Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
  • H03M13/27—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes using interleaving techniques
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
  • H03M13/27—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes using interleaving techniques
  • H03M13/2771—Internal interleaver for turbo codes
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
  • H03M13/27—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes using interleaving techniques
  • H03M13/2789—Interleaver providing variable interleaving, e.g. variable block sizes
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
  • H03M13/27—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes using interleaving techniques
  • H03M13/2703—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes using interleaving techniques the interleaver involving at least two directions
  • H03M13/271—Row-column interleaver with permutations, e.g. block interleaving with inter-row, inter-column, intra-row or intra-column permutations
  • H03M13/2714—Turbo interleaver for 3rd generation partnership project [3GPP] universal mobile telecommunications systems [UMTS], e.g. as defined in technical specification TS 25.212
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
  • H03M13/27—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes using interleaving techniques
  • H03M13/2735—Interleaver using powers of a primitive element, e.g. Galois field [GF] interleaver
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
  • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
  • H03M13/65—Purpose and implementation aspects
  • H03M13/6522—Intended application, e.g. transmission or communication standard
  • H03M13/6558—3GPP2

Definitions

• This invention relates generally to communication systems and, more particularly to interleavers for performing code modulation.
• Coded modulation has been found to improve the bit error rate (BER) of electronic communication systems such as modem and wireless communication systems.
• Turbo coded modulation has proven to be a practical, power-efficient, and bandwidth- efficient modulation method for " random-error" channels characterized by additive white Gaussian noise (AWGN) or fading.
• AWGN additive white Gaussian noise
• CDMA code division multiple access
• turbo coders which makes them so effective is an interleaver which permutes the original received or transmitted data frame before it is input to a second encoder.
• the permuting is accomplished by randomizing portions of the signal based upon one or more randomizing algorithms.
• a conventional interleaver collects, or frames, the signal points to be transmitted into an array, where the array is sequentially filled up row by row. After a predefined number of signal points have been framed, the interleaver is emptied by sequentially reading out the array column by column for transmission. As a result, signal points in the same row of the array that were near each other in the original signal point flow are separated by a number of signal points equal to the number of rows in the array. Ideally, the number of columns and rows would be picked such that interdependent signal points, after transmission, would be separated by more than the expected length of an error burst for the channel. Non-uniform interleaving achieves "maximum scattering" of data and "maximum disorder" of the output sequence.
• the redundancy introduced by the two convolutional encoders is more equally spread in the output sequence of the turbo encoder.
• the minimum distance is increased to much higher values than for uniform interleaving.
• a persistent problem for non-uniform interleaving is how to practically implement the interleaving while achieving sufficient "non-uniformity, " and minimizing delay compensations which limit the use for applications with real-time requirements.
• Finding an effective interleaver is a current topic in the third generation CDMA standard activities. It has been determined and generally agreed that, as the frame size approaches infinity, the most effective interleaver is the random interleaver. However, for finite frame sizes, the decision as to the most effective interleaver is still open for discussion.
• the interleaver includes a storage area containing an array large enough to store the largest expected data frame.
• a frame of size L elements to be interleaved is stored in N r rows and N c ⁇ ) columns of the array, where N, ⁇ is a predetermined integer and N c (1) is a prime number which satisfy the inequality N r ⁇ x N e ' 1"11 ⁇ L ⁇ N r ⁇ x N c (1) where N-.' 1"1 ' is the highest prime number less than N c (1) .
• the elements of each row are permuted according to a predetermined mathematical relationship, and the rows are permuted according to predetermined mapping.
• Fig. 1 depicts a fast modulo computing embodiment according to the present invention.
• Fig. 2 depicts the structure of an interleaver according to the present invention.
