1,720,988 research outputs found
Near optimal load-adaptive distributed Dynamic Channel Allocation strategies in cellular mobile networks
No full textIn this paper we focus on the so-called load-adaptive Dynamic Channel Allocation (DCA) strategies for cellular mobile networks. Such strategies envisage the dynamic assignment of radio resources with the constraint that the outage probability (i.e. the probability that the carrier-to-interference power ratio be less than a given threshold) be less than a specified value, even in the worst foreseen propagation scenario. We identify a set of constraints to be satisfied in order that a DCA strategy belongs to the load-adaptive class. This provides a tight lower bound on traffic blocking and dropping performance such that: (i) it implies a dramatically lower computational effort than the known optimum strategy (based on the Maximum Packing algorithm); (ii) it is much tighter than the bound provided by the simple Erlang-B formula. A performance evaluation is carried out to compare the call blocking and dropping probabilities resulting from the tight bound above with those relevant to the Fixed Channel Allocation and to some recently proposed DCA strategies, including the Geometric DCA. The simulations exploit a mobility model that provides different degrees of offered traffic peakedness. It emerges that the Geometric DCA yields a practical way to attain near optimal performance in the load-adaptive class, leading a viable pathway to enhance the capacity of nowadays 2nd generation cellular networks in the short-medium term. © J.C. Baltzer AG, Science Publishers
Effects of imperfect power control and user mobility on a CDMA cellular network
No full textCode-division multiple-access (CDMA) is one of the major candidate access techniques for third generation systems, In recent years, a great deal of effort has been devoted to the study of the capacity it can support, This paper presents analytical derivations which allow the determination of the link availability in the presence of user mobility and power control imperfections in a CDMA network; moreover, it provides the guidelines which permit the implementation of a simple and flexible simulation tool which is independent of the specific CDMA implementations. As a matter of fact, the reported concepts can be applied to any asynchronous CDMA system, i.e., they hold both for the American Standard IS-95 and for the European Community Standard developed in the framework of the RACE CODIT Project
Fixed and adaptive blocking thresholds in CDMA cellular networks
No full textRecent papers have shown that, in a code-division multiple access cellular network, bursty user mobility causes remarkable negative effects on link availability, and hence on cellular network capacity. This article shows that a possible provision for contrasting such negative effects is the introduction of a blocking threshold which produces an increase in the link availability and a decrease in the dropping probability at the expense of the appearance of a non-null blocking probability. In order to maximize the capacity of the cellular network, the blocking threshold has to be selected so that a proper balancing of the blocking probability, dropping probability, and link availability is achieved. In particular, the article presents a simple self-adaptive mechanism for selecting the blocking threshold, which achieves good performance and has the fundamental advantage of not requiring any a priori knowledge of the system parameters
Tecnica per l'allocazione dinamica in maniera geometrica delle risorse radio in un sistema di comunicazione radiomobile cellulare
No full textA recursive multistage structure for multicast ATM switching
No full textA recursive multistage structure for multicast asynchronous transfer mode (ATM) switching is proposed, based on a connection network with a copying facility and external links connecting the outlets to the inlets. While the network generates only a few copies of an output multicast cell, the remaining are obtained by recycling the output copied cells to the corresponding inputs as many times as necessary. The basic features of a prototype binary multicast switch following the strategy are described. Its performance is also evaluated in terms of throughput and delay, via computer simulation. It is shown that due to the recursive mechanism, the copy generation is spatially distributed in the whole structure and is spread in time. This favorably affects the network's performanc
Effects of user mobility on the capacity of a CDMA cellular network
No full textIn the recent technical literature on cellular networks Code Division Multiple Access (CDMA) has received a large attention as a promising radio interface access technique. Many studies are devoted to the capacity evaluation of the radio interface adopting CDMA, but seemingly none of them accounts for the variability of the user spatial density due to user mobility. This should be a concern especially in a microcellular environment, where it cannot be relied upon a significant spatial average over the radio coverage area of a Base Station. The major aim of this work is a preliminary assessment of the effects of ''bursty'' user mobility on the capacity of the CDMA radio interface. To this end, we introduce a user mobility model apt to describe large fluctuations of the number of users in a radio cell area. A reference model of a CDMA network is used to evaluate the effects of user mobility on the capacity for a wide range of the model parameters, by means of simulations accounting for shadowing, call attempt process, voice activity and antenna directivity and assuming perfect power control. We show that user mobility can remarkably affect the CDMA capacity, mainly because of the resulting highly bursty behaviour of self-noise. A simple traffic control scheme is devised to increase the capacity of the CDMA network, under a joint constraint on link availability, call blocking and call dropping probabilities. It is pointed out that the concepts introduced in this paper are independent of the specific CDMA implementation, i.e. they hold for any asynchronous CDMA based cellular network
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