Abstract:
A method of communicating data to a receiving antenna from N transmitting antennas, where N is an integer, includes the steps of determining whether a legacy transmission mode has been selected, producing N data streams from outbound data, and applying the N data streams to a space/time encoder to produce N encoded signals. When the legacy transmission mode has not been selected, the N encoded signals are transmitting from N transmitting antennas and when the legacy transmission mode has been selected, the one encoded signal is transmitted from one of the N transmitting antennas. The legacy transmission mode allows receivers to receive and process transmitted signals when the receivers are only configured to receive the transmitted signals from a single transmitting antenna.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority of U.S. Provisional Patent Application Ser. No. 60/581,122, filed on Jun. 18, 2004. The subject matter of this earlier filed application is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Technical Field of the Invention  
         [0003]     This invention relates generally to wireless communication systems and more particularly to a transmitter transmitting at high data rates with such wireless communication systems.  
         [0004]     2. Description of Related Art  
         [0005]     Communication systems support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, BLUETOOTH™, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.  
         [0006]     For each wireless communication device to participate in wireless communications, it may include a built-in radio transceiver (i.e., receiver and transmitter) or may be coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). The transmitter may include a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.  
         [0007]     The transmitter may include a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage can convert raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.  
         [0008]     The transmitter includes at least one antenna for transmitting the RF signals, which are received by a single antenna, or multiple antennas, of a receiver. When the receiver includes two or more antennas, the receiver will select one of them to receive the incoming RF signals. In this instance, the wireless communication between the transmitter and receiver is a single-output-single-input (SOSI) communication, even if the receiver includes multiple antennas that are used as diversity antennas (i.e., selecting one of them to receive the incoming RF signals). For SISO wireless communications, a transceiver includes one transmitter and one receiver.  
         [0009]     Other types of wireless communications include single-input-multiple-output (SIMO), multiple-input-single-output (MISO), and multiple-input-multiple-output (MIMO). In a SIMO wireless communication, a single transmitter processes data into radio frequency signals that are transmitted to a receiver. The receiver includes two or more antennas and two or more receiver paths. Each of the antennas receives the RF signals and provides them to a corresponding receiver path (e.g., LNA, down conversion module, filters, and ADCs). Each of the receiver paths processes the received RF signals to produce digital signals, which are combined and then processed to recapture the transmitted data.  
         [0010]     For a multiple-input-single-output (MISO) wireless communication, the transmitter includes two or more transmission paths (e.g., digital to analog converter, filters, up-conversion module, and a power amplifier) that each converts a corresponding portion of baseband signals into RF signals, which are transmitted via corresponding antennas to a receiver. The receiver includes a single receiver path that receives the multiple RF signals from the transmitter. In this instance, the receiver uses beam forming to combine the multiple RF signals into one signal for processing.  
         [0011]     For a multiple-input-multiple-output (MIMO) wireless communication, the transmitter and receiver each include multiple paths. In such a communication, the transmitter parallel processes data using a spatial and time encoding function to produce two or more streams of data. The transmitter includes multiple transmission paths to convert each stream of data into multiple RF signals. The receiver receives the multiple RF signals via multiple receiver paths that recapture the streams of data utilizing a spatial and time decoding function. The recaptured streams of data are combined and subsequently processed to recover the original data.  
         [0012]     In addition, current wireless local area network standards also need to be considered. With respect to IEEE 802.11a, such communication can operate at 5 GHz frequency bands, which can achieve up to 54 Mbps based on Orthogonal Frequency Division Multiplexing (OFDM). With respect to IEEE 802.11b, such communication can operate at 2.4 GHz, which can achieve up to 11 Mbps based on DSSS-CCK (Direct Sequence Spread Spectrum—Complementary Code Keying). Both types of wireless communication been widely used. In order to achieve the higher data rates at 2.4 GHz, IEEE 802.11g was approved in 2003 by adopting OFDM to achieve 54 Mbps. For coexistence with existing 802.11b system in 2.4 GHz bands, 802.11g was designed to have backward compatibility. Such systems are all SISO systems.  
         [0013]     Giving consideration to more reliable and faster data transmission systems, MIMO may be applied in IEEE 802.11n. Among many other techniques considered, STBC is one of popular choices to enhance the transmission coverage. However, due to the unique design of STBC over pairs of transmit antennas, the MIMO may be bulky to utilize STBC MIMO design to enhance the coverage, as well as SISO design for existing IEEE 802.11a/b/g. In order to have additional data paths, there may be additional costs to including both legacy and STBC implementations. Therefore, there is a need for simpler approaches that allow for backward compatibility and simplicity of design.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     According to one embodiment of the present invention, A method of communicating data to a receiving antenna from N transmitting antennas, where N is an integer, includes the steps of determining whether a legacy transmission mode has been selected, producing N data streams from outbound data, and applying the N data streams to a space/time encoder to produce N encoded signals. When the legacy transmission mode has not been selected, the N encoded signals are transmitting from N transmitting antennas and when the legacy transmission mode has been selected, the one encoded signal is transmitted from one of the N transmitting antennas. The legacy transmission mode allows receivers to receive and process transmitted signals when the receivers are only configured to receive the transmitted signals from a single transmitting antenna.  
         [0015]     Also, when the legacy transmission mode has not been selected, the step of applying the N data streams to the space/time encoder includes producing at least one conjugate encoded signal or adding a Long Training Sequence immediately before data in a frame. Additionally, the step of adding a Long Training Sequence may be performed such that a receiver processor will process the frame in a Space/Time Block Coding mode. Also, when the legacy transmission mode has not been selected, the step of applying the N data streams to the space/time encoder may include encoding the two data streams so that channel estimates can be performed by the receivers according to:  
           [             h   ~     1                 h   ~     2           ]     =         C   *     ×     [           r   ⁡     (     t   0     )                 r   ⁡     (     t   1     )             ]       =         [             ∑     i   =   1     2     ⁢            c   ⁡     (     t   i     )            2           0           0           ∑     i   =   1     2     ⁢            c   ⁡     (     t   i     )            2             ]     ×     [           h   1               h   2           ]       +     [             n   ~     1                 n   ~     2           ]           ,       where   ⁢     
     [           r   ⁡     (     t   0     )                 r   ⁡     (     t   1     )             ]     =           [           c   ⁡     (     t   0     )             -       c   *     ⁡     (     t   1     )                   c   ⁡     (     t   1     )               c   *     ⁡     (     t   0     )             ]     ⁡     [           h   1               h   2           ]       +     [           n   1               n   2           ]       =       C   ×     [           h   1               h   2           ]       +     [           n   1               n   2           ]               
        where where r i (t) and c i (t) are the received and transmitted signals, respectively, n i  represent noise terms and h i  represents relationships between signals sent from the two transmitting antennas to the receiving antenna.        
 
