Nikos I. Passas

Media-independent handover for seamless service provision in heterogeneous networks

The performance of current Internet applications is based mainly on the capabilities of the underlying network technologies. Modern access systems usually can satisfy delay, loss, or bandwidth requirements; however, design inconsistencies can lead to service degradation as the terminals move across different systems. In this article, the focal point is the satisfaction of service requirements during mobility and more specifically, how the emerging IEEE 802.21 standard enables seamless, inter-technology handover. Based on prior work and a well-known example of seamless mobility, the main seamless mobility principles are identified and used as the basis for further evaluating the potential of the IEEE 802.21 standard to meet the requirements of applications for minimum disruption during an inter-technology handover.

Quality-of-service oriented medium access control for wireless ATM networks

The medium access control (MAC) protocol and the underlying traffic scheduling algorithm developed within project Magic WAND (Wireless ATM Network Demonstrator) are presented. Magic WAND is investigating wireless ATM technology for customer premises networks in the framework of the Advanced Communications Technologies and Services (ACTS) program funded by the European Union. The MAC protocol, known as MASCARA, is a hub-based, adaptive TDMA scheme which combines reservation- and contention-based access methods to provide multiple access efficiency and quality-of-service guarantees to wireless ATM terminal connections sharing a common radio channel. The traffic scheduling algorithm is delay-oriented to meet the requirements of the various traffic classes defined by the ATM architecture. The results of the simulation of a number of scenarios are presented to assess the performance of the proposed algorithm.

Mobility Management for Femtocells in LTE-Advanced: Key Aspects and Survey of Handover Decision Algorithms

Support of femtocells is an integral part of the Long Term Evolution - Advanced (LTE-A) system and a key enabler for its wide adoption in a broad scale. Femtocells are short-range, low-power and low-cost cellular stations which are installed by the consumers in an unplanned manner. Even though current literature includes various studies towards understanding the main challenges of interference management in the presence of femtocells, little light has been shed on the open issues of mobility management (MM) in the two-tier macrocell-femtocell network. In this paper, we provide a comprehensive discussion on the key aspects and research challenges of MM support in the presence of femtocells, with the emphasis given on the phases of a) cell identification, b) access control, c) cell search, d) cell selection/reselection, e) handover (HO) decision, and f) HO execution. A detailed overview of the respective MM procedures in the LTE-A system is also provided to better comprehend the solutions and open issues posed in real-life systems. Based on the discussion for the HO decision phase, we subsequently survey and classify existing HO decision algorithms for the two-tier macrocell-femtocell network, depending on the primary HO decision criterion used. For each class, we overview up to three representative algorithms and provide detailed flowcharts to describe their fundamental operation. A comparative summary of the main decision parameters and key features of selected HO decision algorithms concludes this work, providing insights for future algorithmic design and standardization activities.

ARROW: An Efficient Traffic Scheduling Algorithm for IEEE 802.11e HCCA

In this paper we present a novel traffic scheduling algorithm for IEEE 802.11e, referred to as ARROW (adaptive resource reservation over WLANs), which aims at providing improved performance for the support of multimedia traffic. The novel characteristic of this algorithm, compared to previous proposals, is that it performs channel allocations based on the actual traffic buffered in the various mobile stations, i.e., on the exact transmission requirements. This feature renders ARROW ideal for variable bit rate traffic. However, an enhancement is also presented that improves ARROW performance under constant bit rate traffic. The ARROW algorithm and its enhancement are discussed and evaluated against two other schedulers found in the open technical literature, namely the simple scheduler and SETT-EDD. Results from a detailed simulation model verify that ARROW provides much better channel utilization and considerably improved performance, in terms of mean delay and packet loss

Seamless continuity of real-time video across UMTS and WLAN networks: challenges and performance evaluation

