Abstract:
A multichannel filter-based handheld UWB communication transceiver is presented for outdoor operations. Using eleven multichannels with multicarrier modulations, the invented handheld UWB communication transceiver can transmit and receive UWB signals at a data rate up to 7.15 Gcps with scalability capabilities. In addition, the handheld UWB communication transceiver can be controlled in a programmable way to avoid interference with WLAN devices.

Description:
BACKGROUND 
   This invention is generally relative to wireless outdoor handheld 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. It has been known that UWB technology offers significant benefits for Government, public safety, businesses and consumers under an unlicensed basis of operation spectrum. 
   UWB 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. In other words, FCC limits outdoor use of UWB devices to imaging systems, vehicular radar systems and handheld 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. 
   The outdoor handheld UWB systems are intended to operate in a peer-to-peer mode without restriction on location. The handheld UWB device must operate in the frequency band from 3.1 GHz to 10.6 GHz, with an extremely conservative out of band emission mask to address interference with other devices. The handheld UWB devices are permitted to emit at or below the Part 15.209 limit in the frequency band below 960 MHz. The emissions above 960 MHz must conform to the following emissions mask as shown in Table 1: 
   
     
       
             
             
             
           
         
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
               Frequency (MHz) 
               EIRP (dBm) 
             
             
                 
                 
             
           
           
             
                 
                0-960 
               −41.3 
             
             
                 
                960-1610 
               −75.3 
             
             
                 
               1610-1900 
               −63.3 
             
             
                 
               1900-3100 
               −61.3 
             
             
                 
                3100-10600 
               −41.3 
             
             
                 
               Above 10600 
               −61.3 
             
             
                 
                 
             
           
        
       
     
   
   FCC proposed to define a 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 with a scalability of the transmission data rate, which not only reduces the interference with WLAN 802.11a devices but also has a lower cost for an outdoor handheld UWB transceiver. The multichannel UWB solution highly depends on a multichannel filter, which must meet the FCC request of the outdoor emission limitation, to provide the multichannel-based multi-carrier modulation. Therefore, in this embodiment, the multichannel filter-based outdoor handheld ultra wideband communications is invented for wireless broadband communications. 
   Thus, there is a continuing need of the multichannel filter-based outdoor handheld UWB transceivers that enables a user to transmit the data rate with programmability and scalability and avoid the interference with WLAN 802.11a devices. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block diagram of one embodiment of a multichannel filter-based outdoor handheld UWB communication system in accordance with the present invention. 
       FIG. 2  is a block diagram of a multichannel filter-based UWB transmitter of outdoor handheld UWB transceiver according to some embodiments. 
       FIG. 3  is a block diagram of a multichannel filter-based UWB receiver of outdoor handheld UWB transceiver according to some embodiments. 
       FIG. 4  is a transmitter spectrum mark of an outdoor power spectral density according to some embodiments. 
       FIG. 5  is a frequency and impulse response of a digital FIR lowpass-shaping filter for use in the transmitter and/or receiver according to one embodiment. 
       FIG. 6  is a frequency spectrum of 11 multichannel spectrums and outdoor FCC emission limit according to some embodiments. 
       FIG. 7  is a block diagram of a digital cascaded FIR filter including a digital multiband FIR lowpass shaping filter and digital FIR rejected lowpass filter according to one embodiment. 
       FIG. 8  is an enlarged transmitter spectrum mark of the outdoor power spectral density according to some embodiments. 
       FIG. 9  is a frequency and impulse response of digital enlarged FIR lowpass shaping filter for use in the transmitter and/or receiver according to one embodiment. 
       FIG. 10  is a frequency response of digital multiband FIR lowpass shaping filter with image response for use in the transmitter and/or receiver according to one embodiment. 
       FIG. 11  is a rejected transmitter image spectrum mark of the outdoor power spectral density according to some embodiments. 
       FIG. 12  is a frequency and impulse response of digital FIR rejected filter to eliminate the image response for use in the transmitter and/or receiver according to one embodiment. 
       FIG. 13  is a frequency response of digital cascaded FIR filter of combining the digital multiband FIR lowpass shaping filter and the digital FIR rejected filter. 
       FIG. 14  is a frequency spectrum of 11 multichannel spectrums using the digital FIR cascaded filter and the outdoor FCC outdoor emission limit according to some embodiments. 
       FIG. 15  is a frequency spectrum including 10-multichannel spectrums (without the fourth channel) and the outdoor FCC emission limit according to some embodiments. 
       FIG. 16  is a frequency spectrum including 10-multichannel spectrums (without the fifth channel) and the outdoor FCC emission limit according to some embodiments. 
       FIG. 17  is a frequency spectrum including 9-multichannel spectrums (without the fourth and fifth channel) and the outdoor FCC emission limit according to some embodiments. 
   

