Patent Application
20130318416
This invention relates to rate matching and channel interleaving for a communications system.
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.
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.
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.
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.
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.
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 Nr rows and Nc columns, in which data bits to be interleaved are represented row by row, in accordance with:
I
r(k)=[αrk+fc(l)] mod Nr Row Permutation
I
c(l)=[αcl+fr(k)] mod Nc Column Permutation
where Ir(k) represents a data bit with a row index k, k is an integer from 1 to Nr, αr is an integer, fc(l) is a non-zero function of a column index l, l is an integer from 1 to NC, IC(l) represents a data bit with the column index l, αc is an integer, fr(k) is zero or a function of the row index k, and mod Nr and mod Nc represent modulo-Nr and modulo-Nc arithmetic respectively, interleaved data bits being derived from the matrix column by column.
It is currently considered optimum to choose fc(l)=ml+[Nr+1] mod 2, where m is an integer, m approximately equal to Nr/Nc, fr(k)=2k+[Nc+1] mod 2, and αr as the largest prime number less than Nr/log2(log2(Nr)).
The invention also provides rate matching apparatus arranged for carrying out a method as recited above.
Another aspect of this invention provides a method of interleaving data bits comprising permuting rows and columns of a matrix of Nr rows and Nc columns, in which data bits to be interleaved are represented row by row, in accordance with:
I
r(k)=[αrk+fc(l)] mod Nr Row Permutation
I
c(l)=[αcl+fr(k)] mod Nc Column Permutation
where Ir(k) represents a data bit with a row index k, k is an integer from 1 to Nr, αr is an integer, fc(l)=ml+[Nr+1] mod 2 is a non-zero function of a column index l, l is an integer from 1 to Nc, m is an integer, Ic(l) represents a data bit with the column index l, αc is an integer, fr(k)=2k+[Nc+1] mod 2, and mod 2, mod Nr and mod Nc represent modulo-2, modulo-Nr, and modulo-Nc arithmetic respectively, interleaved data bits being derived from the matrix column by column.
The invention also provides a data interleaver arranged for carrying out this method.
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.
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.
The invention further provides coding, interleaving, and rate matching apparatus arranged to carry out these methods.
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
The invention will be further understood from the following description with reference to the accompanying drawings, in which:
Referring to
The multiplexed signals are subjected to rate matching (puncturing (deletion) of redundant data symbols (bits) or repetition of data symbols (bits)) in a block 26 to match the data rate to the radio communications rate (air rate) with radio frames of 10 ms duration. Primarily in order to separate adjacent bits to reduce the adverse effects of errors due to fading in the radio channel, the data bits are interleaved in a first interleaver 28, which is referred to as a channel or inter-frame interleaver because it operates to permute blocks each of 10 ms of data bits. Although in
Following the functions 26 and 28, the resulting rate matched and interleaved signals are segmented for radio frames and physical channels in segmentation blocks 30 and 32 respectively to produce the signals for multiplexing by the multiplexer 10. Signals output by the multiplexer 10 are interleaved by a second interleaver 34 the outputs of which are segmented and mapped to dedicated physical channels in a segmentation and mapping block 36 for communications via a CDMA radio communications path in known manner.
As described in the related application referred to above, the first interleaver 28 can have a performance that is sufficiently good to enable the second interleaver 34 to be omitted or reduced to a simple shuffling operation, for example as described below. This is desirable in particular because otherwise the second interleaver 34 has the potential to degrade the interleaving performed by each first interleaver 28, whereas each first interleaver 28 can be optimized for its particular rate matched data stream and QoS.
Accordingly, the first interleaver 28 is implemented as an algebraic interleaver providing a good random spreading property. The multiple encoded bit blocks or data transport frames for each QoS channel are mapped into a 2-dimensional matrix and are subjected to linear congruential rules to permute the rows and columns of the matrix to implement the interleaving function. A maximum interleaving depth and time span can be determined by searching a set of best parameters. The interleaver consequently has a relatively simple form without disadvantages of known interleavers, such as requiring large memory sizes for look-up tables or inadequately accommodating the rate matching function.
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.
