Unsounded MIMO Channel Construction via PMI Projection
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Solution Overview
Problem
Current channel construction methods for new radio (NR) unsounded channels in reciprocity-based massive MIMO wireless transmission are inadequate, particularly for user equipment (UE) with four receive antennas, as existing solutions can only be applied to UEs with two receive antennas, leading to partial channel sounding and reduced performance.
Innovation Solution
The proposed method involves acquiring UE channel state information (CSI) feedback and constructing an unsounded channel by ordering, down-selecting, projecting, and scaling the precoding matrix indicator (PMI) or its variants, and using singular value decomposition to derive linear combination weights, thereby concatenating the sounded and unsounded channels into a full channel for robust beamforming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If antenna switching is used to perform uplink sounding, then the base station can obtain full downlink channel, but additional cost is incurred for UE vendors
Solution Approach 1:
The patent uses the uplink sounding channel as a copy of the downlink channel based on channel reciprocity in TDD systems. Instead of requiring the UE to physically sound all receive antennas in the downlink direction (which would require antenna switching hardware), the system exploits the mathematical equivalence between uplink and downlink channels to derive downlink channel information from uplink measurements, eliminating the need for expensive antenna switching hardware in the UE.
2Ease of manufacture
If UE is equipped with limited transmit antennas, then UE cost and size are reduced, but full reciprocity channel cannot be obtained
Solution Approach 1:
The patent makes the limited uplink transmit antennas serve multiple functions: they not only transmit data but also perform channel sounding for all downlink receive antennas simultaneously through channel reciprocity. The uplink transmit antennas act as universal elements that enable both communication and channel estimation functions, allowing the base station to obtain complete downlink channel information without requiring the UE to have multiple transmit antennas.
3Reliability
If existing channel construction methods are used, then performance is good for UEs with two receive antennas, but the methods cannot be applied to UEs with four receive antennas
Solution Approach 1:
The patent segments the downlink channel matrix into two parts: the sounded channel (obtained directly from uplink reciprocity) and the unsounded channel (to be constructed). For UEs with four receive antennas, the base station sounds only one receive antenna and then constructs the remaining three unsounded channels using the segmentation approach. This allows the system to handle any antenna configuration by dividing the channel estimation task into sounded and unsounded portions.
Solution Approach 2:
The patent changes the parameter of channel construction from fixed (only applicable to 2 receive antennas) to variable (adaptable to any number of receive antennas). By introducing flexible construction methods that can handle arbitrary numbers of unsounded antennas, the system adapts to different UE configurations (2, 4, or more receive antennas) while maintaining reliable channel estimation performance.
Data Source
AI summary
According to certain embodiments, a method for use in a network node for constructing an unsounded channel in a wireless network wherein the network node comprises more antennas than a wireless device and the wireless device comprises more than one receive antenna comprises: receiving channel state information (CSI) feedback and a sounded reference signal from the wireless device; estimating a sounded channel from the sounded reference signal; deriving a partial downlink channel based on the sounded reference signal; constructing an unsounded channel as a function of the CSI feedback and the partial downlink channel; concatenating the sounded channel and unsounded channel into a full channel; and transmitting a wireless signal to the wireless device using the full channel for beamforming or link adaptation.