Abstract:
A spread spectrum based multichannel modulation Ultra-Wideband (UWB) communication transceiver for indoor wireless operations is presented according to some embodiments. The spread spectrum based multichannels are orthogonal to each other and allow for an operation in parallel. The UWB communication transceiver can also avoid interference with WLAN 802.11a devices in the same environment. In addition, the UWB communication transceiver of the present invention can transmit and receive the scalability chip data rates from 650 Mcps to 7.15 Gcps.

Description:
BACKGROUND 
   This invention is generally relative to wireless spread spectrum based multichannel modulation for ultra wideband communications. 
   On Apr. 22, 2002, U.S. Federal Communications Commission (FCC) released the revision of Part 15 of the Commission&#39;s rules regarding ultra-wideband (UWB) transmission systems to permit the marketing and operation of certain types of new products incorporating UWB technology. With appropriate technology, UWB device can operate using spectrum occupied by existing radio service without causing interference, thereby permitting scarce spectrum resources to be used more efficiently. The UWB technology offers significant benefits for Government, public safety, businesses, and consumers under an unlicensed basis of operation spectrum. 
   UWB device devices can be classified in three types based on the operating restrictions: (1) imaging system including ground penetrating radars and wall, through-wall, surveillance, and medical imaging device, (2) vehicular radar systems, and (3) communications and measurement systems. In general, FCC is adapting unwanted emission limits for UWB devices that are significantly more stringent than those imposed on other Part 15 devices. Limiting the frequency band, which is based on the −10 dB bandwidth of the UWB emission, within certain UWB products will be permitted to operate. For indoor communications and measurement systems, FCC provides a wide variety of UWB devices, such as high-speed home and business networking devices as well as storage tank measurement devices under Part 15 of the Commission&#39;s rules subject to certain frequency and power limitations. The indoor UWB devices must operate in the frequency band from 3.1 GHz to 10.6 GHz. UWB communication devices should also satisfy the Part 15.209 limit, which sets the indoor FCC emission limits for UWB system, for the frequency band below 960 MHz and conform the FCC&#39;s emission mask for the frequency band above 960 MHz in Table 1: 
   
     
       
             
             
             
           
         
             
                 
               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 
             
             
                 
                 
             
           
        
       
     
   
   The indoor UWB devices must be designed to ensure that operation can only occur indoor or must consist of hand held devices that may be employed for such activities as peer-to-peer operation. Such UWB devices can be used for wireless communications, particularly for short-range high-speed data transmissions suitable for broadband communication access to networks. 
   FCC proposed to define an UWB device as any device where the fractional bandwidth is greater than 0.25 based on the formula as follows: 
                   FB   =     2   ⁢     (         f   H     -     f   L           f   H     +     f   L         )         ,           (   1   )               
where f H  is the upper frequency of the −10 dB emission point and f L  is the lower frequency of the −10 dB emission point. The center frequency of the UWB transmission is defined as the average of the upper and lower −10 dB points as follows:
 
                   F   C     =           f   H     +     f   L       2     .             (   2   )               
In addition, a minimum frequency bandwidth of 500 MHz must be used for an UWB device regardless of center frequency.
 
