Slow adaptation of modulation and coding for packet transmission

1. A method comprising:

transmitting packets to a receiver using an MCS (modulation and coding scheme);

receiving a plurality of NACKs (negative acknowledgement) in respect of packets transmitted to the receiver; and

determining an updated MCS (modulation and encoding scheme) used to transmit subsequent packets to the receiver as a function of the plurality of NACKs,

wherein determining the updated MCS comprises counting a number of the plurality of NACKs received over a time period and wherein the time period is at least 400ms.

2. The method of claim 1 further comprising:

signaling the updated MCS to the receiver.

3. The method of claim 2 wherein signaling the updated MCS comprises:

signaling using at least one of high layer signaling, optional field of a Media Access Control header, and physical layer signaling.

4. The method of claim 1 wherein determining the updated MCS further comprises:

moving to a less aggressive MCS if the number of NACKs received over the time period exceeds a first threshold;

moving to a more aggressive MCS if the number of NACKs received over the time period is less than a second threshold.

5. The method of claim 1 wherein the MCS is adjusted independently for each of a plurality of receivers.

6. The method of claim 1 further comprising:

initially assigning each of a plurality of receivers to one of a plurality of groups of receivers, each group having a respective MCS;

wherein moving to a more aggressive MCS for a given receiver and moving to a less aggressive MCS for a given receiver comprises changing the group assigned to the given receiver.

7. The method of claim 1 wherein the time period comprises a sliding window.

8. The method of claim 1 wherein transmitting packets comprises transmitting a sequence of VoIP packets.

9. The method of claim 1 further comprising assigning an initial MCS to the receiver based on initial feedback.

10. The method of claim 1 further comprising using a NACK-only signaling scheme.

11. The method of claim 1 further comprising signaling new packet notification using at least one of group ID, bitmap, and resource index.

12. A method comprising:

a receiver receiving packets over a wireless channel;

the receiver making a channel quality measurement in respect of the wireless channel;

the receiver making an MCS adaptation decision based on the channel quality measurement; and

the receiver feeding back the MCS adaptation decision in a slow rate manner, wherein the feeding back is performed at least every 400 ms.

13. The method of claim 12 further comprising:

a transmitter receiving the MCS adaptation decision; and

the transmitter updating the MCS used for subsequent packet transmissions to that receiver in accordance with the MCS adaptation decision.

14. The method of claim 12 wherein the receiver feeding back the MCS adaptation decision comprises:

feeding back a first signal to indicate that a more aggressive MCS should be used;

feeding back a second signal to indicate that a less aggressive MCS should be used; and

feeding back a third signal to indicate that no change in the MCS should be made.

15. The method of claim 12 wherein the receiver feeding back the MCS adaptation decision comprises:

feeding back the MCS adaptation decision using at least one of high layer signaling, optional field of a Media Access Control header, and physical layer signaling.

16. The method of claim 12 further comprising:

the receiver transmitting a NACK for each packet that was not correctly received;

the receiver transmitting nothing for each packet that is correctly received.

17. The method of claim 12 further comprising:

initially assigning each receiver to one of the a plurality of groups of receivers, each group having a respective MCS;

wherein moving to a more aggressive MCS for a given receiver and moving to a less aggressive MCS for a given receiver comprise changing the group assigned to the receiver.