Multi-Antenna Precoding Matrix Determination Using Antenna Grouping
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Solution Overview
Problem
Current LTE Release 8 standard does not enable effective use of instantaneous channel knowledge with more than four transmit antennas, particularly when channel reciprocity does not hold, limiting the use of UE-specific reference signals and preventing efficient spatial multiplexing and beamforming in systems with multiple antennas.
Innovation Solution
The technique involves grouping transmit antennas based on correlated channel coefficients, using cell-specific reference signals to determine beam-forming vectors, and calculating a final precoding matrix through the Kronecker product of recommended precoder matrices and beam-forming vectors, allowing effective data transmission even with uncorrelated uplink and downlink channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If more than four transmit antennas are deployed to increase system throughput and reliability, then multi-antenna performance gains are improved, but the number of available reference signals becomes insufficient for effective channel feedback and precoding matrix determination
Solution Approach 1:
The patent divides the transmit antennas into multiple groups, where each group is associated with a specific reference signal. This segmentation allows the system to handle more antennas than reference signals by organizing them in a structured manner, enabling effective channel feedback and precoding matrix determination despite the limited number of reference signals.
2Measurement precision
If cell-specific reference signals are used for channel estimation and precoding, then downlink channel information can be obtained, but instantaneous channel knowledge cannot be effectively exploited when channel reciprocity does not hold
Solution Approach 1:
The patent introduces an intermediary approach where the base station determines precoding matrices by combining channel feedback from reference signals with beamforming vector information. This intermediary method enables the system to exploit instantaneous channel information even when channel reciprocity does not hold, bridging the gap between downlink channel estimation and uplink channel knowledge.
3Reliability
If the number of transmit antennas exceeds the number of available reference signals, then antenna diversity and beamforming capabilities are enhanced, but control signaling overhead increases
Solution Approach 1:
The patent applies partial action by having each reference signal associated with a group of antennas rather than requiring a dedicated reference signal for each antenna. This approach provides sufficient channel information for reliable transmission while avoiding the excessive control signaling overhead that would result from one-to-one antenna-reference signal mapping.
Data Source
AI summary
Techniques are disclosed for determining transmitter antenna weights at a base station (12) having more available transmit antennas (150) than the available number of reference signals. An exemplary method includes transmitting (530) a plurality of reference signals and receiving (540) channel feedback data derived by a mobile terminal (14) from the reference signals. The reference signals are each assigned to a corresponding one of two or more antenna groupings, wherein at least a first one of the antenna groupings comprises two or more transmit antennas (150), and transmitted using at least one transmit antenna (150) from the corresponding antenna grouping. The method further includes determining (550) a first beam-forming vector for the first one of the antenna grouping and mapping (570) the one or more data streams to the transmit antennas (150) according to a final precoding matrix that depends on the channel feedback data and the first beam-forming vector, to obtain a weighted transmit signal for each of the antennas (150).