Michalis E. Theologou

Network-Based Access Selection in Composite Radio Environments

In this paper, we introduce a network-based approach for access and interface selection (AIS) in the context of resource management in heterogeneous wireless environments (UMTS, WLAN and DVB-T). We focus on the optimization of the resource utilization, while ensuring acceptable QoS provision to the end users. Our objective is to optimally manage the overall system resources and minimize the possibility of QoS handovers (non-mobility handovers). The adopted architecture applies to typical heterogeneous environments and network entities (access routers) are enhanced with extra functionalities. We propose an AIS algorithm that exploits the multihoming concept and globally manages network resources at both radio access and IP backbone networks. The algorithm can estimate near optimal solutions in real time and we also introduce a novel triggering policy. We present simulation results that demonstrate the advantages of our approach. System performance metrics, derived from the simulations, show minimum degradations in high load and congestion situations.

Vehicle Velocity Estimation Based on RSS Measurements

This paper presents a technique which is based on pattern recognition techniques, in order to estimate Mobile Terminal (MT) velocity. The proposed technique applies on received signal strength (RSS) measurements and more precisely on information extracted from Iub air interface, in wIDeband code-division multiple access (WCDMA) systems for transmission control purposes. Pattern recognition is performed by HIDden Markov Model (HMM), which is trained with downlink signal strength measurements for specific areas, employing Clustering LARge Applications (CLARA) like a clustering method. Accurate results from a single probe vehicle show the potential of the method, when applied to large scale of MTs.

Design of the Access Network Segment of Future Mobile Communications Systems

An important component of future mobile communications systems is their access network segment that enables interworking between the mobile unit and the fixed network. In this paper we define and solve two important problems, related to the design of this segment. First, the efficient utilisation of the available radio spectrum. In this context we present a scheme that may be used for reconfiguring the frequency allocation, therefore, improving the spectrum utilisation. The second problem that we address is that of deploying Cell Site Switches (CSSs), and Local Exchanges (LEs). Our aim in this paper is the following. First, to formally define and optimally formulate these problems. Second, to solve them resorting also to computationally efficient heuristic algorithms. Finally, to provide results and draw subsequent conclusions.

Location- and Service-Aware Downlink Transmission Power Allocation in WCDMA-Based Cellular Networks

Power constitutes an essential controllable resource for the improvement of the radio link performance in Wideband Code Division Multiple Access (WCDMA)-based cellular networks. In addition, complementary to traditional services, location-based services (LBS) have emerged as a growing area for mobile service providers bringing in the foreground the potential for a location-aware resource management. To this effect, this paper addresses a location- and service-aware downlink transmission power allocation problem (DTPA), the solution of which is suitable for the management or control domain of multi-service, WCDMA-based cellular networks. Given a specific traffic load situation that includes location and required service information, the solution of the DTPA problem aims at finding the optimum feasible allocation of power to the set of downlink connections that should be supported by the system. The problem is concisely defined, mathematically formulated and solved by a computationally efficient algorithm. Simulation and numerical results are presented.

Performance of a multi-service GSM/GPRS-capable network under various loading conditions

The aim of this paper is to investigate the performance of the air-interface of a GPRS-capable network, under various loading conditions and various data services, taking into account environmental conditions, user behavior, services QoS requirements (i.e., data session dropping and blocking probabilities, required slots for data transfer). For this reason, a GSM/GPRS simulation platform has been developed which takes into account both, environmental (e.g., propagation conditions, service characteristics) and network configuration aspects (network elements, interconnections, element capabilities, etc.). Results have shown that in general, the maximum load of a certain service that the system can withstand, depends on the circuit-switched traffic load, the specific services characteristics (e.g., requested slots in uplink and downlink) and the characteristics of the data services that coexist.

Establishment of Mobile Extranets through Mobile IPv6 and GPRS: Enabling Universal Access to Corporate Intranets

Mobile Extranets (MEs) are seen as a natural evolution of the Internet and Intranet concepts. Their role is to provide universal (ubiquitous) access to corporate Intranet services, along with security, location transparency, costefficiency and QoS. The aim of this paper is to present and comment on an approach for the realisation of an ME platform. GPRS and the IPv6 protocol suite, with its integral mobility and security functionality, are key technologies for the platform. Aspects covered in the platform presentation are the requirements posed by various application types, the platform architecture, the role and limitations of the technologies encompassed, and the prototype terminal architectures. Finally, issues for further work are presented and concluding remarks are made.

Service and network management platforms for UMTS

Advanced management strategies and tools will be essential to the success of third generation cellular systems like UMTS. The aim of this paper is to present an approach for the management of services and network resources in UMTS. Our starting points are the presentation of a business model and corresponding management framework. Problems related to the negotiation plane in the management framework are presented so as to form a theoretical basis on which the management of services and network resources in UMTS can be based.

Advanced platforms and software technologies applied in the management of cellular networks

The efficient operation of future cellular networks is coupled with software tools for element, network and service management. This paper describes a pertinent management platform and presents the software technologies applied in its realisation.

Planning problems for the intelligent network segment of future mobile networks

It is envisaged that future cellular systems, e.g., UMTS, will consist of three network segments, namely, core, access, and intelligent. In this paper, we discuss about planning problems related to the design of the intelligent network segment. Two major problem areas are identified. First, the association of local exchange (LE) areas to mobility and services control point (MSCP) areas (MSCP level problem), and second, the association of MSCP areas to mobility and services data point (MSDP) areas (MSDP level problem). In our discussion we formally define the problems, outline their corresponding optimal formulations and, where appropriate, discuss directions for the construction of computationally efficient solutions.

Traffic adaptive spectrum allocation for mobile communications systems

A fundamental notion in third generation mobile systems is efficient spectrum utilisation. A first approach of the traffic adaptive spectrum allocation problem is the following: given the set of channels, the cell structure and the load to be accommodated in each cell, find the optimal allocation of channels to cells, subject to the restrictions arising from the minimum permissible distance of cells where the same channel can be used at the same time. This problem presupposes a traffic load that is fixed with time. In this paper we extend this scheme in order to include fluctuating traffic loads. This extended scheme is theoretically formulated, and found to be a difficult problem. Finally, a set of results is presented.