Transmission mode and rate selection for a wireless communication system

• US 7,564,814 B2
• Filed: 04/06/2005
• Issued: 07/21/2009
• Est. Priority Date: 05/07/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Walton, Jay Rodney, Abraham, Santosh, Meylan, Arnaud
• Primary Examiner(s): Anderson; Matthew D
• Assistant Examiner(s): Aminzay; Shaima Q
• Application Number:
  US11/101,086
• Publication Number:
  US 20050249159A1
• Time in Patent Office: 1,567 Days
• Field of Search: 370/329, 370/200, 370/203, 370/208, 370/334, 370/335, 370/339, 342/367, 342/368, 375/260, 455/67.13, 455/63.1, 455/67.11, 455/562.1, 455/92, 455/151.1, 455/13, 455/67, 700/53, 700/46
• US Class Current: 370/329
• CPC Class Codes: H04B 7/0421 utilizing implicit feedback, e.g. steered pilot signals
• CPC Class Codes: H04L 1/0002 by adapting the transmission rate
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 25/0202 Channel estimation
• CPC Class Codes: Y02D 30/50 in wire-line communication networks, e.g. low power modes or reduced link rate

Abstract

To select a transmission mode to use for a data transmission via a MIMO channel from station A to station B, station A obtains channel information used for spatial processing and determines the age of this information. Station A selects one of multiple transmission modes based on the age of the channel information and possibly other information (e.g., the fading characteristic of the MIMO channel). To select rate(s) to use for the data transmission, station A obtains channel state information (CSI) indicative of the received signal quality for the MIMO channel, e.g., received SNRs or “initial” rates. Station A determines the age of the CSI and selects one or more “final” rates based on the CSI, the age of the CSI, the selected transmission mode, and possibly other information. Station A processes data in accordance with the selected transmission mode and final rate(s) and transmits the processed data to station B.

Claims

1. A method of selecting a transmission mode and rate selection in a multiple-input multiple-output (MIMO) wireless communication system, comprising:

obtaining channel state information indicative of received signal quality for a wireless channel used for data transmission;

obtaining channel information used to transmit data on eigenmodes of a MIMO channel from a steered or unsteered MIMO pilot, wherein the steered MIMO pilot is a pilot sent on the eigenmodes of the MIMO channel and the unsteered MIMO pilot is a pilot comprised of N pilot transmissions sent from N transmit antennas;

determining the age of the channel information and the channel state information;

selecting a transmission mode from among a plurality of transmission modes based on the age of the channel information, wherein the plurality of transmission modes comprises a steered mode wherein data is transmitted on the eigenmodes of the MIMO channel and an unsteered mode wherein the channel information is not used to transmit data on spatial channels of the MIMO channel; and

selecting at least one rate for data transmission based on the channel state information and the age of the channel state information, wherein data is transmitted via the wireless channel in accordance with the selected transmission mode and the selected at least one rate.

2. The method of claim 1, further comprising:

determining the age of a pilot used to derive the channel information, and wherein the age of the channel information is determined based on the age of the pilot; and

determining the age of a pilot used to derive the channel state information, and wherein the age of the channel state information is determined based on the age of the pilot.

3. The method of claim 1, wherein the selecting one of the plurality of transmission modes comprises

comparing the age of the channel information against a threshold, and

selecting the steered mode if the age of the channel information is less than or equal to the threshold, and wherein the channel information is used for spatial processing to transmit data in the steered mode.

4. The method of claim 3, wherein the selecting one of the plurality of transmission modes further comprises

selecting the unsteered mode if the age of the channel information is greater than the threshold.

5. The method of claim 3, further comprising:

determining the threshold based on a function of a time variant characteristic of the wireless channel.

6. The method of claim 1, wherein a plurality of rates are supported by the system, and wherein each of the at least one rate is selected from among the plurality of rates supported by the system.

7. The method of claim 6, wherein the channel state information comprises a plurality of initial rates for a plurality of spatial channels of a multiple-input multiple-output (MIMO) channel, one initial rate for each spatial channel.

8. The method of claim 7, wherein the selecting the at least one rate for data transmission comprises

determining a required signal-to-noise-and-interference ratio (SNR) for each of the plurality of spatial channels based on the initial rate for the spatial channel,

determining an SNR back-off based on the age of the plurality of initial rates,

determining an adjusted SNR for each of the plurality of spatial channels based on the required SNR for the spatial channel and the SNR back-off, and

determining a final rate for each of the plurality of spatial channels based on the adjusted SNR for the spatial channel, wherein data is transmitted on the plurality of spatial channels of the MIMO channel using a plurality of final rates determined for the plurality of spatial channels, and wherein the at least one rate selected for data transmission comprises the plurality of final rates.

9. The method of claim 7, wherein the selecting the at least one rate for data transmission comprises

determining a required signal-to-noise-and-interference ratio (SNR) for each of the plurality of spatial channels based on the initial rate for the spatial channel,

determining an SNR back-off based on the age of the plurality of initial rates,

determining an adjusted SNR for each of the plurality of spatial channels based on the required SNR for the spatial channel and the SNR back-off,

determining an average SNR for a plurality of adjusted SNRs determined for the plurality of spatial channels, and

determining a final rate for the plurality of spatial channels based on the average SNR, wherein data is transmitted on the plurality of spatial channels using the final rate determined for the plurality of spatial channels, and wherein the at least one rate selected for data transmission comprises the final rate.

