Open-loop Beamforming MIMO via Uplink Covariance
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Solution Overview
Problem
In frequency division duplex (FDD) wireless communication systems, determining downlink beamforming weights without feedback information from mobile stations is challenging due to the lack of instantaneous downlink channel covariance, which complicates improving downlink MIMO transmission performance and increases uplink channel overhead.
Innovation Solution
The system computes orthogonal or partially orthogonal beamforming weights using uplink channel information received from mobile stations, employing methods such as channel covariance estimation and spatial subspace decomposition to generate weights that can be applied for MIMO transmissions without relying on feedback, thus enabling improved downlink performance in macrocell/microcell environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback information is provided by mobile station to base station for downlink beamforming, then downlink beamforming performance is improved, but communication overhead increases and uplink channel capacity is reduced
Solution Approach 1:
The patent introduces an intermediary approach by using uplink channel covariance matrix as a proxy for downlink channel statistics. Instead of direct feedback, the system uses the uplink channel information (which is already available at the base station) to compute beamforming weights, thereby avoiding the overhead of feedback while still achieving improved downlink performance
Solution Approach 2:
The patent creates a copy of downlink beamforming weights by computing them from uplink channel covariance. The base station computes candidate beamforming weights based on uplink channel statistics and selects optimal weights without requiring actual feedback from mobile stations, effectively copying the benefit of feedback-based beamforming without the overhead
2Productivity
If downlink channel covariance is used to determine beamforming weights, then downlink MIMO transmission performance is improved, but the system requires feedback information that increases complexity
Solution Approach 1:
The patent inverts the traditional approach by not using downlink channel covariance directly, but instead using uplink channel covariance to compute downlink beamforming weights. This inversion eliminates the need for feedback mechanisms while still achieving the goal of improved downlink MIMO transmission performance
Solution Approach 2:
The system serves itself by using its own uplink channel measurements to generate downlink beamforming weights without requiring external feedback from mobile stations. The base station autonomously computes the beamforming weights using available uplink channel information, reducing system complexity
3Quantity of substance
If uplink channel covariance is used to compute downlink beamforming weights, then feedback overhead is reduced, but beamforming accuracy may be compromised
Solution Approach 1:
The patent changes the parameter basis from downlink channel covariance to uplink channel covariance. By computing beamforming weights based on uplink channel statistics and using appropriate transformations, the system maintains beamforming accuracy while eliminating feedback overhead
Solution Approach 2:
The uplink channel covariance matrix serves multiple functions: it characterizes the uplink channel conditions and simultaneously enables the computation of downlink beamforming weights. This multi-functionality allows the system to achieve accurate beamforming without dedicated feedback mechanisms
Data Source
AI summary
Techniques are provided for wireless communication between a first wireless communication device and a second wireless communication device. At a plurality of antennas of the first wireless communication device, one or more signals transmitted by a second wireless communication device in a first frequency band are received. Beamforming weights are computed from information derived from the signals received at the plurality of antennas using one or more of a plurality of methods without feedback information from the second wireless communication device about a wireless link from the first wireless communication device to the second wireless communication device. The beamforming weights are applied to at least one transmit signal to beamform the at least one transmit signal for transmission to the second wireless communication device in a second frequency band.