Rate matching and channel interleaving for a communications system

Abstract

A method of and apparatus for matching a rate of data bits, in a matrix of data bits interleaved by a predetermined interleaving process, to a desired rate by deletion of redundant data bits or repetition of data bits derived from the matrix, includes steps of determining in a non-interleaved matrix of the data bits a pattern of bits to be deleted or repeated to provide the desired data rate, decoding an address of each bit in said pattern in a manner inverse to the interleaving process to produce a respective address of the bit in the matrix of interleaved data bits, and deleting or repeating the respective bit in the interleaved data bits in dependence upon the respective address. The address decoding is performed in the same manner as a coding of addresses for producing the interleaved data bits from the non-interleaved matrix of the data bits. The specification also discloses an advantageous interleaving process for channel interleaving in a 3rd generation CDMA wireless communications system, a shuffling method for a second stage of interleaving in such a system, and how the rate matching can be conveniently applied to turbo-coded data.

1 . A method of matching a rate of data bits, in a matrix of data bits interleaved by a predetermined interleaving process, to a desired rate by deletion of redundant data bits or repetition of data bits derived from the matrix, including the steps of: 
 determining in a non-interleaved matrix of said data bits a pattern of bits to be deleted or repeated to provide said desired data rate;    decoding an address of each bit in said pattern in a manner inverse to the interleaving process to produce a respective address of the bit in the matrix of interleaved data bits; and    deleting or repeating the respective bit in the interleaved data bits in dependence upon the respective address.    
     
     
         2 . A method as claimed in  claim 1  wherein the address decoding is performed in the same manner as a coding of addresses for producing the interleaved data bits from the non-interleaved matrix of said data bits.  
     
     
         3 . A method as claimed in  claim 1  wherein the pattern of bits to be deleted or repeated is dependent upon the number of bits to be deleted or repeated and a column index of the matrix.  
     
     
         4 . A method as claimed in  claim 1  wherein the interleaving process comprises permuting rows and columns of a matrix of N r  rows and N c  columns, in which data bits to be interleaved are represented row by row, in accordance with:  
       Row Permutation  I   r ( k )=[α r   k+f   c ( l )]modN r  Column Permutation  I   c ( l )=[α c   l+f   r ( k )]modN c    
       where I r (k) represents a data bit with a row index k, k is an integer from 1 to N r , α r  is an integer, f c (l) is a non-zero function of a column index l, l is an integer from 1 to N c , I c (l) represents a data bit with the column index l, α c  is an integer, f r (k) is zero or a function of the row index k, and modN r  and modN c  represent modulo-N r  and modulo-N c  arithmetic respectively, interleaved data bits being derived from the matrix column by column.  
     
     
         5 . A method as claimed in  claim 4  wherein f c (l)=ml+[N r +1]mod2, where m is an integer.  
     
     
         6 . A method as claimed in  claim 5  wherein m is approximately equal to N r /N c .  
     
     
         7 . A method as claimed in  claim 4  wherein f r (k)=2k+[N c +1]mod2.  
     
     
         8 . A method as claimed in  claim 4  wherein α r  is the largest prime number less than N r /log 2 (log 2 (N r )).  
     
     
         9 . Rate matching apparatus arranged for carrying out a method as claimed  claim 1 .  
     
     
         10 . A method of interleaving data bits comprising permuting rows and columns of a matrix of N r  rows and N c  columns, in which data bits to be interleaved are represented row by row, in accordance with:  
       Row Permutation  I   r ( k )=[α r   k+f   c ( l )]modN r  Column Permutation  I   c ( l )=[α c   l+f   r ( k )]modN c    
       where I r (k) represents a data bit with a row index k, k is an integer from 1 to N r , α r  is an integer, f c (l)=ml+[N r +1]mod2 is a non-zero function of a column index l, l is an integer from 1 to N c , m is an integer, I c (l) represents a data bit with the column index l, α c  is an integer, f r (k)=2k+[N c +1]mod2, and mod2, modN r  and modN c  represent modulo-2, modulo-N r , and modulo-N c  arithmetic respectively, interleaved data bits being derived from the matrix column by column.  
     
     
         11 . A method as claimed in  claim 10  wherein m is approximately equal to N r /N c .  
     
     
         12 . A method as claimed in  claim 10  wherein α r  is the largest prime number less than N r /log 2 (log 2 (N r )).  
     
     
         13 . A data interleaver arranged for carrying out the method of  claim 10 .  
     
     
         14 . A method of interleaving and rate matching parallel concatenated convolutional coded data by deletion of coded data bits, the coded data bits comprising systematic bits and parity bits, including the steps of interleaving the systematic bits separately from the parity bits, and deleting parity bits from the interleaved parity bits to provide the rate matching.  
     
     
         15 . Coding, interleaving, and rate matching apparatus arranged to carry out the method of  claim 14 .  
     
     
         16 . A method of interleaving and rate matching parallel concatenated convolutional coded data by repetition of coded data bits, the coded data bits comprising systematic bits and parity bits, including the steps of interleaving the systematic bits separately from the parity bits, and repeating parity bits of the interleaved parity bits with a greater repetition factor than any repetition of systematic bits of the interleaved systematic bits, to provide the rate matching.  
     
     
         17 . Coding, interleaving, and rate matching apparatus arranged to carry out the method of  claim 16.