   DETAILED DESCRIPTION 
   Some embodiments described herein are directed to a multichannel filter-based handheld UWB communications for outdoor operation. The outdoor handheld UWB communication 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. 
   A multichannel filter-based handheld UWB communication transceiver  100  for outdoor operations is shown in  FIG. 1  in accordance with one embodiment of the present invention. This outdoor handheld UWB transceiver  100  contains a UWB multi-carrier and multichannel RF section  114  that receives and/or transmits multichannel-based UWB signals from an antenna  110  or to an antenna  112 . The section  114  is coupled to an analog and digital interface section  116  that includes A/D and D/A converters. The interface section  116  is also connected with a digital baseband processing section  118  that implements multichannel digital filtering, rake processing, spread and de-spread processing, interleaver and de-interleaver, and code and de-code processing. The digital baseband processing section  118  has an interface with a UWB network interface section  120 , which is coupled to a UWB network  122 . In accordance with one embodiment of the present invention, the UWB communication transceiver  100  is used for the outdoor handheld UWB communications that can both transmit and receive speech, audio, images and video and data information with programmability and scalability. 
   The handheld UWB communication transceiver  100  can transmit and/or receive the UWB signals by using one single channel and/or up to 11-multichannel. Each channel has a frequency bandwidth of 650 MHz. The UWB transceiver  100  can transmit 40.625 Msps with a single channel. A total of 11-multichannel can allow the UWB transceiver  100  to transmit 446.875 Msps in parallel. With 16 PN spread sequence codes for each symbol, the UWB transceiver  100  can transmit 650 Mcps within each channel. As a result, the handheld UWB communication transceiver  100  can transmit and/or the chip data rate up to 7.150 Gcps for the outdoor operation. 
     FIG. 2  is a block diagram of a multichannel filter-based UWB transmitter  200  of the outdoor handheld UWB transceiver according to some embodiments. The UWB transmitter  200  receives user data bits  210  with information data rate of 223.4375 Mbps. The information data bits  210  are passed through a ½-rate convolution encoder  212  that may produce a double data rate of 446.875 Msps by adding redundancy bits. The symbol data is then interleaved by using a block interleaver  214 . Thus, the output symbols of the block interleaver  214  are formed the 11-multichannel UWB signal by using a multichannel PN sequence mapping  218 . Each channel has the symbol data rate of 40.625 Msps. The multichannel PN sequence mapping  218  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  230 . A PN sequence look-up table  216  provides the unique orthogonal sequences for each channel spreading. Then each channel symbol data are sequentially passed through a digital FIR shaping filter system  220  to limit the frequency bandwidth of UWB signal with 650 MHz for each channel transmission. Each channel signal is then passed through a D/A converter  222 . The output chip data of each channel from the D/A converter  222  is thus modulated with a multi-carrier by using a multichannel based multi-carrier modulator  224 . Then, the output analog signals of the multichannel-based multi-carrier modulator  224  are passed to the power amplifier (PA)  226  through an antenna into air. 
     FIG. 3  is a block diagram of a multichannel filter-based outdoor handheld UWB receiver  300  according to some embodiments. A low noise amplifier (LNA)  310  that is connected with a multichannel-based multi-carrier down converter  312  receives the UWB signals from an antenna. The output of the LNA  310  is passed through the multichannel-based multi-carrier down converter  312  to produce the baseband signal for an A/D converter  314 . A multichannel control  320  and synchronization and time control  318  restrain the multichannel-based multi-carrier down converter  312 . The bandlimited UWB analog signals are then sampled and quantized by using the A/D converter  314 , with the sampling rate at ≧650 MHz. The digital signals of the output of the A/D converter  314  are filtered by using a digital FIR receiver lowpass filter  316  to remove the out of band signals with controlling from the synchronization and time control  318 . The output data from the digital FIR receiver lowpass filter  316  is used for a rake receiver  324 . The channel estimator  322  is used to estimate the channel phase and frequency that are passed into the rake receiver  324 . The rake receiver  324  calculates the correlation between the received UWB signals and the channel spread sequences, which are provided by using the PN sequence look-up table  332 , and performs coherent combination. The output of the rake receiver  324  is passed to an equalizer  326 , which also receives the information from the channel estimator  322 , to eliminate inter-symbol interference (ISI) and inter-channel interference (ICI). Then, the output of the equalizer  326  produces the signals for a de-spreading of PN sequence and de-mapping  328  to form the UWB signals of symbol rate at 446.875 Msps. The symbol data is de-interleaved by using a block de-interleaver  330 . Thus, the output data of the block de-interleaver  330  is used for the Viterbi decoder  334  to decode the encoded data and to produce the information data bits at 223.4375 Mbps. 
     FIG. 4  is a transmitter spectrum mark  420  of the outdoor power spectral density  400  for the use in the each channel filter 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,
 (−41.8−δ i )≦| H ( f )|≦(−41.8+δ 1 ), |f−f c |≦0.26,  (3) | H ( f )|≦(−61.8+δ 2 ), |f−f c |=0.325,  (4) | H ( f )|≦(−63.8+δ 3 ), |f−f c |=0.39,  (5) | H ( f )|≦(−75.8+δ 4 ), 0.45≦|f−f c |≦0.5.  (6) 
The transmitter spectrum mark  420  serves as a rule for designing a digital FIR lowpass-shaping transmitter and/or receiver filters.
 