         [0017]     Additionally, when the legacy transmission mode has been selected, the receivers which are capable of processing a data frame in a Space/Time Block Coding mode bypass the Space/Time Block Coding mode. Also, the receivers that are only configured to receive the transmitted signals from a single transmitting antenna may be receivers that comply with standards of IEEE 802.11. In addition, the step of applying the N data streams to the space/time encoder may include encoding the two data streams so that data can be retrieved by the receivers according to:  
         [             c   ~     ⁡     (     t   0     )                     c   ~     *     ⁡     (     t   1     )             ]     =         H   *     ×     [           r   ⁡     (     t   0     )                   r   *     ⁡     (     t   1     )             ]       =         [             ∑     i   =   1     2     ⁢            h   i          2           0           0           ∑     i   =   1     2     ⁢            h   i          2             ]     ×     [           c   ⁡     (     t   0     )                   c   *     ⁡     (     t   1     )             ]       +       [             n   ~     1                 n   ~     2           ]     .             
 
         [0018]     According to another embodiment, a transmitter for communicating data to a receiving antenna from N transmitting antennas, where N is an integer, includes determining means for determining whether a legacy transmission mode has been selected, producing means for producing N data streams from outbound data, encoding means for space/time encoding the N data streams to produce N encoded signals and N transmitting antenna means for transmitting the N encoded signals or one signal. The N encoded signals are transmitted from N transmitting antenna means when the legacy transmission mode has not been selected, the one encoded signal is transmitted from one of the N transmitting antenna means when the legacy transmission mode has been selected, and the legacy transmission mode allows receivers to receive and process transmitted signals when the receivers are only configured to receive the transmitted signals from a single transmitting antenna.  
         [0019]     According to another embodiment, a transmitter for communicating data to a receiving antenna from N transmitting antennas, where N is an integer, includes a legacy switch indicator, configured to determine whether a legacy transmission mode has been selected, a demultiplexer, configured to produce N data streams from outbound data, a space/time encoder, configured to encode the N data streams to produce N encoded signals and N transmit antennas, configured to transmit the N encoded signals or one signal. The N encoded signals are transmitted from N transmit antennas when the legacy transmission mode has not been selected, one encoded signal is transmitted from one of the N transmit antennas when the legacy transmission mode has been selected, and the legacy transmission mode allows receivers to receive and process transmitted signals when the receivers are only configured to receive the transmitted signals from a single transmitting antenna.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     For the present invention to be easily understood and readily practiced, the present invention will now be described, for purposes of illustration and not limitation, in conjunction with the following figures:  
         [0021]      FIG. 1  is a schematic block diagram of a wireless communication device in accordance with one embodiment of the present invention;  
         [0022]      FIG. 2  illustrates schematic block diagrams of a transmitter and receiver, with  FIG. 2 ( a ) providing a schematic block diagram of an RF transmitter and with  FIG. 2 ( b ) providing a schematic block diagram of an RF receiver, in accordance with embodiments of the present invention;  
         [0023]     FIGS.  3 ( a ) and  3 ( b ) are a schematic block diagram of a transmitter in accordance one embodiment of with the present invention;  
         [0024]     FIGS.  4 ( a ) and  4 ( b ) are a schematic block diagram of a receiver in accordance with one embodiment of the present invention;  
         [0025]      FIG. 5  is a diagram illustrating a Space-Time Block Coding (STBC) method, in accordance with one embodiment of the present invention;  
         [0026]      FIG. 6  is a diagram illustrating another Space-Time Block Coding (STBC) method used in channel estimation and communication of data, in accordance with one embodiment of the present invention;  
         [0027]      FIG. 7  is a diagram of a transmitter configuration, in accordance with one embodiment of the present invention;  
         [0028]      FIG. 8  is another diagram of a transmitter configuration, in accordance with one embodiment of the present invention;  
         [0029]      FIG. 9  provides a diagram of a packet structure for legacy systems, in accordance with one embodiment of the present invention; and  
