Patent Document

The present invention claims priority to U.S. Provisional Application Ser. No. 60/282,059 filed Apr. 6, 2001. 

   TECHNICAL FIELD OF THE INVENTION 
   The present invention is directed, in general, to digital communication systems and, more specifically, to an apparatus and method for dynamic allocation of Walsh codes in an adaptive antenna array (AAA) CDMA base transceiver station (BTS) utilizing spatial diversity for communications links with mobile users to support a traffic channel count greater than the Walsh code limit such as that found 2G (IS-95) systems, with a limit of 64, or in 3G (IS2000) systems, with limits of either 64 or 128. 
   BACKGROUND OF THE INVENTION 
   The radio frequency (RF) spectrum is a limited commodity. Only a small portion of the spectrum can be assigned to each communications industry. The assigned spectrum, therefore, must be used efficiently in order to allow as many frequency users as possible to have access to the spectrum. Multiple access modulation techniques are some of the most efficient techniques for utilizing the RF spectrum. Examples of such modulation techniques include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA). 
   CDMA modulation employs a spread spectrum technique for the transmission of information. The CDMA wireless communications system spreads the transmitted signal over a wide frequency band. This frequency band is typically substantially wider than the minimum bandwidth required to transmit the signal. A signal having a bandwidth of only a few kilohertz can be spread over a bandwidth of more than a megahertz. 
   All of the wireless access terminals, including both mobile stations (e.g., cell phone) and fixed terminals, that communicate in a CDMA system transmit on the same frequency. In order for the base station to identify the wireless access terminals, each wireless access terminal is assigned a unique pseudo-random (PN) long spreading code that identifies that particular wireless access terminal to the wireless network. Typically, each long code is generated using the electronic serial number (ESN) of each mobile station or fixed terminal. The ESN for each wireless access terminal is unique to that wireless access terminal. 
   Similarly, each sector of a base station uses a unique short code (containing 2 15  bits) to identify itself to access terminals. Those familiar with the art will recognize that a sector is defined by the coverage provided by the pilot, paging and synch overhead channels transmitted by the BTS for both non-adaptive and adaptive antenna systems. 
   In a preferred implementation, the user data to be transmitted to a wireless access terminal is first framed, convolutionally encoded, repeated, interleaved, and encoded with the long code to form a baseband signal. The baseband signal is then separated into an in-phase (I) component and a quadrature (Q) component prior to quadrature modulation of an RF carrier and transmission. The I-component and Q-component are spread with a unique Walsh code of length M=2 N  uniquely assigned to each access terminal assigned to a traffic channel in the sector. The I-component is modulated by a time-offset short pseudo-random noise (I-PN) binary code sequence derived from the short code of length 2 15  bits. The Q-component is modulated by a time-offset short pseudo-random noise (Q-PN) binary code sequence derived from the short code of length 2 15  bits. In an alternate embodiment, the quadrature binary sequence may be offset by one-half of a binary chip time. Those skilled in the art will recognize that the in-phase component and the quadrature component are used for quadrature phase shift keying (QPSK) modulation of an RF carrier prior to transmission. 
   The maximum capacity of a base transceiver station in a CDMA wireless network is limited by the number of unique orthogonal codes (Walsh codes) that are available for assignment to traffic channels in each sector. The number of orthogonal codes available for traffic channel assignment is limited to 56-61 for IS-95; to 56-61 for Radio Configuration  1 ,  2  or  3  of IS-2000; and 119-125 for Radio Configuration  4  or higher in IS-2000, depending on the number of paging channels assigned. The codes allocated to traffic channels may support either voice or packet data services. 
   Those acquainted with the art will recognize that the number of simultaneous traffic channels supported over the RF links to wireless access terminals depends on the propagation environment experienced by the access terminals. For a typical, good propagation mobile environment (defined in the art as Vehicular B model), the EVRC capacity supported on the forward and reverse RF links is approximately 24 Erlangs per CDMA carrier per sector in a three-sector antenna configuration. A traffic load of 24 Erlangs corresponds to 34 EVRC traffic channels with a 1% blocking probability. With an average soft handoff capacity gain of 40%, this requires 48 Walsh codes per sector on the forward link. A handoff gain of 60%, which may occur in some dense urban or highly congested areas, would require up to 54 Walsh codes. 
