Abstract:
The present invention presents a method and apparatus for phase hopping and space-time coding signals for transmission on multiple antennas. The method and apparatus provides expansion of a N×N′ space time block code to a M×M′ space time block code, where M&gt;N, by using phase hopping on the symbols within the N×N′ space time block code to allow transmission of the space time block code on a number of diversity antennas greater than N′. A result of M antenna diversity may be achieved for M transmit antennas.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a method and apparatus for achieving transmit diversity in telecommunication systems and, more particularly, to a method and apparatus for non-zero complex weighting and space-time coding signals for transmission on multiple antennas.  
         BACKGROUND OF THE INVENTION  
         [0002]    As wireless communication systems evolve, wireless system design has become increasingly demanding in relation to equipment and performance requirements. Future wireless systems, which will be third and fourth generation systems compared to the first generation analog and second generation digital systems currently in use, will be required to provide high quality high transmission rate data services in addition to high quality voice services. Concurrent with the system service performance requirements there will be equipment design constraints, which will strongly impact the design of mobile terminals. The third and fourth generation wireless mobile terminals will be required to be smaller, lighter, more power-efficient units that are also capable of providing the sophisticated voice and data services required of these future wireless systems.  
           [0003]    Time-varying multi-path fading is an effect in wireless systems whereby a transmitted signal propagates along multiple paths to a receiver causing fading of the received signal due to the constructive and destructive summing of the signals at the receiver. Several methods are known for overcoming the effects of multi-path fading, such as time interleaving with error correction coding, implementing frequency diversity by utilizing spread spectrum techniques, or transmitter power control techniques. Each of these techniques, however, has drawbacks in regard to use for third and fourth generation wireless systems. Time interleaving may introduce unnecessary delay, spread spectrum techniques may require large bandwidth allocation to overcome a large coherence bandwidth, and power control techniques may require higher transmitter power than is desirable for sophisticated receiver-to-transmitter feedback techniques that increase mobile terminal complexity. All of these drawbacks have negative impact on achieving the desired characteristics for third and fourth generation mobile terminals.  
           [0004]    Antenna diversity is another technique for overcoming the effects of multi-path fading in wireless systems. In diversity reception, two or more physically separated antennas are used to receive a transmitted signal, which is then processed by combining and switching to generate a received signal. A drawback of diversity reception is that the physical separation required between antennas may make diversity reception impractical for use on the forward link in the new wireless systems where small mobile terminal size is desired. A second technique for implementing antenna diversity is transmit diversity. In transmit diversity a signal is transmitted from two or more antennas and then processed at the receiver by using e.g. maximum likelihood sequence estimator (MLSE), minimum mean square error (MMSE) receivers, Maximum-a Posteriori receivers, or their approximations. Transmit diversity has more practical application to the forward link in wireless systems in that it is easier to implement multiple antennas in the base station than in the mobile terminal.  
           [0005]    Transmit diversity for the case of two antennas is well studied. Alamouti has proposed a method of transmit diversity for two antennas that offers second order diversity for complex valued signals. S. Alamouti, “ A Simple Transmit Diversity Technique for Wireless Communications,”IEEE Journal on Selected Areas of Communications , pp. 1451-1458, October 1998. The Alamouti method involves simultaneously transmitting two signals from two antennas during a symbol period. During one symbol period, the signal transmitted from a first antenna is denoted by S 0  and the signal transmitted from the second antenna is denoted by S 1 . During the next symbol period, the signal −S 1 * is transmitted from the first antenna and the signal S 0 * is transmitted from the second antenna, where * is the complex conjugate operator. A similar diversity transmission system may also be realized in code domain. As an example, two copies of the same symbol can be transmitted in parallel using two orthogonal Walsh codes. Similar techniques can be also used to construct a space-frequency coding method.  
           [0006]    Extension of the Alamouti method to more than two antennas is not straightforward. Tarokh et al. have proposed a method using rate=½, and ¾ SpaceTime Block codes for transmitting on three and four antennas using complex signal constellations. V. Tarokh, H. Jafarkhani, and A. Calderbank, “ Space - Time Block Codes from Orthogonal Designs,” IEEE Transactions on Information Theory , pp. 1456-1467, July 1999. This method has a disadvantage in a loss in transmission rate and the fact that the multi-level nature of the ST coded symbols increases the peak-to-average ratio requirement of the transmitted signal and imposes stringent requirements on the linear power amplifier design. Additional techniques that mitigate these problems are proposed in O. Tirkkonen and A. Hottinen, “Complex space-time block codes for four Tx antennas,” Proc. Globecom 2000, November 2000, San Francisco, USA. Other methods proposed include a rate=1, orthogonal transmit diversity (OTD)+space-time transmit diversity scheme (STTD) four antenna method. L. Jalloul, K. Rohani, K. Kuchi, and J. Chen, “Performance Analysis of CDMA Transmit Diversity Methods,” Proceedings of IEEE Vehicular Technology Conference, Fall 1999, and M. Harrison, K. Kuchi, “Open and Closed Loop Transmit Diversity at High Data Rates on 2 and 4 Elements,” Motorola Contribution to 3GPP-C30-19990817-017. This method requires an outer code and offers second order diversity due to the STTD block (Alamouti block) and a second order interleaving gain from use of the OTD block. The performance of this method depends on the strength of the outer code. Since this method requires an outer code, it is not applicable to uncoded systems. For the case of rate=⅓ convolutional code, the performance of the OTD +STTD method and the Tarokh rate=¾ method ST block code methods are about the same. Another rate I method is proposed in O. Tirkkonen, A. Boariu, and A. Hottinen, “Minimal non-orthogonality rate 1 space-time block code for 3+Tx antennas,” in Proc. ISSSTA 2000, September 2000. The method proposed in this publication attains high performance but requires a complex receiver.  
