Abstract:
A MIMO-based multiuser OFDM multiband of UWB communications is presented to meet FCC emission limitations for indoor UWB operations. The present UWB system divides a single UWB frequency band of 7.5 GHz into eleven frequency bands as a multiband. Each frequency band has 650-MHz frequency bandwidth, uses an OFDM with multicarrier, and employs different modulations. The present UWB system can be programmable not only to transmit different data rates in a relatively longer distance but also to avoid interference with other devices by controlling the multiband and/or some of the multicarrier within each of the OFDM. The present UWB system can transmit a very high data rate up to 11 Gbps approximately.

Description:
BACKGROUND 
   This invention is generally relative to a Multiple-Input-Multiple-Output (MIMO)-base multiuser Orthogonal Frequency Division Multiplexing (OFDM) multiband of Ultra Wideband (UWB) Communications for short-distance wireless broadband communications. 
   U.S. Federal Communications Commission (FCC) released a revision of Part 15 of Commission&#39;s rules regarding UWB transmission systems to permit marketing and operation of certain types of new products incorporating UWB technology on Apr. 22, 2002. With appropriate technologies, UWB device can operate using spectrum occupied by existing radio service without causing interference, thereby permitting scarce spectrum resources to be used more efficiently. Adapting UWB technology offers significant benefits for Government, public safety, businesses, and consumers under an unlicensed basis of operation spectrum. 
   In general, FCC is adapting unwanted emission limits for UWB communication devices that are significantly more stringent than those imposed on other Part 15 devices. For indoor UWB operations, FCC allows a wide variety of the UWB communication devices, such as high-speed home and business networking devices, subject to certain frequency and power limitations. An emission limitation is −10 dBm for the indoor UWB operations. The UWB communication devices must operate in the frequency band from 3.1 GHz to 10.6 GHz. In addition, the UWB communication devices should satisfy the Part 15.209 emission-mask limitations for the frequency band below 960 MHz and above 960 MHz. 
   For indoor UWB communication devices, Table 1 lists the FCC restrictions of the emission masks (dBm) along with the frequencies (GHz) as follows: 
   
     
       
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               Frequency (MHz) 
               EIRP (dBm) 
             
             
                 
                 
             
           
           
             
                 
                0-960 
               −41.3 
             
             
                 
                960-1610 
               −75.3 
             
             
                 
               1610-1990 
               −53.3 
             
             
                 
               1990-3100 
               −51.3 
             
             
                 
                3100-10600 
               −41.3 
             
             
                 
               Above 10600 
               −51.3 
             
             
                 
                 
             
           
        
       
     
   
   FCC defines an UWB communication device device where a fractional bandwidth (FB) is greater than 0.25 given by, 
                   FB   =     2   ⁢     (         f   H     -     f   L           f   H     +     f   L         )         ,           (   1   )               
where f h  is the upper frequency of −10 dBm emission point, and f L  is the lower frequency of −10 dBm emission point.
 
   The center frequency F c  of an UWB transmission system is obtained by using an average of the upper and lower −10 dBm emission points as follows: 
                   F   c     =           f   H     +     f   L       2     .             (   2   )               
Furthermore, a minimum frequency bandwidth of 500 MHz must be used for any indoor UWB communication devices regardless of the center frequency.
 
