Abstract:
Embodiments of this invention describe a method to reduce the effective inter carrier spacing between the sub-carriers of wireless, wired or optical transmissions and thereby increase the spectral efficiency of the communication system. Signal transmitted from multiple transmit chains are shifted in frequency at the transmitter. At the receiver a plurality of receive chains is used, the received signals are similarly shifted in frequency and used to reduce the inter carrier interference. Embodiments also describe a method for Full Duplex communication where the transmitters transmit using different frequency shifts. The receiver receives the transmitted signal and an echo of it&#39;s transmission. As the received transmission is shifted in frequency from it&#39;s transmission, it can cancel out the echo and receive the intended signal.

Description:
FIELD 
       [0001]    The embodiments pertain to wireless communication systems. Some embodiments pertain to OFDM systems. Some embodiments pertain to Full-duplex wireless communication. Some embodiments pertain to IEEE 802.11 standard. Some embodiments pertain to 3GPP and LTE standards. 
       BACKGROUND 
       [0002]    Wireless Networks have evolved rapidly over the past two decades. Wireless LAN networks as described by the IEEE 802.11 specification has evolved from 1 Mbps to 11 Mbps, 54 Mbps, 200 Mbps and now 1 Gbps. This evolution has allowed the user to surf the internet, share content with others and share media in the home between devices. Cellular networks have also evolved over the past two decades from GSM, EDGE, 3G and now LTE. The evolution of the cellular network has allowed the consumers to stay always connected with devices which can surf the internet, download maps etc. and get information from the World Wide Web anywhere. 
         [0003]    However with the rapid growth of these mobile devices and consumers using these devices more frequently, the cellular network is unable to keep up with the consumer demand. Rapid advances in cellular technology from GSM to OFDM based LTE has allowed the operators to increase the efficiency measured in bits/sec/Hz of these networks. Operators have also purchased more spectrums and increased the deployment of LTE. 
         [0004]    Thus there exists a need to increase the spectral efficiency of wireless transmissions; this is achieved through the use of enhanced modulations schemes proposed. 
       SUMMARY 
       [0005]    Wireless communication systems are used to transmit data from one wireless modem, the wireless transmitter, to the other wireless modem, the wireless receiver. When OFDM is used to transmit data the subcarriers are by design orthogonal therefore limiting the inter carrier interference. Embodiments describe a transmit mechanism to reduce the inter carrier spacing between the carriers and a method to therefore increase the spectral efficiency of the wireless system. Multiple transmit chains are used and the signal from the various transmit chains are shifted in frequency at the transmitter and then transmitted. Embodiments also describe a receive mechanism which includes a plurality of wireless receive chains which shift the received data in frequency and cancel out the inter carrier interference. 
         [0006]    Wireless communication systems typically are not full duplex. Embodiments describe a transmit mechanism for Full Duplex wireless communication which includes a Wireless Modem which includes a wireless transmitter and a wireless receiver. The wireless modem communicates to a plurality of other wireless modems. Wireless transmitter transmits using OFDM. Other Wireless modems also simultaneously transmit using OFDM on a shifted set of sub carriers. The wireless receiver receives the transmitted signal from other wireless modems and an echo of it&#39;s wireless transmission. As the received signal is shifted in frequency from its wireless transmission, it can cancel out the echo and receive the wireless signal. 
         [0007]    These methods can also be used for wired and optical communication. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  illustrates a mobile wireless system including a mobile wireless transmitter and mobile wireless receivers. 
           [0009]      FIG. 2  illustrates a wireless local area network system including a wireless transmitter and wireless receivers. 
           [0010]      FIG. 3  illustrates the Access Point and Client. 
           [0011]      FIG. 4  describes the modulator flow for a coded OFDM system. 
           [0012]      FIG. 5  describes the de-modulator flow for a coded OFDM System. 
           [0013]      FIG. 6  illustrates the transmit flow for a coded OFDM system using the Enhanced modulator. 
           [0014]      FIG. 7  illustrates the mechanism of shifting carriers and combining them. 
           [0015]      FIG. 8  illustrates another instantiation of the transmit flow for a coded OFDM system using the Enhanced modulator. 
           [0016]      FIG. 9  describes the receive flow for a coded OFDM system using the Enhanced modulator. 
           [0017]      FIG. 10  describes the Quadrature Amplitude Modulator. 
           [0018]      FIG. 11  illustrates simplified receiver architecture for the enhanced OFDM receiver. 
           [0019]      FIG. 12  illustrates another instantiation of the enhanced OFDM system. 
           [0020]      FIG. 13  describes another instantiation of the receiver for an enhanced OFDM system. 
           [0021]      FIG. 14  illustrates another instantiation of the enhanced OFDM system where a single power amplifier is used to transmit the signal. 
           [0022]      FIG. 15  illustrates another instantiation of the enhanced OFDM system where pulse code modulation is as a constellation mapper. 
           [0023]      FIG. 16  describes the PCM modulator for one bit, 2 bit, 3 bit and 4 bit mapper. 
           [0024]      FIG. 17  describes the receive flow for an enhanced OFDM system using the PCM system. 
           [0025]      FIG. 18  illustrates the enhanced OFDM system using PCM Modulator where a single power amplifier is used to transmit the signal. 
           [0026]      FIG. 19  illustrates the enhanced OFDM system when used with a MIMO system. 
           [0027]      FIG. 20  illustrates the enhanced OFDM system when used a Multi-user MIMO system. 
           [0028]      FIG. 21  shows the 802.11a preamble. 
           [0029]      FIG. 22  shows the 802.11n mixed mode preamble. 
           [0030]      FIG. 23  shows the 802.11ac preamble. 
           [0031]      FIG. 24  describes the enhanced modulator preamble. 
           [0032]      FIG. 25  describes the transmit flow for the SVHT PLCP. 
           [0033]      FIG. 26  describes the receive flow for the SVHT PLCP. 
           [0034]      FIG. 27  describes a mechanism where the transmit frequency shift is achieved in the frequency domain. 
           [0035]      FIG. 28  describes a mechanism where receive frequency shift is achieved in the time domain. 
           [0036]      FIG. 29  illustrates a Full Duplex Wireless modem using frequency shifting. 
           [0037]      FIG. 30  illustrates the frequency shift on the transmitter and receiver for a Full Duplex modem. 
           [0038]      FIG. 31  illustrates the embodiment of the Full Duplex modem where the echo is removed prior to shifting of the signal in the receiver path. 
           [0039]      FIG. 32  illustrates the embodiment of the Full Duplex modem where the frequency shift is applied on the transmitter. The leading digit(s) of each reference numeral used in this specification indicates the number of the drawing in which the reference numeral first appears. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    The expected network throughput in Exbytes from 2011 to 2016 shows a CAGR of 78%. This increase in demand is expected to be met using increased spectrum, smaller cells and improved spectral efficiency. The Shannon Theorem provides an upper bound for the number of bps/Hz. Table-1 compares the Shannon limit to the bps/Hz of IEEE 802.11n. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 MaxCap 
                 802.11n 
                   
