Abstract:
Disclosed is a common transmitter architecture having incorporated both open loop transmit diversity schemes using a plurality of binary switches. Employment of binary switches allows for the sharing of certain components whether the transmitter is utilizing a orthogonal transmit diversity (OTD) scheme or a space time spreading (STS) scheme. Accordingly, the number of components in the transmitter is minimized and the complexity of the transmitter is simple enough to be implemented into a single application specific integrated chip.

Description:
RELATED APPLICATION 
     Related subject matter is disclosed in the following application and assigned to the same assignee hereof: U.S. patent application Ser. No. 09/294,661 entitled, “Method And Apparatus For Downlink Diversity In CDMA Using Walsh Codes,” inventors R. Michael Buehrer, Robert Atmaram Soni, and Jiann-an Tsai, filed on Apr. 19, 1999. Related subject matter is disclosed in the following concurrently filed application and assigned to the same assignee hereof: U.S. patent application Ser. No. 09/395,325 entitled, “A Receiver Architecture Employing Space Time Spreading And Orthogonal Transmit Diversity Techniques,” inventors R. Michael Buehrer, Robert Atmaram Soni and Stephen A. Allpress. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to wireless communication systems and, in particular, to wireless communication employing transmit diversity. 
     BACKGROUND OF THE RELATED ART 
     Several third generation wireless communication systems are being developed. One such third generation wireless communication system is known as CDMA 2000. In CDMA 2000, a variety of techniques are being incorporated for improving call quality. Open loop transmit diversity is one such technique in which user signals are transmitted using two antennas. In a first phase of CDMA 2000, open loop transmit diversity is currently being implemented in a form of orthogonal transmit diversity (OTD). In OTD, separate antennas are used to transmit even data bits and odd data bits to achieve transmit diversity and improved call quality. 
     In a second phase of CDMA 2000, open loop transmit diversity may be implemented in a form of space time spreading (STS) using Walsh functions or codes. STS enhances call quality by providing variable gain over OTD depending on the coding rate being used. Specifically, in STS, odd data bits and even data bits are jointly, not separately, transmitted over two antennas. However, the manner in which the odd and even data bits are modulated/processed before being transmitted over one antenna will be different from the manner in which the odd and even data bits are modulated/processed being transmitted over the other antenna. 
     There has been some concern that including both open loop transmit diversity schemes as options in CDMA 2000 would be very complex in terms of implementing them into a common transmitter architecture. Accordingly, there exists a need for a simple way to implement common transmitter architecture that has incorporated orthogonal transmit diversity and space time spreading schemes. 
     SUMMARY OF THE INVENTION 
     The present invention is a common transmitter architecture having incorporated both open loop transmit diversity schemes using a plurality of binary switches. Employment of binary switches allows for the sharing of certain components whether the transmitter is utilizing a orthogonal transmit diversity (OTD) scheme or a space time spreading (STS) scheme. Accordingly, the number of components in the transmitter is minimized and the complexity of the transmitter is simple enough to be implemented into a single application specific integrated chip. 
     The transmitter has an OTD and a STS mode, and comprises a first and second antenna system. The first antenna system comprises time multiplexers, mixers, switches and adders. The time multiplexers are used to time multiplex an in-phase first signal with a second in-phase first signal to produce a first time multiplexed signal; a quadrature phase first signal with a second quadrature phase first signal to produce a second time multiplexed signal; an in-phase second signal with an inverted in-phase second signal to produce a third time multiplexed signal; and a quadrature phase second signal with an inverted quadrature phase second signal to produce a fourth time multiplexed signal. The mixers are used to mix outputs of the time multiplexers with a Walsh function to produce first, second, third and fourth mixed time multiplexed signals. The first and second time multiplexed signals are directed to the adders. If the transmitter is in STS mode, the switches direct the third and fourth mixed time multiplexed signals to the adders so they may be added with the first and second mixed time multiplexed signals, respectively. If the transmitter is in OTD mode, the switches do not direct the third and fourth mixed time multiplexed signals to the adders. 