   In indoor environments, the UWB communication devices can be used for wireless broadband communications within a short-distance range, particularly for a very high-speed data transmission suitable for broadband access to networks, a device access to any devices, and Internet access to high-definite television, etc. 
   An UWB frequency bandwidth of 7.5 GHz from 3.1 GHz to 10.6 GHz is used as a single frequency band, an analog-to-digital (A/D) and a digital-to-analog (D/A) converter must operate at a very-high sampling rate F, so that an UWB communication transceiver can be directly implemented in a digital domain. However, this leads to a very-high requirement for the A/D and D/A converter in an UWB transmitter and receiver. Presently, developing such a very high-speed A/D and D/A converter may not be possible with a reasonable cost, thereby having a difficult problem to apply the A/D and the D/A converter for the UWB communication transceiver based on the single frequency band. On the other hand, a single frequency band-based UWB communication transceiver may not have flexibility and scalability for transmitting and receiving a user data. In addition, the single frequency band-based UWB communication transceiver may have interference with a Wireless Local Area Network (WLAN) 802.11a transceiver without using a special filter system since the WLAN 802.11a transceiver operates at a lower U-NII frequency range from 5.15 GHz to 5.35 GHz and at an upper U-NII upper frequency range from 5.725 GHz to 5.825 GHz. 
   Furthermore, since FCC is adapting unwanted emission limits for indoor UWB communication devices that are significantly more stringent than those imposed on other Part 15 devices, transmitting distance of the indoor UWB communication devices is limited if employing a convention approach, such as a single antenna for the single frequency band in the UWB communication devices. As a result, transmitting distance is approximately in a range of one meter to ten meters depending on a transmitting data rate. 
   An OFDM is an orthogonal multicarrier modulation technique that has been extensively used in a digital audio and video broadcasting, and a WLAN 802.11a. The OFDM has its capability of multifold increasing symbol duration. With increasing the number of subcarriers, the frequency selectivity of a channel may be reduced so that each subcarrier experiences flat fading. Thus an OFDM approach has shown in a particular useful for wireless broadband communications over fading channels. 
   A direct sequence spread spectrum (DSSS) is to use a pseudorandom (PN) sequence to spread a user signal. The PN sequence is an ordered stream of binary ones and zeros that referred to as chips rather than bits. The DSSS can be used to separate signals coming from multiuser. Thus the multiple access interference (MAI) among multiuser can be avoided if a set of PN sequences is designed with as low crosscorrelation as possible. 
   A MIMO is a multiple-input-multiple-output as a wireless link and is also a space-time signal processing so that a natural dimensional of transmitting data is complemented with a spatial dimension inherent in the use of multiple spatially distributed antennas. Thus, the MIMO is able to turn multipath propagation into a benefit for a user. In a MIMO communication system, signals on transmitter antennas at one-end and receiver antennas at the other-end are integrated in such a way that the quality of bit error rate (BER), data rate of communication for each user, or transmitting distance is improved, thereby enhancing a communication network&#39;s quality of service. 
   A MIMO-based multiuser OFDM multiband for an UWB communication transceiver system is disclosed herein according to some embodiments of the present invention. The present invention uses eleven frequency bands as a multiband, each of the frequency bands having 650 MHz frequency bandwidths. Each of the frequency bands employs an OFDM modulation for a multiuser UWB communication transceiver. A base station of UWB communications employs eleven antennas while a mobile station of the UWB communications uses two antennas. A solution of MIMO-based OFDM multiband allows using a set of low-speed A/D and D/A converters in parallel. A unique of the PN sequences is assigned to each user so that multiuser can share the same frequency band or the multiband to transmit and receive information data. An orthogonal sequence is also used to spread the data within each of the frequency bands, thereby leading to multiband orthogonality. On the other hand, since the OFDM is an orthogonal multicarrier modulation, subcarriers within each of the frequency bands may be flexibility turned on or off avoiding the interference with the WLAN 802.11a during the indoor UWB operations. In addition, the MIMO-based multiuser OFDM multiband of the UWB communication transceiver system improves the capability of transmitting very-high data rate in a much longer distance than the convention approach does. Moreover, the present invention of the MIMO-based multiuser OFDM multiband of the UWB communication transceiver system has a scalability to transmit and receive the data rate of 2.770 Gbps by using one of the frequency bands up to the data rate of 11.082 Gbps by using all of the eleven frequency bands. 
   Thus, there is a continuing need of the MIMO-based multiuser OFDM multiband of the UWB communication transceiver system for transmitting a very-high data rate in a greater distance range in indoor environments. 
   SUMMARY 
   In accordance with one aspect, a MIMO-based multiuser OFDM multiband of an UWB base station communication transmitter comprises a multiuser encoding and spreading unit, a polyphase-based multiband, an inverse fast Fourier transform (IFFT) unit, a filtering and spreading unit, a MIMO-based multiband modulation and multicarrier radio unit, and a multiple antenna unit. 
   Other aspects are set forth in the accompanying detailed description and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of showing a MIMO-based multiuser OFDM multiband of the UWB communication transceiver system including different users of UWB mobile stations and a single UWB base station according to some embodiments. 
       FIG. 2  is a block diagram of a MIMO-based multiuser OFDM multiband of an UWB base station communication transmitter employing eleven antennas according to some embodiments. 
       FIG. 3  is a detailed block diagram of a polyphase-based multiband according to some embodiments. 
       FIG. 4  is a detailed block of a 1024-point IFFT employing 1000 subcarriers and 24 NULLs according to some embodiments. 
       FIG. 5  is a detailed block diagram of a filtering and spreading section according to some embodiments. 
       FIG. 6  is a detailed block diagram of a MIMO-based multiband modulation and multicarrier RF section according to some embodiments. 
       FIG. 7  is a frequency spectrum output of the MIMO-based multiuser OFDM multiband of the UWB base station communication transmitter for the indoor UWB operation according to one embodiment. 
       FIG. 8  is a block diagram of a MIMO-based OFDM multiband of an UWB mobile communication receiver for a single user according to some embodiments. 
       FIG. 9  is a detailed block diagram of a two-antenna multiband RF receiver unit according to some embodiments. 
       FIG. 10  is a detailed block diagram of a combination subsection including a set of A/D converters, a set of digital receiver filters, and a set of multiband spreading. 
       FIG. 11  is a detailed block diagram of a combination subsection including a fast Fourier transform (FFT) and frequency-domain equalizers (FEQ) according to some embodiments. 
       FIG. 12  is a detailed block diagram of a polyphase-based demultiband according to some embodiments. 
       FIG. 13  is a detailed block diagram of a despreading, deinterleaver, and decoding unit for a single user of the UWB mobile communication receiver according to some embodiments. 
   