• the present invention finds embodiment as a turbo encoder in a CDMA radio communication system.
• a stream of bits to be transmitted is divided into a series of frames, each frame including a number L of elements, each element being at least one bit .
• Each frame is to be interleaved prior to transmission. If there are a large number of possible frame sizes L, specifying an interleaver for each possible frame size results in a necessity for storing a large number of parameters.
• the invention reduces the number of parameters that must be stored by providing a reduced number of prototype interleavers (or mother interleavers) , each for a one of a subset of frame sizes, selecting one of the mother interleavers at least large enough to interleave a current frame of size L, and puncturing the interleaved frame to a size of L bits.
• the maximum size of an array for storing a frame to be interleaved is N r rows x N c columns.
• a mother interleaver is chosen having an array of size of
• N r ⁇ rows x N c (1) columns, such that : N r (1) x N ⁇ 1'1' ⁇ L ⁇ N r x N c (1) and after interleaving the array is punctured to size L.
• the invention provides an interleaver which can adapt to arbitrary frame size by providing a scheme for proper selection (optimization) of parameters
• N c ⁇ 1 1, 2, ... C (max. no. of columns)
• the advantage of using this special reduced system is to add additional constraints on the intra-row permutation roots to simplify the search computing for the parameter optimization.
• a set of prime numbers is chosen:
• the intra-row permutation rule is a deterministic one.
• Example 1 For each prime (column number) such a set is chosen. To cover a range of frame sizes from 320 bits to 8192 bits, at least 75 mother interleavers are provided. The column dimensions used for each are listed in Table 1 together with associated primitive roots. Seventy-six primes are listen in Table 1 in order to provide a value for the lowest N 1"1 ' .
• the storage requirement for the set of primitive roots is reduced by using a set of twenty-one consecutive primes (in the present example (Example 1) , adding the prime 89 to the exemplary twenty primes p(l) given above) .
• a multiplier may be employed that is 2k bits in width. Also: log 2 [m] ⁇ k and log 2 [c] ⁇ k.
• the modulo P value can be computed according to Eq. 1 by multiplying a k-bit LSB with 1 and then adding a k-bit MSB. If the sum is more than k bits wide, Eq. 1 must be reinvoked, i.e.:
• FIG. 1 An embodiment of the modulo P calculation presented here is depicted in Fig. 1.
• FIG. 2 An overall embodiment of the interleaver presented here is depicted in Fig. 2.
• the interleaver parameters are to be selected according to the given intra-row congruential rule. It is known that once the recursive convolutional code (RCC) constituent code is determined, error performance is characterized by the input and output weight of error events of the constituent decoders. (The input weight is the number of bit errors.) It is known that the performance of Turbo codes at high SNR is dictated by output error events with input weight 2. The effective free distance is the minimum output weight of all error events of input weight 2.
• RRC recursive convolutional code
• weight-2 e.g., two 1 bits with six 0's between them
• Weight-2 column of Table 3 a set of interleaver parameters is sought that produce an output with 1 bits in the zero'th (initial) and seventh, fourteenth, twenty-first, or twenty- eight positions (according to length) with six, thirteen, twenty, or twenty-seven 0 bits, respectively, between the two one bits. This may be expressed as verifying 1 bits in zero'th and i ' th positions.
• weight-3 streams are checked for 1 bits in the zero'th, i'th, and j ' th positions.
• Weight-4 streams are checked for 1 bits in the zero'th i'th, j'th, and k ' th positions .
• turbo encoder such as is found in a CDMA system
• those skilled in the art realize that the practice of the invention is not limited thereto and that the invention may be practiced for any type of interleaving and de-interleaving in any communication system.
• the invention efficiently attains the objects set forth above, among those made apparent from the preceding description.
• the invention provides improved apparatus and methods of interleaving codes of finite length while minimizing the complexity of the implementation and the amount of storage space required for parameter storage.

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• Physics & Mathematics (AREA)
• Probability & Statistics with Applications (AREA)
• Engineering & Computer Science (AREA)
• Theoretical Computer Science (AREA)
• Error Detection And Correction (AREA)
• Detection And Prevention Of Errors In Transmission (AREA)

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• 1999
  • 1999-04-14 US US09/291,353 patent/US6543013B1/en not_active Expired - Lifetime
• 2000
  • 2000-03-29 WO PCT/IB2000/000375 patent/WO2000062426A1/en not_active Ceased
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