10. The method of claim 9, wherein the adjusted SNR for each of the plurality of spatial channels is further determined based on a second SNR back-off applicable when one final rate is used for the plurality of spatial channels.

11. The method of claim 1, further comprising:

determining a back-off factor based on the age of the channel state information, and wherein the at least one rate is further selected based on the back-off factor.

12. The method of claim 11, wherein the back-off factor is determined based on a function of time variant characteristic of the wireless channel.

13. The method of claim 1, further comprising:

determining a back-off factor based on a transmission mode selected for use for data transmission, wherein a plurality of transmission modes are supported by the system, and wherein the at least one rate is further selected based on the back-off factor.

14. An apparatus for selecting a transmission mode and rate selection in a multiple-input multiple-output (MIMO) wireless communication system, comprising:

a controller to obtain channel state information indicative of received signal quality for a wireless channel used for data transmission, to obtain channel information used to transmit data on eigenmodes of a MIMO channel from a steered or unsteered MIMO pilot, wherein the steered MIMO pilot is a pilot sent on the eigenmodes of the MIMO channel and the unsteered MIMO pilot is a pilot comprised of N pilot transmissions sent from N transmit antennas, to determine the age of the channel information and the channel state information, to select a transmission mode from among a plurality of transmission modes based on the age of the channel information, wherein the plurality of transmission modes comprises a steered mode wherein data is transmitted on the eigenmodes of the MIMO channel and an unsteered mode wherein the channel information is not used to transmit data on spatial channels of the MIMO channel, to select at least one rate for data transmission based on the channel state information and the age of the channel state information; and

a spatial processor to spatially process data in accordance with the selected transmission mode and the selected at least one rate.

15. The apparatus of claim 14, wherein the controller determines the age of a pilot used to derive the channel information and determines the age of the channel information based on the age of the pilot;

and

determining the age of a pilot used to derive the channel state information, and wherein the age of the channel state information is determined based on the age of the pilot.

16. The apparatus of claim 14, wherein the controller compares the age of the channel information against a threshold and selects a steered mode if the age of the channel information is less than or equal to the threshold, and wherein the spatial processor uses the channel information for spatial processing in the steered mode.

17. The apparatus of claim 16, wherein the controller selects an unsteered mode if the age of the channel information is greater than the threshold, and wherein the spatial processor does not use the channel information for spatial processing in the unsteered mode.

18. An apparatus for selecting a transmission mode and rate selection in a multiple-input multiple-output (MIMO) wireless communication system, comprising:

means for obtaining channel state information indicative of received signal quality for a wireless channel used for data transmission;

means for obtaining channel information used to transmit data on eigenmodes of a MIMO channel from a steered or unsteered MIMO pilot, wherein the steered MIMO pilot is a pilot sent on the eigenmodes of the MIMO channel and the unsteered MIMO pilot is a pilot comprised of N pilot transmissions sent from N transmit antennas;

means for determining the age of the channel information and the channel state information; and

means for selecting a transmission mode from among a plurality of transmission modes based on the age of the channel information wherein the plurality of transmission modes comprises a steered mode wherein data is transmitted on the eigenmodes of the MIMO channel and an unsteered mode wherein the channel information is not used to transmit data on spatial channels of the MIMO channel; and

means for selecting at least one rate for data transmission based on the channel state information and the age of the channel state information, wherein data is transmitted via the wireless channel in accordance with the selected transmission mode and the selected at least one rate.

19. The apparatus of claim 18, further comprising:

means for determining the age of a pilot used to derive the channel information, and wherein the age of the channel information is determined based on the age of the pilot; and

means for determining the age of a pilot used to derive the channel state information, and wherein the age of the channel state information is determined based on the age of the pilot.

20. The apparatus of claim 18, wherein the means for selecting one of the plurality of transmission modes comprises

means for comparing the age of the channel information against a threshold, and

means for selecting a steered mode if the age of the channel information is less than or equal to the threshold, and wherein the channel information is used for spatial processing to transmit data in the steered mode.

21. The apparatus of claim 20, wherein the means for selecting one of the plurality of transmission modes further comprises

means for selecting an unsteered mode if the age of the channel information is greater than the threshold, and wherein the channel information is not used for spatial processing to transmit data in the unsteered mode.

22. An integrated circuit for selecting a transmission mode and rate selection in a multiple-input multiple-output (MIMO) wireless communication system, comprising:

a processor operable to;

obtain channel state information indicative of received signal quality for a wireless channel used for data transmission;

obtain channel information used to transmit data on eigenmodes of a MIMO channel from a steered or unsteered MIMO pilot, wherein the steered MIMO pilot is a pilot sent on the eigenmodes of the MIMO channel and the unsteered MIMO pilot is a pilot comprised of N pilot transmissions sent from N transmit antennas;

determine the age of the channel information and the channel state information;

select a transmission mode from among a plurality of transmission modes based on the age of the channel information, wherein the plurality of transmission modes comprises a steered mode wherein data is transmitted on the eigenmodes of the MIMO channel and an unsteered mode wherein the channel information is not used to transmit data on spatial channels of the MILMO channel; and

select at least one rate for data transmission based on the channel state information and the age of the channel state information, wherein data is transmitted via the wireless channel in accordance with the selected transmission mode and the selected at least one rate.