           [0007]    It would be advantageous, therefore, to have a method and apparatus that provided the advantage of transmit diversity on greater than two antennas while at the same time not greatly increasing the complexity of system design.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention presents a method and apparatus for non-zero complex weighting and space-time coding signals for transmission on multiple antennas. The method and apparatus provides expansion of an N×N′ space-time block code, where N is the number of transmit paths and N′ is the number of output symbols per transmit path, to a M×M′ space-time block code, where M&gt;N, generated by using repetition and non-zero complex weighting of the symbols within the N×N′ space time block code, to allow transmission of the space time block code on a number M of diversity transmit paths. The diversity transmit paths may comprise separate antennas or beams. The temporal length of the larger code M′, may equal the temporal length of the original code, N′. In the method and apparatus, a transform is performed on an input symbol stream, to generate a transform result comprising a space-time block code. The N output streams of the space-time block code, each consisting of N′ output symbols, are then repeated and at least one of the repeated streams non-zero complex weighted over time to generate M streams of N′ output symbols for transmission on M diversity transmit paths. The non-zero complex weighting may include phase shifting.  
           [0009]    In an embodiment, N is at least 2 and M is at least 3. At least two of the N streams of N′ output symbols, corresponding to the original N streams of N′ output symbols, are then each transmitted on a first at least one antenna and at least one of the M−N non-zero complex weighted streams of N′ symbols are transmitted on one of a second at least one antenna. The first at least one antenna and second at least one antenna may comprise of any one of the M antennas.  
           [0010]    In another embodiment, the method and apparatus may be implemented in a transmitter having common or dedicated pilot channels that enable efficient channel estimation of the coefficients that are required to decode the space-time code. In this embodiment the common and dedicated pilot channels may be implemented alone or both together in the transmitter. In one alternative of this embodiment, training symbols are transmitted on N transmit diversity paths, making it possible to estimate the N independent diversity transmit paths. For this, a dedicated pilot channel code sequence may be multiplexed into each of the N streams of N′ output symbols of the original space-time block code, to generate N streams of N′ output symbols and pilot channel sequence. Repetition and non-zero complex weighting may then be applied to generate M phase shifted streams of N′ symbols and pilot channel sequence. At least two of the N original streams of N′ output symbols and pilot channel sequence are then transmitted on one of the first at least one antenna and at least one of the M−N complex weighted streams of N′ output symbols and pilot channel sequence are transmitted on one of the second at least one antenna. Another way of enabling estimation of N channels is to transmit common pilot channels so that N common pilot channel are transmitted on each of the first at least one antenna, and M−N complex weighted copies of some of the N common pilot channels are transmitted on each of the second at least one antenna. The complex weighting factors used for the common channels on each of the second at least one antenna are the same as the ones used to construct the M−N additional complex weighted streams of N′ output symbols from the original N streams of N′ output symbols. In these embodiments, the receiver may or may not know the method used to expand the N×N′ space-time block code to an M×N′ space-time block code, and the temporal weighting sequences employed.  
           [0011]    In other embodiments, where N is at least 2 and M may be at least 3, the pilot channels may be arranged to enable estimation of at least N+1 diversity transmit paths. At least one of the N streams of N′ output symbols, corresponding to the original N streams of N′ output symbols, are then each transmitted on a first at least one antenna and at least one of the M−N complex weighted streams of N′ symbols are each transmitted on one of a second at least one antenna. Different common pilot channels are transmitted on each of the first at least one antenna and on at least one of the second at least one antenna. In these embodiments, the receiver needs at least partial knowledge of the method used to expand the N×N′ space-time block code to an M×N′ space-time block code, and the temporal weighting sequences employed.  
           [0012]    Complex weighting in the various embodiments may be applied by applying a periodic or random complex weighting pattern to each of the symbol streams that are complex weighted. The relationship between the complex weights of the symbol streams transmitted on the various antennas may also be predefined. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0013]    FIG  1   a  shows a block diagram of a transmitter according to an embodiment of the invention;  
         [0014]    [0014]FIG. 1 b  shows a block diagram of portions of a common pilot channel STTD transmitter according to an embodiment of the invention;  
         [0015]    [0015]FIG. 2 shows a block diagram of portions of a common pilot channel STTD transmitter according to another embodiment of the invention;  
         [0016]    [0016]FIG. 3 shows a block diagram of portions of a dedicated pilot channel STTD transmitter according to a further embodiment of the invention;  
         [0017]    [0017]FIG. 4 shows a block diagram of portions of an embodiment of a receiver for use with the transmitter of FIG. 1;  
         [0018]    [0018]FIG. 5 shows a block diagram of portions of an embodiment of a receiver for use with the transmitter of FIG. 2 or the transmitter of FIG. 3;  
         [0019]    [0019]FIG. 6 shows rake finger embodiment of STTD demodulator  508  of FIG. 5;  
         [0020]    [0020]FIG. 7 shows a block diagram of portions of an STS transmitter according to an embodiment of the invention;  
         [0021]    [0021]FIG. 8 shows a block diagram of portions of an OTD transmitter according to an embodiment of the invention;  
         [0022]    [0022]FIG. 9 shows a block diagram of portions of an embodiment of a receiver for use with the transmitter of FIG. 7;  
         [0023]    [0023]FIG. 10 shows a block diagram of portions of an embodiment of a receiver for use with the transmitter of FIG. 8;  
         [0024]    [0024]FIG. 11 shows a block diagram of portions of a long ST block code transmitter according to an embodiment of the invention;  
         [0025]    [0025]FIG. 12 shows a block diagram of portions of a common/dedicated pilot channel STTD transmitter according to another embodiment of the invention;  
         [0026]    [0026]FIG. 13 shows a block diagram of portions of a receiver for use with the transmitter of FIG. 12; and  
         [0027]    [0027]FIG. 14 shows a block diagram of portions of a receiver for use in power control of the transmitter of FIG. 12.  
