Receiver

1. A receiver for recovering data from a received symbol of signal samples generated in accordance with Orthogonal Frequency Division Multiplexing (OFDM), the symbol including pilot signals provided at different sub-carrier locations for each of a set of OFDM symbols, the sub-carrier locations of the pilot signals being repeated for subsequent sets of symbols, said receiver comprising:

a pilot assisted channel estimator operable to generate an estimate of a transfer function of a transmission channel through which the received OFDM symbol has passed, the pilot assisted channel estimator including

a pilot extractor operable to extract the pilot carrier signals from the signal samples, and to generate an estimate of a sample of a channel frequency response for each pilot signal in the received OFDM symbol, by comparing the extracted pilot carrier signals with predetermined versions of the pilot carriers,

a time interpolation filter controller; and

an adaptive bandwidth time interpolation filter operable to interpolate the samples of the channel frequency response estimate derived from the pilot carrier signals at corresponding said sub-carrier locations within temporally separated OFDM symbols to generate an interpolated version of the channel frequency response estimate,

wherein the time interpolation filter controller is operable to generate an estimate of a rate of change of the channel frequency response with time and to adapt a pass bandwidth of the time interpolation filter in accordance with the estimated rate of change of the channel.

2. The receiver as claimed in claim 1 , wherein the time interpolation filter controller is operable to reduce the pass bandwidth of the time interpolation filter to reduce noise with respect to an amount of energy in the channel frequency response.

3. The receiver as claimed in claim 1 , wherein the adaptive bandwidth time interpolation filter comprises a plurality of interpolation filters each having a predetermined pass bandwidth, and the time interpolation filter controller is operable to select one of the plurality of predetermined filters in accordance with the estimated rate of change of the channel.

4. The receiver as claimed in claim 1 , wherein the time interpolation filter controller is operable to generate the estimate of the rate of change of the channel frequency response from a comparison of at least two samples of the channel frequency response determined from corresponding sub-carrier locations within temporally separated OFDM symbols.

5. The receiver as claimed in claim 4 , wherein the rate of change of the channel frequency response is generated from a look-up table, the table providing rate of change values with respect to values from the comparison of samples of the channel frequency response, the comparison being used as an index to the look-up table to provide the estimate of the rate of change.

6. The receiver as claimed in claim 4 , wherein the time interpolation filter controller is operable to generate the estimate of the rate of change of the channel frequency response from a ratio of a first comparison of samples of the channel frequency response from corresponding said sub-carrier locations from OFDM symbols separated by an integer value n OFDM symbols and a second comparison of samples of the channel frequency response from corresponding sub-carrier locations from OFDM symbols separated by an integer value m in OFDM symbols.

7. The receiver as claimed in claim 6 , wherein the rate of change of the channel frequency response is generated from a look-up table, the table providing rate of change values with respect to values from the ratio of first and second comparisons, the ratios being used as an index to the look-up table to provide the estimate of the rate of change.

8. The receiver as claimed in claim 4 , wherein the comparison of the samples of the channel frequency response from corresponding sub-carrier locations comprises forming a difference between the samples.

9. The receiver as claimed in claim 4 , wherein the comparison of the samples of the channel frequency response from corresponding said sub-carrier locations comprises forming a correlation between the samples.

10. The receiver as claimed in claim 1 , wherein the generated estimate of the rate of change of the channel corresponds to a Doppler frequency of the OFDM symbol as experienced by the receiver.

11. The receiver according to claim 1 , further comprising;

a channel correction processor operable to reduce the effects of the propagation channel in the received symbol by substantially cancelling the channel frequency response estimate from the received symbol.

12. A pilot assisted channel estimator operable to generate an estimate of a transmission channel through which a received Orthogonal Frequency Division Multiplexed (OFDM) symbol has passed, the OFDM symbol including pilot signals provided at different sub-carrier locations for each of a set of OFDM symbols, the sub-carrier locations of the pilot signals being repeated for subsequent sets of symbols, the pilot assisted channel estimator comprising

a pilot extractor operable to extract the pilot carrier signals from samples of the received OFDM symbol, and to generate an estimate of a sample of a channel frequency response for

each pilot signal in the received OFDM symbol, by comparing the extracted pilot carrier signals with predetermined versions of the pilot carriers;

a time interpolation filter controller; and

an adaptive bandwidth time interpolation filter operable to interpolate the samples of the channel frequency response estimate derived from the pilot carrier signals at corresponding said sub-carrier locations within temporally separated OFDM symbols to generate an interpolated version of the channel frequency response estimate;

wherein the time interpolation filter controller is operable to generate an estimate of a rate of change of the channel frequency response with time and to adapt a pass bandwidth of the time interpolation filter in accordance with the estimated rate of change of the channel.