   Given an entire frequency bandwidth of 7.5 GHz (3.1-10.6 GHz), it is difficult to design a transmitter and/or receiver device for a single UWB signal that occupies the entire frequency bandwidth from 3.1 GHz to 10.6 GHz directly. This is because we need to have a very-high speed A/D and D/A converter as well as a high-speed circuit and digital signal processor to operate an UWB device for the wireless communications. As a result, the cost of the UWB device could be expense. In addition, interference between the UWB and other devices, such as a WLAN 802.11a device, can occur because the WLAN 802.11a device operates in the lower frequency range from 5.15 GHz to 5.35 GHz or in the upper frequency range from 5.725 GHz to 5.825 GHz. Moreover, the UWB device may not be able to transmit data with scalability. 
   Due to the proliferation of 7.5 GHz UWB for wireless broadband communications, it would be desirable to have a new technology of developing one multichannel UWB solution, to reduce the interference with the WLAN 802.11a devices and to transmit and receive the transmission data rate with scalability as well as to reduce the cost for indoor UWB devices. Therefore, in this embodiment, the spread spectrum based multichannel modulation is invented for wireless indoor UWB communications. 
   Thus, there is a continuing need of spread spectrum based multichannel modulation for indoor UWB devices that enable a user to transmit the data rate with scalability and avoid the interference with WLAN 802.11a devices. 
   SUMMARY 
   In accordance with one aspect, a spread spectrum based multichannel modulation UWB communication transceiver consists of a pseudorandom noise (PN) sequence look-up table coupled to a multichannel PN sequence mapping, the multichannel PN sequence mapping coupled to a digital lowpass finite impulse response (FIR) shaping filter, and the digital lowpass FIR shaping filter coupled to a digital-to-analog (D/A) converter. 
   Other aspects are set forth in the accompanying detailed description and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of one embodiment of a wireless transmitter and receiver of an UWB communication transceiver using spread spectrum based multichannel modulation in accordance with the present invention. 
       FIG. 2  is a block diagram of a spread spectrum based multichannel modulation UWB transmitter according to some embodiments. 
       FIG. 3A  is a block diagram of one embodiment of the multichannel PN sequence mapping of the present invention. 
       FIG. 3B  is a block diagram of a polyphase implementation structure of the multichannel PN sequence mapping according to some embodiments. 
       FIG. 4  is a table of 16 orthogonal spread codes in which each code has 16 PN sequence codes according to one embodiment. 
       FIG. 5  is an indoor transmitter spectrum mark according to some embodiments. 
       FIG. 6  is a frequency response of digital shaping transmitter and/or receiver FIR filter according to one embodiment. 
       FIG. 7  is an impulse response of digital shaping transmitter and/or receiver FIR filter according to one embodiment. 
       FIG. 8  is a block diagram of one embodiment of the multichannel based multi-carrier modulation according to some embodiments. 
       FIG. 9  is a frequency spectrum including eleven transmitter channel spectrums along with an indoor FCC emission limit according to some embodiments. 
       FIG. 10  is a frequency spectrum including ten transmitter channel spectrums without the fourth channel along with an indoor FCC emission limit according to some embodiments. 
       FIG. 11  is a frequency spectrum including ten transmitter channel spectrums without the fifth channel along with an indoor FCC emission limit according to some embodiments. 
       FIG. 12  is a frequency spectrum including nine transmitter channel spectrums without the fourth and fifth channel along with an indoor FCC emission limit according to some embodiments. 
       FIG. 13  is a block diagram of a spread spectrum based multichannel demodulation UWB receiver according to some embodiments. 
       FIG. 14  is a block diagram of one embodiment of the multichannel and multi-carrier-based down converter of the present invention. 
   

