P. Stavroulakis

Technical University of Crete, La Canée, Crete, Greece

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Publications (32)17.55 Total impact

  • P. Stavroulakis, N. Farsaris, T.D. Xenos
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    ABSTRACT: 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.
    Signal Processing, Communications and Networking, 2008. ICSCN '08. International Conference on; 02/2008
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    N.J. Farsaris, P.P. Stavroulakis, T.D. Xenos
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    ABSTRACT: 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.
    Electromagnetic Compatibility and Electromagnetic Ecology, 2007 7th International Symposium on; 07/2007
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    NIKOS J. FARSARIS, THOMAS D. XENOS, PETER P. STAVROULAKIS
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    ABSTRACT: In certain naval and coast guard security operations a video must be transmitted from an aerial platform - aircraft, helicopter, unmanned aerial vehicle or airship - to a surface station in real time. In this paper the radio channel characteristics and the antenna systems needed are examined in order to achieve a robust direct communication channel with enough bandwidth between the airborne vehicle and the base station. Simulation and experimental work has shown that for a reliable operation, diversity (spatial or frequency) techniques must be used in order to achieve the most reliable link between a moving and a stationary platform over any terrain, and any troposphere conditions.
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    ABSTRACT: This paper presents a neural network model for routing in the space segment of a Satellite Personal Communication System. At first, a proper energy function is constructed from the constraints of the system, which are clearly indicated. The combinatorial nature of the problem is clearly shown and hence a properly modified Hopfield neural network can be easily applied to provide increased survivability and thus improve security.
    Proceedings of the International Conference on Wireless Communications and Mobile Computing, IWCMC 2006, Vancouver, British Columbia, Canada, July 3-6, 2006; 01/2006
  • Nikos J. Farsaris, Thomas D. Xenos, Peter P. Stavroulakis
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    ABSTRACT: A totally passive multistatic radar or Transmitter-Independent Receiver Network (TIRN) [1], can be defined as a number of independent bistatic receivers [2], connected to a communication network, in order to detect and track targets in their coverage area using the signal(s) of non-cooperative transmitter(s). In this paper, an Angle of Arrival (AOA) method of transmitter and target detection is investigated. Linear systems of equations are extracted, and then solved by recurrent Artificial Neural Networks (ANN) for detection and tracking of moving and ballistic targets. These linear systems are often over determined by using a redundant number of receivers in order to achieve a minimal false alarm probability and increase the survivability of the TIRN. Finally it is shown that practical ANN designs are attractive and simple solutions for an AOA based TIRN for moving target tracking purposes, combining fast and robust convergence, ease of design and construction and - in case of adequate redundancy - adequate survivability.
    Proceedings of the 9th WSEAS International Conference on Communications; 07/2005
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    ABSTRACT: 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.
    International Journal of Communication Systems 02/2004; 17(1). DOI:10.1002/dac.630 · 1.11 Impact Factor
  • G. Charalabopoulos, P. Stavroulakis, A.H. Aghvami
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    ABSTRACT: OFDM is regarded as a viable solution to combat the impact of frequency selective fading; however, the channel does not have flat amplitude over the entire bandwidth, thus channel equalization is still required at the receiver. Radial basis function (RBF) neural networks have been widely considered for channel equalization, since they offer certain advantages over conventional equalizer structures. In this paper, a novel RBF channel equalizer structure, which performs Bayesian estimation, is proposed for OFDM communication systems. The proposed equalizer structure is shown to outperform existing equalizers; it can therefore be considered as a better practical alternative for OFDM channel equalization.
    Global Telecommunications Conference, 2003. GLOBECOM '03. IEEE; 01/2004
  • G. Charalabopoulos, P. Stavroulakis, A.H. Aghvami
