State Unnersity of New Yorkat Stony Brook

The use of real time channel borrowing in digital cellular TDMA systems is considered. Some systems (such as IS-54) are asynchronous in the sense that time slots in different cells are not aligned. CBWL (channel borrowing without locking) techniques can be applied but (without cell-to-cell synchronization) borrowing individual time slots from adjacent cells would violate co-channel interference constraints. Instead, frequency carriers can be borrowed. But (for example) in IS-54, a carrier supports three TDMA channels. So if only one TDMA channel is needed in the borrowing cell, two TDMA channels are unnecessarily transferred. We devised an appropriate carrier borrowing scheme and an analytical model to determine the traffic performance of TDMAKBWL. Fast carrier returning is used to increase channel utilization by returning borrowed carriers as soon as possible. An efficient computational method that uses macro-states, decomposition, combinatorial analysis and the convolution algorithm is devised to find blocking probabilities. The results show that in comparison with FCA, the new CBWL scheme can significantly improve system performance of asynchronous TDMA cellular systems that use FDMAITDMA multiplexes. The research reported in this paper was supported in part by the U.S. National Science Foundation under Grant No. NCR 9025 13 1 and in part by BMDO/IST under Grant No. N0001491-J4063, administered by the U.S. Office of Naval Research.