   DETAILED DESCRIPTION 
   Some embodiments described herein are directed to a spread spectrum based multichannel modulation UWB communication transceiver. A UWB communication transceiver 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. 
     FIG. 1  illustrates a spread spectrum based multichannel modulation for a wireless UWB communication transmitter and receiver system  100  in accordance with one embodiment of the present invention. This system  100  includes a UWB multi-carrier and multichannel RF section  114  that receives and/or transmits multichannel UWB signals from an antenna  110  or to an antenna  120 . The section  114  is connected with an analog and digital interface section  116  that contains A/D and D/A converters. The interface section  116  is coupled to a digital baseband processing section  118 , which performs multichannel digital filtering, rake processing, spread and de-spread processing, interleaver and de-interleaver, as well as code and de-code processing. The digital baseband processing section  118  has an interface with an UWB network interface section  120 , which is coupled to an UWB network  122 . In accordance with one embodiment of the present invention, the system  100  is a so-called the spread spectrum based multichannel modulation UWB transceiver that can both transmit and receive speech, audio, images and video and data information for indoor wireless communications. 
   According to some embodiments, the spread spectrum based multichannel modulation for the UWB communication transceiver can transmit and receive the UWB signals by using one channel and/or up to 11 channels. Each channel has a frequency bandwidth of 650 MHz that can transmit 40.625 Msps. That is, a total transmission data of passing through the 11 channels can transmit the data up to 446.875 Msps. With 16 pseudorandom noise (PN) spread sequence codes for each symbol, the transmission of data rate in each channel can achieve 650 Mcps. As a result, the spread spectrum based multichannel modulation UWB system can transmit the chip data rate up to 7.150 Gcps by using all the 11 channels. 
     FIG. 2  is a block diagram of a spread spectrum based multichannel modulation UWB transmitter  200  according to some embodiments. The spread spectrum based multichannel modulation UWB transmitter  200  receives user data bits  230  with information data rate of 223.4375 Mbps. The information data bits  230  are passed through a one-second-rate convolution encoder  232  that may produce the double data rate of 446.875 Msps by adding redundancy bits. The symbol data is then interleaved by using a block interleaver  234 . Thus, the output symbols of the block interleaver  234  are formed 11 channels with the symbol data rate at 40.625 Msps by using a multichannel PN sequence mapping  238 . The multichannel PN sequence mapping  238  is to perform spreading for each channel symbol data with 16 orthogonal spread sequence chips and to produce 650 Mcps for each channel under a multichannel control  250 . A PN sequence look-up table  236  provides the unique orthogonal sequences for each channel spreading. Then each channel symbol data are sequentially passed through a digital FIR lowpass-shaping filter  240  to limit the frequency bandwidth with 650 MHz for each channel signal. Each channel signal is passed through a D/A converter  242 . The output chip data of each channel from the D/A converter  242  is then modulated with a multi-carrier by using a multichannel based multi-carrier modulator  244 . Thus, the output analog signals of the multichannel-based multi-carrier modulator  244  are passed through a power amplifier (PA)  246  through an antenna into air. 
   Referring to  FIG. 3A  is a more detailed block diagram of the multichannel PN sequence mapping  238  as shown in  FIG. 2  according to some embodiments. The serial output symbol data of the block interleaver  234  at the symbol data rate of 446.875 Msps are down-sampling by a factor of 11 using delay functions z −1    300 A- 300 J and down-sampling blocks  302 A- 302 K to generate 11 channel symbol data in parallel. Each channel symbol data rate is 40.625 Msps and each channel symbol data is passed through an Exclusive OR (XOR) function  304 A- 304 K to spread the symbol data to the chip data rate at 650 Mcps by using the 16 orthogonal spreading codes from the PN sequence look-up table  236 . As a result, a total of the chip data rate in all of the 11 channels from  306 A to  306 K is 7.15 Gcps. Each channel  306 A- 306 K is sequentially connected to the digital FIR lowpass-shaping filter  240  by using a switch  308 , thereby producing a bandlimited frequency of 650 MHz for each channel. 
   Referring to  FIG. 3B  is an alternatively detailed block diagram  300 B of implementing polyphase structure-based multichannel PN sequence mapping  238  according to a second embodiment. The serial output symbol data of the block interleaver  234  at the symbol data rate of 446.875 Msps is an input for the block diagram  300 B. A polyphase switch  301  rotates in a counterclockwise direction for the decimation system to connect the positions from  303 A to  303 K at each of symbol data. This method generates 11-multichannel symbol data in parallel. Each channel symbol data rate is 40.625 Msps. Each channel symbol data is then passed through a XOR function  304 A- 304 K to spread the symbol data to the chip data rate at 650 Mcps by using the 16 orthogonal spreading codes from the PN sequence look-up table  236 . As a result, a combination of the chip data rate in all of the 11 channels from  306 A to  306 K is 7.15 Gcps. Each channel  306 A- 306 K is sequentially connected to the digital FIR lowpass-shaping filter  240  by using a switch  308  at each 16-chip data, thereby producing a bandlimited frequency of 650 MHz for each channel. 
     FIG. 4  is a detailed table  410  of containing the 16 orthogonal spread sequences in the PN sequence look-up table  236 . Each orthogonal code has 16 spread codes in the table  410 . The orthogonal sequences have zero correlation. If the process of “XOR” is for two orthogonal binary sequences, the results are in an equal number of 1&#39;s and 0&#39;s. In the present embodiments, only 11 orthogonal sequences out of 16 orthogonal sequences in the table  410  are used for spreading in the 11 channels, thereby resulting in orthogonal channels. 
     FIG. 5  is an indoor transmitter spectrum mark  520  of a power spectral density  500  for each channel according to some embodiments. The magnitudes (dBm) of the frequency response with an error of ±δ i  (i=1, 2, 3, 4) for corresponding frequencies (GHz) are given by, 
                     (       -   41.4     -     δ   1       )     ⁢     &lt;   _     ⁢          H   ⁡     (   f   )            ⁢     &lt;   _     ⁢     (       -   41.4     +     δ   1       )       ,                    f   -     f   c            ⁢     &lt;   _     ⁢   0.26     ,                   ⁢     (   3   )                          H   ⁡     (   f   )            ⁢     &lt;   _     ⁢     (       -   51.8     +     δ   2       )       ,                    f   -     f   c            =   0.325     ,                   ⁢     (   4   )                          H   ⁡     (   f   )            ⁢     &lt;   _     ⁢     (       -   54.3     +     δ   3       )       ,                    f   -     f   c            =   0.39     ,                   ⁢     (   5   )                          H   ⁡     (   f   )            ⁢     &lt;   _     ⁢     (       -   76.8     +     δ   4       )       ,           0.45   ⁢     &lt;   _     ⁢          f   -     f   c            ⁢     &lt;   _     ⁢     0.5   .                     ⁢     (   6   )                 
The indoor transmit spectrum mark  520  serves as a rule for designing digital lowpass FIR shaping transmitter and receiver filters.
 
