Two-Stage Beamformer User Scheduling for Massive MIMO
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Solution Overview
Problem
Conventional user scheduling methods for multi-user MIMO downlink, such as random beamforming, are not optimal in terms of data rate performance and feedback efficiency, especially in realistic user number ranges, leading to severe performance degradation.
Innovation Solution
A two-step feedback user scheduling and beamformer design method using a reference orthonormal set of transmit beam vectors, partitioning users into subsectors based on inner product comparisons, and adaptive beamformer design with reduced feedback, selecting users with large channel norms and orthogonal properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If random beamforming-based user scheduling method is used, then feedback amount is reduced, but data rate performance deteriorates severely in realistic user number ranges
Solution Approach 1:
The patent divides the user scheduling process into two stages: first, users are partitioned into subsectors based on channel statistics and a selected beam index; second, users within each subsector are scheduled using zero-forcing beamforming based on reduced feedback. This segmentation allows the system to achieve near-optimal performance with significantly reduced feedback overhead compared to full CSI-based methods.
Solution Approach 2:
The patent performs preliminary user partitioning into subsectors using channel statistics and beam index selection before the actual scheduling decision. This preliminary action reduces the complexity of the subsequent scheduling step and enables the system to achieve good performance with reduced feedback, as users are pre-grouped based on their channel characteristics.
2Device complexity
If conventional single-stage MIMO beamforming is used, then implementation is simpler, but sum rate performance is not optimal for realistic user numbers
Solution Approach 1:
The patent extends two-stage beamforming to multi-user MIMO downlink by dividing users into subsectors in the first stage and applying zero-forcing beamforming within each subsector in the second stage. This segmentation approach achieves sum rate performance close to the theoretical upper bound while maintaining implementation feasibility.
Solution Approach 2:
The patent changes the beamforming design parameters by using channel statistics and beam indices in the first stage, then using reduced feedback information in the second stage. This parameter transformation allows the system to achieve near-optimal performance without requiring full CSI feedback from all users.
3Loss of information
If two-stage beamforming with reduced CSI feedback is used, then feedback amount is reduced, but user scheduling optimality deteriorates
Solution Approach 1:
The patent performs preliminary partitioning of users into subsectors based on channel statistics and beam index selection before the actual scheduling decision. This preliminary action ensures that even with reduced feedback, the scheduling algorithm can make optimal decisions within each subsector by using zero-forcing beamforming based on the pre-established user groups.
Data Source
AI summary
Disclosed herein are a user scheduling and beamformer design method, apparatus, and storage medium for multi-user MIMO downlink based on two-stage beamforming or single-stage beamforming. The user scheduling and beamformer design method includes 1) a two-step feedback approach, 2) the use of orthonormal reference beam vectors, 3) computation of the angle between the user's channel vector and each of the orthonormal reference beam vectors, 4) first-step feedback of the reference beam index to which the user's channel vector's angle is less than a certain threshold and feedback of the user's channel vector's norm, 5) selection of roughly orthogonal users with large channel norm based on the use of reference beam vectors and the channel norm feedback, 6) second-step feedback of the channel state information (CSI) from the scheduled users, 7) design of multi-user downlink beamformer for the scheduled users based on the second-step feedback of the CSI of the scheduled users. The main key point of this invention is that in the first step of user selection, we propose to use the channel norm or noise-plus-interference-divided channel norm as the feedback quantity and we propose to use only the angle between each of the reference beam vectors and the user's channel vector to identify the closest reference beam vector.