Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04M—TELEPHONIC COMMUNICATION
  • H04M1/00—Substation equipment, e.g. for use by subscribers
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/30—TPC using constraints in the total amount of available transmission power
  • H04W52/34—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
  • H04W52/04—TPC
  • H04W52/38—TPC being performed in particular situations
  • H04W52/42—TPC being performed in particular situations in systems with time, space, frequency or polarisation diversity

Definitions

• the present invention relates generally to wireless communications, and more specifically, to transmission diversity systems.
• the field of wireless communications has many applications including, e.g., cordless telephones, paging, wireless local loops, personal digital assistants (PDAs), Internet telephony, and satellite communication systems.
• PDAs personal digital assistants
• a particularly important application is cellular telephone systems for remote subscribers.
• the term "cellular" system encompasses systems using either cellular or personal communications services (PCS) frequencies.
• PCS personal communications services
• Various over-the-air interfaces have been developed for such cellular telephone systems including, e.g., frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA).
• FDMA frequency division multiple access
• TDMA time division multiple access
• CDMA code division multiple access
• IS-95 Advanced Mobile Phone Service
• GSM Global System for Mobile
• IS-95A IS-95A
• IS-95B IS-95B
• ANSI J-STD-008 IS-95
• Telecommunication Industry Association Telecommunication Industry Association
• Cellular telephone systems configured in accordance with the use of the IS-95 standard employ CDMA signal processing techniques to provide highly efficient and robust cellular telephone service.
• Exemplary cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. Patent Nos. 5,103,459 and 4,901 ,307, which are assigned to the assignee of the present invention and incorporated by reference herein.
• An exemplary system utilizing CDMA techniques is the cdma2000 ITU-R Radio Transmission Technology (RTT) Candidate submission (referred to herein as cdma2000), issued by the TIA.
• RTT Radio Transmission Technology
• CDMA standard is the W-CDMA standard, as embodied in 3 rd Generation Partnership Project "3GPP". Document Nos. 3G TS 25.211 , 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214. [1004]
• the telecommunication standards cited above are examples of only some of the various communications systems that can be implemented. Most of these systems are now configured to use a single antenna for forward link transmissions to a single remote station, but it is envisioned that multiple antennas will eventually be used for forward link transmissions to a single remote station. Multiple antennas provide transmit diversity (TD), which increases the quality of the forward link. When the quality of the forward link improves, less transmission power is required to convey information to a remote station.
• TD transmit diversity
• forward link refers to transmissions from a base station to a remote station while the term “reverse link” refers to transmissions from a remote station to a base station.
• antenna phase information and amplitude information are acquired by a remote station through a pilot channel transmitted from each antenna.
• One of the antennas is considered to be the primary antenna, whereas the other antennas are considered to be the auxiliary antennas.
• the embodiments that follow will be described as two- antenna systems. The number of antennas can be extended without affecting the scope of the embodiments described herein.
• the signals originating from one antenna transmission are orthogonal and the magnitude of the interference between these orthogonal signals is correlated.
• the transmission medium will introduce imperfections such as multi- path, which will degrade the orthogonality between signals.
• Signals received by the remote stations will not be entirely orthogonal and will thereby interfere with each other.
• the magnitude of the interference between one antenna transmission path and another antenna transmission path is generally not correlated, since the signals from the different antennas propagate along different wireless paths. If the magnitude of the interference between the various antenna paths is not correlated, then the transmission gains arising from combining multipaths are no longer present for non- TD remote stations. A more detailed explanation of this phenomenon is presented below.
• each antenna has its own separate power amplifier.
• Power amplifiers are rated for a maximum power, based on design constraints and regulatory constraints. There is therefore a limit to the amount of power with which each antenna can transmit.
• the system is designed to be limited whenever one of the power amplifiers reaches its maximum load, even if another power amplifier has capacity available. In other words, available power from an under-utilized antenna cannot be redistributed to a heavily loaded antenna. This problem may occur when multiple antennas are not loaded with the same transmission load, or when different power amplifiers have different power ratings.
