MIMO precoding enabling spatial multiplexing, power allocation and adaptive modulation and coding
View Patent ↗In a closed-loop wireless communication system, a codebook-based feedback mechanism is provided to enable non-unitary precoding for multi-stream transmission, where in each stream is optimized with suitable transmission power allocation and AMC. The codebook-based feedback mechanism uses a precoding codebook having a power allocation matrix which is constrained to specify that beamforming always applies full power to a predetermined beam. With this constraint, a one-bit power allocation feedback index may be used to switch between beamforming and spatial multiplexing.
1. A method for precoding signals in a multiple input multiple output (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 from a first codebook that corresponds to the channel state information, where the first codebook comprises a plurality of codewords, where each codeword comprises:
a unitary precoding matrix portion, and
a diagonal power control matrix portion to provide power control values for a plurality of streams, where a first power control value for beamforming specifies that full power is always applied to a predetermined one of the streams such that the unitary precoding matrix chosen for beamforming aligns the predetermined one of the streams to a dominant spatial channel of the plurality of streams, and where a second power control value for spatial multiplexing specifies that equal power is applied to each of the plurality of streams; and
quantizing the precoding information corresponding to the first precoding profile into a precoding index.
2. The method of claim 1 , where the first codebook is located at the first receiving device, further comprising sending the precoding index 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.
3. The method of claim 1 , where the first codebook is located at the transmitting device, further comprising sending the precoding index 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.
4. The method of claim 1 , where a codebook portion corresponding to the diagonal power control matrix contains m^(n-1) indexed power control entries corresponding to each stream taking one of m power levels and which may be accessed by an index of log2(m^(n-1)) bits.
5. The method of claim 1 , where quantizing the precoding information comprises generating a one-bit power control feedback to control power allocation on two streams such that a beamforming power allocation for the two streams is specified by the one-bit power control feedback having a first value and a spatial multiplexing power allocation for the two streams is specified by the one-bit power control feedback having a second value.
6. The method of claim 1 , where generating precoding information for the transmission channel comprises:
choosing a beamforming power control value for the diagonal power control matrix from a portion of the first codebook corresponding to the diagonal power control matrix; and
choosing a precoding matrix value for the unitary precoding matrix from a portion of the first codebook corresponding to the unitary precoding matrix such that a first column of a chosen precoding matrix aligns with the dominant spatial channel.
7. The method of claim 1 , where the precoding index comprises a first index portion for indicating a precoding matrix value and a second index portion for indicating a power allocation value.
8. The method of claim 1 , where the precoding index comprises a first index portion for indicating a precoding matrix value, a second index portion for indicating a power allocation value, and a third index portion for indicating an adaptive modulation and coding value.
9. The method of claim 1 , where the unitary precoding matrix comprises an identity matrix value for use with precoding for open-loop transmission in conjunction with equal power for each of the plurality of streams.
10. The method of claim 1 , where the precoding index comprises a quantized power control value that is used to switch between beamforming and spatial multiplexing transmission.
11. The method of claim 1 , where the first codebook further comprises a plurality of indexed values to indicate modulation and coding used on the streams.
12. The method of claim 1 , where the diagonal power control matrix comprises first and second indexed power control values, where the first indexed power control value specifies a beamforming power allocation for the plurality of streams so that full power is provided only to a first stream with zero power to the other streams, and where the second indexed power control value specifies a spatial multiplexing power allocation for the plurality streams so that equal power is provided for all of the streams.
13. The method of claim 1 , where the transmission channel is a 2×2 MIMO channel, a 2×4 MIMO channel, a 4×2 MIMO channel or a 4×4 MIMO channel.
14. A receiver for precoding signals in a multiple input multiple output (MIMO) communication system, comprising:
a precoding module for generating a transmission profile for a transmission channel by:
identifying a first precoding value for a unitary precoding matrix that corresponds to estimated channel state information for the transmission channel;
quantizing the first precoding value into a precoding index;
computing a channel quality indicator (CQI) value for at least a first spatial stream based on the estimated channel state information;
encoding the CQI value into an encoded cqi value to indicate whether the first spatial stream is turned on or off and to indicate the cqi value for the first spatial stream if the first spatial stream is turned on; and
an antenna array for sending the precoding index and the encoded cqi value over a feedback channel to a transmitter for use in generating the transmission profile, where the encoded cqi value is used to control transmission over the transmission channel from the transmitter to the receiver.
15. The communication device of claim 14 , where the precoding module comprises a processor for generating precoding information for a transmission channel.
16. The communication device of claim 14 , where the CQI value is encoded into an encoded cqi value by setting a predetermined CQI value below a threshold value to indicate that the first spatial stream is turned off.
17. The communication device of claim 14 , where the CQI value is encoded into an encoded CQI value by differentially encoding the CQI value to indicate a relative value of the CQI value as compared to a previous CQI value and to indicate if the first spatial stream is turned off.
18. A method for generating a transmission profile for a multiple input multiple output (MIMO) transmission channel, comprising
quantizing a first precoding value from a precoder matrix that corresponds to estimated channel state information for the transmission channel, thereby forming a precoder index;
encoding a feedback value into an encoded feedback value to indicate a number of spatial streams to be used during transmission of a data signal sent over the transmission channel, where the feedback value comprises a power control value or a channel quality indicator value; and
sending the precoder index and the encoded feedback value over a feedback channel to a transmitter for use in controlling transmission over the transmission channel from the transmitter to a receiver by specifying the number of spatial streams to be used during transmission.