Decoding system for distinguishing different types of convolutionally-encoded signals

• US 5,230,003 A
• Filed: 02/08/1991
• Issued: 07/20/1993
• Est. Priority Date: 02/08/1991
• Status: Expired due to Term

• Current Assignee: Ericsson GE Mobile Communications Inc (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson GE Mobile Communications Holding, Inc. A Corp. Of New Jersey (Telefonaktiebolaget LM Ericsson)
• Inventors: Dent, Paul W., Raith, Alex K.
• Primary Examiner(s): Beausoliel, Jr., Robert W.
• Assistant Examiner(s): CHUNG, PHUNG M
• Application Number:
  US07/652,544
• Time in Patent Office: 893 Days
• Field of Search: 371/43, 371/44, 371/45, 371/49.1, 371/25.1, 371/38.1, 371/39.1, 371/25.1
• US Class Current: 714/794
• CPC Class Codes: H03M 13/00 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 error detection or error correction for analogue/digital, digital/analogue or code conversion H03M1/00 – H03M11/00; specially adapted for digital computers G06F11/08; for information storage based on relative movement between record carrier and transducer G11B, e.g. G11B20/18; for static stores G11C
• CPC Class Codes: H04L 1/0046 Code rate detection or code type detection H04L1/0038 takes precedence; detection of the data rate H04L25/0262; for packet format H04L1/0091
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27

Abstract

A decoding system discriminates between different types of communications traffic signals. Each type of traffic signal is encoded using a different error correction code. Plural, parallel decoders each decode a received traffic signal using a different decoding technique. Each decoding technique operates in accordance with one of the error correction codes. A quantitative measurement of the reliability of a decoded result is generated by each decoder. A comparison processor accumulates the quantitative measurements made by each decoder and compares the accumulated values. That decoder having the most reliable, accumulated value is selected to decode the current traffic signals. The remaining decoders are deactivated to conserve processing time.

Claims

1. A communications system providing for discrimination between different types of encoded communications traffic signals, the different types of encoded communications traffic signals being encoded in accordance with respective error correction codes comprising:

a plurality of decoders for decoding the encoded communications traffic signals, each decoder providing a confidence factor representing a degree of correlation between the encoded communications traffic signals and a respective encoded traffic signal postulate, each decoder including;

means for comparing an encoded traffic signal postulate with said encoded communications traffic signal, and

means for generating a confidence factor based on said comparison, and

selection means for selecting one of said plurality of decoders based on the plurality of confidence factors so that said encoded communications traffic signals are decoded only by said selected decoder.

2. The system according to claim 1, wherein said encoded communications traffic signals are encoded using conventional error correction codes.

3. The system according to claim 1, wherein each decoder uses a sequential maximum likelihood estimation technique to optimally decode said encoded communications traffic signals, each decoder using a rate code and constraint length corresponding to a respective error correction code of a type of encoded communications traffic signal.

4. The system according to claim 3, wherein each decoder includes memory for storing encoded traffic signal postulate bit sequences, a history of selected bits corresponding to each of said encoded traffic signal postulate bit sequences, and a confidence factor corresponding to each of said encoded traffic signal postulate bit sequences.

5. The system according to claim 1, further comprising:

a transmitter having a convolutional encoder including;

an N-bit shift register for storing N bits of traffic information;

a logic circuit, coupled to the N-bit shift register, for logically combining particular ones of said N bits of traffic information in order to generate parity bits; and

means for transmitting said parity bits to a receiver in the system.

6. The system according to claim 5, wherein the encoded communications traffic signals are encoded using convolutional error correction codes, and each decoder uses a respective convolutional error correction code to decode said encoded communications traffic signals.

7. The system according to claim 1, wherein said encoded communications traffic signals are parity bits.

8. The system according to claim 1, wherein said different types of encoded communications traffic signals include a first type corresponding to voice traffic signals and a second type corresponding to data traffic signals, and wherein said first and second types are encoded with different convolutional codes.

9. The system according to claim 1, wherein each of said decoders optimally decodes a respective one of said different types of encoded communications traffic signals.

10. The system according to claim 1, wherein said selection means includes:

means for accumulating, over a plurality of iterations, said plurality of confidence factors provided by the plurality of decoders, and said selection means selects that decoder having an optimal accumulated confidence factor, the optimal accumulated confidence factor indicating that the respective decoder is most likely to have correctly decoded the encoded communications traffic signals.

11. The system according to claim 1, further comprising:

a transmitter having a convolutional encoder including;

interleaving means for interleaving sequential traffic symbols for each of the different types of encoded communications traffic signals in a non-sequential order, said non-sequential order being used for all of said different types of encoded communications traffic signals, and

a receiver, including said plurality of decoders, for receiving said interleaved traffic symbols, said receiver further including;

de-interleaving means for de-interleaving said interleaved traffic symbols in said non-sequential order.