         [0030]      FIG. 10  provides another diagram of a packet structure for MIMO systems, in accordance with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]      FIG. 1  is a schematic block diagram illustrating a wireless communication device, according to an example of the invention. The device includes a baseband processing module  63 , memory  65 , a plurality of radio frequency (RF) transmitters  67 ,  69 ,  71 , a transmit/receive (T/R) module  73 , a plurality of antennas  81 ,  83 ,  85 , a plurality of RF receivers  75 ,  77 ,  79 , and a local oscillation module  99 . The baseband processing module  63 , in combination with operational instructions stored in memory  65 , execute digital receiver functions and digital transmitter functions, respectively. The digital receiver functions include, but are not limited to, digital intermediate frequency to baseband conversion, demodulation, constellation demapping, decoding, de-interleaving, fast Fourier transform, cyclic prefix removal, space and time decoding, and/or descrambling. The digital transmitter functions include, but are not limited to, scrambling, encoding, interleaving, constellation mapping, modulation, inverse fast Fourier transform, cyclic prefix addition, space and time encoding, and/or digital baseband to IF conversion. The baseband processing module  63  may be implemented using one or more processing devices. Such a processing device may be a microprocessor, micro-controller, digital signal processor, microcomputer, central processing unit, field programmable gate array, programmable logic device, state machine, logic circuitry, analog circuitry, digital circuitry, and/or any device that manipulates signals (analog and/or digital) based on operational instructions. The memory  66  may be a single memory device or a plurality of memory devices. Such a memory device may be a read-only memory, random access memory, volatile memory, non-volatile memory, static memory, dynamic memory, flash memory, and/or any device that stores digital information. Note that when the processing module  63  implements one or more of its functions via a state machine, analog circuitry, digital circuitry, and/or logic circuitry, the memory storing the corresponding operational instructions is embedded with the circuitry comprising the state machine, analog circuitry, digital circuitry, and/or logic circuitry.  
         [0032]     In operation, the baseband processing module  63  receives the outbound data  87  and, based on a mode selection signal  101 , produces one or more outbound symbol streams  89 . The mode selection signal  101  will indicate a particular mode as are indicated in mode selection tables. For example, the mode selection signal  101  may indicate a frequency band of 2.4 GHz, a channel bandwidth of 20 or 22 MHz and a maximum bit rate of 54 megabits-per-second. In this general category, the mode selection signal will further indicate a particular rate ranging from 1 megabit-per-second to 54 megabits-per-second. In addition, the mode selection signal will indicate a particular type of modulation, which includes, but is not limited to, Barker Code Modulation, BPSK, QPSK, CCK, 16 QAM and/or 64 QAM. A code rate is supplied as well as number of coded bits per subcarrier (NBPSC), coded bits per OFDM symbol (NCBPS), data bits per OFDM symbol (NDBPS), error vector magnitude in decibels (EVM), sensitivity which indicates the maximum receive power required to obtain a target packet error rate (e.g., 10% for IEEE 802.11a), adjacent channel rejection (ACR), and an alternate adjacent channel rejection (AACR).  
         [0033]     The mode selection signal may also indicate a particular channelization for the corresponding mode. The mode select signal may further indicate a power spectral density mask value. The mode select signal may alternatively indicate a rate that has a 5 GHz frequency band, 20 MHz channel bandwidth and a maximum bit rate of 54 megabits-per-second. As a further alternative, the mode select signal  101  may indicate a 2.4 GHz frequency band, 20 MHz channels and a maximum bit rate of 192 megabits-per-second. A number of antennas may be utilized to achieve the higher bandwidths. In this instance, the mode select would further indicate the number of antennas to be utilized. Another mode option may be utilized where the frequency band is 2.4 GHz, the channel bandwidth is 20 MHz and the maximum bit rate is 192 megabits-per-second. Various bit rates ranging from 12 megabits-per-second to 216 megabits-per-second utilizing 2-4 antennas and a spatial time encoding rate may be employed. The mode select signal  101  may further indicate a particular operating mode, which corresponds to a 5 GHz frequency band having 40 MHz frequency band having 40 MHz channels and a maximum bit rate of 486 megabits-per-second. The bit rate may range, in this example, from 13.5 megabits-per-second to 486 megabits-per-second utilizing 1-4 antennas and a corresponding spatial time code rate.  
