OVERVIEW

Bandpass modulation techniques encode information as the amplitude, frequency, phase, or phase and amplitude of a sinusoidal carrier. These bandpass modulation schemes are known by their acronyms ASK (amplitude shift keying), FSK (frequency shift keying), PSK (phase shift keying), and QAM (quaternary amplitude modulation), where keying or modulation is used to indicate that a carrier signal is modified in some manner.

The carrier is a sinusoidal signal that is initially devoid of any information. The purpose of the carrier is to translate essentially a baseband information signal to a frequency and wavelength that can be sent with a guided or propagating electromagnetic (EM) wave.

Bandpass ASK is similar to baseband pulse amplitude modulation (PAM) in Chapter 2, "Baseband Modulation and Demodulation," but FSK, PSK, and QAM are new non-linear modulation techniques. ASK, FSK, and PSK can be readily extended to multiple level (M-ary) signaling and demodulated coherently or non- coherently. The optimum receiver for bandpass symmetrical or asymmetrical signals is the correlation receiver, which is developed for baseband signals in Chapter 2. Coherent demodulation uses a reference signal with the same frequency and phase as the received signal. Noncoherent demodulation of bandpass signaling may use differential encoding of the information to derive the reference signal in the correlation receiver.

The observed bit error rate (BER) for a single, limited trial in a SystemVue simulation for several bandpass digital communication systems with coherent and noncoherent correlation receivers is compared to the theoretical probability of...