MMSE Pre-Equalization for Multi-Antenna CDMA Receivers
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Solution Overview
Problem
Conventional Rake receivers in multi-user communication systems, especially in CDMA systems, face inefficiencies due to increased computational complexity when dealing with multi-user interference, limiting their ability to provide optimal performance across all users, especially in scenarios with limited computational resources.
Innovation Solution
A low-complexity user-independent spatial and temporal minimum mean square error (MMSE) pre-equalization method that separates channel equalization into temporal and spatial pre-equalization stages, performed once across all receiver antennas, reducing computational demands and maintaining performance regardless of the number of users.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MMSE-optimized Rake or Generalized Rake receiver is employed to handle multi-user interference, then receiver performance is improved, but computational complexity increases significantly
Solution Approach 1:
The patent segments the equalization process into two independent parts: user-independent spatial pre-equalization and user-dependent temporal processing. The spatial pre-equalization filter is computed once using only channel correlation matrices, separating the computationally intensive part from the user-specific processing. This segmentation allows MMSE optimization to be applied without the complexity scaling with number of users.
Solution Approach 2:
The patent performs preliminary spatial pre-equalization before user-specific detection. By computing the spatial pre-equalization filter in advance using only channel statistics (correlation matrices) that are independent of specific users, the system prepares the received signals to suppress spatial interference beforehand. This preliminary action reduces the computational burden during user-specific processing.
2Device complexity
If conventional Rake receiver is used, then device complexity is low, but interference suppression capability is insufficient in multi-user environments
Solution Approach 1:
The patent introduces a spatial pre-equalization filter as an intermediary component between the received signal and the user-specific Rake receiver. This filter acts as a mediator that performs MMSE-optimized spatial filtering to suppress multi-user interference before the signals are processed by conventional low-complexity user-specific receivers. The intermediary filter bridges the gap between simple receiver structure and advanced interference suppression.
3Stability of the object's composition
If ideal equalization scheme is applied to cancel channel effects, then frequency-flat channel is achieved, but noise amplification occurs
Solution Approach 1:
The patent changes the equalization parameter from ideal inversion (which causes noise amplification) to MMSE optimization. The spatial pre-equalization filter is designed to minimize the mean square error between the transmitted and received signals, taking into account both signal power and noise power. This parameter change achieves frequency-flat channel response while controlling noise amplification through the MMSE criterion.
Data Source
AI summary
The present invention describes a channel equalizer and a method for channel equalization in a receiver in a multi-user communication system. The method comprises the steps of receiving a signal with at least two antennas to produce at least two antenna input streams, measuring the temporal of each antenna input stream and the spatial correlation between the antenna input streams, determining a user-independent pre-equalization filter from the temporal and spatial correlation, filtering the antenna input streams with the pre-equalization filter, and finally inputting the filtered signal to a user-dependent receiver configured to detect the received data symbols of a given user.