         [0034]     The baseband processing module  63 , based on the mode selection signal  101  produces the one or more outbound symbol streams  89  from the output data  88 . For example, if the mode selection signal  101  indicates that a single transmit antenna is being utilized for the particular mode that has been selected, the baseband processing module  63  will produce a single outbound symbol stream  89 . Alternatively, if the mode select signal indicates 2, 3 or 4 antennas, the baseband processing module  63  will produce 2, 3 or 4 outbound symbol streams  89  corresponding to the number of antennas from the output data  88 .  
         [0035]     Depending on the number of outbound streams  89  produced by the baseband module  63 , a corresponding number of the RF transmitters  67 ,  69 ,  71  can be enabled to convert the outbound symbol streams  89  into outbound RF signals  91 . The implementation of the RF transmitters  67 ,  69 ,  71  will be further described with reference to  FIG. 2 . The transmit/receive module  73  receives the outbound RF signals  91  and provides each outbound RF signal to a corresponding antenna  81 ,  83 ,  85 .  
         [0036]     When the radio  60  is in the receive mode, the transmit/receive module  73  receives one or more inbound RF signals via the antennas  81 ,  83 ,  85 . The T/R module  73  provides the inbound RF signals  93  to one or more RF receivers  75 ,  77 ,  79 . The RF receiver  75 ,  77 ,  79 , which will be described in greater detail with reference to  FIG. 4 , converts the inbound RF signals  93  into a corresponding number of inbound symbol streams  96 . The number of inbound symbol streams  95  will correspond to the particular mode in which the data was received. The baseband processing module  63  receives the inbound symbol streams  89  and converts them into inbound data  97 .  
         [0037]     As one of average skill in the art will appreciate, the wireless communication device of  FIG. 1  may be implemented using one or more integrated circuits. For example, the device may be implemented on one integrated circuit, the baseband processing module  63  and memory  65  may be implemented on a second integrated circuit, and the remaining components, less the antennas  81 ,  83 ,  85 , may be implemented on a third integrated circuit. As an alternate example, the device may be implemented on a single integrated circuit.  
         [0038]      FIG. 2 ( a ) is a schematic block diagram of an embodiment of an RF transmitter  67 ,  69 ,  71 . The RF transmitter may include a digital filter and up-sampling module  475 , a digital-to-analog conversion module  477 , an analog filter  479 , and up-conversion module  81 , a power amplifier  483  and a RF filter  485 . The digital filter and up-sampling module  475  receives one of the outbound symbol streams  89  and digitally filters it and then up-samples the rate of the symbol streams to a desired rate to produce the filtered symbol streams  487 . The digital-to-analog conversion module  477  converts the filtered symbols  487  into analog signals  489 . The analog signals may include an in-phase component and a quadrature component.  
         [0039]     The analog filter  479  filters the analog signals  489  to produce filtered analog signals  491 . The up-conversion module  481 , which may include a pair of mixers and a filter, mixes the filtered analog signals  491  with a local oscillation  493 , which is produced by local oscillation module  99 , to produce high frequency signals  495 . The frequency of the high frequency signals  495  corresponds to the frequency of the RF signals  492 .  
         [0040]     The power amplifier  483  amplifies the high frequency signals  495  to produce amplified high frequency signals  497 . The RF filter  485 , which may be a high frequency band-pass filter, filters the amplified high frequency signals  497  to produce the desired output RF signals  91 .  
         [0041]     As one of average skill in the art will appreciate, each of the radio frequency transmitters  67 ,  69 ,  71  will include a similar architecture as illustrated in  FIG. 2 ( a ) and further include a shut-down mechanism such that when the particular radio frequency transmitter is not required, it is disabled in such a manner that it does not produce interfering signals and/or noise.  
         [0042]      FIG. 2 ( b ) is a schematic block diagram of each of the RF receivers  75 ,  77 ,  79 . In this embodiment, each of the RF receivers may include an RF filter  501 , a low noise amplifier (LNA)  503 , a programmable gain amplifier (PGA)  505 , a down-conversion module  507 , an analog filter  509 , an analog-to-digital conversion module  511  and a digital filter and down-sampling module  513 . The RF filter  501 , which may be a high frequency band-pass filter, receives the inbound RF signals  93  and filters them to produce filtered inbound RF signals. The low noise amplifier  503  amplifies the filtered inbound RF signals  93  based on a gain setting and provides the amplified signals to the programmable gain amplifier  505 . The programmable gain amplifier further amplifies the inbound RF signals  93  before providing them to the down-conversion module  507 .  
