Multi-h CPM Waveform Frequency Hopping via Phase State Reset
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Solution Overview
Problem
Current frequency hopping systems using non-coherent FSK waveforms are slow and limit payload throughput due to the need for pilot symbols for coherent demodulation, which restricts their effectiveness in tactical communication systems.
Innovation Solution
Incorporating frequency hopping into multi-h continuous phase modulation (CPM) waveforms, specifically the 181B-CPM waveform, allowing data frames to start and end with a zero phase state, enabling independent demodulation of each hop frame without pilot symbols and using rotational invariance for phase synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pilot symbols are added to every hop frame for coherent demodulation, then phase coherence is achieved, but payload throughput is severely limited
Solution Approach 1:
The patent extracts and removes the pilot symbols from the hop frame structure. By eliminating the need for pilot symbols while maintaining phase coherence through the inherent properties of multi-h CPM waveforms and rotational invariance, the system achieves both coherent demodulation and improved payload throughput simultaneously.
Solution Approach 2:
The multi-h CPM waveform itself provides the necessary phase reference information through its inherent structure and rotational invariance properties. The waveform serves its own function of providing phase coherence without requiring additional pilot symbols, enabling the system to be self-sufficient for coherent demodulation.
2Productivity
If frequency hopping is implemented with multi-h CPM waveforms, then payload throughput increases, but system complexity increases
Solution Approach 1:
The patent applies universality by using the same multi-h CPM waveform structure and receiver architecture for both coherent demodulation and frequency hopping operations. The receiver is designed to handle both functions with a single unified approach, avoiding the need for separate processing paths and reducing overall system complexity despite the added capability of frequency hopping.
3Reliability
If frequency hopping rate increases, then ECCM capabilities improve, but constraint length requirements increase
Solution Approach 1:
The patent utilizes parameter changes by alternating between different modulation indices (h1 and h2) in a systematic pattern within the hop frame. This parameter variation enables the system to achieve the necessary constraint length for ECCM while maintaining the benefits of frequency hopping at high rates, as the modulation index alternation provides the required phase relationships for coherent demodulation across frequency hops.
Data Source
AI summary
A system and method improves ECCM and data payload for a multi-h continuous phase modulated waveform with the addition of frequency hopping capabilities. The system and method exploit the short constraint length and rotational invariance of the multi-h CPM waveform to enable frequency hopping using current system capabilities. The transmitted data is structured such that the initial phase state of each hopping frame is in the zero state and the final phase state of each hopping frame is cycled to zero by the addition of flushing symbols and transition symbols. The transition symbols allow the oscillator to change frequency without disrupting the phase progression. The system and method uses synchronous demodulation of the transmitted data at a plurality of phase offsets and determines the best phase offset based on the total sum of the branch metrics for each symbol and phase offset. The system and method alternatively demodulated with a phase offset that is tracked and adjusted over each hop by accumulation of the frequency error.