• an apparatus for providing transmission diversity gains to a non-transmission diversity receiver, the apparatus comprising: a primary antenna; at least one auxiliary antenna; and a redistribution unit configured to receive a combined non-transmit diversity and first transmit diversity signal, to receive a second transmit diversity signal, to generate a time-varying version of the combined non-transmit diversity and first transmit diversity signal, to generate a time-varying version of the second transmit diversity signal, and to redistribute the time-varying versions over the primary antenna and the at least one auxiliary antenna.
• a redistribution unit for processing a primary transmission signal and an auxiliary transmission signal within a transmission diversity system to provide transmission diversity gains to non-transmission diversity receivers, the redistribution unit comprising: a distribution path for the primary transmission signal toward a primary antenna; a first time-varying element for generating a time-varying copy of the primary transmission signal and redistributing the time-varying copy of the primary transmission signal to an auxiliary antenna; and a second time-varying element for generating a time-varying copy of the auxiliary transmission signal and for redistributing the time-varying copy of the auxiliary transmission signal to the auxiliary antenna, wherein the auxiliary transmission signal is not distributed to the auxiliary antenna.
• a method for providing transmission diversity gains to non-transmission diversity receivers in a transmission diversity system, wherein the transmission diversity provided using a primary antenna and an auxiliary antenna, the method comprising: generating a time-varying version of a combined non-transmit diversity and first transmit diversity signal; generating a time- varying version of a second transmit diversity signal; directing the combined non- transmit diversity and first transmit diversity signal toward the primary antenna; directing the time-varying version of combined non-transmit diversity and first transmit diversity signal toward the auxiliary antenna; and directing the time-varying version of the second transmit diversity signal toward the auxiliary antenna instead of the second transmit diversity signal.
• an apparatus for balancing the transmission power of multiple antennas in a transmission diversity system, the apparatus comprising: a distribution path for a primary transmission signal toward a primary antenna; a distribution path for a first auxiliary transmission signal toward an auxiliary antenna; a first time-varying element for generating a time-varying copy of the primary transmission signal and redistributing the time-varying copy of the primary transmission signal towards the auxiliary antenna; and a second time-varying element for generating a time-varying copy of a second auxiliary transmission signal and for redistributing the time-varying copy of the second auxiliary transmission signal toward the auxiliary antenna, wherein the second auxiliary transmission signal is not distributed to the auxiliary antenna.
• an apparatus for conveying power-balanced transmission signals of a transmission diversity system, the apparatus comprising: a primary antenna; an auxiliary antenna; and a redistribution unit configured to receive a non-transmit diversity signal directed to the primary antenna, a first transmit diversity signal directed to the primary antenna, and a second transmit diversity signal directed to the auxiliary antenna, wherein the redistribution unit is further configured to generate a time-varying version of the non-transmit diversity signal and a time-varying version of the second transmit diversity signal and to redistribute the time-varying version of the non-transmit diversity signal to the auxiliary antenna and the time-varying version of the second transmit diversity signal to the auxiliary antenna instead of the second transmit diversity signal.
• a method for balancing transmission loads of antennas in a transmit diversity environment, the method comprising: directing the non-transmit diversity and a first transmit diversity signal toward a primary antenna; generating a time-varying version of a non-transmit diversity signal; generating a time-varying version of a second transmit diversity signal; directing the time-varying version of the non-transmit diversity signal to an auxiliary antenna; and directing the time-varying version of the second transmit diversity signal toward the auxiliary antenna instead of the second transmit diversity signal.
• an apparatus for balancing transmission loads of multiple antennas, the apparatus comprising: means for directing the non-transmit diversity signal and a first transmit diversity signal toward a primary antenna; means for generating a time-varying version of a non-transmit diversity signal; means for generating a time-varying version of a second transmit diversity signal; means for directing the time-varying version of the non-transmit diversity signal to an auxiliary antenna; and means for directing the time-varying version of the second transmit diversity signal toward the auxiliary antenna instead of the second transmit diversity signal.
• FIG. 1 is a diagram of a wireless communication network.
