Method of switching transmission modes in IEEE 802.11n MIMO communication systems

• US 20070147414A1
• Filed: 12/22/2005
• Published: 06/28/2007
• Est. Priority Date: 12/22/2005
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Niu, Huaning, Ngo, Chiu
• Granted Patent: US 7,620,067 B2
• Time in Patent Office: Days
• US Class Current: 370/465
• CPC Class Codes: H04B 7/0669 using different channel coding between antennas space-time coding H04L1/0618
• CPC Class Codes: H04B 7/0671 using different delays between antennas
• CPC Class Codes: H04B 7/0689 using different transmission schemes, at least one of them being a diversity transmission scheme
• CPC Class Codes: H04B 7/0697 using spatial multiplexing
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0019 in which mode-switching is based on a statistical approach
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 1/0631 Receiver arrangements
• CPC Class Codes: H04L 1/0668 Orthogonal systems, e.g. using Alamouti codes
• CPC Class Codes: H04L 1/0675 characterised by the signaling

Abstract

A method and system is provided that selects transmission modes between spatial multiplexing, delay diversity and space-time coding in 802.11n systems. As such, eigen-value computation for mode selection is not required. This provides efficiency, in particular for basic receiver structure where a linear MMSE or ZF MIMO detector is applied. Further, mode selection using a simple metric provides accurate mode selection. In addition by switching between different transmission modes, a link adaptation algorithm according to the present invention provides improved system performance.

Claims

1. A method of switching between transmission modes in an IEEE802.11n wireless communication system, comprising the steps of:

determining a decision metric as a function of post-detection constellation-coding SNR; and

selecting between transmission modes based on the decision metric.

2. The method of claim 1, wherein the step of selecting between transmission modes further includes the steps of selecting between spatial multiplexing, delay diversity and space-time coding transmission modes based on the decision metric.

3. The method of claim 1 further including the steps of comparing MCS of different transmission modes using the decision metric.

4. The method of claim 1 wherein the step of selecting between transmission modes further includes the steps of selecting between transmission modes based on the decision metric to achieve the best system performance.

5. The method of claim 1, wherein the step of determining a decision metric further includes the steps of determining a decision metric as a function of the constellation distance and coding rate.

6. The method of claim 5 wherein the step of determining a decision metric further includes the steps of:

estimating communication channel information based on long preamble;

computing a post-detection SNR (ρ

_MIMO) for different transmission modes;

computing a coding loss of higher coding rate (ρ

_coding);

computing a squared min-distance of constellation (d²_{min-constellation}) for different MCS with the same transmission rates; and

computing a decision metric D for each transmission mode, such that each transmission mode has a corresponding decision metric.

7. The method of claim 6 wherein the step of selecting the transmission modes further includes the steps of switching between the transmission modes based on the decision metric of each transmission mode.

8. The method of claim 6 wherein the step of selecting the transmission modes further includes the steps of selecting the transmission mode with the largest decision metric.

9. The method of claim 8 wherein the communication system comprises a transmitter and a receiver, the method further comprising the steps of feeding back the selection information to the transmitter for switching between transmission modes accordingly.

10. The method of claim 6 wherein the step of computing a decision metric D for each transmission mode further includes the steps of, for each transmission mode computing:

D=ρ

_MIMO+d²_{min-constellation}−

ρ

_coding.

11. The method of claim 1, wherein eigen-value computation for transmission mode selection is not performed.

12. The method of claim 1, wherein the communication system comprises a MIMO system.

13. A controller for switching between transmission modes in an IEEE802.11n wireless communication system, comprising:

a decision metric calculator that determining a decision metric as a function of post-detection constellation-coding SNR; and

a selector that selects between transmission modes based on the decision metric.

14. The controller of claim 13, wherein the selector selects between transmission modes further by selecting between spatial multiplexing, delay diversity and space-time coding transmission modes based on the decision metric.

15. The controller of claim 13 further including means for comparing MCS of different transmission modes using the decision metric.

16. The controller of claim 13 wherein the selector selects between transmission modes further by selecting between transmission modes based on the decision metric to achieve the best system performance.

17. The controller of claim 13, wherein the decision metric calculator determines the decision metric further by determining a decision metric as a function of post detection SNR, the constellation distance and coding rate.