   For a wireless mobile application, the voice traffic capacity for EVRC vocoding may be as high is 65 Erlangs, or 80 traffic channels with a 1% blocking probability. For an adaptive antenna array base transceiver subsystem, a capacity increase of two to four times (i.e., 2×to 4×) translates into a requirement for up to 192 Walsh codes for 40% soft handoff gain and up to 216 Walsh codes for 60% soft handoff gain. In a non-mobile, wireless application, up to 320 Walsh codes are required. Thus, there are numerous scenarios in which the number of channels supported over the air exceeds the limit of 64 available Walsh codes for Radio Configuration  3  or lower or 128 available Walsh codes for Radio Configuration greater than 3. 
   Quasi-orthogonal codes have been used for increasing Walsh code availability. However, this technique results in degraded performance and lower-than-expected RF capacity due to requirements for greater Eb/No at the receiver. Another prior art method includes a segmentation of the coverage area into six sectors in non-adaptive antenna systems, which allows greater Walsh code reuse. However, the result is greater handoff transitions and increased probability of dropped calls. Those familiar with the art will recognize that doubling the number of sectors does not allow a doubling of Walsh code reuse due to the number of codes required to support soft handoff and due to added overlap regions of adjacent sector antenna patterns. However, this method is not applicable for an adaptive antenna array base transceiver subsystem (BTS) in which multiple antennas and a baseband AAA processor module are employed per sector. 
   Therefore, there is a need for improved CDMA wireless networks in which the number of users per sector is not limited by the number of available Walsh codes. In particular, there is a need for a wireless CDMA adaptive antenna array base station that can more efficiently use the available Walsh codes by dynamically allocating Walsh codes in the base station sectors so that a single Walsh code may be used to communicate simultaneously with two or more wireless access terminals within the same sector. More particularly, there is a need for a CDMA wireless base station that can dynamically allocate Walsh codes in beams formed by adaptive antenna arrays of the base station so that a single Walsh code may be used to communicate simultaneously with two or more wireless access terminals in the same sector. 
   SUMMARY OF THE INVENTION 
   The present invention provides an apparatus and method for using the spatial isolation provided by an adaptive antenna array to maximize the re-use of Walsh codes in a base transceiver subsystem of a wireless network base station. This allows the BTS to support the full capacity of the air interface in adaptive antenna array operation so that the capacity is not constrained by the 64 or 128 Walsh code limit. 
   To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide an apparatus for allocating orthogonal codes used for downlink transmissions to a plurality of wireless access terminals for use in a base station of a code division multiple access (CDMA) wireless network, wherein the base station communicates with the plurality of wireless access terminals using transmit beams formed by an adaptive antenna array. According to an advantageous embodiment of the present invention, the apparatus comprises: 1) a database capable of storing R active wireless terminal records, each of the R active wireless terminal records containing: a) an active orthogonal code and b) corresponding downlink beamforming coefficients used to communicate with one of the wireless access terminals; and 2) a controller associated with the database capable of receiving a notification that a new wireless access terminal is accessing the base station and, in response to the notification, comparing the each of the R active wireless terminal records to new downlink beamforming coefficients suitable for forming a downlink transmit beam for transmitting to the new wireless access terminal and, in response to the comparison, determines at least one active wireless terminal record containing corresponding downlink beamforming coefficients that have the least correlation with the new downlink beamforming coefficients. 
   According to one embodiment of the present invention, the controller assigns an active orthogonal code in at least one active wireless terminal record to be used in downlink transmissions to the new wireless access terminal. 
   According to another embodiment of the present invention, the base station uses up to K orthogonal codes for the downlink transmissions and the controller compares each of the R active wireless terminal records to the new downlink beamforming coefficients in response to a determination that all of the K orthogonal codes are in use. 
   According to still another embodiment of the present invention, the controller determines a first plurality of active wireless terminal records containing corresponding downlink beamforming coefficients that have the least correlation with the new downlink beamforming coefficients and further determines from the first plurality of active wireless terminal records a first active wireless terminal record containing an active orthogonal code used for downlink transmissions to a least number of the plurality of wireless access terminals. 
   According to yet another embodiment of the present invention, the controller assigns the active orthogonal code in the first active wireless terminal record to be used in downlink transmissions to the new wireless access terminal. 
   According to a further embodiment of the present invention, the base station is operable to communicate in S sectors of a cell site associated with the base station and the base station uses up to K orthogonal codes in each of the S sectors for the downlink transmissions and wherein the controller compares each of the R active wireless terminal records to the new downlink beamforming coefficients in response to a determination that all of the K orthogonal codes are in use in a first sector in which the new wireless access terminal is accessing the base station. 
