Performance analysis of borrowing with directional carrier locking strategy in cellular radio systems

A new carrier based dynamic channel assignment for FDMA/TDMA cellular syste ms, called borrowing with directional carrier locking strategy, is proposed in this paper. When a call arrives at a cell and finds all voice channels busy, a carrier which consists of multiple voice channels can be borrowed f rom its neighboring: cells for carrying the new call if such borrowing will not violate the cochannel interference constraint. Two analytical models, cell group decoupling analysis and phantom cell analysis, are constructed f or evaluating the performance of the proposed strategy. Using cell group de coupling (CGD) analysis, a cell is decoupled together with its neigbors fro m the rest of the network for finding its call blocking probability. Unlike conventional approaches, decoupling enables the analysis to be confined to a local/small problem size and thus efficient solution call be found. For a planar cellular system with three-cell channel reuse pattern, using CGD a nalysis involves solving of seven-dimenional Markov chains. it becomes less efficient as the number of carriers assigned to each cell increases. To ta ckle this, we adopt the phantom cell analysis which can simplify the seven- dimensional Markov chain to two three-dimentional Markov chains. Using phan tom cell analysis for finding the call blocking probability of a cell, two phantom cells are used to represent its six neighbors. Based on extensive n umerical results, we show that the proposed strategy is very efficient in s haring resources among base stations. For low to medium traffic loads and s mall number of voice channels per carrier, we show that both analytical mod els provide accurate prediction on the system call blocking probability.