Patent Publication Number: US-8983480-B2

Title: Multiplexing on the reverse link feedbacks for multiple forward link frequencies

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. §§119 AND 120 
     The present Application for Patent is a divisional of patent application Ser. No. 11/397,873, titled “Multiplexing on the Reverse Link Feedbacks for Multiple Forward Link Frequencies” filed Apr. 3, 2006, pending, which claims priority to Provisional Application No. 60/669,437, titled “Multiplexing on the Reverse Link Feedbacks for Multiple Forward Link Frequencies” filed Apr. 8, 2005, expired, and assigned to the assignee hereof, and expressly incorporated herein by reference. 
    
    
     FIELD 
     The present invention pertains generally to communications, and more specifically to multiplexing feedback information in a multiple carrier communication system. 
     BACKGROUND 
     There is a recent interest in multicarrier transmission systems, wherein multiple frequencies are used for transmission channels. 
     SUMMARY OF THE INVENTION 
     In view of the above, the described features of the present invention generally relate to one or more improved systems, methods and/or apparatuses for communicating speech. 
     In one embodiment, the present method comprises a method for multiplexing reverse link feedback channels on a single reverse link frequency supporting multiple forward link frequencies for forward link channels, comprising assigning the reverse link frequency to a mobile station, assigning one or more of the forward link frequencies to the reverse link frequency, and code division multiplexing a plurality of the reverse link feedback channels on the reverse link frequency. 
     In another embodiment, the present apparatus comprises a communication apparatus configured to multiplex reverse link feedback channels on a single reverse link frequency supporting multiple forward link frequencies for forward link channels, comprising a transmitter, a receiver operably connected to the transmitter, a processor operably connected to the transmitter and the receiver, and memory operably connected to the processor, wherein the communication apparatus is adapted to execute instructions stored in the memory comprising assigning the reverse link frequency to a mobile station, assigning one or more of the forward link frequencies to the reverse link frequency, and code division multiplexing a plurality of the reverse link feedback channels on the reverse link frequency. 
     Further scope of the applicability of the present method and apparatus will become apparent from the following detailed description, claims, and drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features, objects, and advantages of the presently disclosed method and apparatus will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein: 
         FIG. 1A  is a wireless communication system; 
         FIG. 1B  is a wireless communication system supporting high data rate transmissions; 
         FIG. 2  is a block diagram of an Access Network (AN) in a wireless communication system; 
         FIG. 3  illustrates generation of Feedback Multiplexing Mask according to one embodiment; 
         FIG. 4  illustrates multiplexing of reverse link frequencies in a multicarrier communication system; 
         FIG. 5  is a flowchart illustrating the steps executed when multiplexing reverse link frequencies in a multicarrier communication system; 
         FIGS. 6A and 6B  illustrate a traffic channel assignment message; 
         FIG. 7  is a functional block diagram illustrating an embodiment of an access terminal; and 
         FIG. 8  is a functional block diagram illustrating the multiplexing of reverse link frequencies in a multicarrier communication system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Communication systems, and wireless systems in particular, are designed with the objective of efficient allocation of resources among a variety of users. Wireless systems in particular aim to provide sufficient resources to satisfy the requirements of all subscribers while minimizing costs. Various scheduling algorithms have been developed, each based on a predetermined system criteria. 
     In a wireless communication system employing a code division-multiple access (CDMA) protocol, one scheduling method assigns each of the subscriber units all code channels at designated time intervals on a time multiplexed basis. A central communication node, such as a base station (BS) implements the unique carrier frequency or channel code associated with the subscriber to enable exclusive communication with the subscriber. Time division multiple access (TDMA) protocols may also be implemented in landline systems using physical contact relay switching or packet switching. A CDMA system may be designed to support one or more standards such as: (1) the “TIA/EIA/IS-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” referred to herein as the IS-95 standard; (2) the standard offered by a consortium named “3rd Generation Partnership Project” referred to herein as 3GPP; and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214, 3G TS 25.302, referred to herein as the W-CDMA standard; (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” referred to herein as 3GPP2, and TR-45.5 referred to herein as the cdma2000 standard, formerly called IS-2000 MC, or (4) some other wireless standard. 
