Abstract:
A universal transmitter and a universal receiver for respectively transmitting and receiving orthogonal frequency-division multiplexing (OFDM) signals using the international television bands respectively use fixed subcarrier spacing; fixed Fast Fourier Transform (FFT)/Inverse Fast Fourier Transform (IFFT) period values; a fixed symbol duration for each cyclic prefix option; and fixed WRAN frame parameters, but a selectable channel bandwidth for transmission and reception.

Description:
RELATED APPLICATIONS 
     This is the first application filed for this invention. 
     FIELD OF THE INVENTION 
     This invention relates in general to television band signal transmitters and receivers and, in particular, to a universal transmitter and a universal receiver for the international television bands. 
     BACKGROUND OF THE INVENTION 
     The IEEE 802.22 for wireless regional area networks (WRANS) is designed to operate in the TV broadcast bands, while ensuring that harmful interference does not occur with incumbent services, e.g., digital and analog TV broadcasts, and low power licensed devices such as wireless microphones. IEEE 802.22 defines a standard for each of three channel bandwidths, namely: 6 MHz based channels; 7 MHz based channels; and, 8 MHz based channels. For each of the respective channel bandwidths the 802.22 standard defines different: subcarrier spacing and FFT/IFFT period values based on sampling frequency; symbol duration for different cyclic prefix options; OFDM parameters; and WRAN frame parameters. The use of the respective channel bandwidths is regionalized, and a universal standard does not exist. 
     Table 1 shows the IEEE 802.22 subcarrier spacing and FFT/IFFT period values for the three different channel bandwidths based on a sampling frequency equivalent to 8/7 of the channel bandwidth. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 6 MHz based 
                   
                   
               
               
                   
                 channels 
                 7 MHz based channels 
                 8 MHz based channels 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Basic sampling 
                 6 * 8/7 = 6.857143 
                 7 * 8/7 = 8 
                 8 * 8/7 = 9.144857 
               
               
                 frequency (MHz) 
               
               
                 Inter-carrier spacing, 
                 (6 × 10 6  * 8/7)/2048 ≈ 
                 (7 × 10 6  * 8/7)/2048 = 
                 (8 × 10 6  * 8/7)/2048 ≈ 
               
               
                 ΔF (Hz) 
                 3348.214 
                 3906.25 
                 4464.286 
               
               
                 FFT/IFFT period, 
                 ≈298.666 . . . 
                 =256.000 
                 =224.000 
               
               
                 T FFT  (μs) = 1/ΔF 
               
               
                 Time Unit (ns) 
                 1000/(6 × 10 6  * 8/7) = 
                 1000/(7 × 10 6  * 8/7) = 125 
                 1000/(8 × 10 6  * 8/7) = 
               
               
                 TU = T FFT /2048 
                 145.833 . . . 
                   
                 109.375 
               
               
                   
               
             
          
         
       
     
     Table 2 shows the IEEE 802.22 symbol duration for different cyclic prefixes and bandwidth options. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                 CP = 
                 CP = 
               
               
                   
                 CP = T FFT /32 
                 CP = T FFT /16 
                 T FFT /8 
                 T FFT /4 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 T SYM  = 
                 6 MHz 
                 308.000 
                 317.333 
                 336.000 
                 373.333 
               
               
                 T FFT  + 
                 7 MHz 
                 264.000 
                 272.000 
                 288.000 
                 320.000 
               
               
                 T CP   
                 8 MHz 
                 231.000 
                 238.000 
                 252.000 
                 280.000 
               
               
                 (μs) 
               
               
                   
               
             
          
         
       
     
     Table 3 shows IEEE 802.22 OFDM parameters for the three channel bandwidths of 2K FFT mandatory mode. 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 TV channel 
               
               
                   
                 bandwidth(MHz) 
               
             
          
           
               
                   
                 6 
                 7 
                 8 
               
               
                   
                   
               
             
          
           
               
                   
                 Total no. of sub-carriers, 
                 2048 
               
               
                   
                 N FFT   
               
               
                   
                 No. of guard sub-carriers, 
                 368 (184, 1, 183) 
               
               
                   
                 N G  (L, DC, R) 
               
               
                   
                 No. of used sub-carriers, 
                 1680 
               
               
                   
                 N T  = N D  + N P   
               
               
                   
                 No. of data sub-carriers, 
                 1440 
               
               
                   
                 N D   
               
               
                   
                 No. of pilot sub-carriers, N P   
                  240 
               
             
          
           
               
                   
                 Signal bandwidth (MHz) 
                 5.625 
                 6.566 
                 7.504 
               
               
                   
                   
               
             
          
         
       
     
     Table 4 shows the IEEE 802.22 WRAN frame parameters for the three channel bandwidths. 
     