   According to a still further embodiment of the present invention, the controller determines a first plurality of active wireless terminal records containing corresponding downlink beamforming coefficients that have the least correlation with the new downlink beamforming coefficients and further determines from the first plurality of active wireless terminal records a first active wireless terminal record containing an active orthogonal code used for downlink transmissions to a least number of the plurality of wireless access terminals. 
   According to a yet further embodiment of the present invention, the controller assigns the active orthogonal code in the first active wireless terminal record to be used in downlink transmissions to the new wireless access terminal. 
   In one embodiment of the present invention, the controller receives the new downlink beamforming coefficients from a beamforming controller that determines the new downlink beamforming coefficients from an uplink signal transmitted by the new wireless is access terminal. 
   In another embodiment of the present invention, the base station is operable to communicate in S sectors of a cell site associated with the base station and the new wireless access terminal is being handed off from a first sector of the cell site to a second sector of the cell site, wherein each of the R active wireless terminal records are associated with the second sector and the controller receives the new downlink beamforming coefficients from active wireless terminal records associated with the first sector. 
   The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form. 
   Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which: 
       FIG. 1  illustrates an exemplary wireless network according to one embodiment of the present invention; 
       FIG. 2  illustrates selected portions of an exemplary base station according to one embodiment of the present invention; 
       FIG. 3  illustrates various exemplary transmit beams associated with different sectors of the exemplary base station according to one embodiment of the present invention; and 
       FIG. 4  is a flow diagram illustrating the operation of the exemplary base station according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 through 4 , discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged wireless network base station. 
     FIG. 1  illustrates exemplary wireless network  100  according to one embodiment of the present invention. Wireless network  100  comprises a plurality of cell sites  121 - 123 , each containing one of the base stations, BS  101 , BS  102 , or BS  103 . Base stations  101 - 103  communicate with a plurality of mobile stations (MS)  111 - 114  over, for example, code division multiple access (CDMA) channels. Mobile stations  111 - 114  may be any suitable wireless access terminals, including conventional cellular phones, PCS handset devices, personal digital assistants, portable computers, or metering devices. The present invention is not limited to mobile devices. Other types of wireless access terminals, including fixed wireless terminals, may be used. However, for the sake of simplicity, only mobile stations are shown and discussed hereafter. 
   Dotted lines show the approximate boundaries of the cell sites  121 - 123  in which base stations  101 - 103  are located. The cell sites are shown approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the cell sites may have other irregular shapes, depending on the cell configuration selected and natural and man-made obstructions. 
   As is well known in the art, cell sites  121 - 123  are comprised of a plurality of sectors, each sector being illuminated by a directional antenna coupled to the base station. Those acquainted with the art will recognize that the coverage provided by the overhead signals (pilot, paging and synch channel) transmitted by each sector directional antenna determines the sector geometry and coverage. Each sector of a base station uses a unique short code (containing 2 15  bits) as a modulation or spreading code to identify itself to access terminals. The embodiment of  FIG. 1  illustrates the base station in the center of the cell. Alternate embodiments position the directional antennas in corners of the sectors. The system of the present invention is not limited to any one cell site configuration. 
   In one embodiment of the present invention, BS  101 , BS  102 , and BS  103  comprise a base station controller (BSC) and one or more base transceiver subsystem(s) (BTS). Base station controllers and base transceiver subsystems are well known to those skilled in the art. A base station controller is a device that manages wireless communications resources, including the base transceiver stations, for specified cells within a wireless communications network. A base transceiver subsystem comprises the RF transceivers, antennas, and other electrical equipment located in each cell site. This equipment may include air conditioning units, heating units, electrical supplies, telephone line interfaces, and RF transmitters and RF receivers. For the purpose of simplicity and clarity in explaining the operation of the present invention, the base transceiver subsystem in each of cells  121 ,  122 , and  123  and the base station controller associated with each base transceiver subsystem are collectively represented by BS  101 , BS  102  and BS  103 , respectively. 
   BS  101 , BS  102  and BS  103  transfer voice and data signals between each other and the public switched telephone network (PSTN) (not shown) via communications line  131  and mobile switching center MSC  140 . Line  131  also provides the connection path to transfers control signals between MSC  140  and BS  101 , BS  102  and BS  103  used to establish connections for voice and data circuits between MSC  140  and BS  101 , BS  102  and BS  103 . 
