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In this paper, we construct mathematical models to analyze the probabilities of new call blocking and handoff call (HC) dropping for a sectorized cellular network with fractional frequency reuse (FFR). Because a sectorized FFR network (SFN) consists of two areas, the super group (SG) and the regular group (or sectors), three different types of HCs may happen when a mobile station (MS) moves from the SG to a sector, from a sector to the SG, or from one sector to another sector. To characterize three types of HCs, we first derive the area transition probability, which is defined as the reciprocal of MS's average residence time in an area (i.e., sector or SG). Moreover, we construct the model of Markov chains and derive the state transition rates. Then on the basis of the stationary probabilities of Markovian states, we derive the three types of blocking probabilities of new calls and two types of dropping probabilities of HCs. Finally, we conduct extensive numerical simulations. From the results of numerical simulations, we reveal two important rules for choosing the optimal radius of the SG, with which the system blocking and dropping probability can be effectively minimized. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we present an analytical model of adaptive channel preemption (ACP) for small-cell embedded large-cellular (SCELC) networks. An SCELC network consists of a fixed base station (FBS) with large coverage and many embedded base stations (EBS) with relatively small coverage. Channel capacity in an FBS cell may become insufficient when traffic is unexpectedly increased particularly in some special occasion. This paper considers two aspects of dynamically allocating channels for an SCELC network. First, by increasing one or more EBS cells within an FBS cell, the proposed ACP can reduce blocking probability of new calls. Second, to reduce dropping probability of handoff calls, the proposed ACP allows a handoff call to preempt an on-going call, when the latter is located in an EBS cell or in the overlapping area of two adjacent FBS cells. For the purpose of performance evaluation, we build an analytical model with 4-tuple Markov chains. Numerical results reveal that embedding one or more EBS cells inside an FBS cell needs to be done carefully since it results in a tradeoff between the reduction of new-call blocking probability and the increase of handoff-call dropping probability. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we present a proportional bandwidth adjustment (PBA) scheme using bit-error-rate (BER) ratios in a two-tier hierarchical NEMO system, composed of an access router (AR), mobile routers (MRs), and visiting mobile nodes (MNs). Depending on the location, an MN may use direct link to AR (Tier-0) or indirect link to AR via MR (Tier-1). To increase system utilization, sessions generated by high-speed MNs in one tier are allowed to use a certain amount of free bandwidth in another tier. Since Tier-1 traffic can be temporarily buffered at MR, to reduce the blocking probability of Tier-0, the bandwidth between Tier-0 and Tier-1 can be proportionally adjusted based on BER. In other words, more bandwidth is allocated to the tier with smaller BER. For the purpose of performance evaluation, we build a mathematical model with 6D Markov chains to analyze session blocking probabilities, system utilization, and normalized goodput. Analytical results are validated through a simulation. Both results demonstrate that the proposed PBA can significantly reduce the session blocking probabilities and increase the overall normalized goodput when BER ratio between Tier-0 and Tier-1 is very different. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]