18. The controller of claim 17 wherein the decision metric calculator determines the decision metric further by:

estimating communication channel information based on long preamble;

computing a post-detection SNR (ρ

_MIMO) for different transmission modes;

computing a coding loss of higher coding rate (ρ

_coding);

computing a squared min-distance of constellation (d²_{min-constellation}) for different MCS with the same transmission rates; and

computing a decision metric D for each transmission mode, such that each transmission mode has a corresponding decision metric.

19. The controller of claim 18 wherein the selector selects the transmission modes further by switching between the transmission modes based on the decision metric of each transmission mode.

20. The controller of claim 18 wherein the selector selects the transmission modes further by selecting the transmission mode with the largest decision metric.

21. The controller of claim 20 wherein the communication system comprises a transmitter and a receiver, such that the controller further feeds back the selection information to the transmitter for switching between transmission modes accordingly.

22. The controller of claim 18 wherein decision metric calculator computes the decision metric D for each transmission mode further by, for each transmission mode, computing:

D=ρ

_MIMO+d²_{min-constellation}−

ρ

_coding.

23. The controller of claim 13, wherein eigen-value computation for transmission mode selection is not performed.

24. The controller of claim 13, wherein the communication system comprises a MIMO system.

25. The controller of claim 18, wherein post-detection SNR (ρ

_MIMO) for direct mapping mode is determined as min(1/diag{R^†

R<sup>†

H</sup>}), where R<sup>†

is the MIMO equalizer coefficients computed using the MMSE (Minimum Mean Squared Error) criterion or the ZF (Zero Forcing) criterion.</sup>

26. The controller of claim 18, wherein post-detection SNR (ρ

_MIMO) for spatial spreading mode with number of spatial streams N_SS=1 is determined as ∥

Hq∥

_F where ∥

H∥

_F is the Frobenius norm of the H matrix, defined as

$\underset{j,k}{\sum <br><br>}<br><br>{<br><br>h_{j,k}<br><br>}^2,$

and q is the spatial spreading antenna map vector.

27. The controller of claim 18, wherein post-detection SNR (ρ

_MIMO) for spatial spreading with number of spatial streams N_SS>

1 is determined as min(1/diag{R^†

R<sup>†

H</sup>}) where R^†

is the MIMO equalizer coefficients based on the equivalent channel coefficient HQ, using the MMSE criterion or the ZF criterion, and Qis the spatial spreading matrix.

28. The controller of claim 18, wherein post-detection SNR (ρ

_MIMO) for STBC mode with number of spatial streams N_SS=1 is determined as ∥

H∥

_F where ∥

H∥

_F is the Frobenius norm of the H matrix, defined as

$\underset{j,k}{\sum <br><br>}<br><br>{<br><br>h_{j,k}<br><br>}^2.$

29. The controller of claim 18, wherein post-detection SNR (ρ

_MIMO) for STBC mode with number of spatial streams N_SS=2 is determined as min(∥

H₁∥

_F, ∥

H₂∥

_F) where H₁ is the first two rows of channel matrix H, corresponding to the channel of the first data stream, and H₂ are the third and fourth row of the channel matrix H, corresponding to the second data stream.

30. The controller of claim 18, wherein post-detection SNR (ρ

_MIMO) for basic beamforming mode with power loading is determined as ρ

_MIMO=min(1/diag{R^†

R<sup>†

H</sup>}+diag (P₁,P₂, . . . , P_Nss)), where Q is the eigen-steering vector used in beamforming R^†

is the MIMO equalizer coefficients based on the equivalent channel coefficient HQ, using the MMSE criterion or the ZF criterion, Qis the eigen-steering matrix, P_i is the power loaded in each eigen-mode.

31. The controller of claim 18, wherein coding loss of higher coding rate (ρ

_coding) is determined as;

ρ

_coding (dB) Rate 1/2 codes 0 Rate 2/3 codes 2 Rate 3/4 codes 3 Rate 5/6 codes 4

32. The controller of claim 27 wherein the ρ

_coding values are further optimized based on detailed implementation codes.

33. The controller of claim 18, wherein a squared min-distance of constellation (d²_{min-constellation}) for different MCS with the same transmission rates is determined as:

d²_{min-constellation} d²_{min-constellation} (dB) BPSK 4 6.02 QPSK (2/{square root over (2)})² 3.01 16QAM (2/{square root over (10)})² −

3.98 64QAM (2/{square root over (42)})² −

10.2