Retransmission control technique

1. A retransmission control method comprising:

receiving, at a MIMO transmitter, a NACK signal indicating an unsuccessful decoding of a coded data packet at a MIMO receiver;

receiving a reliability measure associated with one or more transmitted spatial data streams for the unsuccessfully decoded data packet;

comparing the reliability measure with at least one predetermined threshold; and

selecting a retransmission protocol based on the comparison of the reliability measure with the at least one predetermined threshold, the retransmission protocol comprising a Chase combining protocol or an Incremental Redundancy protocol,

wherein the reliability measure comprises a system bits component and a parity bits component, the system bits component including one or more system bits reliability data indicative of the reliability of the system bits of said one or more transmitted spatial data streams, respectively, system bits reliability data associated with each data stream for the unsuccessfully decoded data packet in a Single Code Word (SCW) MIMO transmission, and the parity bits component comprises parity bits reliability data of the unsuccessfully decoded data packet,

wherein the reliability measure is determined based on the one or more transmitted spatial data streams received at the MIMO receiver, and

wherein the selecting of the retransmission protocol comprises:

selecting the Incremental Redundancy protocol for a retransmission data packet if the system bits reliability data is higher than a system bit threshold;

selecting the Chase combining protocol for the retransmission packet if the system bits reliability data is lower than or equal to the system bit threshold;

selecting a lowered coding rate, as compared to an original transmission, for the retransmission data packet using the Chase combining protocol if the parity bits reliability data is lower than or equal to a parity bits threshold; or

selecting a same coding rate, as compared to the original transmission, for the retransmission data packet using the Chase combining protocol if the parity bits reliability data is higher than the parity bits threshold.

2. The retransmission control method according to claim 1 , further comprising the step of retransmitting the data packet according to the selected retransmission protocol.

3. The retransmission control method according to claim 1 , wherein the method further comprises:

segmenting the retransmission data packet into a plurality of spatial data streams over the same antennas as compared to the original transmission using the Chase combining protocol if the system bits reliability measure data is higher than the system bits threshold; or

segmenting the data packet into a plurality of data streams over different antennas as compared to the original transmission using the Chase combining protocol if the system bits reliability data is higher than the system bits threshold.

4. The retransmission control method according to claim 3 , wherein the segmenting of the retransmission data packet is performed after a selecting of a lower or a same coding rate, as compared to the original transmission, for the retransmission data packet using the Chase combining protocol.

5. The retransmission control method according to claim 1 , wherein the system bits component comprises system bits reliability data associated with all data streams in a Multiple Code Words (MCW) MIMO transmission of respective unsuccessfully decoded data packets, and the parity bits component comprises parity bits reliability data associated with said all data streams in the MCW MIMO system.

6. The retransmission method according to claim 1 , wherein the reliability measure is based on magnitudes of logarithmic likelihood ratios (LLRs) of respective demodulated system bits and parity bits of the initial unsuccessfully decoded data packet or the combination of the initial unsuccessfully decoded data packet and one or more retransmitted coded data packets.

7. The retransmission method according to claim 6 , wherein the reliability measure is based on average magnitude of LLRs.

8. The retransmission method according to claim 1 , wherein the reliability measure is based on a least reliable system bit and a least reliably parity bit having lowest respective magnitudes of LLR.

9. A transmitter for a MIMO communication system, the transmitter comprising:

means for receiving a NACK signal indicating an unsuccessful decoding of a coded data packet at a MIMO receiver;

means for receiving a reliability measure associated with one or more transmitted spatial data streams for the unsuccessfully decoded data packet;

means for comparing the reliability measure with at least one predetermined threshold; and

means for selecting a retransmission protocol based on the comparison of the reliability measure with the at least one predetermined threshold, the retransmission protocol comprising a Chase combining protocol or an Incremental Redundancy protocol,

wherein the reliability measure comprises a system bits component and a parity bits component, the system bits component includes one or more system bits reliability data indicative of the reliability of the system bits of said one or more transmitted spatial data streams, respectively, system bits reliability data associated with each data stream for the unsuccessfully decoded data packet in a Single Code Word (SCW) MIMO transmission, and the parity bits component comprises parity bits reliability data of the unsuccessfully decoded data packet,

the reliability measure is determined based on the one or more transmitted spatial data streams received at the MIMO receiver, and

said means for selecting of the retransmission protocol is configured to:

select the Incremental Redundancy protocol for a retransmission data packet if the system bits reliability data is higher than a system bit threshold;

select the Chase combining protocol for the retransmission packet if the system bits reliability data is lower than or equal to the system bit threshold,

select a lowered coding rate, as compared to an original transmission, for the retransmission data packet using the Chase combining protocol if the parity bits reliability data is lower than or equal to a parity bits threshold; or

select a same coding rate, as compared to the original transmission, for the retransmission data packet using the Chase combining protocol if the parity bits reliability data is higher than the parity bits threshold.