Sub-optimal iterative receiver method and system for a high-bit-rate CDMA transmission system

• US 7,298,778 B2
• Filed: 08/09/2002
• Issued: 11/20/2007
• Est. Priority Date: 09/06/2001
• Status: Active Grant

• Current Assignee: Orange S.A.
• Original Assignee: Orange S.A.
• Inventors: Visoz, Raphael, Boujemaa, Hatem
• Primary Examiner(s): Payne; David C.
• Assistant Examiner(s): Guarino; Rahel
• Application Number:
  US10/488,827
• Publication Number:
  US 20050013348A1
• Time in Patent Office: 1,929 Days
• Field of Search: 375/130, 375/135, 375/140, 375/144, 375/147, 375/148, 375/233, 375/265, 375/316, 375/340, 375/341, 375/348, 375/347, 375/260, 714/755, 714/786, 714/792, 714/795
• US Class Current: 375/148
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04L 25/0236 using estimation of the other symbols
• CPC Class Codes: H04L 25/0242 using matrix methods
• CPC Class Codes: H04L 25/025 using least-mean-square [LMS] method
• CPC Class Codes: H04L 25/03235 with state-reduction using feedback filtering
• CPC Class Codes: H04L 25/06 Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection

Abstract

A reception method and receiver structure that are relatively simple, that have close to optimum performance, and that use high order modulation combined with a low spreading factor are disclosed. The method receives a signal transmittal in the form of sequences of coded binary symbols comprising both predefined pilot symbols and date symbols multiplied by a spreading sequence. The method also includes a step of determining a channel estimate using received predefined pilot symbols. A system for receiving a signal transmitted on a multipath transmission channel using a spread spectrum technique and low spreading factor is also disclosed.

Claims

1. A method for receiving a signal transmitted on a multipath transmission channel using a spread spectrum technique with a low spreading factor, said signal being transmitted in the form of sequences of coded binary symbols comprising predefined pilot symbols and data symbols, multiplied by a spreading sequence, said method including a step of determining a channel estimate using received predefined pilot symbols, the method comprising

reconstituting the transmitted signal by means of a rake receiver using a rake receiver that utilizes the channel estimate on the basis of received signals that were transmitted over the multiple paths of the transmission channel,

determining an equivalent model of the channel as seen at the output of the rake receiver as a function of the channel estimate,

reducing intersymbol interference in the reconstituted transmitted signal resulting from the low spreading factor, using the channel equivalent model and a DDFSE detector based on a trellis with a reduced number of states and delivering at its output estimated values of the received coded symbols,

de-interleaving the coded symbols, and

decoding the estimated values of the de-interleaved coded symbols to reconstitute the transmitted data symbols.

2. The method according to claim 1, wherein the estimated values of the received coded symbols obtained after interference reduction and decoding are weighted or flexible values.

3. The method according to claim 2, wherein the steps of reducing intersymbol interference and decoding are included in an iterative process wherein the coded and de-interleaved symbols obtained in an iteration n are re-estimated during decoding as a function of the data symbols obtained after decoding and error correction, the difference between the re-estimated coded symbols obtained in the same iteration and the de-interleaved coded symbols obtained in the next iteration n+1 is re-interleaved and then applied to the input of the DDFSE detector and subtracted from the coded symbols obtained in the iteration n 1 at the output of the DDFSE detector.

4. The method according to claim 1, wherein the channel estimate is improved using a least squares (LS) method.

5. The method according to claim 1, wherein the channel estimate is improved using a minimum mean square error (MMSE) algorithm.

6. The method according to claim 1, wherein the channel is estimated in an iterative process and the coded and de-interleaved symbols obtained in an iteration n are re-estimated during decoding as a function of the data symbols obtained after decoding and error correction, the re-estimated coded symbols are interleaved, a channel estimate is obtained on the basis of the re-estimated and interleaved coded symbols, an equivalent channel model is determined from the channel estimate, and the channel estimate and the channel equivalent model determined in an iteration n are respectively used to reconstitute the transmitted signal and to reduce intersymbol interference in the next iteration n+1.

7. A system for receiving a signal transmitted on a multipath transmission channel using a spread spectrum technique and a low spreading factor, said signal being transmitted in the form of a sequence of coded binary symbols comprising predefined pilot symbols and data symbols and multiplied by a spreading sequence, said system comprising a rake receiver for reconstituting the transmitted signal using a channel estimate on the basis of the signals received and transmitted by the multiple paths of the transmission channel and first channel estimation means for estimating the channel on the basis of the pilot symbols received, to deliver a transmission channel estimate to the rake receiver, wherein the system further comprises:

channel modeling means for determining an equivalent model of the channel as seen at the output of the rake receiver as a function of the channel estimate,

reduction means for reducing intersymbol interference between received symbols, the reducing means comprising a DDFSE detector based on a trellis with a reduced number of states, for reducing intersymbol interference between received symbols using the equivalent channel model and reconstituting estimated values of the coded symbols received,

de-interleaving means for de-interleaving the estimated values of the coded symbols received, and

decoding means for decoding the estimated and de-interleaved values and supplying the data symbols transmitted.

8. The reception system according to claim 7, wherein the estimated and de-coded values delivered by the intersymbol interference reduction means and the decoding means are weighted or flexible values.

9. The reception system according to claim 7, further comprising:

means for re-estimating the coded symbols as a function of the decoded data symbols after error correction,

first subtraction means for subtracting the estimated and de-interleaved coded symbols from the re-estimated coded symbols and obtaining a sequence of extrinsic re-estimated coded symbols,

first interleaving means for interleaving the sequence of extrinsic re-estimated coded symbols, and

second subtraction means for subtracting the sequence of extrinsic re-estimated coded symbols from the sequence of symbols received and estimated by the reduction means on the next iteration.

10. The reception system according to claim 9, further comprising:

second interleaving means for interleaving the sequence of re-estimated coded symbols at the output of the decoding means, and

second channel estimation means for supplying a transmission channel estimate on the basis of the interleaved sequence of re-estimated coded symbols to the means for determining an equivalent channel model and to the rake receiver.