Effective bypass of error control decoder in a digital radio system

• US 6,035,007 A
• Filed: 03/12/1996
• Issued: 03/07/2000
• Est. Priority Date: 03/12/1996
• Status: Expired due to Term

• Current Assignee: Blackberry Limited
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Khayrallah, Ali S., Ramesh, Rajaram, Toy, Raymond
• Primary Examiner(s): Vo, Don N.
• Assistant Examiner(s): PARK, ALBERT C
• Application Number:
  US08/614,317
• Time in Patent Office: 1,456 Days
• Field of Search: 375/341, 375/262, 371/43.1, 371/43.6, 371/43.7
• US Class Current: 375/341
• CPC Class Codes: H03M 13/01 Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
• CPC Class Codes: H03M 13/39 Sequence estimation, i.e. using statistical methods for the reconstruction of the original codes
• CPC Class Codes: H04L 1/004 by using forward error control H04L1/0618 takes precedence; coding, decoding or code conversion, for error detection or correction H03M13/00

Abstract

A digital radio communications system including a suboptimal soft decision (e.g., errors and erasures) channel decoder and a speech decoder can be upgraded to effectively bypass the hard decision channel decoder and allow a higher performance soft decision (e.g., maximum likelihood sequence estimate (MLSE)) decoder to be used--without requiring physical removal or disconnection of the hard decision channel decoder. The new decoder can feed the existing decoder the right choice of received vector r'"'"' to force the existing decoder to produce a certain codeword y'"'"' and a certain bit error estimate b'"'"'. This technique is useful to test new MLSE decoders on existing radios, or to add an MLSE decoder as an upgrade on existing receivers.

Claims

1. A method of bypassing a decoder that, in use, decodes a received digital signal, said method comprising:

(1) decoding a received digital signal to produce at least one codeword;

(2) generating information including error patterns and an error estimate based on decoding step (1); and

(3) feeding, to said decoder, said error patterns to force the decoder to produce (a) a codeword corresponding to the codeword produced by step (1), and (b) an error estimate corresponding to the error estimate generated by step (2), thereby effectively bypassing said decoder.

2. A method as in claim 1 wherein the decoding step (1) comprises soft decision decoding, and said decoder performs hard decision decoding.

3. A method as in claim 1 wherein feeding step (3) includes the step of conditionally feeding the decoder a signal corresponding to the received digital signal uncorrected by decoding step (1).

4. A method as in claim 1 wherein said step (3) includes generating at least some artificial error patterns based at least in part on the error estimate produced by step (2).

5. A method of decoding a received digital signal comprising:

(1) decoding a received digital signal to produce at least one codeword;

(2) generating an error estimate based on decoding step (1); and

(3) feeding information including said error estimate and said codeword to a further decoding process that forces the further decoding process to produce (a) a codeword corresponding to the codeword produced by step (1), and (b) an error estimate corresponding to the error estimate produced by step (2),

wherein step (3) includes the step of feeding artificial errors to the further decoding process.

6. A method as in claim 5 further including generating the artificial errors based at least in part on the error estimate produced by step (2).

7. A method of decoding a received digital signal comprising:

(1) decoding a received digital signal to produce at least one codeword;

(2) generating an error estimate based on decoding step (1); and

(3) feeding information to a further decoding process that forces the further decoding process to produce (a) a codeword corresponding to the codeword produced by step (1), and (b) an error estimate corresponding to the error estimate produced by step (2),

wherein step (2) includes the step of determining the number of bit errors, and step (3) includes the step of determining whether the further decoding process can correct the determined number of bit errors.

8. A digital signal decoding arrangement for bypassing a decoder that, in use, decodes a received digital signal, said arrangement comprising:

a first decoder for decoding the received digital signal to produce at least one codeword and for generating an error estimate based on said decoding; and

output means coupled to the first decoder for feeding, to a further decoder to be bypassed, information including error patterns that forces the further decoder to produce (a) a codeword corresponding to the codeword produced by the first decoder, and (b) an error estimate corresponding to the error estimate produced by the first decoder, thereby effectively bypassing said further decoder.

9. A decoding arrangement as in claim 8 wherein the decoding arrangement further includes the further decoder.

10. A decoding arrangement as in claim 9 wherein the further decoder includes a circuit that produces, in response to the information fed to it by the outputting means, a codeword equal to the codeword produced by the first decoder.

11. A decoding arrangement as in claim 9 wherein the further decoder includes a circuit that produces, in response to the information fed to it by the outputting means, an error estimate that matches the error estimate produced by the first decoder.

12. A decoding arrangement as in claim 9 wherein the first decoder includes means for making a soft decision, and the further decoder comprises means for making a hard decision.

13. A decoding arrangement as in claim 8 wherein outputting means includes means for conditionally feeding the further decoder a signal corresponding to the received digital signal uncorrected by the first decoder.

