A Simple Demodulation Method in Zero-IF Receiver for FSK Signals in Wireless Communication Systems

S. Vasana (USA)


FSK modulation and demodulation, Non-coherentdetection, Zero-IF, Soft-decision detection, zero-crossingdetection.


A Zero-IF receiver with non-coherent demodulation and detection method is devised for M-ary Frequency-shift keying (FSK) modulation in digital communication. For M-ary baseband FSK signal half of the modulated signals utilize positive frequencies and half negative frequencies. The received signals can be detected by counting the speed and the direction of the complex signal phasor rotation. Conventional methods such as zero crossing detection used this FSK signal property. The demodulation and detection approach in this paper is comprised of simple logic by counting number of quadrant-crossings in a symbol period. Counting quadrant-crossings acts as a low-pass filter and improves the noise performance. The performance is improved further by using decision rules at fuzzy boundary - the soft decision detection. Simulation results of a 4-ary FSK signal example on wireless Rayleigh fading channels show the performance comparison and improvement by using soft decision detection.

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