Introduction

A successful communication system must establish synchronization, in addition to utilizing the modulation and demodulation techniques discussed so far. Synchronization is required at several levels. At the physical-layer level the receiver needs to know or estimate three parameters: (i) the incoming carrier frequency, fc (hertz); (ii) for coherent demodulation any phase shift or phase drift, θ(t) (radians), introduced during transmission; (iii) the bit (symbol) timing, i.e., where on the time axis do the kTb (or kTs) (seconds) ticks occur. How to obtain estimates of these parameters is the subject of this chapter.

The reader should realize, however, that one needs to establish other levels of synchronization. After detection of the transmitted bit sequence the sequence needs to be segmented or parsed into “words.” The best example of this is perhaps voice where the bit sequence needs to be segmented typically into eight-bit words, each word representing a voice sample. If error coding has been used, the sequence needs to be parsed properly into codewords for error decoding. Another example occurs in time-division multiple access where the communication channel is time shared. In this case the time slots need to be properly segmented to route the information from the different users properly. Such synchronization is typically called frame synchronization.