   DETAILED DESCRIPTION 
   Some embodiments described herein are directed to the MIMO-based multiuser OFDM multiband of the UWB communication transceiver system during the indoor UWB operation. The MIMO-based multiuser OFDM multiband of the UWB communication transceiver system may be implemented in hardware, such as in an Application Specific Integrated Circuits (ASIC), digital signal processor, field programmable gate array (FPGA), software, or a combination of hardware and software. 
   MIMO-Based Multiuser OFDM multiband UWB System 
   A MIMO-based multiuser OFDM multiband of the UWB communication system  100  for the indoor UWB operation is illustrated in  FIG. 1  in accordance with one embodiment of the present invention. UWB mobile stations from  110   a  to  110   p  can communicate with a MIMO UWB base station  140  to transmit and receive information data through MIMO-based frequency bands in an indoor environment simultaneously. The UWB mobile station  110   a  transmits and receives the information data through its two antennas of  120   a   1  and  120   a   2  into air, and communicates with the MIMO UWB base station  140  through its eleven antennas from  130   a  to  130   k . In a similar way, other UWB mobile stations from  110   b  to  110   p  also transmit and receive the information data through their antennas from  120   b   1  and  120   b   2  to  120   p   1  and  120   p   2 , respectively, and communicate with the MIMO UWB base station  140  through the antennas from  130   a  to  130   k  as well. The MIMO UWB base station  140  is coupled to an UWB network interface section  150 , which is connected with an UWB network  160 . 
   Each of the UWB mobile stations from  110   a  to  110   p  uses a unique PN sequence to spread and despread a user source signal. The MIMO UWB base station  140 , knowing all of the PN sequences of the UWB mobile stations from  110   a  to  110   p , can transmit and receive all of the information data from all of the UWB mobile stations from  110   a  to  110   p  based on a MIMO-based OFDM multiband solution by spreading and despreading of the user PN sequences. The MIMO-based OFDM multiband of the UWB communication system uses one of modulations, binary phase-shifted keying (BPSK), quadrature phase-shifted keying (QPSK) or 16-ary quadrature-amplitude modulation (16-QAM), and multicarrier within each of the frequency bands to transmit and receive the information data rate of 2.770 Gbps on one frequency band up to the information data rate of 11.082 Gbps on eleven frequency bands. As a result, the present invention of the MIMO-based multiuser OFDM multiband of the UWB communication system  100  can simultaneously transmit and/or receive the maximum data rate up to 11.082 Gbps by using all of the eleven frequency bands, with an enhancement of transmitting in a longer distance. 
   MIMO-Based UWB Base Station Transmitter Architecture 
     FIG. 2  is a block diagram of showing the MIMO-based multiuser OFDM multiband of UWB base station transmitter architecture  200  for the indoor UWB operation according to some embodiments. There are a number of p users from a user-1 bitstream  210   a  to a users bitstream  210   p , respectively. The user-1 bitstream  210   a  is coupled to a ½-rate convolution encoder  212   a , which is connected to an interleaver  214   a . Using a unique PN sequence of a user-1 key  218   a  spreads the output sequence of the interleaver  214   a . In a similar way, the user-p bitstream  210   p  is coupled to the ½-rate convolution encoder  212   p  that is connected to the interleaver  214   p . Using the unique PN sequence of the user-p key  218   p  spreads the output sequences of the interleaver  214   p . All of the PN sequences from the user-1 key  218   a  to the user-p key  218   p  are orthogonal each other. This means that a cross-correlation between one PN sequence and other PN sequences is almost zero, while a self-correlation of a user PN sequence is almost equal to one. Then, the p output sequences from the interleaver  214   a  to the interleaver  214   p  in a parallel operation are added together to form a serial sequence output by using a sum over block duration  220 . The serial output of the sum over block duration  220  is converted into eleven parallel sequences by using a