                   
               
               
                 SNR 
                 (Mbps) 
                 (Mbps) 
                 N bps     —     max   
                 N bps   
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 15.2 
                 6.5 
                 1.17 
                 0.5 
               
               
                 4 
                 23.6 
                 13 
                 1.8 
                 1.0 
               
               
                 6 
                 30.1 
                 19.5 
                 2.3 
                 1.5 
               
               
                 9 
                 41 
                 26 
                 3.16 
                 2.0 
               
               
                 13 
                 57 
                 39 
                 4.37 
                 3 
               
               
                 17 
                 73.8 
                 52 
                 5.62 
                 4 
               
               
                 18 
                 78 
                 58.5 
                 6 
                 4.5 
               
               
                 19 
                 82.3 
                 65 
                 6.25 
                 5 
               
               
                   
               
             
          
         
       
     
         [0041]    SNR is the Signal to Noise Ratio, MaxCap is the maximum capacity from Shannon Limit, 802.11n (Mbps) is the throughput from the IEEE 802.11n specification, Nbps_max is the maximum bits per second per Hz based on the Shannon Limit, and Nbps is the bits per second per Hz as specified in the IEEE 802.11n specification. As can be seen the bits per second per Hz achieved through the IEEE 802.11n specification is lower than the maximum bits per second per Hz that could be achieved in the channel. The mechanism proposed allows reduction in the gap and reach spectral efficiency closure to the Shannon Limit. 
         [0042]    Wireless LAN networks have continuously increased the spectrum efficiency and throughput from IEEE 802.11 (1 Mbps), to IEEE 802.11b (11 Mbps), IEEE 802.11n (200 Mbps) to IEEE 802.11ac (1-7 Gbps). This has been achieved by increasing the spectral efficiency as measurement in bits/sec/Hz using OFDM and Multiple Input Multiple Output (MIMO). Spectral efficiency as measured using bits/sec/Hz has also been increased using Multi-User MIMO. 
         [0043]    Cellular systems have similarly increased the spectral efficiency and throughput from GSM, to CDMA-2000, to 3G and now LTE systems. Increasing the spectral efficiency allows operators to deploy new technology using existing spectrum and not having to purchase new spectrum. 
         [0044]    Embodiments of the present disclosure enable the use of enhanced modulation and demodulation techniques to improve the link data rate. The protocol is referred to as Enhanced OFDM Modem (EOM) and the mechanism allows the wireless system to transmit more bits/sec/Hz and therefore increase the efficiency and throughput. 
         [0045]      FIG. 1  shows a Mobile Wireless access system  100 , which includes a Base station  101 , clients  102 - 1  and  102 - 2 , the wireless signal  103 - 1  and  103 - 2 . Although in the described embodiments the elements of the wireless network access system  100  are presented in one arrangement, other embodiments may feature other arrangements. The base station could be a cellular, micro, femto or pico base station. The clients could be a phone, a Smartphone, tablet or laptop. In some embodiments the wireless network could also be a fixed wireless network. The data is transmitted by the base station  101  is modulated using the methods described in this application. The data received by clients  102 - 1  and  102 - 2  are demodulated using the methods described in this application. The data transmitted by the Clients  102 - 1  and  102 - 2  are described in this application. The data received by the base station  101  is described in this application. 
         [0046]      FIG. 2  shows a Wireless Local Area Network system  200 , which includes a Wireless Access Point  201 , Wireless clients  202 - 1  and  202 - 2 , the wireless signal  203 - 1  and  203 - 2 . Although in the described embodiment the elements of the wireless LAN system  200  are presented in one arrangement, other embodiments may feature other arrangements. The Wireless Access Point  201  could be deployed for residential wireless broadband access, wireless mobile hotspot access, enterprise wireless LAN access or for sensor networks. The clients  202 - 1  and  202 - 2  could be a laptop, a Smartphone, a tablet or a sensor node. In some embodiments the wireless network could also be a fixed wireless network. The data transmitted by the Wireless Access Point  201  is modulated using the methods described in this application. The data received by Wireless clients  202 - 1  and  202 - 2  are demodulated using the methods described in this application. The data transmitted by the Wireless Clients  202 - 1  and  202 - 2  is modulated as described in this application. The data received by the Wireless Access Point  201  is described in this application. 
         [0047]      FIG. 3  shows the Wireless Access Point  301  which includes the host processor  303 , the Network Interface  304  which includes the MAC  305 , the PHY  306 . The PHY  306  includes a plurality of transceivers  307  and the Antenna  308  which is used to transmit the wireless signal. In one embodiment the MAC and the PHY are configured to operate using the EOM protocol. In other embodiment of the MAC and PHY are configured to operate using a cellular protocol like LTE, in other embodiments the MAC and the PHY are configured to operate using the IEEE 802.11ac protocol. In yet other embodiment the MAC and the PHY are configured to operate using the IEEE 802.11a or IEEE 802.11n protocol. 
