Virtually fixed channel assignment in cellular mobile networks with recall and handoffs

Abstract

A promising approach for implementing channel assignment and control in cellular mobile telephone networks is the virtually fixed channel assignment (VFCA) scheme. In VFCA channels are allocated to cells according to the fixed channel assignment (FCA) scheme, but cells are allowed to borrow channels from one another. As such, VFCA maintains the efficiency of FCA, but adds the flexibility lacking in FCA. One feature of a VFCA network is that, to prevent co-channel interference, it requires several channels to be locked to serve a single call that borrows a channel. This feature raises the concern that VFCA may lead to chain reaction in channel borrowing among cells and cause the network performance to degrade, especially under heavy traffic conditions. In this paper, we propose the virtually fixed channel assignment with recall (VFCAWR) scheme: The network is implemented according to VFCA, but a cell can recall a locked channel to service an arriving handoff call, which occurs when a mobile unit crosses the boundary of its cell. We model the network as a three-dimensional Markov chain and derive its steady-state performance. Through modification of this basic model, we evaluate two dynamic channel assignment strategies, the virtual channel reservation (VCR) strategy and the linear switch-over (LSO) strategy, which exploit the unique borrowing/recall capability of VFCAWR to reduce the weighted cost of blocking fresh and handoff calls by reserving several virtual channels (the channels that may be borrowed from adjacent cells when necessary) for handoff calls. We validate the analytical models by simulation; the simulation test cases show that our models accurately predict the system performance measures of interest. Numerical and simulation results also show that both dynamic strategies outperform conventional channel reservation schemes based on fixed channel assignment and hybrid channel assignment.