polyphase-based multiband  230 . Thus, the first of the output sequence from the polyphase-based multiband  230  is converted into a 512-parallel sequence by using a serial-to-parallel (S/P)  240   a . The 512-parallel sequence is formed to 512-parallel complex sequence with symmetric conjugate. The 512-parallel complex sequence is passed through an IFFT  242   a  to produce a 1024-parallel real sequence. The IFFT  242   a  is coupled to a guard  244   a  to insert 256 samples as a guard interval for the output sequence of the IFFT  242   a . As a result, the output of the guard  244   a  is a 1280-parallel real sequence. Then, the 1280-parallel real sequences are passed through a filtering and spreading section  246   a  to produce even and odd modulated signal sequences. Carriers multiply the even and odd modulated signal sequence outputs of the filtering and spreading section  246   a  by using a MIMO-based multiband modulation and multicarrier RF section  250 . In the same way, the eleventh of the output sequence from the polyphase-based multiband  230  is converted into a 512-parallel sequence by using an S/P  240   k . The 512-parallel sequence is formed to 512-parallel complex sequence with symmetric conjugate. The 512-parallel complex sequence is passed through an IFFT  242   k  to produce a 1024-parallel real sequence. The IFFT  242   k  is coupled to a guard  244   k  to insert 256 samples as a guard interval for the output sequence of the IFFT  242   k . Thus, the output of the guard  244   k  is a 1280-parallel real sequence. The guard interval is used to avoid intersymbol interference (ISI) between IFFT frames. Then, the 1280-parallel real sequences are passed through a filtering and spreading section  246   k  to produce even and odd modulated signal sequences. Carriers multiply the even and odd modulated signal sequences of the filtering and spreading section  246   k  by using the MIMO-based multiband modulation and RF multicarrier  250 . Finally, the eleven output signals of the MIMO-based multiband modulation and RF multicarrier  250  are added together to form a new eleven signals in parallel, and passed through their power amplifiers and multiple antennas from  260   a  to  260   k  into air. 
   Referring to  FIG. 3  is a detailed block diagram  300  of the polyphase-based multiband  230  according to some embodiments. The polyphase-base multiband  230  includes a random access memory (RAM) bank  310  storing a serial input data, and eleven RAM banks from  320   a  to  320   k  storing parallel data. The serial input sequence with a length of N data in the RAM bank  310  is divided into eleven parallel sequences with a length of N/11 data by mapping each data of the serial input sequences in the RAM bank  310  into eleven RAM banks from  320   a  to  320   k . The number size of data in each of the RAM banks of  310  and  320   a  to  320   k  may be programmed depending on the block size as required by the MIMO UWB communication system. 
   Referring to  FIG. 4  is a detailed block diagram  400  of the 1024-point IFFT  410  according to some embodiments. There are 24 Nulls including # 0  (DC), and # 501  to # 523 . The values of the input # 0  (DC) and # 501  to # 523  are set to zero. The coefficients from 1 to 500 are mapped to the same numbered IFFT inputs # 1  to # 500 , while the coefficients from 500 to 1 are passed through a complex conjugate  420  and also copied into IFFT inputs from # 524  to # 1023  to form a complex sequence. Thus, there are a total of 1,000 subcarriers for transmitting data and pilot information. In order to make a coherent detection robust against frequency offsets and phase noise, eight of the 1,000 subcarriers are dedicated to pilot signals that are assigned into the subcarriers of # 100 , # 200 , # 300 , # 400 , and # 624 , # 724 , # 824 , and # 924 . These pilots are BPSK modulated by a pseudo binary sequence to prevent a generation of spectral lines. In this case, other 992 subcarriers of each OFDM are dedicated to assign for transmitting data information. After performing the IFFT operation, an output of the 1,024-point IFFT is cyclically extended to a desired length in each of the frequency bands. 
   Table 2 lists data rate-dependent parameters of the 1,024-point IFFT operation for each of the frequency bands: 
   