   Referring to  FIG. 5  is a frequency response (dBm)  510  and impulse response  520  of digital FIR lowpass-shaping transmitter and/or receiver filter  500  based on the transmitter spectrum mask  420  in  FIG. 4  for the use in each channel according to one embodiment. The result of designing the digital FIR lowpass-shaping filter  520  does meet the requirements of the transmitter spectrum mask  420  of the outdoor power spectrum density  400  as defined in  FIG. 4 . The sampling frequency rate F s  of this filter is 2 GHz. This impulse response  520  of the digital FIR lowpass-shaping filter is an even coefficient symmetric about h[0] at n=0 with a total of 83 filter coefficients. Table 2 lists all the filter coefficients of the digital FIR lowpass-shaping filter. 
   
     
       
             
             
             
           
             
             
             
           
         
             
                 
               TABLE 2 
             
             
                 
                 
             
             
                 
               Coefficients 
               Value 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               h[0] 
               7.6488735705936605e-005 
             
             
                 
               h[−1], h[1] 
               6.2636205884599369e-005 
             
             
                 
               h[−2], h[2] 
               3.8360738472336015e-005 
             
             
                 
               h[−3], h[3] 
               1.1315222826039952e-005 
             
             
                 
               h[−4], h[4] 
               −7.5438087863256088e-006 
             
             
                 
               h[−5], h[5] 
               −1.3715350107903802e-005 
             
             
                 
               h[−6], h[6] 
               −9.6549464333329795e-006 
             
             
                 
               h[−7], h[7] 
               −1.4025569435129311e-006 
             
             
                 
               h[−8], h[8] 
               5.3003810907673923e-006 
             
             
                 
               h[−9], h[9] 
               7.2459334117828691e-006 
             
             
                 
               h[−10], h[10] 
               4.3825454945279616e-006 
             
             
                 
               h[−11], h[11] 
               −7.3762240948801741e-007 
             
             
                 
               h[−12], h[12] 
               −4.5458747488001017e-006 
             
             
                 
               h[−13], h[13] 
               −4.7131566336279298e-006 
             
             
                 
               h[−14], h[14] 
               −1.6403017957724223e-006 
             
             
                 
               h[−15], h[15] 
               2.0411082705529443e-006 
             
             
                 
               h[−16], h[16] 
               3.6642171169389545e-006 
             
             
                 
               h[−17], h[17] 
               2.4832733363889074e-006 
             
             
                 
               h[−18], h[18] 
               −1.2626402560439206e-007 
             
             
                 
               h[−19], h[19] 
               −2.1121354877069656e-006 
             
             
                 
               h[−20], h[20] 
               −2.3106300667210457e-006 
             
             
                 
               h[−21], h[21] 
               −9.9696474129624093e-007 
             
             
                 
               h[−22], h[22] 
