Variable rate coding for forward link

Abstract

A forward error correction (FEC) block size is maintained at a constant size. Coding rate adjustments may be made by changing the number of information bits per symbol, or Forward Error Code (FEC) coding rate. Therefore, as the number of information bits per symbol is changed, the number of output bits is always maintained. The scheme permits for a greater flexibility and selection of effective data rates.

1 . A subscriber unit comprising:
 a forward error correction (FEC) encoder configured to encode a plurality of frames, each of the plurality of frames including a variable number of data bits, to include an error correction code such that a resulting number of output symbols remains fixed, wherein the error correction code is selected based on a channel condition associated with the subscriber unit.   
     
     
         2 . The subscriber unit of  claim 1 , further comprising:
 a modulator configured to modulate the output symbols according to a multiple-access modulation technique to produce a modulated encoded signal.   
     
     
         3 . The subscriber unit of  claim 2 , further comprising:
 a radio frequency up-converter configured to transmit the modulated encoded signal.   
     
     
         4 . The subscriber unit of  claim 1 , wherein one of the plurality of frames is selected to produce, when encoded, a desired number of output symbols in an encoded frame. 
     
     
         5 . The subscriber unit of  claim 1 , wherein the FEC encoder is further configured to include an error correction code such that a resulting number of output symbols remains fixed by varying a coding rate of the encoder. 
     
     
         6 . The subscriber unit of  claim 1 , further comprising:
 a processor configured to generate a coding rate signal; and   the FEC encoder includes an error correction code such that a resulting number of output symbols remains fixed is based on the coding rate signal.   
     
     
         7 . A subscriber unit comprising:
 a framer configured to receive data bits and generate frames having a predetermined length; and   a forward error correction (FEC) encoder configured to encode the frames to include an error correction code, wherein a length of the encoded frame remains fixed as a number of data bits varies.   
     
     
         8 . The subscriber unit of  claim 7 , further comprising:
 a modulator configured to modulate the encoded frame according to a multiple-access modulation technique to produce a modulated encoded signal.   
     
     
         9 . The subscriber unit of  claim 8 , further comprising:
 a radio frequency up-converter configured to transmit the modulated encoded signal.   
     
     
         10 . The subscriber unit of  claim 7 , further comprising:
 a processor configured to generate a coding rate signal; and   the FEC encoder encodes the frames to include an error correction code, wherein a length of the encoded frame remains fixed as a number of data bits varies based on the coding rate signal.   
     
     
         11 . A method for encoding data, the method comprising:
 receiving a plurality of frames, each of the plurality of frames including a unique number of bits of data; and   forward error correction (FEC) encoding each of the plurality of frames to include a plurality of error correction codes, one error correction code for each of the plurality of frames, to produce a plurality of encoded frames such that a resulting number of encoded symbols of each of the plurality of encoded frames is the same, wherein the error correction code is selected based on a channel condition associated with a subscriber unit.   
     
     
         12 . The method of  claim 11 , further comprising:
 selecting a code rate of the plurality of error corrections codes such that a resulting number of encoded symbols of each of the plurality of encoded frames is the same.   
     
     
         13 . The method of  claim 11 , further comprising:
 modulating the plurality of encoded frames to produce a modulated encoded signal.   
     
     
         14 . The method of  claim 11 , further comprising:
 transmitting the modulated encoded signal.