     
       
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
           
         
             
               TABLE 2 
             
             
                 
             
             
               Eleven band 
               One 
                 
                 
                 
                 
                 
             
             
               frequency 
               frequency 
                 
                 
               Coded bits 
               Coded bits 
               Data bits per 
             
             
               data rate 
               band data rate 
                 
               Coding 
               per sub- 
               per OFDM 
               OFDM 
             
             
               (Gbits/s) 
               (Mbits/s) 
               Modulation 
               rate 
               carrier 
               symbol 
               symbol 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               2.770 
               251.866 
               BPSK 
               ½ 
               1 
               991.999 
               495.999 
             
             
               5.541 
               503.732 
               QPSK 
               ½ 
               2 
               1983.998 
               991.999 
             
             
               11.082 
               1007.464 
               16-QAM 
               ½ 
               4 
               3967.997 
               1983.998 
             
             
                 
             
           
        
       
     
   
   Table 3 lists the 1,024-point IFFT of detailed timing-related parameters for each of the frequency bands: 
   
     
       
             
             
             
           
         
             
               TABLE 3 
             
             
                 
             
             
               Parameters 
               Descriptions 
               Value 
             
             
                 
             
           
           
             
               N ds   
               Number of data subcarriers 
                992 
             
             
               N ps   
               Number of pilot subcarriers 
                 8 
             
             
               N ts   
               Number of total subcarriers 
               1000 
             
             
               D fs   
               Frequency spacing for subcarrier 
               0.6347 MHz 
             
             
                 
               (650 MHz/1024) 
             
             
               T FFT   
               IFFT/FFT period (1/D fs ) 
               1.5755 μs 
             
             
               T gd   
               Guard duration (T FFT /4) 
               0.3938 ρs 
             
             
               T signal   
               Duration of the signal BPSK-OFDM symbol 
               1.9693 μs 
             
             
                 
               (T FFT  + T gd ) 
             
             
               T sym   
               Symbol interval (T FFT  + T gd ) 
               1.9693 μs 
             
             
               T short   
               Short duration of training sequence 
               3.938 μs 
             
             
                 
               (10 × T FFT /4) 
             
             
               T gd2   
               Training symbol guard duration 
               0.7877 μs 
             
             
                 
               (T FFT /2) 
             
             
               T long   
               Long duration of training sequence) 
               3.938 μs 
             
             
                 
               (2 × T FFT  + T gd2 ) 
             
             
               T preamble   
               Physical layer convergence procedure 
               7.876 μs 
             
             
                 
               preamble duration 
             
             
                 
               (T short  + T long ) 
             
             
                 
             
           
        
       
     
   
     FIG. 5  is a detailed block diagram  500  of the filtering and spreading section  246  according to some embodiments. A switch unit  510  including two switches of  520   a  and  520   b  is used to split a 1,280-parallel data sequences into two parallel data sequences with an even and an odd number, respectively. The switch  520   a  rotates to the even number of data (for example, b 2 , b 4 , b 6 , . . . ) to form a serial even data sequence, and the switch  520   b  rotates to the odd number of data (for example, b 1 , b 3 , b 5 , . . . ) to form a serial odd data sequence. The output sequences of the switches  520   a  and  520   b  are spread with a multiband spreading  524  by using two exclusive OR (XOR) of  522   a  and  522   b , respectively. Using a transmitter shaped filter  540   a  to shape the transmitter spectrum and limit the frequency band filters the serial output sequence of the XOR  522   a . The output of the transmitter shaped filter  540   a  is passed through a D/A converter  550   a , which is coupled to an analog reconstruction-filter  560   a . The analog reconstruction-filter  560   a  does a smooth of signal of the D/A converter  550   a  output. In the same way, using a transmitter shaped filter  540   b  to shape the transmitter spectrum and limit the frequency band filters the output of the serial output sequence of the XOR  522   b . The output of the transmitter shaped filter  540   b  is passed through a D/A converter  550   b  that is coupled to an analog reconstruction-filter  560   b . The analog reconstruction-filter  560   b  does smooth of the output signal of the D/A converter  550   b.    
   Referring to  FIG. 6  is a detailed block diagram  600  of the MIMO-based multiband modulation and multicarrier RF section  250  according to some embodiments. Analog output signals of the filtering and spreading from  246   a  to  246   k  as shown in  FIG. 2  in parallel are passed through eleven multiband modulations from  610   a  to  610   k . All of the multiband modulations from  610   a  to  610   k  are equivalent. The multiband modulations from  610   a  to  610   k  may be one of modulations including BPSK, QPSK, or 16-QAM. The output signals of the multiband modulations from  610   a  to  610   k  are coherently added together by using eleven sum units from  620   a  to  620   k . Then, the outputs of eleven sum units from  620   a  to  620   k  are in parallel passed through eleven analog bandpass filters from  630   a  to  630   k  to produce bandlimited signals for multiple antennas transmitter. 
   Spectrums of MIMO-Based UWB Base Station Transmitter 
     FIG. 7  is an output frequency spectrum  700  of the MIMO-based multiuser OFDM multiband of the UWB base station communication transmitter, including eleven frequency band spectrums from  720 A to  720 K according to some embodiments. A FCC emission limitation  710  for the indoor UWB operation is also shown in  FIG. 7 . Each transmitter frequency bandwidth of the eleven frequency band spectrums from  720 A to  720 K is 650 MHz and is fitted under the indoor FCC emission limitation  710  with different carrier frequencies. The detail positions of each transmitter frequency band spectrums (dBm) along with the center, lower and upper frequencies (GHz) as well as the channel frequency bandwidth (MHz) are listed in Table 4: 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE 4 
             