     The second antenna system comprises time multiplexers, mixers, switches and adders. The time multiplexers are used to time multiplex an in-phase second signal with an inverted in-phase second signal when the transmitter is in the first operating mode and with an in-phase second signal when the transmitter is in the second operating mode to produce a fifth time multiplexed signal; a quadrature phase second signal with an inverted quadrature phase second signal when the transmitter is in the first operating mode and with a quadrature phase second signal when the transmitter is in the second operating mode to produce a sixth time multiplexed signal; an in-phase first signal with an inverted in-phase first signal to produce a seventh time multiplexed signal; and a quadrature phase first signal with an inverted quadrature phase first signal to produce an eighth time multiplexed signal. The mixers are used to mix outputs of the time multiplexers with a Walsh function to produce fifth, sixth, seventh and eighth mixed time multiplexed signals. The fifth and sixth time multiplexed signals are directed to the adders. If the transmitter is in STS mode, the switches direct the seventh and eighth mixed time multiplexed signals to the adders so they may be added with the fifth and sixth mixed time multiplexed signals, respectively. If the transmitter is in OTD mode, the switches do not direct the seventh and eighth mixed time multiplexed signals to the adders. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
     FIG. 1 depicts a transmitter employing orthogonal transmit diversity and space time spreading using Walsh functions in accordance with the present invention; and 
     FIG. 2 depicts one finger of a receiver employing orthogonal transmit diversity and space time spreading using Walsh functions in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 depicts a common transmitter architecture  10  in accordance with the present invention. Transmitter  10  is typically incorporated at a base station, and is operable to modulate/process user signals employing either orthogonal transmit diversity or space time spreading (using Walsh or some other orthogonal function) techniques. Transmitter  10  comprises of a first antenna system  11  and a second antenna system  28 . For ease of discussion, the present invention will be described herein with respect to one user signal. It should be understood, however, that the present invention can be applied to multiple user signals. 
     Transmitter  10  receives a user signal Y. Before user signal is modulated/processed by first and/or second antenna systems  11  and  28 , user signal Y is parsed and partitioned into even and odd data bits and then into in-phase and quadrature phase signals, i.e. signal Y is converted into signals Y I1 , Y Q1 , Y I2 , and Y Q2 , wherein I represents an in-phase signal, Q represents a quadrature phase signal, 1 represents even data bits and 2 represents odd data bits. Signals Y I1 , Y Q1 , Y I2 , and Y Q2  are provided as inputs to first and second antenna systems  11  and  28 . 
     First antenna system  11  comprises time multiplexers  12 , inverters  14 , switches  16  and  26 , amplifiers  18  and  20 , mixers  22  and adders  24 . Switches  16  and  26  have a first position and second position. When switches  16  and  26  are all in the first position, first antenna system  11  operates in orthogonal transmit diversity mode. By contrast, when switches  16  and  26  are all in the second position, first antenna system  11  operates in space time spreading mode. 
     User signal Y I1  is provided twice as input to time multiplexer  12 - 1 . The output of time multiplexer  12 - 1  is a time multiplexed signal of signal Y I1  with itself. When switch  16 - 1  is in the first position, i.e., OTD mode, the output of time multiplexer  12 - 1  is directed to amplifier  18 - 1  where it is amplified a gain G by amplifier  18 - 1 . When switch  16 - 1  is in the second position, i.e., STS mode, the output of time multiplexer  12 - 1  is directed to amplifier  20 - 1  where it is amplified a gain        G     2                            
     by amplifier  20 - 1 . 
     The outputs of amplifier  18 - 1  and amplifier  20 - 1  are mixed at mixer  22 - 1  with a Walsh function W 1 , and then provided as input to adder  24 - 1 . Note that mixer  22 - 1  should only receive an input from either amplifier  18 - 1  or  20 - 1  at any one time, and that some other orthogonal (or quasi-orthogonal) function may be used to mix the output of amplifier  18 - 1  and  20 - 1  instead of Walsh functions. If first antenna system  11  is in STS mode, i.e., switches  16  and  26  are all in the second position, the output of mixer  22 - 1  is added to an output of mixer  22 - 3  by adder  24 - 1  before being transmitted. By contrast, if first antenna system  11  is in OTD mode, i.e., switches  16  and  26  are all in the first position, the output of mixer  22 - 1  is not added to the output of mixer  22 - 3  by adder  24 - 1  before being transmitted. 
     User signal Y QI  is processed in a similar manner as user signal Y I1  using time multiplexer  12 - 2 , switch  16 - 2 , amplifiers  18 - 2  and  20 - 2 , mixer  22 - 2 , adder  24 - 2  and Walsh function W 1 . 
     User signal Y I2  is provided as input to time multiplexer  12 - 3  along with an inverted signal of Y I2  (i.e. output of inverter  14 - 1 ). The output of the time multiplexer  12 - 3  is then provided as input to amplifier  20 - 3 , where it is amplified a gain          G     2       .                          
     The output of amplifier  20 - 3  is mixed with a Walsh function W 2  by mixer  22 - 3 . When switch  26 - 1  is in the second position, the output of mixer  22 - 3  is provided as input to adder  24 - 1  where it can be added to the output of mixer  22 - 1 . By contrast, when switch  26 - 1  is in the first position, the output of mixer  22 - 3  is not provided as input to adder  24 - 1 . 
     Note that the amplifiers used by first antenna system  11  has a gain of        G     2                            
     when it is in STS mode and a gain of G when it is in OTD mode. Such configuration allows for a same output power by first antenna system  11  regardless of the mode. But it should be understood that any configuration of amplifiers and gains may be used. Further note that when first antenna system  11  is in OTD mode, it transmits only even data bits. By contrast, when first antenna system  11  is in STS mode, it transmits both even and odd data bits. 
