Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1999-01-25
2001-10-02
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S784000, C714S795000
Reexamination Certificate
active
06298461
ABSTRACT:
This invention relates to encoding and decoding methods and apparatus. The invention can be applied to various systems which may be used for example for the communication or storage of signals, but is particularly applicable to, and is described below in the context of, CDMA (code division multiple access) communications which are increasingly being used in cellular wireless communications systems. As can be fully appreciated from the description below, the term “decoding” is used herein to embrace not only the function of decoding but also, where applicable, the functions of demodulation or other detection of a signal using soft and/or hard decisions, and the term “decoder” is used correspondingly.
BACKGROUND
A class of parallel concatenated convolutional codes, also known as PCCCs or turbo codes, is known for example from an article by C. Berrou et al. entitled “Near Shannon Limit Error-Correcting Coding And Decoding: Turbo-Codes”, Proceedings of the IEEE International Conference on Communications, 1993, pages 1064-1070. That article showed that a turbo code together with an iterative decoding algorithm could provide performance in terms of BER (Bit Error Rate) that is close to the theoretical limit. A turbo code encoder provides a parallel concatenation of two (or more) RSC (Recursive Systematic Convolutional) codes which are typically, but not necessarily, identical, applied to an input bit sequence and an interleaved version of this input bit sequence. The output of the encoder comprises systematic bits (the input bit sequence itself) and parity bits which can be “punctured ” (selected) to provide a desired rate of encoding.
Various schemes are being proposed and developed to provide, especially for the communication of data in a CDMA (code division multiple access) communications system a greater bandwidth (signal transmission rate) than is provided in a so-called IS-95 system which is compatible with TIA/EIA (Telecommunications Industry Association/Electronic Industries Association) Interim Standard IS-95-A, “Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System”. Turbo coding has been proposed for such WCDMA (wideband CDMA) systems. However, turbo coding does not provide a great increase in code distance, which is a significant disadvantage for a BER of less than about 10
−5
which is desirable for WCDMA systems.
It is desirable to optimize the application of turbo coding to WCDMA systems, in order to obtain maximum coding gains.
An object of this invention is to provide improved encoding and decoding methods and apparatus.
SUMMARY OF THE INVENTION
One aspect of this invention provides a method of encoding information comprising: a first step of encoding said information in accordance with an outer code to produce encoded information; and a subsequent step of encoding said encoded information in accordance with an inner code in a parallel concatenated convolutional code encoder. Preferably the first step comprises Reed-Solomon encoding.
Another aspect of the invention provides encoding apparatus comprising a first encoder for encoding information in accordance with an outer code serially concatenated with a second encoder for encoding in accordance with an inner code the information encoded by the first encoder, the second encoder comprising a parallel concatenated convolutional code encoder comprising an interleaver for interleaving the information encoded by the first encoder and two recursive systematic convolutional encoders for encoding the information encoded by the first encoder at an input and an output of the interleave).
A further aspect of the invention provides parallel concatenated convolutional code decoding apparatus comprising: a first convolutional code decoder for providing soft decoding decisions of at least one input signal comprising systematic and parity information; an interleaver; a second convolutional code decoder for providing soft decoding decisions in response to an output from the first decoder derived via the interleaver and a further input signal comprising parity information, and a parallel feedback path including a deinterleaver for feeding back to the first decoder information derived from the second decoder for enhancing soft decoding decisions by the first decoder in at least one subsequent decoding iteration; characterized by further comprising summing functions in the paths from the first decoder to the interleaver and from the second decoder to the deinterleaver for subtracting information from the output of the deinterleaver and interleaver respectively to produce extrinsic information for supply to the interleaver and deinterleaver respectively.
Yet another aspect of the invention provides a method of decoding information encoded by the method recited above, comprising the steps of decoding a parallel concatenated convolutional code (PCCC) encoded signal using an iterative PCCC decoder to produce soft decoder decisions, decoding the soft decoder decisions using a soft outer code decoder, and enhancing the iterative decoding by the PCCC decoder using information fed back from the Soft outer code decoder.
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Bakouline Mikhail G.
Chloma Alexandre M.
Kreindeline Vitali B.
Shinakov Yuri S.
Tong Wen
De'cady Albert
Haszko Dennis R.
Lamarre Guy J.
Nortel Networks Limited
Smart & Biggar
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