• FIG. 2 shows non-transmit diversity signals detected at RAKE receiver fingers.
• FIG. 3 shows transmit diversity signals detected at RAKE receiver fingers.
• FIG. 4A is a block diagram of an apparatus that provides transmission diversity gains to a non-TD receiver.
• FIGS. 4B and 4C are illustrations of signal processing and redistribution within the redistribution unit of FIG. 4A
• FIG. 5A is a block diagram of an apparatus that provides transmission diversity gains.
• FIGS. 5B, 5C, and 5D are illustrations of signal processing and redistribution within the redistribution unit of FIG. 5A.
• FIG. 6 is a block diagram of an apparatus that provides transmission diversity gains.
• a wireless communication network 10 generally includes a plurality of remote stations (also called subscriber units or mobile stations or user equipment) 12a-12d, a plurality of base stations (also called base station transceivers (BTSs) or Node B). 14a-14c, a base station controller (BSC) (also called radio network controller or packet control function 16), a mobile switching center (MSC) or switch 18, a packet data serving node (PDSN) or internetworking function (IWF) 20, a public switched telephone network (PSTN) 22 (typically a telephone company), and an Internet Protocol (IP) network 24 (typically the Internet).
• BSC base station controller
• MSC mobile switching center
• IWF internetworking function
• PSTN public switched telephone network
• IP Internet Protocol
• remote stations 12a-12d For purposes of simplicity, four remote stations 12a-12d, three base stations 14a-14c, one BSC 16, one MSC 18, and one PDSN 20 are shown. It would be understood by those skilled in the art that there could be any number of remote stations 12, base stations 14, BSCs 16, MSCs 18, and PDSNs 20.
• the wireless communication network 10 is a packet data services network.
• the remote stations 12a-12d may be any of a number of different types of wireless communication device such as a portable phone, a cellular telephone that is connected to a laptop computer running IP-based Web-browser applications, a cellular telephone with associated hands-free car kits, a personal data assistant (PDA) running IP-based Web-browser applications, a wireless communication module incorporated into a portable computer, or a fixed location communication module such as might be found in a wireless local loop or meter reading system.
• PDA personal data assistant
• remote stations may be any type of communication unit.
• the remote stations 12a-12d may advantageously be configured to perform one or more wireless packet data protocols such as described in, for example, the EIA/TIA/IS-707 standard.
• the remote stations 12a-12d generate IP packets destined for the IP network 24 and encapsulates the IP packets into frames using a point-to-point protocol (PPP).
• PPP point-to-point protocol
• the IP network 24 is coupled to the PDSN 20, the PDSN 20 is coupled to the MSC 18, the MSC is coupled to the BSC 16 and the PSTN 22, and the BSC 16 is coupled to the base stations 14a-14c via wirelines configured for transmission of voice and/or data packets in accordance with any of several known protocols including, e.g., E1 , T1 , Asynchronous Transfer Mode (ATM), Internet Protocol (IP), Point-to-Point Protocol (PPP), Frame Relay, High-bit-rate Digital Subscriber Line (HDSL), Asymmetric Digital Subscriber Line (ADSL), or other generic digital subscriber line equipment and services (xDSL).
• the BSC 16 is coupled directly to the PDSN 20, and the MSC 18 is not coupled to the PDSN 20.
• the base stations 14a-14c receive and demodulate sets of uplink signals from various remote stations 12a-12d engaged in telephone calls, Web browsing, or other data communications. Each uplink signal received by a given base station 14a-14c is processed within that base station 14a-14c. Each base station 14a-14c may communicate with a plurality of remote stations 12a-12d by modulating and transmitting sets of downlink signals to the remote stations 12a-12d. For example, as shown in FIG. 1 , the base station 14a communicates with first and second remote stations 12a, 12b simultaneously, and the base station 14c communicates with third and fourth remote stations 12c, 12d simultaneously.
• the resulting packets are forwarded to the BSC 16, which provides call resource allocation and mobility management functionality including the orchestration of soft handoffs of a call for a particular remote station 12a-12d from one base station 14a-14c to another base station 14a-14c.