               6.8001098631267257e-007 
             
             
                 
               h[−23], h[23] 
               1.6055470083229580e-006 
             
             
                 
               h[−24], h[24] 
               1.3544197859980424e-006 
             
             
                 
               h[−25], h[25] 
               2.8906713844065611e-007 
             
             
                 
               h[−26], h[26] 
               −7.7640460252440758e-007 
             
             
                 
               h[−27], h[27] 
               −1.1590268443143087e-006 
             
             
                 
               h[−28], h[28] 
               −7.2082016980864959e-007 
             
             
                 
               h[−29], h[29] 
               1.0449113646872343e-007 
             
             
                 
               h[−30], h[30] 
               7.0581527869524552e-007 
             
             
                 
               h[−31], h[31] 
               7.2894825863413297e-007 
             
             
                 
               h[−32], h[32] 
               2.7772069871654161e-007 
             
             
                 
               h[−33], h[33] 
               −2.5824128353050490e-007 
             
             
                 
               h[−34], h[34] 
               −5.0913724964550914e-007 
             
             
                 
               h[−35], h[35] 
               −3.7669532172385286e-007 
             
             
                 
               h[−36], h[36] 
               −3.2564239303970273e-008 
             
             
                 
               h[−37], h[37] 
               2.4370835675220430e-007 
             
             
                 
               h[−38], h[38] 
               2.9201867311458947e-007 
             
             
                 
               h[−39], h[39] 
               1.4137476178313894e-007 
             
             
                 
               h[−40], h[40] 
               −5.5504489846808052e-008 
             
             
                 
               h[−41], h[41] 
               −1.7766983155229356e-007 
             
             
                 
                 
             
           
        
       
     
   
   The digital FIR lowpass-shaping filter may be designed using the least square method with weighting function for each frequency band. Other techniques such as equiripple approximations and windowing may also be used. 
   The implementation output y[n] of the digital FIR lowpass-shaping filter with 83 even symmetric coefficients can be expressed as, 
                     y   ⁡     [   n   ]       =       ∑     k   =   0     82     ⁢           ⁢       h   ⁡     [   n   ]       ⁢     x   ⁡     [     n   -   k     ]             ,           (   7   )               
where h[n] is a set of the digital FIR lowpass-shaping filter coefficients as shown in Table 2 and x[n] is the digital input signal. Since the digital FIR lowpass-shaping filter  520  is even symmetric coefficients, the above equation (7) can be rewritten as
 
                   y   ⁡     [   n   ]       =         ∑     k   =   0     40     ⁢           ⁢       h   ⁡     [   n   ]       ⁢     (       x   ⁡     [     n   -   k     ]       +     x   ⁡     [     n   -   82   +   k     ]         )         +       h   ⁡     [   42   ]       ⁢       x   ⁡     [     n   -   42     ]       .                 (   8   )               
The equation (8) can be implemented with saving half taps of the computation. The computation complexity of implementing this digital FIR lowpass-shaping filter in equation (8) is 42 multiplications and 82 additions.
 