         [0048]    The Wireless Access Point communicates to a plurality of clients. The Client is shown in  302 . The client includes the host processor  311 , the Network interface  312  which includes the MAC  313  and the PHY  314 . The PHY includes a plurality of transceivers  315  which are connected to a plurality of Antennas  316 . The wireless signal is transmitted out of the Antenna. In one embodiment the MAC and the PHY are configured to operate using the EOM protocol. In other embodiment of the MAC and PHY are configured to operate using a cellular protocol like LTE, in other embodiments the MAC and the PHY are configured to operate using the IEEE 802.11ac protocol. In yet other embodiment the MAC and the PHY are configured to operate using the IEEE 802.11a or IEEE 802.11n protocol. 
         [0049]      FIG. 4  shows the modulator flow of a coded OFDM system. Similar modulators are used in Wireless LAN systems using IEEE 802.11a, 802.11n and 802.11ac systems. Similar modulation techniques are also used for cellular system like LTE. The modulator  400  consists of an encoder  401  which could be a trellis encoder or a LDPC encoder or other encoder. The encoded bits are then sent to the interleaver  402 . The interleaver changes the bit order such that due to noise continuous bits are not lost. The output of the interleaver is sent to the QAM modulator  403 . The QAM modulator could use Gray encoding to map the bits to real and imaginary values. The real and imaginary samples are then transformed from the frequency domain to the time domain using the IFFT  404 . Cyclic prefix is added to the bit stream in  405 . The digital samples are then converted to analog using the Digital to Analog convertor. The baseband signal is then modulated with a carrier frequency by the RF in  407 . The signal power is then boosted using the PA in  408 . Finally the wireless signal is transmitted through the antenna  409 . 
         [0050]      FIG. 5  shows the de-modulator flow of a coded OFDM system. Similar de-modulators are used in IEEE 802.11a, 802.11n and 802.11ac systems. Similar de-modulation techniques are also used for cellular system like LTE. The de-modulator  500  consists of an antenna  501  which receives the wireless signal; the signal amplitude is increased by the LNA  502 . The RF  503  converts the signal from the carrier frequency to baseband frequency. The ADC  504  converts the analog bits to digital; the timing adjustment module detects the start of the symbol and adjusts the timing of the ADC to match with the transmitter&#39;s frequency. The Cyclic prefix is removed by the Remove CP block  506 . The FFT  507  computes the Fourier transform and converts the time domain signal to frequency domain. The Pilot Track block  508 , tracks the phase of the receive pilots and adjusts the frequency of the demodulation. The channel is equalized by the Channel Equalizer  509 . The demodulator  510  slices the received I/Q samples and determines the closest constellation point. The samples are then sent to the de-interleaver which reverses the sample ordering based on the interleaver. These samples are then fed to the decoder which could be a viterbi or LDPC or other decoder. The decoded bit stream is then processed by the MAC or other entity. 
         [0051]      FIG. 6  shows the modulator flow of an embodiment of the enhanced OFDM modulator. The EOM  600  consists of an encoder  601  which could be a trellis encoder or a LDPC encoder or other encoder. The encoded bits are then sent to the interleaver  602 . The output of the interleaver is sent to the Frequency segment  603 . The Frequency segment takes interleaved bits and then maps them to the plurality of transmit chains  612 . The mapping of bits to the plurality of transmit chains could be done by sending the first bit to the first transmit chain, the second bit to the second transmit chain and so on. The mapping of bits could also be done where the first ‘m1’ bits are sent to the first transmit chain, the next ‘m2’ bits are sent to the next transmit chain and so on. 
         [0052]    Other Frequency segment parsing techniques could also be used. 
         [0053]    Transmit chain  612 - 1  consists of a QAM modulator  604 - 1 . The QAM modulator could use Gray encoding to map the bits to real and imaginary values. Typical QAM modulators are BPSK, QPSK, 16-QAM, 64-QAM and 256-QAM. Other QAM modulators could also be used. The real and imaginary samples are then transformed from the frequency domain to the time domain using the IFFT  605 - 1 . Cyclic prefix is added to the bit stream in  606 - 1 . The digital samples are then converted to analog using the Digital to Analog convertor  607 - 1 . The baseband signal is then modulated with a carrier frequency by the RF in  608 - 1 . The signal power is then boosted using the PA in  609 - 1 . Finally the wireless signal is transmitted through the antenna  610 . 
         [0054]    Transmit chain  612 - 2  consists of a QAM modulator  604 - 2 . The QAM modulator could use Gray encoding to map the bits to real and imaginary values. Typical QAM modulators are BPSK, QPSK, 16-QAM, 64-QAM and 256-QAM. Other QAM modulators could also be used. The QAM encoder used in each of the transmit chains could be different. Transmit chain  612 - 1  could use QAM modulator 16-QAM while transmit chain  612 - 2  could use QAM modulator QPSK. The real and imaginary samples are then transformed from the frequency domain to the time domain using the IFFT  605 - 2 . The time domain samples are then shifted in frequency by  611 - 2 . The frequency shift is done to allow transmission of multiple streams in the same bandwidth using a single antenna. Frequency shift is applied to all N chains or (N-1) chains. Cyclic prefix is added to the bit stream in  606 - 2 . The digital samples are then converted to analog using the Digital to Analog convertor  607 - 2 . The baseband signal is then modulated with a carrier frequency by the RF in  608 - 2 . The signal power is then boosted using the PA in  609 - 2 . Finally the wireless signal is transmitted through the antenna  610 . 
         [0055]    The increase in throughput comes from the reduction in subcarrier spacing due to multiple transmit chains and the increased transmit power from using multiple Power Amplifies (PA). A plurality of transmit chains can be combined. 
         [0056]    Frequency shift allows for transmission of multiple streams in the same bandwidth. It reduces the inter carrier spacing but increases the transmission capacity. Frequency shift is applied in the time domain by multiplying the time domain samples by the exponent 
         [0000]    
       