         [0043]     The down-conversion module  507  includes a pair of mixers, a summation module, and a filter to mix the inbound RF signals with a local oscillation (LO) that is provided by the local oscillation module to produce analog baseband signals. The analog filter  509  filters the analog baseband signals and provides them to the analog-to-digital conversion module  511  which converts them into a digital signal. The digital filter and down-sampling module  513  filters the digital signals and then adjusts the sampling rate to produce the inbound symbol stream  95 .  
         [0044]     FIGS.  3 ( a ) and  3 ( b ) illustrate a schematic block diagram of a multiple transmitter in accordance with the present invention. In  FIG. 3 ( a ), the baseband processing is shown to include a scrambler  172 , channel encoder  174 , interleaver  176 , demultiplexer  170 , a plurality of symbol mappers  180 - 1  through  180 - m , a space/time encoder  190  and a plurality of inverse fast Fourier transform (IFFT)/cyclic prefix addition modules  192 - 1  through  192 - m . The baseband portion of the transmitter may further include a mode manager module  175  that receives the mode selection signal and produces settings for the radio transmitter portion and produces the rate selection for the baseband portion.  
         [0045]     In operations, the scrambler  172  adds (in GF 2 ) a pseudo random sequence to the outbound data bits  88  to make the data appear random. A pseudo random sequence may be generated from a feedback shift register with the generator polynomial, for example, of S(x)=x 7 +x 4 +1 to produce scrambled data. The channel encoder  174  receives the scrambled data and generates a new sequence of bits with redundancy. This will enable improved detection at the receiver. The channel encoder  174  may operate in one of a plurality of modes. For example, for backward compatibility with standards such as IEEE 802.11(a) and IEEE 802.11(g), the channel encoder has the form of a rate 1/2 convolutional encoder with 64 states and a generator polynomials of G 0 =133 8  and G 1 =171 8 . The output of the convolutional encoder may be punctured to rates of 1/2, 2/3rds and 3/4 according to the specified rate tables. For backward compatibility with IEEE 802.11(b) and the CCK modes of IEEE 802.11(g), the channel encoder has the form of a CCK code as defined in IEEE 802.11(b). For higher data rates, the channel encoder may use the same convolution encoding as described above or it may use a more powerful code, including a convolutional code with more states, a parallel concatenated (turbo) code and/or a low density parity check (LDPC) block code. Further, any one of these codes may be combined with an outer Reed Solomon code. Based on a balancing of performance, backward compatibility and low latency, one or more of these codes may be optimal.  
         [0046]     The interleaver  176  receives the encoded data and spreads it over multiple symbols and transmit streams. This allows improved detection and error correction capabilities at the receiver. In one embodiment, the interleaver  176  will follow the IEEE 802.11(a) or (g) standard in the backward compatible modes. For higher performance modes, the interleaver will interleave data over multiple transmit streams. The demultiplexer  170  converts the serial interleave stream from interleaver  176  into M-parallel streams for transmission.  
         [0047]     Each symbol mapper  180 - m  through  180 - m  receives a corresponding one of the M-parallel paths of data from the demultiplexer. Each symbol mapper locks maps bit streams to quadrature amplitude modulated QAM symbols (e.g., BPSK, QPSK, 16 QAM, 64 QAM, 256 QAM, et cetera) according to the rate tables. For IEEE 802.11(a) backward compatibility, double gray coding may be used.  
         [0048]     The map symbols produced by each of the symbol mappers  180  are provided to the space/time encoder  190 . Thereafter, output symbols are provided to the IFFT/cyclic prefix addition modules  192 - 1  through  192 - m , which performs frequency domain to time domain conversions and adds a prefix, which allows removal of inter-symbol interference at the receiver. In general, a 64-point IFFT will be used for 20 MHz channels and 128-point IFFT will be used for 40 MHz channels.  
         [0049]     In one embodiment, the number of M-input paths will equal the number of P-output paths. In another embodiment, the number of output paths P will equal M+1 paths. For each of the paths, the space/time encoder multiples the input symbols with an encoding matrix that has the form of:  
             [           C   1           -     C   2   *             C   3         …         -     C     2   ⁢   M     *                 C   2           C   1   *           C   4         …         C     (       2   ⁢   M     -   1     )     *           ]         
 