         [0028]    [0028]FIG. 15 shows a constellation defining a phase shifting pattern that may be used in various embodiments of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    Referring now to FIG. 1 a , therein is shown a block diagram of a transmitter  150  according to an embodiment of the invention. Transmitter  150  includes input  152  for receiving an input symbol stream, block code processor  154  for performing a transform on the input symbol stream to generate a transform result representable by an orthogonal space time block code and outputting  2  streams of symbols of the transform result, non-zero complex weighter  156  for non-zero complex weighting a first one of the two streams of symbols, a non-zero complex weighter  158  for non-zero complex weighting the second of the two streams of symbols, an RF transmitter  160  for transmitting the first stream of symbols on Ant. 1, RF transmitter  162  for transmitting the non-zero complex weighted stream of symbols on Ant. 2, RF transmitter  164  for transmitting the second stream of symbols on Ant. 3, and RF transmitter  166  for transmitting the phase shifted second stream of symbols on Ant. 4. The antennas Ant. 1-Ant. 4 may be polarized relative to one another to provide enhanced diversity reception. For example, Ant. 1 or Ant. 2 may be vertically polarized relative to a horizontal polarization of Ant. 3 or Ant. 4, respectively. The embodiment of transmitter  150  of FIG. 1 a  may be implemented in various forms suitable for different technologies and systems to expand a 2×N′ block code for transmission over  4  transmit diversity paths. In transmitter  150 , each of the 4 transmit diversity paths includes a separate antenna, Ant. 1-Ant. 4. This may include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, or any other type of digital communications system into which transmit diversity may be introduced. In an alternative of the embodiment of FIG. 1 a , the non-zero complex weighting may be all performed on selected ones of the transmission paths to create relative phase shifts between the transmissions on Ant. 1 and Ant. 2 or on Ant. 3 and Ant. 4. For example, non-zero complex weighting could also be applied before the inputs to RF transmitters  160  and  164 , creating a non-zero complex weighted version of each of the symbol streams, but maintaining a relative phase shift between the transmitted signals. An alternative of the embodiment of transmitter  150  may be implemented using less than  4  antennas, to implement the 4 diversity paths. As an example, the signals input to RF transmitters  164  or  166  may be connected together and transmitted on a single antenna. Also other alternatives are possible in which less than 4 diversity paths are used, for example, only one of the 2 data streams may be non-zero complex weighted and transmit on two diversity paths. In an alternative embodiment of FIG. 1 a , the non-zero complex weighing operation may be performed after RF transmitter blocks  160 ,  162 ,  164 ,  166 , i.e., non-zero complex weighing could be implemented as a continuous phase sweep after the modulation, and baseband filtering of Space-Time coded symbols.  
         [0030]    The non-zero complex weighting for these transmissions on Ant. 2 and Ant. 4 may be performed according to various alternatives. For example, a phase pattern W 1 (t)=exp(j*pi*phase_in_degrees/180) used on Ant. 2 may be applied and the phase pattern −W 1 (t), which is 180 degrees out of phase with W 1 (t) may be used on Ant. 4. Examples of this would be a phase pattern of shifts in degrees of {0, 90, 180, 270} on Ant. 2 and {180, 270, 0, 90} on Ant. 4 for 4PSK constellation. Other example patterns {0, 45, 90,135,180, 225, 270, 315} for 8PSK and {0, 22.5, 45, 67.5 . . . . . . 337.5} for 16PSK. FIG. 15 shows a constellation defining another phase shifting pattern that may be used in various embodiments of the invention. This sequence of shifts in degrees of {0, 135, 270, 45, 180, 315, 90, 225} may be transmitted on antenna 2 while using the pattern of shifts in degrees of {180, 315, 90, 225, 0,135,270, 45} on antenna 4. The phase shifting may be periodic or random. Periodic phase shifting refers to a predefined phase pattern for e.g. complex weight W 1 (t) repeated periodically. The complex weights can be defined so that the sequence of complex weights defines a maximal length path, to make successive samples of the effective channel as independent as possible. This can make interleaving redundant and thus enable low delay transmission. Pseudo-random phase shifting used may be a sequence of random phase selections from a MPSK constellation. Alternatively, another non-zero complex weighting scheme where the phase difference between successive phase states is as small as possible is advantageous when estimating channel coefficients or metrics related to power control from a non-zero complex weighted channel. In this case, the phase states may still cover 360 degrees during the duration of one encoding block. Channel interleaving may be used in the embodiments as in conventional systems. It is also possible to implement the non-zero complex weighting sequence and the interleaver jointly, so that the symbols at the output of the interleaver are as independent as possible. Furthermore, by changing the relative phase between antennas 1 and 2, and 3 and 4, respectively, the method can be implemented so that there is a phase shift or sweep in all antenna elements, but relative phase shifts between antennas 1 and 2, and 3 and 4 are maintained. As an example, with phase sweep, one may have a 50 Hz phase sweep on antenna 1 and −50 Hz phase sweep on antenna 2, in order to implement a 100 Hz effective sweep. Similarly for antennas 3 and 4.  
         [0031]    The phase rotation may be changed every T seconds. The choice of T depends on total time duration of the data symbols and the method used for estimating the channel coefficients. The phase may be kept constant for the total time duration occupied by the data symbols within at least one space-time encoding block and the corresponding dedicated or common pilot sequence/training sequence can be used to enable proper channel estimation. The pilot sequence could be a walsh code, as used in CDMA systems, or sequence of training symbols with good correlation properties used for channel estimation in TDMA. The pilot symbols may apply the same non-zero complex weighting coefficients as the data within the space-time block. Alternatively, the pilots may be transmitted without phase hopping. In this case the effective channel for the data can be derived jointly from the a priori known hopping pattern and the channel estimate obtained from a non-hopping channel. In cases where non-zero complex weighting is applied to common pilots, the same or different phase pattern may be applied to both data and common pilots. Channel estimation using non-hopping pilot or training sequences (either transmitted on common or dedicated channels) provides better channel estimates as the channel is more stationary.  