         
           
             
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                   j 
                    
                   
                       
                   
                    
                   2 
                    
                   
                       
                   
                    
                   Π 
                    
                   
                       
                   
                    
                   mn 
                 
                 N 
               
             
             , 
           
         
       
     
         [0000]    where m is the shift applied in frequency, x(n) is the time domain sample n th  sample and N is the size of the IFFT. If X(k) is the DFT of x(n) then X(K+m) is realized in the time domain by x(n). 
         [0000]    
       
         
           
             
                
               
                 
                   j 
                    
                   
                       
                   
                    
                   2 
                    
                   
                       
                   
                    
                   Π 
                    
                   
                       
                   
                    
                   mn 
                 
                 N 
               
             
             . 
           
         
       
     
         [0057]      FIG. 7  describes the mechanism of combining of the subcarriers which leads to the increased throughput of EOM. The subcarriers in transmit chain one are represented by  701 , the subcarriers in transmit chain two are represented in  702 . The combined subcarriers obtained by adding the signals from transmit chain one and two are represented in  703 . Plurality of chains can be added to achieve the combined sub-carrier realization. 
         [0058]      FIG. 8  shows a different realization of the EOM transmitter. The EOM  800  consists of an encoder  601  which could be a trellis encoder or a LDPC encoder or other encoder. The encoded bits are then sent to the interleaver  602 . The output of the interleaver is sent to the Frequency segment parser  603 . The Frequency segment parser takes interleaved bits and then maps them to the plurality of transmit chains. Transmit chain  812 - 1  consists of a QAM modulator  604 - 1 . The QAM modulator could use Gray encoding to map the bits to real and imaginary values. The real and imaginary samples are then transformed from the frequency domain to the time domain using the IFFT  605 - 1 . 
         [0059]    Transmit chain  812 - 2  consists of a QAM modulator  604 - 2 . The QAM modulator could use Gray encoding to map the bits to real and imaginary values. The real and imaginary samples are then transformed from the frequency domain to the time domain using the IFFT  605 - 2 . 
         [0060]    The samples from transmit chains  812 - 1  and  812 - 2  are combined using addition to form one sample stream. Cyclic prefix is added to the bit stream in  806 . The digital samples are then converted to analog using the Digital to Analog convertor  807 . The baseband signal is then modulated with a carrier frequency by the RF in  808 . The signal power is then boosted using the PA in  809 . Finally the wireless signal is transmitted through the antenna  610 . 
         [0061]    The increase in throughput comes from the reduction in subcarrier spacing due to multiple transmit chains. A plurality of transmit chains can be used. 
         [0062]      FIG. 9  describes an instance the EOM receiver. The receiver  900  consists of an antenna  901  which receives the wireless signal; the signal amplitude is increased by the LNA  902 . The RF  903  converts the signal from the carrier frequency to baseband frequency. The ADC  904  converts the analog bits to digital; the timing adjustment module  905  detects the start of the symbol and adjusts the timing of the ADC to match with the transmitter&#39;s frequency. The Cyclic prefix is removed by the Remove CP block  906 . The FFT  907  computes the Fourier transform and converts the time domain signal to frequency domain. The Equalizer in  907  is used to equalize the signal. 
         [0063]    The signal is then sent to transmit chains  908 - 1  and  908 - 2 . In transmit chain  908 - 2  the signal Y 2  is shifted by −f 1  in block  909 - 2 . This was the frequency shift applied in the transmitter on transmit chain  611 - 2  of FIG.  6  and  811 - 2  in  FIG. 8 . The output of  909 - 2  is passed to the Slicer  912 - 2 . 
         [0064]    The slicer  912 - 2  determines the closest constellation point corresponding to the signal and outputs that value. The modulation used could be a QAM modulation in which case the slicer converts the received I/Q samples to the closest constellation point based on the modulation used (BPSK, QPSK, 16-QAM, 64-QAM etc.). Gray encoded QAM constellations are shown in  FIG. 10 .  FIG. 10-1  shows BPSK constellation,  FIG. 10-2  QPSK constellation, FIG  10 - 3  16-QAM constellation. The slicer  912 - 2  determines the closest constellation point the received signal belongs to based on minimum distance from that constellation point and outputs the I/Q value for that constellation. 
         [0065]    The output of  912 - 2  is then shifted by frequency “f 1 ” in block  913 - 1 . The output signal Y′ 2 (f) is then subtracted from the signal Y 1  in transmit chain  908 - 1  by  910 - 1 . The output of  910 - 1  is then QAM demodulated by the Slice,  912 - 1 . The signal is then sent to the QAM-Demodulator  911 - 1  which converts the I/Q samples to soft bits. Soft bits represent the bit stream along with a fraction which represents the distance from the constellation point. 
         [0066]    In transmit chain  908 - 2  the signal Y 2  is shifted by f 1  in block  909 - 2 . The shifted signal Y′ 1 (f−f 1 ) is subtracted from Y 2 (f−f 1 ) in  910 - 2 . This signal is then QAM demodulated by block  911 - 2  which converts the I/Q samples to soft bits. Soft bits represent the bit stream along with a fraction which represents the distance from the constellation point. 
         [0067]    The signals from transmit chain  908 - 1  and  908 - 2  is then combined in the same manner as the signal was parsed into the transmit chains by the Bit de-parser  914 . If a round robin mechanism was used to distribute the bits over the transmit chains, a similar round robin mechanism is used to combine the bit streams from the received chains into a single bit stream. If the Frequency Segmenter Block  603  sent “m1” bits to transmit chain  612 - 1  and “m2” bits to transmit chain  612 - 2 , then block  914  also first takes “m1” bits from chain  908 - 1  and “m2” bits from chain  908 - 2 . 
         [0068]    The samples are then sent to the de-interleaver  915 , which reverses the sample ordering based on the interleaver. These samples are then fed to the decoder  916  which could be a viterbi or LDPC or other decoder. The decoded bit stream is then processed by the MAC or other entity. 
         [0069]    A plurality of received chains can be combined. The number of received chains is equal to the number of transmit chains. 
         [0070]      FIG. 11  describes a simplified decoder for EOM where the received signal is shift by the appropriate frequency and the QAM demodulation computed on the samples. The receiver  1100  consists of an antenna  901  which receives the wireless signal; the signal amplitude is increased by the LNA  902 . The RF  903  converts the signal from the carrier frequency to baseband frequency. The ADC  904  converts the analog bits to digital; the timing adjustment module detects the start of the symbol and adjusts the timing of the ADC to match with the transmitter&#39;s frequency. The Cyclic prefix is removed by the Remove CP block  906 . The FFT  907  computes the Fourier transform and converts the time domain signal to frequency domain. The Equalizer in  907  is used to equalize the signal. 
         [0071]    The signal is then sent to transmit chains  1108 - 1  and  1108 - 2 . In transmit chain  1108 - 1  the signal Y 1  is QAM demodulated by block  911 - 1  which converts the I/Q samples to soft bits. Soft bits represent the bit stream along with a fraction which represents the distance from the constellation point. 
