Abstract
This chapter focuses on the design of 4-Quadrature Amplitude Modulation (QAM) modem system. This system consists several functional modules namely message source, pulse shape filter, QAM modulator, Hilbert transformer, QAM demodulator, frame synchronizer, and phase and frequency tracker. The system is essentially divided into two parts—transmitter and receiver. The first three modules constitute the transmitter side and the other modules the receiver side. The chapter also discusses the building process of each functional module in detail. The first module of the transmitter side is the message source. It readily uses PN sequences for this purpose. Frame marker bits are inserted in front of these sequences to achieve frame synchronization. The first module on the receiver side is the Hilbert transformer. This module builds the required analytic signal for demodulation based on the transmitted QAM signal. A Hilbert transformer is built by using the digital filter design (DFD) Remez Design virtual instrument (VI) of the DFD toolkit.
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