Compressed Feedforward Codebooks for MU-MIMO Precoding
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Solution Overview
Problem
Current MIMO-SDMA systems face challenges in efficiently conveying precoding matrix information to receivers without requiring advance knowledge of other receivers or base station scheduling algorithms, and they suffer from high feed forward data rates and limited resources.
Innovation Solution
A finite rate feed forward system using compressed codebooks for precoding matrix information, generated through zero-forcing beamforming techniques, is implemented to efficiently provide precoding information by sharing a compressed codebook at the transmitter and receiver, allowing for reduced feedforward indexing and efficient multi-user beamforming transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If full precoding matrix information is fed forward to receivers, then precoding performance is improved, but signaling overhead and feed forward data rate requirements increase
Solution Approach 1:
The patent extracts only the essential precoding matrix information needed for receiver performance into a compressed codebook structure. Instead of transmitting the full precoding matrix, the system extracts and transmits only the necessary index information that points to pre-computed optimal precoding matrices, thereby reducing signaling overhead while maintaining precoding performance.
Solution Approach 2:
The precoding matrix information is segmented into a codebook structure where multiple possible precoding matrices are pre-computed and stored. The actual transmission only requires sending the index of the selected matrix rather than the full matrix data, dividing the information transmission into a reference structure (codebook) and a compact index identifier.
2Loss of information
If compressed codebook is used for feed forward signaling, then signaling overhead is reduced, but receiver complexity increases due to codebook search
Solution Approach 1:
The patent applies preliminary action by pre-computing and pre-storing optimal precoding matrices in the codebook structure before actual communication occurs. This allows the receiver to simply search for and retrieve pre-computed matrices based on received index information, avoiding the need for complex real-time precoding calculations and reducing operational receiver complexity.
3Object-generated harmful factors
If zero-forcing beamforming is used, then interference is minimized, but system complexity increases
Solution Approach 1:
The patent uses copying by creating a codebook that contains pre-computed zero-forcing beamforming matrices. Instead of calculating zero-forcing beams in real-time, the system copies pre-computed optimal beamforming matrices from the codebook, reducing computational complexity while maintaining the interference-minimizing properties of zero-forcing beamforming.
Data Source
AI summary
A multi-user multiple-input multiple-output (MIMO) downlink beamforming system with limited feed forward is provided to enable precoding matrix information to be efficiently provided to a subset of user equipment devices, where zero-forcing transmit beamformers are computed at the base station and assembled into a precoding matrix. The precoding matrix is encoded using a compact reference signal codebook for forward link signaling, either by sending bits indicating the index of the transmission matrix used, or by transmitting one or more precoded pilots or reference signals wherein the pilot signals are precoded using vectors uniquely representative of the transmission matrix used which includes candidate reference signal matrices which meet a predetermined condition number requirement, such as a condition number threshold. The precoding matrix information is extracted at the user equipment devices using the compact reference signal codebook and used by the MMSE receiver to generate receive beamformers.