         [0072]    In transmit chain  1108 - 2  the signal Y 2  is shifted by “−f 1 ” in block  909 - 2 . The shifted signal Y′ 2 (f−f 1 ) is then QAM demodulated by block  911 - 2  which converts the I/Q samples to soft bits. Soft bits represent the bit stream along with a fraction which represents the distance from the constellation point. 
         [0073]    The signals from transmit chain  1108 - 1  and  1108 - 2  is then combined in the same manner as the signal was parsed into the transmit chains by the Bit de-parser  914 . If a round robin mechanism was used to distribute the bits over the transmit chains, a similar round robin mechanism is used to combine the bit streams from the received chains into a single bit stream. If the Frequency Segmenter Block  603  sent “m1” bits to transmit chain  612 - 1  and “m2” bits to transmit chain  612 - 2 , then block  914  also first takes “m1” bits from chain  908 - 1  and “m2” bits from chain  908 - 2 . 
         [0074]    Other Frequency segment parsing techniques could also be used. 
         [0075]    The samples are then sent to the de-interleaver  915 , which reverses the sample ordering based on the interleaver. These samples are then fed to the decoder  916  which could be a viterbi or LDPC or other decoder. The decoded bit stream is then processed by the MAC or other entity. 
         [0076]    A plurality of received chains can be combined. The number of received chains is equal to the number of transmit chains. 
         [0077]      FIG. 12  describes an instantiation of the EOM modulator where the real and imaginary values obtained from the QAM modulator are transmitted over two chains. The imaginary value is shifted in frequency by “f 1 ” to reduce the inter carrier spacing of the signal. The signal is encoded in  601 , interleaved in  602  and then sent to the QAM modulator. One type of QAM modulator using Gray encoding of signals is described in  FIG. 10 . The Real samples obtained from the QAM modulator is sent over transmit chain  1202 - 1  and the imaginary values obtained the QAM modulator is sent over transmit chain  1202 - 2 . 
         [0078]    In transmit chain  1202 - 1 , The IFFT of the signal is computed in  605 - 1 , Cyclic Prefix added in  606 - 1 , the digital samples converted to analogue in  607 - 1 . The RF block,  608 - 1  modulates the signal to the RF carrier frequency and the PA,  609 - 1  increases the signal gain. 
         [0079]    In transmit chain  1202 - 2 , The IFFT of the signal is computed in  605 - 2 , the signal is shifted by frequency “f 1 ” by  611 - 2 , Cyclic Prefix added in  606 - 2 , the digital samples converted to analogue in  607 - 2 . The RF block,  608 - 2  modulates the signal to the RF carrier frequency and the PA,  609 - 2  increases the signal gain. 
         [0080]    The signal from transmit chain  1202 - 1  and  1202 - 2  are combined and then transmitted out of antenna  1203 . 
         [0081]    In other instances transmit chain  1201 - 1  could be used to receive the imaginary samples and  1201 - 2  could be used to receive the real samples. 
         [0082]      FIG. 13  describes another instance of the EOM receiver which is used to receive signals from EOM transmitter  1200 . The EOM receiver  1300  consists of an antenna  901  which receives the wireless signal; the signal amplitude is increased by the LNA  902 . The RF  903  converts the signal from the carrier frequency to baseband frequency. The ADC  904  converts the analog bits to digital; the timing adjustment module detects the start of the symbol and adjusts the timing of the ADC to match with the transmitter&#39;s frequency. The Cyclic prefix is removed by the Remove CP block  906 . The FFT  907  computes the Fourier transform and converts the time domain signal to frequency domain. The Equalizer in  907  is used to equalize the signal. 
         [0083]    The signal is then sent to receive chains  1301 - 1  and  1301 - 2 . In receive chain  1301 - 2  the signal Y 2  is shifted by “−f 1 ” in block  909 - 2 . This was the frequency shift applied in the transmitter. The output of  909 - 2  is passed to the Slicer  912 - 2 . 
         [0084]    The slicer  912 - 2  determines the closest constellation point corresponding to the signal and outputs that value. If QAM modulation is used at the transmitter, the slicer converts the received I/Q samples to the closest co-ordinates based on the modulation used (BPSK, QPSK, 16-QAM, 64-QAM etc.). The slicer  912 - 2  determines the closest constellation point the received signal belongs to based on minimum distance from that constellation point and outputs the I/Q value for that constellation. 
         [0085]    The output of  912 - 2  is then shifted by frequency “f 1 ” in block  913 - 1 . The output signal Y′ 2 (f) is then subtracted from the signal Y 1  in transmit chain  1301 - 1  by  910 - 1 . The output of  910 - 1  is then QAM demodulated by the Slice,  912 - 1 . 
         [0086]    In receive chain  1301 - 2  the signal Y 2  is shifted by −f 1  in block  909 - 2 . The shifted signal Y′ 1 (f−f 1 ) is subtracted from Y 2 (f−f 1 ) in  910 - 2 . The slicer  1303  determines the closest constellation point corresponding to the signal and outputs that value. The modulation used could be a QAM modulation in which case the slicer converts the received I/Q samples to the closest co-ordinates based on the modulation used (BPSK, QPSK, 16-QAM, 64-QAM etc.). 
         [0087]    The samples from receive chain  1301 - 1  is considered as the real samples and the samples from receive chain  1301 - 2  the imaginary samples. These samples are QAM demodulated by block  1304  which converts the I/Q samples to soft bits. Soft bits represent the bit stream along with a fraction which represents the distance from the constellation point. 
         [0088]    The samples are then sent to the de-interleaver  915 , which reverses the sample ordering based on the interleaver. These samples are then fed to the decoder  916  which could be a viterbi or LDPC or other decoder. The decoded bit stream is then processed by the MAC or other entity. 
         [0089]    In other instances receive chain  1301 - 1  could be used to receive the imaginary samples and  1301 - 2  could be used to receive the real samples. 
         [0090]      FIG. 14  describes an instantiation of the EOM modulator where the real and imaginary values obtained from the QAM modulator are transmitted over two chains. However unlike the EOM transmitter  1200  only one transmit PA is used. The imaginary value is shifted in frequency by “f 1 ” to reduce the inter carrier spacing of the signal. The signal is encoded in  601 , interleaved in  602  and then sent to the QAM modulator. One type of QAM modulator using Gray encoding of signals is described in  FIG. 10 . The Real samples obtained from the QAM modulator is sent over transmit chain  1401 - 1  and the imaginary values obtained the QAM modulator is sent over transmit chain  1401 - 2 . 
         [0091]    In transmit chain  1401 - 1 , The IFFT of the signal is computed in  605 - 1 . In transmit chain  1401 - 2 , The IFFT of the signal is computed in  605 - 2 , the signal is shifted by frequency “f 1 ” by  611 - 2 . The signals from transmit chains  1401 - 1  and  1401 - 2  are combined by adding the samples the both the chains. 
         [0092]    Cyclic Prefix added in  1402 , the digital samples converted to analogue in  1403 . The RF block,  1404  modulates the signal to the RF carrier frequency and the PA,  1405  increases the signal gain. The wireless signal is then transmitted out of the antenna  1406 . 
         [0093]    In other instances transmit chain  1401 - 1  could be used to transmit the imaginary samples and  1401 - 2  could be used to transmit the real samples. 
         [0094]    The EOM receiver  1300  as described in  FIG. 13  receives and demodulates the received signal. 
