Filter structure for iterative signal processing

• US 8,411,767 B2
• Filed: 08/21/2008
• Issued: 04/02/2013
• Est. Priority Date: 05/02/2002
• Status: Expired due to Term

• Current Assignee: Cohda Wireless Pty Ltd., University of South Australia (University of Adelaide)
• Original Assignee: Cohda Wireless Pty Ltd., University of South Australia (University of Adelaide)
• Inventors: Alexander, Paul Dean, Grant, Alexander James, Rasmussen, Lars Kildehoj, Jakas, Stephen Peter
• Primary Examiner(s): NGUYEN, LEON VIET Q
• Application Number:
  US12/195,492
• Publication Number:
  US 20080317150A1
• Time in Patent Office: 1,685 Days
• Field of Search: 370/203, 370/208, 370/330, 370/350, 370/503, 375/147, 375/260, 375/267, 375/343, 375/344
• US Class Current: 375/260
• CPC Class Codes: H04L 25/0202 Channel estimation
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/03171 Arrangements involving maximum a posteriori probability [MAP] detection
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

The present invention relates to improved multiple access communications. In one form, the invention relates to an improved signal processing method and apparatus for an iterative method of determining the reception of a signal in a multi user packet based wireless OFDM (Orthogonal Frequency Division Multiplexing) communication system. In other forms the present invention provides recursive filtering for joint iterative decoding in a variety of systems and functions such as linear multiple access channel decoders, iterative equalization, iterative joint channel estimation and detection/decoding, iterative space-time processing, iterative multi user interference cancellation and iterative demodulation. In one particular form the present invention provides an iterative decoding circuit for a wireless multiuser communications receiver comprising a first signal processing means for receiving at least one received signal, said first signal processing means comprising at least two linear iterative filters such that the first linear iterative filter provides an estimate of a selected received signal to an estimated signal output and a second linear iterative filter provides estimates of at least one other received signal, delayed by one iteration cycle, to an input of said first linear iterative filter, a second signal processing means for receiving the estimated signal output of the first linear iterative filter and providing a further received signal estimate to the input of the first signal processing means in a succeeding iteration cycle of the decoding circuit.

Claims

1. A method of communicating in a multiple access network using a time varying channel estimate in a receiver for receiving packets, the receiver retrieving orthogonal frequency-division multiplexing (OFDM) data symbols from a received signal and transforming the retrieved OFDM data symbols to a frequency domain, the method comprising:

determining a matrix of training data symbols comprising data symbol estimates derived from a decoder;

determining a matrix of frequency domain received OFDM data symbols;

determining an intermediate channel estimate matrix by multiplying the matrix of frequency domain received OFDM data symbols by a conjugate of the matrix of training data symbols;

determining an intermediate matrix of training weights comprising an absolute value of the matrix of training data symbols;

performing a smoothing operation on both intermediate matrices comprising two-dimensional filtering; and

determining the time varying channel estimate by dividing the smoothed channel estimate matrix with the smoothed training weight matrix.

2. The method according to claim 1 further comprising:

storing the time varying channel estimate in a channel estimate database at the receiver.

3. The method according to claim 2 further comprising transforming the retrieved OFDM data symbols to the frequency domain prior to updating the stored time varying channel estimate to provide a time smoothed channel estimate reference.

4. The method according to claim 1 further comprising:

for each subsequent OFDM data symbol, pipelining demodulating and modulating; and

updating a channel estimate reference with forward error correction (FEC) decoding.

5. The method according to claim 1 wherein a first coded data symbol is received after a preamble data symbol.

6. The method according to claim 1 wherein each retrieved OFDM data symbol comprises an FEC data symbol.

7. The method according to claim 1 further comprising:

performing a decoder operation comprising processing a set of channel impairment estimates and the received packet to determine a set of transmit data symbol estimates; and

using an output of the decoder operation to update the set of channel impairment estimates.

8. A method of communicating in a multiple access network by estimating time and frequency offsets in a receiver for receiving packets, the method comprising:

determining a matrix of frequency domain received orthogonal frequency-division multiplexing (OFDM) data symbols;

determining a matrix of conjugated data symbols, the conjugated data symbols comprising one or more of preamble, training and estimated data symbols;

determining a two-dimensional Fourier transform matrix comprising the matrix of frequency domain received OFDM data symbols multiplied with the matrix of conjugated data symbols;

filtering the two-dimensional Fourier transform matrix; and

determining time and frequency offsets by locating at least one peak power occurrence in the filtered Fourier transform matrix.

9. The method according to claim 8 further comprising:

for each subsequent OFDM data symbol, pipelining demodulating and modulating; and

updating a channel estimate reference with forward error correction (FEC) decoding.

10. The method according to claim 8 wherein a first coded data symbol is received after a preamble data symbol.

11. The method according to claim 8 wherein each OFDM data symbol comprises an FEC data symbol.

12. The method according to claim 8 further comprising:

performing a decoder operation comprising processing a set of channel impairment estimates and the received packets to determine a set of transmit data symbol estimates; and

using an output of the decoder operation to update the set of channel impairment estimates.