     The CDMA system allows for voice and data communications between users over a terrestrial link. In a CDMA system, communications between users are conducted through one or more base stations. In wireless communication systems, forward link (FL) refers to the channel through which signals travel from a base station to a subscriber station, and reverse link (RL) refers to channel through which signals travel from a subscriber station to a base station. By transmitting data on a reverse link to a base station, a first user on one subscriber station communicates with a second user on a second subscriber station. The base station receives the data from the first subscriber station and routes the data to a base station serving the second subscriber station. Depending on the location of the subscriber stations, both may be served by a single base station or multiple base stations. In any case, the base station serving the second subscriber station sends the data on the forward link. Instead of communicating with a second subscriber station, a subscriber station may also communicate with a terrestrial Internet through a connection with a serving base station. In wireless communications such as those conforming to the IS-95 standard, forward link and reverse link signals are transmitted within disjoint frequency bands. 
     At any given time, each base station may be expected to maintain concurrent wireless communication links with numerous mobile units. To reduce interference between the concurrent wireless communication links, the base station and the mobile units in the wireless communication system modulate signals transmitted on the assigned traffic channels using a predetermined Pseudo-random Noise PN code that uniquely identifies the mobile unit. Thus, the mobile is distinguished from other mobiles by its long PN code which may be generated by a long code mask. In IS-95 CDMA, PN code sets are generated using linear feedback shift registers (LFSR). 
     In a wireless communication system operating according to the CDMA 2000 standard, a long code mask may also be used to differentiate reverse link transmissions, i.e. from the mobile unit to the base station, over different traffic channels. The long code mask in CDMA 2000 is a 42-bit number that serves as a logical address for Reverse CDMA Channel spreading codes. It is used to select specific bits from the long code linear feedback shift register to be added, modulo-two, in order to produce the actual long PN code, at the proper phase. The resultant of the sum, that is, the modulo-2 inner product of the generator state with the mask, is the generator output, or PN code, corresponding to that mask and is used to identify a particular access terminal or mobile station. The use of this 42-bit distinct user long code sequence allows separation of 2 42-1  different user (or mobile) signals at the base station. 
       FIG. 1A  serves as an example of a communications system  100  that supports a number of users and is capable of implementing at least some aspects and embodiments of the invention. The communication system  100  comprises a number of communication apparatuses. Any of a variety of methods may be used to schedule transmissions in system  100 . System  100  provides communication for a number of cells  102 A through  102 G, each of which is serviced by a corresponding base station  820 A through  820 G, respectively. In the exemplary embodiment, some of base stations  820  have multiple receive antennas and others have only one receive antenna. Similarly, some of base stations  820  have multiple transmit antennas, and others have single transmit antennas. There are no restrictions on the combinations of transmit antennas and receive antennas. Therefore, it is possible for a base station  820  to have multiple transmit antennas and a single receive antenna, or to have multiple receive antennas and a single transmit antenna, or to have both single or multiple transmit and receive antennas. 
     Increasing demand for wireless data transmission and the expansion of services available via wireless communication technology have led to the development of specific data services. One such service is referred to as High Data Rate (HDR). An exemplary HDR service is proposed in “EIA/TIA-IS856 Cdma2000 High Rate Packet Data Air Interface Specification” referred to as “the HDR specification.” HDR service is generally an overlay to a voice communication system that provides an efficient method of transmitting packets of data in a wireless communication system. As the amount of data transmitted and the number of transmissions increases, the limited bandwidth available for radio transmissions becomes a useful resource. 
