CDMA Receiver Interference Cancellation with Unknown Spreading Factors
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Solution Overview
Problem
In CDMA communication systems, multi-access interference (MAI) is challenging to suppress when the spreading factor of one or more users is unknown, as current multi-user detection or interference cancellation techniques require known spreading factors for all users.
Innovation Solution
A receiver is designed to estimate the smallest possible spreading factor for unknown signals, use this estimate for despreading, and partially cancel interference, employing separate signal paths for known and unknown spreading factors, allowing for effective interference removal even when some users' spreading factors are unknown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-user detection or interference cancellation is performed with unknown spreading factors, then interference cancellation capability is improved, but device complexity increases due to the need for spreading factor estimation and multiple signal paths
Solution Approach 1:
The receiver is divided into separate signal paths: a first path for signals with unknown spreading factors and a second path for signals with known spreading factors. This segmentation allows independent processing of different signal types while enabling interference cancellation across all users through the combined output of both paths.
Solution Approach 2:
The spreading factor estimation is performed preliminarily on the first path before the interference cancellation process. By estimating the spreading factors in advance for unknown signals, the system prepares the necessary information needed for subsequent joint detection and interference cancellation operations.
2Measurement precision
If spreading factor estimation is performed for unknown signals, then interference removal accuracy is improved, but processing time increases due to additional estimation and despreading operations
Solution Approach 1:
The system performs spreading factor estimation only for signals with unknown spreading factors (partial action) rather than all signals. This selective estimation reduces unnecessary processing time while maintaining accurate interference removal for the affected signals.
Solution Approach 2:
Spreading factor estimation is performed in advance on the first path before the final interference cancellation. This preliminary estimation allows the main processing to proceed more efficiently using the estimated values, reducing overall processing time compared to iterative approaches.
3Productivity
If separate signal paths are used for known and unknown spreading factors, then processing efficiency is improved, but device complexity increases
Solution Approach 1:
The receiver processes signals through segmented paths: the first path handles signals with unknown spreading factors through estimation and despreading, while the second path handles signals with known spreading factors directly. This segmentation improves processing efficiency by applying appropriate methods to each signal type while the combined structure enables comprehensive interference cancellation.
Data Source
AI summary
A receiver arranged to receive a plurality of spread spectrum signals including a first spread spectrum signal from which interference caused by one or more others of said plurality of signals is to be removed, wherein at least one of said other spread spectrum signals has a spreading factor which is unknown to said receiver. The receiver comprises means for estimating a spreading factor of said at least one other spread spectrum signal having an unknown spreading factor, said estimating means selecting the spreading factor to be smallest possible spreading factor, means for despreading said at least one other spread spectrum signal using said estimated spreading factor, and means for estimating interference in the first spread spectrum signal caused by said at least one other spread spectrum signal.