12. The system according to claim 1, further comprising:

a transmitter having a convolutional encoder including;

interleaving means for interleaving sequential traffic symbols for each of the different types of encoded communications traffic signals in a respective non-sequential order, the respective non-sequential orders being different for different types of traffic signals; and

a receiver, including the plurality of decoders, for receiving said interleaved traffic symbols including;

de-interleaving means for de-interleaving said interleaved traffic symbols in the non-sequential orders corresponding to the different types of encoded communications traffic signals.

13. The system according to claim 1, wherein said selection means terminates operation of nonselected decoders.

14. The system according to claim 1, wherein two of the different types of encoded communications traffic signals are, respectively, encoded speech signals and encoded data signals, and the encoded speech signals are encoded using fewer parity bits than the encoded data signals.

15. The system according to claim 1, wherein said decoders are in parallel.

16. The system according to claim 1, further comprising:

a transmitter including;

a convolutional encoder for encoding different types of communications traffic signals using corresponding different convolutional codes; and

scrambling means for scrambling said different types of encoded communications traffic signals, the scrambling means using a scrambling pattern selected from a plurality of different scrambling patterns, wherein the selected scrambling pattern corresponds to the type of encoded communications traffic signal being scrambled; and

a receiver, including the plurality of decoders, for receiving said scrambled different types of communications traffic signals, the receiver further including;

descrambling means for descrambling said scrambled different types of communications traffic signals using all of said plurality of different scrambling patterns and generating a plurality of descrambled signals and for transmitting said descrambled signals to said plurality of decoders.

17. A communications system providing for discrimination between different types of encoded communications traffic signals, the different types of encoded communications traffic signals being distinguished from one another by their tolerance of errors, comprising:

a plurality of decoders for iteratively decoding the encoded communications traffic signals, each decoder including;

first means for generating a plurality of communications traffic signal postulate bit states;

means for encoding each of said communications traffic signal postulate bit states to generate a respective series of communications traffic signal postulate parity bits;

means for comparing said communications traffic signal postulate parity bits with parity bits of received communications traffic signals;

second means, coupled to the comparing means, for generating an error signal representing a degree of correlation between said communications traffic signal postulate parity bits and the received communications traffic signal parity bits; and

means, coupled to the first and second means, for selecting the communications traffic signal postulate bit state which corresponds to the series of communications traffic signal postulate parity bits for which a lowest error signal was generated and for providing the selected bit state at an output, and

selection means for selecting the decoder which generated the lowest of the lowest error signals, wherein said selected decoder optimally decodes one of the different types of encoded communications traffic signals received.

18. The communications system according to claim 17, wherein said encoding means encodes said communications traffic signal postulate bit states using a convolutional coding procedure used to encode one of the different types of encoded communications traffic signals.

19. The system according to claim 17, further comprising:

a transmitter having a convolutional encoder including;

interleaving means for interleaving sequential traffic symbols for each of the different types of encoded communications traffic signals in a non-sequential order, said non-sequential order being used for all of said different types of encoded communications traffic signals, and

a receiver, including said plurality of decoders, for receiving said interleaved traffic symbols including;

de-interleaving means for de-interleaving said interleaved traffic symbols in said non-sequential order.

20. The system according to claim 17, further comprising:

a transmitter having a convolutional encoder including;

interleaving means for interleaving sequential traffic symbols for each of the different types of encoded communications traffic signals in a respective non-sequential order, the respective non-sequential orders being different for different types of traffic signals; and

a receiver, including the plurality of decoders, for receiving said interleaved traffic symbols including;

de-interleaving means for de-interleaving said interleaved traffic symbols in the non-sequential orders corresponding to the different types of encoded communications traffic signals.

21. The system according to claim 17, wherein said selection means terminates operation of nonselected decoders.

22. The system according to claim 17, further comprising:

a transmitter including;

a convolutional encoder for encoding different types of communications traffic signals using corresponding different convolutional codes; and

scrambling means for scrambling said different types of encoded communications traffic signals, the scrambling means using a scrambling pattern selected from a plurality of different scrambling patterns, wherein the selected scrambling pattern corresponds to the type of encoded communications traffic signal being scrambled; and

a receiver, including the plurality of decoders, for receiving said scrambled different types of communications traffic signals, the receiver further including;

descrambling means for descrambling said scrambled different types of communications traffic signals using all of said plurality of different scrambling patterns and generating a plurality of descrambled signals and for transmitting said descrambled signals to said plurality of decoders.

23. In a communications system of the type in which different types of information are transmitted with different respective types of encoding, the different types of information being distinguished from one another by their respective tolerance of errors, a method for decoding received encoded information, comprising the steps of:

decoding the received encoded information by a decoding technique which operates in accordance with a code used to encode a first type of information, and providing a first quantitative measurement of reliability of a first decoded result;

decoding the received encoded information by a decoding technique which operates in accordance with a code used to encode a second type of information, and providing a second quantitative measurement of reliability of a second decoded result;

comparing the first and second quantitative measurements; and

selecting one of the first and second decoded results based on said comparison.

24. The method of claim 23 further including the steps of:

continuing one of said decoding steps based on said comparison; and

terminating the other decoding step.