Liljana Gavrilovska

Device discovery in short-range wireless ad hoc networks

The performance of many envisioned applications in short-range wireless ad hoc networking will critically rely on the promptness of the self-configuring network procedures. In that sense, a fundamental problem in ad hoc networks, is device discovery and/or network initialization. We propose a randomized distributed algorithm for rapid device discovery during the deployment of an ad hoc network. The algorithm uses the approach of the non-blocked stack algorithm to resolve collisions, which ensures time-efficient execution when the number of devices in the network is large. The self-starting concepts used may be significant for inferring other self-configuring algorithms for ad hoc networks.

Performance evaluation of a SIP-based state-sharing mechanism

The Session Initiation Protocol (SIP) has been selected to manage sessions within the 3GPP IP-based multimedia subsystem (IMS). SIP sessions have to be highly available and reliable. This paper presents a performance evaluation of a novel state-sharing algorithm for providing reliable SIP services. The novelty is a result of sharing SIP (application-protocol) states as opposed to transport-protocol states. The most important performance parameters are evaluated in terms of the system variables such as server failure and repair time distributions, call arrival and call duration distributions, and link parameters, i.e., delay and bandwidth. The considered performance parameters are availability, reliability and dependability. Concerning the state transport mechanism, the results show that TFTP significantly outperforms FTP with respect to the overall performance.

Energy-efficient interference avoidance for interconnected Bluetooth personal area networks

A Bluetooth personal area network (PAN) supports wireless communications among devices within short range. Since PAN-devices are usually battery powered, the protocols applied in PAN should employ economic energy usage. Basic networking entity in Bluetooth is piconet and piconets can be interconnected into a scatternet. Since the piconets in scatternet are not mutually coordinated at the medium access layer, there is an interpiconet interference, which can seriously degrade the communication performance and cause energy wasting. In this paper we propose a distributed algorithm for interference avoidance in Bluetooth scatternets. The algorithm avoids collision by ensuring distributed consensus among piconets in case of concurrent transmission. The overhead introduced by the algorithm is low, while there are high gains in energy efficiency and throughput.

QoS-based policy for call admission control in mobile cellular network

This paper proposes a QoS-based strategy for call admission in mobile cellular networks, based on the past systems behavior. The algorithm is an extension of the conventional guard scheme (CGC) and demonstrates improvements compared to CGC. It reduces the new call blocking probability, increases the total carried traffic and keeps the forced call termination probability almost unchanged. The proposed policy falls into the class of fractional guard policies. Each cell builds cumulative statistics from its experience and accepts a new call only when predetermined handoff failure probability is not exceeded. The generic form of the algorithm is independent of cellular network topology.

Novel strategy for call admission control in mobile cellular network

This paper presents a novel history-based policy for call admission control (CAC) in mobile cellular networks, which is based on the statistics of the past systems behavior. This algorithm can be used as an extension of the conventional guard channel (CGC) scheme or it can perform independently of CGC. It shows improvements compared to CGC by reducing the new call blocking probability, increasing the carried traffic, while the forced call termination probability is kept almost constant. These results are confirmed via simulation of a one-dimensional system. The proposed policy is a fractional guard policy and introduces a variable threshold for guard channels. Each cell builds cumulative statistics from its operating history and accepts a new call only when predefined upper bound of handoff failure probability is not exceeded. A great advantage of this scheme stems from the fact that its generic form is independent of cellular network topology.

Technical work of the ICT-ACROPOLIS Network of Excellence in its first year

ICT-ACROPOLIS is a new Network of Excellence (NoE) supported by the European Commissions Framework Programme 7. This paper provides an overview of some of the technical work that has been performed in the ACROPOLIS NoE within its first year. Moreover, it highlights achievements in ACROPOLIS based around phases of the cognition cycle, and some initial inputs to standardization work and contacts with industry. Among the numerous technical achievements covered include methods for out-of-band emissions reduction in secondary NC-OFDM, means of cognitive radio beamforming to secondary users in various scenarios including multihop routing in cognitive radio networks, and pioneering applications for cognitive radio technologies such self organization and interference mitigation in femtocells. It should be noted, however, that this paper only selects some highlights of the work performed; it is not intended to be an exhaustive representation of the work in ACROPOLIS.

Distributed adaptive admission control in mobile multimedia network

There is a fast deploying of high-speed multimedia services in mobile cellular networks. Call admission control (CAC) is the most significant issue in quality of service (QoS) provisioning for these services. This paper proposes an adaptive CAC which demonstrates improvements compared to the upper limit (UL) scheme by reducing new call blocking probability, increasing the carried traffic, while the forced call termination probability is kept almost unchanged. A new call request is accepted if the estimated average handoff failure-to-attempt ratio of each traffic class in the cell is not greater than a corresponding predefined QoS value. The basic form of the algorithm is independent of cellular network structure.