Concatenated Precoder Selection for OFDMA Multi-BS MIMO
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Solution Overview
Problem
In multi-BS MIMO OFDMA systems, precoder selection challenges arise due to non-coherent signal combination from different base stations, leading to performance degradation at cell-edge mobile stations, where signals are not always constructively combined, resulting in reduced received signal strength and quality.
Innovation Solution
A method for concatenating precoder selection, where a cell-edge mobile station determines precoding matrix indexes (PMIs) and weight factors for each base station to optimize system performance, specifically using individual or joint optimization methods, and quantizes weight factors for reduced computation complexity and efficient feedback, enabling coherent signal combination by adjusting signal phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-BS MIMO techniques are used to improve cell-edge throughput, then received signal strength and quality are enhanced, but precoder selection becomes challenging due to non-coherent signal combination from different base stations
Solution Approach 1:
The patent segments the precoder selection process into two independent stages: first selecting precoders for each base station individually based on their respective channels, then combining the results. This segmentation avoids the complexity of joint optimization while maintaining coherent signal combination through separate precoder matrix index (PMI) selection and phase rotation application at each base station.
Solution Approach 2:
The patent introduces phase rotation as an additional parameter to adjust the phase of signals from different base stations. By changing the phase parameter independently at each base station, the system achieves coherent signal combination without requiring complex joint precoder optimization, thus resolving the contradiction between signal quality and selection complexity.
2Power
If joint optimization of PMIs for multiple base stations is performed to maximize coherent signal combination, then received signal power is maximized, but computation complexity increases significantly
Solution Approach 1:
The patent divides the joint optimization problem into separate individual optimization problems for each base station. Each base station independently selects its PMI based on its own channel conditions, then applies phase rotation to ensure coherent combination. This segmentation reduces computation from exponential joint optimization to linear individual optimizations while maintaining near-optimal signal power through phase adjustment.
Solution Approach 2:
The patent performs preliminary PMI selection for each base station independently before combining signals. By pre-selecting optimal PMIs for individual base stations and then applying phase rotation, the system achieves coherent signal combination without the computational burden of simultaneous joint optimization, thus resolving the power-complexity contradiction.
3Productivity
If individual base stations select PMIs independently without coordination, then computation complexity is reduced, but signals from different base stations are not coherently combined, reducing received signal strength
Solution Approach 1:
The patent introduces phase rotation as an intermediary mechanism between independent PMI selection and final signal combination. Each base station independently selects its PMI, then applies phase rotation to the selected precoder output. This intermediary step ensures coherent signal combination at the receiver, maintaining high received signal strength while preserving the computational efficiency of independent PMI selection.
Solution Approach 2:
The patent changes the phase parameter of the transmitted signal at each base station independently after PMI selection. By adjusting this phase parameter, the system enables coherent signal combination from independently selected precoders, thus resolving the contradiction between system throughput (independent selection) and received signal strength (coherent combination).
Data Source
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AI summary
A method for concatenating precoder selection is provided for orthogonal frequency division multiple access (OFDMA)-based multi-base station (BS) multiple-input multiple-output (MIMO). A cell-edge mobile station first determines precoding matrix indexes (PMIs) for a serving base station and one or more cooperative base stations to optimize system performance. The mobile station then determines a plurality of corresponding weight factors for each of the base stations to further optimize system performance. The mobile station recommends the selected PMIs and weight factors to the serving base station, which shares the PMIs and weight factors with cooperative base stations. Each base station then applies precoding using the recommended PMIs and weight factors. The weight factors are quantized to reduce computation complexity and to facilitate information feedback. In one embodiment, the weight factors are determined based on a pre-defined 3-bit uniform phase quantization rule. The concatenated precoder leads to large performance gain without introducing high computation complexity.