Wireless Receiver Demodulation Using Complex Conjugate Correlation
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Solution Overview
Problem
In wireless communications, existing demodulation methods face performance degradation due to time-varying channels caused by multipath effects and varying noise statistics, which affect the accuracy of channel estimation and decoding in receivers.
Innovation Solution
A method and apparatus that generate modified observations by multiplying received observations with the complex conjugate of channel estimates, and use these modified observations to calculate log-likelihood ratios (LLRs) for maximum-likelihood-based decoders, reducing dependence on channel amplitude and improving decoding performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If channel equalisation is used to counteract channel effects, then the received signal can be recovered, but the noise statistics become time-varying which degrades decoding performance
Solution Approach 1:
The patent changes the processing parameter from direct channel equalisation (division by channel estimate) to correlation-based processing (multiplication by complex conjugate of channel estimate). This parameter change transforms the time-varying noise statistics into stationary noise statistics, resolving the contradiction between channel estimation accuracy and decoding performance.
2Object-affected harmful factors
If standard channel equalisation is applied, then signal distortion is corrected, but dependence on channel amplitude remains which affects performance in varying channel conditions
Solution Approach 1:
The patent extracts the channel amplitude dependence from the equalisation process by using correlation-based processing instead of direct division. This removes the harmful dependency on channel amplitude variations, allowing the system to maintain adaptability across varying channel conditions while still correcting signal distortion.
3Reliability
If maximum-likelihood decoding is used, then optimal decoding performance is achieved, but the decoder requires accurate knowledge of noise statistics which are distorted by channel equalisation
Solution Approach 1:
The patent introduces an intermediary processing step (correlation with complex conjugate of channel estimate) between channel reception and decoding. This intermediary transforms the received signal into a form where noise statistics are preserved and stationary, allowing maximum-likelihood decoding to achieve optimal performance with accurate noise statistics.
Data Source
AI summary
The present invention relates to a method and apparatus for demodulation in a wireless communications system transmitted across a wireless communications channel. The described wireless receiver includes a first antenna for receiving a wireless signal including a symbol transmitted across a wireless communications channel perceived by the first antenna, an observation modifier for generating a modified observation (y) of the symbol based on a product of the received observation (r) and the complex conjugate of a channel estimate (h*), a log-likelihood ratio (LLR) module generating log-likelihood ratios (LLRs) based on the modified observation and the channel estimate, and a maximum-likelihood-based decoder for decoding the symbol based on the LLRs.