MU-SCMA Code Domain Multiplexing Reduces Feedback Overhead
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Solution Overview
Problem
Multi-user MIMO systems face challenges with channel aging and high overhead due to required CSI feedback, limiting performance gains and increasing complexity in detection.
Innovation Solution
The implementation of MU-SCMA, which enables open-loop multiplexing with low sensitivity to channel aging and feedback overhead by allocating SCMA layers to multiple users for code and power domain multiplexing, using pairing and power allocation based on user parameters like CQI and average rate, and employing non-linear detection techniques like SIC and MPA.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If MU-MIMO is used to increase downlink throughput through user multiplexing, then throughput is improved, but feedback overhead and sensitivity to channel aging increase
Solution Approach 1:
The patent changes the fundamental parameter of multiple access from spatial domain (MU-MIMO) to code domain (SCMA). By using sparse codebooks with different sparsity patterns, the system achieves user multiplexing without requiring precise CSI feedback, thus maintaining throughput improvement while eliminating the feedback overhead problem.
Solution Approach 2:
The patent replaces the closed-loop mechanical feedback system of MU-MIMO with an open-loop code domain multiplexing system. Instead of relying on continuous CSI feedback and dynamic precoder adjustment, the system uses pre-defined sparse codebooks that provide robust multiplexing performance independent of channel state feedback.
2Productivity
If MU-MIMO uses closed-loop precoding to serve multiple users, then user multiplexing performance is improved, but system complexity and detection difficulty increase
Solution Approach 1:
The patent transforms the detection problem by changing from spatial domain signal separation to code domain correlation detection. The sparse codebook structure converts the complex MIMO detection problem into a simpler sparse signal recovery problem, reducing detector complexity while maintaining multiplexing performance.
Solution Approach 2:
The patent extracts the essential multiplexing function from the complex MU-MIMO precoding system and implements it independently in the code domain. By separating the multiplexing mechanism from the spatial processing, the system achieves user multiplexing with significantly reduced detection complexity at the receiver.
3Measurement precision
If MU-MIMO requires precise CSI estimation for precoder design, then cross-layer interference is reduced, but system robustness to channel aging deteriorates
Solution Approach 1:
The patent performs preliminary action by pre-defining sparse codebooks with optimized sparsity patterns before transmission. These codebooks are designed to provide robust multiplexing performance across varying channel conditions, eliminating the need for real-time CSI estimation and precoder adjustment, thus improving robustness to channel aging.
Solution Approach 2:
The patent uses simple, robust sparse codebook structures that do not require expensive or complex CSI measurement and tracking mechanisms. The code domain multiplexing provides sufficient performance with minimal channel state information, making the system robust to channel variations without requiring precise CSI estimation.
Data Source
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AI summary
In a multi-access communication system having a plurality of multiplexed layers and a plurality of mobile devices, mobile devices are paired over time-frequency and space resources. Transmission power is allocated such that a total power is shared among the plurality of multiplexed layers. The plurality of multiplexed layers and rate of each of the plurality of mobile devices are adjusted according to a power and a channel quality of the mobile device. Power and rate are adjusted until a scheduling criterion such as a weighted sum-rate is maximized.