MU-MIMO Receiver Weights for Nonlinear Interference Cancellation
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Solution Overview
Problem
Conventional MU-MIMO systems using linear precoding struggle to effectively combine signals received by terminals with non-linear precoding, leading to deteriorated receiving characteristics, especially when signals are subjected to spatial multiplexing with THP, as they fail to appropriately handle interference and channel variations.
Innovation Solution
A receiving apparatus with N receiving antennas performs nonlinear arithmetic on combined information signals, using a receiving weight that minimizes mean square error and includes a term for subtracted interference, while the transmitting apparatus calculates and subtracts interference coefficients based on channel information from multiple terminals, enabling modulo arithmetic for efficient spatial multiplexing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If linear precoding is used for MU-MIMO transmission, then spatial multiplexing to multiple terminals is achieved with simple processing, but receiving characteristics deteriorate when non-linear precoding (such as THP) is used because conventional receivers cannot effectively combine signals from multiple antennas
Solution Approach 1:
The patent changes the receiving weight parameters to include interference subtraction terms, transforming the receiver from a simple linear combiner to an intelligent signal processor that can handle non-linear precoding effects. This parameter modification enables the receiver to compensate for the complex interference patterns introduced by non-linear precoding while maintaining the ability to combine signals from multiple antennas effectively.
Solution Approach 2:
The patent implements feedback mechanisms where terminals notify the base station of channel states, and the base station calculates appropriate receiving weights based on this feedback information. This feedback loop enables the system to adapt the receiving weights to match the actual channel conditions and non-linear precoding applied, ensuring optimal signal combination and interference suppression.
2Productivity
If signals are subjected to non-linear spatial multiplexing with THP, then frequency usage efficiency is improved, but receiving characteristics deteriorate due to inability to properly handle interference and channel variations
Solution Approach 1:
The patent converts the harmful interference effects introduced by non-linear precoding into beneficial information by incorporating interference subtraction terms in the receiving weights. The interference that would normally degrade signal quality is instead used to construct cancellation terms that actively remove the interference from the received signal, transforming a harmful effect into a useful signal processing capability.
Solution Approach 2:
The base station performs preliminary calculation of receiving weights based on predicted channel states and non-linear precoding parameters before actual signal reception. This preliminary action allows the receiver to be pre-configured with the appropriate weight vectors that will optimally combine signals and subtract interference when the actual transmission occurs, ensuring readiness to handle the complex interference patterns.
3Device complexity
If conventional receivers are used with non-linear precoding, then device complexity is reduced, but signal combination across multiple antennas becomes ineffective leading to poor receiving characteristics
Solution Approach 1:
The patent segments the receiving weight into distinct functional components: a main weight component for signal combination and an interference subtraction component for eliminating multi-user interference. This segmentation allows the receiver to process signals from multiple antennas through separate, well-defined operations, making the complex task of handling non-linear precoding effects more manageable and systematic.
Data Source
AI summary
When spatial multiplexing is performed to any of a plurality of receiving antennas included in each terminal, it becomes possible to obtain excellent receiving characteristics by combining signals received by all antennas appropriately. A receiving antenna unit 28 receives channel state information from each terminal, a channel matrix H is obtained. A transmit weight/interference coefficient calculation unit 24 calculates a transmit weight and an interference coefficient based on channel matrix. The transmit weight is input to transmit weight multiplication units 17 and 23. The interference generation unit 15 generates an interference signal based on the interference coefficient. An interference subtraction unit 13 subtracts the interference signal from a desired signal. A modulo unit 14 adds a signal so that amplitude of an information signal output from the interference subtraction unit 13 falls within a constant range. A signal multiplexing unit 18 performs spatial multiplexing to the signal performed nonlinear arithmetic.