Interference cancellation receiver and method

1. A method of receiving a signal formed from information bits propagated through a channel, which has been subjected to interference, the method comprising the steps of:

(a) filtering the received signal with a linear interference cancellation filter using estimated filter coefficients to generate a signal;

(b) processing the signal in a detection unit using an estimated final impulse response of the channel to generate estimates of the transmitted bits;

(c) wherein the filter coefficients are calculated using the separate steps of:

(c1) estimating, using the received signal, an initial impulse response of the propagation channel;

(c2) deriving, using the estimated initial channel impulse response and the received signal, the filter coefficients,

wherein a real part of a first filter coefficient of the filter coefficients is constant.

2. A method according to claim 1 , wherein the method further comprises the step of:

(d) estimating, in a separate calculation to the step of calculating the filter coefficients, the final impulse response of the channel.

3. A method according to claim 2 , wherein the final impulse response of the channel is estimated by using the estimated channel initial impulse response and the filter coefficients.

4. A method according to claim 3 , wherein the final impulse response of the channel is estimated by convolving the initial impulse response with the filter coefficients.

5. A method according to claim 2 , wherein the final impulse response of the channel is estimated directly from the signal.

6. A method according to claim 5 , wherein a sequence of known modulation symbols is embedded in the transmitted bits and the step of estimating the final impulse response of the channel uses the known modulation symbols.

7. A method according to claim 1 , wherein the filter coefficients are derived by the steps of:

generating estimated samples of noise in the received signal by calculating the difference between received samples and information symbols filtered with the estimated initial channel impulse response;

deriving the filter coefficients using the generated noise samples.

8. A method according to claim 7 , wherein a sequence of known modulation symbols is embedded in the transmitted bits and the information symbols comprise the known modulation symbols.

9. A method according to claim 7 , wherein the information symbols comprise estimated modulation symbols generated by using a decision-directed technique.

10. A method according to claim 7 , wherein the filter coefficients are derived from the noise samples by using a Least Square (LS) solution.

11. A method according to claim 7 , wherein the filter coefficients are derived from the noise samples by using a Minimum Mean Square Error (MMSE) solution.

12. A method according to claim 1 , wherein the step of estimating the initial impulse response of the propagation channel also uses a sequence of known modulation symbols transmitted with the propagated signal to estimate the initial impulse response of the propagation channel.

13. A method according to claim 7 , further comprising the step of:

comparing characteristics of the noise samples against a pre-determined template; and

disabling the linear interference cancellation filter based on the result of the comparison.

14. A method according to claim 13 , wherein the step of comparing comprises comparing the power of the noise samples against a threshold; and

the linear interference cancellation filter is disabled when the power of the noise samples is lower than a threshold.

15. A method according to claim 13 , wherein the step of comparing comprises analysing the frequency response of the noise samples.

16. A method according to claim 15 , wherein the frequency response of the noise samples is used to identify if the main source of noise is thermal noise, in-band band-limited noise or out-of-band noise.

17. A method according to claim 1 , wherein the number of filter coefficients is determined adaptively based on the power delay profile of the initial channel impulse response.

18. A method according to claim 1 , wherein one of the estimated filter coefficients is fixed in one dimension in the complex plane.

19. A receiver for receiving a signal formed from information bits propagated through a channel, which has been subjected to interference, the receiver comprising:

a linear interference cancellation filter arranged to filter the received signal using estimated filter coefficients to generate a signal;

a detector arranged to process the signal using an estimated final impulse response of the channel to generate estimates of the transmitted bits;

an initial channel estimation unit arranged to estimate, using the received signal, an initial impulse response of the propagation channel;

an interference cancellation filter estimation unit, separate to the initial channel estimation unit, and arranged to derive, using the estimated initial channel impulse response and the received signal, the filter coefficients,

wherein a real part of a first filter coefficient of the filter coefficients is constant.

20. A receiver according to claim 19 , further comprising means for estimating, in a separate calculation to the step of calculating the filter coefficients, the final impulse response of the channel.

21. A receiver according to claim 20 , wherein the means for estimating the final impulse response of the channel is the interference cancellation filter estimation unit, and the interference cancellation filter estimation unit is arranged to estimate the final impulse response of the channel by using the estimated channel initial impulse response and the filter coefficients.

22. A receiver according to claim 20 , wherein the means for estimating the final impulse response of the channel is a final channel estimation unit arranged to estimate the final impulse response of the channel directly from the signal.

23. A cellular telephone handset including a receiver according to claim 19 .