   Referring to  FIG. 6  is a frequency response (dBm) of the digital lowpass FIR shaping transmitter and/or receiver filter  630  for the use in each channel according to one embodiment. The result of designing this digital lowpass FIR shaping transmitter filter  630  does meet the requirements of the power spectrum density  500  as defined in  FIG. 5 . The filter sampling rate F s  may be great than or equal to 1 GHz. The present embodiment uses 2 GHz sampling rate for the digital lowpass FIR shaping transmitter filter  630 . The digital lowpass FIR shaping filter  630  may be designed using least square method with different weighting functions for each frequency band. Other techniques such as equiripple approximations and windowing may also be used. 
   Referring to  FIG. 7  is an impulse response  740  of digital lowpass FIR shaping transmitter and/or receiver FIR filter according to one embodiment. This impulse response  740  of the digital lowpass FIR shaping transmitter filter is symmetric with a total of 79 filter coefficients. Table 2 lists all the filter coefficients. The filter coefficients in Table 1 are relatively small values. However, the filter coefficients can be expressed by h[n]=C(h[n]/C). Thus, a new set of digital lowpass FIR filter coefficients q[n] is given by 
                     q   ⁡     [   n   ]       =       h   ⁡     [   n   ]       C       ,           (   7   )               
where C=10 −5 , which is referred to as a constant amplitude of the digital lowpass FIR shaping filter  740 . This expression in the equation (7) reduces the need of quantization bits for the filter coefficients.
 