         [0032]    Referring now to FIG. 1 b , therein is a block diagram of portions of a common pilot channel space time transmit diversity (STTD) transmitter  100  according to an embodiment of the invention. Transmitter  100  may operate as a 4-antenna transmit diversity extension to release  99  of the wideband CDMA (WCDMA) third generation system standard. Transmitter  100  comprises input  126 , block code processor  124 , traffic channel symbol stream processing branch inputs  102   a - 102   d , antenna gain blocks  104   a ,- 104   d , phase shifters  106   a  and  106   b , phase shifter inputs  112   a  and  112   b , Code multipliers  108   a - 108   d , pilot sequence processing branch inputs  114   a - 114   d , antenna gain blocks  116   a - 116   d , code multipliers  118   a - 118   d , RF transmitter  128 , including RF transmitters  128   z - 128   d , and antennas Ant.1-Ant. 4.  
         [0033]    In FIG. 1 b , data to be transmitted including a channel coded and interleaved input symbol stream X(t) comprising the symbols S 1 S 2  is received at input  126 . Block code processor  124  performs a transform on every two received symbols S 1 S 2  to generate a transform result comprising a 2×2 orthogonal space-time block code. In the embodiment, block code processor  124  may perform an Alamouti transform to generate the block code in the form represented by the following matrix:  
             [           S   1           S   2               -     S   2   *             S   1   *           ]           (   1   )                               
 
         [0034]    The matrix is then divided into 4 streams of 2 symbols with each of the streams being input to one of the traffic channel symbol stream processing branch inputs  102   a - 102   d . As shown in FIG. 1, the stream S 1 S 2  is input to  102   a , S 1 S 2  is input to  102   b , −S 2 *S 1  in input to  102   c , and to −S 2 *S 1 * is input to  102   d . The non-zero complex weighting is performed by antenna gain blocks  104   a - 104   d  and phase shifters  106   a  and  106   b . Antenna gain for each of the processing branches is adjusted in antenna gain blocks  104   a - 104   d . After antenna gain is adjusted, phase shifters  106   a  and  106   b  apply a phase shift to the stream S 1 S 2  output from antenna gain block  104   b  and stream −S 2 *S 1  * output from antenna gain block  104   d . The phase shifter control blocks  112   a  and  112   b  may control phase shifters  106   a  and  106   b  by causing shifting using a continuous or discrete phase hopping pattern. A CDMA scrambling code is then input to code multipliers  108   a - 108   d  to generate the stream S 1 S 2  to RF transmitter  128   a  for transmission on Ant. 1, S 1 S 2  (exp(jΦ 21  k1)) to RF transmitter  128   b  for transmission Ant. 2,-S 1 *S 2 * to RF transmitter  128   c  for transmission on Ant. 3 and −S 2 *S 1 * (exp(jΦk2)) to RF transmitter  128   d  for transmission on Ant. 4. The RF transmitters may perform of baseband pulse shaping, modulation, and carrier up conversion. In some implementations one may choose to apply phase hopping or sweep after baseband pulse shaping and modulation steps.  
         [0035]    Common pilot channel sequences X 1 -X 4  are input to pilot sequence processing branch inputs  114   a - 114   d . The pilot sequences are then separately processed through antenna gain blocks  116   a - 116   d , and code multipliers  118   a - 118   d . The coded outputs from code multipliers  118   a - 118   d  are then input to RF transmitters  128   a - 128   d , respectively, of RF transmitter  130 .  
         [0036]    The pilot sequence X 1  is then transmit on Ant. 1, the pilot sequence X 2  is transmit on Ant. 2, the pilot sequence X 3  is transmit on Ant. 3, and the pilot sequence X 4  is transmit on Ant. 4.  
         [0037]    Referring now to FIG. 4, therein is a block diagram of portions of a receiver for use with transmitter  100  of FIG. 1 b . FIG. 4 shows the signal processing for one rake finger receiver section of a receiver. The received pilot sequences X 1 -X 4  transmit from transmitter  100  are received and input to channel estimation processing branch  402   a - 402   d , respectively. Channel estimator  404  then performs a channel estimation function, for example a low pass filter moving average function, for each of channel 1-channel 4. The estimates of channel 1-channel 4 are then output from outputs  406   a - 406   d  to summer  410   a , phase shifter  408   a , summer  410   b  and phase shifter  408   b . Phase shifter  408   a  receives input from phase shifter control block  414   a  and shifts the estimate for channel 2 by the same phase shift used on the traffic channel symbols S 1 S 2  transmitfrom Ant. 2 in transmitter  100 . Phase shifter  408   b  receives input from phase shifter control block  414   b  shifts the estimate for channel 4 by the same phase shift used on the traffic channel symbols −S 2 * S 1 * transmit from Ant. 4 in transmitter  100 . The phase shifted version of the estimate for channel 2 is combined with the estimate for channel 1 by summer  410   a ,and the phase shifted version of the estimate for channel is combined with the estimate for channel 3 in summer  410   b . The combined estimate for channels 1 and 2 ( 412   a ) and the combined estimate for channel 3 and 4 ( 412   b ) are then input to STTD demodulator  418 , which processes the received traffic signals from input  416  using the channel estimates. The demodulated signal is then processed in rake combiner, deinterleaver and channel decoder  420  to generate the received symbols S 1 S 2 .  
         [0038]    In an alternative common pilot channel embodiment for 4-antenna diversity, common pilot channels are phase shifted in the same manner as the traffic channels before transmission. Referring now to FIG. 2, therein is a block diagram of portions of a common pilot channel STTD transmitter  200  according to another embodiment of the invention. Transmitter  200  comprises input  226 , block code processor  224 , traffic channel symbol stream processing branch inputs  202   a - 202   d , antenna gain blocks  204   a ,- 204   d , phase shifters  206   a  and  206   b , phase shifter inputs  212   a  and  212   b , Code multipliers  208   a - 208   d , Code multiplier input  210 , pilot sequence processing branch inputs  214   a - 214   d , antenna gain blocks  216   a - 216   d , phase shifters  218   a  and  218   b , phase shifter control blocks  224   a  and  224   b , code multipliers  220   a - 220   d , code multiplier input  222 , RF transmitter  228 , including RF transmitters  228   a - 228   d , and antennas Ant 1-Ant. 4.  
