Iterative Chip Equalization for MIMO CDMA Interference
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Solution Overview
Problem
Existing digital communication systems face challenges in decoding data transmitted over frequency-selective MIMO channels due to multi-user interference (MUI), spatial multi-antenna interference (MAI), and intersymbol interference (ISI), which limit capacity and make data recovery difficult, especially in overloaded CDMA systems with no channel state information (CSI) at the sender.
Innovation Solution
A receiver system that employs chip interleaving, linear filtering, and iterative decoding to separate and subtract MAI and MUI interference, using spatial diversity and Gaussian white noise assumptions to improve signal quality and bit rate, while maintaining fixed spectral efficiency and signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If iterative interference cancellation techniques are used to combat MUI, MAI, and ISI in overloaded CDMA systems, then detection performance approaches maximum likelihood performance, but computational complexity increases significantly
Solution Approach 1:
The patent segments the interference cancellation process into distinct stages: chip-level interference cancellation for MAI and ISI using linear filtering, followed by symbol-level interference cancellation for MUI. This segmentation allows each stage to handle specific interference types with appropriate complexity, avoiding the need for full joint optimization while achieving near-ML performance through iterative refinement of interference estimates and subtraction.
2Reliability
If linear filtering is applied to cancel MAI and ISI at chip level, then signal quality improves, but processing complexity increases
Solution Approach 1:
The patent extracts and removes MAI and ISI components from the received signal at the chip level using linear filtering operations. By explicitly modeling and subtracting these interference components before proceeding to symbol detection, the system improves signal quality while keeping the extraction process computationally tractable through efficient linear algebra operations rather than exhaustive search methods.
3Measurement precision
If chip interleaving is used to decorrelate noise samples, then the Gaussian white noise assumption becomes valid improving detection accuracy, but additional processing steps are required
Solution Approach 1:
The patent applies chip interleaving as a preliminary processing step before interference cancellation and detection. This preliminary action permutes the chip sequence to decorrelate noise samples, validating the Gaussian white noise assumption required for optimal linear filtering. By performing this preparation beforehand, the subsequent detection algorithms can operate under idealized assumptions, improving accuracy without requiring complex adaptive noise modeling during the main detection process.
Data Source
AI summary
The invention relates to a reception method for communication over frequency-selective channels with a plurality of send antennas and a plurality of receive antennas, to process data received by the receive antennas that, on sending, was successively modulated and spread.To this end, reception uses:first linear filtering (202, 202′);first interference subtraction (201) that uses an estimate of previously regenerated multi-antenna interference (MAI) and intersymbol interference (ISI);second linear filtering (205, 205′);second interference subtraction (204) that uses an estimate of previously regenerated multi-user interference (MUI);processing to generate an MAI+ISI interference estimate and an MUI interference estimate for the received data from the data filtered in this way.The invention relates further to a reception system adapted to implement the method and a transmission system including the reception system.