Closed-loop rate control for a MIMO communication system

• US 8,194,563 B2
• Filed: 04/26/2010
• Issued: 06/05/2012
• Est. Priority Date: 11/16/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Walton, J. Rodney, Wallace, Mark S.
• Primary Examiner(s): Harper, Kevin C
• Application Number:
  US12/767,648
• Publication Number:
  US 20100208839A1
• Time in Patent Office: 771 Days
• Field of Search: None
• US Class Current: 370/252
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0619 using feedback from receiving side feedback signaling for adaptive modulation/coding H04L1/0001
• CPC Class Codes: H04L 1/0002 by adapting the transmission rate
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0006 by adapting the transmission format
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0025 Transmission of mode-switching indication
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 1/208 involving signal re-encoding
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems
• CPC Class Codes: Y02D 30/50 in wire-line communication networks, e.g. low power modes or reduced link rate

Abstract

In a MIMO system, rate control is achieved with an inner loop that selects rates for data streams sent via a MIMO channel and an outer loop that regulates the operation of the inner loop. For the inner loop, SNR estimates are obtained for each data stream based on received pilot symbols and/or received data symbols. An effective SNR is derived for each data stream based on the SNR estimates, a diversity order, a MIMO backoff factor, and an outer loop backoff factor for the data stream. The rates are then selected for the data streams based on the effective SNRs for the data streams. The outer loop adjusts the outer loop backoff factor for each data stream based on the performance (e.g., packet errors and/or decoder metrics) for the data stream.

Claims

1. An apparatus for rate selection in a wireless communications system comprising:

at least one processor configured to obtain at least one SNR estimate for a data stream, to determine a diversity order for the data stream based on a number of data streams being transmitted and a number of receive antennas, to determine an SNR variance for the data stream, and to select a rate for the data stream based on the at least one SNR estimate, the diversity order for the data stream, and the SNR variance for the data stream; and

a memory coupled to the at least one processor.

2. The apparatus of claim 1, wherein the at least one processor is configured to derive the at least one SNR estimate based on received pilot symbols.

3. The apparatus of claim 1, wherein the at least one processor is configured to derive the at least one SNR estimate based on received data symbols.

4. The apparatus of claim 1, wherein the at least one processor is configured to determine the diversity order for the data stream further based on an index for the data stream.

5. A method for rate selection by a station in a wireless communications system comprising:

obtaining at least one SNR estimate for a data stream;

determining a diversity order for the data stream based on a number of data streams being transmitted and a number of receive antennas;

determining an SNR variance for the data stream; and

selecting a rate for the data stream based on the at least one SNR estimate, the diversity order for the data stream, and the SNR variance for the data stream.

6. The method of claim 5, wherein the obtaining comprises deriving the at least one SNR estimate based on received pilot symbols.

7. The method of claim 5, wherein the obtaining comprises deriving the at least one SNR estimate based on received data symbols.

8. The method of claim 5, wherein the determining comprises determining the diversity order for the data stream further based on an index for the data stream.

9. An apparatus for rate selection by a station in a wireless communications system comprising:

means for obtaining at least one SNR estimate for a data stream;

means for determining a diversity order for the data stream based on a number of data streams being transmitted and a number of receive antennas;

means for determining an SNR variance for the data stream; and

means for selecting a rate for the data stream based on the at least one SNR estimate, the diversity order for the data stream, and the SNR variance for the data stream.

10. The apparatus of claim 9, wherein the means for obtaining comprises means for deriving the at least one SNR estimate based on received pilot symbols.

11. The apparatus of claim 9 wherein the means for obtaining comprises means for deriving the at least one SNR estimate based on received data symbols.

12. The apparatus of claim 9, wherein the means for determining comprises means for determining the diversity order for the data stream further based on an index for the data stream.

13. A memory unit for rate selection by a station in a wireless communications system including one or more software modules stored therein, the one or more software modules including software codes and being executable by one or more processors, the software codes comprising:

code for obtaining at least one SNR estimate for a data stream;

code for determining a diversity order for the data stream based on a number of data streams being transmitted and a number of receive antennas;

code for determining an SNR variance for the data stream; and

code for selecting a rate for the data stream based on the at least one SNR estimate, the diversity order for the data stream, and the SNR variance for the data stream.

14. The memory unit of claim 13, wherein the code for obtaining comprises code for deriving the at least one SNR estimate based on received pilot symbols.

15. The memory unit of claim 13, wherein the obtaining comprises deriving the at least one SNR estimate based on received data symbols.

16. The memory unit of claim 13, wherein the code for determining comprises code for determining the diversity order for the data stream further based on an index for the data stream.