Iterative decoding of data packets employing decision feedback equalization

• US 6,570,919 B1
• Filed: 07/30/1999
• Issued: 05/27/2003
• Est. Priority Date: 07/30/1999
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Lee, Inkyu
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): TRAN, KHANH C
• Application Number:
  US09/363,743
• Time in Patent Office: 1,397 Days
• Field of Search: 375/232, 375/233, 375/340, 375/341, 375/348, 375/346, 375/350, 714/755, 714/759, 714/774, 714/786, 714/794, 714/795
• US Class Current: 375/233
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0065 Serial concatenated codes
• CPC Class Codes: H04L 1/0066 Parallel concatenated codes
• CPC Class Codes: H04L 25/03146 with a recursive structure H04L25/03127 takes precedence

Abstract

A data transmission system employs an iterative decoder that applies decision feedback equalization (DFE) to channel output samples of a packet of data. The iterative decoder receives a stream of channel output samples as packets that may, for example, be read from a sector of a recording medium. Each packet may represent user data encoded, for example, with a concatenated code formed from N component codes, N a positive integer. The iterative decoder employs I decoding iterations, I a positive integer. DFE employs two filters: a feedforward filter and a feedback filter. The feedforward filter, which may be a whitened-matched filter used for detection, shifts dispersed channel output energy into the current sample. The feedback filter cancels energy of trailing inter-symbol interference from previous symbols. In each iteration by the iterative decoder, the DFE is applied to channel output samples of a packet by filtering with the feedforward filter, and then filtering with the feedback filter to cancel interference energy in the current sample from previous samples. The feedback filter uses soft information corresponding to tentative decisions for decoded data of the packet. During the first iteration, the soft information for applying DFE to the current sample is derived from the slicer output directly, and during the second and subsequent iterations the soft data of the decoder is provided to the feedback filter of the equalizer as soft information.

Claims

1. A method of iteratively decoding a data packet, comprising the steps of:

(a) applying decision feedback equalization (DFE) to the data packet during a first decoding iteration of the data packet; and

(b) applying DFE to the data packet during a second iteration, wherein the DFE employs soft data generated for the data packet during the first iteration, wherein the soft data is generated by the step of decoding the data packet to which DFE is applied, the step of decoding being in accordance with a concatenated code.

2. The invention as recited in claim 1, further comprising step of (c) applying DFE to the data packet during one or more iterations after the second iteration, wherein for each iteration the step of applying DFE employs soft data generated for the data packet during the previous iteration.

3. The invention as recited in claim 1, wherein the data packet comprises a plurality of samples, and for steps (a) and (b), applying DFE includes the steps of feedforward filtering of the data packet to shift dispersed energy to a current sample;

and feedback filtering of soft information derived from the feedforward-filtered data packet to reduce precurser energy in the current sample.

4. The invention as recited in claim 3, wherein, for step (a), feedback filtering employs soft information estimated from the plurality of samples of the packet.

5. The invention as recited in claim 3, wherein for step (b), feedback filtering employs as soft information the soft data generated by decoding the samples of the data packet to which DFE is applied in a previous iteration.

11. The invention as recited in claim 1, wherein the iterative decoder is included in either a read side of a recording system, a receiver of a communication system, or an interface card of a packet network.

6. Apparatus for iteratively decoding data packets, comprising:

an equalizer for applying decision feedback equalization (DFE) to the data packet; and

a decoder for decoding the data packet to provide soft data,

wherein the equalizer applies DFE to the data packet during a first decoding iteration of the data packet; and

applies DFE to the data packet during a second iteration, the DFE employing the soft data generated for the data packet during the first iteration, and

wherein the soft data is generated by the decoder by decoding, in accordance with a concatenated code, the data packet to which DFE is applied.

7. The invention as recited in claim 6, wherein the equalizer applies DFE to the data packet during one or more iterations after the second iteration, wherein for each iteration the step of applying DFE employs soft data generated for the data packet by the decoder during the previous iteration.

8. The invention as recited in claim 6, wherein the data packet comprises a plurality of samples, and the equalizer comprises a feedforward filter and a feedback filter, the feedforward filter filtering the packet to shift dispersed energy to a current sample;

and the feedback filter filtering of soft information derived from the feedforward-filtered data packet to reduce precursor energy in the current sample.

9. The invention as recited in claim 8, further comprising a slicer wherein the feedback filter employs soft information estimated by the slicer from the plurality of samples of the data packet.

10. The invention as recited in claim 8, wherein the feedback filter employs as soft information the soft data generated by decoding the samples of the data packet to which DFE is applied in a previous iteration.

12. A computer-readable medium having stored thereon a plurality of instructions, the plurality of instructions including instructions which, when executed by a processor, cause the processor to implement a method for iteratively decoding data packets, the method comprising the steps of:

(a) applying decision feedback equalization (DFE) to the data packet during a first decoding iteration of the data packet, wherein the DFE employs soft information for the data packet in the first decoding iteration; and

(b) applying DFE to the data packet during a subsequent iteration, wherein the DFE employs soft data generated for the data packet during a previous decoding iteration,

wherein, for step (b), the soft data is generated by the step of decoding the data packet to which DFTE is applied, the step of decoding being in accordance with a concatenated code.

13. The invention as recited in claim 12, further comprising step of (c) applying DFE to the data packet during one or more iterations after the second iteration, wherein for each iteration the step of applying DFE employs soft data generated for the data packet during the previous iteration.

14. An integrated circuit having a decoder for iteratively decoding data packets, comprising:

a slicer generating decisions for a data packet,

an equalizer for applying decision feedback equalization (DFE) to the data packet; and

a decoder for decoding the data packet to provide soft data,

wherein the equalizer applies DFE to the data packet during a first decoding iteration of the data packet and the DFE employs soft information for the data packet in the first decoding iteration; and

wherein the equalizer applies DFE to the data packet during a subsequent iteration, the DFE employing the soft data generated for the data packet during a previous decoding iteration, and

wherein the soft data is generated by the decoder by decoding, in accordance with a concatenated code, the data packet to which DFE is applied.

15. The invention as recited in claim 14, wherein the equalizer applies DFE to the data packet during one or more iterations after the second iteration, wherein for each iteration the step of applying DFE employs soft data generated for the data packet by the decoder during the previous iteration.