2.1 The General Concept of Synchronization

Let us first have a look at the concept of synchronization at the most general and perhaps familiar level. Although we may have a synchronized system within the smallest physical element (e.g., in a small integrated circuit), it is usual to define this process as happening between a local and another more distant system. Synchronization is defined as forcing a local system to track a remote target, either manually or automatically, in terms of some attribute such as speed or frequency.

Driving within urban traffic provides an example of synchronization, and the physical attribute is vehicle speed. In heavy traffic we are forced to match our speed to that of the car in front of us and should also try to avoid sudden braking so as not to frighten the driver behind us. Coordinating all the members of a symphony orchestra involves synchronization around a common beat. The reference is the conductor, and all musicians attempt to reproduce the beat as set by the conductor's baton. All the instruments, however, have to be tuned to follow the same scale of notes. Otherwise we would hear painful intermodulation products or the orchestra would seem to play out of tune. This situation is an elementary example of combined timing and frequency synchronization. Many low-cost radios still use simple manual tuning; the user captures the desired channel by adjusting the internal local oscillator frequency until the observed signal strength is maximized and the best sound quality is...