         [0095]      FIG. 15  shows the transmitter flow of an embodiment of the enhanced OFDM modulator  1500  where a Pulse Code Modulator (PCM) is used as a constellation Mapper. The EOM  1500  consists of an encoder  601  which could be a trellis encoder or a LDPC encoder or other encoder. The encoded bits are then sent to the interleaver  602 . The output of the interleaver is sent to the Frequency segment  603 . The Frequency segment takes interleaved bits and then maps them to the plurality of transmit chains  1501 . The mapping of bits to the plurality of transmit chains could be done by sending the first bit to the first transmit chain, the second bit to the second transmit chain and so on. The mapping of bits could also be done where the first ‘m1’ bits are sent to the first transmit chain, the next ‘m2’ bits are sent to the next transmit chain and so on. 
         [0096]    Other Frequency segment parsing techniques could also be used. 
         [0097]    Transmit chain  1501 - 1  consists of a PCM modulator  1502 - 1 . Embodiments of PCM Mappers are shown in  FIG. 16. 1601  consists of a PCM mapper which maps 1 bits,  1602  which maps 2 bits,  1603  which maps 3 bits and  1604  which maps 4 bits. The PCM encoded samples are then transformed from the frequency domain to the time domain using the IFFT  605 - 1 . Cyclic prefix is added to the bit stream in  606 - 1 . The digital samples are then converted to analog using the Digital to Analog convertor  607 - 1 . The baseband signal is then modulated with a carrier frequency by the RF in  608 - 1 . The signal power is then boosted using the PA in  609 - 1 . 
         [0098]    Transmit chain  1502 - 2  consists of a PCM modulator  1502 - 2 . Transmit chain  612 - 1  could use 2-level PCM modulator while transmit chain  612 - 2  could use 4-level PCM modulator. The samples are then transformed from the frequency domain to the time domain using the IFFT  605 - 2 . The time domain samples are then shifted in frequency. The frequency shift is done to allow transmission of multiple streams in the same bandwidth using a single antenna. Frequency shift is applied to all N chains or (N-1) chains. Cyclic prefix is added to the bit stream in  606 - 2 . The digital samples are then converted to analog using the Digital to Analog convertor  607 - 2 . The baseband signal is then modulated with a carrier frequency by the RF in  608 - 2 . The signal power is then boosted using the PA in  609 - 2 . 
         [0099]    The signal from all the transmit chains are combined and the wireless signal is transmitted through the antenna  610 . 
         [0100]    The increase in throughput comes from the reduction in subcarrier spacing due to multiple transmit chains and the increased transmit power from using multiple Power Amplifies (PA). A plurality of transmit chains can be combined. 
         [0101]      FIG. 17  describes an instance the EOM receiver which receives and demodulates signal received from the instance of the EOM transmitter  1500  in  FIG. 15 . The receiver  1700  consists of an antenna  901  which receives the wireless signal; the signal amplitude is increased by the LNA  902 . The RF  903  converts the signal from the carrier frequency to baseband frequency. The ADC  904  converts the analog bits to digital; the timing adjustment module detects the start of the symbol and adjusts the timing of the ADC to match with the transmitter&#39;s frequency. The Cyclic prefix is removed by the Remove CP block  906 . The FFT  907  computes the Fourier transform and converts the time domain signal to frequency domain. The Equalizer in  907  is used to equalize the signal. 
         [0102]    The signal is then sent to transmit chains  1701 - 1  and  1702 - 2 . In transmit chain  1702 - 2  the signal Y 2  is shifted by −f 1  in block  909 - 2 . The output of  909 - 2  is passed to the PCM Slicer  1702 - 2 . The PCM slicer computes the nearest constellation point of the PCM constellation as described in  FIG. 16 . 
         [0103]    The PCM slicer  1702 - 2  determines the closest constellation point corresponding to the signal and outputs that value. The modulation used could be a 1-bit, 2-bit, 3-bit or 4-bit modulation. 
         [0104]    The output of  1702 - 2  is then shifted by frequency “f 1 ” in block  913 - 1 . The output signal Y′ 2 (f) is then subtracted from the signal Y 1  in transmit chain  1701 - 1  by  910 - 1 . The output of  910 - 1  is then demodulated by PCM Slicer,  1702 - 1  which converts the received samples to soft bits. Soft bits represent the bit stream along with a fraction which represents the distance from the constellation point. 
         [0105]    In transmit chain  1701 - 2  the signal Y 2  is shifted by −f 1  in block  909 - 2 . The shifted signal Y′ 1 (f−f 1 ) is subtracted from Y 2 (f−f 1 ) in  910 - 2 . This signal is then demodulated by PCM Slicer block  1703 - 2  which converts the samples to soft bits. Soft bits represent the bit stream along with a fraction which represents the distance from the constellation point. 
         [0106]    The signals from transmit chain  1701 - 1  and  1701 - 2  are then combined in the same manner as the signal was parsed into the transmit chains by the Bit de-parser  914 . The signals from transmit chain  1701 - 1  and  1701 - 2  is then combined in the same manner as the signal was parsed into the transmit chains by the Bit de-parser  914 . If a round robin mechanism was used to distribute the bits over the transmit chains, a similar round robin mechanism is used to combine the bit streams from the received chains into a single bit stream. If the Frequency Segmenter Block  603  sent “m1” bits to transmit chain  612 - 1  and “m2” bits to transmit chain  612 - 2 , then block  914  also first takes “m1” bits from chain  908 - 1  and “m2” bits from chain  908 - 2 . 
         [0107]    The samples are then sent to the de-interleaver  915 , which reverses the sample ordering based on the interleaver. These samples are then fed to the decoder  916  which could be a viterbi or LDPC or other decoder. The decoded bit stream is then processed by the MAC or other entity. 
         [0108]    A plurality of received chains can be combined. The number of received chains is equal to the number of transmit chains. 
         [0109]      FIG. 18  describes the transmitter flow of an embodiment of the enhanced OFDM modulator  1800  which uses a single Power Amplifier instead of a Power Amplifier per transmit chain. The EOM  1800  consists of an encoder  601  which could be a trellis encoder or a LDPC encoder or other encoder. The encoded bits are then sent to the interleaver  602 . The output of the interleaver is sent to the Frequency segment  603 . The Frequency segment takes interleaved bits and then maps them to the plurality of transmit chains  1801 . The mapping of bits to the plurality of transmit chains could be done by sending the first bit to the first transmit chain, the second bit to the second transmit chain and so on. The mapping of bits could also be done where the first ‘m1’ bits are sent to the first transmit chain, the next ‘m2’ bits are sent to the next transmit chain and so on. 
         [0110]    Other Frequency segment parsing techniques could also be used. 
         [0111]    Transmit chain  1801 - 1  consists of a PCM modulator  1802 - 1 . Embodiments of PCM Mappers are shown in  FIG. 16 . The PCM encoded samples are then transformed from the frequency domain to the time domain using the IFFT  605 - 1 . 
         [0112]    Transmit chain  1802 - 2  consists of a PCM modulator  1802 - 2 . Transmit chain  1801 - 1  could use 2-level PCM modulator while transmit chain  1801 - 2  could use 4-level PCM modulator. The samples are then transformed from the frequency domain to the time domain using the IFFT  605 - 2 . The time domain samples are then shifted in frequency. The frequency shift is done to allow transmission of multiple streams in the same bandwidth using a single antenna. Frequency shift is applied to all N chains or (N-1) chains. 
         [0113]    The samples from the transmit chains are then combined through addition. Cyclic prefix is added to the bit stream in  1803 . The digital samples are then converted to analog using the Digital to Analog convertor  1804 . The baseband signal is then modulated with a carrier frequency by the RF in  1805 . The signal power is then boosted using the PA in  1806 . 
         [0114]    The wireless signal is transmitted through the antenna  1807 . 
