Method of transmitting data in a communication system

1. A method of encoding a signal to be transmitted from a terminal via a channel in a communication network comprising:

receiving the signal at the terminal;

determining characteristics of the channel to determine a first frequency portion of the signal;

determining the first frequency portion of the signal based on the determined characteristics of the channel;

encoding the first frequency portion of the signal in accordance with a first encoding method to produce a first encoded signal portion;

selectively encoding a second frequency portion of the signal in accordance with a second encoding method to produce a second encoded signal portion, the second frequency portion of the signal comprising a portion of the signal that is not encoded with the first encoding method and is defined by at least one cut off frequency, and the cut off frequency configured to be adjusted to be inversely proportional to available bandwidth of the channel; and

transmitting the first encoded signal portion and the second encoded signal portion via the channel.

2. The method as claimed in claim 1 further comprising determining the second frequency portion of the signal based on the first frequency portion of the signal.

3. The method as claimed in claim 1 wherein the second frequency portion of the signal is not encoded with the first encoding method.

4. The method as claimed in claim 1 wherein the first encoding method is a model based encoding method.

5. The method as claimed in claim 1 wherein the second encoding method is a non model based encoding method.

6. The method as claimed in claim 1 wherein the characteristics of the channel relate to at least one of channel capacity, channel bandwidth, channel jitter and channel packet loss.

7. The method as claimed in claim 1 wherein the cut off frequency is adjustable.

8. The method as claimed in claim 7 wherein the cut off frequency is further configured to be adjusted to be proportional to at least one of a measure of packet loss and a measure of jitter.

9. The method as claimed in claim 7 wherein the cut of frequency is further configured to be adjusted to be proportional to a channel degradation indicator value.

10. The method as claimed in claim 9 wherein the channel degradation indicator value is determined from at least one of a measure of packet loss, a measure of jitter or a measure of bandwidth of the channel.

11. The method as claimed in claim 1 wherein a plurality of cut off frequencies defines at least one range to be encoded by the first encoding method.

12. The method as claimed in claim 11 wherein the at least one range is configured to be adjusted based on characteristics of the channel.

13. The method as claimed in claimed in claim 11 wherein the at least one range corresponds to a harmonic frequency.

14. The method as claimed in claim 1 further comprising:

decoding the first encoded signal portion to produce a first decoded signal portion; and

subtracting the first decoded signal portion from the received signal to determine the second frequency portion of the signal.

15. The method as claimed in claim 1 wherein the received signal is a Linear Prediction residual signal.

16. The method as claimed in claim 1 wherein the second frequency portion of the signal is not encoded.

17. The method as claimed in claim 1 further comprising detecting periods of unvoiced sound in the received signal.

18. The method as claimed in claim 17 wherein the periods of unvoiced sound are modelled by white random noise in combination with a spectral envelope by the first encoding method.

19. The method as claimed in claim 1 wherein the first encoding method provides a waveform approximation of the received signal.

20. The method as claimed in claim 1 wherein the first encoding method is a non interframe encoding method.

21. The method as claimed in claim 1 wherein the second encoding method is a high quality encoding method.

22. The method as claimed in claim 1 wherein the second encoding method is a waveform encoding method.

23. The method as claimed in claim 1 wherein the signal is an audio signal.

24. A device for encoding a signal to be transmitted from a terminal via a channel in a communication network comprising:

means for receiving the signal at the terminal;

means for determining characteristics of the channel to determine a first frequency portion of the signal;

means for determining the first frequency portion of the signal based on the determined characteristics of the channel;

means for encoding the first frequency portion of the signal in accordance with a first encoding method to produce a first encoded signal portion;

means for selectively encoding a second frequency portion of the signal in accordance with a second encoding method to produce a second encoded signal portion, the second frequency portion of the signal comprising a portion of the signal that is not encoded with the first encoding method and is defined by at least one cut off frequency, and the cut off frequency configured to be adjusted to be inversely proportional to available bandwidth of the channel; and

means for transmitting the first encoded signal portion and the second encoded signal portion via the channel.

25. A device configured to encode a signal to be transmitted from a terminal via a channel in a communication network comprising:

a receiver configured to receive the signal at the terminal;

a channel determiner configured to determine characteristics of the channel to determine a first frequency portion of the signal;

a portion determiner configured to determine the first frequency portion of the signal based on the determined characteristics of the channel;

a first encoder configured to encode the first frequency portion of the signal in accordance with a first encoding method to produce a first encoded signal portion;

a second encoder configured to selectively encode a second frequency portion of the signal in accordance with a second encoding method to produce a second encoded signal portion, the second frequency portion of the signal comprising a portion of the signal that is not encoded with the first encoding method and is defined by at least one cut off frequency, and the cut off frequency configured to be adjusted to be inversely proportional to available bandwidth of the channel; and

a transmitter configured to transmit the first encoded signal portion and the second encoded signal portion via the channel.