Method and apparatus for enhancing performance of channel quality indicator (CQI) channel in wireless communications system
View Patent ↗The channel quality indicator (CQI) transmitted by a mobile terminal to a base station is indicative of the E c /N t pilot SNR of the pilot signal transmitted by the base station and measured by the mobile terminal. The base station uses the CQI for purposes such as determining a downlink rate, a modulation scheme, and downlink power. Knowledge by the base station of whether the received and detected CQI is likely to be “good” or “bad” would be useful in determining how and whether the value of the received and detected CQI should be used. In a first embodiment, at the base station, a reliability of the received CQI that is detected from received soft symbol metrics is determined in conjunction with the detected CQI value for the received CQI word as a whole. In a second embodiment, a minimum bit error probability receiver is used that makes a maximum likelihood decision for each CQI bit individually from the plurality of metrics derived from the received soft symbol metrics, and the reliability of each CQI bit is individually determined.
1. A method comprising the steps of:
receiving soft symbol metrics associated with a transmitted channel quality indicator;
detecting the transmitted channel quality indicator from the received soft symbol metrics; and
determining a reliability associated with the detected transmitted quality indicator, wherein the transmitted channel quality indicator is a multi-bit word and the received soft symbol metrics associated with the transmitted channel quality indicator are converted to a plurality of metrics, each of the metrics are associated with a different channel quality word, and the reliability associated with the detected transmitted channel quality indicator is determined based on each of the metrics.
2. The method of claim 1 wherein the reliability is determined for the channel quality indicator word as a whole.
3. The method of claim 2 wherein the transmitted channel quality indicator is an n-bit word and the received soft symbol metrics associated with the transmitted channel quality indicator are converted to 2″ metrics w 0 , w 2 , . . . , w 2″-1 , that are each associated with a different channel quality word, wherein the detected word is the channel quality word associated with the largest metric, w j , and wherein the reliability of the detected channel quality word is determined by
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4. The method of claim 3 wherein the received soft symbol metrics are the received metrics of a Hadamard encoding of the channel quality indicator.
5. The method of claim 1 wherein each bit of the channel quality indicator word is individually detected from the received soft symbol metrics, and wherein the reliability of the detected channel quality indicator word is determined for each bit individually.
6. The method of claim 5 wherein the transmitted channel quality indicator is an n-bit word and the received soft symbol metrics associated with the transmitted channel quality indicator are converted to 2″ metrics w 0 , w 2 , . . . , w 2″-1 , that are each associated with a different channel quality word, wherein each bit b i (i=0 ton-1) of the channel quality indicator word is determined according to whether the likelihood ratio LR i equal to
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7. The method of claim 6 wherein the received soft symbol metrics are the received metrics of a Hadamard encoding of the channel quality indicator.
8. The method of claim 1 wherein the method is performed at a base station in a wireless communications system.
9. The method of claim 8 wherein the channel quality indicator is transmitted by a mobile station and is representative of a pilot signal-to-noise ratio E b /N t of a pilot signal received by the mobile station from the base station.
10. Apparatus comprising:
receiving means for receiving soft symbol metrics associated with a transmitted channel quality indicator;
detecting means for detecting the transmitted channel quality indicator from the received soft symbol metrics; and
reliability determining means for determining a reliability associated with the detected transmitted quality indicator, wherein the transmitted channel quality indicator is a multi-bit word and the received soft symbol metrics associated with the transmitted channel quality indicator are converted to a plurality of metrics, each of the metrics are associated with a different channel quality word, and the reliability associated with the detected transmitted channel quality indicator is determined based on each of the metrics.
11. The apparatus of claim 10 wherein the reliability determining means determines the reliability of the channel quality indicator word as a whole.
12. The apparatus of claim 11 wherein the transmitted channel quality indicator is an n-bit word and the received soft symbol metrics associated with the transmitted channel quality indicator are converted to 2″ metrics w 0 , w 2 , . . . , w 2″-1 , that are each associated with a different channel quality word, wherein the detected word is the channel quality word associated with the largest metric, w j , and wherein the reliability determining means determines the reliability of the detected channel quality word by
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13. The apparatus of claim 12 wherein the received soft symbol metrics are the received metrics of a Hadamard encoding of the channel quality indicator.
14. The apparatus claim 10 wherein the detecting means detects each bit of the channel quality indicator word individually from the received soft symbol metrics, and wherein the reliability determining means determines the reliability of the detected channel quality indicator for each bit individually.
15. The apparatus of claim 14 wherein the transmitted channel quality indicator is an n-bit word and the received soft symbol metrics associated with the transmitted channel quality indicator are converted to 2″ metrics w 0 , w 2 , . . . , w 2″-1 , that are each associated with a different channel quality word, wherein the detecting means determines each bit b i (i=0 ton-1) of the channel quality indicator word according to whether the likelihood ratio LR i equal to
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16. The apparatus of claim 15 wherein the received soft symbol metrics are the received metrics of a Hadamard encoding of the channel quality indicator.
17. The apparatus of claim 10 wherein the apparatus is located in a base station in a wireless communications system.
18. The apparatus of claim 17 wherein the channel quality indicator is transmitted by a mobile station and is representative of a pilot signal-to-noise ratio E b /N 1 of a pilot signal received by the mobile station from the base station.