       
         
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                   
                   
                 Transmit-receive 
                 Receive-transmit 
               
               
                 Cyclic 
                 Number of symbols 
                 turnaround gap 2   
                 turnaround gap 3   
               
               
                 Prefix 
                 per frame 1   
                 (TTG) 
                 (RTG) 
               
             
          
           
               
                 BWP 
                 6 MHz 
                 7 MHz 
                 8 MHz 
                 6 MHz 
                 7 MHz 
                 8 MHz 
                 6 MHz 
                 7 MHz 
                 8 MHz 
               
               
                   
               
               
                 1/4 
                 26 
                 30 
                 34 
                   
                 210 μs 
                   
                 83.33 μs   
                 190 μs 
                 270 μs 
               
               
                 1/8 
                 28 
                 33 
                 38 
                   
                 210 μs 
                   
                 307 μs 
                 174 μs 
                 158 μs 
               
               
                 1/16 
                 30 
                 35 
                 40 
                   
                 210 μs 
                   
                 158 μs 
                 174 μs 
                 186 μs 
               
               
                 1/32 
                 31 
                 36 
                 41 
                   
                 210 μs 
                   
                 111 μs 
                 174 μs 
                 221 μs 
               
               
                   
               
             
          
         
       
     
     These three different channel bandwidths and their respective parameters place an onerous burden on transmitter and receiver manufacturers who wish to market internationally because a differently configured transmitter/receiver must be designed, manufactured and distributed for each of the three bandwidths. This not only complicates design, manufacturing and distribution, it also contributes to consumer cost and prohibits device migration between regions that use different channel bandwidths. 
     There therefore exists a need for a universal transmitter and a universal receiver for the international television bands and a WRAN standard that will coexist with any know television technology (NTSC, PAL, SECAM, ATSC-8VSB, DVB-T, etc.) while enabling transmission at any one of the 6 MHz, 7 MHz or 8 MHz channel bandwidths. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a universal transmitter and a universal receiver for the international television bands and WRAN parameters that will coexist with any know television technology while enabling transmission at any one of the 6 MHz, 7 MHz or 8 MHz channel bandwidths. 
     The invention therefore provides a universal transmitter for the international television bands, comprising: a channel bandwidth selector used to select a channel bandwidth to be used for data to be transmitted by the universal transmitter; a subcarrier allocator that receives information about the selected channel bandwidth from the channel bandwidth selector and allocates subcarriers for the data to be transmitted based on the information received; and a pilot subcarrier inserter that receives information about the selected channel bandwidth from one of the channel bandwidth selector and the subcarrier allocator, and inserts pilot subcarriers into the data to be transmitted based on the information received. 
     The invention further provides a universal receiver for the international television band, comprising: a channel bandwidth selector used to select a receiver bandwidth to be used for signal reception by the universal receiver; and a subcarrier deallocator that receives information from the channel bandwidth selector about the channel bandwidth used for the signal reception and deallocates subcarriers from the OFDM signal received. 
     The invention yet further provides a method of transmitting data in a wireless regional area network (WRAN) using the international television bands, comprising: operating a universal transmitter using: fixed subcarrier spacing; fixed Inverse Fast Fourier Transform (IFFT) period values; a fixed symbol duration for each different cyclic prefix option; and fixed WRAN frame parameters; and providing channel bandwidth information indicating a channel bandwidth to be used by the universal transmitter to: a subcarrier allocator of the universal transmitter; and, a pilot subcarrier inserter of the universal transmitter to permit an orthogonal frequency-division multiplexing (OFDM) signal to be transmitted by the universal transmitter to be shaped to fit the channel bandwidth to be used. 
     The invention still further provides a method of receiving data in a wireless regional area network (WRAN) using the international television bands, comprising: operating a universal receiver using: fixed subcarrier spacing; fixed Fast Fourier Transform (FFT) period values; a fixed symbol duration for different cyclic prefixes; and fixed WRAN frame parameters; and providing channel bandwidth information indicating a channel bandwidth to be used by the universal receiver to a subcarrier deallocator of the universal receiver to permit data to be recovered from an orthogonal frequency-division multiplexing (OFDM) signal received by the universal receiver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a universal transmitter in accordance with the invention; and 
         FIG. 2  is a schematic diagram of a universal receiver in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention provides a universal transmitter and a universal receiver for the international television bands. The universal transmitter is operated using: fixed subcarrier spacing; fixed Inverse Fast Fourier Transform (IFFT) period values; a fixed symbol duration for each different cyclic prefix option; and fixed WRAN frame parameters. However, channel bandwidth information indicating a channel bandwidth to be used by the universal transmitter is provided to: a subcarrier allocator of the universal transmitter, and a pilot subcarrier inserter of the universal transmitter to permit an orthogonal frequency-division multiplexing (OFDM) signal to be transmitted by the universal transmitter to be shaped to fit the channel bandwidth to be used. The universal receiver receives data in a wireless regional area network (WRAN) using: fixed subcarrier spacing; fixed Fast Fourier Transform (FFT) period values; a fixed symbol duration for different cyclic prefixes; and fixed WRAN frame parameters. However, channel bandwidth information indicating a channel bandwidth to be used by the universal receiver is provided to a subcarrier deallocator of the universal receiver to permit data to be recovered from an orthogonal frequency-division multiplexing (OFDM) signal received by the universal receiver. 
       FIG. 1  is a schematic diagram of a universal transmitter  10  in accordance with the invention. The universal transmitter  10  receives binary data  12  from a data source (not shown), such as a cable modem, a satellite receiver, an optical fiber, or the like. The binary data flows to a channel coding processor  14  which codes the data for transmission by the universal transmitter  10 . The coding processor  14  includes a data scrambler, a data encoder, a data puncturer, and a bit interleaver, each of which is known in the art. Data encoded by the channel coding processor  14  is passed to a quadrature amplitude modulation (QAM) mapper  16 , which maps the encoded data to a QAM constellation, also known in the art. The QAM mapped data is passed to a subcarrier allocator  18 , which allocates the QAM mapped data to data subcarriers based on information about the channel bandwidth to be used by the universal transmitter  10 , and orthogonal frequency-division multiplexing (OFDM) parameters in accordance with the invention for three bandwidths of the 2K mandatory mode shown in Table 5. 
     
