correlation at a receiver according to the principles of the present invention.
- FIG. 1is a diagram of a wireless communications system 100 according to the principles of the present invention.
- a base station 25maintains wireless communication links with a plurality of access units 42 A, 42 B, 42 C (collectively, access units 42 ) as shown.
- Such wireless linksare established based upon assignment of resources on a forward link 70 and a reverse link 65 between the base station 25 and access units 42 .
- Each link 65 or 70is typically made up of several logical channels 55 or 60 .
- the system 100supports communications between interface 50 and network 20 .
- Network 20is typically a Public Switched Telephone Network (PSTN) or computer network such as the Internet.
- Interface 50is preferably coupled to a digital processing device such as a portable computer (not shown), to provide wireless access to network 20 .
- PSTNPublic Switched Telephone Network
- portable computernot shown
- the forward link channels 60 and reverse link channels 55are defined in the wireless communications system 100 as Code Division Multiple Access (CDMA) channels. That is, each CDMA channel is preferably defined by encoding data to be transmitted over the channel with a channel code. The channel coded data is then modulated onto a radio frequency carrier. This enables a receiver to decipher one CDMA channel from another knowing only the particular channel code assigned to that channel.
- CDMACode Division Multiple Access
- the forward link channels 60include at least three logical channel types. Included among these are a Link Quality Management (LQM) channel 60 L, a paging channel 60 P, and multiple traffic channels 60 T.
- LQMLink Quality Management
- the reverse link 65includes heartbeat channels 55 H, an access channel 55 A and multiple traffic channels 55 T.
- the reverse link channels 55are similar to the forward link channels 60 except that each reverse link traffic channel 55 T may support variable data rates from 2.4 kbps to a maximum of 160 kbps.
- Data transmitted between base station 25 and an access unit 42typically consists of encoded digital information, such as hypertext transfer protocol (HTTP) encoded Web page data.
- HTTPhypertext transfer protocol
- data transfer ratesare generally limited by the number of available traffic channels 55 T, 60 T.
- the forward link LQM channel 60 Lis partitioned into a predetermined number of periodically repeating time slots for the transmission of messages to each of multiple access units 42 .
- Each access unit 42 Aidentifies messages directed to itself based upon messages received in an assigned time slot.
- the reverse link heartbeat channel 55 His shared among multiple users.
- the heartbeat channel 55 His also partitioned into periodically repeating time slots. Each time slot is assigned to one of many access units 42 for transmitting heartbeat messages to the base station 25 . Accordingly, the base station 25 identifies from which access unit 42 A a message is transmitted based upon the receipt of a message in a particular time slot.
- the heartbeat channel 55 H and the LQM channel 60 Lare described in more detail below.
- LQM channel 60 and heartbeat channel 55 Hare referenced to FIG. 2 .
- access units 42transmit link request messages on the access channel 55 A to base station receiver 35 via access unit transmitter 40 . Messages are then acknowledged and processed at the base station 25 . If available, resources are then allocated at the base station 25 to establish a bidirectional communication link with the requesting access unit 42 A.
- the paging channel 60 Pis used by the base station transmitter 30 to send overhead and paging messages or commands to the access unit receiver 45 .
- Overhead informationincludes data such as system configuration parameters for establishing wireless links with access units 42 .
- wireless communication system 100includes a heartbeat channel 55 H in the reverse link 65 and link quality management channel (LQM) 60 L in the forward link 70 .
- LQMlink quality management channel
- These channelsare shared between the base station 25 and multiple access units 42 . That is, the base station 25 transmits messages to multiple access units 42 using the same forward link LQM channel 60 L, where a message to a particular access unit 42 A is transmitted in an assigned time slot. In this way, time slot assignments serve as a way of addressing messages to a particular access unit and corresponding communication link.
- the present systemcan support users that require on-demand, sporadic high speed throughput.
- remote users connected to the Internet over a wireless linktypically require high speed throughput when downloading an object file such as a Web page.
- Such usersthen typically do not require any data transfer for a period of time.
- traffic channels 55 Tare allocated on an as-needed basis to support data transfers, optimizing the use of available resources in wireless communication system 100 .
- FIG. 2is a timing diagram for the heartbeat channel 55 H and LQM channel 60 L.
- only one of each channel typeis shown in FIG. 2 for illustrative purposes.
- time slotsare defined per EPOCH period in each of the heartbeat 55 H and LQM 60 L channels.
- the EPOCH period in the illustrated embodimentis 13.3 mS, so that each time slot is 208 mS or 256 code chips where a chip is a unit of time that corresponds to the output interval of the spreading code. Because time slots repeat on a periodic basis, base station 25 exchanges information with a particular access unit 42 A every EPOCH or 13.3 mS.
- Data transmissions on the LQM channel 60 Lare maintained by the base station 25 , which is preferably used as a master timing reference. That is, timing of the access units 42 is aligned with base station 25 . Access units 42 , therefore, must synchronize themselves to the base station 25 , and specifically to the LQM channel 60 L, in order to maintain synchronization with the base station 25 .
- a link between the base station 25 and an access unit 42 Ais maintained in one of three modes: active, standby or idle. Synchronization between base station 25 and a particular access unit 42 A is maintained only for the active and standby mode.
- Each access unit 42 A in the standby modeis assigned one time slot in the forward link LQM channel 60 L and one time slot in the reverse link heartbeat channels 55 H. Accordingly, information is targeted to a receiving access unit 42 A (subscriber) based upon the transmission of a message in a particular time slot. For example, an access unit 42 A assigned to time slot # 1 decodes information received in time slot # 1 on the forward link LQM channel 60 L, while data is transmitted back to the base station 25 from access unit 42 A in time slot # 1 of the reverse link heartbeat channel 55 H. Both base station 25 and access unit 42 A identify to which link a message pertains based on receipt of a message in a particular time slot.
- LQM channel 60 Lis used as the time reference as described above, the principles of the present invention equally apply where the heartbeat channel 55 H is alternatively used as a master timing reference rather than the LQM channel 60 L.
- base station 25is optionally synchronized with respect to an access unit 42 A.