   
     
       
             
             
             
           
             
             
             
           
         
             
                 
               TABLE 2 
             
             
                 
                 
             
             
                 
               Coefficients 
               Value 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               h[0] 
               8.4011931856093516e−005 
             
             
                 
               h[−1], h[1] 
               6.6460293297797776e−005 
             
             
                 
               h[−2], h[2] 
               3.4899656505824461e−005 
             
             
                 
               h[−3], h[3] 
               4.3116710798781203e−006 
             
             
                 
               h[−4], h[4] 
               −1.1214285545543695e−005 
             
             
                 
               h[−5], h[5] 
               −1.1091966005094216e−005 
             
             
                 
               h[−6], h[6] 
               −4.0631985867674594e−006 
             
             
                 
               h[−7], h[7] 
               1.6925543297452028e−006 
             
             
                 
               h[−8], h[8] 
               3.7995683513152043e−006 
             
             
                 
               h[−9], h[9] 
               3.5715207002110990e−006 
             
             
                 
               h[−10], h[10] 
               2.1069446071156423e−006 
             
             
                 
               h[−11], h[11] 
               −3.6643652826194515e−007 
             
             
                 
               h[−12], h[12] 
               −2.8164861523475095e−006 
             
             
                 
               h[−13], h[13] 
               −3.3131485713709617e−006 
             
             
                 
               h[−14], h[14] 
               −1.1423931641665744e−006 
             
             
                 
               h[−15], h[15] 
               1.8766255546648780e−006 
             
             
                 
               h[−16], h[16] 
               3.0434874609545600e−006 
             
             
                 
               h[−17], h[17] 
               1.5335471709233686e−006 
             
             
                 
               h[−18], h[18] 
               −9.2517743205833720e−007 
             
             
                 
               h[−19], h[19] 
               −2.0795608829123639e−006 
             
             
                 
               h[−20], h[20] 
               −1.3294520798670319e−006 
             
             
                 
               h[−21], h[21] 
               1.5173609022831139e−007 
             
             
                 
               h[−22], h[22] 
               1.0025701140610793e−006 
             
             
                 
               h[−23], h[23] 
               8.8427894743416094e−007 
             
             
                 
               h[−24], h[24] 
               3.2126248293514667e−007 
             
             
                 
               h[−25], h[25] 
               −1.6257131448705735e−007 
             
             
                 
               h[−26], h[26] 
               −4.2373069355925035e−007 
             
             
                 
               h[−27], h[27] 
               −4.9081265774967211e−007 
             
             
                 
               h[−28], h[28] 
               −3.2008852157750218e−007 
             
             
                 
               h[−29], h[29] 
               7.1976640681523624e−008 
             
             
                 
               h[−30], h[30] 
               4.4865425611366231e−007 
             
             
                 
               h[−31], h[31] 
               4.8145760999611724e−007 
             
             
                 
               h[−32], h[32] 
               1.1716686662078990e−007 
             
             
                 
               h[−33], h[33] 
               −3.2175597663148811e−007 
             
             
                 
               h[−34], h[34] 
               −4.3124038368895124e−007 
             
             
                 
               h[−35], h[35] 
               −1.5028657655143136e−007 
             
             
                 
               h[−36], h[36] 
               2.0356981673707622e−007 
             
             
                 
               h[−37], h[37] 
               2.8036698051837603e−007 
             
             
                 
               h[−38], h[38] 
               7.1364948530875849e−008 
             
             
                 
               h[−39], h[39] 
               −1.4582779654249872e−007 
             
             
                 
                 
             
           
        
       
     
   
   The implementation output y[n] of the digital lowpass FIR shaping transmitter filter with 79 symmetric coefficients can be expressed as, 
                     p   ⁡     [   n   ]       =       ∑     k   =   0     78     ⁢           ⁢       q   ⁡     [   n   ]       ⁢     x   ⁡     [     n   -   k     ]             ,           (   8   )               
and
   y[n]=Cp[n],   (9) 
where q[n]=h[n]/C is the new set of the digital lowpass FIR shaping filter coefficients  740  and x[n] is the digital input signal. Since the digital lowpass FIR shaping transmitter filter  740  is symmetric coefficients, the above equation (8) can be rewritten as
 