• a remote station 12c is communicating with two base stations 14b, 14c simultaneously. Eventually, when the remote station 12c moves far enough away from one of the base stations 14c, the call will be handed off to the other base station 14b.
• the BSC 16 will route the received data to the MSC 18, which provides additional routing services for interface with the PSTN 22. If the transmission is a packet-based transmission such as a data call destined for the IP network 24, the MSC 18 will route the data packets to the PDSN 20, which will send the packets to the IP network 24. Alternatively, the BSC 16 will route the packets directly to the PDSN 20, which sends the packets to the IP network 24.
• a base station can also be referred to as a Radio Network Controller (RNC) operating in a UMTS Terrestrial Radio Access Network (U-TRAN), wherein "UMTS” is an acronym for Universal Mobile Telecommunications Systems.
• RNC Radio Network Controller
• U-TRAN UMTS Terrestrial Radio Access Network
• ECC Error Control Coding
• An example of an ECC technique is convolutional coding.
• convolutional coding binary data bits are input to a finite state machine (FSM), which produces one or more binary outputs for every input data bit.
• the outputs of this FSM are called code symbols.
• a typical method for constructing such an FSM is through one or more convolutional encoders, i.e., finite impulse response (FIR) binary digital filters operating using arithmetic in the Galois Field GF(2). If the code symbols are corrupted by noise and interference during transmission over a noisy channel, the data bits may still be recoverable through suitable inferences based upon the corrupted code symbols.
• FIR finite impulse response
• the code symbols are "redundant", i.e., the code symbols contain information about not only the input data bits but also the "internal state" of the FSM.
• Methods for optimally inferring the input data bits from the received code symbols are known in the art and are commonly referred to as Trellis Decoding Algorithms, e.g., the Viterbi Algorithm, or the Stack Algorithm.
• Another example of an ECC technique is turbo coding.
• Turbo coding employs two or more convolutional encoders in parallel, in series, or in a combination thereof. The resulting sequence of code symbols also possesses redundant information about the input data bits.
• methods for optimally inferring the input data bits from the received code symbols are known in the art and are commonly referred to as turbo decoding algorithms.
• a "source” In a typical cornmunication system, a "source” generates a stream of information bits representing, for example, voice or data "traffic". This stream of bits is subdivided and grouped, various control bits are appended, and the result is packed into a suitable format for transmission. Voice and data traffic can be transmitted in various formats, such as, e.g. frames, packets, and subpackets.
• the scope of the embodiments described herein extends to all wireless communication systems using any of the various transmission formats. However, for the purpose of illustrative ease, the term "frame” will be used herein to describe the transmission format in which traffic is carried.
• frames comprising bits are convolutionally or turbo encoded, repeated, and punctured to produce a sequence of binary code symbols.
• the resulting code symbols are interleaved to obtain a frame of modulation symbols.
• the output of the interleaver is referred to herein as modulation symbols.
• the modulation symbols are then Walsh covered and combined with a pilot sequence on the orthogonal-phase branch, PN- spread, baseband filtered, and modulated onto the transmit carrier signal.
• the signal propagates to the receiver over multiple transmission paths and is received as a superposition of multiple components, each with its own amplitude, phase and time delay.
• multipaths are commonly caused by reflections off objects present in the transmission path.
• the signal is match-filtered, sampled, digitized and down-converted to complex baseband before it is fed to a searcher and a RAKE processor.
• the searcher usually determines the time delays of the multipath components in the received signal.
• the RAKE processor comprises multiple "fingers", each of which is synchronized to the time delay of a particular multipath component.
• Each RAKE finger is configured to PN-despread the sampled and digitized waveform using the PN code synchronized to that finger's particular time delay. Additionally, each RAKE finger is able to perform Walsh de-covering to separate the modulation symbols from the orthogonal pilot symbols.
• the received modulation and pilot symbols are complex vectors of length L, where L is the number of fingers in the RAKE processor. When L RAKE fingers are assigned to L different multipath components in the received signal, the situation is sometimes called multipath diversity.