- synchronizationis maintained between the forward link LQM channel 60 L and reverse link heartbeat channel 55 H based upon messages sent in the appropriate time slot on the LQM channel 60 L indicating to a particular access unit 42 A whether messages transmitted to the base station 25 from that access unit are received in the appropriate time slot.
- Message transmissions from the access unit transmitter 40 to base station 25 on the heartbeat channel 55 Hare analyzed at base station receiver 35 to achieve fine tuning alignment between base station 25 and each of multiple access units 42 .
- time slots A, through A, 6 of the LQM channel 60 Lare reserved for access units 42 in the active mode, indicating that data is being transferred between the access unit 42 A and the base station 25 .
- time slots numbered 1 - 48are reserved for access units 42 operating in the standby mode on the LQM channels 60 L.
- a set of channel codesare used at the access units 42 , one code of which is generally to be transmitted in the assigned time slot in the reverse link heartbeat channel 55 H.
- the transmission of this codeis used as a signal received by the base station 25 to retain synchronization with the access unit 42 A while in a “standby” mode.
- Each codemay also correspond to a particular command or request.
- one codeis used to notify the base station that the access unit 42 A is ready to begin transmitting a data payload to the base station, i.e., an access unit requests to go into an “active” transmission mode. This is referred to herein as a “heartbeat with request” signal.
- Another codeis used to notify the base station that the access unit desires to remain in standby mode. This is referred to herein as a “heartbeat” signal.
- the wireless systemprovides three tiers of data rates, i.e., tier 1 , tier 2 , and tier 3 , for use by the CDMA channels.
- a transmittertransmits 8 chips per symbol to a receiver.
- the transmittertransmits 32 chips per symbol to the receiver.
- the transmittertransmits 128 chips per symbol.
- FIG. 3shows the relationship between tiers 1 , 2 and 3 in more detail.
- a tier 1 codecomprises an 8 chip sequence J 1 through J 8 .
- the tier 2 codecomprises 4 code elements, K 1 through K 4 .
- Each of the code elements K 1 through K 4is composed of, is aligned with, and has a duration equal to, a tier 1 code sequence J 1 through J 8 . That is, the code boundary of the tier 1 code coincides with each of the tier 2 code elements K 1 through K 4 .
- the tier 2 coderepeats every 32 chips.
- the tier 3 codecomprises code elements, L 1 through L 4 .
- Each code element of the tier 3 codeis composed of, is aligned with a corresponding tier 2 code sequence, K 1 through K 4 .
- the tier 3 code sequence, L 1 through L 4has a duration of 128 chips.
- the difference between the channel code assigned to the heartbeat signal versus the heartbeat with request signalis the specific tier 3 code that is applied. That is, the channel codes assigned to the heartbeat and heartbeat with request signals are selected such that the tier 1 and tier 2 codes are the same for each signal. The difference is only in the tier 3 code sequence that nests the tier 1 and tier 2 codes.
- FIG. 4shows a tree structure for the tiered codes.
- codes that are assigned to heartbeat and heartbeat with request signalsare indicated as individual branches connected to a common tier 2 branch that is in turn connected to a particular tier 1 branch.
- Other branchesare shown to indicate channel code assignments for other channels, e.g., traffic, maintenance and access channels.
- the notation (X, Y, Z)is used to indicate the branches assigned at each tier to the particular code.
- one code (7,3,0)is reserved for the heartbeat signal while another code (7,3,1) is reserved for the heartbeat with request signal.
- Another optional heartbeat signaling pairuses codes (7,3,2) and (7,3,3). Note that other channels (e.g., traffic, access and maintenance) can be assigned other unique codes, as shown in the tree structure.
- the tier 3 codesare preferably orthogonal to each other.
- the orthogonal codescan be Walsh codes or Gutleber codes or other code such as maximal length (M)-sequences or PN-sequences.
- Mmaximal length
- a three-level or three-tiered codeis used in the preferred embodiment, other embodiments can use two tiers. For example, a 64 chip tier 1 code nested in a four element tier 2 code, that is, 256 chips in length could be used.
- Another two-tiered codeincludes a 16 chip tier 1 code nested in an eight element tier 2 code, that is, 128 chips in length.
- the channel encoding processtakes an input data signal 101 that represents information to be transmitted.
- the datahas a value of 1 for the duration of the time slot, i.e., 256 code chips.
- a serial to parallel converter 102provides an in-phase (i) and quadrature (q) signal path to a pair of multipliers 106 - i and 106 - q.
- a spreading code generator 104provides a spreading code used for spectrum spreading purposes. Typically, the spreading code is a short pseudorandom noise code.
- a second code modulation stepis applied to the (i) and (q) signal paths by multiplying the two signal paths with a tier 1 code. This is accomplished by the tier 1 code generator 110 and code multipliers 120 - 1 and 120 - q.
- a third step in the encoding processis to apply a tier 2 code as generated by tier 2 code generator 112 . This is accomplished by the multipliers 122 - i and 122 - q impressing the tier 2 code on each of the in-phase and quadrature signal paths.
- a tier 3 codeis applied to the (i) and (q) signal paths. This is accomplished by the tier 3 code generator 114 and the code multipliers 124 - i and 124 - q. As noted previously, the tier 3 code (x) for sending the heartbeat signal is selected to be different from the tier 3 (y) code selected for sending the heartbeat with request signal.
- the tier 3 encoded in-phase and quadrature signal pathsmodulate a carrier wave as generated by carrier wave source 126 using an RF modulator 128 .
- the modulated signalis amplified through amplifier 130 and transmitted via antenna 132 .
- a chip clock 108provides chip clock timing at the rate of 1.2288 MHz to the tier 1 , tier 2 , and tier 3 generators 110 , 112 and 114 .
- the tier 1 codeis at a rate of 8 chips per symbol.
- the chip clockis divided down by a factor of 8 using divider 116 .
- the tier 2 code generatoroperates at 32 chips per symbol.
- the chip clockis divided again by a factor of 4 by divider 118 for the tier 3 generator 114 which provides 128 chips per symbol.
- FIG. 6is a block diagram that illustrates channel correlation at a receiver 35 of base station 25 ( FIG. 1 ) in accordance with principles of the present invention.