             
                 
             
             
                 
               Center 
               Lower 
               Upper 
               Frequency 
             
             
               Multichannel 
               Frequency 
               Frequency 
               Frequency 
               Bandwidth 
             
             
               Label 
               (GHz) 
               (GHz) 
               (GHz) 
               (MHz) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               720A 
               3.45 
               3.125 
               3.775 
               650 
             
             
               720B 
               4.10 
               3.775 
               4.425 
               650 
             
             
               720C 
               4.75 
               4.425 
               5.075 
               650 
             
             
               720D 
               5.40 
               5.075 
               5.725 
               650 
             
             
               720E 
               6.05 
               5.725 
               6.375 
               650 
             
             
               720F 
               6.70 
               6.375 
               7.025 
               650 
             
             
               720G 
               7.35 
               7.025 
               7.675 
               650 
             
             
               720H 
               8.00 
               7.675 
               8.325 
               650 
             
             
               720I 
               8.65 
               8.325 
               8.975 
               650 
             
             
               720J 
               9.30 
               8.975 
               9.625 
               650 
             
             
               720K 
               9.95 
               9.625 
               10.275 
               650 
             
             
                 
             
           
        
       
     
   
   During the indoor UWB operation, the fourth and/or fifth frequency bands of the MIMO-based multiuser OFDM multiband of the UWB base station transmitters can be turned off in order to avoid interference with the WLAN 802.11a lower U-NII frequency band and/or upper U-NII frequency band. In some cases, the MIMO multiuser OFDM multiband of the UWB base station and mobile transmitters can turn off some subcarriers within the OFDM in the fourth and/or fifth multi-frequency bands if the WLAN 802.11a only uses certain subchannels in the lower U-NII or in the upper U-NII frequency bands. 
   MIMO-Based UWB Mobile Receiver Architecture 
     FIG. 8  is a block diagram of a MIMO-based OFDM multiband of UWB mobile communication receiver  800  for the indoor UWB operation according to some embodiments. A two-antenna based multiband RF receiver unit  810 , which is coupled to an A/D unit  822 , receives the MIMO-based multiuser OFDM multiband of UWB signals from two antennas  808   a  and  808   b . The eleven bandlimited MIMO-based multiuser OFDM multiband of UWB analog signal outputs of the two-antenna based multiband RF receiver unit  810  are in parallel sampled and quantized by using an A/D converter unit  822 , with the sampling rate at 720 MHz. Using a digital receiver filter unit  824  to remove out of band signals filters the digital signals of output of the A/D converter unit  822 . Then the outputs of digital receiver filter unit  824  despread with a despreading sequence of a multiband-despreading unit  826 . The output digital signals of the multiband-despreading unit  826  are passed through time-domain equalizers (TEQ)  828 . The TEQ  828  is used to reduce the length of cyclic prefix to a more manageable number without reducing performance significantly. In other words, the TEQ  828  can produce a new target channel with a much smaller effective constraint length when concatenated with the channel. Thus, the outputs of the TEQ  828  in parallel are passed through a set of S/Ps from  830   a  to  830   k  to produce parallel digital sequences. Each of the S/Ps from  830   a  to  830   k  produces 1280 parallel digital sequences for each of guard removing units from  832   a  to  832   k . The guard removing units from  832   a  to  832   k  remove 256 samples from the 1280 parallel digital sequences of the S/Ps from  830   a  to  830   k  to produce 1024 