 Note that the rows of the encoding matrix correspond to the number of input paths and the columns correspond to the number of output paths. 
 
         [0050]      FIG. 3 ( b ) illustrates the radio portion of the transmitter that includes a plurality of digital filter/up-sampling modules  195 - 1  through  195 - m , digital-to-analog conversion modules  200 - 1  through  200 - m , analog filters  210 - 1  through  210 - m  and  215 - 1  through  215 - m , I/Q modulators  220 - 1  through  220 - m , RF amplifiers  225 - 1  through  225 - m , RF filters  230 - 1  through  230 - m  and antennas  240 - 1  through  240 - m . The P-outputs from the other stage are received by respective digital filtering/up-sampling modules  195 - 1  through  195 - m.    
         [0051]     In operation, the number of radio paths that are active correspond to the number of P-outputs. For example, if only one P-output path is generated, only one of the radio transmitter paths will be active. As one of average skill in the art will appreciate, the number of output paths may range from one to any desired number.  
         [0052]     The digital filtering/up-sampling modules  195 - 1  through  195 - m  filter the corresponding symbols and adjust the sampling rates to correspond with the desired sampling rates of the digital-to-analog conversion modules  200 . The digital-to-analog conversion modules  200  convert the digital filtered and up-sampled signals into corresponding in-phase and quadrature analog signals. The analog filters  210  and  215  filter the corresponding in-phase and/or quadrature components of the analog signals, and provide the filtered signals to the corresponding I/Q modulators  220 . The I/Q modulators  220  based on a local oscillation, which is produced by a local oscillator  100 , up-converts the I/Q signals into radio frequency signals. The RF amplifiers  225  amplify the RF signals which are then subsequently filtered via RF filters  230  before being transmitted via antennas  240 .  
         [0053]     FIGS.  4 ( a ) and  4 ( b ) illustrate a schematic block diagram of another embodiment of a receiver in accordance with the present invention.  FIG. 4 ( a ) illustrates the analog portion of the receiver which includes a plurality of receiver paths. Each receiver path includes an antenna  250 - 1  through  250 - n , RF filters  255 - 1  through  255 - n , low noise amplifiers  260 - 1  through  260 - n , I/O demodulators  265 - 1  through  265 - n , analog filters  270 - 1  through  270 - n  and  275 - 1  through  275 - n , analog-to-digital converters  280 - 1  through  280 - n  and digital filters and down-sampling modules  290 - 1  through  290 - n.    
         [0054]     In operation, the antennas  250  receive inbound RF signals, which are band-pass filtered via the RF filters  255 . The corresponding low noise amplifiers  260  amplify the filtered signals and provide them to the corresponding I/Q demodulators  265 . The I/Q demodulators  265 , based on a local oscillation, which is produced by local oscillator  100 , down-converts the RF signals into baseband in-phase and quadrature analog signals.  
         [0055]     The corresponding analog filters  270  and  275  filter the in-phase and quadrature analog components, respectively. The analog-to-digital converters  280  convert the in-phase and quadrature analog signals into a digital signal. The digital filtering and down-sampling modules  290  filter the digital signals and adjust the sampling rate to correspond to the rate of the baseband processing, which will be described in  FIG. 4 ( b ).  
         [0056]      FIG. 4 ( b ) illustrates the baseband processing of a receiver. The baseband processing portion includes a plurality of fast Fourier transform (FFT)/cyclic prefix removal modules  294 - 1  through  294 - n , a space/time decoder  296 , a plurality of symbol demapping modules  300 - 1  through  300 - n , a multiplexer  310 , a deinterleaver  312 , a channel decoder  314 , and a descramble module  316 . The baseband processing module may further include a mode managing module  175 . The receiver paths are processed via the FFT/cyclic prefix removal modules  294  which perform the inverse function of the IFFT/cyclic prefix addition modules  192  to produce frequency domain symbols as M-output paths. The space/time decoding module  296 , which performs the inverse function of space/time encoder  190 , receives the M-output paths.  
         [0057]     The symbol demapping modules  300  convert the frequency domain symbols into data utilizing an inverse process of the symbol mappers  180 . The multiplexer  310  combines the demapped symbol streams into a single path.  
         [0058]     The deinterleaver  312  deinterleaves the single path utilizing an inverse function of the function performed by interleaver  176 . The deinterleaved data is then provided to the channel decoder  314  which performs the inverse function of channel encoder  174 . The descrambler  316  receives the decoded data and performs the inverse function of scrambler  172  to produce the inbound data  98 .  
         [0059]      FIG. 5  is a basic diagram illustrating one embodiment of STBC realization or transmission by the receiver  121 . In this embodiment, a first antenna  110   b  of a transmitting device transmits a first complex training signal (e.g., −c*(t 1 ) c(t 0 ), where c(t) represents a long training sequence and “*” represents a conjugate function) and a second antenna  110   a  of the transmitting device transmits a second complex training signal (e.g., c*(t 0 ) c(t 1 )). In this way, the input modulation signals will be shown as described in equation (3) below.  
         [0060]     The receiver  121  receives the complex training signals, which is represented by “r”. For data processing, “r” may be expressed as:  
               [           r   ⁡     (     t   0     )                   r   *     ⁡     (     t   1     )             ]     =         [           h   1           h   2               h   2   *           -     h   1   *             ]     ⁡     [           c   ⁡     (     t   0     )                 c   ⁡     (     t   1     )             ]       +     [           n   1               n   2           ]               (   1   )             
 
