Demodulating Colliding Signals via Phase State Segmentation
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Solution Overview
Problem
Existing methods for demodulating signals in multi-access transmission systems, such as AIS, face significant challenges when signals collide, especially when they have identical Doppler frequencies and power levels, leading to degraded bit error rates and inability to access both signals in worst-case scenarios.
Innovation Solution
A method using the Viterbi algorithm to demodulate signals by measuring the phase of the overall signal, determining phase states, and eliminating ambiguities, allowing for efficient demodulation of synchronized or desynchronized signals with identical or different carrier frequencies, even when signals are affected by Doppler shifts and have varying power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional demodulation methods are used for colliding signals, then the system is simple to implement, but the bit error rate performance is greatly degraded when signals have identical Doppler frequencies and power levels
Solution Approach 1:
The patent segments the colliding signals by separating them into different processing branches based on their phase characteristics. The received signal is divided into in-phase (I) and quadrature (Q) components, and further segmented into different hypothesis paths (H1, H2, H3, H4) corresponding to different phase state combinations. This segmentation allows the system to process each signal component separately and combine results to achieve reliable demodulation of both colliding signals.
Solution Approach 2:
The patent transitions from conventional one-dimensional signal processing to two-dimensional phase space analysis. By representing signals in the I-Q plane and analyzing phase differences across multiple dimensions (I1, Q1, I2, Q2 components), the system can distinguish between colliding signals that are identical in amplitude and frequency but differ in phase relationships. This dimensional expansion enables resolution of signals that would be indistinguishable in conventional processing.
2Adaptability or versatility
If signals with identical power and Doppler frequency collide, then the collision scenario is worst-case, but conventional methods cannot access both signals
Solution Approach 1:
The patent performs preliminary synchronization and phase estimation before the actual demodulation process. By pre-establishing reference phases and calculating expected phase relationships between colliding signals, the system prepares multiple hypothesis paths in advance. This preliminary action enables the system to quickly adapt to worst-case collision scenarios without requiring complex real-time adjustments during signal processing.
Solution Approach 2:
The patent implements feedback mechanisms where the demodulation process continuously monitors phase relationships and adjusts hypothesis selection based on measured signal characteristics. The system uses feedback from phase difference measurements to determine which hypothesis paths (H1-H4) are most likely correct, and dynamically adjusts processing to maximize the probability of successfully recovering both colliding signals even in worst-case scenarios.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances signal detection performance by effectively demodulating both the strongest and weakest signals in collision scenarios, improving bit error rates and enabling access to colliding signals that would otherwise be inaccessible.
Implementation Method 1
with phase modulation of the signals to be transmitted by all the transmitters of the system
Implementation Method 2
carrier frequencies, affected by the Doppler
Data Source
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AI summary
The method involves measuring a phase of a global signal common to two mutually collided time-multiplexed signals (S1, S2). An expected value of the global signal phase is estimated depending on a pair of phase states of the two signals and for each scenario of a received pair of bits of the two signals. A metric associated with the scenario is calculated. A bit-stream pair of each of the signals offering smallest aggregate metric is conserved, where an aggregate metric is a sum of an aggregate metric calculated in preceding iteration and the metric calculated with the scenario. An independent claim is also included for an equipment for demodulating two mutually collided signals.