       FIG. 1B  illustrates an architecture reference model for a communication system  100  having an access network  122  communicating with an access terminal (AT),  106  via an air interface  124 . An access network  122  is defined as network equipment which provides data connectivity between a packet switched data network (typically the Internet) and one or more access terminals  106 . An access terminal  106  is equivalent to a mobile station or a remote station and provides data connectivity to a user. In one embodiment, the system  120  is a CDMA system having a High Data Rate, HDR, overlay system, such as specified the HDR standard. The AN  122  communicates with AT  106 , as well as any other ATs  106  within system  120  (not shown), by way of the air interface  124 . The AN  122  includes multiple sectors, wherein each sector provides at least one channel. A channel is defined as the set of communication links for transmissions between the AN  122  and the ATs within a given frequency assignment. A channel consists of a forward link for transmissions from a base station  820  in the AN  122  to AT  106  and a reverse link for transmissions from the AT  106  to the BS  820  in the AN  122 . The BS  820  is operably connected to a base station controller (BSC)  810  as illustrated in  FIG. 2 . 
     For data transmissions, the AN  122  receives a data request from the AT  106 . The data request specifies the data rate at which the data is to be sent, the length of the data packet transmitted, and the sector from which the data is to be sent. The AT  106  determines the data rate based on the quality of the channel between AN  122  and AT  106 . In one embodiment the quality of the channel is determined by the carrier-to-interference ratio (C/I). Alternate embodiments may use other metrics corresponding to the quality of the channel. The AT  106  provides requests for data transmissions by sending a data rate control (DRC) message via a specific channel referred to as the DRC channel. The DRC message includes a data rate portion and a sector portion. The data rate portion indicates the requested data rate for the AN  122  to send the data, and the sector indicates the sector from which the AN  122  is to send the data. Both data rate and sector information are typically required to process a data transmission. The data rate portion is referred to as a DRC value, and the sector portion is referred to as a DRC cover. The DRC value is a message sent to the AN  122  via the air interface  124 . In one embodiment, each DRC value corresponds to a data rate in kbits/sec having an associated packet length according to a predetermined DRC value assignment. The assignment includes a DRC value specifying a null data rate. In practice, the null data rate indicates to the AN  122  that the AT  106  is not able to receive data. In one situation, for example, the quality of the channel is insufficient for the AT  106  to receive data accurately. 
     In operation, the AT  106  continuously monitors the quality of the channel to calculate a data rate at which the AT  106  is able to receive a next data packet transmission. The AT  106  then generates a corresponding DRC value; the DRC value is transmitted to the AN  122  to request a data transmission. Note that typically data transmissions are partitioned into packets. The time required to transmit a packet of data is a function of the data rate applied. 
     This DRC signal also provides the information, which a channel scheduler  812  uses to determine the instantaneous rate for consuming information (or receiving transmitted data) for each of the remote stations  106  associated with each queue. According to an embodiment, a DRC signal transmitted from any remote station  106  indicates that the remote station  106  is capable of receiving data at any one of multiple effective data rates. 
     One example of a communication system supporting HDR transmissions and adapted for scheduling transmissions to multiple users is illustrated in  FIG. 2 .  FIG. 2  is detailed hereinbelow, wherein specifically, a base station  820  and base station controller (BSC)  810  interface with a packet network interface  806 . Base station controller  810  includes a channel scheduler  812  for implementing a scheduling algorithm for transmissions in system  120 . The channel scheduler  812  determines the length of a service interval during which data is to be transmitted to any particular remote station  106  based upon the remote station&#39;s associated instantaneous rate for receiving data (as indicated in the most recently received DRC signal). The service interval may not be contiguous in time but may occur once every n slots. According to one embodiment, the first portion of a packet is transmitted during a first slot at a first time and the second portion is transmitted 4 slots later at a subsequent time. Also, any subsequent portions of the packet are transmitted in multiple slots having a similar 4 slots spread, i.e., 4 slots apart from each other. According to an embodiment, the instantaneous rate of receiving data R i  determines the service interval length L i  associated with a particular data queue. 