         [0061]     For channel estimation, this equation may be written as:  
               [           r   ⁡     (     t   0     )                 r   ⁡     (     t   1     )             ]     =           [           c   ⁡     (     t   0     )             c   ⁡     (     t   1     )                 -       c   *     ⁡     (     t   1     )                 c   *     ⁡     (     t   0     )             ]     ⁡     [           h   1               h   2           ]       +     [           n   1               n   2           ]       =       C   ×     [           h   1               h   2           ]       +     [           n   1               n   2           ]                 (   2   )             
 
         [0062]     From this equation, the channel may be estimated using STBC, which can be expressed as:  
               [             h   ~     1                 h   ~     2           ]     =         C   *     ×     [           r   ⁡     (     t   0     )                 r   ⁡     (     t   1     )             ]       =         [             ∑     i   =   1     2     ⁢            c   ⁡     (     t   i     )            2           0           0           ∑     i   =   1     2     ⁢            c   ⁡     (     t   i     )            2             ]     ×     [           h   1               h   2           ]       +       [             n   ~     1                 n   ~     2           ]     .                 (   3   )             
 
         [0063]     When the training sequence, i.e., c(t), in a Long Training Sequence (LTS) is known, h 1  and h 2  can be found from equation (3).  
         [0064]     For the data process, the receiver  121  receives the complex signals, which is represented by “r”. The equation of “r” may be expressed as:  
               [           r   ⁡     (     t   0     )                   r   *     ⁡     (     t   1     )             ]     =           [           h   1           h   2               h   2   *           -     h   1   *             ]     ⁡     [           c   ⁡     (     t   0     )                 c   ⁡     (     t   1     )             ]       +     [           n   1               n   2           ]       =       H   ×     [           c   ⁡     (     t   0     )                 c   ⁡     (     t   1     )             ]       +     [           n   1               n   2           ]                 (   4   )             
 
         [0065]     After STBC decoding:  
               [             c   ~     ⁡     (     t   0     )                   c   ~     ⁡     (     t   1     )             ]     =         H   *     ×     [           r   ⁡     (     t   0     )                   r   *     ⁡     (     t   1     )             ]       =         [             ∑     i   =   1     2     ⁢            h   i          2           0           0           ∑     i   =   1     2     ⁢            h   i          2             ]     ×     [           c   ⁡     (     t   0     )                 c   ⁡     (     t   1     )             ]       +     [             n   ~     1                 n   ~     2           ]                 (   5   )             
 
         [0066]      FIG. 7  is a simplified diagram of the transmitter  160  to produce the first and second complex signals of  FIG. 5 . With the buffers/conjugate functions being selectable, the transmitter may operate in a variety of modes. For example, when the switch is selects the legacy path  108 , the transmitter operates as a legacy IEEE 802.11a and 802.11 g, i.e. “11a/g”, transmitter. That is to say, only antenna  118   b  is used to transmit signals to the receive antenna  125   a.    
         [0067]     When the switch is in the alternate position, the transmitter operates with STBC. The buffer/conjugate functions,  108   a  and  108   b , are utilized in this latter mode so that the code signals illustrated in  FIG. 5  may be transmitted. It is noted that the function illustrated in  FIG. 7  is performed by the space/time encoder  190 . As such, the transmitter can be chosen to be legacy system or STBC system by an external switch.  
         [0068]      FIG. 6  is a basic diagram illustrating another embodiment of STBC realization or transmission by the receiver  121 . In this embodiment, a first antenna  110   b  of a transmitting device transmits a first complex training signal (e.g., c(t 1 ) c(t 0 ), where c(t) represents a long training sequence and “*” represents a conjugate function) and a second antenna  10   a  of the transmitting device transmits a second complex training signal (e.g., c*(t 0 ) −c*(t 1 )).  
         [0069]     In one embodiment, the number of M-input paths will equal the number of P-output paths. In another embodiment, the number of output paths P will equal M+1 paths. For each of the paths, the space/time encoder multiplies the input symbols with an encoding matrix that has the form of:  
             [           C   1           C   2           C   3         …         C     2   ⁢   M                 -     C   2   *             C   1   *           -     C   4   *           …         C     (       2   ⁢   M     -   1     )     *           ]         
 
 Note that the rows of the encoding matrix correspond to the number of input paths and the columns correspond to the number of output paths. 
 
