Mobile radio traffic consideration

In a trunked mobile radio system a number of mobiles or stations in a "fleet" (user) communicate with their respective "dispatcher" or among themselves using a number of radio channels common to other users. The literature to date has attempted to characterize the subtle differences between this sort of trunked system with that found in telephone systems. In particular, traffic patterns and loads associated with mobile radio are different resulting in what is termed as "unbalanced" load. In telephone systems where the sources produce nearly equal load, the load is assumed to be balanced. Another obvious consideration is that the number of originating traffic sources is limited and usually small. These factors make it difficult to apply classical Erlang trunking formulas to mobile systems and suggest that data of measured traffic can be used in determining the number of radio channels required and the grade of service. The first part of the paper will focus on these problems and will suggest a novel technique for measuring traffic in general and mobile radio traffic in particular. This will require measurement of the mean as well as the variance of the traffic from which the equivalent number of traffic sources and the corresponding calling rate can be determined. The required number of channels and the grade of service can then be calculated using the Erlang trunking formulas. Traffic measurements will be required both at the home dispatch station and at the base station. For this type of measurement the system is required to produce a pulse when a call is initiated, a pulse when a call is terminated and a pulse when all the channels are simultaneously occupied. These pulses are ordinarily used to operate event counters, but when used in a simple digital measuring device based on the principle of state transitions will yield a running mean and variance of the traffic. The second part will focus on the specifications for the grade of service and its thresholds under normal and overload conditions. It may also be appropriate to express the grade of service for each user differently. These considerations will be demonstrated by computer simulation.