     In addition, the channel scheduler  812  selects the particular data queue for transmission. The associated quantity of data to be transmitted is then retrieved from a data queue  830  and provided to the channel element  826  for transmission to the remote station  106  associated with the data queue  830 . As discussed below, the channel scheduler  812  selects the queue for providing the data, which is transmitted in a following service interval using information including the weight associated with each of the queues. The weight associated with the transmitted queue is then updated. 
     Base station controller  810  interfaces with packet network interface  806 , Public Switched Telephone Network, PSTN,  808 , and all base stations  820  in the communication system (only one base station  820  is shown in  FIG. 2  for simplicity). Base station controller  810  coordinates the communication between remote stations in the communication system and other users connected to packet network interface  806  and PSTN  808 . PSTN  808  interfaces with users through a standard telephone network (not shown in  FIG. 2 ). 
     Base station controller  810  contains many selector elements  816 , although only one is shown in  FIG. 2  for simplicity. Each selector element  816  is assigned to control communication between one or more base stations  820  and one remote station  106  (not shown). If selector element  816  has not been assigned to a given remote station  106 , call control processor  818  is informed of the need to page the remote station  106 . Call control processor  818  then directs base station  820  to page the remote station  106 . 
     Data source  802  contains a quantity of data, which is to be transmitted to a given remote station  106 . Data source  802  provides the data to packet network interface  806 . Packet network interface  806  receives the data and routes the data to the selector element  816 . Selector element  816  then transmits the data to each base station  820  in communication with the target remote station  106 . In the exemplary embodiment, each base station  820  maintains a data queue  830 , which stores the data to be transmitted to the remote station  106 . 
     The data is transmitted in data packets from data queue  830  to channel element  826 . In the exemplary embodiment, on the forward link, a “data packet” refers to a quantity of data which is a maximum of 1024 bits and a quantity of data to be transmitted to a destination remote station  106  within a predetermined “time slot” (such as 1.667 msec). For each data packet, channel element  826  inserts the necessary control fields. In the exemplary embodiment, channel element  826  performs a cyclic redundancy check, CRC, encoding of the data packet and control fields and inserts a set of code tail bits. The data packet, control fields, CRC parity bits, and code tail bits comprise a formatted packet. In the exemplary embodiment, channel element  826  then encodes the formatted packet and interleaves (or reorders) the symbols within the encoded packet. In the exemplary embodiment, the interleaved packet is covered with a Walsh code, and spread with the short PNI and PNQ codes. The spread data is provided to RF unit  828  which quadrature modulates, filters, and amplifies the signal. The forward link signal is transmitted over the air through an antenna to the forward link. 
     At the remote station  106 , the forward link signal is received by an antenna and routed to a receiver. The receiver filters, amplifies, quadrature demodulates, and quantizes the signal. The digitized signal is provided to a demodulator (DEMOD) where it is despread with the short PNI and PNQ codes and decovered with the Walsh cover. The demodulated data is provided to a decoder which performs the inverse of the signal processing functions done at base station  820 , specifically the de-interleaving, decoding, and CRC check functions. The decoded data is provided to a data sink. 
     The hardware, as pointed out above, supports variable rate transmissions of data, messaging, voice, video, and other communications over the forward link. The rate of data transmitted from the data queue  830  varies to accommodate changes in signal strength and the noise environment at the remote station  106 . Each of the remote stations  106  preferably transmits a data rate control signal to an associated base station  820  at each time slot. The DRC signal provides information to the base station  820 , which includes the identity of the remote station  106  and the rate at which the remote station  106  is to receive data from its associated data queue. Accordingly, circuitry at the remote station  106  measures the signal strength and estimates the noise environment at the remote station  106  to determine the rate information to be transmitted in the DRC signal. 
