Mobile network operators are interested in providing Vehicle-to-Vehicle (V2V) communication services using their cellular infrastructure. Regional split of operators is one possible approach to support multi-operator infrastructure-based cellular V2V communication. In this approach, a geographical area is divided into non-overlapping regions, each one served by a unique operator. Its main drawback is the communication interruption motivated by the inter-operator handover in border areas, which prevents the fulfillment of the maximum end-to-end (E2E) latency requirements of fifth generation (5G) V2V services related to autonomous driving. In this work, we enable a fast inter-operator handover based on the pre-registration of the users on multiple operators, which substantially reduces the handover time to guarantee maximum E2E latency values of 100 ms in non-congested scenarios. To further reduce the latency of time-critical services to always less than 70 ms, even with the handover interruption time, while providing a latency around 20 ms in the majority of locations, we propose to complement the former technique with a mobile edge computing approach. Our proposal consists in the localization of application servers and broadcasting entities in all the base stations, to avoid the communication through the core network, together with the use of a new set of nodes in the base stations of cross-border areas called inter-operator relays, to minimize the communication latency between operators. Based on analytic and simulation results, it is demonstrated that the proposed techniques are effective to support low-latency infrastructure-based cellular V2V communications in multi-operator environments with regional split.

In this paper we consider a cloud radio access network (C-RAN) architecture where the baseband signal processing servers, named baseband units (BBUs) are separated from the remote radio heads (RRHs). The RRHs form a single cluster while the BBUs form a centralized pool of data center resources. Each RRH of the C-RAN accommodates bursty traffic which is expected to play a dominant role in 5G networks. We approximate bursty traffic via the compound Poisson process according to which batches of calls, with a generally distributed batch size, occur at time points that follow a negative exponential distribution. Each call of a new batch is treated separately from the other calls of the same batch. A new call requires a computational resource unit from the centralized pool of BBUs and a radio resource unit from the serving RRH. If both units are available, then the call is accepted in the RRH for an exponentially distributed service time. Otherwise, call blocking occurs. We model this C-RAN as a loss system and show that the steady state probabilities have a product form solution (PFS). Based on the PFS, we propose an efficient convolution algorithm for the accurate calculation of the main performance measures which are time and call congestion probabilities. The accuracy of this algorithm is verified via simulation.

The long-term evolution multimedia broadcast multicast service (MBMS) infrastructure has been shown to efficiently fulfill the requirements of classical vehicle-to-vehicle services, such as cooperative awareness message and decentralized environmental notification message delivery, which involve the transmission of the same message to a set of destination receivers in close proximity. When targeting autonomous driving applications, related 5G V2X services, such as cooperative collision avoidance (CCA), impose challenging latency and reliability requirements that cannot be generally guaranteed using the current MBMS architecture. In this paper, we propose a low-latency multicast scheme aimed at decreasing the end-to-end (E2E) communication latency. The proposed approach concentrates the multicast network functionalities into the layer-2 of the base stations (BSs) protocol stack, including a message passing between neighboring BSs, to achieve a fast management of multicast groups and a reduction of the communication path through the network infrastructure. The results show that the proposed technique can substantially decrease the E2E latency of conventional MBMS and ensure the correct operation of demanding services, such as CCA moving toward 5G communication systems.

The standardization for the fifth generation (5G) of mobile and wireless networks is at its early phase and has recently completed the first study item in Release 14. Nevertheless, there is a consensus that 5G will address the diverse service requirements of high-variety use cases. The network shall cope with such variation effectively and cost-efficiently even though the requirements can change over space and time. The design of the radio topology for the peak service demand is, thus, not desirable for network operators. As a consequence, the trend is towards more flexible network deployment. In this context, dynamic radio topology through vehicular nomadic nodes (VNNs) is an emerging concept towards 5G to efficiently address non-uniformly distributed traffic. VNNs are aimed to overcome the lack of flexibility induced by small cells that are deployed at fixed locations via network planning in current wireless networks. A VNN is a low-power access node with wireless self-backhaul, which can be activated temporarily to provide additional system capacity and/or coverage on demand. VNNs can be integrated into vehicles, e.g., in car-sharing fleets. In this paper, we evaluate the performance of radio access network (RAN) moderation of VNNs in a multi-cell environment considering composite fading/shadowing environments with co-channel interference, where active VNNs are selected from a set of available candidate VNNs based on the signal-to-interference-plus-noise ratio (SINR) on the wireless backhaul link. The results show that RAN moderation can significantly improve the end- to-end rate and SINR performances along with clear amount-of-fading (AoF) reduction.

