MLSE Receiver Deviation Error Compensation for H-CPM Bursts
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Solution Overview
Problem
Receivers in P25 Phase 2 systems face challenges in compensating for deviation error in received signals, which is caused by variance in transmitter components, leading to demodulation errors due to the complexity of Harmonized Continuous Phase Modulation (H-CPM) techniques.
Innovation Solution
A method and device that estimate deviation error using pilot symbols and apply the estimate to a Maximum Likelihood Sequence Estimation (MLSE) receiver to adjust matched filter coefficients, thereby compensating for deviation error in the received signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If H-CPM modulation is used in P25 Phase 2 systems, then communication capabilities are improved, but receiver complexity and processing requirements increase significantly
Solution Approach 1:
The patent applies preliminary action by estimating deviation error using pilot symbols before the main signal demodulation process. The deviation error estimator calculates the error using known pilot symbols, and this estimate is then used to adjust the received signal before MLSE processing, thereby simplifying the overall receiver operation while maintaining H-CPM capabilities
Solution Approach 2:
The patent introduces an intermediary deviation error estimator that acts as a mediator between the received signal and the MLSE demodulator. This estimator uses pilot symbols to calculate deviation error, which then adjusts the received signal parameters before they enter the complex MLSE process, reducing the burden on the main receiver architecture
2Device complexity
If deviation error compensation is not implemented, then receiver processing complexity is reduced, but demodulation accuracy deteriorates
Solution Approach 1:
The deviation error compensation is performed as a preliminary step using pilot symbols before the main demodulation process. By estimating and compensating for deviation error early in the signal processing chain, the patent improves demodulation accuracy without requiring complex real-time adjustments during the main MLSE process
Solution Approach 2:
The system uses its own pilot symbols to estimate and compensate for deviation error, making the compensation process self-contained and integrated within the receiver architecture. The pilot symbols embedded in the transmitted signal provide the necessary reference information for the deviation error estimator to self-correct the received signal
Data Source
AI summary
A method is described to compensate for deviation error in a H-CPM sync or data burst received by a MLSE receiver in a communication device. The deviation error is estimated and matched filter coefficients are adjusted using the estimated deviation error. Metrics are determined for the current state using the adjusted matched filter coefficients. The state having the minimum metric is determined to be the most likely current state. The most likely previous state is similarly determined. The burst is reconstructed backward from the last state to the initial state. The metric is the squared magnitude of the difference between the channel estimate multiplied by the matched filter coefficient associated with one of the possible states and the current state. Timing and frequency errors are compensated for before estimation and correction of the deviation error. Pilot or sync symbols are used in estimating the deviation error.