Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1999-08-20
2001-12-18
Baker, Stephen M. (Department: 2784)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S792000
Reexamination Certificate
active
06332209
ABSTRACT:
BACKGROUND OF THE INVENTION
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 termination stage that ensures the same number of transmitted bits for each trellis stage during the information bit transmission and trellis termination stages.
The process of forward and reverse link turbo encoding and decoding, specifically for Code Division Multiple Access (CDMA) communications channels, is thoroughly described in copending U.S. patent application Ser. No. 09/248,338 of Eroz, et al., for SETS OF RATE-COMPATIBLE UNIVERSAL TURBO CODES NEARLY OPTIMIZED OVER VARIOUS RATES AND INTERLEAVER DELAYS, filed Feb. 11, 1999, and copending U.S. patent application Ser. No. 09/235,582, of Eroz, et al., for FORWARD ERROR CORRECTION SCHEME FOR DATA CHANNELS USING UNIVERSAL TURBO CODE, filed Jan. 22, 1999, both of which are incorporated herein by reference.
In a convolutional encoding scheme, tail bits are inserted after information bits, to zero out all shift registers of an encoder. For feed forward encoders, tail bits are equal to zero. For feedback encoders the value of tail bits depend on the contents of the shift register current values.
A turbo encoder consists of a parallel concatenation of two (2) or more recursive (feedback) convolutional encoders. Because each constituent encoder processes the information bits in a different order due to a turbo interleaver, 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 in the third generation CDMA systems is desirable. Included in the desirable general method is a method of puncturing tail bit sequences.
SUMMARY OF THE INVENTION
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 rates when transmitting information bits.
In its most general form, 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 at each of two or more constituent encoders, including the step of deriving the tail input bits from each of the two or more constituent encoders separately from the contents 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.
In yet another variation, 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.
REFERENCES:
patent: 5721745 (1998-02-01), Hladik et al.
patent: 6023783 (2000-02-01), Divsalar et al.
patent: 6289486 (2001-09-01), Lee et al.
patent: 19520987A1 (1996-12-01), None
patent: WO 99/07076 (1999-02-01), None
D. Divsalar & F. Pollara, Turbo Codes for PCS Applications, Jun. 18, 1995, pp. 54-59.
Eroz Mustafa
Hammons, Jr. A. Roger
Baker Stephen M.
Hughes Electronics Corporation
Sales Michael W.
Whelan John T.
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