The Fifth Generation (5G) of mobile and wireless networks is expected to fulfill the requirements of high variety of new use cases. One of the key challenges will be the varying capacity and coverage demands, non-uniformly distributed over space and time. In the current wireless networks, small cells are deployed at fixed locations via network planning, and, hence, lack the flexibility of reacting to spatially varying service requirements. Dynamic radio topology is an emerging concept towards 5G to address the real- time provisioning of services by means of flexible network deployment. In this regard, one promising system element of flexible network deployment to complement the existing heterogeneous networks (HetNets) is Vehicular Nomadic Nodes (VNNs). A VNN is a low-power access node which has a flexible backhaul, is movable, and activated temporarily to provide additional system capacity and/or coverage on demand. VNNs can be integrated into vehicles especially in urban areas, such as those of car sharing fleets or taxicab services. In this work, system-level performance of VNNs considering several flexible deployment scenarios is evaluated. Experiments are carried out separately in uplink (UL) and downlink (DL), where the performance of VNNs in terms of the user throughputs is compared with that of stationary picocells in a fixed HetNet, taking the macrocell- only deployment as the reference. The results show that flexible network deployment via VNNs is a promising enhancement to the current HetNets.

The need for 5G to adapt the radio access network to the spatial and temporal traffic variations makes the paradigm of moving networks essential. Dynamic network topology and moving cells through vehicular nomadic nodes (NN) will provide coverage extension and capacity improvement on demand as well as achieve reduced capital and operational expenditure when compared to fixed node deployment, such as microcells. Thus, it is of great importance to validate the envisioned performance of this paradigm change in a realistic scenario. To this end, this paper investigates the performance of NN operation in the context of a realistic multicellular wireless network, with the help of site-specific propagation modelling and real geographical databases. The results show that the NN operation can provide clear improvements relative to macrocell-only deployment and also propose the best values for the key systemic parameters that offer the optimum trade-off between throughput and complexity.

The design of an efficient radio access selection mechanism for 5G cellular networks is of paramount importance. Several proposals exist in the literature, but up to now the deployed systems are still using simple mechanisms mainly related to the evaluation of the RSS to make a handover decision. However, this is an inadequate solution for 5G networks. In this paper, we describe a novel multi-criteria handover scheme, we provide details on solutions for acquiring the necessary contextual information and we describe the algorithm to select the most appropriate RAT. Our solution is based on the use of fuzzy logic controllers for combining diverse inputs (such as a user's mobility, the load of the candidate base stations etc.) The efficiency of our mechanism is evaluated through appropriate simulations. The results related to throughput, delay and the number of the executed handovers clearly show the merits of our proposal when compared to a well-established LTE handover algorithm.

A cross-layer mechanism for the performance improvement of real-time applications over IEEE 802.16e networks is proposed. The mechanism coordinates i) adaptation capabilities at different layers of the protocol stack, and ii) the handover initiation procedure. It uses information from the physical (PHY) and medium access control (MAC) layers to determine the appropriate burst profile, transmission power level and media encoding rate for a connection, or initialize a handover. The main contribution of this mechanism is the integration of the handover initiation into an existing cross-layer logic mechanism to improve the overall system performance. Extensive simulation results show that the proposed design achieves significantly improved performance in terms of packet loss rate, power consumption, and throughput, as well as an increased system capacity.

Next generation mobile and wireless systems will enhance the operators' network management capabilities and will considerably improve the users' experience. However, these systems form a complex heterogeneous environment that calls for new management techniques targeting efficiency, robustness and adaptability. Cognition techniques as well as the ability for network components to act autonomously are considered as the main tools to achieve these goals. In this paper we present the functional architecture (FA) for the management and control of reconfigurable radio systems of the EU funded IP project called ¿E3 - End to End Efficiency¿ that has been designed to enhance existing procedures usually performed in traditional O&M systems (e.g., spectrum management, network planning, configuration actions etc). We present the rational of our design and provide specific examples to illustrate the role of the different functional entities and their interfaces. A considerable part of this architecture has been recently approved as a feasibility study by ETSI Reconfigurable Radio System (RRS).

