Opportunistic User Scheduling in Two-Cell MIMO Systems
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Solution Overview
Problem
In two-cell multiple user MIMO systems, existing methods face challenges with excessive CSI feedback and limited interference alignment due to unrealistic full channel knowledge and excessive information sharing, leading to marginal performance improvements.
Innovation Solution
A method for opportunistic user scheduling using random beams for broadcasting signals and receiving Channel Quality Information (CQI) from the best K user set, with efficient CQI measures and post-processing matrix design to minimize interference or maximize sumrate, without requiring perfect CSI or backhaul information sharing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interference alignment with full channel knowledge is used, then signal space alignment is achieved, but feedback overhead and computational complexity increase excessively
Solution Approach 1:
The patent applies partial action by using only the necessary portion of channel state information rather than full CSI. Specifically, users feed back CQI values computed based on randomly generated beamforming vectors at the base station, rather than feeding back complete channel matrices. This partial information approach achieves sufficient interference management while dramatically reducing feedback overhead from O(MN) to O(K) per user per resource block.
Solution Approach 2:
The patent uses copying by having the base station generate random beamforming vectors that are also known to users through downlink signaling. Both the base station and users work with identical random beamforming matrices, allowing users to compute CQI values without needing full channel knowledge. This copying approach enables distributed CQI computation with minimal feedback requirements.
2Productivity
If exhaustive user scheduling is implemented, then optimal user selection is achieved, but computational complexity increases significantly
Solution Approach 1:
The patent applies preliminary action by having the base station generate and broadcast random beamforming vectors before user scheduling. Users use these pre-generated vectors to compute CQI values, which are then fed back for user selection. This preliminary generation of beamforming vectors simplifies the scheduling complexity from exhaustive search to comparing pre-computed CQI values, reducing complexity from O(J^K) to O(J×K) while maintaining good throughput performance.
3Reliability
If backhaul information sharing is required, then coordinated beamforming is achieved, but information sharing overhead increases
Solution Approach 1:
The patent applies segmentation by dividing the interference coordination problem into independent cell-level operations. Each base station independently generates random beamforming vectors and schedules users based on local CQI feedback, without requiring information exchange with other cells. This segmentation eliminates backhaul information sharing overhead while still achieving interference coordination through the random beamforming structure that naturally separates interference into manageable components.
Data Source
AI summary
An apparatus and a method for opportunistic user scheduling of two-cell multiple user Multiple Input Multiple Output (MIMO) by a base station, the method comprising: broadcasting signals through random beams to users; and receiving Channel Quality Information (CQI) from best K user set. The CQI is calculated based on all possible combinations of transmit beamforming vectors.