- the correlation processtakes advantage of the structure of the tiered or nested codes used to represent coded signals, for example the heartbeat and heartbeat with request signals in the present system.
- the correlation processuses the output of a higher rate correlator to feed two or more lower rate correlators, as described further below. Therefore, the higher rate correlator structure can be shared to achieve detection of multiple coded signals.
- the channel correlation processincludes a number of codes as generated by spreading code generator 220 , tier 1 code generator 208 and tier 2 code generator 210 .
- tier 3 code generators 212 x and 212 yare generated by tier 3 code generators 212 x and 212 y, respectively.
- a signal 203 received by antenna 202is fed into RF demodulator 204 where the signal is demultiplexed to provide in-phase (i) and quadrature (q) signal paths to a first pair of multipliers 222 - i and 222 - q.
- Spreading code generator 220provides a spreading code used for despreading purposes. This spreading code is the same as the spreading code used in the encoding process with spreading code generator 104 ( FIG. 5 ).
- a second step in the correlation processis to apply the tier 1 code as generated by tier 1 code generator 208 . This is accomplished by the multipliers 224 - i and 224 - q impressing the tier 1 code on each of the in-phase and quadrature signal paths.
- the tier 2 code as generated by the tier 2 code generator 210is applied to each of the in-phase and quadrature signal paths by multipliers 226 - i and 226 - q.
- a particular tier 3 code as generated by the respective tier 3 code generators 212 x and 212 yis applied to each of the in-phase and quadrature signal paths.
- each correlation leg 227 x and 227 yincludes integrators 230 x - i, 230 x - q and 230 y - i, 230 y - q.
- each leg 227 x and 227 yare included squarers 232 x - i, 232 x - q and 232 y - i, 232 y - q.
- the outputs of the value squarersare summed in summers 234 x and 234 y respectively to provide final correlation outputs 236 x and 236 y, respectively.
- the integrators 230integrate over 128 chips.
- the integrationcan be distributed at each tier stage rather than at the final tier 3 stage as shown in FIG. 6 .
- the correlation in FIG. 6can be viewed as a series of correlations at the succeeding tiered code rates. That is, the received coded signal is correlated with the higher rate code (tier 2 ) using a single higher rate correlator (tier 2 code generator 210 , multipliers 226 - i, 226 - q ) to provide a higher rate code correlation result.
- the higher rate code correlation resultis a sub-correlation that corresponds to a code element of the lower rate code.
- the higher rate code correlation resultsare then fed to two or more lower rate code correlators (correlation legs 227 x, 227 y ) that combine multiple higher rate code correlation results, each using a different lower rate code (tier 3 code generators 212 x, 212 y ), to provide corresponding lower rate code correlation results ( 236 x, 236 y ).
- the presence of at least one coded signalcan be determined from the lower rate code correlation results.
- the dual outputs 236 x, 236 yare generated in part from the same sub-correlations or higher rate code correlation results.
- the presence of one or another of two mutually exclusive coded signalscan be determined from the lower rate code correlation results.
- the lower rate code correlation results 236 x, 236 ycan be compared with each other to determine the presence of either heartbeat (code x was sent) or heartbeat with request (code y was sent) signals.
- correlation legs 227 x and 227 yare shown in FIG. 6 , it is possible to have multiple such correlation legs to use combinations of correlation results to achieve detection of multiple coded signals.
- the correlator structurecan be expanded to have N different correlation legs 227 , each one having a different tier 3 code generator 212 corresponding to the N selected codes.
- the N lower rate codescan be used in the detection to provide M lower rate code correlation results. That is, in general, the presence of at least one coded signal can be determined from the N lower rate code correlation results.
- the N lower rate codescan be selected from a set of M possible codes based on a priori system information. The system information can be used to limit the hypothesis outcomes, if any are known, such as the mutual exclusivity of the presence of coded signals.
- the set of M possible codesmay represent a set of nearby base stations that are candidates for possible cell handoff of one or more of the code channels and N may represent the subset of the M nearby base stations that are identified as actual active or preferred candidates based on system criteria such as signal strength or signal-to-noise figure.
- a mobile access unitis moving from an area serviced by one cell site to another.
- the timing of handing over control to a new base stationmust be carefully orchestrated.
- MAHOMobile Assisted Hand Over
- the mobile access unitperforms certain calculations to determine when to communicate to both the current serving base station and a new serving base station that hand over is imminent.
- CDMA based systemsthat employ soft hand-off of the reverse link, this may be transmitted to both base stations simultaneously, but it is not required.
- each access unitmaintains a list of candidate base stations in its general vicinity. This can be done, for example, by detecting the presence of forward link paging channels 60 P or pilot channels from various base stations 25 in the vicinity ( FIG. 1 ). At any given time, this candidate list will consist of N of M possible base stations in the system 100 .
- the access unitperiodically sends the candidate to each base station that it “sees,” such as on a reverse link traffic channel 55 T.
- precise timing of an actual need for hand overis critical. Accordingly, the access unit can use the invention by simply sending a short burst with one of N possible tier 3 codes.
- the base stationhas the candidate list of N preferred base stations available, it can utilize N tier 3 correlators 227 with the N expected codes, and determine which one was sent. In this way, hand over control information can be rapidly and efficiently communicated for selecting service.
- FIG. 6shows sharing of the output of a higher rate (i.e., tier 2 ) correlator with two or more lower rate (i.e., tier 3 ) correlators.
- a higher ratei.e., tier 2
- tier 3lower rate
- the correlation process described above with respect to FIG. 6can be time multiplexed among different access units 42 ( FIG. 1 ) that share the heartbeat channels 55 H, thereby allowing a single correlator structure to be shared.
- the tier 1 , 2 , and 3 codesare shown in FIGS. 5 and 6 as operations using Walsh codes. It should be understood that other orthogonal codes such as Gutleber codes could be used as well as M-sequences or pseudo orthogonal codes.
- detection of the received coded signalcan be provided independent of the correlation method that is used where there is a priori system knowledge available.
