TABLE OF CONTENTS In the previous chapters, we studied the performance of unprotected singlechannel radio systems. The reliability objectives of digital microwave systems is presented in Chapter 5, where it is pointed out that multi-path fading might have a major impact on the availability of radio systems.
A practical example of operational availability is presented in the specification of the Trans-Canada Telephone System (TCTS) [10.1 and 10.4]. It is a 6560 km, two-way, backbone microwave network. This network has an availability of 99.98 %.
The main contributions to the unavailability of a network are categorized as follows:
Those controllable by equipment and route design (fading).
Those caused by operational activities (maintenance, system expansion, etc.).
Catastrophies (fires, antenna/feeder system failures).
About 20% of operational unavailability is apportioned to type (1).
For the two-way, 6560 km, TCTS, radio reference system, one-half of its outage is attributed to equipment failures (0.01%) and the other half to propagation outage (0.01%). Thus, the design availability objective, then, is 99.98%.
To meet these stringent availability objectives most digital microwave systems have incorporated into them protection channels and automatic switching systems. In this chapter we describe the principles of operation of the best-known protection switching systems. These systems have been successfully used to provide excellent P(e) performance and also to minimize loss of service resulting from fading or equipment failure. The systems of interest to us here are the frequency diversity, space diversity, and hot-standby systems.
The effect...
