Hybrid Massive MIMO Precoding Under Noisy CSI and RF Imperfections
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Solution Overview
Problem
Existing precoding techniques in massive MIMO systems are hindered by imperfect channel estimation and hardware imperfections, leading to performance degradation without feasible solutions for hybrid architectures due to high computational complexity and limited robustness.
Innovation Solution
A method for robust hybrid precoding in massive MIMO systems that mitigates side effects of imperfect channel estimation and analog processing imperfections using a digital signal processing approach, applicable in hybrid hardware architectures with fewer RF chains than antennas, optimizing baseband precoders to enhance communication reliability and spectrum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If channel estimation accuracy is increased by using more pilot signals, then communication reliability is improved, but spectrum efficiency decreases due to reduced dedicated bandwidth for user data
Solution Approach 1:
The patent changes the parameter of channel estimation by introducing a robust MMSE channel estimator that incorporates regularization to account for hardware imperfections. This allows accurate channel estimation without requiring excessive pilot signals, thus maintaining spectrum efficiency while improving reliability through better estimation accuracy under imperfect conditions
Solution Approach 2:
The patent performs preliminary calibration of hardware imperfections (phase shifter errors, RF chain mismatches) before the actual data transmission. By pre-characterizing and compensating for these imperfections, the system achieves reliable communication with reduced pilot overhead, resolving the contradiction between estimation accuracy and spectrum efficiency
2Reliability
If the number of antennas is increased to achieve diversity gain in massive MIMO, then communication reliability is improved, but the complexity of channel estimation and processing increases significantly
Solution Approach 1:
The patent changes the estimation approach by using regularized MMSE estimation that explicitly models hardware imperfection parameters. This allows the system to handle massive MIMO configurations efficiently by reducing the computational burden through closed-form solutions that account for antenna correlations and imperfections, maintaining reliability while reducing complexity
Solution Approach 2:
The patent segments the channel estimation process into two parts: first estimating the ideal channel, then separately compensating for hardware imperfections. This segmentation allows the system to handle massive MIMO by processing these components independently, reducing overall complexity while maintaining the diversity gain benefits
3Device complexity
If hybrid precoding is used to reduce hardware complexity with fewer RF chains, then device complexity is reduced, but robustness against imperfect channel estimation and analog processing deteriorates
Solution Approach 1:
The patent changes the precoding approach by designing hybrid precoders that incorporate regularization parameters to account for analog processing imperfections. This allows the system to maintain robustness against phase shifter errors and channel estimation inaccuracies while still using fewer RF chains, thus preserving reliability while reducing hardware complexity
Solution Approach 2:
The patent applies beforehand cushioning by pre-compensating for expected analog processing imperfections in the hybrid precoder design. By incorporating compensation for phase shifter errors and estimation inaccuracies into the precoding matrices before transmission, the system maintains robustness while using reduced hardware complexity hybrid architecture
4Reliability
If robustness against hardware imperfections is increased through advanced signal processing, then communication reliability is improved, but computational complexity increases
Solution Approach 1:
The patent changes the signal processing approach by using regularized MMSE estimation and robust precoding that incorporate hardware imperfection parameters directly into the mathematical formulations. This yields closed-form solutions that provide robustness against imperfections while avoiding iterative optimization, thus improving reliability without excessive computational complexity
Solution Approach 2:
The patent replaces complex iterative optimization procedures with closed-form mathematical solutions that directly compute robust channel estimates and precoders. By substituting mechanical iterative processes with analytical solutions that account for hardware imperfections, the system achieves robustness while reducing computational complexity
Data Source
AI summary
The present invention describes a method, system, and a non-transitory computer readable storage medium to mitigate the side effects of imperfect channel estimation, analog processing imperfections, beamforming misalignment, and other imperfections present in massive MIMO wireless communications systems. Through the present invention, the user will have a better communication experience regarding data rate transmission, spectrum efficiency, and, specially, communication reliability. The core of the present invention relies on how the imperfections present in massive MIMO systems are modeled and faced by adding more robustness to the proposed baseband precoder. In addition, the present invention has the capacity to be implemented in any hybrid hardware architecture, where the number of radiofrequency (RF) chains is lower than the number of antennas. This feature is crucial for massive MIMO devices because having an expensive and energy-intensive RF chain per antenna would be impractical or even prohibit when the number of antennas is large.