     The DRC signal transmitted by each remote station  106  travels through a reverse link channel and is received at base station  820  through a receive antenna coupled to RF unit  828 . In the exemplary embodiment, the DRC information is demodulated in channel element  826  and provided to a channel scheduler  812  located in the base station controller  810  or to a channel scheduler  832  located in the base station  820 . In a first exemplary embodiment, the channel scheduler  832  is located in the base station  820 . In an alternate embodiment, the channel scheduler  812  is located in the base station controller  810 , and connects to all selector elements  816  within the base station controller  810 . 
     For multicarrier transmissions, data is transmitted by dividing the data into several interleaved bit streams and using these to modulate several carriers. Multicarrier transmission is a form of frequency division multiplexing. In a CDMA communication system, multicarrier transmission is used to suppress multipath fading. 
     In a communication system employing multicarrier transmissions, it may be the situation that the number of forward link channels is greater than the number of reverse link channels. In this situation, there is a need to transmit multiple RL channels, corresponding to the multiple FL channels, on a single RL frequency. The RL channels may be channels used for feedback of information. In one example, such a RL channel is the DRC channel as specified in IS-856; in another example, such a RL channel is an ACKnowledge (ACK) channel used for Automatic Repeat reQuest (ARQ) feedback. According to one embodiment, the RL overhead channels are multiplexed together on a single RL frequency, wherein a long code mask (LCM) is used to code multiplex the overhead channels. Thus, the RL overhead channels used for the ACK channel and the DRC channel respectively are separated by code division multiplexing using the long code mask. 
     The AN 122 may assign one or more long code masks to the AT  106  for each of the RL feedback channels on which the access terminal  106  may transmit. The long code mask for each of the RL feedback channels is identified by the value of a feedback multiplexing index which is provided by a route update protocol. A route update protocol provides the means to maintain the route between the access terminal  106  and the access network  122 . 
     In one embodiment, the AT  106  may set the long code for each channel on the RL using the 42-bit mask MI RTCMAC  illustrated in  FIG. 3 . MI RTCMAC  is the long code mask for the in-phase reverse traffic channel (or reverse link). MQ RTCMAC  is the long code mask for the quadrature-phase reverse traffic channel (or reverse link), where the reverse traffic channel may consist of a pilot channel, a reverse rate indicator (RRI) channel, a DRC channel, an ACK channel and a data channel. As illustrated in  FIG. 3 , the LCM includes four bits,  38 ,  39 ,  40  and  41 , that represent the binary index field labeled IDX. However, the values of the bits in field IDX can vary to produce different long code masks (LCM). 
     Also shown in  FIG. 3 , the long code mask contains a 32-bit ATI number (referred to as the Permuted (ATI) field which is derived from the AT&#39;s  106  access terminal identifier (ATI) as shown, for example, below in equation 2. An ATI derived number is derived from the identifier of the access terminal  106 . It is derived from the bits representing the identifier of the access terminal  106 . 
     According to one embodiment, three additional long code masks are created for each RL carrier feedback channel by changing the two most significant bits (MSBs) of the LCM, while keeping the 32-bit Permuted ATI field the same. For example, if the two most significant bits of the LCM for one FL ACK channel carried on RL carrier frequency “x” is 00, then three other LCMs may be created to represent three additional FL carrier frequencies whose DRC or ACK channels are transmitted on RL carrier frequency x by setting the two most significant bits to 01, 10, and 11. (However, it is noted that the present patent application is not limited to changing two bits. In other embodiments, three or more bits may be changed to create additional LCMs. For example,  FIG. 3  shows the four MSBs  38 - 41  as having variable values. 
