Apparatus and method for selecting transmission mode in multi-antenna system

1. A method for selecting a transmission mode in a multi-antenna system, the method comprising:

determining a channel characteristic of each transmit stream received from a transmitter;

determining a difference between the channel characteristic of a first transmit stream and the channel characteristic of a second transmit stream by comparing the channel characteristic of the first transmit stream and the channel characteristic of the second transmit stream; and

determining either a spatial multiplexing mode or a diversity mode as a multi-antenna transmission mode by comparing the determined difference of the channel characteristics with a first threshold.

2. The method of claim 1 , wherein the channel characteristic comprises one of carrier to interference and noise ratios of transmit streams of the transmitter, an average carrier to interference and noise ratio of the transmit streams, a carrier to interference and noise ratio in the multi-antenna transmission mode used at the transmitter to send the signal, and a correlation value between channels of the received signal.

3. The method of claim 1 , further comprising:

determining whether a multi-antenna transmission mode selection request signal is received from the transmitter,

wherein the channel characteristic is determined when the multi-antenna transmission mode selection request signal is received.

4. The method of claim 3 , wherein the multi-antenna transmission mode selection request signal is one of a fast feedback subheader and a Channel Quality Indicator (CQI)Channel_Allocation_Information Element.

5. The method of claim 1 , wherein determining the channel characteristic comprises:

determining carrier to interference and noise ratios of each transmit stream received from the transmitter.

6. The method of claim 5 , wherein either the spatial multiplexing mode or the diversity mode as the multi-antenna transmission mode comprises:

determining the spatial multiplexing mode as the multi-antenna transmission mode when the difference between the carrier to interference and noise ratios of the first transmit stream and the carrier to interference and noise ratios of the second transmit stream is smaller than the first threshold.

7. The method of claim 6 , further comprising:

determining the diversity mode as the multi-antenna transmission mode when the difference between the carrier to interference and noise ratios of the first transmit stream and the carrier to interference and noise ratios of the second transmit stream is greater than the first threshold.

8. The method of claim 1 , wherein determining the channel characteristic comprises:

determining carrier to interference and noise ratios of each transmit stream received from the transmitter; and

determining an average of the carrier to interference and noise ratios.

9. The method of claim 8 , wherein determining the difference of the channel characteristics comprises:

determining a difference between the carrier to interference and noise ratio of the first transmit stream and the carrier to interference and noise ratio of the second transmit stream by comparing the carrier to interference and noise ratio of the first transmit stream and the carrier to interference and noise ratio of the second transmit stream; and

comparing the average of the carrier to interference and noise ratios of the transmit streams with a second threshold when the determined difference of the carrier to interference and noise ratios is smaller than a first threshold.

10. The method of claim 9 , wherein determining either a spatial multiplexing mode or a diversity mode as a multi-antenna transmission mode comprises:

determining the spatial multiplexing mode as the multi-antenna transmission mode of the transmitter when the determined difference of the carrier to interference and noise ratios is smaller than the first threshold and when the average of the carrier to interference and noise ratios of the transmit streams is greater than the second threshold; and

determining a diversity mode of the transmitter as the multi-antenna transmission mode when the determined difference of the carrier to interference and noise ratios is greater than the first threshold or when the average of the carrier to interference and noise ratios of the transmit streams is smaller than the second threshold.

11. The method of claim 1 , further comprising:

sending the determined multi-antenna transmission mode to the transmitter.

12. A method for selecting a transmission mode in a multi-antenna system, the method comprising:

determining a carrier to interference and noise ratio in relation with a multi-antenna transmission mode used by a transmitter to send a signal;

determining a correlation value between channels of a received signal;

comparing a carrier to interference and noise ratio of the multi-antenna transmission mode with a first threshold;

comparing a correlation value of the channels with a second threshold when the carrier to interference and noise ratio of the multi-antenna transmission mode is greater than the first threshold; and

determining a spatial multiplexing scheme as the multi-antenna transmission mode when the inter-channel correlation value is smaller than the second threshold.

13. The method of claim 12 , further comprising:

determining a diversity scheme as the multi-antenna transmission mode of the transmitter when the carrier to interference and noise ratio of the multi-antenna transmission mode is smaller than the first threshold or when the inter-channel correlation value is greater than the second threshold.