- the nested codebeing one of a set of M possible nested codes
- detectioncan be achieved by correlating the received coded signal to provide N nested code correlation results and determining the presence of at least one coded signal from the N nested code correlation results using the system knowledge to limit outcomes.
- the specific N nested codescan change over time, with information indicating the changes in the current set of codes being communicated between base station and access units to provide a priori system information that is current.
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Abstract
Description
- This application is a continuation of U.S. patent application Ser. No. 10/119,522, filed Apr. 9, 2002, now U.S. Pat. No. 7,551,663, issuing on Jun. 23, 2009 which is a continuation-in-part of U.S. patent application Ser. No. 09/775,305 filed Feb. 1, 2001, now U.S. Pat. No. 7,079,523, issued Jul. 18, 2006 and claims priority from U.S. Provisional Application No. 60/282,936, filed on Apr. 10, 2001. This application is also related to U.S. patent application Ser. No. 09/738,934 filed Dec. 15, 2000. The entire teachings of the above applications are incorporated herein by reference.
- Code Division Multiple Access (CDMA) modulation is a multi-user access transmission scheme in which signals from different users overlap both in frequency and in time. This is in contrast with Frequency Division Multiple Access (FDMA) in which user signals overlap in time, but are assigned unique frequencies, and Time Division Multiple Access (TDMA) in which user signals overlap in frequency, but are assigned unique time slots. CDMA signaling is frequently used in cellular communication systems between a base station within a cell and a plurality of access units, e.g., wireless handsets, in the possession of users within the cell. The CDMA transmitted signal for each user that broadcasts from the user's access unit is spread over a wide bandwidth, which is greater than the initial user information bandwidth. Each user's signal is spread by a different spreading code to create a wideband spread. All of the spread wideband signals transmitted by the different users are received at the base station and form a composite received signal. The receiver at the base station distinguishes different users by using a local copy (or local reference) of the spreading code, which is available to both the access units and the base station in the CDMA system. Such a process is called channelization.
- In an exemplary CDMA system according to the IS-95 standard, channels are defined for a reverse link, i.e., when an access unit is transmitting to a base station in the system, using a code called a pseudorandom noise (PN) code. The receiver at the base station detects the desired signal from a particular user out of the composite signal by correlating the composite signal with the original PN code. All other signals having codes that do not match the code for the desired user code are rejected by the correlator.
- An exemplary CDMA reverse link includes a plurality of channels, e.g., access and traffic channels (or even more channel types depending on the design of the CDMA system). The traffic channel is used to transmit user data and voice, as well as signaling messages. The access channel is used on the reverse link to communicate control information to the base station. For example, when the access unit does not have a traffic channel assigned, the access channel is used to make call originations and to respond to pages and orders. The traffic channels are principally used to communicate voice or data payload information but are also used for other functions.
- In presently proposed so-called third generation (3G) systems, multiple traffic channels may be assigned to each user, and the traffic channels may be encoded at different rates. This requires a receiver to configure a correlator for different data rates such that a single output is produced for a particular data rate. However, if multiple outputs and options are required, without a priori knowledge as to which channel is used, multiple codes must be searched, thus requiring multiple correlators. Such requirements contribute to the complexity and increase the cost of the receiver design.
- There is a need for a wireless system with a flexible, simple receiver design. A wireless communications system is particularly needed that provides a single correlator in the receiver which can be used to receive multiple channels.
- In general, the present invention relates to use of combinations of correlation results to achieve detection of multiple coded signals at a receiver in a wireless communications system. One aspect of the invention provides a method of detecting coded signals wherein the code applied to the signal includes a lower rate code and a higher rate code. The lower rate code is a nested or tiered code such that it comprises at least two repetitions or two sequences of the higher rate code. The received coded signal is correlated with the higher rate code using a single higher rate correlator to provide a higher rate code correlation result. The higher rate code correlation results are fed to two or more lower rate code correlators that combine multiple higher rate code correlation results, each using a different lower rate code, to provide corresponding lower rate code correlation results. The presence of at least one coded signal can be determined from the lower rate code correlation results.
- In an embodiment that uses a first lower rate code and a second lower rate code, the presence of one or another of two mutually exclusive coded signals can be determined from the corresponding first and second lower rate code correlation results. In particular, the first and second lower rate code correlation results are compared with each other to determine the presence of either a first indication corresponding to the first lower rate code or a second indication corresponding to the second lower rate code. In one embodiment, one of the two indications corresponds to a request by an access unit to enter an active mode in order to communicate a data payload from the access unit to a base station in a wireless communications system. The other indication corresponds to a notification by the access unit to the base station that the access unit desires to remain in a standby mode.
- According to another aspect of the invention, N lower rate codes are used in the detection to provide M lower rate code correlation results. The presence of at least one coded signal can be determined from the N lower rate code correlation results. The N lower rate codes can be selected from a set of M possible codes based on a priori system information. The system information can be used to limit the hypothesis outcomes, if any are known, such as the mutual exclusivity of the presence of coded signals. In one embodiment, the set of M possible codes may represent data or instructions relating to a set of nearby base stations that are candidates for possible cell handoff and N may represent the subset of the M nearby base stations that are identified as actual active candidates based on system criteria such as signal strength or signal-to-noise figure.
- The lower rate codes are preferably orthogonal to each other and can be Walsh codes, Gutleber codes, maximum length (M)-sequences, or PN-sequences.
- According to another aspect of the invention, detection of the received coded signal is provided independent of the correlation method that is used. In particular, for a code applied to the signal that includes a nested code, the nested code being one of a set of M possible nested codes, the detection method comprises correlating the received coded signal to provide N nested code correlation results and determining the presence of at least one coded signal from the N nested code correlation results.