         [0070]     The receiver  121  receives the complex training signals, which is represented by “r”. For channel estimation, “r” may be expressed as:  
               [           r   ⁡     (     t   0     )                 r   ⁡     (     t   1     )             ]     =           [           c   ⁡     (     t   0     )             -       c   *     ⁡     (     t   1     )                   c   ⁡     (     t   1     )               c   *     ⁡     (     t   0     )             ]     ⁡     [           h   1               h   2           ]       +     [           n   1               n   2           ]       =       C   ×     [           h   1               h   2           ]       +       [           n   1               n   2           ]     .                 (   6   )             
 
         [0071]     From this equation, the channel may be estimated using STBC, which can be expressed as:  
               [             h   ~     1                 h   ~     2           ]     =         C   *     ×     [           r   ⁡     (     t   0     )                 r   ⁡     (     t   1     )             ]       =         [             ∑     i   =   1     2     ⁢            c   ⁡     (     t   i     )            2           0           0           ∑     i   =   1     2     ⁢            c   ⁡     (     t   i     )            2             ]     ×     [           h   1               h   2           ]       +       [             n   ~     1                 n   ~     2           ]     .                 (   7   )             
 
         [0072]     When the training sequence, i.e., c(t), in the Long Training Sequence (LTS) is known, h 1  and h 2  can be found from equation (7).  
         [0073]     In this embodiment, a first antenna  110   b  of a transmitting device transmits a first complex signal (e.g., c(t 1 ) c(t 0 ), where c(t) represents a long training sequence and “*” represents a conjugate function) and a second antenna  110   a  of the transmitting device transmits a second complex signal (e.g., c*(t 0 ) −c*(t 1 )).  
         [0074]     The receiver  121  receives the complex signals, which is represented by “r”. The equation of “r” may be expressed as:  
               [           r   ⁡     (     t   0     )                   r   *     ⁡     (     t   1     )             ]     =           [           h   1           -     h   2                 h   2   *           h   1   *           ]     ⁡     [           c   ⁡     (     t   0     )                   c   *     ⁡     (     t   1     )             ]       +     [           n   1               n   2           ]       =       H   ×     [           c   ⁡     (     t   0     )                   c   *     ⁡     (     t   1     )             ]       +     [           n   1               n   2           ]                 (   8   )             
 
         [0075]     By keeping c(t 0 ), but conjugate on c*(t 1 ), after STBC decoding, yields:  
               [             c   ~     ⁡     (     t   0     )                     c   ~     *     ⁡     (     t   1     )             ]     =         H   *     ×     [           r   ⁡     (     t   0     )                   r   *     ⁡     (     t   1     )             ]       =         [             ∑     i   =   1     2     ⁢            h   i          2           0           0           ∑     i   =   1     2     ⁢            h   i          2             ]     ×     [           c   ⁡     (     t   0     )                   c   *     ⁡     (     t   1     )             ]       +     [             n   ~     1                 n   ~     2           ]                 (   9   )             
 
         [0076]      FIG. 8  is a simplified diagram of the transmitter  160  to produce the first and second complex signals of  FIG. 6 . With the conjugate function  119  being selectable, the transmitter may operate in a variety of modes. For example, when the switch is opened, the transmitter operates as a legacy IEEE 802.11a and 802.11g, i.e. “11a/g”, transmitter. When the switch is closed, the transmitter operates with STBC. As such, the transmitter can be chosen to be legacy system or STBC system by external switch.  
         [0077]      FIG. 9  is a diagram of a packet structure when the switch is open (i.e., the transmitter is acting as a legacy transmitter). In this mode, a 11a/g legacy receiver can receive the packet. Further, STBC compliant receivers can detect Short Training Sequence (STS)  1001  and know there is one transmit antenna (detect legacy mode), then process the packet, bypassing STBC mode. The preamble also includes a Long Training Sequence (LTS)  1002 , a signal  1003  and data  1005 . The STS is used for signal detection and frequency offset estimation and the LTS is used for channel estimation. Still further, both a 11a/g legacy receiver and a STBC compliant receiver can receive the legacy 11a/g packet.  
         [0078]      FIG. 10  is a diagram of a packet structure when the switch is closed (i.e., the transmitter is using the STBC). In this mode, STS  1001  is cyclic shifted per each transmit antenna. The MAC (firmware) of transmitter can add LTS  1006  in front of Data  1007  for the packet. Further, an STBC compliant receiver can detect STS (or 2nd LTS after Signal), and know there are two transmit antennas, then process the packet with STBC mode.  
         [0079]     Although the invention has been described based upon these preferred embodiments, it would be apparent to those skilled in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention. In order to determine the metes and bounds of the invention, therefore, reference should be made to the appended claims.