Composite Interference Vector Cancellation for CDMA Rake Receivers
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Solution Overview
Problem
Existing interference cancellation techniques in wireless communication systems are inadequate in addressing co-channel and cross-channel interference caused by multipath environments, leading to degraded communication quality, reduced capacity, and coverage issues.
Innovation Solution
The development of a method to form and utilize a composite interference vector (CIV) for optimal interference cancellation, employing soft weighting in projective operations within receivers, such as Rake receivers, to enhance the signal-to-interference-and-noise ratio (SINR) by mitigating inter-finger interference through soft estimates of user waveforms and adaptive feedback terms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional interference cancellation techniques are used in multipath environments, then some interference can be reduced, but co-channel and cross-channel interference still correlate subchannels causing degraded communication quality and error floors
Solution Approach 1:
The invention segments the interference cancellation process by applying it separately to each Rake finger before combining the outputs. Each finger processes its received signal independently to cancel interference from specific users and paths, then the cleaned signals are combined. This per-finger approach allows targeted interference removal without corrupting other path information, resolving the contradiction between reducing interference and maintaining communication quality.
Solution Approach 2:
The invention employs feedback mechanisms where soft estimates of user waveforms from previously processed fingers are fed back to subsequent fingers for interference cancellation. The canceller uses decoded symbols and channel estimates from earlier stages to construct interference signals that are subtracted from later fingers, creating a feedback loop that progressively eliminates interference while preserving signal integrity.
2Productivity
If interference cancellation is applied to improve SINR, then communication capacity and coverage can be increased, but the complexity of processing multiple subchannels and multipath components increases
Solution Approach 1:
The invention performs preliminary interference cancellation at each Rake finger before the combining stage. By canceling interference early in the processing chain for each individual finger, the system prepares cleaned signals that can be efficiently combined later. This preliminary action reduces the burden on subsequent processing stages and enables higher capacity operations without proportionally increasing overall complexity.
Solution Approach 2:
The invention changes processing parameters by applying interference cancellation with adaptive weights and soft estimates specific to each finger's received signal characteristics. The system adjusts cancellation parameters dynamically based on channel conditions, user activity, and path parameters, allowing optimized capacity improvement while managing complexity through adaptive rather than fixed processing.
Data Source
AI summary
An interference canceller comprises a composite interference vector (CIV) generator configured to produce a CIV by combining soft and/or hard estimates of interference, an interference-cancelling operator configured for generating a soft-projection operator, and a soft-projection canceller configured for performing a soft projection of the received baseband signal to output an interference-cancelled signal. Weights used in the soft-projection operator are selected to maximize a post-processing SINR.