Method of and apparatus for transmit noise reduction at a receiver

1. A method of reducing transmitter noise leaking into a receiver, the method comprising:

processing an up-converted signal from a transmitter in an observation channel to provide an observed transmitter signal, the observation channel comprising an observation filter and a down-converter;

estimating filter coefficients for a filter configured to inject a filtered version of a signal from the transmitter into the receiver to cause an impact of transmitter noise at the receiver across a plurality of channels to be reduced, said estimating being based on the observed transmitter signal; and

updating the filter coefficients by weighting estimates of transmitter noise for active channels in each of a plurality of update sequences.

2. A method as claimed in claim 1 , in which during an update sequence of the plurality of update sequences, estimates for transmitter noise leakage are generated for each active channel within a receiver band, and these estimates are carried forward into a filter update operation.

3. A method as claimed in claim 1 , in which during an update sequence of the plurality of update sequences, estimates for transmitter noise leakage are either:

a) not generated for inactive channels, or

b) are generated for inactive channels and weighted so as to reduce their contribution to an update process.

4. A method as claimed in claim 1 , in which said updating is periodically repeated.

5. A method as claimed in claim 1 , in which active channels are identified for said updating.

6. A method as claimed in claim 1 , wherein, an estimate of at least one of transmitter power or received signal strength is examined to estimate an effect of noise leakage within the receiver.

7. A method as claimed in claim 6 , in which the weighting estimates of transmitter noise for a particular channel is modified based on an estimate of an effect of the transmitter noise.

8. A method as claimed in claim 1 , in which the filter is a single filter operable across a full receiver bandwidth in the digital domain of the receiver.

9. A method as claimed in claim 1 , in which the filter comprises a plurality of filters provided to operate over a plurality of channels, where a number of channels is greater than a number of filters of the plurality of filters, such that an individual filter of the plurality of filters is configured to provide noise reduction for at least two channels.

10. An apparatus for reducing an effect of transmitter noise leaking into a receiver, the apparatus comprising:

an observation channel configured to process an up-converted signal from a transmitter and to provide an observed transmitter signal;

a transmitter noise cancellation filter configured to apply a cancellation signal in a digital domain of the receiver, the transmitter noise cancellation filter configured to apply the cancellation signal across a plurality of receiver channels; and

an adaptation engine configured to repeatedly update the transmitter noise cancellation filter, the adaptation engine configured to estimate transmitter noise in the up-converted signal from the transmitter on a channel by channel basis based on the observed transmitter signal and weight estimates of the transmitter noise.

11. An apparatus as claimed in claim 10 , in which the adaptation engine is configured such that channels of the receiver channels that are inactive are given reduced weight or inhibited from contributing data to an update process for updating the transmitter noise cancellation filter.

12. An apparatus as claimed in claims 10 , in which the adaptation engine is configured such that channels of the receiver channels where a received signal strength is large or transmitter noise leaking from a transmitter is small are given less weight in an update process or inhibited from contributing to the update process.

13. An apparatus as claimed in claim 10 , where a digital output of the observation channel is filtered by the transmitter noise cancellation filter, wherein the transmitter noise cancellation filter comprises a single filter operable to simultaneously provide a noise reduction signal to a plurality of channels.

14. An apparatus as claimed in claim 10 , the adaptation engine comprises a channel filter.

15. An apparatus as claimed in claim 10 , in which the apparatus is responsive to a signal from a second transmitter to reduce noise from the second transmitter on the plurality of receiver channels.

16. An apparatus as claimed in claim 10 , in which the transmitter noise cancellation filter is configured to apply the cancellation signal to an output of an analog-to-digital converter of the receiver.

17. An apparatus as claimed in claim 10 , wherein the transmitter noise cancellation filter comprises a plurality of taps, and wherein the adaptation engine is configured to update the plurality of taps based on the weighted estimates of transmitter noise.

18. An electronic system comprising:

a transmitter comprising an up-converter;

an observation channel configured to process an up-converted signal from the transmitter and to provide an observed transmitter signal; and

a receiver comprising:

a transmitter noise cancellation filter configured to apply a cancellation signal to a digital signal of the receiver across a plurality of receiver channels; and

an adaptation engine configured to:

generate channel by channel estimates of transmitter noise in a signal of the transmitter at a node between the up-converter and an antenna based on the observed transmitter signal; and

provide updated filter coefficients to the transmitter noise cancellation filter based on weighting the channel by channel estimates of transmitter noise.

19. An electronic system as claimed in claim 18 , wherein an indication of the up-converted signal is converted into a digital baseband signal for the transmitter noise cancellation filter by the observation channel.

20. An electronic system as claimed in claim 18 , wherein the up-converted signal is an output of a power amplifier of the transmitter.