• RAKE fingers are assigned to different multipath components on different carriers. This method is called frequency or carrier diversity.
• RAKE fingers are assigned to different multipath components on the different time slots. This is sometimes known as time diversity.
• specialized RAKE fingers may be designed to simultaneously receive one multi-path component from each antenna.
• transmission diversity more modulation symbols can be transmitted to a receiver, which increase the data throughput of the system.
• transmission diversity increases the robustness of the communications system to noise and interference by providing alternative signal paths. For example, if a transmission from one antenna to a remote station fails due to a physical blockage, i.e., a tree, or due to closely spaced multi-paths combining destructively, it is likely that a transmission from another antenna may reach the remote station instead.
• transmission diversity increases the reliability of the connection, which on average, requires less transmission power.
• the first type of transmission diversity system is referred to as an Orthogonal Transmit Diversity (OTD) system, wherein the evenly-numbered modulation symbols are transmitted on a first antenna and the odd-numbered modulation symbols are transmitted on a second antenna. Hence, half of the modulation symbols are sent on each antenna. The transmissions from the antennas are separated by the use of different Walsh codes for each antenna.
• the second type of transmit diversity system is referred to as a Space- Time Spreading (STS) system. In an STS system, all modulation symbols are sent on all antennas.
• STS Space- Time Spreading
• the transmissions from the antennas are modulated using an "Alamouti" matrix, which allows the separation and combining of two modulation symbols at a time by a remote station.
• Alamouti matrix
• two different symbols are simultaneously transmitted from two antennas and the complex conjugate of the other symbol is then transmitted within one symbol period. For example, a symbol s 0 is transmitted through a first antenna while a second symbol Si is concurrently transmitted through a second antenna. Within one symbol period, the complex conjugate of the second signal s-i* is transmitted through the first antenna while the complex conjugate of the signal s 0 * is concurrently transmitted through the second antenna.
• the first antenna transmits ⁇ s 0 , Si* ⁇ while the second antenna transmits ⁇ si, s 0 * ⁇ .
• a combiner builds two combined symbols s 0 ' and s-i' using a matrix H, which models the channel response for each antenna transmission path. The combined symbols are then used in a maximum likelihood decision rule to reach a decision as to the value of a received symbol.
• the interference between one antenna transmission path and another antenna transmission path is not necessarily correlated. If the magnitude of the interference between the various antenna paths is not correlated, then the transmission gains arising from combining multipaths are no longer present.
• the signal and the noise are correlated in the above example, e.g., if the noise increases then the signal increases as well, so that the SNR stays constant.
• a TD system with two antennas uses one of the antennas to transmit to a receiver, and the received signal is also subject to 10% of self- interference.
• the receiver sees a signal with a signal strength Ai and noise that is 10% of (Ai + A 2 ), wherein A 2 is the signal strength of the second antenna transmitting to another receiver.
• the SNR is:
• FIG. 2 and FIG. 3 illustrate the above-described phenomenon.
• a RAKE processor assigns Fingeri (not shown) to a first multipath signal 200 received at a first time offset of a scrambling code and Finger 2 (not shown) to a second multipath signal 210 received at a second time offset of the scrambling code.
• the first multipath signal 200 directly interferes with the second multipath signal 210 as noise (shown as dashed lines on figures), and the second multipath signal 210 directly interferes with the first multipath signal 200 as noise.
• a RAKE processor assigns Fingen to a first multipath signal 310 from a first antenna and a second multipath signal 320 from second antenna.
• the RAKE processor assigns Finger 2 to a third multipath signal 330 from the first antenna and a fourth multipath signal 340 from the second antenna.
• the magnitude of the interference between the first antenna and the second antenna is not correlated.
• the first multipath signal 310 decreases in amplitude, then the amplitude of the second multipath signal 320 may remain the same.
• the receiver fingers would capture, as an example, the first multipath signal 310 and the third multipath signal 330, but these signals would still be affected by the interference of the second multipath signal 320 and the fourth multipath signal 340. Hence, the gain arising from using multipath receivers is not realized for non-TD stations.