                     p   ⁡     [   n   ]       =         ∑     k   =   0     38     ⁢           ⁢       q   ⁡     [   n   ]       ⁢     (       x   ⁡     [     n   -   k     ]       +     x   ⁡     [     n   -   78   +   k     ]         )         +       q   ⁡     [   39   ]       ⁢     x   ⁡     [     n   -   39     ]             ,           (   10   )               
and
   y[n]=Cp[n].   (11) 
The equation (10) can be implemented with saving half computation complexities and with reducing the number of quantization bits for the digital lowpass FIR shaping transmitter filter  740 .
 
     FIG. 8  is a block diagram  800  of the multichannel-based multi-carrier modulator  244  according to some embodiments. The output signal of the D/A converter  242  is first passed through an analog lowpass filter  850  in which reconstructs and smoothes the UWB signal into a time-domain UWB signal. The time-domain UWB signal is multiplied  852  by one of the multi-carriers of the commutator unit  856 . The commutator unit  856  can select one of the multi-carriers from selectable multi-carrier frequencies  858  by using a switch function  854 . Both the commutator unit  856  and the selectable multi-carrier frequencies  858  are controlled to form a serial multi-carrier signal by the multichannel control  250 . Then, the time-domain UWB signals with multi-carriers are sequentially passed the PA  246  through an antenna into air. 
   Referring to  FIG. 9 , which is an output of multi-carrier frequency spectrums (dBm)  900  including 11 transmitter channel spectrums  962 A- 962 K along with the indoor FCC emission limitation  960  according to some embodiments. Each channel frequency bandwidth is 650 MHz and is fitted under the indoor FCC emission limitation  960  with different carrier frequencies. The detail positions of each transmitter channel spectrums (dBm) along with the center, lower and upper frequencies (GHz) as well as channel frequency bandwidth (MHz) are listed in Table 3. 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE 3 
             
             
                 
             
             
               Label of 
               Center 
               Lower 
               Upper 
               Frequency 
             
             
               transmitter 
               Frequency 
               Frequency 
               Frequency 
               Bandwidth 
             
             
               channels 
               (GHz) 
               (GHz) 
               (GHz) 
               (MHz) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               962A 
               3.45 
               3.125 
               3.775 
               650 
             
             
               962B 
               4.10 
               3.775 
               4.425 
               650 
             
             
               962C 
               4.75 
               4.425 
               5.075 
               650 
             
             
               962D 
               5.40 
               5.075 
               5.725 
               650 
             
             
               962E 
               6.05 
               5.725 
               6.375 
               650 
             
             
               962F 
               6.70 
               6.375 
               7.025 
               650 
             
             
               962G 
               7.35 
               7.025 
               7.675 
               650 
             
             
               962H 
               8.00 
               7.675 
               8.325 
               650 
             
             
               962I 
               8.65 
               8.325 
               8.975 
               650 
             
             
               962J 
               9.30 
               8.975 
               9.625 
               650 
             
             
               962K 
               9.95 
               9.625 
               10.275 
               650 
             
             
                 
             
           
        
       
     
   