parallel digital sequences, which are used as inputs for FFT units from  834   a  to  834   k . Each of the FFT units from  834   a  to  834   k  produces 512 frequency-domain signals that are used for frequency-domain equalizer (FEQ) units from  836   a  to  836   k . The FEQ units from  836   a  to  836   k  are used to compensate for phase distortions, which are a result of phase offsets between the sampling clocks in the transmitter and the receiver of the MIMO-based multiuser OFDM multiband of the UWB communication transceiver. This is because the phases of the received outputs of the multiband FFT units from  834   a  to  834   k  are unlikely to be exactly the same as the phases of the transmitter symbols at the input to the IFFT units from  242   a  to  242   k  of the MIMO-based multiuser OFDM multiband of UWB base station transmitter as shown in  FIG. 2 . Thus, the outputs of the FEQ units from  836   a  to  836   k  are passed through a set of P/S units from  838   a  to  838   k  to produce a serial sequence for all of the eleven frequency bands. All of the serial sequences from the parallel-to-serial (P/S) units from  838   a  to  838   k , with each sequence length of N, are added together to produce a sequence length of 11N by using a polyphase-based demultiband  840 . The output sequence of the polyphase-based demultiband  840  is passed through a despreading, deinterleaver, and decoding unit  850 . The despreading, deinterleaver, and decoding unit  850  perform despreading, deinterleaving and decoding for the MIMO-based multiuser OFDM multiband of the UWB mobile communication receiver. 
   Referring to  FIG. 9  is a detailed block diagram  900  of the two-antenna based multiband RF section receiver section  810  according to some embodiments. The outputs of the two-antenna  808   a  and  808   b  in  FIG. 8  are in parallel passed into two low noise amplifiers (LNA) from  910   a  and  910   b , which are coupled to two automatic gain controls (AGC) of  920   a  and  920   b . The outputs of the AGCs  920   a  and  920   b  are passed through two analog bandpass filters of  930   a  and  930   b  to produce two output signals that are added together by using a sum over block duration  940 . Then, an output signal of the sum over block duration  940  is in parallel passed into eleven-multiband down converters and demodulations from  950   a  to  950   k . Each of the multiband down converters and demodulations from  950   a  to  950   k  produces two output signals. 
   Referring to  FIG. 10  is a detailed block diagram  1000  of one combination section  820  according to some embodiments. This combination section  820  includes twenty-two A/D converters from  1010   a   1  and  1010   a   2  to  1010   k   1  and  1010   k   2 , twenty-two digital receiver filters from  1020   a   1  and  1020   a   2  to  1020   k   1  and  1020   k   2 , and twenty-two XOR from  1030   a   1  and  1030   a   2  to  1030   k   1  and  1030   k   2 , and eleven multiband despreading from  1040   a  to  1040   k . The outputs of the multiband down converters and demodulations from  950   a  to  950   k  in  FIG. 9  are in parallel passed through the twenty-two A/D converters from  1010   a   1  and  1010   a   2  to  1010   k   1  and  1010   k   2  to produce the quantized digital signals. All of the A/D converters from  1010   a   1  and  1010   a   2  to  1010   k   1  and  1010   k   2  use the same bit resolution and the same sampling rate. The A/D converters from  1010   a   1  and  1010   a   2  to  1010   k   1  and  1010   k   2  are coupled to the twenty-two digital receiver filters from  1020   a   1  and  1020   a   2  to  1020   k   1  and  1020   k   2 , respectively. All of the twenty-two digital receiver filters from  1020   a   1  and  1020   a   2  to  1020   k   1  and  1020   k   2  filter out of unwanted digital signals from the outputs of the twenty-two A/D converters from  1010   a   1  and  1010   a   2  to  1010   k   1  and  1010   k   2 , respectively. All of the twenty-two digital receiver filters from  1020   a   1  and  1020   a   2  to  1020   k   1  and  1020   k   2  are equivalent, which contain the same filter attenuations and the filter bandwidths with the same filter coefficients and a linear phase. The outputs of the twenty-two digital receiver filters from  1020   a   1  and  1020   a   2  to  1020   k   1  and  1020   k   2  are despread with the output sequences of the eleven multiband despreading from  1040   a  to  1040   k , respectively, by using the twenty-two XOR from  1030   a   1  and  1030   a   2  to  1030   k , and  1030   k   2 , respectively. All of the output sequences of the eleven multiband despreading from  1040   a  to  1040   k  are orthogonal each other. 