A cross-layer mechanism to improve the performance of real-time applications over IEEE 802.16e metropolitan area networks is presented. The proposed mechanism uses channel quality and service quality information from the physical and medium access control layers, respectively, to determine the most suitable burst profile, transmission power level and media encoding rate for a connection, or even initialize a handover execution. The main contribution of this mechanism is the integration of the handover initiation into the cross layer logic, aiming to improve the overall system performance. Extensive simulation results show that the proposed mechanism offers significant performance improvement in terms of packet loss rate, power consumption, throughput, and system capacity.

The proliferation of WLANs and the ubiquitous coverage of cellular networks have resulted in several integration proposals towards 4G networks. Among them, the tight- coupled WLAN/UMTS architectures promise seamless service continuity to users and enhanced network performance. Most of these solutions assume that only one interface is active at a time, while much fewer consider the concurrent use of both WLAN and UMTS interfaces as this is expected to consume more energy. This paper presents a detailed description of power consumption for the two different tight-coupled WLAN/UMTS approaches based on the states of the wireless devices. A simple analytical model is provided for estimating the power consumption in each approach, while a simulation model measures the power needs for more complicated cases. Moreover, the enhancement due to a power-saving mechanism in WLAN is also assumed in the system and useful deductions are provided about the average power consumption per mobile terminal.

Radio resources management in integrated cellular and wireless networks is a very complex and important issue. Although a number of proposals exist in the literature that present considerable improvement in several aspects, they also present some disadvantages that affect their implementation and deployment. In an attempt to tackle this, we propose a simple distributed algorithm that enables terminals to build prioritised lists of target access network independently for each of their connections. The algorithm also provides specific details on how the core network components can treat each connection based on a number of parameters, which are of paramount importance for the operators. The final choice is a trade-off between the user preferences, the terminal capabilities, the network load and the location and speed of the terminal. The algorithm is designed to provide an easy method for defining user preferences. Finally, we provide an initial evaluation of the signalling load required inside the core network to support the proposed decision making mechanism and make suggestions on the best functional architecture of the radio resource management entities.

In this paper we propose and study a cross-layer mechanism that can improve real-time QoS provisioning over IEEE 802.16 metropolitan area networks. This mechanism utilizes information provided by the Physical and MAC layers and using a heuristic algorithm it derives new operational parameters for the Physical and Application layers, which can improve the performance of real-time applications. The main idea is to coordinate the adaptive modulation capability of the Physical layer and the multi-rate data-encoding capability of modern real-time applications in order to avoid inefficiencies caused by their independent operation. Simulations show that the proposed mechanism can assist 802.16 systems better adapt to frequent channel and traffic changes, leading to considerably reduced packet loss rates, especially under heavy traffic conditions.

The proliferation of wireless access technologies, mostly wireless LANs, along with the ubiquitous coverage of cellular networks, has spurred many researchers to consider schemes for integrated network provision. In overlaying network environments, flexible resource management and service continuity during handover play a crucial role in the quality-of-service seen by the user. This paper describes an integrated UMTS/WLAN architecture that manages to establish every connection in a mobile terminal through the most appropriate access network, based on both network policies and user preferences. Moreover, connections are handed over independently between UMTS and WLAN, aiming at seamless service continuity. A detailed simulation model is used to measure the performance of the proposed architecture against existing schemes

Abstract ‘Always Best Connected’ (ABC) is considered one of the main requirements for next generation networks. The ABC concept allows a person to have access to applications using the devices and network technologies that best suits his or her needs or profile at any time. Clearly, this requires the combination of a set of existing and new technologies, at all levels of the protocol stack, into one integrated system. In this paper, a considerable set of the technologies, that are expected to play a key role towards the ABC vision, are presented. Starting from a reference architecture, the paper describes the required enhancements at certain levels of a traditional protocol stack, as well as technologies for mobility and end‐to‐end Quality of Service (QoS) support. The paper concludes with a case study that reveals the advantages of the ABC concept. This article replaces a previously published version (Wireless Communications and Mobile Computing; 5(2): 175‐191. [DOI: 10.1002/wcm.207]). Retraction notice DOI: 10.1002/wcm.426 . Copyright © 2006 John Wiley & Sons, Ltd.