• the embodiments that are described herein are for a transmission diversity system that supports both non-TD and TD remote stations while providing the gains associated with transmission diversity to non-TD remote stations.
• the embodiments will also provide a mechanism for balancing the load between multiple power amplifiers, which are each communicatively coupled to the multiple transmission antennas.
• the embodiments will also provide a mechanism that will allow any traffic channel to utilize all the available power of the power amplifiers.
• TD and non-TD transmission signals are transmitted over multiple antennas in a manner that correlates the interference between the multiple antenna transmission paths.
• transmission signals directed to non-TD remote stations are referred to as XN and transmission signals directed to TD remote stations are referred to as X T D-
• the embodiments encompass the use of an apparatus that performs a time-varying transformation of transmission diversity signals and non-transmission diversity signals that are then mapped to multiple antenna paths.
• transmission signals is used rather than the term "modulation symbols” to denote the signal that is directed over the antennas, since different modulation symbols associated with one or several channels may be combined for transmission.
• a time-varying transformation is implemented to provide good coverage to non-TD stations over portions of the interleaved modulation symbols within the transmission signal.
• the uncorrupted bits will arrive in good enough condition so that the receiver can effectively use the error control coding techniques described previously.
• the time-varying transformation of the transmission signals will correlate the interference between the antenna paths.
• FIG. 4A is a block diagram of an apparatus that provides transmission diversity gains to a non-TD receiver.
• This embodiment is coupled to a base station 400 that is configured to transmit signals directed towards the non-TD receivers on a primary antenna alone.
• Base station 400 outputs signal X for transmission over a first antenna Ai to non-TD receivers, and outputs signals XTDI and X T 2 for transmission over the first antenna Ai and a second antenna A 2 , wherein the signals XTDI and XTD2 are directed towards TD receivers.
• Redistribution unit 410 comprises hardware and software for processing and re-distributing the symbols over the antenna transmission paths Yi and Y 2 .
• FIGS. 4B and 4C illustrates the signal processing and redistribution within the redistribution unit 410 of FIG. 4A.
• the redistribution unit 410 receives signals XN and XTDI , which are originally directed for transmission over Yi (the primary antenna), and generates a time-varying version of XN and XTDI over path Y 2 using any time- varying element 415a.
• the redistribution unit causes the system to transmit signals X and XTDI over path Yi and time-varying versions of XN and XTDI over path Y 2 .
• the redistribution unit 410 further receives signal XTD 2 that is originally for transmission over path Y 2 (the secondary channel), and generates a time-varying version of XT D 2 using a time-varying element 415b. The time-varying version of XTD 2 is then transmitted over path Y 2 , rather than the original signal XT D 2-
• FIG. 4C illustrates the redistribution of the pilot signals on paths Yi and Y 2 .
• the apparatus 410 receives a primary pilot Pi and generates a time-varying version of Pi.
• the primary pilot is sent over path Yi and the time-varying version of Pi is sent over path Y 2 .
• the apparatus 410 further receives a second pilot P and generates a time-varying version of P 2 .
• the apparatus directs only the time-varying version of P 2 onto path Y 2 .
• Elements 440A, 440B, 450A, and 450B are used to represent the generation of time-varying signals.
• the time- varying versions are generated by multiplying the original signal with a complex sinusoid e ⁇ f , where t is the time and is a constant that determines the rate of phase change.
• the embodiment shown in FIG. 5A is for transmission diversity systems wherein the number of antennas that are required for a transmission diversity system is based upon the number of signal types.
• the number of signal types shown in the figure is three: signals XN, XTDI and X TD2 -
• a redistribution unit 510 that configured to process, redirect, and mix input signals is coupled to a base station 500 that is configured to transmit signal XN towards non-TD receivers and signals XTDI and XTD 2 towards TD receivers.
• the redistribution unit 510 outputs signals on path Yi, where the signals are amplified by a first power amplifier 520a before transmission on antenna Ai and outputs signals on path Y 2 , which are amplified by a second power amplifier 520b before transmission on antenna A 2 .
