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
  • H03M13/63—Joint error correction and other techniques
  • H03M13/635—Error control coding in combination with rate matching
  • H03M13/6362—Error control coding in combination with rate matching by puncturing
• • 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
  • H03M13/29—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 combining two or more codes or code structures, e.g. product codes, generalised product codes, concatenated codes, inner and outer codes
  • H03M13/2903—Methods and arrangements specifically for encoding, e.g. parallel encoding of a plurality of constituent 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
  • H03M13/29—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 combining two or more codes or code structures, e.g. product codes, generalised product codes, concatenated codes, inner and outer codes
  • H03M13/2957—Turbo codes and decoding
  • H03M13/2993—Implementing the return to a predetermined state, i.e. trellis termination
• • 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
  • H03M13/29—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 combining two or more codes or code structures, e.g. product codes, generalised product codes, concatenated codes, inner and outer codes
  • H03M13/2957—Turbo codes and decoding
  • H03M13/2996—Tail biting
• • 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
  • H03M13/37—Decoding methods or techniques, not specific to the particular type of coding provided for in groups H03M13/03 - H03M13/35
  • H03M13/39—Sequence estimation, i.e. using statistical methods for the reconstruction of the original codes
  • H03M13/41—Sequence estimation, i.e. using statistical methods for the reconstruction of the original codes using the Viterbi algorithm or Viterbi processors
  • H03M13/4123—Sequence estimation, i.e. using statistical methods for the reconstruction of the original codes using the Viterbi algorithm or Viterbi processors implementing the return to a predetermined state

