Feedback reduction for MIMO precoded system by exploiting channel correlation
View Patent ↗In a closed-loop wireless communication system, a codebook-based precoding feedback compression mechanism is provided to remove redundancy from the precoding feedback that is caused by channel correlation in time and frequency. Redundancy due to temporal correlation of the transmission channel is removed by sending precoding feedback only if there is a change in the precoder state for the channel to the receiver. Redundancy due to frequency correlation is removed by run length encoding the precoding feedback, thereby compressing the precoding feedback prior in the frequency domain. By compressing the precoding feedback, the average rate of precoder feedback is reduced.
1. A method for precoding signals in a MIMO communication system, comprising:
estimating channel state information for a transmission channel from a transmitting device to a first receiving device by receiving one or more signals;
generating precoding information for the transmission channel by identifying a first precoding profile for a cluster of sub-carriers from a first codebook that corresponds to the channel state information; and
compressing the precoding information to remove redundancy in the frequency domain by run length encoding the precoding information for the cluster of sub-carriers, thereby generating compressed precoding information.
2. The method of claim 1 , where the precoding information comprises quantized precoding parameters corresponding to the first precoding profile.
3. The method of claim 1 , where the first codebook is located at the first receiving device, further comprising sending the compressed precoding information over a feedback channel to the transmitting device for use in accessing a second codebook at the transmitting device to retrieve a second precoding profile that matches the first precoding profile, where the second precoding profile is used to control transmission over the transmission channel from the transmitting device to the first receiving device.
4. The method of claim 1 , where the first codebook is located at the transmitting device, further comprising sending the compressed precoding information over a feed forward channel to the first receiving device for use in accessing a second codebook at the first receiving device to retrieve a second precoding profile that matches the first precoding profile, where the second precoding profile is used to control processing of a signal transmitted over the transmission channel by the transmitting device to the first receiving device.
5. The method of claim 1 , where generating precoding information comprises retrieving an index value from the first codebook that is associated with the first precoding profile that corresponds to the channel state information.
6. The method of claim 1 , where generating precoding information for the transmission channel comprises identifying a plurality of precoding profiles for a corresponding plurality of sub-carrier clusters in a broadband channel.
7. The method of claim 1 , further comprising sending compressed precoding information for only a first predetermined number F of the sub-carrier clusters whose precoding information has changed, where the predetermined number is fixed across a plurality of feedback intervals.
8. The method of claim 7 , further comprising sending alternate information along with the temporally compressed precoding information when a number C of sub-carrier clusters whose precoding information has changed is less than the first predetermined number F, such that the alternate information is sent in place of the F—C sub-carrier clusters.
9. The method of claim 1 , further comprising sending compressed precoding information for only a first predetermined number F of the sub-carrier clusters whose precoding information has changed, where the predetermined number varies across a plurality of feedback intervals.
10. The method of claim 6 , where each sub-carrier cluster comprises one or more sub-carriers.
11. A method for precoding signals in a MIMO communication system, comprising:
estimating channel state information for a transmission channel from a transmitting device to a first receiving device by receiving one or more signals;
generating precoding information for the transmission channel by identifying a first precoding profile for a cluster of sub-carriers from a first codebook that corresponds to the channel state information; and
compressing the precoding information to remove redundancy from the precoding information, thereby generating compressed precoding information, by run length encoding the precoding information for the cluster of sub-carriers to remove frequency domain redundancy from the precoding information.
12. The method of claim 11 , where compressing the precoding information comprises:
parsing the precoding information to identify a sequence formed from a value that is repeated a plurality of times in the sequence; and
encoding the sequence in the precoding information as a first coding value and a second coding value, where the first coding value specifies the value of the sequence and the second coding value specifies how many times the value is repeated in the sequence.
13. The method of claim 11 , further comprising feeding back the compressed precoding information to the transmitting device which performs run length decoding on the compressed precoding information, where the compressed precoding information was compressed at the first receiving device by performing run length encoding on the precoding information.
14. The method of claim 11 , where a processor is used to generate and compress the precoding information.
15. The method of claim 11 , where the precoding information comprises a plurality of precoder indices for a plurality of clusters of sub-carriers which are run length encoded to remove frequency domain redundancy.
16. A communication device for precoding signals in a MIMO communication system, comprising a precoder compression module for generating a transmission profile for a cluster of sub-carriers from a codebook that corresponds to estimated channel state information for a MIMO transmission channel and compressing the transmission profile to remove redundancy from the transmission profile by run length encoding precoding information for the cluster of sub-carriers to remove frequency domain redundancy from the precoding information.
17. The communication device of claim 16 , where the precoder compression module comprises a processor for generating and compressing a transmission profile.
18. The communication device of claim 16 , where the precoder compression module compresses a plurality of transmission profiles for a corresponding plurality of sub-carrier clusters in a broadband channel.
19. The communication device of claim 18 , where the precoder compression module sends quantized transmission profile information for up to a predetermined number F of the sub-carrier clusters whose transmission profile information has changed.