13. The pilot assisted channel estimator as claimed in claim 12 , wherein the time interpolation filter controller is operable to reduce the pass bandwidth of the time interpolation filter to reduce noise with respect to an amount of energy in the channel frequency response.

14. The pilot assisted channel estimator as claimed in claim 12 , wherein the adaptive bandwidth time interpolation filter comprises a plurality of interpolation filters each having a predetermined pass bandwidth, and the time interpolation filter controller is operable to select one of the plurality of predetermined filters in accordance with the estimated rate of change of the channel.

15. The pilot assisted channel estimator as claimed in claim 12 , wherein the time interpolation filter controller is operable to generate the estimate of the rate of change of the channel frequency response from a comparison of at least two samples of the channel frequency response taken from corresponding said sub-carrier locations within temporally separated OFDM symbols.

16. A method of generating an estimate of a transmission channel through which a received Orthogonal Frequency Division Multiplexed (OFDM) symbol has passed, the OFDM symbol including pilot signals provided at different sub-carrier locations for each of a set of OFDM symbols, the sub-carrier locations of the pilot signals being repeated for subsequent sets of symbols, the method comprising:

extracting the pilot carrier signals from samples of the received OFDM symbol, generating an estimate of a sample of a channel frequency response for each said pilot signal in the received OFDM symbol, by comparing the extracted pilot carrier signals with predetermined versions of the pilot carriers;

interpolating the samples of a channel frequency response derived from the pilot carrier signals at corresponding sub-carrier locations within temporally separated OFDM symbols to generate an interpolated version of the channel frequency response estimate using a time interpolation filter,

generating an estimate of a rate of change of the channel frequency response with time, and

adapting a pass bandwidth of the time interpolation filter in accordance with the estimated rate of change of the channel.

17. A method of generating an estimate of a transmission channel as claimed in claim 16 , wherein the adapting of the pass bandwidth includes

reducing the pass bandwidth of the time interpolation filter to reduce noise with respect to an amount of energy in the channel frequency response.

18. A method of generating an estimate of a transmission channel as claimed in claim 16 , wherein the generating the estimate of the rate of change includes comparing at least two samples of the channel frequency response taken from corresponding said sub-carrier locations within temporally separated OFDM symbols.

19. A method of generating an estimate of a transmission channel as claimed in claim 18 , wherein the generating the estimate of the rate of change by comparing at least two samples includes

generating a ratio of a first comparison of samples of the channel frequency response from corresponding said sub-carrier locations from OFDM symbols separated by an integer value n OFDM symbols and a second comparison of samples of the channel frequency response from corresponding sub-carrier locations from OFDM symbols separated by an integer value m in OFDM symbols, and

determining the rate of change of the channel frequency response from the comparison.

20. An apparatus for generating an estimate of a transmission channel through which a received Orthogonal Frequency Division Multiplexed (OFDM) symbol has passed, the OFDM symbol including pilot signals provided at different sub-carrier locations for each of a set of OFDM symbols, the sub-carrier locations of the pilot signals being repeated for subsequent sets of symbols, the apparatus comprising:

means for extracting the pilot carrier signals from samples of the received OFDM symbol,

means for generating an estimate of a sample of a channel frequency response for each of the pilot signal in the received OFDM symbol, by comparing the extracted pilot carrier signals with predetermined versions of the pilot carriers;

means for interpolating the samples of a channel frequency response derived from pilot carrier signals at corresponding said sub-carrier locations within temporally separated said OFDM symbols to generate an interpolated version of the channel frequency response estimate,

means for generating an estimate of a rate of change of the channel frequency response with time, and

means for adapting a pass bandwidth of the means for interpolating in accordance with the estimated rate of change of the channel.