After narrow UWB pulses are generated, they need to be modulated with data prior to transmission. Data modulation for carrierless UWB systems is typically done using pulse-modulation techniques in the time domain. The choice of modulation method can affect a number of design parameters in UWB system development: data rate, robustness to interference and noise, spectral characteristics of the transmitted signal, and transceiver complexity that directly impacts the overall size and cost of the system. In this chapter, we consider some commonly employed UWB modulation options and discuss the advantages and challenges of each method. The modulation techniques we cover are on-off keying (OOK), pulse-amplitude modulation (PAM), pulse-position modulation (PPM), biphase modulation, and transmitted-reference (TR) modulation. We also discuss detection methods for each modulation option.
Later in this chapter, we cover the data modulation options for UWB multiple-access channels. Most short-range, high-data-rate applications require several transmitters to coexist in the covered area. Therefore, proper multiple-access techniques are needed to perform channelization for multiple UWB users.
First we briefly discuss the two basic pulse-detection techniques: energy detectors and classical matched filters (CMFs). Most UWB receivers use one of these techniques for data demodulation. Hence, the basic concepts behind energy detectors and CMFs are fundamental to the rest of our discussion in this chapter.