Multiuser Receiver Iterative Interference Cancellation
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Solution Overview
Problem
Existing multiuser communication systems face challenges in efficiently sharing a shared communication medium, particularly in satellite or satellite-like channels where multiple transmitters experience time and frequency offsets, leading to multiple-access interference, which degrades system performance.
Innovation Solution
A multiuser receiver employing iterative soft interference cancellation, using a predefined signal to aid acquisition and employing low-complexity algorithms for estimating channel parameters, allows for uncoordinated channel access and accurate SINR estimation, enabling effective cancellation of interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If orthogonal access schemes are used to share the communication medium, then multiple transmitters can communicate simultaneously, but tight time and frequency synchronisation is required which increases system complexity and cost
Solution Approach 1:
The patent converts the harmful multiple-access interference caused by unsynchronized transmissions into a beneficial signal structure. By allowing transmitters to use uncoordinated channel access without tight synchronisation, the system transforms what would normally be destructive interference into a pattern that can be exploited by iterative soft interference cancellation algorithms at the receiver, enabling simultaneous communications from multiple transmitters without requiring complex synchronisation mechanisms
2Object-affected harmful factors
If guard bands and guard intervals are used to provide time and frequency separation, then multiple-access interference is reduced, but bandwidth efficiency decreases
Solution Approach 1:
The patent extracts and removes the harmful multiple-access interference components from the received signal through iterative soft interference cancellation. Instead of using guard bands to prevent interference, the system actively detects and subtracts interference signals from multiple transmitters, allowing full utilization of the available bandwidth without requiring protective guard intervals or bands
3Reliability
If feedback channels are used to provide channel parameter estimates to transmitters for pre-compensation, then channel offsets are corrected, but system complexity and implementation cost increase
Solution Approach 1:
The patent inverts the traditional approach by having the receiver perform interference cancellation without requiring feedback to transmitters. Instead of correcting channel offsets at the transmitter through feedback, the receiver directly estimates and cancels interference from multiple transmitters using their uncoordinated transmission patterns, eliminating the need for feedback channels while maintaining reliable communication
4Productivity
If iterative soft interference cancellation is employed to detect multiple transmissions, then throughput is improved, but computational complexity increases
Solution Approach 1:
The patent segments the interference cancellation process into iterative steps where each iteration focuses on detecting and canceling specific user signals. The receiver processes transmissions from multiple transmitters in successive iterations, with each iteration improving the detection accuracy for remaining signals. This segmented approach enables high throughput by systematically eliminating interference while managing computational complexity through iterative refinement rather than attempting to process all signals simultaneously
Data Source
AI summary
A multiuser communication system comprises multiple transmitters and a multiuser receiver that detects multiple transmissions via iterative soft interference cancellation. An initial acquisition module and single user decoder module are also described. The multiuser receiver acquires and subtracts known users in the residual signal before acquiring new users in the residual signal, which is performed iteratively until no new users are detected or a stopping criterion is met. To aid receiver acquisition, the transmitters insert discrete tones into the transmitted signals. These allow the multiuser receiver to obtain initial estimates of the frequency, time, gain, and/or phase offset for each user. To improve the quality of cancellation the receiver refines estimates of gain, time, frequency and phase offsets for each user after each iteration, and calculates time varying SINR estimates for each user. The multiuser receiver may be satellite based, may be a distributed receiver, or process users in parallel.