TABLE OF CONTENTS The choice of a modulation method and pulse-shaping scheme depends greatly on the availability of the spectrum, the desired data rate, and the radio channel itself. In turn, the modulation method influences the design complexity of the modem. In several SDR applications, the designer is faced with supporting multiple waveforms each with its own modulation and pulse-shaping technique, bandwidth, transmit mask and transmit power, etc.
A modulation scheme is influenced by various factors. The most commonly desired features of any waveform are:
Spectrally efficient modulation that occupies the least amount of spectrum and minimally interferes with adjacent and neighboring channels
Robust performance under certain channel conditions, such as multipath fading and heavy shadowing, Doppler and frequency drifts, interference and intentional jamming, etc.
Achievement of a low bit error rate performance at low SNR and minimal transmit power
Allowance for cost effective, low power, small size and weight solutions
Analog modulation is still widely used in one form or another in both military and civilian applications. These applications still rely on legacy waveforms that use amplitude modulation (AM), phase modulation (PM), and frequency modulation (FM) for their modulation scheme. In today's state of the art JTRS-SDRs, for example, these waveforms are generated digitally and not in the analog domain. Therefore, when discussing analog modulation in the context of SDR, the reader must keep in mind that, despite the classifications of these waveforms as analog, they are often generated digitally.
The aim of this chapter is to present an...
