Receiver having an adaptive filter and method of optimising the filter
A receiver comprises an adaptive filter having an input for a digitized input signal, means for storing a pre-designed filter characteristic, means for analyzing a digital representation of the input signal to determine a desired position of the filter characteristic to match the system requirements, and means for adapting the stored pre-designed filter characteristic in the frequency domain and/or the time domain to match the system requirements and for transforming the adapted filter characteristic to the time domain to update coefficients for the adaptive filter and for loading updated coefficients into adaptive filter. The updating of the coefficients may be done periodically. The adaptation may be one or more of adjusting bandwidth, frequency shift and, in the case of a bandpass characteristic, superimposing characteristics.
1. A method of dynamically adapting a digital filter characteristic, the method comprising:
storing a frequency domain representation of the filter characteristic;
analyzing an input signal to determine a required filter characteristic based on a frequency of a narrowband interfering signal included in the input signal;
adapting the frequency domain representation to match the required filter characteristic;
transforming the adapted frequency domain representation to a time domain so as to obtain filter coefficients relating to the required filter characteristic; and
applying the filter coefficients to effect the adaptation of the filter characteristic, wherein adapting the frequency domain representation to match the required filter characteristic includes at least one of:
altering a bandwidth of the frequency domain representation by reducing or increasing a number of samples in the frequency domain representation according to the frequency of the narrowband interfering signal; and
altering a frequency of the frequency domain representation by shifting samples of the frequency domain representation to a lower or higher frequency according to the frequency of the narrowband interfering signal.
2. The method as claimed in claim 1 wherein the filter characteristic is further adapted in the time domain.
3. The method as claimed in claim 1 wherein said filter coefficients are periodically calculated.
4. The method as claimed in claim 1 wherein the filter characteristic includes a bandstop interference blocking characteristic and the adapting includes shifting the filter characteristic to block the interfering signal.
5. A receiver, comprising:
an adaptive filter;
an input to receive a digitized input signal;
a memory to store a frequency domain representation of a filter characteristic of the filter; and
a digital signal processor coupled to the adaptive filter and having a first stage and a second stage, the first stage being configured to receive and to analyze a digital representation of the input signal to determine a required filter characteristic based on a frequency of a narrowband interfering signal included in the input signal, and the second stage being configured to adapt the frequency domain representation to match the required filter characteristic and to transform the adapted frequency domain representation into a time domain so as to obtain filter coefficients relating to the required filter characteristic, wherein the second stage is configured to adapt the frequency domain representation by at least one of:
altering a bandwidth of the frequency domain representation by reducing or increasing a number of samples in the frequency domain representation according to the frequency of the narrowband interfering signal; and
altering a frequency of the frequency domain representation by shifting samples of the frequency domain representation to a lower or higher frequency according to the frequency of the narrowband interfering signal.
6. The receiver as claimed in claim 5 wherein the second stage of the digital signal processor is configured to further adapt the filter characteristic in the time domain.
7. The receiver as claimed in claim 5 , wherein the digital signal processor is configured to periodically calculate new ones of said filter coefficients.
8. The receiver as claimed in claim 5 , wherein the filter characteristic includes a bandstop interference blocking characteristic, and the second stage is configured to shift the filter characteristic to block the interfering signal.
9. A method of dynamically adapting a digital filter characteristic, the method comprising:
storing a frequency domain representation of the filter characteristic;
analyzing, under control of a digital signal processor, an input signal to determine a required filter characteristic based on a frequency of a narrowband interfering signal included in the input signal;
adapting, under control of the digital signal processor, the frequency domain representation to match the required filter characteristic;
transforming, under control of the digital signal processor, the adapted frequency domain representation to a time domain so as to obtain filter coefficients relating to the required filter characteristic; and
applying the filter coefficients to effect the adaptation of the filter characteristic, wherein adapting the frequency domain representation to match the required filter characteristic includes at least one of:
altering a bandwidth of the frequency domain representation by reducing or increasing a number of samples in the frequency domain representation according to the frequency of the narrowband interfering signal; and
altering a frequency of the frequency domain representation by shifting samples of the frequency domain representation to a lower or higher frequency according to the frequency of the narrowband interfering signal.
10. The method of claim 9 wherein the filter characteristic includes a bandstop interference blocking characteristic and the adapting includes shifting the filter characteristic to block the interfering signal.
11. The method of claim 9 , further comprising prestoring a hopping sequence to facilitate the adapting.
12. The method of claim 9 wherein the filter characteristic includes a bandpass characteristic and the adapting includes shifting the filter characteristic to select a required channel.
13. The method of claim 9 wherein the adapting the frequency domain representation to match the required filter characteristic comprises:
selectively altering a bandwidth of the frequency domain representation by reducing or increasing a number of samples in the frequency domain representation; and
selectively altering a frequency of the frequency domain representation by shifting samples of the frequency domain representation to a lower or higher frequency.
14. The receiver of claim 5 wherein the second stage is configured to:
selectively reduce or increase a number of samples in the frequency domain representation; and
selectively shift samples of the frequency domain representation to a lower or higher frequency.
15. The method of claim 1 wherein the adapting the frequency domain representation to match the required filter characteristic comprises:
selectively altering a bandwidth of the frequency domain representation by reducing or increasing a number of samples in the frequency domain representation; and
selectively altering a frequency of the frequency domain representation by shifting samples of the frequency domain representation to a lower or higher frequency.