Method and arrangement for demodulating data symbols

• US 6,269,116 B1
• Filed: 09/18/1998
• Issued: 07/31/2001
• Est. Priority Date: 09/19/1997
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Javerbring, Stefan, H{umlaut over (oo)}k, Mikael
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Corrielus, Jean B.
• Application Number:
  US09/156,627
• Time in Patent Office: 1,047 Days
• Field of Search: 375/229, 375/230, 375/232, 375/233, 375/316, 375/341, 375/346, 375/348, 375/349, 375/377, 375/340, 375/227, 708/323
• US Class Current: 375/229
• CPC Class Codes: H04L 2025/0356 Switching the time direction of equalisation
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence

Abstract

The present invention relates to a method and an arrangement for demodulating data symbols (d₁-d_N) having been transmitted through a communication channel, particularly a channel suffering from one or more impairments. Received signal samples ({overscore (ρ)}), representing the sent data symbols (d₁-d_N), are stored (310) and demodulated in both the forward (320) and the backward direction (330), via a demodulator/equaliser. In course of the demodulations are produced a first (S_F) and a second (S_B) respective set of soft values (s_k^F; s_k^B), which each is associated with a certain data symbol (d_k). (340) From every pair of soft values (s_k^F; s_k^B) is then determined a joint soft value (S_k^J), which e.g. may be utilised for deriving a resulting set of data symbols ({circumflex over (d)}₁-{circumflex over (d)}_N) or for directly decoding the payload information contained in the data symbols (d₁-d_N).

Claims

1. A method of demodulating data symbols transmitted through a communication channel, comprising the steps of:

sequentially receiving a plurality of signal samples representing the data symbols;

storing the received plurality of signal samples;

forward-demodulating the stored signal samples into a first set of soft values, each associated with a particular data symbol;

backward-demodulating the stored signal samples into a second set of soft values, each associated with a particular data symbol;

determining, from the first and the second sets of soft values, a joint set of soft values, which for each data symbol expresses a joint soft value.

2. A method according to claim 1, wherein the data symbols are multi-bit symbols.

3. A method according to claim 2, wherein the soft values are vectors, in which each element reflects the probability for a particular demodulated data symbol.

4. A method according to claim 2, wherein a soft value having a sign and a modulus is determined for each individual data bit of the data symbols;

and

wherein each soft value reflects the probability for a particular demodulated data bit.

5. A method according to claim 1, wherein the data symbols are binary.

6. A method according to claim 4, wherein the sign of the soft value indicates a decided data bit of a corresponding hard data decision;

and

wherein the modulus of the soft value.

7. A method according to claim 6, wherein each joint soft value is constituted by the sum of the first and the second soft values for a particular data bit.

8. A method according to claim 6, wherein the soft values are expressed as log-likelihood functions.

9. A method according to claim 4, wherein all soft values are probability functions.

10. A method according to claim 4, wherein all soft values are probabilities.

11. A method according to claim 3, wherein all soft values are probabilities.

12. A method according to claim 10, wherein each joint soft value is determined as an element-by-element average value between a first soft value from the first set of soft values and a corresponding first soft value from the second set of soft values.

13. A method according to claim 3, wherein all soft values are probability functions.

14. A method according to claim 1, wherein the signal samples are demodulated via linear equalisation.

15. A method according to claim 1, wherein the signal samples are demodulated via decision feedback equalisation.

16. A method according to claim 1, wherein the signal samples are demodulated via decision feedback sequence estimation.

17. A method according to claim 1, wherein the signal samples are demodulated via reduced state sequence estimation.

18. An arrangement for demodulating data symbols transmitted through a communication channel, comprising:

means for sequentially receiving a plurality of signal samples;

means for storing the received plurality of signal samples;

means for forward-demodulating the stored signal samples into a first set of soft values;

means for backward-demodulating the stored signal samples into a second set of soft values;

means for deriving a joint soft value from a first soft value of the first set from soft values and a corresponding first soft value of the second set from soft values, for each data symbol.

19. An arrangement according claim 18, further comprising:

means for storing the first set of soft values; and

means for storing the second set of soft values.

20. An arrangement according claim 18, further comprising:

means for deriving a resulting set of data symbols from the joint soft values.

21. An arrangement according to claim 18, wherein said arrangement is a component in a radio base station.

22. An arrangement according to claim 18, wherein said arrangement is a component in a radio base station controller.

23. An arrangement according to claim 18, wherein said arrangement is a component in a mobile radio station.