     Thus, using the LCM of  FIG. 3  as an example, bits  40  and  41  would take on the three values 01, 10 and 11, while the 32 bits in the ATI field would not change their value, to identify three additional LCMs. This is illustrated when the first 4 LCMs represented by feedback multiplexing indexes  0  to  3 , have an identical value in their ATI field and differ in their IDX field by the first two bits, 00, 10, 01, and 11. The LCM with MSBs of 00 could represent the DRC channel of FL frequency “a,” while the LCM with MSBs of 01 could represent the DRC channel of FL frequency “b.” Likewise, the LCM with MSBs of 10 could represent the ACK channel of FL frequency “a,” while the LCM with MSBs of 11 could represent the ACK channel of FL frequency “b.” 
     As shown in  FIG. 3 , part of the long code mask is derived from the access terminal&#39;s identifier. If more than one identifier is assigned to the access terminal, additional long code masks can be derived for the terminal For example, additional LCMs may be created by the AN  122  reserving the value of ATIs (i.e., not assigning them to other ATs  106 ) and by the AT  106  using the ATI values to construct the 32 least significant bits (LSBs) of the LCM as described herein. In one example, three additional ATIs would allow for construction of a total of 16 long code masks. 
     In a communication system employing multicarrier transmissions, it may be the situation that the number of forward link channels is equal to the number of reverse link channels. In this situation it is desirable to allow the mobile  106  to turn off transmission of the pilot and data signals on certain RL frequencies, i.e., turn off the RL frequency. This allows the access terminal  106  to conserve transmission power headroom. Such control of transmission (i.e., turn on/off) may be done autonomously by the access terminal  106 .  FIG. 4  illustrates the relationship of multiplexed RL frequencies to the multicarrier FL frequencies. 
     In one embodiment shown in the flowchart of  FIG. 5 , a traffic channel assignment (TCA) message is sent by a base station  820  to assign a reverse traffic channel or reverse link to a given mobile station  106 , i.e., access terminal (step  100 ). 
     The traffic channel assignment message, as illustrated in  FIGS. 6A and 6B , includes a Frame Offset field, a Pilot Pseudo-random Noise Code (Pilot PN) information field, and a MAC Index field as forward traffic channel information, and includes a DRC (Data Rate Control) information Length field, a DRC Channel Gain Base field, an ACK Channel Gain field, a DRC Cover Code field, a Number of Sectors field, and a Number of Reverse Active Sets field. It also contains a Message Id field, a Message Sequence field, an Assigned Channel Included field, a Scheduler Tag Included field, a Feedback Multiplexing Enabled field, a Softer Handoff field, a DSC field, a DSC Channel Gain Base field, a RA Channel Gain field, a Number of Forward Channels This Sub Active Set field, and a Reserved field. 
     The TCA message also includes an Assigned Channel field, a Feedback Enabled field, a Feedback Multiplexing Index field, a Feedback Reverse Channel Index field, a Sub Active Set Carrier Control Channel field, a This Sub Active Set Not Reportable field, a DSC For This Sub Active Set Enabled field, and a Next 3 Fields Same as Before field. 
     In addition, the TCA message includes a Number Reverse Channels Included field, a Number Reverse Channels field, a Reverse Channel Configuration field, a Reverse Band Class field, a Reverse Channel Number field, a Reverse Channel Dropping Rank field, a Pilot This Sector Included field, a Forward Channel Index This Pilot field, a Pilot Group ID field, a Numbers Unique Forward Traffic MAC Indices field, a Scheduler Tag field, an Auxiliary DRC Cover Included field, an Auxiliary DRC Cover field, a Forward Traffic MAC Index Per Index Enabled field, an Assigned Interlaces field, a Reverse Link MAC index field, and a RAB MAC Index field. 
     The TCA message represents an improvement over the prior art in that it further specifies the relationships detailed in  FIG. 4 . In one embodiment, the TCA message conveys the feedback multiplexing index to the mobile  106 . As illustrated in the example of  FIG. 4  (and the flowchart of  FIG. 5 ) the mobile station  106  then uses the TCA message to assign multiple carrier FL frequencies “a” through “b” to one RL frequency “x.” (Step  110 ) The RL frequency x is then used for transmission of feedback and/or overhead information corresponding to one or more of the FL frequencies a through b. 