   Referring to  FIG. 6 , which is an output of a multichannel spectrum (dBm) with multi-carrier frequencies  600  including 11-transmitter channel spectrums  620 A- 620 K and the outdoor FCC emission limitation  610  according to some embodiments. Each channel frequency bandwidth is 650 MHz with different carrier frequencies, and is fitted under the outdoor FCC emission limitation  610 . 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 
             
             
                 
             
             
                 
               Center 
               Lower 
               Upper 
               Frequency 
             
             
               Label of the channel 
               Frequency 
               Frequency 
               Frequency 
               Bandwidth 
             
             
               frequency spectrums 
               (GHz) 
               (GHz) 
               (GHz) 
               (MHz) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               620A 
               3.45 
               3.125 
               3.775 
               650 
             
             
               620B 
               4.10 
               3.775 
               4.425 
               650 
             
             
               620C 
               4.75 
               4.425 
               5.075 
               650 
             
             
               620D 
               5.40 
               5.075 
               5.725 
               650 
             
             
               620E 
               6.05 
               5.725 
               6.375 
               650 
             
             
               620F 
               6.70 
               6.375 
               7.025 
               650 
             
             
               620G 
               7.35 
               7.025 
               7.675 
               650 
             
             
               620H 
               8.00 
               7.675 
               8.325 
               650 
             
             
               620I 
               8.65 
               8.325 
               8.975 
               650 
             
             
               620J 
               9.30 
               8.975 
               9.625 
               650 
             
             
               620K 
               9.95 
               9.625 
               10.275 
               650 
             
             
                 
             
           
        
       
     
   
   In order to reduce the number of filter taps for the digital FIR lowpass shaping transmitter filter, an efficient design method  700  of the two cascaded filters may be used as shown in  FIG. 7 . The first filter  710  is referred to as the digital multiband lowpass-shaping filter. The second filter  720  is called the digital rejected lowpass filter. The combinations of the first digital FIR lowpass-shaping filter  710  and the second digital rejected lowpass filter  720  meet the frequency spectrum requirement of the transmitter spectrum mark  420  of the outdoor power spectrum density  400  as shown in  FIG. 4 . 
   Referring to  FIG. 8 , which is an enlarged transmitter spectrum mark  820  of the power spectral density  800  for the use of the digital multiband lowpass-shaping filter  710  according to some embodiments. The enlarged transmitter spectrum mark  820  is a double frequency bandwidth of the transmitter spectrum mask  420  of the outdoor power spectrum density  400  as shown in  FIG. 4 . 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,
 
(−41.8−δ i )≦| H ( f )|≦(−41.8+δ 1 ), |f−f c |≦0.26,  (3)
 
| H ( f )|≦(−61.8+δ 2 ), |f−f c |=0.325,  (4)
 
| H ( f )|≦(−63.8+δ 3 ), |f−f c |=0.39,  (5)
 
| H ( f )|≦(−75.8+δ 4 ), 0.45≦|f−f c |≦0.5.  (6)
 
The enlarged transmitter spectrum mark  820  serves as a rule for designing a digital multiband lowpass-shaping transmitter filter for the multichannel modulation.
 
   Referring to  FIG. 9  is a frequency response (dBm)  910  and impulse response  920  of the digital enlarged lowpass-shaping transmitter  900  based on the enlarged transmitter spectrum mask  820  of the power spectrum density  800  in  FIG. 8  according to one embodiment. This impulse response  920  of the digital enlarged lowpass-shaping filter is an even coefficient symmetric about h[0] at n=0 with a total of 51 filter coefficients. Table 4 lists all the enlarged filter coefficients. 
   
