Active User Selection in Massive MIMO via Channel Correlation
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Solution Overview
Problem
Conventional Massive MIMO systems face significant throughput degradation due to access terminals with similar channel vectors, particularly when max-min power control is employed, as it reduces the performance of better terminals to improve worse ones, and existing exhaustive search methods are impractical for large numbers of access terminals within the coherence interval.
Innovation Solution
A method for selecting access terminals to drop from service based on pair-wise channel correlations, where channel correlations are calculated and updated until a maximum correlation satisfies a threshold, allowing one of the correlated access terminals to be reallocated to a different coherence time slot or frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If max-min power control is employed to equalize throughput for all access terminals, then the performance of worst performing access terminals is improved, but the performance of best performing access terminals is reduced
Solution Approach 1:
The patent extracts problematic access terminals from the service group by identifying and dropping terminals with high channel correlation to other active terminals. This removal eliminates the source of interference and allows max-min power control to function more effectively for remaining terminals without sacrificing overall system throughput
Solution Approach 2:
The patent changes the system configuration by dynamically adjusting the number of active access terminals through selective dropping. By modifying the population of served terminals based on channel correlation metrics, the system optimizes the balance between fairness (max-min power control) and overall throughput
2Reliability
If conventional exhaustive search is performed to determine which access terminals to drop, then optimal access terminal selection can be achieved, but the calculation complexity becomes impossible for large numbers of access terminals within coherence interval
Solution Approach 1:
The patent segments the complex exhaustive search problem into manageable pairwise comparisons. Instead of evaluating all possible combinations of access terminals simultaneously, the system evaluates channel correlations between pairs of terminals iteratively, making the computation feasible for large numbers of terminals within the coherence interval
Solution Approach 2:
The patent applies partial action by performing only the necessary pairwise channel correlation calculations needed to identify terminals for dropping, rather than conducting a complete exhaustive search of all possible terminal combinations. This partial evaluation approach achieves sufficient optimization without the prohibitive complexity of full enumeration
Data Source
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AI summary
A first channel correlation is calculated for each pair of access terminals in a population of access terminals. A particular pair of access terminals is identified from the population of access terminals based on the first channel correlations. The population of access terminals includes a first access terminal of the particular pair of access terminals, a second access terminal of the particular pair of access terminals, and at least one remaining access terminal from the population of access terminals. A second channel correlation is calculated between the first access terminal and each of the at least one remaining access terminal. A third channel correlation is calculated between the second access terminal and each of the at least one remaining access terminal. One of the first access terminal and the second access terminal is selected to drop from service based on the second channel correlations and the third channel correlations.