         [0115]    The increase in throughput comes from the reduction in subcarrier spacing due to multiple transmit. A plurality of transmit chains can be combined. 
         [0116]    The EOM receiver to demodulate signals transmitted from  1800  is described in  FIG. 17 . 
         [0117]      FIG. 19  describes an instantiation of the Enhanced OFDM Modulator when used with a Multiple Input Multiple Output (MIMO) transmitter. The EOM  1900  consists of an encoder  1901  which could be a trellis encoder or a LDPC encoder or other encoder. The encoded bits are then sent to the interleaver  1902 . The output of the interleaver is sent to the Frequency segment  1903 . The Frequency segment takes interleaved bits and then maps them to the plurality of transmit chains. The mapping of bits to the plurality of transmit chains could be done by sending the first bit to the first transmit chain, the second bit to the second transmit chain and so on. The mapping of bits could also be done where the first ‘m1’ bits are sent to the first transmit chain, the next ‘m2’ bits are sent to the next transmit chain and so on. 
         [0118]    Other Frequency segment parsing techniques could also be used. 
         [0119]    Transmit chain  1904 - 1  consists of a MIMO Stream Parser  1905 - 1  which are then mapped to various constellation points using the Constellation mapper in  1906 - 1 - 1 . The samples are then provided to the STBC block  1907 - 1 . The output of the STBC is if required shifted using the CSD block  1908 - 1 . These samples are then mapped to the various RF transmit chains using the spatial mapping block  1909 - 1 . The output of the spatial mapper are then converted from frequency domain to time domain samples through the IFFT  1910 - 1 - 1  and  1910 - 1 - 2  for the different spatial streams. Cyclic prefix is added to the bit stream in  1911 - 1 - 1  and  1911 - 1 - 2 . The digital samples are then converted to analog using the Digital to Analog convertor  1912 - 1 - 1  and  1912 - 2 . The baseband signal is then modulated with a carrier frequency by the RF in  1913 - 1 - 1 . The signal power is then boosted using the PA in  1914 - 1 - 1 . 
         [0120]    Transmit chain  1904 - 2  consists of a MIMO Stream Parser  1905 - 2  which are then mapped to various constellation points using the Constellation mapper in  1906 - 2 - 1 . The samples are then provided to the STBC block  1907 - 2 . The output of the STBC is if required shifted using the CSD block  1908 - 2 . These samples are then mapped to the various RF transmit chains using the spatial mapping block  1909 - 2 . The output of the spatial mapper are then converted from frequency domain to time domain samples through the IFFT  1910 - 2 - 1 . 
         [0121]    The time domain samples are then shifted in frequency. The frequency shift is done to allow transmission of multiple streams in the same bandwidth. Frequency shift is applied to all N chains or (N-1) chains. 
         [0122]    Cyclic prefix is added to the bit stream in  1911 - 2 - 1  and  1911 - 2 - 2 . The digital samples are then converted to analog using the Digital to Analog convertor  1912 - 2 - 1 . The baseband signal is then modulated with a carrier frequency by the RF in  1913 - 2 - 1 . The signal power is then boosted using the PA in  1914 - 2 - 1 . 
         [0123]    The signal from all the transmit chains are combined and the wireless signal is transmitted through the antenna  1915 . 
         [0124]    The increase in throughput comes from the reduction in subcarrier spacing due to multiple transmit. A plurality of transmit chains can be combined. 
         [0125]      FIG. 20  describes an instantiation of the Enhanced OFDM Modulator when used with a Multi-User Multiple Input Multiple Output (MIMO) transmitter. The EOM  2000  describes the transmit chain when data is transmitted to two users. The transmit chain consists of encoders  2001 - 1  and  2001 - 2  which encode the bit stream per user. The encoders could be a trellis encoder or a LDPC encoder or other encoder. The encoded bits are then sent to the interleavers  2002 - 1  and  2002 - 2 . The output of the interleaver is sent to the Frequency segment  2003 - 1  and  2003 - 2 . The Frequency segment takes interleaved bits and then maps them to the plurality of transmit chains. The mapping of bits to the plurality of transmit chains could be done by sending the first bit to the first transmit chain, the second bit to the second transmit chain and so on. The mapping of bits could also be done where the first ‘m1’ bits are sent to the first transmit chain, the next ‘m2’ bits are sent to the next transmit chain and so on. 
         [0126]    Other Frequency segment parsing techniques could also be used. 
         [0127]    Transmit chain  2004 - 1  consists of a MIMO Stream Parser  2005 - 1  which are then mapped to various constellation points using the Constellation mapper in  2006 - 1 - 1 . The samples are then provided to the STBC block  2007 - 1 . The output of the STBC is if required shifted using the CSD block  2008 - 1 . These samples are then mapped to the various RF transmit chains using the spatial mapping block  2009 - 1 . The output of the spatial mapper are then converted from frequency domain to time domain samples through the IFFT  2010 - 1 - 1  and  2010 - 1 - 2  for the different spatial streams. Cyclic prefix is added to the bit stream in  2011 - 1 - 1  and  2011 - 1 - 2 . The digital samples are then converted to analog using the Digital to Analog convertor  2012 - 1 - 1  and  2012 - 2 . The baseband signal is then modulated with a carrier frequency by the RF in  2013 - 1 - 1 . The signal power is then boosted using the PA in  2014 - 1 - 1 . 
         [0128]    Transmit chain  2004 - 2  consists of a MIMO Stream Parser  2005 - 2  which are then mapped to various constellation points using the Constellation mapper in  2006 - 2 - 1 . The samples are then provided to the STBC block  2007 - 2 . The output of the STBC is if required shifted using the CSD block  2008 - 2 . These samples are then mapped to the various RF transmit chains using the spatial mapping block  2009 - 2 . The output of the spatial mapper are then converted from frequency domain to time domain samples through the IFFT  2010 - 2 - 1 . 
         [0129]    The time domain samples are then shifted in frequency. The frequency shift is done to allow transmission of multiple streams in the same bandwidth. Frequency shift is applied to all N chains or (N-1) chains. 
         [0130]    Cyclic prefix is added to the bit stream in  2011 - 2 - 1  and  2011 - 2 - 2 . The digital samples are then converted to analog using the Digital to Analog convertor  2012 - 2 - 1 . The baseband signal is then modulated with a carrier frequency by the RF in  2013 - 2 - 1 . The signal power is then boosted using the PA in  2014 - 2 - 1 . 
         [0131]    The signal from all the transmit chains are combined and the wireless signal is transmitted through the antenna  2015 . 
         [0132]    The increase in throughput comes from the reduction in subcarrier spacing due to multiple transmit. A plurality of transmit chains can be combined. Data can be transmitted to a plurality of wireless clients. 
         [0133]      FIG. 21  describes the IEEE 802.11a preamble. The L-STF  2101  is the short training field, the L-LTF  2102  is the long training field, the L-SIG  2103  contains header information to decode the data. The data is contained in  2104 . 
         [0134]      FIG. 22  describes the IEEE 802.11n Mixed mode preamble. The L-STF  2101  is the short training field, the L-LTF  2102  is the long training field, the L-SIG  2103  contains legacy header information. The HT-SIG  2201  contains information to decode the data. This is followed by the HT short training field HT-STF  2202  and the HT long training field  2203 . This is followed by the data is contained in  2204 . 
         [0135]      FIG. 23  describes the IEEE 802.11ac preamble. The L-STF  2101  is the short training field, the L-LTF  2102  is the long training field, the L-SIG  2103  contains legacy header information. The VHT-SIG  2301  contains information to decode the data. This is followed by the VHT short training field, VHT-STF  2302  and the VHT long training field  2303 . This is followed by the data is contained in  2304 . 
