Re-transmission in a MIMO communication system

1. A method for re-transmission in a multiple-input multiple-output (MIMO) communication system, the method comprising:

performing spatial mapping of one or more retransmitted data streams and one or more newly transmitted data streams,

wherein the spatial mapping comprises switching bits between the re-transmission data streams and the new transmission data streams.

2. The method as claimed in claim 1 , further comprising bit to symbol mapping for generating modulated symbols for transmission, wherein the data bits of the one or more retransmitted data streams and the one or more newly transmitted data streams are switched such that the data bits of the retransmitted data stream are mapped to the MSB bits of the modulated symbols transmitted over both reliable and unreliable antennas.

3. The method as claimed in claim 2 , wherein the reliable antennas are the antennas from which the data streams transmitted in a previous transmission interval receive an ACK signal fed back from a receiver.

4. The method as claimed in claim 2 , wherein the unreliable antennas are the antennas from which the data streams transmitted in a previous transmission interval received a NACK signal feedback from a receiver.

5. The method as claimed in claim 2 , wherein the bit to symbol mapping is performed using Quadrature Amplitude Modulation (QAM).

6. The method as claimed in claim 2 , wherein the reliable antenna over which some of the data bits of the re-transmitted data streams are transmitted is an antenna least correlated with the antenna over which the data stream transmitted in a previous transmission interval received a NACK signal feedback from the receiver.

7. A method as claimed in claim 1 , the method further comprising:

performing, at the receiver, CRC validation on the decoded data streams to determine a HARQ status comprising ACK or NACK signal.

8. A transmitter for re-transmission in a multiple-input multiple-output (MIMO) communication system, the transmitter comprising:

a spatial mapping module for performing spatial mapping of one or more re-transmission streams and one or more new transmission streams,

wherein the spatial mapping module switches bits between the re-transmission data streams and the new transmission data streams.

9. The transmitter as claimed in claim 8 , further comprising a bit to symbol mapping module for generating modulated symbols for transmission, wherein the data bits of the one or more retransmitted data streams and the one or more newly transmitted data streams are switched such that the data bits of the retransmitted data stream are mapped to the MSB bits of the modulated symbols transmitted over both reliable and unreliable antennas.

10. The transmitter as claimed in claim 9 , wherein the reliable antennas are the antennas from which the data streams transmitted in a previous transmission interval receive an ACK signal fed back from a receiver.

11. The transmitter as claimed in claim 9 , wherein the unreliable antennas are the antennas from which the data streams transmitted in a previous transmission interval received a NACK signal feedback from a receiver.

12. The transmitter as claimed in claim 9 , wherein the bit to symbol mapping is performed using Quadrature Amplitude Modulation (QAM).

13. The transmitter as claimed in claim 9 , wherein the reliable antenna over which some of the data bits of the re-transmitted data streams are transmitted is an antenna least correlated with the antenna for which the data stream transmitted in a previous transmission interval received a NACK signal feedback from the receiver.

14. A receiver for re-transmission in a multiple-input multiple-output (MIMO) communication system, the receiver comprising:

a spatial de-mapping module for performing spatial de-mapping of one or more re-transmission streams and one or more new transmission streams,

wherein the spatial de-mapping module switches bits of symbols received to recover the re-transmission data streams and the new transmission data streams.

15. The receiver as claimed in claim 14 , wherein the data bits of the symbols transmitted from both reliable and unreliable antennas are switched such that the re-transmission data streams are recovered from MSB bits of the symbols.

16. The receiver as claimed in claim 14 , wherein the symbols are based on Quadrature Amplitude Modulation (QAM).

17. The receiver as claimed in claim 14 , further comprising a CRC validation module for performing CRC validation on the decoded data streams to determine an HARQ status comprising ACK or NACK signal.