The interleaver 26 as described in the related application referred to above operates to implement the following three steps:
1. Represent a number Nc of encoded blocks of data bits each of length Nr data bits as a matrix of Nr rows and Nc columns.
2. Permute the rows and columns of the matrix in accordance with:
I
r(k)=[αrk+fc(l)] mod Nr Row Permutation
I
c(l)=[αcl+fr(k)] mod Nc Column Permutation
where Ir(k) represents a data bit with a row index k, k is an integer from 1 to Nr, αr is a row permutation parameter and is an integer, fc(l) is a positive function of a column index l, l is an integer from 1 to Nc, Ic(l) represents a data bit with the column index l, αc is a column permutation parameter and is an integer, fr(k) is a positive function of the row index k, and mod Nr and mod Nc represent modulo-Nr and modulo-Nc arithmetic respectively.
3. Derive interleaved data bits from the matrix column by column.
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 Nc=8 columns for Nc/γ data transport frames where γ=1, 2, 4, or 8, the matrix having Nr/γ rows accordingly, with a consequent modification of step 3 to read out γ columns of the matrix per radio frame accordingly. For simplicity in the description below, it is assumed that γ=1 with Nc=8.
For step 2, the row permutation parameter αr is chosen to be the largest prime number less than └Nr/log2(log2(Nr))┘, the column permutation parameter αc is chosen to be the largest prime number less than └Nc┘, the function fc(l)=ml+[Nr+1] mod 2, where m is an integer equal to ┌Nr/Nc┐, and the function fr(k)=2k+[Nc+1] mod 2. The symbols └ ┘ refer to rounding down to an integer, and the symbols ┌ ┐ refer to rounding up to an integer. It can be appreciated that [Nr+1] mod 2 is zero when Nr is odd and is one when Nr is even, and that [Nc+1] mod 2 is zero when Nc is odd and is one when Nc is even, so that these parts of the functions fc(l) and fr(k) are simply the addition of one when the respective number Nr or Nc is even.
As indicated above, the rate matching punctures (deletes) redundant data bits (which are present as a result of the FEC encoding blocks 22) in the event that the data transport frame size is larger than the radio frame size, a maximum puncturing ratio being 20% of the transport frame size. Conversely, if the data transport frame size is smaller than the radio frame size, bits of the transport frame are repeated to achieve the rate matching. The rate matching is desired as far as possible to maximize the separation distances between the punctured bits and to equalize the number of punctured bits in each radio frame, i.e. to distribute the punctured bits uniformly among the radio frames with maximum separation.
In the case where the rate matching block 26 precedes the channel interleaves 28 as shown in
Referring to
If y>0, puncturing of y of the Nr bits of the transport frame is required to produce the Ni bits of the radio frame. In this case in a block 42 a parameter e is initialized to a starting offset eos which is determined in any desired manner for the particular radio frame, and a row counter r is initialized to 1. In a block 43, it is determined whether r≦Nr and, if so, in a block 44 the value of e is reduced by 2y. In a subsequent decision block 45 it is determined whether and if so the bit in the row r is punctured at a block 46, the value of e is increased by 2Nr in a block 47, the row counter r is increased by 1 in a block 48, and a return is made to the decision block 43. A negative decision at the block 45 (i.e. e>0) results in a return to the block 43 via the block 48 to increment the row counter r without any puncturing or change in the value of e. A negative decision at the block 43 (i.e. r>Nr) indicates that the end of the frame has been reached, and accordingly the sequence ends at the stop block 41.
However, in the case where the rate matching block 26 follows the channel interleaver 28, the rate matching is carried out on the permuted (interleaved) bit stream and the problem of rate matching is considerably more complicated. Generally, the requirements of the channel interleaving and rate matching processes are not consistent.
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.
If the number of rows Nr is a power of two, then the address combiner 62 can simply combine the output of the modulo function 61 as the least significant bits, and the output of the modulo function 59 as the most significant bits, of the read address for the memory 50; equivalently the output of the function 61 is added by the address combiner 62 to Nr times the output of the function 59.
