Modern Communications A Systematic Introduction

In this chapter, we consider how to map bits to a sequence of voltages or signal levels at complex baseband. We introduce the idea of a constellation, which defines a lattice of allowed baseband signaling voltages. We provide a discussion of modulation-specific capacities. We introduce the idea of pulse shaping that we use to reduce the spectral spread of our signals. We discuss channel estimation and compensation. We evaluate the raw bit error rate of BPSK and symbol error rates of QPSK modulations. We discuss demodulation and consider both hard decisions and soft decisions, which involves estimating likelihoods of possible symbols.