Peter Stavroulakis

A novel approach in handover initiation for microcellular systems

A handover initiation algorithm based on signal level measurements and modelled as a composite binary hypothesis test is presented. The implementation of the algorithm is made by a neural network structure which allows fast response (compared to previous methods based on hysteresis margins) as well as adaptability to traffic conditions. Although traffic measurements performed by the base stations (BS) may, also, facilitate the decision for handover initiation, the final decision is made by the mobile terminal (MT), thus, leading to a mobile controlled handover (MCHO) strategy.<<ETX>>

Ant based probabilistic routing with pheromone and antipheromone mechanisms

Using the idea of probabilistic routing, calls in an ant based decentralized scheme are not routed according to the largest probabilities in the pheromone tables but randomly according to these probabilities. This principle can be particularly helpful in order to further minimize possible node congestion problems. An additional incorporation of the antipheromone mechanism in the operation of artificial ants helps in better biasing the network. This paper examines the behaviour of such a routing scheme using a proper set of suitable metrics. Copyright

Optimizing the QoS of high speed moving terminals in cellular networks

This paper presents a dynamic guard channel assignment technique based on a two-layer cellular architecture which optimizes the blocking probability performance of high-speed moving terminals (HSMT) and handoff calls of low-speed moving terminals (LSMT), in a congested urban area. The lower layer of the proposed architecture is based on a microcellular solution, for absorbing the traffic loads of LSMT. The higher layer is based on a macro-cell umbrella solution, for absorbing the traffic load of the HSMT. The results show that using the optimum number of channels and adjusting dynamically the number of guard channels in each layer, the blocking probability of the HSMT and the handoff blocking probability of LSMT is optimized having the minimum bad effect on the new call blocking probability of LSMT. Copyright

Anti-Jamming Transmitter Independent Radar Networks

A transmitter independent receiver network (TIRN) is a network of radar receivers that operates in an area without cooperating with a particular radar transmitter, but rather using transmitters of opportunity (TOA) in order to detect and track airborne, ballistic or surface targets. In this paper a brief vulnerability analysis is given in both the detection/tracking and the communication subsystems of such a network. Electronic Defense (ED) solutions and interference avoidance techniques are given. A TIRN is mostly based in silent (low emission) operation and redundancy techniques. It is briefly described in the introduction. In the following paragraphs dealing with jamming techniques and is discussed, for both the detection and communication subsystems, comparing the results with the classic radar equivalent where applicable. It is finally concluded that such a network less vulnerable than conventional radars in most cases and in some cases even detect possible jammer effectively, at a fraction of the cost of classic radar network.

Introduction to special issue on secure multimedia services

With the rapid development of communication technology, it becomes a reality to hear or watch anything, anywhere. Multimedia (image, video, audio, etc.) enriches human’s daily life, and various multimedia services attract more and more users, such as multimedia message services, color rings, mobile TV, IPTV, User Generated Content (UGC), p2p sharing, etc. However, its prosperity also attracts malicious attackers and abusers with different motivations, such as political reasons, illegal financial benefits, or simply to win a prestige reputation in the hacker community. The typical example is piracy, i.e., the original multimedia content is stolen and then redistributed to unauthorized users illegally, which causes great profit-losses to content producers or service providers. Solutions are needed to protect multimedia service systems. During the last decade, various techniques have been proposed to improve multimedia service systems’ security. For example, multimedia encryption is used for confidentiality protection of multimedia content, multimedia authentication for integrity detection, digital watermarking for ownership authentication or copy tracing, Conditional Access (CA) for access control, and Digital Rights Management (DRM) for copyright management, etc. In addition, in different networks, such as the Internet, 3G wireless, DVB-H and sensor network, different secure protocols and algorithms are required to provide system security. All these topics are in active development.