It may be desired to interleave data bits in arbitrary-sized frames that are not an integer multiple of Nc. In this case, the number of rows of the matrix is selected to accommodate all of the data bits to be interleaved, and the last few (less than Nc) memory locations in the working memory 50 are not written into. In order to omit the data bits of these memory locations from the interleaved data bits, the interleaver 28 of
The interleaved data bits on the line 66 are supplied to the rate matching block or function 26 also illustrated in
The rate matching address generator 70 generates at its output, as described further below, the address in the natural matrix NM of each punctured or repeated bit in accordance with the puncturing or repetition pattern which is determined for this process. This address is separated into most significant and least significant components by the address separator 71, whose operation is inverse to that of the read address combiner 62 described above. Thus if the number of rows Nr is a power of two, then the address separator 71 can simply separate the address bits output by the generator 70 into most significant bits and least significant bits; equivalently the address from the generator 70 is divided by Nr to produce an integer quotient and a remainder which constitute the two outputs of the address separator 71.
The address decoder 72 performs the inverse function of the address encoder 53. As indicated above, with the algebraic interleaving process described herein the structure of the de-interleaver can be exactly the same as the structure of the interleaver, and correspondingly the address decoder 72 is exactly the same as the address encoder 53. Accordingly, the detailed structure of the address decoder 72 is not illustrated in
The outputs of the address decoder 72 are buffered in the store 73, and the buffered outputs from the store are compared in the comparators 74 with the current counts k and l of the row counter 51 and column counter 52 respectively of the channel interleaver 28, to provide a selector control signal on a line 77 with a predetermined state when the compared values are the same. The selector control signal is thus produced on the line 77 with this state at each time that a bit on the line 66 is to be punctured or repeated. At other times, for bits which are not punctured or repeated, the control signal on the line 77 controls the selector 75 to supply to its output line 76, synchronously as determined by the clock signal CLK, a bit from the line 66 supplied to a middle one (as shown in
Because of the address decoding provided by the decoder 72 in the rate matching function 26, the rate matching address generator 70 can simply determine the desired pattern of punctured or repeated bits in terms of the normal matrix addresses in the manner described above with reference to
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 Nc=8 and Nr=10. Table 1 illustrates entry of the 80 data bits, numbered 0 to 79, row by row in a 10 by 8 natural matrix with the row index k from 1 to 10 and the column index l from 1 to 8:
The channel interleaving as described above produces a randomized matrix as shown by the following Table 2:
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:
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 eos, can be provided to optimize the puncturing process.
As indicated above, it is desirable for operation of the second interleaver 34 not to degrade the performance achieved as a result of the first interleaver 28, and to this end it is advantageous for the second interleaver 34 to be reduced to a simple shuffling operation, which interleaves data streams with different QoS while retaining the spreading properties achieved by the first interleaver 28 for each QoS data stream.
Referring to
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
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 22. One preferred form of encoding is so-called turbo (parallel concatenated convolutional) coding, in which the encoded data bits comprise the input data bits themselves, referred to as systematic data bits S, and parity bits P1 and P2 provided by convolutional coders operating on the input data bits and on interleaved input data bits. The parity bits P1 and P2 are typically punctured within the turbo coder to provide a desired rate turbo coder. For encoders 22 constituted by turbo coders, it is necessary to ensure that the subsequent rate matching function 26 does not puncture any of the systematic bits S, but only the parity bits P1 and/or P2. In the case of repetition, it has been determined that repetition of the parity bits P1 and P2 by a factor of the order of 2 or 3 times the repetition of the systematic bits S provides a performance gain.
To these ends,
Instead of a single channel interleaver as described above,
The rate matching function, which follows the channel interleavers 93, is shown within a dashed line box 94. A puncturing function 95 is applied only to the channel-interleaved parity bit streams, whereas a repetition function 96 can be provided to the parity and systematic bit streams, a selector 97 being illustrated to couple the channel-interleaved bits accordingly. The puncturing and repetition can be as described above. It can be appreciated that the illustration in
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2,268,853 | Apr 1999 | CA | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09544981 | Apr 2000 | US |
| Child | 10753546 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10753546 | Jan 2004 | US |
| Child | 13683011 | US |
