Interference Estimation Circuit for Fast-Fading CDMA Channels
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Solution Overview
Problem
Current interference estimation methods in CDMA receivers are inadequate for high-speed environments, particularly in fast-fading channels where Doppler frequency is high, leading to significant interference power estimation offsets.
Innovation Solution
An interference estimation circuit and method that generates an orthogonal signal orthogonal to partial symbols of pilot signals, extracts and mixes these signals to separate interference from the received signal, using a combination of symbol extractors and mixers to process the signals for accurate interference estimation, even in fast-fading channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the orthogonal code de-spread method is used to cancel pure-signal component, then channel estimation precision is not required and the method is more robust in fast fading channels, but large interference power estimation offset occurs when Doppler frequency is high
Solution Approach 1:
The received signal is segmented into multiple slots, and only specific symbols from specific slots are selected for de-patterning processing. This segmentation allows the system to avoid symbols affected by severe fading while still canceling the pure-signal component, thereby reducing interference power estimation offset in high Doppler frequency environments.
Solution Approach 2:
Instead of processing all symbols uniformly, the invention applies de-patterning only to selected symbols from selected slots. This local quality approach ensures that symbols with better channel conditions are used for interference estimation, improving measurement precision while maintaining robustness in fast fading channels.
2Measurement precision
If channel estimation algorithm is used to rebuild pure-signal component, then interference can be estimated by subtraction, but the method is not reliable for tracking rapidly varying channel effect in fast fading channels
Solution Approach 1:
The invention extracts and removes the pure-signal component from the received signal using orthogonal code de-spread method, then estimates interference from the remaining signal. This extraction approach avoids the need for channel estimation algorithms, eliminating the reliability problem associated with tracking rapidly varying channel effects in fast fading channels.
Solution Approach 2:
The system uses the inherent orthogonality of CDMA codes to automatically separate and cancel the pure-signal component without requiring external channel estimation assistance. This self-service mechanism makes the interference estimation independent of channel estimation reliability, solving the contradiction between precision and reliability.
Data Source
AI summary
The present application provides an interference estimation circuit which includes a signal generator, a first symbol extractor and a first mixer. The signal generator generates an orthogonal signal orthogonal to partial symbols of a plurality of pilot signals. The first symbol extractor extracts partial symbols of a first decoded signal decoded from a received signal wherein the first decoded signal contains one of the plurality of pilot signals, and includes an input node for receiving the first decoded signal and an output node for outputting a first extracted signal. The first extracted signal is substantially orthogonal to the orthogonal signal. The first mixer is coupled to the signal generator for receiving the orthogonal signal and to the first symbol extractor for receiving the first extracted signal, and outputs a first mixed signal of the orthogonal signal and the first extracted signal for interference estimation.