• FIGS. 5B, 5C and 5D are block diagrams indicating the way input signals are processed, redirected and mixed within the redistribution unit 510 of FIG. 5A.
• the redistribution unit 510 receives symbols XN, XTDI , and XTD2, which were originally for transmission on separate antennas.
• the redistribution unit 510 then generates a time-varying version of X and XTD 2 at elements 540a and 540b, respectively.
• the redistribution unit 510 outputs the original symbols X and XTDI onto path Yi and outputs the time-varying versions of XN and XTD 2 onto path Y 2 .
• FIG. 5C illustrates the transmission of the pilot signals Pi and P on paths
• FIG. 5D illustrates an alternate transmission scheme for the pilot signals Pi and P 2 , wherein a time-varying transformation is performed upon the primary pilot signal Pi.
• the redistribution unit 510 outputs pilot Pi onto path Yi and outputs a mixed pilot signal on path Y 2 , wherein the mixed pilot signal comprises pilot signal P 2 and the time-varying version of primary pilot Pi.
• the alternate pilot transmission scheme described in FIG. 5D requires a modification of the new TD remote stations at the factory, but not in the old, non-TD remote stations, which already operate within the system.
• the non-TD remote stations will merely listen for the primary pilot according to its original programming, but the TD remote stations must be configured to subtract the time-varying version of Pi from the signals received over path Y 2 .
• the time-varying version of Pi on path Y 2 serves to provide transmission diversity gains to the non-TD remote station.
• Redistribution unit 610 may be represented in a mathematical form by a matrix multiplication. Let Y be a vector of transmission paths, Z be a vector of input signals, and W be a matrix of time-varying operations performed by the apparatus. w,. w, In
• the matrix W varies smoothly in time, e.g. the values Win vary smoothly in time. Furthermore, each row of the matrix W sequentially takes the initial value of all of the other rows.
• the embodiment of FIG. 6 is particularly interesting because it redistributes any number of input signals to any number of antennas.
• W * is the conjugate transpose (also called Hermitian) of W and I is the identity matrix.
• This embodiment which is referred to herein as "sin-cos", is interesting in that it can be implemented as a switching unit that does not distort the phase of the signal.
• the signals Z ⁇ and Z 2 are alternatively transmitted on Yi and Y 2 with smooth transitions.
• the "sin-cos" embodiment may be further generalized for any even integer value n.
• n the number of integers in the matrix W(t)
• W(t) the time-varying function.
• each of the n signals Z ⁇ is applied to each of the antennas in turn with smooth variations between.
• the matrix W is a unitary transformation that scales and sums the input symbols in pairs to form the output symbols.
• the matrix W is a unitary transformation. Moreover, the matrix W loads the power over the power amplifiers PAi and PA 2 evenly, as follows:
• the power output of the two antennas are balanced, even though the original signals Pi, P 2 , YN, XTDI , and XTD 2 may have different power.
• the signal XN can be set to use up all the remaining power in the system, even though it is not transmitted in TD mode.
• Using the signal X to use up all the remaining power in the system can be very useful to a system such as cdma2000.
• cdma2000 there are some channels that are configured for transmission over the primary antenna alone, even when transmission diversity is available.
• the Packet Data Channel and Packet Data Control Channel are designed to use all the unused power in the system to transmit packet data.
• Unfortunately these two channels are only transmitted on the primary antenna if the system is configured for transmit diversity.
• the Packet Data Channel and Packet Data Control Channel therefore cannot utilize available power from the auxiliary antenna, which would be very desirable.
• the "exp-exp" embodiment can be generalized as a type of beamforming transformation over N antennas. Let wu denote the /c 77 row and f 1 column of the matrix W(t). Then matrix W(t) can be generated by setting w ki ⁇ -— e J2 *w» k/N . N
• DSP digital signal processor
• ASIC application specific integrated circuit
• FPGA field programmable gate array
• a general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine.
• a processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
• the steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two.
• a software module may 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 storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium.
• 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 user terminal.
• the processor and the storage medium may reside as discrete components in a user terminal.

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