DEQPSK Receiver Soft Decision Scaling for BER Reduction
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Solution Overview
Problem
Current DEQPSK demodulation systems face performance degradation due to noise in the last received symbol, which affects bit error rate (BER) and requires complex phase/frequency tracking, making it challenging to meet stringent BER performance requirements.
Innovation Solution
A receiver system that incorporates a demodulator for both differential and coherent bit decisions, using a processor to scale soft decisions and a phase tracker for coherent demodulation, allowing for improved noise reduction and BER performance by estimating data through phase changes between symbols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If differential demodulation is used to eliminate phase/frequency tracking, then receiver complexity is reduced, but noise from the last received symbol degrades BER performance
Solution Approach 1:
The demodulation process is segmented into two independent paths: differential demodulation and coherent demodulation. Each path processes the received signal separately using different methods, allowing the system to leverage the simplicity of differential demodulation while compensating for its noise issues through coherent demodulation and soft decision weighting.
Solution Approach 2:
The patent merges the outputs of differential and coherent demodulation by computing soft decisions from both paths and combining them through weighted averaging. The coherent demodulation path is weighted more heavily when phase/frequency errors are detected, effectively combining the advantages of both demodulation methods.
2Reliability
If coherent demodulation with phase/frequency tracking is used, then BER performance is improved, but receiver complexity increases
Solution Approach 1:
Instead of implementing full coherent demodulation with complex phase/frequency tracking, the system performs partial coherent demodulation using a simplified phase tracker that operates intermittently or with reduced complexity. This provides enough coherent processing to improve BER performance without the full computational burden.
3Reliability
If soft decisions are scaled to account for noise, then BER performance is improved, but computational complexity increases
Solution Approach 1:
The system changes the parameter of soft decision weighting by introducing a scaling factor that varies based on the reliability of the differential demodulation output. When phase/frequency errors are detected, the scaling factor increases the weight of coherent decisions; when conditions are good, the weight remains balanced. This dynamic parameter adjustment optimizes performance without excessive computation.
Data Source
AI summary
A receiver includes a signal input for receiving a differentially-encoded quadrature phase-shift keyed (DEQPSK) communication signal. A demodulator performs bit decisions on a received coherent symbol and bit decisions on a received differential symbol. A processor is operative with the demodulator and scales a soft decision by a factor from 0 to 1 when the results of the bit decisions on the received coherent branch and differential branch are different.