Adaptive channel estimation

1. A method comprising:

at a wireless receiver in wireless communication with a wireless transmitter, adaptively estimating a wireless communication channel between the wireless receiver and the wireless transmitter by:

receiving via an antenna an observation (r) of a transmitted coded symbol (d);

generating, by an adaptive channel estimator, a first coefficient (v) for weighting the received observation based on an estimate of the transmitted coded symbol (d_est), the first coefficient having a magnitude that is invariable with an amplitude of the transmitted coded symbol;

forming, by the adaptive channel estimator, a new channel estimate (h_est) based on a weighted observation using the first coefficient (v); and

estimating, at a decoder, information bits of a subsequently transmitted coded symbol using the new channel estimate.

2. The method of claim 1 wherein the first coefficient is based on a quotient of the complex conjugate (d_est*) of the estimate of the transmitted coded symbol to a magnitude (|d_est|) of the estimate of the transmitted coded symbol.

3. The method of claim 1 wherein the estimate of the transmitted coded symbol is obtained from decoder traceback outcomes.

4. A method of adaptive channel estimation at a wireless receiver in wireless communication with a wireless transmitter, the method comprising:

receiving, at an antenna, an observation (r) of a transmitted coded symbol (d);

generating, at an adaptive channel estimator, a first coefficient (v) for weighting the received observation based on an estimate of the transmitted coded symbol (d_est);

generating, at the adaptive channel estimator, a second coefficient (beta) for weighting an initial channel estimate based on the estimate of the transmitted coded symbol (d_est);

combining, at an adaptive channel estimator, a weighted observation using the first coefficient and a weighted initial channel estimate using the second coefficient to form a new channel estimate (h_est); and

estimating, at a decoder, information bits of a subsequently transmitted coded symbol using the new channel estimate.

5. The method of claim 4 wherein combining includes generating a linear combination of the observation and the initial channel estimate.

6. The method of claim 4 wherein generating a first coefficient includes generating the first coefficient based on a complex conjugate (d_est*) of the estimate of the transmitted coded symbol and a magnitude (|d_est|) of the estimate of the transmitted coded symbol.

7. The method of claim 6 wherein the first coefficient is generated based on a quotient of the complex conjugate (d_est*) to the magnitude (|d_est|) of the estimate of the transmitted symbol.

8. The method of claim 4 wherein generating the second coefficient includes generating an increased second coefficient for a decreased magnitude (|d_est|) of the estimate of the transmitted coded symbol.

9. The method of claim 4 wherein the first coefficient equals a (d_est*)/|d_est|, and the second coefficient equals 1−α|d_est|, where a is between 0 and 1.

10. The method of claim 4 wherein generating the first coefficient and/or generating the second coefficient includes retrieving the first coefficient and/or the second coefficient from a look-up table containing entries of all possible transmitted coded symbols.

11. The method of claim 4 wherein the initial channel estimate is obtained based on a preamble of a packet.

12. The method of claim 4 wherein the initial channel estimate is obtained based on channel estimates obtained from one or more previous symbol periods.

13. The method of claim 4 wherein the new channel estimate is a channel estimate for a subcarrier in an OFDM communications system, the method further comprising generating the initial channel estimate for the subcarrier by smoothing channel estimates for a plurality of subcarriers.

14. The method of claim 4 wherein the combining includes a linear combination of the observation and the initial channel estimate.

15. A wireless receiver in wireless communication with a wireless transmitter, the wireless receiver estimating a wireless communication channel between the wireless receiver and the wireless transmitter, the wireless receiver comprising:

an antenna for receiving an observation (r) of a transmitted coded symbol (d);

an adaptive channel estimator for:

generating a first coefficient (v) for weighting the received observation based on an estimate of the transmitted coded symbol,

generating a second coefficient (beta) for weighting an initial channel estimate based on the estimate of the transmitted coded symbol (d_est); and

combining a weighted observation using the first coefficient and a weighted initial channel estimate using the second coefficient to form a new channel estimate (h_est); and

a decoder estimating information bits of a subsequently transmitted coded symbol using the new channel estimate.

16. The wireless receiver of claim 15 wherein the adaptive channel estimator is configured to generate a linear combination of the observation and the initial channel estimate to form the new channel estimate (h_est).

17. The wireless receiver of claim 16 wherein the adaptive channel estimator includes a look up table for retrieving at least one-weight based on the estimate the transmitted coded symbol (d_est).

18. The wireless receiver of claim 15 further including a frequency domain smoothing unit configured to generate the initial channel estimate for a subcarrier by smoothing channel estimates for a plurality of subcarriers.

19. The wireless receiver of claim 18 wherein the adaptive channel estimator further includes a symbol delay block for providing synchronisation between the input of the combiner and the output of the frequency domain smoothing unit.