- The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
FIG. 1 is a general diagram illustrating a wireless communication system.FIG. 2 is a timing diagram illustrating heartbeat slot and link quality management (LQM) slot timing.FIG. 3 is a diagram illustrating the relationship amongtier 1,tier 2 andtier 3 code sequences.FIG. 4 is a diagram illustrating a selected set of codes in a tiered code structure.FIG. 5 is a block diagram of channel encoding at a transmitter in the system ofFIG. 1 .FIG. 6 is a block diagram of channel correlation at a receiver according to the principles of the present invention.FIG. 1 is a diagram of awireless communications system 100 according to the principles of the present invention. Abase station 25 maintains wireless communication links with a plurality ofaccess units forward link 70 and areverse link 65 between thebase station 25 and access units42. Eachlink logical channels - The
system 100 supports communications betweeninterface 50 andnetwork 20.Network 20 is typically a Public Switched Telephone Network (PSTN) or computer network such as the Internet.Interface 50 is preferably coupled to a digital processing device such as a portable computer (not shown), to provide wireless access tonetwork 20. - In an illustrative embodiment, the
forward link channels 60 andreverse link channels 55 are defined in thewireless communications system 100 as Code Division Multiple Access (CDMA) channels. That is, each CDMA channel is preferably defined by encoding data to be transmitted over the channel with a channel code. The channel coded data is then modulated onto a radio frequency carrier. This enables a receiver to decipher one CDMA channel from another knowing only the particular channel code assigned to that channel. - The
forward link channels 60 include at least three logical channel types. Included among these are a Link Quality Management (LQM)channel 60L, apaging channel 60P, and multiple traffic channels60T. - The
reverse link 65 includesheartbeat channels 55H, anaccess channel 55A andmultiple traffic channels 55T. Generally, thereverse link channels 55 are similar to theforward link channels 60 except that each reverselink traffic channel 55T may support variable data rates from 2.4 kbps to a maximum of 160 kbps. - Data transmitted between
base station 25 and an access unit42 typically consists of encoded digital information, such as hypertext transfer protocol (HTTP) encoded Web page data. Based on the allocation of traffic channels in thereverse link 65 orforward link 70, data transfer rates are generally limited by the number ofavailable traffic channels 55T,60T. - As shown in
FIG. 2 , the forwardlink LQM channel 60L is partitioned into a predetermined number of periodically repeating time slots for the transmission of messages to each of multiple access units42. Eachaccess unit 42A identifies messages directed to itself based upon messages received in an assigned time slot. - The reverse
link heartbeat channel 55H is shared among multiple users. For example, theheartbeat channel 55H is also partitioned into periodically repeating time slots. Each time slot is assigned to one of many access units42 for transmitting heartbeat messages to thebase station 25. Accordingly, thebase station 25 identifies from whichaccess unit 42A a message is transmitted based upon the receipt of a message in a particular time slot. Theheartbeat channel 55H and theLQM channel 60L are described in more detail below. - In the following description, reference is again generally made to
FIG. 1 , but more specific details ofLQM channel 60 andheartbeat channel 55H are referenced toFIG. 2 . - Generally, to establish a synchronized link with the
base station 25, access units42 transmit link request messages on theaccess channel 55A tobase station receiver 35 viaaccess unit transmitter 40. Messages are then acknowledged and processed at thebase station 25. If available, resources are then allocated at thebase station 25 to establish a bidirectional communication link with the requestingaccess unit 42A. - Within the
forward link 70, thepaging channel 60P is used by thebase station transmitter 30 to send overhead and paging messages or commands to theaccess unit receiver 45. Overhead information includes data such as system configuration parameters for establishing wireless links with access units42. - As mentioned previously,
wireless communication system 100 includes aheartbeat channel 55H in thereverse link 65 and link quality management channel (LQM)60L in theforward link 70. These channels are shared between thebase station 25 and multiple access units42. That is, thebase station 25 transmits messages to multiple access units42 using the same forwardlink LQM channel 60L, where a message to aparticular access unit 42A is transmitted in an assigned time slot. In this way, time slot assignments serve as a way of addressing messages to a particular access unit and corresponding communication link. - The present system can support users that require on-demand, sporadic high speed throughput. For example, remote users connected to the Internet over a wireless link typically require high speed throughput when downloading an object file such as a Web page. Such users then typically do not require any data transfer for a period of time. To support such users, it is advantageous to maintain synchronization with the base station for future on-demand data transfers. This is achieved in the
wireless communication system 100 by maintaining a minimal connection with thebase station 25 even when no data is being actively transferred between thebase station 25 and a specific access unit42. - Repeatedly creating or reviving connections for users who sporadically need a link can be time consuming and an inefficient use of resources. It is also inefficient to reserve resources such as
traffic channels 55T for subscribers who are not transmitting data. Accordingly,traffic channels 55T are allocated on an as-needed basis to support data transfers, optimizing the use of available resources inwireless communication system 100. FIG. 2 is a timing diagram for theheartbeat channel 55H andLQM channel 60L. Preferably, there are twoLQM channels 60L and twoheartbeat channels 55H since channels are typically allocated in pairs. However, only one of each channel type is shown inFIG. 2 for illustrative purposes.- As shown,64 time slots (in each direction) are defined per EPOCH period in each of the
heartbeat 55H andLQM 60L channels. The EPOCH period in the illustrated embodiment is 13.3 mS, so that each time slot is 208 mS or256 code chips where a chip is a unit of time that corresponds to the output interval of the spreading code. Because time slots repeat on a periodic basis,base station 25 exchanges information with aparticular access unit 42A every EPOCH or 13.3 mS. - Data transmissions on the
LQM channel 60L are maintained by thebase station 25, which is preferably used as a master timing reference. That is, timing of the access units42 is aligned withbase station 25. Access units42, therefore, must synchronize themselves to thebase station 25, and specifically to theLQM channel 60L, in order to maintain synchronization with thebase station 25. - Generally, a link between the
base station 25 and anaccess unit 42A is maintained in one of three modes: active, standby or idle. Synchronization betweenbase station 25 and aparticular access unit 42A is maintained only for the active and standby mode. - While in the active mode, synchronization of the forward and reverse link is maintained between the