Efficient zero — Knowledge identification based on one way Boolean transformations

An innovative method for formulating non-linear, oneway Boolean transformations is presented. These transformations are used at the core of an efficient implementation of the theoretically strict concept of zero knowledge identification of users. This implementation uses oneway non-linear Boolean transformations instead of operations on large numbers as a means of reducing the computational overheads related to user authentication for legitimate users and computational systems, without compromising system security. The principles, related to user identification and authentication using Boolean functions, are first presented. The necessary properties of the Boolean functions required are hence determined. A procedure for formulating non-linear one-way Boolean transformations, suitable for use in the context of user identification and authentication is presented. The procedure is iterative and scalable. The steps comprising the procedure are analytically presented. A numerical example of the calculations involved is also given. The computational effort required for formulating one such function of average complexity that is suitable for a large variety of applications, is approximated analytically. The results of statistical experiments verifying the validity of the approximation are also presented. These calculations demonstrate that the proposed method can be feasibly applied, even the only available computational capability is derived from an ordinary personal computer.

Fuzzy-Neural Applications in Handoff

Handoff is a process of transferring a mobile station from one base station or channel, to another. The channel change due to handoff occurs through a change in a time slot, frequency band, codeword, or a combination of these, for time division multiple access (TDMA), frequency division multiple access (FDMA), code division multiple access (CDMA), or a hybrid scheme, respectively. The handoff process determines the spectral efficiency (i.e., the maximum number of calls that can be served in a given area) and the quality perceived by users. Efficient handoff algorithms cost-effectively preserve and enhance the capacity and Quality of Service (QoS) of communication systems.

Block truncation coding using neural network-based vector quantization for image compression

A new method is introduced by which a block truncation coder (BTC) is cascaded with a neural network-based vector quantizer (VQ). The proposed coder is very attractive for real time image transmission due to its simplicity and performance. It preserves important characteristics of the image, while cascading the BTC coder with a VQ results in high compression ratios of about 0.5 bpp without significantly increasing the coding time, due to fast coding look-up tables of the VQs. Additional advantages are fast codebook design and reduction of the codebook size required for a given reconstructed image quality.

Operability Aspects of a Transmitter - Independent Receiver Network Against Radar and Communication Jamming

A transmitter independent receiver network (TIRN) is a network of radar receivers that operates in an area without cooperating with a particular radar transmitter, but rather using transmitters of opportunity (TOA) in order to detect and track airborne, ballistic or surface targets. In this paper a brief vulnerability analysis is given in both the detection/tracking and the communication subsystems of such a network. Electronic defense (ED) solutions and interference avoidance techniques are given. A TIRN is mostly based in silent (low emission) operation and redundancy techniques. It is briefly described in the introduction. In the following paragraphs dealing with jamming techniques and is discussed, for both the detection and communication subsystems, comparing the results with the classic radar equivalent where applicable. It is finally concluded that such a network less vulnerable than conventional radars in most cases and in some cases even detect possible jammer effectively, at a fraction of the cost of classic radar network.

Technological and Legal Aspects of CIS

The Subject of Communication and Information Security (CIS) [38.1, 2], the transfer of accurate and uncompromised information as well as the secure transfer of information has become an international issue ever since 31 December 1999. The year 2000 scare, which has been coded as the Y2K scare, refers to what prominent scientists and business people feared that all computer networks and the systems that are controlled or operated by them could break down with the turn of the millennium since their synchronizing clocks could lose synchronization by not recognizing a number (instruction) with three zeros. A positive outcome of this scare was the creation of the various CERTS (Computer Emergency Response Teams) around the world which now work cooperatively to exchange expertise, information and are coordinated in case of major problems arise in the modern IT environment. The nucleus of this effort, initially, was the collaboration of the USA, UK and Australia by forming the first international CERT in order to cooperatively solve this type of problems. The terrorist attack in New York on 11 September 2001 caused this scare to become a permanent international nightmare. The international community responded quickly to face both fronts using sophisticated technology. One front being the transfer of reliable information via secure networks and the other being the collection of information about potential terrorists even via sophisticated surveillance and information collecting mechanisms. Now all people around the word live more or less under the impression that the whole world is nothing but a “Big Brother” living space and thus the need of the legal framework to protect them.