US 20040146029 A1 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.
Claims(17) 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 3. A method as claimed in 4. A method as claimed in _{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 _{c}(l)=ml+[N_{r}+1]mod2, where m is an integer. 6. A method as claimed in _{r}/N_{c}. 7. A method as claimed in _{r}(k)=2k+[N_{c}+1]mod2. 8. A method as claimed in _{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 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 _{r}/N_{c}. 12. A method as claimed in _{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 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 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 Description [0001] This invention relates to rate matching and channel interleaving for a communications system. [0002] U.S. patent application Ser. No. 09/531,470 filed Mar. 20, 2000 in the names of Wen Tong et al., entitled “Data Interleaver And Method Of Interleaving Data”, describes and claims a method of interleaving data and a data interleaver which advantageously can be used to provide the channel interleaving referred to below. [0003] It is well known to perform interleaving of data in a communications system using forward error correction (FEC) in order, on deinterleaving, to distribute errors to facilitate their correction. Typically, such interleaving uses a block interleaver to interleave blocks of data. So-called turbo coding (parallel concatenated convolutional coding) uses an interleaver between inputs to two convolutional coders which produce respective parity bits from the input data before and after interleaving. With increasing attention being given to the use of turbo coding, particularly in wireless communications systems, attention has also been given to the form of the interleaver. [0004] So-called 3rd generation CDMA (code division multiple access) wireless communications systems are also being developed which require a channel or inter-frame interleaver which operates to interleave or permute data in blocks corresponding to the radio frame duration, typically 10 ms. In such systems the channel interleaver either precedes or follows a rate matching function which serves to match various data rates to the radio frame rate, and which typically involves puncturing (omission) or repetition of data symbols, in this case data bits. It is desirable to distribute the omitted or repeated bits as evenly as possible, with as great a distance as possible between punctured or repeated bits in the de-interleaved frames, in a manner that is easy to implement and that is relatively independent of variables such as the frame size, number of frames, and puncturing rate. [0005] The present invention is concerned with rate matching in a manner which can be used with particular advantage for data after channel interleaving as described and claimed in the related application referred to above, but which is also applicable to other forms of interleaved data. This invention also provides improvements in and further applications of such channel interleaving. [0006] According to one aspect, this invention provides 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. [0007] It is particularly advantageous, and may be necessary in practice, for the address decoding to be 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. This is facilitated in preferred embodiments of the method of the invention by the interleaving process comprising permuting rows and columns of a matrix of N Row Permutation Column Permutation [0008] where I [0009] It is currently considered optimum to choose f [0010] The invention also provides rate matching apparatus arranged for carrying out a method as recited above. [0011] Another aspect of this invention provides a method of interleaving data bits comprising permuting rows and columns of a matrix of N Row Permutation Column Permutation [0012] where I [0013] The invention also provides a data interleaver arranged for carrying out this method. [0014] Another aspect of the invention provides 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. [0015] A further aspect of the invention provides 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. [0016] The invention further provides coding, interleaving, and rate matching apparatus arranged to carry out these methods. [0017] Yet another aspect of this invention relates to a method of shuffling interleaved and rate matched data streams in the manner described below with reference to FIG. 4 of the drawings, and to the recursive application of this method to more than two such data streams. [0018] The invention will be further understood from the following description with reference to the accompanying drawings, in which: [0019]FIG. 1 illustrates a known arrangement for service multiplexing and channel interleaving in a 3rd generation CDMA communications system; [0020]FIG. 2 is a flow chart relating to a known rate matching algorithm; [0021]FIG. 3 illustrates an implementation of an interleaver and a rate matching arrangement in accordance with an embodiment of this invention; [0022]FIG. 4, which is on the same sheet as FIG. 2, is a flow chart relating to shuffling for a second stage of interleaving in the arrangement of FIG. 1; and [0023]FIG. 5 illustrates a modification of part of the arrangement of FIG. 1 for channel interleaving and rate matching of data encoded by turbo (parallel concatenated convolutional) coding. [0024] Referring to FIG. 1, there is illustrated a known arrangement for service multiplexing and channel interleaving in a 3rd generation CDMA radio communications system. The arrangement includes a service multiplexer [0025] The multiplexed signals are subjected to rate matching (puncturing (deletion) of redundant data symbols (bits) or repetition of data symbols (bits)) in a block [0026] Following the functions [0027] As described in the related application referred to above, the first interleaver [0028] Accordingly, the first interleaver [0029] Although