   Communications line  131  may be any suitable connection means, including a T 1  line, a T 3  line, a fiber optic link, a network packet data backbone connection, or any other type of data connection. Line  131  links each vocoder in the BSC with switch elements in MSC  140 . Those skilled in the art will recognize that the connections on line  131  may provide a transmission path for transmission of analog voice band signals, a digital path for transmission of voice signals in the pulse code modulated (PCM) format, a digital path for transmission of voice signals in an Internet Protocol (IP) format, a digital path for transmission of voice signals in an asynchronous transfer mode (ATM) format, or other suitable connection transmission protocol. Those skilled in the art will recognize that the connections on line  131  may a provide a transmission path for transmission of analog or digital control signals in a suitable signaling protocol. 
   MSC  140  is a switching device that provides services and coordination between the subscribers in a wireless network and external networks, such as the PSTN or Internet. MSC  140  is well known to those skilled in the art. In some embodiments of the present invention, communications line  131  may be several different data links where each data link couples one of BS  101 , BS  102 , or BS  103  to MSC  140 . 
   In the exemplary wireless network  100 , MS  111  is located in cell site  121  and is in communication with BS  101 . MS  113  is located in cell site  122  and is in communication with BS  102 . MS  114  is located in cell site  123  and is in communication with BS  103 . MS  112  is also located close to the edge of cell site  123  and is moving in the direction of cell site  123 , as indicated by the direction arrow proximate MS  112 . At some point, as MS  112  moves into cell site  123  and out of cell site  121 , a hand-off will occur. 
   As is well known, the hand-off procedure transfers control of a call from a first cell site to a second cell site. As MS  112  moves from cell  121  to cell  123 , MS  112  detects the pilot signal from BS  103  and sends a Pilot Strength Measurement Message to BS  101 . When the strength of the pilot transmitted by BS  103  and received and reported by MS  112  exceeds a threshold, BS  101  initiates a soft hand-off process by signaling the target BS  103  that a handoff is required as described in TIA/EIA IS-95 or TIA/EIA IS-2000. 
   BS  103  and MS  112  proceed to negotiate establishment of a communications link in the CDMA channel. Following establishment of the communications link between BS  103  and MS  112 , MS  112  communicates with both BS  101  and BS  103  in a soft handoff mode. Those acquainted with the art will recognize that soft hand-off improves the performance on both forward (BS to MS) channel and reverse (MS to BS) channel links. When the signal from BS  101  falls below a predetermined signal strength threshold, MS  112  may then drop the link with BS  101  and only receive signals from BS  103 . The call is thereby seamlessly transferred from BS  101  to BS  103 . 
   The above-described soft hand-off assumes the mobile station is in a voice or data call. An idle hand-off is a hand-off of a mobile station, between cells sites, that is communicating in the to control or paging channel. 
     FIG. 2  illustrates selected portions of the base transceiver subsystem (BTS) of exemplary base station  101 . According to an advantageous embodiment of the present invention, base station  101  is divided into three sectors, referred to arbitrarily as Sector A, Sector B, and Sector C. Each sector is covered by an adaptive antenna array that uses up to M antennas to form transmit beams that directionally transmit voice and data from the base station to one or more mobile stations in the forward channel (i.e., downlink traffic). Base station  101  comprises Sector A transceiver unit  210 A, Sector B transceiver unit  210 B, and Sector C transceiver unit  210 C, N channel element and CDMA units  254 , N adaptive antenna array (AAA) and beamforming (BF) controllers  252 , resource management controller and database  260  and call processing manager  270 . 
   Sector A transceiver unit  210 A, Sector B transceiver unit  210 B, and Sector C transceiver unit  210 C, N channel element and CDMA units  254 , N adaptive antenna array (AAA) and beamforming (BF) controllers  252  operate like a conventional three sector, adaptive antenna array BTS with respect to communicating with wireless access terminals (i.e., mobile stations) in the forward channel using transmit beams. However, resource management controller and database  260  provides base station  101  with unique and novel capabilities for using the same Walsh code (or other orthogonal code) to communicate simultaneously with two or more wireless access terminals within the same sector and in different sectors of base station  101 . Resource management controller and database  260  comprises a processor and memory that execute an algorithm that performs resource management in the adaptive antenna array BTS of base station  101 . As will be explained below in greater detail, the algorithm is based on spatial isolation of mobile users which fall into different downlink beams in the same sector or in adjacent sectors of the same BTS. 
