Use of a Coherent Square Wave Reference to Demodulate BPSK (Binary Phase Shift Keying) Carriers and a Visual Indicator of the Quality of Received QPSK (Quadrature Phase Shift Keying) Carriers

摘要

This report consists of two parts. Part 1 compares the noise performance of a coherent phase demodulator when using as a carrier reference a square-wave signal versus a sinusoidal signal. Analyses for both signal references are included for the cases of allpass noise and of bandpass noise at the demodulator input. The theory indicates the demodulator operating with either the square-wave signal or the sinusoidal signal as a carrier will result in identical noise performance for the theoretical case of bandpass noise. However, experimental results demonstrate that the demodulator operating with the square-wave signal has a 0.4 dB performance advantage for digital data transmission using binary phas shift keying, when compared under similar conditions to operations with the sinusoidal reference signal. Part 2 investigates the features of a visual indicator (x-y oscilloscope display) depicting the quality of received quadrature phase shift keyed carriers. Such display allows for visualization of the signal-degrading effects due to noise, channel bandlimiting induced ISI, and multipath propagation. The observed pattern formed by the visual indicator allows an operator to determine these channel impairments. With experience, an operator can assess the system probability of a bit error under a variety of operating conditions. Keywords: Theses, Digital communications.