   Referring to  FIG. 10  is an output of multi-carrier frequency spectrums  1000  including 10 transmitter channel spectrums  1064 A- 1064 C,  1064 E- 1064 K, along with the indoor FCC emission limitation  960  according to some embodiments. There is no fourth channel with a frequency range from 5.075 GHz to 5.725 GHz in the frequency spectrums  1000 . By not transmitting the fourth channel, the interference between indoor UWB communication devices and WLAN 802.11a lower band can be avoided since the WLAN 802.11a lower band is in the frequency range from 5.15 GHz to 5.35 GHz, thereby resulting in coexistence. 
   Referring to  FIG. 11  is an output of multi-carrier frequency spectrums  1100  including 10 transmitter channel spectrums  1166 A- 1166 D,  1166 F- 1166 K, along with the indoor FCC emission limitation  960  according to some embodiments. Note that there is no fifth channel with a frequency range from 5.725 GHz to 6.375 GHz in the frequency spectrums  1100 . By not transmitting the fifth channel, the interference between UWB communication devices and WLAN 802.11a upper band can be eliminated. This is because the WLAN 802.11a upper band is in the frequency range from 5.725 GHz to 5.825 GHz, thereby resulting in UWB and WLAN 802.11a coexistence. 
   Now referring to  FIG. 12  is an output of multi-carrier frequency spectrums  1200  including 9 transmitter channel spectrums  1268 A- 1268 C,  1268 F- 1268 K, along with the indoor FCC emission limitation  960  according to some embodiments. The frequency spectrum  1200  does not include both of the fourth and the fifth channels with a frequency range from 5.075 GHz to 6.375 GHz. By not transmitting the fourth and fifth channels at the same time, the interference between UWB communication devices and WLAN 802.11a lower and upper bands can be avoided. This is because the WLAN 802.11a lower and upper bands are in the frequency ranges from 5.150 GHz to 5.350 GHz and from 5.725 GHz to 5.825 GHz, respectively. As a result, the interference can be avoided between indoor UWB devices and WLAN 802.11a devices by not transmitting the fourth and fifth channels of the spread spectrum based multichannel modulation for UWB communication devices. 
     FIG. 13  is a block diagram of spread spectrum based multichannel demodulation UWB receiver  1300  according to some embodiments. A low noise amplifier (LNA)  1360 , which is coupled to a multichannel based multi-carrier down converter  1362 , receives the UWB signals from an antenna. The output of the LNA  1360  is passed through the multichannel based multi-carrier down converter  1362  to produce baseband signal for an A/D converter  1364 . A multichannel control  1370  and synchronization and time control  1368  restrain the multichannel-based multi-carrier down converter  1362 . The bandlimited UWB analog signals are then sampled and quantized by using the A/D converter  1364 , with the sampling rate at ≧650 MHz. The digital UWB signals of the output of the A/D converter  1364  are filtered by using a digital FIR receiver lowpass filter  1366  to remove the out of band signals with controlling from the synchronization and time control  1368 . The output data from the digital FIR receiver lowpass filter  1366  is used for a rake receiver  1374 . A channel estimator  1372  is used to estimate channel phase and frequency that are passed into the rake receiver  1374 . The rake receiver  1374  calculates a correlation between the received UWB signals and the channel spread sequences, which are provided by using the PN sequence look-up table  1382 , and performs coherent combination. The output of the rake receiver  1374  is passed to an equalizer  1376 , which also receives the information from the channel estimator  1372 , to eliminate inter-symbol interference (ISI) and inter-channel interference (ICI). Then, the output of the equalizer  1376  produces the signals for a de-spreading of PN sequence and de-mapping  1378  to form the UWB signals of symbol rate at 446.875 Msps. The symbol data is de-interleaved by using a block de-interleaver  1380 . Thus, the output data of the block de-interleaver  1380  is used for the Viterbi decoder  1384  to decode the encoded data and to produce the information data bits at 223.4375 Mbps. 
   Referring to  FIG. 14 , which is a detailed block diagram  1400  showing one embodiment of the multichannel based multi-carrier down converter  1362  of the present invention. The analog bandpass filter  1470  receives the signals from the LNA  1360  to produce the bandlimited signals for a down converter  1472 . The down converter  1472  then generates the baseband signals by multiplying a multi-carrier signal from a commutator unit  1478 , which selects one of 11 multi-carriers from selectable multi-carrier frequencies  1480  by a switch  1476 . The output of the down converter  1472  is passed through a multichannel filter  1474  to reduce the unwanted signal bands. Thus, the bandlimited signal is passed to the A/D converter  1364  with the sampling rate at ≧650 MHz. 
   While the present inventions have 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 these present inventions.