DOWNLINK PDSCH TRANSMISSION MODE SELECTION AND SWITCHING ALGORITHM FOR LTE

• US 20120057538A1
• Filed: 08/22/2011
• Published: 03/08/2012
• Est. Priority Date: 09/03/2010
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Tayloe, Daniel R., Adhikari, Shubhodeep
• Granted Patent: US 8,553,637 B2
• Time in Patent Office: Days
• US Class Current: 370/329
• 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 1/0034 where the transmitter decides based on inferences, e.g. use of implicit signalling
• CPC Class Codes: H04L 1/1812 Hybrid protocols; Hybrid automatic repeat request [HARQ]
• CPC Class Codes: H04L 1/203 Details of error rate determination, e.g. BER, FER or WER
• CPC Class Codes: H04W 72/54 based on quality criteria

Abstract

A method, system, and base station for deterministically selecting a downlink transmission mode and rank in a Long Term Evolution (LTE) configured wireless communication system. The Transmission Mode Selection (TMS) utility receives from a wireless device a request for downlink physical downlink shared channel (PDSCH) service using a particular transmission mode and specific rank. The TMS utility determines an estimate of the throughput corresponding to the request. In addition, the TMS utility obtains throughput estimates of other distinct pairings of transmission mode and rank to compare with the throughput estimate corresponding to the request. The TMS utility utilizes device feedback information and HARQ error information that are already existing/available in order to determine the best transmission mode and rank pair, according to the best Error-Adjusted-Throughput.

Claims

1. In a wireless communication system having an Evolved Universal Terrestrial Radio Access Network Node B (eNodeB), a method for allocating communication resources to wireless devices, said method comprising:

receiving a request from a wireless device for downlink physical shared channel (PDSCH) downlink transmission via a particular transmission mode and a specific rank that represents a first pairing;

retrieving one or more of;

(a) historical Hybrid Automatic Repeat Request (HARQ) feedback information corresponding to said particular transmission mode and rank;

(b) Channel Quality Indicators (CQIs) corresponding to one or more layers of the precoder corresponding to the specific rank requested;

(c) a Precoder Matrix Index (PMI) report that provides a best precoder corresponding to said particular transmission mode and said specific rank; and

(d) a rank indicator (RI) report;

obtaining an estimation of a first HARQ error adjusted throughput associated with said particular transmission mode and said specific rank requested by said wireless device;

providing estimates of HARQ error adjusted throughput corresponding to other distinct pairings of transmission mode and rank;

comparing said estimation of said first HARQ error adjusted throughput with said estimates of HARQ error adjusted throughput;

in response to said comparing, selecting a best pairing of transmission mode and rank with a higher HARQ error adjusted throughput for transmission service for said wireless device; and

in response to the selection, periodically switching from the selected pairing of transmission mode and rank to other pairings of other transmission modes and rank to check if conditions have adequately improved to warrant transmission at a different pairing of transmission mode and rank.

2. The method of claim 1, wherein said obtaining further comprises:

evaluating one or more adjusted CQI values from a modification of the one or more CQI values by said historical HARQ feedback information;

determining one or more data rates corresponding to the one or more adjusted CQI values; and

determining a first estimate of maximum data rate corresponding to said first pairing that is supportable via downlink transmission based on one of;

(a) the one data rate corresponding to a single CQI value; and

(b) addition of multiple data rates corresponding to a plurality of CQI values.

3. The method of claim 1, wherein said providing further comprises:

when a first rank of the first pairing is higher than a second rank of another distinct pairing;

identifying a larger value among a plurality of reported CQI values corresponding to said specific rank of said first pairing;

calculating a HARQ error adjusted CQI for the distinct pairing with the second rank, by adding a corresponding, stored HARQ error feedback value to said larger value among a plurality of reported CQI values corresponding to said first rank of said first particular pairing; and

calculating an estimate of a maximum CQI for said second rank by adding a configurable constant to said HARQ error adjusted CQI for said distinct pairing having the second rank.

4. The method of claim 1, wherein said providing further comprises:

when said second rank is not lower than said first rank;

deriving estimated adjusted CQI values for the distinct pairing from reported CQI values for said first pairing;

calculating HARQ error adjusted CQI values for the distinct pairing with the second rank, by adding a corresponding, stored HARQ error feedback value to estimated adjusted CQI values;

calculating estimates of maximum CQI values for said second rank by subtracting a configurable constant from said HARQ error adjusted CQI for said distinct pairing having the second rank;

wherein said configurable constant is based on experimentation and previous measurements; and

evaluating a second estimate of maximum data rate corresponding to said estimate of said maximum CQI for said second rank.