     User signal Y Q2  is processed in a similar manner as signal Y I2  using time multiplexer  12 - 4 , inverter  14 - 2 , amplifier  20 - 4 , mixer  22 - 4 , switch  26 - 2 , adder  24 - 2  and Walsh function W 2 . 
     Second antenna system  28  comprises switches  29 ,  33  and  40 , inverters  30 , time multiplexers  32 , amplifiers  34  and  36 , mixers  38  and adders  42 . Switches  29 ,  33  and  40  have a first and second position. When switches  29 ,  33  and  40  are in the first position, second antenna system  28  operates in OTD mode. By contrast, when switches  29 ,  33 , and  40  are in the second position, second antenna system  28  operates in STS mode. 
     When switch  29 - 1  is in the first position, user signal Y I2  is provided as input to time multiplexer  32 - 1  along with an inverted user signal Y I2  (i.e., output of inverter  30 - 1 ). When switch  29 - 1  is in the second position, user signal Y I2  is provided twice as input to time multiplexer  32 - 1 . In time multiplexer  32 - 1 , user signal Y I2  is time multiplexed with itself or its inverted self depending on the position of switch  29 - 1  (or mode of second antenna system  28 ). 
     When switch  33 - 1  is in the first position, the output of time multiplexer  32 - 1  is directed to amplifier  34 - 1 , where the time multiplexed signal is amplified a gain G by amplifier  34 - 1 . When switch  33 - 1  is in the second position, the output of time multiplexer  32 - 1  is directed to amplifier  36 - 1 , where the time multiplexed signal is amplified a gain        G     2                            
     by amplifier  36 - 1 . 
     The outputs of amplifiers  34 - 1  and  36 - 1  are provided as input to mixer  38 - 1 , where they are mixed with Walsh functions W 3 . Note that mixer  38 - 1  should only receive an input from either amplifier  34 - 1  or  36 - 1  at any one time, not both simultaneously. If second antenna system  28  is in STS mode, i.e., switches  29 ,  33  and  40  are all in the second position, the output of mixer  38 - 1  is added to an output of mixer  38 - 3  by adder  42 - 1  before being transmitted. By contrast, if second antenna system  28  is in OTD mode, i.e., switches  29 ,  33  and  40  are all in the first position, the output of mixer  38 - 1  is not added to the output of mixer  38 - 3  by adder  42 - 1  before being transmitted. 
     User signal Y Q2  is processed in a similar manner to user signal Y I2  using switches  29 - 2 ,  33 - 2  and  40 - 2 , inverter  30 - 2 , time multiplexer  32 - 2 , amplifiers  34 - 2  and  36 - 2 , mixer  38 - 2 , adder  42 - 2  and Walsh function W 3 . 
     User signal Y I1  is provided as input to time multiplexer  32 - 3  along with an inverted user signal Y I2 . In time multiplexer  32 - 3 , user signal Y I1  is time multiplexed with its inverted self. The output of time multiplexer  32 - 3  is amplified a gain        G     2                            
     by amplifier  36 - 3 . 
     The output of amplifier  36 - 3  is mixed in mixer  38 - 3  with Walsh function W 4 . When switch  40 - 1  is in the second position, the output of mixer  38 - 3  is provided as input to adder  42 - 1  where it is added to the output of mixer  38 - 1 . When switch  40 - 1  is in the first position, the output of mixer  38 - 3  is not provided as input to adder  42 - 1 . 
     User signal Y QI  is processed in a similar manner to user signal Y I1  using inverter  30 - 4 , time multiplexer  32 - 4 , amplifier  36 - 4 , mixer  38 - 4 , switch  40 - 2  and adder  42 - 2 . 
     Note that, like the amplifiers of first antenna system  11 , the amplifiers of second antenna system  28  has a gain of        G     2                            
     when it is in STS mode and a gain of G when it is in OTD mode. Such configuration allows for a same output power by second antenna system  11  regardless of the mode. But it should be understood that any configuration of amplifiers and gains may be used. Further note that when second antenna system  28  is in OTD mode, it transmits only odd data bits. By contrast, when second antenna system  28  is in STS mode, it transmits both even and odd data bits. 
     In a preferred embodiment, Walsh functions W 1 , W 2 , W 3  and W 4  are identical. Note that for ease of discussion, a common receiver architecture is disclosed herein that assumes that Walsh functions W 1 , W 2 , W 3  and W 4  are identical. It should be understood that the different Walsh functions W 1 , W 2 , W 3  and W 4  or combinations thereof may also be used, and that the common receiver architecture disclosed herein could be adapted for different Walsh functions W 1 , W 2 , W 3  and W 4  or combinations thereof. 
