Abstract: This paper addresses the problem of Radio Access Technology (RAT) selection in heterogeneous multi-access/multi-service scenarios. For such purpose, a Markov model is proposed to compare the performance of various RAT selection policies within these scenarios. The novelty of the approach resides in the embedded definition of the aforementioned RAT selection policies within the Markov chain. In addition, the model also considers the constraints imposed by those users with terminals that only support a subset of all the available RATs (i.e. multi-mode terminal capabilities). Furthermore, several performance metrics may be measured to evaluate the behaviour of the proposed RAT selection policies under varying offered traffic conditions. In order to illustrate the validation and suitability of the proposed model, some examples of operative radio access networks are provided, including the GSM/EDGE Radio Access Network (GERAN) and the UMTS Radio Access Network (UTRAN), as well as several service-based, load-balancing and terminal-driven RAT selection strategies. The flexibility exhibited by the presented model enables to extend these RAT selection policies to others responding to diverse criteria. The model is successfully validated by means of comparing the Markov model results with those of system-level simulations.

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Abstract: The benefits of jointly managing the combined radio resources offered by heterogeneous networks consisting of several Radio Access Technologies (RATs) have been profusely studied and assessed in recent years. Nevertheless, most of the existing work assumes scenarios where all RATs are accessible (provided the RAT is not at full capacity) to all users demanding service. If this is so, the obtained benefits become rather optimistic given that we neglect the fact that the deployed RATs may have different coverage overlapping conditions among them and that users may not have terminals that support all RATs (i.e. multimode terminals). In this paper we extend a previously developed Markov framework in order to capture the effect of having different coverage overlapping conditions along with the capability of certain terminals to support all or a subset of available RATs. As a result, we assess the degradation, in terms of Erlang capacity, that a heterogeneous network undergoes in scenarios with limited terminal and coverage conditions and compare it to the ideal case of full coverage and full terminal availability.

Abstract: An efficient and utmost utilization of radio spectrum resources has stimulated the introduction of what has been termed dynamic spectrum access methodologies and implementations. While the traditional approach has been based on licensed (or primary) spectrum access, this new communication paradigm enables an opportunistic secondary access to shared spectrum resources provided mutual interference is kept below predefined margins. In this paper we propose a novel and flexible framework so as to account for primary-secondary spectrum sharing scenarios. In this sense, the use of a Discrete Time Markov Chain (DTMC) model is suggested and further justified. Some illustrative results are provided and validated against a system-level simulator thus confirming the suitability of the proposed approach.

Abstract: Common Radio Resource Management (CRRM) represents a key functionality in heterogeneous Beyond 3G scenarios where several radio access technologies coexist. In this context, this paper presents a general CRRM functional model, accompanied by different splits of functionalities between the involved entities. This paper also introduces several principles for the Radio Access Technology (RAT) selection problem and presents a specific algorithm that is able to combine in a smart way the service, load-balancing and interference principles. Throughput improvements of up to 24% compared to other reference approaches are obtained with the proposed algorithm.

Abstract: Among the common radio resource management (CRRM) functions that are responsible for the proper allocation of resources in a multi-access network, congestion control is the one devoted to overcome potential QoS failures due to the inherent dynamics of the network. In this paper we address the problem of congestion control in a scenario considering the GSM/EDGE radio access network (GERAN) and the UMTS terrestrial radio access network (UTRAN). In particular, we face the problem where the two available radio access technologies (RATs) undergo simultaneous congestion situations. For this case, a congestion resolution scheme based on vertical (inter-system) handover (VHO) jointly with a bit-rate reduction (BRR) scheme is proposed and evaluated for a mixed services scenario considering voice and data users.

Abstract: In order to support the conceptual development of Common Radio Resource Management (CRRM) algorithms, this paper provides an analytical approach to the performance evaluation of Radio Access Technology (RAT) selection procedures in a multi-RAT/multiservice environment. In particular, a 4-Dimensional (4D) Markovian model is devised so as to consider the allocation of voice and data services in a GERAN/UTRAN system. Through the analytical definition of well-established Key Performance Indicators (KPIs) we provide numerical results on the evaluation of a load balancing RAT allocation policy.

Abstract: This paper addresses the problematic of congestion control in the radio access interface when considering the allocation of voice and data services over several radio access technologies (RATs). In particular, the GSM/EDGE radio access network (GERAN) and the UMTS terrestrial radio access network (UTRAN) are considered for the evaluation of congestion control strategies. After a congestion situation in the radio access is detected, congestion resolution mechanisms are triggered in order to reduce the overload in the congested RAT(s). In this paper, a framework for the detection and resolution of congestion conditions in a multi-access network is presented. Moreover, three approaches intending to solve congestion situations are proposed and the evaluation of an inter-RAT handover algorithm for solving congestion events in GERAN is also presented.

Abstract: Beyond 3G (B3G) networks will encompass, among other features, a wide range of radio access technologies (RATs) providing users with a flexible and efficient access to the increasing pool of demanding services. This will allow users to get connected using the access technology that is most suitable according to some specified criteria. Consequently, to take full advantage of B3G networks, mobile terminals will need to support a larger set of capabilities. Among those, the support of different RATs, i.e. multi-mode capacity, is a must. This paper addresses the impact of multi-mode terminals in an EDGE/UMTS heterogeneous network with multi-service provisioning. Results indicate that multi-mode terminal availability should be considered when designing common radio resource management strategies in heterogeneous wireless access networks. Specifically, a service-based initial RAT selection policy is evaluated, revealing different behaviors for different multi-mode terminal availabilities and service-class mixings. In order to compensate the limitations imposed by non-multi-mode terminals, it is suggested to actuate over GERAN by using a resource reservation scheme for interactive users. By doing so, we tradeoff the QoS between multi-service/multi-mode users.

Abstract: Initial RAT selection is a key Common RRM strategy, where users requiring service are to be efficiently allocated in the existing and available RATs. Although load balancing is a possible guiding allocation principle, sometimes it may not be convenient. This paper evaluates and compares a load balancing and a service-class RAT selection policy in order to discuss the suitability of the former in situations where different service-class mixings are present. Results indicate a tight dependency between this appropriateness and the mixing of demanding services.

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Abstract: Future military tactical communication networks must be highly mobile, survivable and recongurable. Distributed multi-hop packet radio architectures have been adopted, combining robustness and autonomous operation. In order to meet the requirements for Quality of Service (QoS) and delay guarantees, Spatial Time Division Multiple Access (STDMA) schemes have been proposed. Key problems in STDMA are: to nd ecient distributed algorithms for STDMA scheduling, slot synchronisation and to handle mobility. In this thesis focus is on slot synchronisation. Time synchronisation is a critical piece of infrastructure for any distributed system. Moreover, slotted TDMA schemes are of special interest because of the natural mechanism it provides for refereeing the access to the medium: time. To consider timing inaccuracies and propagation delay effects a guard band is usually introduced and, therefore, perfect synchronisation is not required. Hence, good time synchronisation is important not only because it enables Time Division Multiple Access to the data link, but because it shortens the guard time allowing bigger packets to be sent. In this thesis the performance in terms of synchronisation convergence and timing accuracy will be evaluated for a STDMA scheme in Tactical Radio Area Networks (TRAN). A network set-up environment will be considered and a description of how the synchronisation algorithm ts in the initialization process will be made. We also investigate some parameters related to the synchronisation algorithm and the effects when different topology congurations are used.