The development, delivery and management of mobile services are the subject of many research activities in both the academia and industry. The ultimate goal of these efforts is a dynamic environment that enables the delivery of situation-aware, personalized multimedia services over heterogeneous, ubiquitous infrastructures, commonly termed as systems beyond 3rd generation (3G). Reconfigurability and adaptability are key aspects of the mobile systems beyond 3G. Reconfigurable mobile systems and networks introduce additional requirements and complexity. Using the existing network control plane is inadequate for the realization of the reconfigurability process. Introducing a reconfiguration management plane is very important for the deployment of network/system wide reconfigurability. We intend to discuss the basic functionality of RMP and respective interrelations.

SIP is evolving as the dominant protocol for multimedia call control in IP networks and is expected to be widely deployed in the near future. Using SIP for supporting mobility in SIP-based networks appears as a very attractive alternative to mobile IP, taking advantage of existing SIP infrastructure and signaling, while avoiding duplication of functionality. However, existing proposals for supporting mobility with SIP are not efficient in handling micro-mobility and do not cater for all types of traffic. In this paper, we introduce hierarchical mobile SIP (HMSIP), for efficient micro-mobility management in SIP environments. HMSIP is a SIP-based scheme that builds on existing IP mobility protocols, aiming at integrating their key concepts in the most beneficial way. Our proposed scheme minimizes the handoff latency and the backbone signaling overhead, while catering for all types of traffic. Moreover, HMSIP can be effectively combined with micro-mobility schemes for QoS flows, producing, thus, a complete micro-mobility solution for SIP flows with QoS guarantees.

In the framework of the design of a flexible service provision platform for 3G systems and beyond, an integrated system for enabling advanced Charging, accounting and billing has been introduced. The CAB system is adaptive to VAS charging requirements and network/business environment concepts. Part of the system has been developed in the frame of IST-MOBIVAS project.

The provision of location-based services is expected to have essential impact in the competition among 3G network operators. To support the realization of this functionality the standard UMTS infrastructure will probably need to be supplemented with additional intelligent components. Furthermore, flexible location-based charging mechanisms have to be designed and deployed to allow subscribers to be charged with different rates, depending on their location and profiles. In this paper a proposed platform for location-aware service provision is introduced and the interactions among its constituent components for applying an efficient location-based charging scheme are discussed in detail.

Mobility and QoS provision are the two most important burdens to solve before IP becomes truly ubiquitous. Mobile IP and RSVP (resource reservation protocol) are the most visible proposals for those problems. Their interoperability, though, is inefficient. To ameliorate the compatibility problem and performance gap, we have proposed the introduction of the RSVP mobility proxy (see Paskalis, S. et al., "RSVP Mobility Proxy", Internet Draft, 2001; Workshop on Wireless Local Networks, 2001). We present a performance evaluation of our scheme versus the plain RSVP operation.

Mobile hosts utilize Mobile IP to retain connectivity, while roaming in various networks, and acquire new IP addresses through the mechanisms that Mobile IP supports. One of today's most demanding application requirements is QoS support. RSVP (resource reservation protocol), the protocol implementation of the IETF integrated services architecture (IntServ), cannot handle hosts that change their IP addresses during a connection lifetime, and thus, must re-establish any given reservation states. To overcome this limitation, we propose the adoption of a mobility management scheme, that maintains a single contact IP address throughout the mobility session. Furthermore, we introduce RSVP mobility proxy, an enhanced RSVP enabled border router to deal with QoS signaling at any mobility related network topology modification.

The introduction of ATM in wireless CPN environments (WATM) necessitates the design of mobility related protocols, since the existing versions of B-ISDN signalling (ITU-T Q.2931, ATMF UNI 3.1) do not provide the means for terminal mobility. Such protocols can be deployed either as extensions to the standard signalling capabilities or as individual solutions that have little or no impact on existing infrastructures (switches, signalling software, etc.). In this paper, after presenting a WATM architecture, we study the problem of the switching/rerouting of the signalling connections that need to be performed whenever a mobile terminal crosses cell boundaries (handover, location update). Registration and forward hard handover algorithms are proposed.

The introduction of ATM in wireless CPN environments (WATM) necessitates the design of mobility signaling protocols, since the existing versions of B-ISDN signaling do not support terminal mobility. These protocols can be deployed as overlay solutions that have little or no impact on existing infrastructures (switches, signaling software, etc.). We present a WATM architecture and discuss the design of a mobility management and control protocol (MMC). After presenting what procedures the protocol specifies for the forward handover scenario we provide simulation results related to the performance of the system.