the following description refers to rows and columns of a matrix, it should be understood that this is for convenience and clarity, that the rows and columns can be interchanged without changing the function of the interleaver, and that in practice- and as described below the interleaver can operate by equivalent control of read or write addressing of memory locations of a linear memory in which data bits are stored, without any actual movement of the stored bits among the memory locations. [0030] The interleaver [0031] 1. Represent a number N [0032] 2. Permute the rows and columns of the matrix in accordance with: Row Permutation Column Permutation [0033] where I [0034] 3. Derive interleaved data bits from the matrix column by column. [0035] Step 1 can be slightly modified to accommodate different numbers of data transport frames with a given number of columns of the matrix. For example the matrix can have N [0036] For step 2, the row permutation parameter α [0037] As indicated above, the rate matching punctures (deletes) redundant data bits (which are present as a result of the FEC encoding blocks [0038] In the case where the rate matching block [0039] Referring to FIG. 2, for each radio frame of segmentation size N [0040] If y>0, puncturing of y of the N [0041] However, in the case where the rate matching block [0042] More particularly, the design of an appropriate, and desirably optimized, rate matching pattern of punctured or repeated bits within the matrix of bits after the channel interleaving process represents a very complex or impractical task. This invention avoids this problem by providing an appropriate, and desirably optimized, rate matching pattern of punctured or repeated bits for the matrix before interleaving, and using a de-interleaving or decoding process to determine corresponding bits to be punctured or repeated at the output of the channel interleaver. This process is facilitated by the fact that the de-interleaving, or decoding, process can be implemented by exactly the same structure as the interleaving process, as further described below. For convenience and clarity, the following description refers to the matrix of bits before interleaving (or after de-interleaving) as the natural matrix NM, and to the matrix of bits after interleaving as the randomized matrix RM. [0043]FIG. 3 illustrates an implementation of a channel interleaver [0044] If the number of rows N [0045] It may be desired to interleave data bits in arbitrary-sized frames that are not an integer multiple of N [0046] The interleaved data bits on the line [0047] The rate matching address generator [0048] The address decoder [0049] The outputs of the address decoder [0050] Because of the address decoding provided by the decoder [0051] This example, with interleaving as described above of 8 data transport frames each of 10 bits, and requiring a maximum puncturing ratio of 20% to produce channel interleaved and rate matched radio frames each of 8 bits (a total of 16 out of 80 bits being punctured or deleted), is further illustrated by the following Tables 1, 2, and 3. Thus N
[0052] The channel interleaving as described above produces a randomized matrix as shown by the following Table 2:
[0053] The rate matching as described above then punctures 16 bits, 2 from each column of the randomized matrix, in a pattern produced by the rate matching algorithm to give a punctured randomized matrix as shown by the following Table 3:
[0054] The channel interleaved and rate matched data bits are derived column by column from Table 3, i.e., with the order [57, 35, . . . , 51, 7, 67, 40, . . . , 26, 4]. The punctured bits are 2, 9, 11, 16, 25, 29, . . . 31, 32, 34, 38, 47, 54, 61, 64, 68, and 75, for which the maximum puncture distance is 9 (25−16) and the minimum puncture distance is 1 (32−31); this small minimum puncture distance indicates that this particular example is not optimum, a larger minimum puncture distance being desirable. It can be appreciated that numerous other determinations of the parameters, and in particular of the parameter e [0055] As indicated above, it is desirable for operation of the second interleaver [0056]FIG. 4 shows a flow chart of a bit shuffling algorithm which can be used advantageously to interleave bits of two data streams of interleaved radio frames provided as described above from respective service blocks [0057] Referring to FIG. 4, initially in a block [0058] For more than two data streams, the same process is applied recursively for the successive data streams. It can be appreciated from the above description and the illustration in FIG. 4 that the steps of this process have a direct correlation with the steps of the puncturing and repetition processes of FIG. 2, so that implementation of this recursive shuffling process can be particularly convenient. [0059] As indicated above, the puncturing of bits to achieve the desired rate matching is applied to data bits which have redundancy due to the FEC encoding provided by the encoders [0060] To these ends, FIG. 5 illustrates a modification of part of the arrangement of FIG. 1 for channel interleaving and rate matching of data encoded by turbo coding. Referring to FIG. 5, a turbo coder constituting one of the FEC encoders [0061] Instead of a single channel interleaver as described above, FIG. 5 illustrates that individual channel interleavers [0062] The rate matching function, which follows the channel interleavers [0063] Although the above description refers to separate functions and units for the various processes described herein, it can be appreciated that these can in many cases be implemented using functions of one or more digital signal processors or other integrated circuits. [0064] Although particular embodiments and examples of the invention have been described above, it can be appreciated that numerous modifications, variations, and adaptations may be made without departing from the scope of the invention as defined in the claims. Referenced by
Classifications
Legal Events
Rotate |