     Opposite of transmitter  10  is a receiver (typically incorporated at a mobile-station) for receiving and demodulating/processing the signals transmitted by transmitter  10 . FIG. 2 depicts one finger  50  of a common receiver architecture in accordance with the present invention. Finger  50  being operable to demodulate/process received signals (transmitted by transmitter  10  or equivalent) employing either orthogonal transmit diversity or space time spreading (using Walsh or some other orthogonal function) techniques. Finger  50  comprises mixers  52 ,  54 ,  56 ,  58 ,  60  and  62 , adders  64 ,  66 ,  68  and  70 , time multiplexer  72 , inverters  59 ,  61  and  63 , integrators  53  and  55  and switches  74 ,  76  and  78 . Switches  74 ,  76  and  78  have a first and a second position. When switches  74 ,  76  and  78  are all in the first position, finger  50  operates in OTD mode. By contrast, when switches  74 ,  76  and  78  are all in the second position, finger  50  operates in STS mode. 
     When finger  50  receives a signal r(t), received signal r(t) is provided as inputs to mixers  52  and  54 . In mixer  52 , received signal r(t) is mixed with an extended Walsh function w(t), i.e., repeated Walsh function w(t). The output of mixer  52  is provided as input to integrator  53 . In mixer  54 , received signal r(t) is mixed with a function {overscore (w)}(t), which is a complement of the extended Walsh function w(t). The output of mixer  54  is provided as input to integrator  55 . Recall that for ease of discussion, it is assumed that Walsh functions W 1 , W 2 , W 3  and W 4  are identical at transmitter  10 . Accordingly, Walsh function w(t) is identical to Walsh functions W 1 , W 2 , W 3  and W 4 . 
     In integrators  53  and  55 , the outputs of mixers  52  and  54  are integrated over the length of the Walsh functions w(t) or {overscore (w)}(t) (or symbol rate) and then dumped. Note that the mixers  52  and  54  mixes at a chip rate. The output of integrator  53  is provided as inputs to mixers  56  and  62 . The output of integrator  55  is provided as input to mixer  58 , and a conjugate of the output of mixer  54  is provided as input to mixer  60 , wherein the conjugate of the output of mixer  54  is obtained by inverting a quadrature stream of the output of mixer  54  using inverter  61 . 
     In mixer  56 , the output of mixer  52  is mixed with a signal ĥ 1 * representing a conjugate of a channel estimate for first antenna system  11 . In mixer  62 , the output of mixer  52  is mixed with a signal ĥ 2 * representing a conjugate of a channel estimate for second antenna system  28 . In mixer  58 , the output of mixer  54  is mixed with the signal ĥ 2 *. In mixer  60 , the conjugate of the output of mixer  54  is mixed with a signal ĥ 1  representing a channel estimate for first antenna system  11 . Note that, in one embodiment, the channel estimates for first and second antenna systems  11  and  28  are obtained using pilot signals transmitted from first and second antenna systems  11  and  28 , respectively. 
     The output of mixer  56  is provided as input to adder  64 . When switch  74  is in the second position, a conjugate of the output of mixer  58  is also provided as input to adder  64  where the conjugate of the output of mixers  58  and the output of mixer  56  are added together. Note that the conjugate of the output of mixer  58  is obtained by inverting a quadrature stream of the output of mixer  58  using inverter  59 . The output of adder  64  is provided as input to adder  68 , where it is added with outputs of same relative mixers from other fingers. 
     When switch  74  is in the first position, the output of mixer  58  is provided as input to adder  66 . When switches  76  and  78  are in the second position, an inverted output of mixer  60  (via inverter  63 ) and the output of mixer  62  are provided as inputs to adder  66 . When switches  76  and  78  are in the first position, the inverted output of mixer  60  and the output of mixers  62  are not provided as inputs to adder  66 . Note that the output mixer  58  should not be provided as input to adder  66  at the same time as the inverted output of mixer  60  and output of mixer  62 . The output of adder  66  is provided as input to adder  70 , where it is added with outputs of same relative mixers from other fingers. 
     The outputs of adders  68  and  70  are time multiplexed with each other by time multiplexer  72  and directed to a decoder, not shown. Note that in either mode, output of mixer  64  corresponds to a received version of the even data bits and the output of mixer  66  corresponds to a received version of the odd data bits. 
     The present invention is described herein with reference to certain embodiments, such as wireless communication systems based on third generation code division multiple access techniques. It should be understood that the present invention may be applicable to wireless communications based on other multiple access techniques. Additionally, instead of even and odd data bits for a same user signal, the present invention may be applied to even and odd data bits for different user signals or some other combinations. The present invention may also be applied to two identical non-partitioned (into odd and even data bits) user signals. Accordingly, the present invention should not be limited to the embodiments disclosed herein.