     
       
             
             
             
           
             
             
             
           
         
             
                 
               TABLE 4 
             
             
                 
                 
             
             
                 
               Coefficients 
               Value 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               h[0] 
               1.4905382621261000e-004 
             
             
                 
               h[−1], h[1] 
               7.6680648491640600e-005 
             
             
                 
               h[−2], h[2] 
               −1.5178410889857596e-005 
             
             
                 
               h[−3], h[3] 
               −1.9246816367394734e-005 
             
             
                 
               h[−4], h[4] 
               1.0575089944159355e-005 
             
             
                 
               h[−5], h[5] 
               8.8048715073563623e-006 
             
             
                 
               h[−6], h[6] 
               −9.0052188618312217e-006 
             
             
                 
               h[−7], h[7] 
               −3.4989976830573730e-006 
             
             
                 
               h[−8], h[8] 
               7.2999338857814008e-006 
             
             
                 
               h[−9], h[9] 
               1.3688399180492002e-007 
             
             
                 
               h[−10], h[10] 
               −4.7454858992689909e-006 
             
             
                 
               h[−11], h[11] 
               8.2887506682015732e-007 
             
             
                 
               h[−12], h[12] 
               3.1263713712333295e-006 
             
             
                 
               h[−13], h[13] 
               −1.0335732862655074e-006 
             
             
                 
               h[−14], h[14] 
               −2.2027524428255945e-006 
             
             
                 
               h[−15], h[15] 
               1.1349107902073455e-006 
             
             
                 
               h[−16], h[16] 
               1.5322309394969939e-006 
             
             
                 
               h[−17], h[17] 
               −1.1207672214842861e-006 
             
             
                 
               h[−18], h[18] 
               −1.0179971177063034e-006 
             
             
                 
               h[−19], h[19] 
               9.9455220021528296e-007 
             
             
                 
               h[−20], h[20] 
               7.1533195938216734e-007 
             
             
                 
               h[−21], h[21] 
               −8.7419141944548621e-007 
             
             
                 
               h[−22], h[22] 
               −5.5965129818442147e-007 
             
             
                 
               h[−23], h[23] 
               9.0256580368692782e-007 
             
             
                 
               h[−24], h[24] 
               2.8080835334095955e-007 
             
             
                 
               h[−25], h[25] 
               −7.3657896684832648e-007 
             
             
                 
                 
             
           
        
       
     
   
   Referring to  FIG. 10  is a frequency response (dBm)  1010  of the digital multiband lowpass-shaping transmitter filter according to some embodiments. The center frequency band shaping of the frequency response  1010  meets the requirement of the transmitter spectrum mark  420  of the power spectrum density  400  as shown in  FIG. 4 . This digital multiband lowpass-shaping filter has a symmetric image band that is created by inserting one zero in between every two filter coefficients of the digital enlarged lowpass shaping filter. In other words, the digital multiband lowpass-shaping filter  1010  has 51 filter taps and 50 zeros. The filter does not need to implement the zero coefficients. As a result, the computation complexity of implementing this digital multiband lowpass-shaping filter  1010  is 26 multiplications and 50 additions. 
     FIG. 11  is a rejected transmitter image spectrum mark  1120  of the power spectral density  1100  for the use to eliminate the image bands of the digital multiband lowpass-shaping filter  1010  according to some embodiments. The magnitudes (dBm) of the frequency response with an error of ±δ i  (i=1, 2) for corresponding frequencies (GHz) are given by,
 (30.0−δ 1 )≦| H ( f )|≦(30+δ 1 ), |f−f c |≦0.28,  (3) | H ( f )|≦(−18.3+δ 2 ), 0.7≦|f−f c |≦1.  (6) 
The rejected transmitter image spectrum mark  1120  serves as a rule for designing a second digital rejected lowpass filter  720  as shown in  FIG. 7 .
 