         [0039]    The traffic channel processing and transmission in transmitter  200  is performed in the same manner as used for the traffic channel processing in transmitter  100  of FIG. 1. Transmitter  200 , however, uses common pilot channels, which are phase shifted. Common pilot channel sequence P 1  is input to pilot sequence processing branch inputs  214   a  and  214   b  and common pilot channel sequence P 2  is input to pilot sequence processing branch inputs  214   c  and  214   d . The pilot sequences are then separately processed through antenna gain blocks  216   a - 216   d . The pilot sequence P 1  output from antenna gain block  216   a  is input to code multiplier  220   a . The pilot sequence P 2  output form antenna gain block  216   c  is input to code multiplier  220   c . Pilot sequence P 1  output from antenna gain block  216   b  is input to phase shifter  218   a . Pilot sequence P 2  output from antenna gain block  216   d  is input to phase shifter  218   b . Phase shifter  218   a  and  218   b  apply a phase shift under the control of phase shifter control block  224   a  and  224   b , respectively. The phase shift may be the same continuous or discrete phase hopping pattern used for the traffic channels. The phase shifted pilot sequence P 1  output from phase shifter  218   a  is then input to code multiplier  220   b  and the phase shifted pilot sequence P 2  output from phase shifter  218   b  is then input to code multiplier  220   d . The coded pilot sequence P 1  output from code multiplier  220   a  is then input to RF transmitter  228   a  for transmission on Ant. 1. The coded phase shifted pilot sequence P 1  output from code multiplier  220   b  is input to RF transmitter  228   b  for transmission on Ant. 2, the coded pilot sequence P 2  output from code multiplier  220   c  is input to RF transmitter  228   c  for transmission on Ant. 3, and the coded phase shifted pilot sequence P 2  output from code multiplier  220   d  is input to RF transmitter  228   d  for transmission on Ant. 4.  
         [0040]    The phase shifting performed by phase shifters  218   a  and  218   b  may according to various alternatives, for example, as described for the phase shifting performed in the embodiment of FIG. 1.  
         [0041]    Referring now to FIG. 5, therein is a block diagram of portions of an embodiment of a receiver  500  for use with the transmitter of FIG. 2. Receiver  500  comprises channel 1 and channel 2 estimate processing branch input  502   a  and channel 3 and channel 4 estimate processing branch input  502   b , channel estimator  504 , STTD demodulator  508 , traffic signal input  510  and rake combiner, deinterleaver and channel decoder  512 .  
         [0042]    The received pilot sequence P 1  (ch1+ch2Ø) received on channels 1 and 2 from Ant. 1 and Ant. 2, respectively, of transmitter  200  is input to input  502   a . The received pilot sequence P 2  (ch3+ch4Ø) received on channels 3 and 4 from Ant. 3 and Ant. 4, respectively, of transmitter  200  is input to input  502   b . Channel estimator  504  performs channel estimation using, for example, a low pass filter moving average function, and outputs combined estimate for channels 1 and 2 (chest 1,2), and a combined estimate for channels 3 and 4 (chest 3,4). The channel estimates are then input to STTD demodulator  508 , which processes the received traffic signals from input  510  using the channel estimates. The demodulated signal is then processed in rake, combiner, deinterleaver and channel decoder  512  to generate the received symbols S 1 S 2 . FIG. 6 shows an embodiment of a rake finger of STTD demodulator  508  of FIG. 5 that utilizes chest1,2 and chest3,4 for demodulating the received traffic signals.  
         [0043]    In another embodiment for 4-antenna diversity, dedicated pilot channels may be implemented in a WCDMA version of transmitter  150  of FIG. 1. Referring now to FIG. 3, therein is a block diagram of portions of a dedicated pilot channel STTD transmitter  300  according to a further embodiment of the invention Transmitter  300  comprises input  318 , block code processor  316 , channel symbol stream processing branch inputs  302   a - 302   d , antenna gain blocks  304   a ,- 304   d , phase shifters  306   a  and  306   b , phase shifter inputs  312   a  and  312   b , code multipliers  308   a - 308   d , code multiplier input  310 , and antennas Ant. 1-Ant 4.  
         [0044]    Transmitter  300  of FIG. 3 is an implementation that uses dedicated pilot channels that are transmitted by embedding pilot sequences in the traffic channel symbol stream. Input  318  and block code processor  316  function in the same manner as input  126  and block code processor  124  of FIG. 1. In transmitter  300 , as symbols S 1 S 2  are input to symbol stream processing branch inputs  302   a  and  302   b , pilot channel sequence U 1  is input into inputs  302   a  and  302   b  multiplexed between the symbol sets of S 1 S 2 . Also, −S 2 *S 1 * is input to symbol stream processing branch inputs  302   c  and  302   d , and pilot channel sequence U 2  is input onto inputs  302   c  and  302   d , and multiplexed between the symbol sets of −S 2 *S 1 *. Another possibility is to define  4  different dedicated pilot sequences, one for each transmit antenna  
         [0045]    The multiplexed symbol streams at inputs  302   a - 302   d  are then input to antenna gain blocks  304   a - 304   d , respectively. Channel gain is applied in antenna gain blocks  304   a - 304   d . The stream comprising S 1 S 2  and pilot sequence U 1  is output from antenna gain block  304   a  to code multiplier  308   a . The stream comprising S 1 S 2  and pilot sequence U 1  is output from antenna gain block  304   b  to phase shifter  306   a , where it is phase shifted according to input from phase shifter control block  312   a  and then input to code multiplier  308   b . The stream comprising −S 2 *S 1 * and pilot sequence U 2  is output from antenna gain block  304   c  to code multiplier  308   c , and the same stream, −S 2 *S 1 * and pilot sequence, is output from antenna gain block  304   d  to phase shifter  306   b , where it is phase shifted according to input from phase shifter control block  312   b  and then input to code multiplier  308   d . Code multipliers  308   a - 308   d  multiply the appropriate stream by a scrambling code. The code multiplied stream S 1 S 2  and pilot sequence U 1  is then input to RF transmitter  314   a  for transmission on Ant. 1. The code multiplied phase shifted stream S 1 S 2  and pilot sequence U 1  is input to RF transmitter  314   b  for transmission on Ant. 2. The code multiplied stream −S 2 *S 1 * and pilot sequence U 2  is input to RF transmitter  314   c  for transmission on Ant. 3, and the code multiplied phase shifted stream −S 2 *S 1 * and pilot sequence U 2  is input to RF transmitter  314   d  for transmission on Ant. 4. RF transmitter  314   a - 314   d  perform modulation and carrier up conversions before transmitting the streams on Ant. 1-Ant. 4. The RF transmitters may perform of baseband pulse shaping, modulation, and carrier up conversion. In some implementations one may choose to apply the non-zero weighting after baseband pulse shaping and modulation.  
