OVERVIEW

Measurements, whether performed in a research laboratory, on the manufacturing floor of a factory, or on an installed digital radio system are one of the most important tasks of the digital transmission engineer. Measurements are performed on simple building blocks such as prototype breadboards, but they may also be of extreme importance in more sophisticated systems, as in the case of the continuous performance monitoring of complex long-haul traffic-carrying systems. Space limitations does not permit us to describe, in depth, all the measurement methods and techniques which are currently in use. However, we shall describe some of the most important digital performance-measurement techniques. We shall also present original concepts and techniques of on-line (in-service) P(e) and jittermonitor measurements. We assume that the reader of this chapter has some familiarity with the conventional measurement techniques used in analog communications systems [11.5, 11.7].

Unfortunately, many practicing engineers and students in the digital transmission field do not take the time and effort to carefully study the capabilities and limitations of their instrumentation; as a result serious measurement errors occur frequently. (To confess, I lost the equivalent of about two weeks of valuable time on a rush project because I did not pay sufficient attention to constraints imposed by my measurement set-up, so I had to repeat all the measurements. Hopefully, my boss won t get too upset now that I have let the cat out of the bag.)

Off-line (out-of-service) laboratory, factory, and field-acceptance testing methods are described...