In 4G cellular networks, call admission control (CAC) has a direct impact on quality of service (QoS) for individual\nconnections and overall system efficiency. Reservation-based CAC schemes have been previously proposed for\ncellular networks where a certain amount of system bandwidth is reserved for high-priority calls, e.g., hand-off calls\nand real-time new calls. Traditional reservation-based schemes are not efficient for 4G vehicular networks, as the\nreserved bandwidth may not be utilized effectively in low hand-off rates. We propose a channel borrowing approach\nin which new best effort (BE) calls can borrow the reserved bandwidth for high-priority calls. Later, if a hand-off call\narrives and all the channels are busy, it will pre-empt the service of a borrower BE call if there exists any. The\npre-empted BE calls are kept in a queue and resume their service whenever a channel becomes available. The\nanalytical model for this scheme is a mixed loss-queueing system for which it is difficult to calculate call blocking\nprobability (CBP) and call dropping probability (CDP). Our focus in this paper is on the system modeling and\nperformance evaluation of the proposed scheme. We present two system models that approximate the operation of\nthe proposed scheme. For these models, we derive the CBP and CDP analytically. It is shown that our analytical results\nare very close to the ones obtained from simulations. Furthermore, it is observed that our channel borrowing\napproach decreases the CBP considerably while increases the CDP slightly over a large range of hand-off rates.
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