14. The method of claim 12 , wherein determining the inter-channel correlation value comprises:

estimating channels using the received signal; and

determining the inter-channel correlation value by estimating an eigenvalue spread of the estimated channels.

15. An apparatus for selecting a transmission mode in a multi-antenna system, the apparatus comprising:

a receiver configured to receive a signal over at least two antennas;

a channel estimator configured to determine a channel characteristic of each transmit stream received from a transmitter; and

a transmission mode determiner configured to:

determine a difference between the channel characteristic of a first transmit stream and the channel characteristic of a second transmit stream by comparing the channel characteristic of the first transmit stream and the channel characteristic of the second transmit stream, and

determine either a spatial multiplexing mode or a diversity mode as a multi-antenna transmission mode by comparing the determined difference of the channel characteristics with a first threshold.

16. The apparatus of claim 15 , wherein the channel estimator estimates one of carrier to interference and noise ratios (CINRs) of transmit streams of the transmitter, an average carrier to interference and noise ratio of the transmit streams, a carrier to interference and noise ratio in the multi-antenna transmission mode used at the transmitter to send the signal, and a correlation value between channels of the received signal.

17. The apparatus of claim 15 , wherein the channel estimator determines the channel characteristic when a multi-antenna transmission mode selection request signal is received from the transmitter through the receiver.

18. The apparatus of claim 17 , wherein the receiver receives the multi-antenna transmission mode selection request signal which includes one of a fast feedback subheader and a Channel Quality Indicator (CQI) Channel_Allocation_Information Element.

19. The apparatus of claim 15 , wherein the channel estimator determines carrier to interference and noise ratios of the transmit streams.

20. The apparatus of claim 19 , wherein the transmission mode determiner determines the spatial multiplexing mode as the multi-antenna transmission mode when the difference between the carrier to interference and noise ratios of the first transmit stream and the carrier to interference and noise ratios of the second transmit stream is smaller than the first threshold, and

the transmission mode determiner determines the diversity mode as the multi-antenna transmission mode when the difference between the carrier to interference and noise ratios of the first transmit stream and the carrier to interference and noise ratios of the second transmit stream is greater than the first threshold.

21. The apparatus of claim 15 , wherein the channel estimator determines a carrier to interference and noise ratio of the each transmit stream and an average of the carrier to interference and noise ratios of the transmit streams.

22. The apparatus of claim 21 , wherein the transmission mode determiner determines the spatial multiplexing mode as the multi-antenna transmission mode when the difference between the carrier to interference and noise ratios of the first transmit stream and the carrier to interference and noise ratios of the second transmit stream is smaller than a first threshold and the average of the carrier to interference and noise ratios of the transmit streams is greater than a second threshold, and

wherein the transmission mode determiner determines the diversity mode as the multi-antenna transmission mode when the difference between the carrier to interference and noise ratios of the first transmit stream and the carrier to interference and noise ratios of the second transmit stream is greater than the first threshold or the average of the carrier to interference and noise ratios of the transmit streams is smaller than the second threshold.

23. The apparatus of claim 15 , further comprising:

a sender configured to send the determined multi-antenna transmission mode to the transmitter over at least two antennas.

24. An apparatus for selecting a transmission mode in a multi-antenna system, the apparatus comprising:

a receiver configured to receive a signal over at least two antennas;

a channel estimator configured to determine a carrier to interference and noise ratio of the multi-antenna transmission mode used by the transmitter to send a signal;

a correlation part configured to determine a correlation value between channels of the signal; and

a transmission mode determiner configured to:

determine a spatial multiplexing mode as the multi-antenna transmission mode when the carrier to interference and noise ratio of the multi-antenna transmission mode used by the transmitter to send the signal, which is determined at the channel estimator, is greater than a first threshold and the inter-channel correlation value is smaller than a second threshold, and

determine a diversity mode as the multi-antenna transmission mode when the carrier to interference and noise ratio of the multi-antenna transmission mode is smaller than the first threshold or the inter-channel correlation value is greater than the second threshold.

25. The apparatus of claim 24 , wherein the correlation part estimates channels using the received signal, and

the correlation part determines the inter-channel correlation value by estimating an eigenvalue spread of the estimated channels.