         [0136]      FIG. 24  describes the Enhanced Modulator preamble when used in an IEEE 802.11 system. The L-STF  2101  is the short training field, the L-LTF  2102  is the long training field, the L-SIG  2103  contains legacy header information. The SVHT-SIG  2401  contains information to decode the data. This is followed by the SVHT short training field, SVHT-STF  2402  and the SVHT long training field  2403 . This is followed by the data is contained in  2404 . The packet header indicates the frequency shift applied at the transmitter. This could be indicated in the legacy packet header or in the SVHT part of the packet header. 
         [0137]      FIG. 25  describes the transmitter flow of an embodiment of the enhanced OFDM modulator which is used to transmit the preamble  2400  as described in  FIG. 24 . The EOM Preamble transmitter  2500  consists of the multiple transmit chains  2508 - 1  and  2508 - 2 . 
         [0138]    Transmit chain  2508 - 1  includes a block to generate the training sequence  2501 - 1 . The training sequence is then transformed from the frequency domain to the time domain using the IFFT  2502 - 1 . Cyclic prefix is added to the bit stream in  2503 - 1 . The digital samples are then converted to analog using the Digital to Analog convertor  2504 - 1 . The baseband signal is then modulated with a carrier frequency by the RF in  2505 - 1 . The signal power is then boosted using the PA in  2506 - 1 . 
         [0139]    Transmit chain  2508 - 2  includes a block to generate the training sequence  2501 - 1 . The training sequence is then transformed from the frequency domain to the time domain using the IFFT  2502 - 1 . The time domain samples are then shifted in frequency by  2508 - 2 . The frequency shift is done to allow transmission of multiple streams in the same bandwidth using a single antenna. Frequency shift is applied to all N chains or (N-1) chains. Cyclic prefix is added to the bit stream in  2503 - 2 . The digital samples are then converted to analog using the Digital to Analog convertor  2504 - 2 . The baseband signal is then modulated with a carrier frequency by the RF in  2505 - 2 . The signal power is then boosted using the PA in  2506 - 2 . 
         [0140]    The signal from all the transmit chains are combined and the wireless signal is transmitted through the antenna  2507 . 
         [0141]    The increase in throughput comes from the reduction in subcarrier spacing due to multiple transmit. A plurality of transmit chains can be combined. 
         [0142]      FIG. 26  describes the receiver flow of an embodiment of the enhanced OFDM receiver which is used to receive the preamble  2400  as described in  FIG. 24 . 
         [0143]    The receiver  2600  consists of an antenna  2601  which receives the wireless signal; the signal amplitude is increased by the LNA  2602 . The RF  2603  converts the signal from the carrier frequency to baseband frequency. The ADC  2604  converts the analog bits to digital; the timing adjustment module detects the start of the symbol and adjusts the timing of the ADC to match with the transmitter&#39;s frequency. The Cyclic prefix is removed by the Remove CP block  2606 . The FFT  2607  computes the Fourier transform and converts the time domain signal to frequency domain. The Equalizer in  2607  is used to equalize the signal. 
         [0144]    The signal is then sent to transmit chains  2608 - 1  and  2608 - 2 . In transmit chain  2608 - 2  the signal S 2  is shifted by −f 1  in block  2611 - 2 . The output of  2611 - 2  is passed to the Training Sequence block  2613 - 2 . The Training Sequence block  2613 - 2  computes the nearest Training Sequence value based on the received signal. 
         [0145]    The output of  2613 - 2  is then shifted by frequency “f 1 ” in block  2612 - 2 . The output signal Y′ 2 (f+f 1 ) is then subtracted from the signal S 1  in transmit chain  2608 - 1  by  2609 - 1 . The output of  2609 - 1  is the receive sequence for receive chain  2608 - 1  represented by S′ 1 . 
         [0146]    In transmit chain  2608 - 2  the signal S 2  is shifted by −f 1  in block  2611 - 2 . The shifted signal S′ 1 (f−f 1 ) is subtracted from S 2 (f−f 1 ) in  2609 - 2 . The output of  2610 - 2  is the receive sequence for receive chain  2608 - 2  represented by S′ 2 (f−f 1 ). 
         [0147]    A plurality of received chains can be used to receive the training signal. The number of received chains is equal to the number of transmit chains. 
         [0148]      FIG. 27  describes an embodiment of the EOM transmitter where the frequency shift is done in the frequency domain instead of the time domain. 
         [0149]    Similarly  FIG. 28  describes an embodiment of the EOM receiver where the frequency shift is done in the time domain instead of the frequency domain. 
         [0150]      FIG. 29  describes the modulator flow of an embodiment of the enhanced OFDM modulator which is capable of Full Duplex wireless transmission and reception. The wireless modem in  2900  transmits and receives wireless signals on the same channel frequency simultaneously. Effective transmit to receive cancellation can be achieved by using separate antennas, an echo canceller and separating transmit and receive frequencies by shifting them in frequency such that the sub-carriers of the receive align within the inter carrier spacing as shown in  FIG. 30 . 
         [0151]    The EOM  2900  consists of an encoder  2901  which could be a trellis encoder or a LDPC encoder or other encoder. The encoded bits are then sent to the interleaver  2902 . The QAM modulator  2903  could use Gray encoding to map the bits to real and imaginary values. Typical QAM modulators are BPSK, QPSK, 16-QAM, 64-QAM and 256-QAM. Other QAM modulators could also be used. The real and imaginary samples are then transformed from the frequency domain to the time domain using the IFFT  2904 . Cyclic prefix is added to the bit stream in  2905 . The digital samples are then converted to analog using the Digital to Analog convertor  2906 . The baseband signal is then modulated with a carrier frequency by the RF in  2907 . The signal power is then boosted using the PA in  2908 . Finally the wireless signal is transmitted through the antenna  2909 . 
         [0152]    The receiver in EOM  2900  consists of an antenna  2911  which receives the wireless signal; the signal amplitude is increased by the LNA  2912 . The RF  2913  converts the signal from the carrier frequency to baseband frequency. The ADC  2914  converts the analog bits to digital; the Cyclic prefix is removed by the Remove CP block  2915 . The FFT  2916  computes the Fourier transform and converts the time domain signal to frequency domain. The Equalizer in  2916  is used to equalize the signal. The signal is then shifted by frequency “−f 1 ” in block  2917 . 
         [0153]    The output of the QAM modulator of the transmitter is sent to the Echo canceller which converts the transmit signal to best represent the received echo. This signal The output signal Y′ 2 (f−f 1 ) is then subtracted from the signal is then shifted by frequency “−f 1 ”. The shifted signal Y′ 1 (f−f 1 ) is subtracted from Y 2 (f−f 1 ) in  2918 . This signal is then QAM demodulated by block  2920  which converts the I/Q samples to soft bits. Soft bits represent the bit stream along with a fraction which represents the distance from the constellation point. The samples are then de-interleaved in  2922  and decoded in  2923 . The decoded bit stream is then processed by the MAC or other entity. 
         [0154]    Effective Full Duplex Wireless transmission is possible as the transmit and receive sub carriers are separated by the frequency shift. The frequency shift could similarly be applied by the wireless transmitter. 
         [0155]      FIG. 31  illustrates the embodiment of the Full Duplex modem where the echo is removed prior to shifting of the signal in the receiver path. 
         [0156]      FIG. 32  illustrates the embodiment of the Full Duplex modem where the frequency shift is applied on the transmitter. 
         [0157]    With sufficient isolation both the transmit and the receive could use the same antenna.