Performance analysis of call assignment and carrier packing schemes for TDMA systems

In IS-136 and GSM time-division multiple-access (TDMA) systems that employ dynamic channel allocation, it is important to minimize the number of active carriers for a given load. This paper studies the carrier packing properties of both call assignment and carrier repacking schemes, where the average number of active carriers and the average number of intra-sector (repack induced) handoffs per call are the relevant metrics. We show that the simple to implement sequential trunk hunt (STH) call assignment scheme is almost as good as the optimal intelligent channel assignment (ICA) scheme and that the MaxPack repacking scheme is optimal for both of these TDMA standards among all call assignment and repacking schemes. The call assignment and repacking schemes considered are shown to have either closed-form or efficient numerical recursive solutions for the North American IS-136 standard, and in most cases we obtain the underlying state space distributions. A mixture of analytic and simulation results is also presented for the GSM standard. Numerical results show that most of the packing efficiency can be achieved simply by a good call assignment scheme such as ICA and that the additional gain from optimal repacking is generally in the 10-15% range for typical IS-136 and GSM configurations.