     Next, the corresponding information, e.g. RL feedback channels DRC and ACK, is code division multiplexed on the single RL frequency “x” by using different long code masks for each. (Step  112 ) For example, the DRC channel for FL carrier frequency “a” is assigned a long code mask represented by feedback multiplexing index  0  on RL carrier “x”, while the DRC channel for FL carrier frequency “b” is assigned a long code mask represented by feedback multiplexing index “ 1 ” on RL carrier x. Likewise, the ACK channel for FL carrier frequency “a” is assigned a long code mask represented by feedback multiplexing index “ 2 ” on RL carrier “x”, while the ACK channel for FL carrier frequency “b” is assigned a long code mask represented by feedback multiplexing index “ 3 ” on RL carrier x. 
     In the example of  FIG. 4 , the RL frequency “z” used for sending data or traffic may be autonomously turned off (i.e., no transmissions at this frequency) to conserve headroom. Thus, a way to conserve headroom is, as stated above, to allow the mobile  106  to turn off transmission on certain RL frequencies. Is AT  106  headroom limited? (Step  115 ) If the answer to step  115  is yes, then turn off RL frequency “z” used for sending data. (Step  120 ). In addition, the AT  106  sends a message to the BS  820  telling the BS  820  that it has dropped the RL (Step  122 ). 
     Also shown in  FIG. 4 , the base station  820  may assign only one of the multiple carrier FL frequencies, “c”, to one RL frequency “y.” The RL feedback channels DRC and ACK for FL frequency “c” may be code division multiplexed on the single RL frequency “y” by using different long code masks for each. For example, the DRC channel for FL carrier frequency “c” is assigned long code mask  0  on RL carrier “y”, while the DRC channel for FL carrier frequency “b” is assigned the long code mask represented by feedback multiplexing index “1” on RL carrier “y.” 
     Permuted (ATI) is defined as follows:
 
ATI=(A 31 ,A 30 ,A 29 , . . . , A 0 )  (1)
 
Permuted (ATI)=(A 0 ,A 31 ,A 22 ,A 13 ,A 4 ,A 26 ,A 17 ,A 8 ,A 30 ,A 21 ,A 12 ,A 3 ,A 25 ,A 16 ,A 7 ,A 29 ,A 20 ,A 11 ,A 2 ,A 24 ,A 15 ,A 6 ,A 28 ,A 19 ,A 10 ,A 1 ,A 23 ,A 14 ,A 5 ,A 27 ,A 18 ,A 9 ).  (2)
 
     The 42-bit mask MQ RTCMAC  is derived from the mask MI RTCMAC  as follows:
 
 MQ   RTCMAC   [k]=MI   RTCMAC   [k− 1], for k=1, . . . , 41  (3)
 
MQ RTCMAC [0]=MI RTCMAC [0]⊕MI RTCMAC [1]⊕MI RTCMAC [2]⊕MI RTCMAC [4]⊕MI RTCMAC [5]⊕MI RTCMAC [6]⊕MI RTCMAC [9]⊕MI RTCMAC [15]⊕MI RTCMAC [16]⊕MI RTCMAC [17]⊕MI RTCMAC [18]⊕MI RTCMAC [20]⊕MI RTCMAC [21]⊕MI RTCMAC [24]⊕MI RTCMAC [25]⊕MI RTCMAC [26]⊕MI RTCMAC [30]⊕MI RTCMAC [32]⊕MI RTCMAC [34]⊕MI RTCMAC [41]  (4)
 
wherein the operator ⊕ denotes the Exclusive OR operation, and MQ RTCMAC [i] and MI RTCMAC [i] denote the i th  least significant bit of MQ RTCMAC  and MI RTCMAC , respectively.