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 OFDM parameters for the 3 bandwidths of 2K FFT mandatory 
               
               
                 mode 
               
             
          
           
               
                   
                 TV channel bandwidth (MHz) 
               
             
          
           
               
                   
                 6 
                 7 
                 8 
               
               
                   
                   
               
             
          
           
               
                 Total no. of sub-carriers, 
                 2048 
                 2048 
                 2048 
               
               
                 N FFT   
               
               
                 No. of guard sub-carriers, 
                 648 
                 368 
                 144 
               
               
                 N G  (L, DC, R) 
                 (324, 1, 323) 
                 (184, 1, 183) 
                 (72, 1, 71) 
               
               
                 No. of used sub-carriers, 
                 1400 
                 1680 
                 1904 
               
               
                 N T  = N D  + N P   
                 (=50 sub 
                 (=60 sub 
                 (=68 sub 
               
               
                   
                 ch) 
                 ch) 
                 ch) 
               
               
                 No. of data sub-carriers, 
                 1200 
                 1440 
                 1636 
               
               
                 N D   
               
               
                 No. of pilot sub-carriers, 
                 200 
                 240 
                 272 
               
               
                 N P   
               
               
                 Signal bandwidth (MHz) 
                 5.46875 
                 6.5625 
                 7.4375 
               
               
                   
               
             
          
         
       
     