         [0046]    The receiver of FIG. 5 may be modified for use with transmitter  300  of FIG. 3. In this case, receiver  500  would function similarly but inputs  502   a  and  502   b  would input U 1  (Ch1+Ch2Ø) and U 2 (Ch3+Ch4Ø), respectively, to channel estimator  504   c.    
         [0047]    In another embodiment for  4  antenna diversity, dedicated pilot channels and common pilot channels may be implemented in a combined embodiment. Referring now to FIG. 12, therein is a block diagram of portions of a dedicated/common pilot channel STTD transmitter  1200  according to another embodiment of the invention.  
         [0048]    Transmitter  1200  functions essentially in the same manner as transmitter  300  of FIG. 3 with the exception being that common pilot channels are added on Ant. 1 and Ant. 3. Common pilot channel sequences P 1  and P 2  are input to pilot sequence processing branch inputs  1218   a  and  1218   b , respectively. The pilot sequences are then separately processed through antenna gain blocks  1220   a  and  1220   b , and code multipliers  1222   a  and  1222   b . The coded outputs from code multipliers  222   a  and  1222   b  are then input to RF transmitters  1214   a  and  1214   c , respectively, of RF transmitter  1214 . The RF transmitters may perform baseband pulse shaping, modulation, and carrier up conversions. In some implementations one may choose to apply the non-zero weighting after baseband pulse shaping and modulation.  
         [0049]    Transmitter  1200  of FIG. 12 provides non-hopped common pilot channels on Ant. 1 and Ant. 3 and dedicated pilot channels on Ant. 1, Ant. 2, Ant. 3, and Ant. 4. The pilot sequences may be multiplexed within one slot, for example in an embodiment where there are 15 slots in a transmission frame. Antenna gains may be set different for the common and dedicated control channels. The antenna gains can also be time varying.  
         [0050]    Referring now to FIG. 13, therein is a block diagram of portions of a receiver  1300  for use with the transmitter of FIG. 12. Receiver  1300  comprises channel 1 and channel 2 processing branch having inputs  1302   a  and  1302   b , and channel 3 and channel 4 processing branch having inputs  1302   c  and  1302   d . Phase shifter input  1304 , channel estimator  1306 , STTD demodulator  1310 , traffic signal input  312 , and deinterleaver and decoder  1314 .  
         [0051]    The received pilot sequences P 1 , U 1 , P 2 , and U 2  and input to inputs  1302   a ,  1302   b ,  1302   c , and  1302   d , respectively, of receiver  1300 . Channel estimator  1306  performs channel estimation using, for example, a low pass filter having average function, and outputs a combined estimate for channels 1 and 2 (chest 1,2)  1308   a , and a combined estimate for channels 3 and 4 (chest 3,4)  1308   b . The channel estimates are then input to STTD demodulator  1310 , which processes the received traffic signals from input  1312  using the channel estimates. The demodulated signal is then processed in rake, combiner, deinterleaver, and channel decoder  1314  to generate the received symbols S 1 , S 2 .  
         [0052]    A prior knowledge of the phase hopping may be used for power control purposes. Referring now to FIG. 14, therein are shown portions of a receiver for estimating power control, according to an embodiment of the invention. Receiver  1400  includes channel estimator  1402 , channel estimating branch inputs  1404   a - 1404   d , phase shifter inputs  1408   a  and  1408   b , phase shifter  1406   a  and  1406   b , channel estimate output  1410   a  and  1410   b , squaring blocks  1412   a  and  1412   b , and power control processor  1414 .  
         [0053]    Channel estimator  1402  computes channel coefficients from the common or dedicated channels from, for example transmitter  1200 , for all four antennas during a given slot “t”. This may be a channel prediction for slot t+ 1 , alternatively the channel estimate for slot t may be used in slowly fading channels . These channel coefficients are denoted by chanest#1 (t), chanest#2(t), chanest#3 (t), and chanest#4 (t) at inputs  1404   a - 1404   d , respectively. For multiple rake fingers, e.g. chanest#1 (t) is a vector channel estimate corresponding to all rake fingers from Ant. 1.  
         [0054]    Using the prior knowledge of phase hopping in phase shifter inputs  1408   a  and  1408   b  and knowledge of channel estimate for the current slot “t”, channel coefficients for slot “t+1” are estimated:  
         chanest#12( t+ 1)=chanest#1( t )+chanest#2( t ) e   φ12(t+1)    
         chanest#34( t+ 1)=chanest#3( t )+chanest#4( t ) e   φ34(t+1)   (2)  
         [0055]    Where φ12, φ34 are known a priority.  
         [0056]    Received signal power estimate for slot (t+1) can be done based on chanest #12(t+1) and chanest #12(t+1);  
         received_power( t+ 1)=∥chanest#12( t+ 1)∥ 2 +∥chanest#34( t+ 1)∥ 2    
         [0057]    A power control command is generated by processor  1414  using the received power estimate.  