5. The method of claim 1, further comprising:

in response to a first rejection of said first pairing of the particular transmission mode and the specific rank that is requested by said wireless device, initializing a counter to track a number of consecutive rejections of said first pairing when a previously requested first pairing was not rejected;

performing a periodic check of other pairings of transmission modes and rank

triggering a switch to the transmission mode and rank that has the best estimated HARQ error adjusted throughput in response to said periodic check; and

selecting service via said best pairing from among distinct pairings corresponding to transmission modes and rank pairings available for use at said wireless device.

6. The method of claim 5, further comprising:

when a preconfigured maximum value for a level of change in performance aggressiveness for said wireless device is less than a potential level of change from a previously selected pairing to said best pairing, scheduling transmission service via an intermediate pairing, according to said preconfigured maximum value;

determining a throughput performance level via the intermediate pairing; and

in response to a determination that said throughput performance level via the intermediate mode is sub-optimal, switching service to said best pairing of transmission mode and rank.

7. The method of claim 5, further comprising:

in response to a second rejection of first pairing, incrementing said counter by 1 if said first pairing was also rejected when last requested;

following said rejection of said first pairing, performing a periodic check to determine whether conditions are adequately improved to merit re-evaluation with potential threshold based HARQ adjustment;

initiating, according to said periodic check, comparisons of one or more of;

(a) said first pairing and said best pairing; and

(b) other distinct pairings and said best pairing;

determining whether a value of said counter is larger than the threshold value; and

in response to a determination that said value of said counter is not larger than the threshold value, obtaining a first estimate of an actual data rate corresponding to said first pairing by using a HARQ error adjustment directly from HARQ error feedback.

8. The method of claim 7, further comprising:

in response to a determination that said value of said counter is larger than the threshold value, obtaining a second estimate of the maximum data rate corresponding to said first pairing by using a HARQ error adjustment divided by a preset value; and

comparing said first pairing and the other distinct pairings, by using said second estimate of said maximum data rate corresponding to said first particular pairing, when said counter value is larger than the threshold value.

9. The method of claim 1, further comprising:

periodically switching downlink transmission service from a second pairing with a lower rank to said first pairing with a higher rank to determine if conditions are adequately improved to provide a practical evaluation of said first particular pairing.

10. A base station comprising:

a processor;

a memory having stored therein a scheduler;

a utility which when executed by the processor, provides the functions of;

receiving a request from a wireless device for downlink physical shared channel (PDSCH) downlink transmission via a particular transmission mode and a specific rank that represents a first pairing;

retrieving one or more of;

(a) historical Hybrid Automatic Repeat Request (HARQ) feedback information corresponding to said particular transmission mode and rank;

(b) Channel Quality Indicators (CQIs) corresponding to one or more layers of the precoder corresponding to the specific rank requested;

(c) a Precoder Matrix Index (PMI) report that provides a best precoder corresponding to said particular transmission mode and said specific rank; and

(d) a rank indicator (RI) report;

obtaining an estimation of a first HARQ error adjusted throughput associated with said particular transmission mode and said specific rank requested by said wireless device;

providing estimates of HARQ error adjusted throughput corresponding to other distinct pairings of transmission mode and rank;

comparing said estimation of said first HARQ error adjusted throughput with said estimates of HARQ error adjusted throughput;

in response to said comparing, selecting a best pairing of transmission mode and rank with a higher HARQ error adjusted throughput for transmission service for said wireless device; and

in response to the selection, periodically switching from the selected pairing of transmission mode and rank to other pairings of other transmission modes and rank to check if conditions have adequately improved to warrant transmission at a different pairing of transmission mode and rank.

11. The base station of claim 10, wherein said obtaining functions further comprises:

evaluating one or more adjusted CQI values from a modification of the one or more CQI values by said historical HARQ feedback information;

determining one or more data rates corresponding to the one or more adjusted CQI values; and

determining a first estimate of maximum data rate corresponding to said first pairing that is supportable via downlink transmission based on one of;

(a) the one data rate corresponding to a single CQI value; and

(b) addition of multiple data rates corresponding to a plurality of CQI values.

12. The base station of claim 10, wherein said providing functions further comprises:

when a first rank of the first pairing is higher than a second rank of another distinct pairing;

identifying a larger value among a plurality of reported CQI values corresponding to said specific rank of said first pairing;

calculating a HARQ error adjusted CQI for the distinct pairing with the second rank, by adding a corresponding, stored HARQ error feedback value to said larger value among a plurality of reported CQI values corresponding to said first rank of said first particular pairing; and

calculating an estimate of a maximum CQI for said second rank by adding a configurable constant to said HARQ error adjusted CQI for said distinct pairing having the second rank.