This article addresses several challenges related to the evolution toward seamless interworking of wireless LAN and 3G cellular networks. The main objective is to evaluate the conditions and restrictions under which seamless continuity of video sessions across the two networks is feasible. For this purpose, we formulate a number of practical interworking scenarios, where UMTS subscribers with ongoing real-time video sessions hand over to WLAN, and we study the feasibility of seamless continuity by means of simulation. We particularly quantify the maximum number of UMTS subscribers that can be admitted to the WLAN, subject to maintaining the same level of UMTS QoS and respecting the WLAN policies. Our results indicate that the WLAN can support seamless continuity of video sessions for only a limited number of UMTS subscribers, which depends on the applied WLAN policy, access parameters, and QoS requirements. In addition to this study, we do address several other issues that are equally important to seamless session continuity, such as the QoS discrepancies across UMTS and WLAN, the vertical handover details, and various means of access control and differentiation between regular WLAN data users and UMTS subscribers. The framework for discussing these issues is created by considering a practical UMTS/WLAN interworking architecture.

A graph-coloring secondary resource allocation for D2D communications in LTE networks

The Long Term Evolution (LTE) system, and especially its current release, LTE-Advanced, is considered as the next step in mobile broadband networks. Two of the main challenges faced by the LTE system are: i) to offer ubiquitous and highly reliable wireless services, and ii) to efficiently utilize the assigned spectrum portion. A promising approach towards this direction is to allow the establishment of direct device-to-device (D2D) communications in the assigned spectrum. In this paper, we study how the traffic load between users located in the same cell (intra-cell communications) can be served by D2D transmissions utilizing uplink spatial spectrum opportunities. Aiming at decongesting the base station (or eNB) and letting more resources for the inter-cell traffic (e.g., web services) extra functionality is added to system users (or UEs) for providing interference information to eNB. The collected information is represented by an enriched node contention graph (eNCG) utilized by graph-coloring algorithms to provide an interference-free secondary allocation. Results show that spatial spectrum opportunities can sufficiently serve the intra-cell traffic, while increased data rates can be offered to the inter-cell traffic.

MAC protocol and traffic scheduling for wireless ATM networks

The Medium Access Control (MAC) protocol defined in the Wireless ATM Network Demonstrator (WAND) system being developed within the project Magic WAND is presented. Magic WAND is investigating extensions of ATM technology to cover wireless customer premises networks, in the framework of the Advanced Communications Technologies and Services (ACTS) programme, funded by the European Union. The MAC protocol, known as MASCARA, uses a dynamic TDMA scheme, which combines reservation‐ and contention‐based access methods to provide multiple access efficiency and quality of service guarantees to wireless ATM terminal connections sharing a common radio channel. The paper focuses on the description of PRADOS, a delay‐oriented traffic scheduling algorithm, which aims at satisfying the requirements of the various traffic classes defined by the ATM architecture. Simulation results are presented to assess the performance of the proposed algorithm in scheduling transmission of variable bit rate connections.

Traffic scheduling in wireless ATM networks

Wireless ATM is enjoying enormous research interest in the last few years, because of its ability to combine multimedia applications support, together with the freedom of mobility. One of the key design issues is the medium access control (MAC) protocol for the radio interface. This paper presents the traffic scheduling algorithm used in the MAC protocol of the Wireless ATM Network Demonstrator (WAND) system being developed within project Magic WAND. Magic WAND is investigating wireless ATM technology for customer premises networks in the framework of the Advanced Communications Technologies and Services (ACTS) programme, funded by the European Union. The proposed algorithm is delay oriented to meet the requirements of the various traffic classes defined by the ATM architecture. Simulation results are presented to assess the performance of the algorithm.

Centralized Resource Allocation for Multimedia Traffic in IEEE 802.16 Mesh Networks

The IEEE 802.16 standard provides a high degree of flexibility for setting up and operating wireless broadband networks in metropolitan environments. The standard supports numerous capabilities, including mesh topologies and multimedia communications. In this paper, we study these two features by investigating how efficiently an IEEE 802.16 mesh network can treat distributed multimedia traffic by providing differentiated quality of service (QoS). A key component of the system is the ldquoenhanced frame registry tree schedulerrdquo (E-FRTS) that provides QoS-aware resource allocation using a tree structure to prepare the creation of time frames and reduce processing requirements at the beginning of each frame. Simulation results show that distributed multimedia traffic can be efficiently supported in mesh 802.16 networks, provided efficient scheduling and a reasonable number of hops.

Enabling technologies for the 'Always Best Connected' concept

‘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