LQM channel 60L andtraffic channels 55T since the heartbeat channel time slot is no longer dedicated on thereverse link 65 to theaccess unit 42A. - Each
access unit 42A in the standby mode is assigned one time slot in the forwardlink LQM channel 60L and one time slot in the reverselink heartbeat channels 55H. Accordingly, information is targeted to a receivingaccess unit 42A (subscriber) based upon the transmission of a message in a particular time slot. For example, anaccess unit 42A assigned totime slot # 1 decodes information received intime slot # 1 on the forwardlink LQM channel 60L, while data is transmitted back to thebase station 25 fromaccess unit 42A intime slot # 1 of the reverselink heartbeat channel 55H. Bothbase station 25 andaccess unit 42A identify to which link a message pertains based on receipt of a message in a particular time slot. It should be noted that although theLQM channel 60L is used as the time reference as described above, the principles of the present invention equally apply where theheartbeat channel 55H is alternatively used as a master timing reference rather than theLQM channel 60L. In other words,base station 25 is optionally synchronized with respect to anaccess unit 42A. - In the standby mode, synchronization is maintained between the forward
link LQM channel 60L and reverselink heartbeat channel 55H based upon messages sent in the appropriate time slot on theLQM channel 60L indicating to aparticular access unit 42A whether messages transmitted to thebase station 25 from that access unit are received in the appropriate time slot. Message transmissions from theaccess unit transmitter 40 tobase station 25 on theheartbeat channel 55H are analyzed atbase station receiver 35 to achieve fine tuning alignment betweenbase station 25 and each of multiple access units42. - As shown in
FIG. 2 , time slots A, through A,6 of theLQM channel 60L are reserved for access units42 in the active mode, indicating that data is being transferred between theaccess unit 42A and thebase station 25. Contrariwise, time slots numbered1-48 are reserved for access units42 operating in the standby mode on theLQM channels 60L. - At any given time, there are typically no more than 48 time slots in the
heartbeat channel 55H orLQM channel 60L assigned to respective access units42. This ensures that on completion of a data transfer between anaccess unit 42A andbase station 25, anaccess unit 42A in the active mode assigned an active time slot can revert back to the standby mode and consequently be assigned an unused standby mode time slot1-48 in theLQM channel 60L again. - The details relating to use of the
LQM channel 60L andheartbeat channels 55H for synchronization and timing alignment are disclosed in the above-mentioned U.S. patent application Ser. No. 09/775,305. - A set of channel codes are used at the access units42, one code of which is generally to be transmitted in the assigned time slot in the reverse
link heartbeat channel 55H. The transmission of this code is used as a signal received by thebase station 25 to retain synchronization with theaccess unit 42A while in a “standby” mode. Each code however, may also correspond to a particular command or request. For example, one code is used to notify the base station that theaccess unit 42A is ready to begin transmitting a data payload to the base station, i.e., an access unit requests to go into an “active” transmission mode. This is referred to herein as a “heartbeat with request” signal. Another code is used to notify the base station that the access unit desires to remain in standby mode. This is referred to herein as a “heartbeat” signal. - The wireless system according to the invention provides three tiers of data rates, i.e.,
tier 1,tier 2, andtier 3, for use by the CDMA channels. Attier 1, a transmitter transmits 8 chips per symbol to a receiver. Attier 2, the transmitter transmits 32 chips per symbol to the receiver. Attier 3, the transmitter transmits 128 chips per symbol. FIG. 3 shows the relationship betweentiers tier 1 code comprises an 8 chip sequence J1through J8. Thetier 2 code comprises 4 code elements, K1through K4. Each of the code elements K1through K4is composed of, is aligned with, and has a duration equal to, atier 1 code sequence J1through J8. That is, the code boundary of thetier 1 code coincides with each of thetier 2 code elements K1through K4. Thus, thetier 2 code repeats every 32 chips. Likewise, thetier 3 code comprises code elements, L1through L4. Each code element of thetier 3 code is composed of, is aligned with acorresponding tier 2 code sequence, K1through K4. Thus, thetier 3 code sequence, L1through L4, has a duration of 128 chips.- In the preferred embodiment, the difference between the channel code assigned to the heartbeat signal versus the heartbeat with request signal is the
specific tier 3 code that is applied. That is, the channel codes assigned to the heartbeat and heartbeat with request signals are selected such that thetier 1 andtier 2 codes are the same for each signal. The difference is only in thetier 3 code sequence that nests thetier 1 andtier 2 codes. The nesting of thetier 1 andtier 2 codes with respect to thetier 3 codes for the heartbeat and heartbeat with request signals is illustrated inFIG. 4 , which shows a tree structure for the tiered codes. In particular, four codes that are assigned to heartbeat and heartbeat with request signals are indicated as individual branches connected to acommon tier 2 branch that is in turn connected to aparticular tier 1 branch. Other branches are shown to indicate channel code assignments for other channels, e.g., traffic, maintenance and access channels. The notation (X, Y, Z) is used to indicate the branches assigned at each tier to the particular code. Thus, one code (7,3,0) is reserved for the heartbeat signal while another code (7,3,1) is reserved for the heartbeat with request signal. Another optional heartbeat signaling pair uses codes (7,3,2) and (7,3,3). Note that other channels (e.g., traffic, access and maintenance) can be assigned other unique codes, as shown in the tree structure. - The
tier 3 codes are preferably orthogonal to each other. The orthogonal codes can be Walsh codes or Gutleber codes or other code such as maximal length (M)-sequences or PN-sequences. It should be noted that while a three-level or three-tiered code is used in the preferred embodiment, other embodiments can use two tiers. For example, a 64chip tier 1 code nested in a fourelement tier 2 code, that is, 256 chips in length could be used. Another two-tiered code includes a 16chip tier 1 code nested in an eightelement tier 2 code, that is, 128 chips in length. - Turning attention now to
FIG. 5 , the channel encoding process for transmission of heartbeat and heartbeat with request signals on theheartbeat channel 55H of thereverse link 65 from atransmitter 40 ataccess unit 42A is described. Specifically, the channel encoding process takes an input data signal101 that represents information to be transmitted. In the case of a heartbeat or heartbeat with request signal, the data has a value of 1 for the duration of the time slot, i.e., 256 code chips. A serial toparallel converter 102 provides an in-phase (i) and quadrature (q) signal path to a pair of multipliers106-iand106-q.A spreadingcode generator 104 provides a spreading code used for spectrum spreading purposes. Typically, the spreading code is a short pseudorandom noise code. - A second code modulation step is applied to the (i) and (q) signal paths by multiplying the two signal paths with a
