Teletraffic analysis of hierarchical cellular communication networks

Abstract

The sustained increase of users and the request for advanced multimedia services are some of the key motivations for designing new high capacity cellular telecommunication systems. The proposals which are being pursued by several studies and field implementations consider hierarchical architectures and dynamic resource allocation. In this paper a hierarchical cellular communication network is analyzed, taking into account user mobility and exploiting dynamic channel allocation schemes. In particular, a finite number of users has been considered, moving at different speeds in a geographical region covered by a finite number of cells structured in two hierarchical levels: microcells and macrocells. For such a system, a mobility model and a traffic model have been developed, both based on queueing networks, analyzing Maximum Packing (MP), a dynamic channel allocation scheme. The obtained results, validated by simulation experiments, allow the evaluation of main system performance parameters in terms of new call blocking probability, handoff blocking probability and forced termination probability as a function of load and system parameters. Index Terms-Cellular Networks, Queueing Model, User Mobility, Hierarchical Network. I. INTRODUCTIONELLULAR telephony is one of the consumer electronics fields that has experienced an explosive development in recent years. In fact, the sustained increase of users together with the request for advanced multimedia services are driving the research for the development of second generation systems (for instance, see the GSM phase 2+ [1]) and the definition of new standards for third generation systems (e.g., UMTS [2]). The transmission frequencies of evolved second generation and third generation systems are about 2 GHz, with a microcell coverage, while the second generation systems (for example, the first version of GSM) use frequencies of about 900 MHz with a macrocell coverage.It should be pointed out that a coverage based only on microcells is not always desirable. In fact, in this kind of cell, the propagation conditions are highly dependent on the environment: width of the streets, moving obstacles and so on. Therefore, when, as an example, users turn a street corner, they may experience a dramatic decrease in signal power. Such rapid variations of the received power level may cause communication interruptions for high-speed users if the network does not have enough time for the handoff process (assuming that there are available resources for this operation). Moreover, such high-speed users may generate lots of handoffs causing a significant increase in signaling traffic in the network. In fact, each handoff process involves various control functions both on wired and wireless networks. Such control procedures, necessary to set up a connection with the new base station and to update state information, introduce delay in the transmission, which can cause catastrophic consequences for multimedia real time traffic. Therefore, it is necessary to preserve the macrocell coverage that m...

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