13. The base station of claim 10, wherein said providing functions further comprises:

when said second rank is not lower than said first rank;

deriving estimated adjusted CQI values for the distinct pairing from reported CQI values for said first pairing;

calculating HARQ error adjusted CQI values for the distinct pairing with the second rank, by adding a corresponding, stored HARQ error feedback value to estimated adjusted CQI values;

calculating estimates of maximum CQI values for said second rank by subtracting a configurable constant from said HARQ error adjusted CQI for said distinct pairing having the second rank;

wherein said configurable constant is based on experimentation and previous measurements; and

evaluating a second estimate of maximum data rate corresponding to said estimate of said maximum CQI for said second rank.

14. The base station of claim 10, wherein the processor execution of the utility performs the functions of:

in response to a first rejection of said first pairing of the particular transmission mode and the specific rank that is requested by said wireless device, initializing a counter to track a number of consecutive rejections of said first pairing when a previously requested first pairing was not rejected;

performing a periodic check of other pairings of transmission modes and rank

triggering a switch to the transmission mode and rank that has the best estimated HARQ error adjusted throughput in response to said periodic check; and

selecting service via said best pairing from among distinct pairings corresponding to transmission modes and rank pairings available for use at said wireless device.

15. The base station of claim 14, wherein the processor execution of the utility performs the functions of:

when a preconfigured maximum value for a level of change in performance aggressiveness for said wireless device is less than a potential level of change from a previously selected pairing to said best pairing, scheduling transmission service via an intermediate pairing, according to said preconfigured maximum value;

determining a throughput performance level via the intermediate pairing; and

in response to a determination that said throughput performance level via the intermediate mode is sub-optimal, switching service to said best pairing of transmission mode and rank.

16. The base station of claim 14, wherein the processor execution of the utility performs the additional functions of:

in response to a second rejection of first pairing, incrementing said counter by 1 if said first pairing was also rejected when last requested;

following said rejection of said first pairing, performing a periodic check to determine whether conditions are adequately improved to merit re-evaluation with potential threshold based HARQ adjustment;

initiating, according to said periodic check, comparisons of one or more of;

(a) said first pairing and said best pairing; and

(b) other distinct pairings and said best pairing;

determining whether a value of said counter is larger than the threshold value; and

in response to a determination that said value of said counter is not larger than the threshold value, obtaining a first estimate of an actual data rate corresponding to said first pairing by using a HARQ error adjustment directly from HARQ error feedback.

17. The base station of claim 10, wherein the processor execution of the utility performs the additional functions of:

in response to a determination that said value of said counter is larger than the threshold value, obtaining a second estimate of the maximum data rate corresponding to said first pairing by using a HARQ error adjustment divided by a preset value; and

comparing said first pairing and the other distinct pairings, by using said second estimate of said maximum data rate corresponding to said first particular pairing, when said counter value is larger than the threshold value.

18. The base station of claim 10, wherein the processor execution of the utility performs the additional functions of:

periodically switching downlink transmission service from a second pairing with a lower rank to said first pairing with a higher rank to determine if conditions are adequately improved to provide a practical evaluation of said first particular pairing.

19. The base station of claim 10, wherein the base station is an Evolved Universal Terrestrial Radio Access Network Node B (eNodeB) within a Long Term Evolution (LTE)-based wireless communication system.

20. An Evolved Universal Terrestrial Radio Access Network Node B (eNodeB) utilized within a Long Term Evolution (LTE)-based wireless communication system, the eNodeB comprising:

a processor;

one or more wireless transmitter/receiver devices (transceivers) communicatively coupled to the processor and which enables communicating with one or more wireless communication devices;

a memory having stored therein a scheduler;

a utility which when executed by the processor, provides the functions of;

receiving a request from a wireless device for downlink physical shared channel (PDSCH) downlink transmission via a particular transmission mode and a specific rank that represents a first pairing;

retrieving one or more of;

(a) historical Hybrid Automatic Repeat Request (HARQ) feedback information corresponding to said particular transmission mode and rank;

(b) Channel Quality Indicators (CQIs) corresponding to one or more layers of the precoder corresponding to the specific rank requested;

(c) a Precoder Matrix Index (PMI) report that provides a best precoder corresponding to said particular transmission mode and said specific rank; and

(d) a rank indicator (RI) report;

obtaining an estimation of a first HARQ error adjusted throughput associated with said particular transmission mode and said specific rank requested by said wireless device;

providing estimates of HARQ error adjusted throughput corresponding to other distinct pairings of transmission mode and rank;

comparing said estimation of said first HARQ error adjusted throughput with said estimates of HARQ error adjusted throughput;

in response to said comparing, selecting a best pairing of transmission mode and rank with a higher HARQ error adjusted throughput for transmission service for said wireless device; and

in response to the selection, periodically switching from the selected pairing of transmission mode and rank to other pairings of other transmission modes and rank to check if conditions have adequately improved to warrant transmission at a different pairing of transmission mode and rank.