   Referring to  FIG. 12  is a frequency response  1210  and impulse response  1220  of the digital rejected lowpass filter according to some embodiments. This digital filter is even symmetric with 10 filter coefficients. The computation complexity of this digital filter is 5 multiplications and 9 additions. Table 5 lists all the filter coefficients of the digital rejected lowpass filter. 
   
     
       
             
             
             
           
             
             
             
           
         
             
                 
               TABLE 5 
             
             
                 
                 
             
             
                 
               Coefficients 
               Value 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               h[−1], h[1] 
               4.4130491021078377e-001 
             
             
                 
               h[−2], h[2] 
               1.3499284445782986e-001 
             
             
                 
               h[−3], h[3] 
               −6.2314200832043407e-002 
             
             
                 
               h[−4], h[4] 
               −3.3159624664790568e-002 
             
             
                 
               h[−5], h[5] 
               1.2925496194348735e-002 
             
             
                 
                 
             
           
        
       
     
   
   Now referring to  FIG. 13  is a frequency response of the digital cascaded FIR filter  1310  by combining the digital multiband lowpass-shaping filter  1010  and the digital rejected lowpass filter  1210 . The result of this digital cascaded FIR filter  1310  exactly meet the requirement of the transmitter spectrum mask  420  of the power spectrum density  400  in  FIG. 4 . 
   The digital cascaded FIR filter  1310  of the digital multiband lowpass-shaping filter  1010  and the digital rejected lowpass filter  1210  has a total of 28 multiplications and 53 additions. Comparing with the single digital FIR lowpass-shaping filter  510 , the digital cascaded FIR filter  1310  can save the computation complexity up to 41.67% of the multiplications and 43.62% additions. This leads to save the processing power, memory, and silicon area for the multichannel filter-based outdoor handheld UWB communication device. 
   Referring to  FIG. 14  is an output of multichannel frequency spectrums (dBm)  1400  with multi-carriers, which are generated by using the digital cascaded FIR filter  1310 , including 11-transmitter channel spectrums  1420 A- 1420 K along with the outdoor FCC emission limitation  610  according to some embodiments. Each channel frequency bandwidth is 650 MHz with different carrier frequencies, and is fitted under the outdoor FCC emission limitation  610 . 
   Referring to  FIG. 15  is an output of multichannel frequency spectrums  1500  with multi-carriers including 10-transmitter channel spectrums  152064 A- 1520 C,  1520 E- 1520 K, along with the outdoor FCC emission limitation  610  according to some embodiments. The fourth channel does not exist with frequency range from 5.075 GHz to 5.725 GHz in the frequency spectrums  1500 . By not transmitting the fourth channel, the interference between the outdoor handheld 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 coexistences. 
   Referring to  FIG. 16  is an output of multichannel frequency spectrums  1600  with multi-carriers including 10 transmitter channel spectrums  1620 A- 1620 D,  1620 F- 1620 K, along with the outdoor FCC emission limitation  610  according to some embodiments. There is not fifth channel with frequency range from 5.725 GHz to 6.375 GHz in the frequency spectrums  1600 . By not transmitting the fifth channel, the interference between the outdoors handheld 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 coexistences. 
   Now referring to  FIG. 17  is an output of multichannel frequency spectrums  1700  with multi-carriers including 9-transmitter channel spectrums  1720 A- 1720 C,  1720 F- 1720 K, along with the outdoor FCC emission limitation  610  according to some embodiments. The frequency spectrum  1700  does not include the fourth and fifth channels with frequency range from 5.075 GHz to 6.375 GHz. By not transmitting the fourth and fifth channels, the interference between the outdoors handheld 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 the outdoor handheld UWB and WLAN 802.11a by no transmitting the fourth and fifth channels of multichannel filter-based outdoor handheld UWB communication device. 
   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.