tier 1 code. This is accomplished by thetier 1code generator 110 and code multipliers120-1 and120-q. - A third step in the encoding process is to apply a
tier 2 code as generated bytier 2code generator 112. This is accomplished by the multipliers122-iand122-qimpressing thetier 2 code on each of the in-phase and quadrature signal paths. - In a fourth and final step of the encoding process, a
tier 3 code is applied to the (i) and (q) signal paths. This is accomplished by thetier 3code generator 114 and the code multipliers124-iand124-q.As noted previously, thetier 3 code (x) for sending the heartbeat signal is selected to be different from the tier3 (y) code selected for sending the heartbeat with request signal. - The
tier 3 encoded in-phase and quadrature signal paths modulate a carrier wave as generated bycarrier wave source 126 using anRF modulator 128. The modulated signal is amplified throughamplifier 130 and transmitted viaantenna 132. - A
chip clock 108 provides chip clock timing at the rate of 1.2288 MHz to thetier 1,tier 2, andtier 3generators tier 1 code is at a rate of 8 chips per symbol. The chip clock is divided down by a factor of 8 usingdivider 116. Thetier 2 code generator operates at 32 chips per symbol. The chip clock is divided again by a factor of 4 bydivider 118 for thetier 3generator 114 which provides 128 chips per symbol. FIG. 6 is a block diagram that illustrates channel correlation at areceiver 35 of base station25 (FIG. 1 ) in accordance with principles of the present invention. In general, the correlation process takes advantage of the structure of the tiered or nested codes used to represent coded signals, for example the heartbeat and heartbeat with request signals in the present system. In particular, the correlation process uses the output of a higher rate correlator to feed two or more lower rate correlators, as described further below. Therefore, the higher rate correlator structure can be shared to achieve detection of multiple coded signals.- The channel correlation process includes a number of codes as generated by spreading
code generator 220,tier 1code generator 208 andtier 2code generator 210. In addition, to detect separate coded signals that are coded at thetier 3 code rate, corresponding separate codes are generated bytier 3code generators 212xand212y,respectively. - As shown in
FIG. 6 , asignal 203 received byantenna 202 is fed intoRF demodulator 204 where the signal is demultiplexed to provide in-phase (i) and quadrature (q) signal paths to a first pair of multipliers222-iand222-q.Spreadingcode generator 220 provides a spreading code used for despreading purposes. This spreading code is the same as the spreading code used in the encoding process with spreading code generator104 (FIG. 5 ). - A second step in the correlation process is to apply the
tier 1 code as generated bytier 1code generator 208. This is accomplished by the multipliers224-iand224-qimpressing thetier 1 code on each of the in-phase and quadrature signal paths. - In a third step of the correlation process, the
tier 2 code as generated by thetier 2code generator 210 is applied to each of the in-phase and quadrature signal paths by multipliers226-iand226-q. - In the final step of the correlation process, a
particular tier 3 code as generated by therespective tier 3code generators 212xand212yis applied to each of the in-phase and quadrature signal paths. - As shown in
FIG. 6 , there are twocorrelation legs 227xand227ythat share thetier 2 correlation results. In the illustrated embodiment, where 2 possible codes could have been sent (x for heartbeat and y for heartbeat with request), there are twotier 3 correlators. Thetier 3 codes are applied by respective multipliers228x-i,228x-qand228y-i,228y-q.Eachcorrelation leg 227xand227yincludes integrators230x-i,230x-qand230y-i,230y-q.In addition, in the in-phase and quadrature signal paths of eachleg 227xand227yare included squarers232x-i,232x-qand232y-i,232y-q.The outputs of the value squarers are summed insummers 234xand234yrespectively to provide final correlation outputs236xand236y,respectively. - As configured, the integrators230 integrate over 128 chips. In other embodiments, the integration can be distributed at each tier stage rather than at the
final tier 3 stage as shown inFIG. 6 . - The correlation in
FIG. 6 can be viewed as a series of correlations at the succeeding tiered code rates. That is, the received coded signal is correlated with the higher rate code (tier2) using a single higher rate correlator (tier 2code generator 210, multipliers226-i,226-q) to provide a higher rate code correlation result. In a sense, the higher rate code correlation result is a sub-correlation that corresponds to a code element of the lower rate code. The higher rate code correlation results are then fed to two or more lower rate code correlators (correlation legs 227x,227y) that combine multiple higher rate code correlation results, each using a different lower rate code (tier 3code generators 212x,212y), to provide corresponding lower rate code correlation results (236x,236y). The presence of at least one coded signal can be determined from the lower rate code correlation results. Thus, thedual outputs 236x,236yare generated in part from the same sub-correlations or higher rate code correlation results. - In particular, the presence of one or another of two mutually exclusive coded signals can be determined from the lower rate code correlation results. For example, the lower rate code correlation results236x,236ycan be compared with each other to determine the presence of either heartbeat (code x was sent) or heartbeat with request (code y was sent) signals.
- It should be understood that while two
correlation legs 227xand227yare shown inFIG. 6 , it is possible to have multiple such correlation legs to use combinations of correlation results to achieve detection of multiple coded signals. For example, there can be a set ofM tier 3 codes with a known subset of N selected codes to be used in communicating coded signals. In that case, the correlator structure can be expanded to have N different correlation legs227, each one having adifferent tier 3 code generator212 corresponding to the N selected codes. - Accordingly, the N lower rate codes can be used in the detection to provide M lower rate code correlation results. That is, in general, the presence of at least one coded signal can be determined from the N lower rate code correlation results. The N lower rate codes can be selected from a set of M possible codes based on a priori system information. The system information can be used to limit the hypothesis outcomes, if any are known, such as the mutual exclusivity of the presence of coded signals.
- In one embodiment, the set of M possible codes may represent a set of nearby base stations that are candidates for possible cell handoff of one or more of the code channels and N may represent the subset of the M nearby base stations that are identified as actual active or preferred candidates based on system criteria such as signal strength or signal-to-noise figure.
