The noise performance of a squaring loop PSK demodulator



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In this research, a receiver was developed and built for the acquisition of pulse signals from Phase-Shift-Keyed (PSK) modulated signals transmitted over a noisy channel. To demodulate a PSK modulated signal, a phase-coherent signal of the carrier frequency is needed. This is quite often obtained from a synchronized pilot tone (in practice, this signal is usually referred to as the sync-subcarrier) transmitted along with the PSK signal. However, there are several disadvantages associated with this method that render it impractical for space communications. A better method is the use of a squaring loop to derive the carrier frequency and phase from the received PSK signal. This method was used in the receiver. A low frequency model of the receiver (at 225 kHz) was built and tested with PSK signal contaminated by white Gaussian additive noise. The performance of the receiver was indicated by the bit-error-rate at different signal-to-noise ratios. These experimental results were then compared with theoretical results obtained elsewhere.