         [0058]    The method and apparatus of the invention may also be implemented with diversity in the Walsh code domain. Referring now to FIG. 7, therein is a block diagram of portions of an space time spreading (STS) transmitter  700  according to an embodiment of the invention;  
         [0059]    Transmitter  700  is a STS embodiment of transmitter  150  of FIG. 1 a  in which the space time block processor performs the transform in the Walsh Code domain. The STS block code matrix used may be represented as:  
                 [             S1          W   ~     1       -       S2   *            W   ~     2                     S2          W   ~     1       +       S1   *            W   ~     2               ]                   where                     W   ~     1       =         [       W   1                     W   1       ]                       W   ~     2       =     [       W   1                -     W   1       ]               (   3   )                               
 
         [0060]    As is done for the embodiment of FIG. 1 a , each row of the matrix and its phase shifted version are each transmitted on separate antennas Ant. 1-Ant. 4. The symbols S 1  and S 2  in each row are each transmitted simultaneously over two symbol periods, rather than sequentially. Data symbols are input to transmitter  700  at input  718  of channel coder  720 . Channel coder  720  codes, punctures, interleaves, and formats the input data symbols and outputs every other coder output symbol S 1  as even data and every other coder output symbol S 2  as odd data. The even data is then processed through symbol repetition blocks  702   a,b,e,f , Walsh function blocks  704   b  and  704   d , Walsh multipliers  706   a,b,e,f , summers  708   a - 708   d  and complex adders  710   a  and  710   b . The odd data is processed through symbol repetition blocks  702   c,d,g,h , Walsh function blocks  704   b  and  704   d , Walsh multipliers  706   c,d,g,h , summers  708   a - 708   d , and complex adders  710   a  and  710   b . The result at the output of complex adder  710   a  is the matrix row S1{tilde over (W)} 1 -S 2 *{tilde over (W)} 2  and the result at the output of complex adder  710   b  is the matrix row S 2 {tilde over (W)} 1 , +S 1 *{tilde over (W)} 2 .  
         [0061]    S 1 {tilde over (W)} 1 -S 2 *{tilde over (W)} 2  is then input to complex multiplier  712   a  to generate {S 1 {tilde over (W)} 1 -S 2 *{tilde over (W)} 2 }e jφ1  and S 2 {tilde over (W)} 1 +S 1 *{tilde over (W)} 2  is input to complex multiplier  712   b  to generate {S 2 {tilde over (W)} 1 +S 1 *{tilde over (W)} 2 }e jφ2 . S 1 {tilde over (W)} 1 -S 2 *{tilde over (W)} 2  is then input to RF transmitter  714   a  for transmission on Ant. 1, {S 1 {tilde over (W)} 1 -S 2 *{tilde over (W)} 2 }e jφ1  is input to RF transmitter  714   b  for transmission on Ant. 2, S 2 {tilde over (W)} 1 +S 1 *{tilde over (W)} 2  is input to RF transmitter  714   c  for transmission on Ant. 3., and {S 2 {tilde over (W)} 1 +S 1 *{tilde over (W)} 2 }e j 2  is input to RF transmitter  714   d  for transmission on Ant. 4.  
         [0062]    Referring now to FIG. 9, therein is shown a block diagram of portions of an embodiment of a receiver  900  for use with transmitter  700  of FIG. 7. Transmitter  700  comprises input  912 , Walsh function blocks  902   b  and  902   d , Walsh multipliers  902   a  and  902   c , channel multipliers  904   a - 904   d , complex adders  906   a  and  906   b , multiplexer (Mux)  908 , and output  910 . A received input signal is received at input  912 , is processed by the STS demodulator. The pilot channel transmission and channels estimation procedures can be same as explained in STTD case. The channel estimates  904   c  and  904   b  can be same as  412   a ,  412   b  from FIG. 4 for non-hopping common pilot channel case. For the case of hopping common pilots or dedicated pilot transmission the channel estimates can be obtained from channel estimation block  504  from FIG. 5. These channel estimates are input to the STS demodulator in FIG. 9 as h1 and h2. h1 corresponds to combined channel estimate from Ant. 1, Ant. 2 and h2 corresponds to channel estimate from Ant. 3, Ant 4. After STS demodulation using  902   a,b,c,d  and  904   a,b,c,d , and  906   a,b  the output from  908  is the STS demodulated signal to be sent to rake combiner, deinterleaver, and channel decoder block  512  from FIG. 5.  
         [0063]    The proposed invention can also be implemented in an orthogonal transmit diversity (OTD) embodiment of the invention. Referring now to FIG. 8, therein is a block diagram of portions of an OTD transmitter  800  according to an embodiment of the invention. Transmitter  800  comprises input  822 , channel coder  820 , symbol repetition blocks  802   a - 802   d , Walsh function blocks  804   a  and  804   b , Walsh multipliers  806   a - 806   d , complex adders  808   a - 808   b , complex multipliers  810   a  and  810   b , RF transmitters  812   a - 812   d . Transmitter is an orthogonal transmit diversity (OTD) embodiment of transmitter  150  of FIG. 1 a  in which the space time block processor performs the transform in the Walsh code domain. The OTD block code matrix used may be represented as:  
                 [           S1          W   ~     1                 S2          W   ~     2             ]                   where                     W   ~     1       =         [       W   1                     W   1       ]                       W   ~     2       =     [       W   1                -     W   1       ]               (   4   )                               
 
         [0064]    As is done for the embodiment of FIG. 1 a , each row of the matrix and its phase shifted version are each transmitted on separate antennas Ant. 1-Ant. 4. Data symbols are input to transmitter  800  at input  822  of channel coder  820 . Channel coder  820  codes, punctures, interleaves, and formats the input data symbols and outputs every other coder output symbol S 1  as even data and every other coder output symbol S 2  as odd data. The even data is then processed through symbol repetition blocks  802   a  and  802   b , Walsh function block  804   a , Walsh multipliers  806   a  and  806   b , and complex adder  808   a . The odd data is processed through symbol repetition blocks  802   c  and  802   d , Walsh function block  804   b , Walsh multipliers  806   c  and  806   d , and complex adder  808   b . The result at the output of complex adder  808   a  is S 1 {tilde over (W)} 1  and the result at the output of complex adder  808   b  is S 2 {tilde over (W)} 2 . S 1 W{tilde over (W)} 1  is then input to complex multiplier  818   a  to generate {S 1 {tilde over (W)} 1 }e jΦ1  and S 2 {tilde over (W)} 2  is input to complex multiplier  818   b  to generate {S 2 {tilde over (W)} 2 }e jφ2 . S 1 {tilde over (W)} 1  is then input to RF transmitter  812   a  for transmission on Ant. 1, {S 1 {tilde over (W)} 1 }e jφ1  is input to RF transmitter  812   b  for transmission on Ant. 2, S 2 {tilde over (W)} 2  is input to RF transmitter  812   c  for transmission on Ant. 3, and {S 2 {tilde over (W)} 2 }e jφ2  is input to RF transmitter  812   d  for transmission on Ant. 4.  