- For example, consider the process of hand over in a cellular communication system, where a mobile access unit is moving from an area serviced by one cell site to another. To avoid disruption of communications (e.g., dropping a call) while the access unit crosses a cell boundary, the timing of handing over control to a new base station must be carefully orchestrated. In a process known as Mobile Assisted Hand Over (MAHO) the mobile access unit performs certain calculations to determine when to communicate to both the current serving base station and a new serving base station that hand over is imminent. For CDMA based systems that employ soft hand-off of the reverse link, this may be transmitted to both base stations simultaneously, but it is not required.
- In this process, each access unit maintains a list of candidate base stations in its general vicinity. This can be done, for example, by detecting the presence of forward
link paging channels 60P or pilot channels fromvarious base stations 25 in the vicinity (FIG. 1 ). At any given time, this candidate list will consist of N of M possible base stations in thesystem 100. The access unit periodically sends the candidate to each base station that it “sees,” such as on a reverselink traffic channel 55T. However, precise timing of an actual need for hand over (such as when thepaging channel 60P or pilot channel from a currently serving base station is diminishing in power) is critical. Accordingly, the access unit can use the invention by simply sending a short burst with one of Npossible tier 3 codes. Thus, because the base station has the candidate list of N preferred base stations available, it can utilizeN tier 3 correlators227 with the N expected codes, and determine which one was sent. In this way, hand over control information can be rapidly and efficiently communicated for selecting service. - The embodiment illustrated in
FIG. 6 shows sharing of the output of a higher rate (i.e., tier2) correlator with two or more lower rate (i.e., tier3) correlators. It should be understood, however, that in other embodiments the output of thetier 1 correlator can be shared with two ormore tier 1 correlators that in turn are shared with two ormore tier 3 correlators depending on the types of nested codes used in the wireless communications system. - The correlation process described above with respect to
FIG. 6 can be time multiplexed among different access units42 (FIG. 1 ) that share theheartbeat channels 55H, thereby allowing a single correlator structure to be shared. - The
tier FIGS. 5 and 6 as operations using Walsh codes. It should be understood that other orthogonal codes such as Gutleber codes could be used as well as M-sequences or pseudo orthogonal codes. - It should also be understood that detection of the received coded signal can be provided independent of the correlation method that is used where there is a priori system knowledge available. In particular, for a code applied to the signal that includes a nested code, the nested code being one of a set of M possible nested codes, detection can be achieved by correlating the received coded signal to provide N nested code correlation results and determining the presence of at least one coded signal from the N nested code correlation results using the system knowledge to limit outcomes. The specific N nested codes can change over time, with information indicating the changes in the current set of codes being communicated between base station and access units to provide a priori system information that is current.
- While the specific embodiments described herein relate to operation on a reverse link, it should be understood that the principles of the present invention are also applicable to embodiments that detect coded signals on a forward link.
- While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
Claims (12)
1. A base station comprising:
a receiver configured to receive and detect a coded signal wherein the code applied to the signal includes a lower rate code comprising at least two code sequences of a higher rate code;
a first correlator configured to correlate the received coded signal with the higher rate code to provide a higher rate code correlation result, and
a second correlator configured to correlate the higher rate code correlation results with a first lower rate code to provide a first lower rate code correlation result, and to correlate the higher rate code correlation results with a second lower rate code to provide a second lower rate code correlation result;
the first lower rate code correlation result compared to the second lower rate code correlation result to determine the presence of the received coded signal.
2. The base station ofclaim 1 , wherein the second correlator is configured to determine the presence of a first indication corresponding to the first lower rate code and the first lower rate code correlation result.
3. The base station ofclaim 1 , wherein the second correlator is configured to determine the presence of a second indication corresponding to the second lower rate code from the second lower rate code correlation result.
4. The base station ofclaim 1 , wherein the second correlator is configured to determine the presence of one or another of two mutually exclusive coded signals form the first and second lower rate code correlation results.
5. The method ofclaim 1 wherein the received coded signal is received periodically.
6. The method ofclaim 1 wherein the lower rate codes are orthogonal to each other.
7. The method ofclaim 1 wherein the lower rate codes are Walsh codes.
8. The method ofclaim 1 wherein the lower rate codes are Gutleber codes.
9. The method ofclaim 1 wherein the lower rate codes are M-sequences.
10. The method ofclaim 1 wherein the lower rate codes are PN-sequences.
11. The method ofclaim 1 wherein the higher rate code is 32 chips in length and the lower rate codes are 128 chips in length.
12. The method ofclaim 1 wherein the lower rate codes are used for timing signals.
Priority Applications (4)
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| US12/488,798US20090257479A1 (en) | 2001-02-01 | 2009-06-22 | Use of correlation combination to achieve channel detection |
| US13/306,547US8638877B2 (en) | 2001-02-01 | 2011-11-29 | Methods, apparatuses and systems for selective transmission of traffic data using orthogonal sequences |
| US14/137,099US9247510B2 (en) | 2001-02-01 | 2013-12-20 | Use of correlation combination to achieve channel detection |
| US14/952,474US10064144B2 (en) | 2001-02-01 | 2015-11-25 | Use of correlation combination to achieve channel detection |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/775,305US7079523B2 (en) | 2000-02-07 | 2001-02-01 | Maintenance link using active/standby request channels |
| US28293601P | 2001-04-10 | 2001-04-10 | |
| US10/119,522US7551663B1 (en) | 2001-02-01 | 2002-04-09 | Use of correlation combination to achieve channel detection |
| US12/488,798US20090257479A1 (en) | 2001-02-01 | 2009-06-22 | Use of correlation combination to achieve channel detection |
Related Parent Applications (1)
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Also Published As
| Publication number | Publication date |
|---|---|
| US20140177608A1 (en) | 2014-06-26 |
| US9247510B2 (en) | 2016-01-26 |
| US10064144B2 (en) | 2018-08-28 |
| US8638877B2 (en) | 2014-01-28 |
| US20160081048A1 (en) | 2016-03-17 |
| US7551663B1 (en) | 2009-06-23 |
| US20120218985A1 (en) | 2012-08-30 |
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