MDPSK Demodulation Unit Using Viterbi Algorithm
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Solution Overview
Problem
Existing demodulation schemes for MDPSK modulated signals struggle with reliability and robustness, especially in noisy transmission networks, due to the noncoherent nature of differential coherent demodulation, which degrades performance and increases bit error probability.
Innovation Solution
A demodulation unit and method that derive phase signals and generate discrimination signals based on current and previous samples, using the Viterbi algorithm to exploit correlations between successive symbols, thereby improving error correction and reducing bit error rate by considering the trajectory of phase differences in MDPSK modulation schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional noncoherent differential coherent demodulation is used for MDPSK signals, then the demodulation process is simpler, but reliability and robustness degrade and bit error probability increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing discrimination signals for all possible phase difference combinations in lookup tables before actual demodulation occurs. During operation, the system simply retrieves pre-computed values based on measured phase differences, avoiding complex real-time calculations while maintaining high reliability through optimized error correction algorithms
Solution Approach 2:
The patent replaces traditional coherent demodulation mechanisms with a noncoherent approach that uses phase difference measurement and discrimination signal comparison. Instead of requiring complex phase synchronization hardware, the system substitutes a simpler measurement and lookup-based approach that achieves comparable or better reliability in noisy environments
2Device complexity
If conventional demodulation methods are used, then device complexity is lower, but bit error rate performance is worse by 1 to 1.5 dB
Solution Approach 1:
The patent pre-computes discrimination signals for all possible phase difference combinations and stores them in lookup tables. This preliminary action allows the demodulator to achieve superior bit error rate performance by retrieving optimized values rather than performing complex real-time calculations, improving reliability by 1 to 1.5 dB without significantly increasing device complexity
Solution Approach 2:
The system uses the measured phase difference itself to index into lookup tables and retrieve the appropriate discrimination signal. The data structure automatically adapts to different MDPSK modulation schemes (BPSK, QPSK, 8PSK, 16PSK) without requiring hardware changes, allowing the same device to serve multiple modulation types with optimized performance
3Reliability
If phase signal samples from multiple time instants are used, then error correction improves, but processing complexity increases
Solution Approach 1:
The patent segments the phase signal processing into distinct stages: measuring phase difference, indexing into lookup tables, retrieving discrimination signals, and comparing with threshold values. This segmentation allows each stage to be independently optimized and implemented with simple, dedicated circuitry, reducing overall processing complexity while maintaining high error correction capability
Solution Approach 2:
The patent performs preliminary computation of discrimination signals for all possible phase differences and stores them in lookup tables. During actual demodulation, the system only needs to perform simple table lookups and comparisons, dramatically reducing processing complexity while maintaining robust error correction through the use of multiple time instant samples
Data Source
AI summary
A demodulation unit for recovering a transmitted symbol from a received signal that has been modulated using an MDPSK modulation scheme is described. The demodulation unit is configured to, for a current time instant, derive a current sample of a phase signal indicative of a phase of the received signal. Furthermore, the demodulation unit is configured to determine a set of discrimination signals for the current sample of the phase signal, based on the current sample of the phase signal and based on one or more previous samples of the phase signal for one or more previous time instants. In addition, the demodulation unit is configured to determine the transmitted symbol for the current time instant based on the set of discrimination signals.