   Since Sector B transceiver unit  210 B and Sector C transceiver unit  210 C are substantially similar to Sector A transceiver unit  210 A, only Sector A transceiver unit  210 A is illustrated and discussed in detail hereafter. Sector A transceiver unit  210 A comprises M transceivers, including exemplary transceivers  215 A,  215 B, and  215 C, which are arbitrarily labeled Transceiver M, Transceiver  2 , and Transceiver  1 , respectively. Since transceivers  215 B and transceiver  215 C are substantially similar to transceiver  215 A, only transceiver  215 A is illustrated and discussed in detail hereafter. 
   The transmit path of transceiver  215 A comprises in-phase (I) and quadrature (Q) combiner block  222 , Sector A I/Q modulator  224 , up-converter and filter block  226 , radio frequency (RF) amplifier  228 , duplexer  230 , and antenna  235 . The receive path of transceiver  215 A comprises antenna  235 , duplexer  230 , low-noise amplifier (LNA)  240 , down-converter and filter block  242 , and Sector A demodulator  244 . Compared to a prior art, non-adaptive BTS, the adaptive antenna array of the BTS of base station  101  employs multiple antennas  235  and multiple (up to M) transceiver units  210  and adaptive antenna array (AAA) and beamforming (BF) controllers  252  to transmit directed beams in the forward channel (i.e., downlink). 
   In the reverse channel (uplink) from a mobile station (MS), the signals received by the multiple antennas (antenna array)  235  are amplified by LNA  240 , filtered and down-converted by down-converter and filter block  242 , and demodulated into digital in-phase (I) and quadrature (Q) streams by Sector A demodulator  244 . Duplexer (DUP)  230  provides isolation of transmitted and received signals. The digital I and Q streams are fed to a CDMA modem for despreading and M-ary symbol detection. Beamforming controller  252  determines the beam forming coefficients of the beamforming vector that describes the angle of arrival and beam characteristics of the signal received from each mobile terminal. 
   During the uplink, adaptive antenna array and beamforming controller  252  estimates over several symbol periods the phase (i.e., time offset) and signal strength of the received uplink signals at each antenna element from each mobile station and determines uplink and downlink beamforming (BF) weight vector coefficients for each mobile station. Adaptive antenna array and beamforming controller  252  passes the beamforming coefficient information to resource management controller and database  260 , which stores them in a database table. Reception of an access signal by the uplink on a specific sector and receiver and detection circuit path is also identified to resource management controller and database  260 . Resource management controller and database  260  uses this information to assign the corresponding sector path for the downlink. 
   Resource management controller and database  260  communicates with call processing manager  270  in order to assign a channel element, a Walsh code and a sector for each traffic channel established between the BTS and a mobile station. Resource management controller and database  260  maintains a database in memory for the beamforming coefficients, idle/active state of each Walsh code, and the assignment of that Walsh code to an active channel. Each channel element and CDMA modem  254  is capable of to supporting the signal processing for N users. 
   For the downlink to the wireless access terminal (i.e., mobile station), the incoming I and Q data streams to the channel element are first processed in the CDMA modem, which selects the Walsh code (WC) according to the algorithm described in  FIG. 4 . The channel element and CDMA modem provides Walsh code modulation and PN code spreading on the downlink. Next, the modem output is multiplied by a Mxl downlink beamforming weight vector for the mobile station in adaptive antenna array and beamforming controller  252  and is distributed to M antenna  235  for transmission in a given sector. 
   Adaptive antenna array and beamforming controller  252  performs amplitude weighting and phase shifting of the digital I and Q data fo each mobile station and conversion into Mxl vector form. I and Q combiner  222  combines digital I and Q streams from N channel element and CDMA modem units  254 . The combined I and Q signals from I and Q combiner  222  are applied to Sector A I/Q modulator  224 , which modulates a carrier signal. The modulated carrier signal is up-converted and filtered by up-converter and filter block  226 , amplified by RF amplifier  228 , and sent to each antenna element  235  via duplexer  230 . Finally, the signals at the antenna array are transmitted to the mobile station. 
     FIG. 3  illustrates various exemplary transmit beams transmitted by exemplary base station  101  into different sectors of cell site  121  according to one embodiment of the present invention. Mobile stations are represented by black dots in  FIG. 3 . Sector A contains three existing transmits beams, B 1 , B 2 , and B 3 . A new mobile station (NEW MS) that is accessing base station  101  is shown disposed within a new beam, B (New), to be formed by base station  101 , as explained below in greater detail. 
