Fabrizio Sestini

The geometric dynamic channel allocation as a practical strategy in mobile networks with bursty user mobility

In this paper we refer to a specific class of Dynamic Channel Allocation (DCA) strategies, namely the interferencefree, timid, not-conditioned class. The main concern of this work is to verify if and to what extent strategies belonging to this class can offer better performance than Fixed Channel Allocation (FCA). The interest in this kind of strategies is motivated by their feasibility with current TDM technologies, the limited amount of information required to carry out channel assignments and their intrinsic stability. In this framework we present a simple, but very attractive DCA strategy, the so-called Geometric DCA (GDCA). A performance evaluation is carried out to compare some representative DCA strategies of the considered class, by using a user mobility model that accounts for the large fluctuations of the number of users in a cell coverage area expected in a microcellular environment. The effect of the non-null propagation time required by the information exchange in the DCA strategies is also taken into account. It emerges that the proposed GDCA allows better performance than more sophisticated strategies already proposed, at the expense of a frequency planning carried out only at network configuration. This is due to the ability of GDCA to exploit the a priori information to maintain a tight geometric packing of used carriers. The reported results also show that DCA strategies in the considered class cope with large and sudden traffic fluctuations remarkably better than the FCA scheme does and that the advantage becomes more evident as the burstiness of the user mobility process (hence of the offered traffic) increases.

Application of dynamic channel allocation strategies to the GSM cellular network

We refer to the implementation and the performance of a specific class of dynamic carrier allocation (DCA) strategies which is suitable for being introduced in the pan-European Global System for Mobile communications (GSM) cellular network. One of the main concerns of this work is to verify if and to what extent strategies belonging to this class can offer better performance than fixed channel allocation (FCA) in realistic traffic and propagation conditions. The impact of the introduction in a real network of two of the more promising DCA strategies in the considered class is assessed. In particular, solutions are presented concerning the signaling exchanges entailed by the implementation of each of the considered DCA strategies. A performance evaluation of a realistic cellular network exploiting the above-mentioned DCA strategies is carried out, taking into account all of the main GSM transmission and network aspects. The simulations have been performed by considering a realistic cell layout corresponding to the urban area of Rome, its realistic propagation environment, and a user mobility model based on the building percentages in such an area. The results of the performance evaluation show that, by carefully choosing the values of the parameters characterizing each of the considered DCA strategies, a conspicuous increase in the number of users supported by the cellular network can be achieved.

Effects of imperfect power control and user mobility on a CDMA cellular network

Code-division multiple-access (CDMA) is one of the major candidate access techniques for third generation systems. 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.

Effects of user mobility on the capacity of a CDMA cellular network

In 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.

The Geometric Dynamic Channel Allocation Strategy for High Traffic FDM/TDMA Mobile Communications Networks

In this paper we refer to a specific class of traffic adaptive Dynamic Channel Allocation (DCA) strategies, namely the conservative interference-free, timid, not conditioned class. In this framework we present a new DCA strategy, the so-called Geometric DCA (GDCA) strategy.

Dynamic carrier allocation in a PRMA cellular network

This paper proposes a technique to allow the dynamic channel allocation in a PRMA personal communication network (PCN) in urban and indoor environments, where cells have small extension and may present large and sudden variations in the number of users. The proposed technique is also suitable for coping with variable-band services. The paper proposes original solutions to the following crucial problems: (i) the determination of a short-term parameter for assessing the link quality of a PRMA carrier in a microcellular environment; (ii) the determination of a procedure the base station can follow in order to perform a real-time estimation of the above-mentioned short-term parameter; (iii) the interworking between the DCA mechanism and the PRMA technique. Simulation results show a remarkable improvement in system performance, due to both the DCA and PRMA techniques.

Handling of user mobility in a CDMA cellular network

In this paper an expression of the link availability in CDMA cellular networks which takes into account user mobility is determined. The performed simulations are based on this expression and on a simple but meaningful mobility which also considers hot cells where mobile users tend to accumulate. Two mechanisms for limiting the negative effects yielded by the bursty user mobility are presented. Such mechanisms aim at preventing the accumulation of a large amount of mobile users in a given cell, thus limiting the occurrence of situations in which the self-noise is so high that the target quality requirements are not met (i.e. the link is unavailable). The consequent increase in link availability takes place at the expense of the rising of non-null blocking and dropping probabilities. In this view, an optimization process is presented which achieves the maximum capacity while satisfying the given performance targets.

Near-optimality of distributed load-adaptive dynamic channel allocation strategies for cellular mobile networks

In this paper we focus on the so-called load-adaptiveDynamic 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 theFixed Channel Allocation and to some recently proposedDCA strategies, including theGeometric DCA. The simulations exploit a mobility model that provides different degrees of offered trafffic 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.

Enhancing the performance of a second generation cellular network in a realistic GSM environment

We refer to the possible performance improvement consequent to the introduction of dynamic carrier allocation (DCA) strategies in the pan-European Global System for Mobile communications (GSM) cellular network. The impact of the introduction in a real network of two of the more promising DCA strategies is assessed, also in terms of the entailed signalling exchanges between base stations. A performance evaluation of a realistic cellular network exploiting the above-mentioned DCA strategies is carried out, taking into account all the main GSM transmission and network aspects. The simulations have been performed by considering a realistic cell layout corresponding to the urban area of Rome, its realistic propagation environment, and an user mobility model based on the building percentages in such area. The results of the performance evaluation show that, by carefully choosing the values of the parameters characterizing each of the considered DCA strategies, a conspicuous increase in the number of users supported by the cellular network can be achieved.

An FDM/PRMA cellular network with dynamic carrier allocation and distributed control

This work considers a frequency division multiplex/packet reservation multiple access (FDM/PRMA) technique. The proposed technique is in line with the guidelines marked out by European Community RACE (now ACTS) projects: the expected evolution of the frequency division multiplex/time division multiple access (FDM/TDMA) technique used in the Global System for Mobile communications (GSM) is just the FDM/PRMA technique. The main enhancements of the proposed FDM/PRMA technique consist in the augmented spectrum efficiency and in the capability of real-time reconfiguration of resources; such enhancements are achieved due to the introduction, on the one hand, of dynamic channel allocation strategies which guarantee a real-time rearrangement of the carriers-to-cells assignment and, on the other hand, of PRMA techniques which guarantee an higher carrier exploitation. This paper proposes solutions to some important problems of the FDM/PRMA technique, namely the carrier management and the interworking between the DCA mechanism and the PRMA technique. The paper also shows simulation results highlighting a remarkable improvement of the carrier utilization, obtained thanks to the adopted PRMA technique.