     The information about the channel bandwidth to be used by the universal transmitter is provided to the subcarrier allocator  18  by a channel bandwidth selector  20  via an information path  21 . The channel bandwidth selector  20  may be implemented in many ways. The channel bandwidth selector  20  may be a switch, or the like, that: applies one of three predetermined voltages that are interpreted by the subcarrier allocator  18  and used to select corresponding subcarrier allocation parameters (shown in Table 5) for the channel bandwidth to be used by the universal transmitter  10 ; points to a read only memory (ROM) that stores the subcarrier allocation parameters for the channel bandwidth to be used by the universal transmitter  10 ; points to an electronically erasable programmable memory (EEPROM) that stores the subcarrier allocation parameters for the channel bandwidth to be used by the universal transmitter  10 ; or indicates 6 MHz, 7 MHz or 8 MHz in any other way, which indication is used by the subcarrier allocator  18  to retrieve from firmware, ROM or EEPROM the subcarrier allocation parameters for the channel bandwidth to be used by the universal transmitter  10 . The channel bandwidth selector  20  may also be software or firmware that: generates a code indicative of the channel bandwidth to be used by the universal transmitter  10 , which code is used by the subcarrier allocator  18  to retrieve from firmware, ROM or EEPROM the subcarrier allocation parameters for the channel bandwidth to be used by the universal transmitter  10 ; points to firmware, ROM or EEPROM that stores the allocation parameters for the channel bandwidth to be used by the universal transmitter  10 ; or indicates, formulates or provides 6 MHz, 7 MHz or 8 MHz channel allocation parameters in any other way. 
     After the proper subcarriers have been allocated to the QAM mapped data by the subcarrier allocator  18 , pilots are inserted into the QAM mapped data by a pilot inserter  22 . The pilot inserter uses the subcarrier information shown in Table 5 to insert the pilot subcarriers. Information about the channel bandwidth to be used by the universal transmitter  10  may be provided to the pilot inserter  22  by the subcarrier allocator  18  or via an information path  23  by the channel bandwidth selector  20  in any of the ways described above with reference to the subcarrier allocator  18 . 
     Once the pilot subcarriers are inserted into the QAM mapped data, a preamble is inserted by a preamble inserter  24  in a manner known in the art, and the data is passed to a serial-to-parallel converter  26 . The serial-to-parallel converter  26  converts the serial QAM mapped data to a parallel data stream for input to an Inverse Fast Fourier Transform (IFFT)  28 . The IFFT processes the data using parameters in accordance with the invention shown in Table 6 that are the same for all of the channel bandwidths that can be used by the universal transmitter  10 . 
     
       
         
               
             
               
               
               
               
             
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Subcarrier spacing and FFT/IFFT period values for different 
               
               
                 bandwidth options based on sampling frequency 
               
               
                 equivalent to 8/7 channel bandwidth. 
               
             
          
           
               
                   
                 6 MHz based 
                 7 MHz based 
                 8 MHz based 
               
               
                   
                 channels 
                 channels 
                 channels 
               
               
                   
                   
               
             
          
           
               
                 Basic sampling 
                 7 * 8/7 = 8 
               
               
                 frequency (MHz) 
               
               
                 Inter-carrier 
                 (7 × 10 6  * 8/7)/2048 = 3906.25 
               
               
                 spacing, 
               
               
                 ΔF (Hz) 
               
               
                 FFT/IFFT period, 
                 256.000 
               
               
                 T FFT  (μs) = 1/ΔF 
               
               
                 Time Unit (ns) 
                 1000/(7 × 10  6  * 8/7) = 125 
               
               
                 TU = T FFT /2048 
               
               
                   
               
             
          
         
       
     
     Parallel output from the IFFT  28  is passed to a parallel-to-serial converter  30 , which converts the parallel IFFT output back to a serial data stream, which is passed to a cyclic prefix inserter  32 . The cyclic prefix inserter  32  frames the data and inserts a cyclic prefix based on a predetermined cyclic prefix option using parameters in accordance with the invention selected by the cyclic prefix inserter  32  from values shown in Tables 7 and 8, which are the same for all of the channel bandwidths that can be used by the universal transmitter  10 . The cyclic prefix inserter  32  frames the data and inserts the cyclic prefix in a manner known in the art. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Symbol duration for different cyclic prefixes and bandwidth 
               
               
                 options 
               
             
          
           
               
                   
                   
                   
                 CP = 
                 CP = 
               
               
                   
                 CP = T FFT /32 
                 CP = T FFT /16 
                 T FFT /8 
                 T FFT /4 
               
               
                   
               
             
          
           
               
                 T SYM  = 
                 6 MHz 
                 264.000 
                 272.000 
                 288.000 
                 320.000 
               
               
                 T FFT  + 
                 7 MHz 
                   
                   
                   
                   
               
               
                 T CP   
                 8 MHz 
                   
                   
                   
                   
               
               
                 (μs) 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 WRAN frame parameters 
               
             
          