14. An arrangement as in claim 8 wherein said output means includes a circuit that generates at least some artificial error patterns based on said generated error estimate.

15. A digital signal decoding arrangement comprising:

a first decoder for decoding the received digital signal to produce at least one codeword and for generating an error estimate; and

output means coupled to the first decoder for feeding, to a further decoder, information that forces the further decoder to produce (a) a codeword corresponding to the codeword produced by the first decoder, and (b) an error estimate corresponding to the error estimate produced by the first decoder,

wherein the decoding arrangement further includes the further decoder, and

wherein the further decoder produces, in response to the information fed to it by the outputting means, an error estimate that is the minimum of;

(i) the error estimate produced by the first decoder, and (ii) the largest corresponding coset leader weight of the further decoder.

16. A digital signal decoding arrangement comprising:

a first decoder for decoding the received digital signal to produce at least one codeword and for generating an error estimate; and

output means coupled to the first decoder for feeding, to a further decoder, information including said error estimate and said code word that forces the further decoder to produce (a) a codeword corresponding to the codeword produced by the first decoder, and (b) an error estimate corresponding to the error estimate produced by the first decoder,

wherein the outputting means includes means for feeding artificial errors to the further decoder.

17. A decoding arrangement as in claim 16 wherein the outputting means further includes means for generating the artificial errors based at least in part on the error estimate produced by the first decoder.

18. A digital signal decoding arrangement comprising:

a first decoder for decoding the received digital signal to produce at least one codeword and for generating an error estimate; and

output means coupled to the first decoder for feeding, to a further decoder, information that forces the further decoder to produce (a) a codeword corresponding to the codeword produced by the first decoder, and (b) an error estimate corresponding to the error estimate produced by the first decoder,

wherein the first decoder includes means for detecting errors, and the output means includes means for determining whether the further decoder can correct the detected errors.

19. In a radio communications system having a demodulator, an existing channel decoder that produces a decoded received signal output and an error estimate, and a speech decoder that expands the received signal output to recover a digitized voice data stream based at least in part on the error estimate, a method for upgrading the radio communications system by supplying a further channel decoder and effectively bypassing the existing channel decoder without removing the existing channel decoder from the system, said method comprising the step of inserting, between the demodulator and the channel decoder, a further channel decoder that:

(a) detects and corrects errors in the demodulator'"'"'s output, and

(b) provides information including error patterns to the existing detector that forces the existing channel decoder to provide the speech decoder with an error estimate that corresponds to the errors corrected by the further channel decoder, thereby effectively bypassing said further channel decoder.

20. A method as in claim 19 wherein step (b) includes generating at least some artificial error patterns based on said error estimate.

21. A radio communications system comprising:

a demodulator,

a first channel decoder that produces a decoded received signal output and an error estimate,

a speech decoder, connected to receive the decoded received signal output and the error estimate, that expands the decoded received signal output to recover a digitized voice data stream based at least in part on the error estimate, and

a further channel decoder connected between the demodulator and the first channel decoder, the further channel decoder including;

a channel decoder arrangement that detects and corrects at least some errors in the demodulator'"'"'s output that the first channel decoder cannot correct, and

an output circuit connected to the channel decoder arrangement that provides information including error patterns to the first channel decoder forcing the first channel decoder'"'"'s error estimate to reflect the errors corrected by the further channel decoder, thereby effectively bypassing said first channel decoder.

22. A radio communications system comprising:

a demodulator,

a first channel decoder that produces a decoded received signal output and an error estimate,

a speech decoder, connected to receive the decoded received signal output and the error estimate, that expands the decoded received signal output to recover a digitized voice data stream based at least in part on the error estimate, and

a further channel decoder connected between the demodulator and the first channel decoder, the further channel decoder including;

a channel decoder arrangement that detects and corrects at least some errors in the demodulator'"'"'s output that the first channel decoder cannot correct, and

an output circuit connected to the channel decoder arrangement that provides information to the first detector forcing the first channel decoder'"'"'s error estimate to reflect the errors corrected by the further channel decoder,

wherein the output circuit includes means for routing the demodulator'"'"'s output to the first decoder if the first decoder can correct all errors contained in the demodulator'"'"'s output.

23. A digital receiver method comprising:

(a) receiving an RF signal;

(b) demodulating the received RF signal to provide a received digital signal;

(c) performing maximum likelihood sequence estimate channel decoding on the received digital signal to produce at least one error-corrected codeword;

(d) generating an error correction estimate based on step (c);

(e) producing an artificial received digital signal, based on the error correction estimate, that contains error information that will force a further decoding step (f) to produce the error-corrected codeword and a further error correction estimate that corresponds to the error correction estimate generated by step (d); and

(f) channel decoding and speech decoding the artificial received digital signal.

24. A method as in claim 23 wherein step (e) includes the step of intentionally introducing at least one artificial error pattern into the codeword, and step (f) includes the step of detecting and correcting the artificial error pattern.