 
       FIG. 7  is a functional block diagram illustrating an embodiment of an AT  106 . The AT  106  includes a processor  2602  which controls operation of the AT  106 . The processor  2602  may also be referred to as a CPU. Memory  2605 , which may include both read-only memory (ROM) and random access memory (RAM), provides instructions and data to the processor  2602 . A portion of the memory  2605  may also include non-volatile random access memory (NVRAM). The steps illustrated in  FIGS. 4 and 5  and the LCM illustrated in  FIG. 3  may be stored as instructions located as software or firmware  42  located in memory  2605 . These instructions may be executed by the processor  2602 . 
     The AT  106 , which may be embodied in a wireless communication device such as a cellular telephone, may also include a housing  2607  that contains a transmitter  2608  and a receiver  2610  to allow transmission and reception of data, such as audio communications, between the AT  2606  and a remote location, such as an AN  122 . The transmitter  2608  and receiver  2610  may be combined into a transceiver  2612 . An antenna  2614  is attached to the housing  2607  and electrically coupled to the transceiver  2612 . Additional antennas (not shown) may also be used. The operation of the transmitter  2608 , receiver  2610  and antenna  2614  is well known in the art and need not be described herein. 
     The AT  106  also includes a signal detector  2616  used to detect and quantify the level of signals received by the transceiver  2612 . The signal detector  2616  detects such signals as total energy, pilot energy per pseudonoise (PN) chips, power spectral density, and other signals, as is known in the art. 
     A state changer  2626  of the AT  106  controls the state of the wireless communication device based on a current state and additional signals received by the transceiver  2612  and detected by the signal detector  2616 . The wireless communication device is capable of operating in any one of a number of states. 
     The AT  106  also includes a system determinator  2628  used to control the wireless communication device and determine which service provider system the wireless communication device should transfer to when it determines the current service provider system is inadequate. 
     The various components of the AT  106  are coupled together by a bus system  2630  which may include a power bus, a control signal bus, and a status signal bus in addition to a data bus. However, for the sake of clarity, the various busses are illustrated in  FIG. 7  as the bus system  2630 . The AT  106  may also include a digital signal processor (DSP)  2609  for use in processing signals. One skilled in the art will appreciate that the AT  106  illustrated in  FIG. 7  is a functional block diagram rather than a listing of specific components. 
     The methods and apparatuses of  FIG. 5  described above are performed by corresponding means plus function blocks illustrated in  FIG. 8 . In other words, steps  100 ,  110 ,  112 ,  115 ,  117 ,  120  and  122  in  FIG. 5  correspond to means plus function blocks  3100 ,  3110 ,  3112 ,  3115 ,  3120  and  3122  in  FIG. 8 . 
     The steps illustrated in  FIGS. 4 and 5  and the long code mask illustrated in  FIG. 3  may be also be stored as instructions located as software or firmware  43  located in memory  45  in the base station  820 . These instructions may be executed by a processor or processing means such as control unit  822  as shown in  FIG. 2 . 
     Those of skill in the art would understand that the data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description are advantageously represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. The various illustrative components, blocks, modules, circuits, and steps have been described generally in terms of their functionality. Whether the functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans recognize the interchangeability of hardware and software under these circumstances, and how best to implement the described functionality for each particular application. As examples, the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented or performed with a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components such as, e.g., registers and FIFO, a processor executing a set of firmware instructions, any conventional programmable software module and a processor, or any combination thereof designed to perform the functions described herein. The processor may advantageously be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, programmable logic device, array of logic elements, or state machine. The software module could reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary processor is advantageously coupled to the storage medium so as to read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a telephone or other user terminal. In the alternative, the processor and the storage medium may reside in a telephone or other user terminal. The processor may be implemented as a combination of a DSP and a microprocessor, or as two microprocessors in conjunction with a DSP core, etc. 
     Preferred embodiments of the present invention have thus been shown and described. It would be apparent to one of ordinary skill in the art, however, that numerous alterations may be made to the embodiments herein disclosed without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited except in accordance with the following claims.