           
               
                   
                   
                 Transmit-receive 
                 Receive-transmit 
               
               
                   
                 Number of symbols per 
                 turnaround gap 2   
                 turnaround gap 3   
               
               
                 Cyclic Prefix 
                 frame (i.e. 10 ms) 
                 (TTG) 
                 (RTG) 
               
               
                 BW 
                 6 MHz 7 MHz 8 MHz 
                 6 MHz 7 MHz 8 MHz 
                 6 MHz 7 MHz 8 MHz 
               
               
                   
               
               
                 ¼  
                 30 
                 210 μs 
                 190 μs 
               
               
                   
                 (Tsym = 320 μs) 
               
               
                 ⅛  
                 33 
                 296 μs 
                 200 μs 
               
               
                   
                 (Tsym = 288 μs) 
               
               
                  1/16 
                 35 
                 280 μs 
                 200 μs 
               
               
                   
                 (Tsym = 272 μs) 
               
               
                  1/32 
                 36 
                 296 μs 
                 200 μs 
               
               
                   
                 (Tsym = 264 μs) 
               
               
                   
               
             
          
         
       
     
     The serial data stream is then passed to a digital-to-analog converter  34 , which is fixed to a sampling rate based on a 7 MHz channel bandwidth. The digital-to-analog converter  34  converts the serial data stream to an analog OFDM signal that is transmitted using an antenna (not shown) in a manner known in the art. 
       FIG. 2  is a schematic diagram of a universal receiver  40  in accordance with the invention. The universal receiver  40  receives an OFDM signal  42  using an antenna (not shown) in a manner well known in the art. The received signal  42  is passed to an analog-to-digital converter  44  fixed to a sampling rate based on a 7 MHz channel bandwidth. The analog to digital converter  44  outputs a digital representation of the received OFDM signal  42  to a synchronizer  46  and a cyclic prefix remover  48 . The synchronizer  46  generates timing information used by the cyclic prefix remover  48  to reverse the operations of the cyclic prefix inserter  32  shown in  FIG. 1 . The cyclic prefix is removed and the data is unframed in accordance with the timing information, the predetermined cyclic prefix option and the information shown above in Tables 7 and 8. After the cyclic prefix is removed, the data is passed to a serial-to-parallel converter  52 , which converts the serial data stream to a parallel data stream for input to a Fast Fourier Transform  54 . The FFT  54  reverses the operations of the IFFT  28  shown in  FIG. 1  using the information shown in Table 6. Parallel output of the FFT  54  is passed through a parallel path to a parallel-to-serial converter  56 , which converts the parallel FFT output to a serial data stream that is passed to a channel estimator  58 , which estimates the broadcast channel using the pilot subcarriers in a manner known in the art. 
     The serial data stream is then passed to a subcarrier deallocator  60 , which selects data subcarriers form the serial data stream using channel bandwidth selection information received via an information path  61  from a channel bandwidth selector  50  and the parameters in accordance with the invention shown above in Table 5. 
     The channel bandwidth selector  50  can be implemented in any of the ways described above with respect to the channel bandwidth selector  20  shown in  FIG. 1 . In addition, in accordance with one embodiment of the invention the channel bandwidth selector  50  is implemented in software or firmware and is transparent to a user of the universal receiver  40 . In this embodiment, the Media Access Control (MAC) layer (not shown) of the universal receiver  40  is adapted to scan for an OFDM signal in each of the 6 MHz, 7 MHz and 8 MHz channel bandwidths. When a channel lock is achieved, an indication of the channel bandwidth is passed from the MAC layer to the channel bandwidth selector  50  via a signal path  53 . The channel bandwith selector  50  then passes the channel bandwidth information directly or indirectly to the subcarrier deallocator  60  via information path  61  in any of the ways described above with reference to  FIG. 1 . 
     The serial data stream is passed from the subcarrier deallocator  60  to the QAM demapper  62 , which demaps the QAM constellations in a manner known in the art. The demapped data is passed to a channel decoding processor  64  which reverses the channel coding described above with reference to the channel coding processor shown in  FIG. 1 , and the recovered binary data  66  is output. 
     The embodiments of the invention described above are only intended to be exemplary of the universal transmitter and the universal receiver for the international television bands in accordance with the invention, and not a complete description of every possible configuration of the transmitter, the receiver or the parameters used to drive them. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.