     FIG. 11  is a detailed block diagram  1100  of a combination subsection including the FFT  834  and the FEQ  836  according some embodiments. The FFT  834  has a 1024-point input of real-value and produces a 512-point complex data with labels from 0 to 511, while a 512-point complex data with labels from 511 to 1023 is disable. The FFT  834  with labels from 0 to 511 also contains 12 Nulls. So, the FFT  834  produces a 500-point complex data for the FEQ  836 . The FEQ  836  contains 500 equalizers from  1110   a   1  to  1110   a   500 , 500 decision detectors from  1120   a   1  to  1120   a   500 , and  500  subtractions from  1130   a   1  to  1130   a   500  that operate in parallel. Each of the equalizers from  1110   a   1  to  1110   a   500  has N-tap with adaptive capability. Each of the decision detectors from  1120   a   1  to  1120   a   500  is a multi-level threshold decision. Each of the subtractions from  1130   a   1  to  1130   a   500  performs subtracting between the output of each of the equalizers from  1110   a   1  to  1110   a   500  and the output of each of the decision detectors from  1120   a   1  to  1120   a   500 . The output of each of the subtraction from  1130   a   1  to  1130   a   500  is referred to as an error signal, which is used to adjust the N-tap coefficients of the each of the equalizers from  1110   a   1  to  1110   a   500  by using an adaptive algorithm  1130 . 
   The phases of the received outputs of the FFT  834  do not have exactly the same as the phases of the transmitter symbols at the input to the IFFT units from  242   a  to  242   k  of the MIMO-based multiuser OFDM multiband of UWB base station transmitter as shown in  FIG. 2 . In addition, the phase responses have to consider the channel, which is coped with the TEQ  828  as shown in  FIG. 8 . Thus, the FEQ  836  in  FIG. 11  is used to compensate for the phase distortion that is a result of a phase offset between the sampling clocks in the transmitter and the receiver of the MIMO-based multiuser OFDM multiband of the UWB communication transceiver. The FEQ  836  also offers the additional benefit of received signal scaling before decoding since the FEQ  836  can be used to adjust the gain of the FFT  834  output so that the decision detectors from  1120   a   1  to  1120   a   500  can be set the same parameters for all subchannels regardless of the different subchannel attenuations. 
     FIG. 12  is a detailed block diagram  1200  of a polyphase-based demultiband  840  according to some embodiments. The polyphase-base demultiband  840  includes eleven RAM banks from  1210   a  to  1210   k  storing parallel data, and one RAM bank of  1220  storing a serial data. The size of RAM banks from  1210   a  to  1210   k  and  1220  can be programmed. At a time unit, one of bit data from all of the eleven RAM banks from  1210   a  to  1210   k  is in parallel shifted into the RAM bank of  1220 . The RAM bank of  1220  then shifts out all the bit data. The above procedure is repeated until finishing all the bit data in the RAM banks from  1210   a  to  1210   k.    
   Referring to  FIG. 13  is a detailed block diagram  1300  of the despreading, deinterleaver, and decoding unit  850  according to some embodiments. This unit  850  includes a despreading  1310 , a user-i key  1320 , a deinterleaver  1330 , a Viterbi decoding  1340 , and a user-i bitstream  1350 . The output sequence of the polyphase-based demultiband  840  in  FIG. 8  is despread with a spreading sequence of the user-i key  1320 , which provides a unique key sequence, by using the despreading  1310 . The despreading  1310  is a XOR operation to produce an encoded user-i data bitstream. This encoded user-i data bitstream is then deinterleaved by using the deinterleaver  1330  that is also coupled to the Viterbi decoding  1340 . The Viterbi decoding  1340  decodes the encoded user-i data bitstream to produce an original transmitted user-i data bitstream that is stored into the user-i bitstream  1350 . 
   While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the present invention.