         [0065]    Referring now to FIG. 10, therein is shown a block diagram of portions of an embodiment of a receiver  1000  for use with transmitter  800  of FIG. 8. Transmitter  800  comprises input  1010 , Walsh function blocks  1002   a  and  1002   b , Walsh multipliers  1010   a  and  1010   b , multipliers  1004   a  and  1004   b , multiplexers  1006  and output  1008 . A received input signal is received at input  912  is demodulated using a OTD demodulator  1000  using the knowledge of channel coefficients h1* and h2*. The channel coefficients h1 and h2 for this OTD block are derived in the same as explained in FIG. 4 and FIG. 5. The OTD demodulator  1000  is implemented using  1010 ,  1010   a,b  and  1012   a,b  and  1004   a,b  and  1006 . The OTD demodulated output  1008  is sent to rake combiner, deinterleaver, and channel decoder block  512  from FIG. 5.  
         [0066]    The embodiment of FIG. 1 may also be implemented in a TDMA transmitter for operation in an EDGE system. Referring now to FIG. 11, therein is a block diagram of portions of a long ST block code transmitter according to an embodiment of the invention. Transmitter  1100  comprises input  1118 , 1120 , symbol stream processing branch inputs  1116   a - 111   6   d , time reversal blocks  1102  and  1104 , complex conjugate blocks  1106   a  and  1106   b , multiplier  1108 , phase multiplier  1110   a  and  1110   b , phase multiplier control blocks  1112   a  and  1112   b , and antennas Ant. 1, Ant. 2, Ant. 3, and Ant. 4. Channel coder  1120  codes, punctures, interleaves, and formats a symbol stream received at input  1118 . Channel coder  1120  also splits the input symbol stream into odd and even data streams. The even data stream is input to branch input  1116   a  and RF transmitter  1122   a  for transmission on Ant. 1 during the first half of a data burst and the odd data stream is input to branch input  1116   c  and RF transmitter  1112   c  for transmission on Ant. 2 during the first half of the data burst. During the second half of a burst, the even data stream is input to branch input  116   b , time received on time reversal block  1102 , complex conjugated in complex conjugate block  1106   a  and sent to RF transmitter  1122   c  for transmission on Ant. 3. The odd data stream is input to branch input  11   16   d , time reversed in time reversal block  1104 , complex conjugated in complex conjugate block  1106   b , multiplied by a negative in multiplier  1108  and sent to RF transmitter  1122   d  for transmission on Ant. 4 during the second half of the data burst. A training sequence SEQ 1  is embedded in the middle of the burst transmit on Ant. 1 and a training sequence SEQ 2  is embedded in the middle of burst transmit on Ant. 2. Phase multipliers  1112   a  and  1112   b , phase shifts the inputs to RF transmitters  1122   b  and  1122   d , using the multiplication blocks  1110   a  and  1110   b  respectively. The output of phase multiplier  1112   a  is then input to RF transmitter  1122   b  for transmission on Ant. 2 and the output of phase multiplier  111   2   b  is input to RF transmitter  1122   d  for transmission on Ant. 4. The RF transmitters may perform of baseband pulse shaping, modulation, and carrier up conversion. In some implementations one may choose to apply the phase multiplication after baseband pulse shaping and modulation steps.  
         [0067]    The phase rotation applied in phase multipliers  1122   a  and  1122   b  is kept constant during the burst length, with the phase being changed on a burst by burst basis. The phase can be chosen periodically or randomly from a MPSK constellation as explained previously. In a preferred embodiment the phase rotation on the Ant. 4 is kept same as phase rotation on ant2 with a 180 degree shift or multiplied by −1. The phase multiplication may be done before or after the base band pulse shaping. In an alternative embodiment of FIG. 11 the transmission on Ant. 1 and Ant. 3 may be intercharged.  
         [0068]    The transmitter shown FIG. 3 can also be applied to EDGE with some modification. The space-time code described in  316  is applied blockwise instead of symbol wise for an EDGE application. The block length can be chosen as first half of the burst. In EDGE the length of the first half and second half of the bursts are equal to 58 symbols. In this case S 1  and S 2  denotes a block of symbols and ( )* denotes time reversal of a block of symbols and complex conjugation operation. S 1 * denotes the block of symbols S 1  is time reversed and complex conjugated. −S 2 * denotes that the block of symbols S 2  is time reversed, complex conjugated and multiplied by −1.0. The pilot sequences U 1  and U 2  can be chosen as two training sequences such as well-known CAZAC sequences. The spreading codes  308   a,b,c,d  will not be applied in EDGE. The phase multiplication blocks  306   a  and  306   b  are retained.  
         [0069]    A receiver designed for a 2-antenna space time block code may be used as a receiver for the embodiments of FIG. 1 or FIG. 2.  
         [0070]    From the preceding description and embodiments, one skilled in the art will realize that, although the method and apparatus of the present invention has illustrated and described with regard to particular embodiments thereof, it will be understood that numerous modifications and substitutions may be made to the embodiments described, and that numerous other embodiments of the invention may be implemented without departing from spirit and scope of the invention as defined in the following claims.