Chapter 5
Modulation/Demodulation
5.1 Introduction
In order to transmit a digital signal over a body area communication band, the digital signal is often impressed onto a carrier signal. The corresponding process is called modulation in which the digital information signal varies one or more properties of the carrier signal, including amplitude, phase and its frequency. The inverse process of modulation is called demodulation where the original digital information is extracted from the modulated carrier signal. In this chapter, we will describe summarily the feasible modulation and demodulation schemes in body area communications. For various available frequency bands described in Chapter 1, different schemes will be covered. Moreover, based on the body area communication channel characteristics, improvements and simplifications on the receiver structure will also be introduced.
In digital modulation and demodulation, the carrier signal is typically a high frequency sinusoid waveform, while a pulse train may also be utilized in wideband communications. The digital signal may be either binary with two levels or M-ary with multiple levels where each level will represent a discrete pattern of information bits. The fundamental digital modulation methods include amplitude-shift keying (ASK), frequency-shift keying (FSK), and phase-shift keying (PSK). There are also various variations based on these three fundamental modulation schemes. Note that these modulation schemes are essentially ...
