FSK Frequency Deviation Scaling and Limiting After Filtering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing wireless communication systems face issues with frequency deviation in FSK signals due to filtering, leading to inter-symbol-interference and hysteresis, which affect signal reception and spectrum characteristics.
Innovation Solution
A transmit apparatus and method that includes an O-QPSK circuit, FSK modulation circuit, frequency deviation circuit, scaler, and limiter to scale and limit frequency deviations, ensuring fixed frequency deviations and phase trajectories, using a two-point injection PLL for transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If filtering is applied to the FSK signal to improve spectrum containment, then adjacent channel interference is reduced, but frequency deviation becomes non-fixed causing inter-symbol-interference and hysteresis
Solution Approach 1:
The patent applies parameter changes by introducing a scaling factor (greater than one) to multiply the filtered frequency deviation signal, thereby restoring the frequency deviation to fixed values while maintaining the spectral benefits of filtering. This resolves the contradiction by adjusting the frequency deviation parameter back to its ideal fixed state after filtering has improved spectrum containment.
2Object-affected harmful factors
If filtering is applied to the FSK signal, then spectrum containment is improved, but phase trajectory deviates from the pre-filtering signal
Solution Approach 1:
The patent uses parameter changes by scaling the filtered frequency deviation signal with a factor greater than one, which restores the phase trajectory to match the pre-filtering signal while preserving the improved spectrum containment achieved through filtering.
3Stability of the object's composition
If frequency deviation is scaled up to restore fixed values, then phase trajectory is maintained, but frequency deviation exceeds predetermined values requiring limiting
Solution Approach 1:
The patent applies dynamics by implementing a limiter circuit that dynamically adjusts the scaled frequency deviation signal. The limiter ensures frequency deviation remains within predetermined values by clipping excess portions, thereby maintaining both phase trajectory stability and frequency control precision simultaneously.
Data Source
AI summary
A transmit apparatus comprising a scaler arranged to scale a frequency deviation signal associated with a frequency shift keying signal (FSK) by a scale factor and a limiter arranged to limit frequency deviations of the scaled frequency deviation signal after a filtering. A power spectral density, phase trajectory, and frequency deviation of an FSK signal based on the limited scaled frequency deviation tracks similar criteria of a minimum phase shift keying (MSK) signal.