Definitions

• the present invention relates to methods for terminating both of the constituent encoders of a turbo code and developing puncturing patterns applicable at a trellis rermination stage that ensures the same number of transmitted bits for each trellis stage during the information bit transmission and trellis termination stages .
• tail bits are inserted after information bits, to zero out all shift registers of an encoder.
• tail birs are equal to zero.
• me value of tail birs depend on the contents of trie shift register current values .
• a turbo encoder consists of a parallel concatenation of rwo (2) or more recursive (feedback) convoiutional encoders. Because each constituent encoder processes the information bits m a different or ⁇ er ⁇ ue to a turbo mterleaver, it is not possible to terminate all constituent encoders by the same tail bits.
• a trellis termination method general enough to be used for a set of turbo codes with different code rates as m the third generation CDMA systems is desirable. Included m the desirable general etno ⁇ is a method of puncturing tail bit sequences .
• the present invention advantageously addresses the needs above as well as other needs by providing a method and apparatus for a general Turbo Code trellis termination which may be employed when a turbo encoder operates within a wide range of turbo code rares when transmitting information bits.
• the invention can be characterized as a method of terminating two or more constituent encoders of a turbo encoder.
• the method comprises the steps of: generating tail input bits ar each of two or more constituent encoders, including the step of deriving the rail input bits from each of the rwo or more constituent encoders separately from the contenrs of shift registers within each of the two or more constituent encoders, after an encoding of information bits by the two or more constituent encoders; and puncturing one or ' more tail output bits such that 1/R tail output bits are transmitted for each of a plurality of trellis stages, wherein R is a turbo code rate employed by the turbo encoder during the information bit transmission.
• the step of puncturing the one or more tail output bits further comprises the step of: transmitting, during trellis termination, the tail output bits only if they are sent from an output branch of one of the two or more constituent encoders that is used during information bit transmission.
• FIG.l is a block diagram of a turbo encoder with interleaved bits entering a second encoder, for use in accordance with one embodiment of the present invention.
• an exemplary turbo code encoder is shown wherein one embodiment of a Turbo Code trellis termination design terminates one encoder 10 (a first encoder) while disabling another encoder 10' (a second encoder) and at a different time terminates the other encoder 10' (second encoder) while disabling the encoder 10 (first encoder) .
• the encoders (first and second encoders) 10, 10' of the turbo code encoder of FIG.l are constituent encoders configured in a parallel concatenation. It is well known in the art that a constituent encoder employ a configuration of modular adders 17, 20, 26, 28, 30, 24, and 25, and shift registers 18, 21, 22, coupled through nodes (such as node 32) to produce output bits, including rail output bits, X(t), Yo(t), Y-_(t), for example, depending upon the encoding scheme.
• Interleaver 16 is employed between an input for X(t) and the second encoder 10', and wherein additionally, a puncturer 36 is employed, switchably coupled ro respective encoder outputs for each of the encoders (first and second encoders) 10, 10'.
• tail input bits will mean the bits X, and X' in FIG. 1
• rail output bits will mean the bits X, X', Yo, YcC , Yi or Yi ' .
• Each of the constituenr encoders may utilize a fewer or greater number of shift registers than in FIG . 1 .
• afrer message nits X(t) are enco ⁇ ed
• a switch 12 is moved to a feedbac position to allow the generation of three (3) consecutive tail input bits, m th s example, generate ⁇ from the contents of each of three shift registers 18, 21, and 22 'also referred to herein as a first shift regisrer 18, a second shift register 21, and a third shift register 22) .
• a number of tail input bits X(t), X' (t) for terminating a constituent encoder is equal to a number of shift registers m that encoder.
• new tail input bits X(t), X' (t) are generated for zeroing out each respective shift register of the three shift registers, 18, 21 and 22.
• the encoders In one embodiment of the invention the encoders
• first encoder 10 is first terminated while the second encoder 10' is disabled, followed by the second encoder 10' being terminated while the first encoder 10 is disabled.
• the encoders 10, 10' can be terminated m consecutive clock cycles, wherein six (6) consecutive clock cycle tail input bits X(t), X' (t) , consecutively terminate both the encoders 10, 10'.
• a second tail input bit sequence 34' for terminating the secon ⁇ encoder 10' is fed back into the second encoder 10' through a switch 12' and circuit 14*.
• Tail input bits X(t), X' (t ⁇ are nor interleaved by the turbo interleaver 16.
• a tail input bit sequence 34 for terminating the first encoder 10 is fed back into the first encoder 10 through another switch 12 and another circuit 14.
• the zeroing of the shift registers 18, 21, 22, prior to implementing a puncturing scheme per an embodiment of the invention, is triggered by a beginning and an ending tail input bit sequence X(t), X' (t), each sequence having a number n of tail input bits X(t), X' (t) equal to the number n of shift registers 18, 21, 22 or 18', 21, 22 coupled to each one of the encoders 10, 10'.
• tail output bits X, Yo, Yi, X 1 , Yo, Y- ' are also punctured by the puncturer 36.
• Table 1 indicates associated tail output bit puncturing patterns having indicator sequences (e.g., "Ill 000") identifying which bits to puncture and which bits to transmit.
• the indicator sequence comprising “l”'s or “0”'s is selected m accordance with an encoder rate. In this notation, “1” indicates the tail output bit should be transmitted and “0” indicates that the tail output should be punctured.
• Certain entries m Table 1 are labeled “repeat”, which means that transmitte ⁇ bits are transmitted twice.
• tail input bit sequences 34, 34' which comprise tail input bits X, and X 1 , are generated after the encoders 10, 10' encode the information bits with the switches 12, 12' (FIG.l), while the switches 12, 12' are m an up position.
• the first n/R tail output bits Xi, Y ⁇ , Y wherein n is the number of shift registers 18, 21, 22 or 18', 21', 22' per constituent encoder (n 3 m FIG.l), ana wherein R is a t ⁇ rbo co ⁇ e rate being employed, are generated by clocking tne first encoder 10 n times w rn its switch 12 in the down position while the second encoder 10' is not clocked, and puncturing or repeating the resulting rail output bits Xi, Y 0 , Yi, X', Y c ' , Y: ' according to Table 1 below.
• the lasr n/R tail outpur bits X',Yo',Yi' are generated by clocking the second encoder 10' n timer with its switch 12' in the down position while the first encoder 10 is not clocked, and puncturing or repeating the resulting tail output bits according to Table 1. These final output bits are denoted by X', Y c ' or Yi ' .
• the tail output bits for each of a first n tail input bit are XYo
• the tail output bits for each of a last n tail bit periods are X ' Yc '
• the tail output bits for each of the first n tail input bits are XXYcY
• the tail ourput bits for each of the lasr n tail bits are X ' X ' Yo '
• the tail output bits for each of the first n tail input bits are XXYoYi and the tail output bits for each of the last n tail input bits periods are X ' X ' Yo ' Yi ' .
• Tail inputs bits are not interleaved by the interleaver 16. They are added after the encoding of the information bits.
• the row designation "repeat” means that for a rate 1/3 or a rate 1/4 turbo code, when transmitted, the bits X and X' are transmitted twice .
• the puncturing table is read first from top to bottom, and then from left to right.
• the puncturing table is read first from top to bottom, repeating X(t) and X' (t) , and then from left to right .
• the puncturing patterns in Table 1 are chosen so that:
• a number of transmitted rail output bits during trellis termination is 1/R for each trellis branch wherein R is the turbo code rate employed during information bit transmission.
• R is the turbo code rate employed during information bit transmission.
• X(t) and X' (t) are selected to be repeated in both the turbo code rate 1/3 and rate 1/4 cases.
• Table 1 may also be employed irrespective of whether the encoders 10, 10' are terminated concurrently or non-concurrently.
• tail output bit is selected to be repeated, such as, for example that corresponding to Yo(t) and Yn ' (t) .
• a code rate lower than 1/4 it may be necessary ro repeat more than one tail output bit per encoder 10, 10', m which case an additional tail bit besides X(t) may be repeated, such as repeating X(t) and Yo(t) or repeating X(t) twice or any combination whatsoever.

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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)
• Detection And Correction Of Errors (AREA)

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• 1999
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