     FIG. 4  depicts flow diagram  400 , which illustrates the operation of exemplary base station  101  according to one embodiment of the present invention. Initially, resource management controller and database  260  is in an idle state, in which execution of the Walsh code (WC) allocation algorithm is not required for resource assignment (process step  405 ). At some point, call processing manager  270  signals resource management controller and database  260  to allocate resources for a traffic channel (process step  410 ). Next, resource management controller and database  260  executes a hashing function or some other selection algorithm in order to assign a physical channel element (CE) to the new mobile station from the set of idle channel elements stored in resource management controller and database  260  (process  415 ). 
   Adaptive antenna array and beamforming controller  252  then estimates the beamforming coefficients of the new mobile station from the reverse channel (i.e., uplink) signals for the new mobile station (process step  420 ). Resource management controller and database  260  then searches the active Walsh codes and corresponding BF coefficients for the sector and selects the Walsh code(s) whose BF weight vector(s) has the least correlation with the estimated BF weight vector of the new mobile station. Thus:
 
i=arg{min[|b* MS   b ( i )|]}, for i=1, 2, 3, . .  . Q; 
 
 WC   MS   =WC ( i );
 
where Q is the number of active users. If the search determines that a group of Walsh codes share the same BF coefficient, then resource management controller and database  260  select the Walsh code which is less assigned among currently active resources (process step  425 ). Resource management controller and database  260  then executes a hashing function or other selection algorithm to assign a Walsh code from the set of Walsh codes identified by resource management controller and database  260  (process step  430 ).
 
   Thereafter, base station  101  and resource management controller and database  260  enter a Call Active state in which the channel element, the Walsh code, the BF weight vector, and the sector are all assigned (process step  435 ). A call softer handoff (i.e., a sector-to-sector handoff) causes resource management to controller and database  260  to test if the Walsh code is active in an adjacent sector of base station  101  (process step  445 ). If the mobile station enters a softer handoff process, resource management controller and database  260  loads the downlink BF weight vector of the mobile station in the handoff sensed by antenna array of the adjacent candidate sector (process step  450 ). The algorithm then loops back and executes the Walsh Code and BF weight search described for process step  425  using with the new BF weight vector. 
   Assuming no handoff occurs, base station  101  and the mobile station continue communicating using the assigned Walsh code until a call release signal is received. If a call release signal is received, resource management controller and database  260  is notified to release and mark as idle the channel element (CE), the Walsh code (if not used by another CE), and other sector resources for use by another call (process steps  455  and  460 ). 
   Returning now to  FIG. 3 , two different scenarios are considered. In the first scenario, the new (or candidate) mobile station (NEW MS) is not in the softer handoff region and there are currently three (3) different beams (B 1 , B 2 , and B 3 ) occupied by a number of active mobile stations. It is assumed that sector A of base station  101  is operating with all Walsh codes used to support traffic channels. 
   The new mobile station (NEW MS) requests service in Sector A. The downlink beamforming coefficients BNEW are estimated by adaptive antenna array and beamforming controller  252  and algorithm described in  FIG. 4  is executed in base station  101 . Resource management controller and database  260  determines that B NEW  of NEW MS has the minimum correlation with the beamforming coefficients of beam B 1 . By way of example, assume that Walsh Codes (W 20 -W 31 , W 33 -W 44 ) are used in beam B 1 . Starting from the first Walsh code in that group (i.e., WC 20 ), resource management controller and database  260  searches for the Walsh code that is least used and, when it finds a Walsh code that is used only once, that Walsh Code is assigned to NEW MS. 
   In the second scenario, NEW MS is located in the softer handoff region between Sector A and Sector B. In this scenario, the new beamforming weight vector of the candidate user (NEW MS) seen by Sector B is loaded and resource management controller and database  260  is notified to execute a search algorithm within the new table for Sector B. In other words, for whichever sector to which the mobile station is handed off, resource management controller and database  260  executes the WC allocation algorithm using the table for that sector. 
   The algorithm provided by the present invention relies on the minimum correlation criteria between downlink beams. This is because signal maximization is considered when constructing downlink beams. Therefore, multiple users may fall into the same beams. However, if interference nulling is considered instead of signal maximization, the algorithm of the present invention needs modification such as using carrier-to-interference ratio (C/I) or some other measures as the criteria when assigning Walsh Codes. 
   Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.

Technology Category: 5