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    ABSTRACT: OFDM is regarded as the solution to channel distortion; however, the channel does not have flat amplitude and linear phase-response over the entire bandwidth, thus channel-equalization is still required at the receiver. In this paper three different alternatives for OFDM channel equalization are discussed: pre- post- and balanced equalization. In the zero-forcing (ZF) case, pre- and balanced equalization lead to better BER performances, at the expense of requiring accurate channel measurements and channel state information (CSI) at the transmitter. The results have been produced via simulation in a HIPERLAN/2 system.
    Vehicular Technology Conference, 2003. VTC 2003-Fall. 2003 IEEE 58th; 11/2003
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    ABSTRACT: 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 © 2003 John Wiley & Sons, Ltd.
    International Journal of Communication Systems 11/2003; 16(9):851-863. DOI:10.1002/dac.621 · 1.11 Impact Factor
  • Peter Stavroulakis
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    ABSTRACT: In this paper, an attempt has been made to provide an exposition of the results on interference suppression techniques developed at least over the last twenty years. Most of the relevant work over this period is included in Stavroulakis (Stavroulakis, Interference Analysis of Communication Systems. IEEE: New York, 1980; Stavroulakis, Wireless Local Loops. Wiley: London, 2001; Stavroulakis, Third Generation Mobile Telecommunication Systems. Springer: Berlin, 2001; Stavroulakis, Interference Analysis and Reduction for Wireless Communications. Artech House: London, 2002; Stavroulakis, Moorthy, Conference Records NTC '79, vol. 3, Washington, DC, 1979; 52.3.1–52.3.5). Interference suppression/cancelling techniques have followed exactly the path of the field of wireless communications over the years. The decade of the 1980s concentrated on techniques applicable mainly to satellite communications whereas the decade of the 1990s concentrated on techniques that provided solutions to mobile communication interference/fading problems. This survey will point out and explain the most fundamental contributions, which opened new directions in the field of interference suppression, and undoubtedly will provide a basis for new researchers for further contributions. Copyright © 2003 John Wiley & Sons, Ltd.
    International Journal of Satellite Communications and Networking 01/2003; 21(1):1 - 12. DOI:10.1002/sat.743 · 0.90 Impact Factor
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    Harilaos G. Sandalidis, Peter Stavroulakis
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    ABSTRACT: Chapter 3 describes fixed channel assignment schemes in cellular networks, with emphasis on recent heuristic algorithms that apply genetic algorithms, tabu search, neural networks, fuzzy logic and other heuristics in solving problems. Dynamic channel assignment, channel borrowing and hybrid channel assignment problems are also discussed.
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    ABSTRACT: Swarm intelligence is a new challenging branch of artificial life which takes advantage of the collective behaviour of animals with limited intellectual faculties (insects, flocking birds, schools of fish) to solve algorithmically complex problems. Recently a new routing method based on the way that ants are communicating with each other has been applied to solve routing problems in telecommunication networks. This paper examines the behavior of an ant based decentralised router using an adequate set of commonly acceptable and some newly introduced metrics.
    Soft Computing 08/2001; 5:313-317. DOI:10.1007/s005000100104 · 1.30 Impact Factor
  • I.S. Barbounakis, P. Stavroulakis, J. Gardiner
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    ABSTRACT: Various PSK modulations as well as minimum shift keying (MSK) have achieved great improvements in the signal-to-noise ratio by utilising the nonredundant error correction (NEC) technique. The cost for this improvement is neither an increase in bandwidth nor an increase in transmission power, but some extra complexity in the receiver. The receiver is only equipped with a bank of differential detectors and a simple error detection/correction circuit, whose complexity depends on the correction capability that the transmit-receive system must have. Here, it is proved that it is possible to differentially detect correlative, nonsymmetric continuous-phase frequency modulations such as tamed frequency modulation (TFM) with NEC receivers. TFM has not been used as much as MSK until now owing to its generation difficulties, but its main advantages of constant envelope and of very high spectrum efficiency make it a perfect candidate to work upon. Hence, TFM is first contaminated with additive white Gaussian noise and is subsequently detected through a single-error-correcting NEC receiver. Both the theoretical analysis and the computer simulations show that substantial error probability reduction is achieved over differentially detected TFM systems
    IEE Proceedings - Communications 07/2000; DOI:10.1049/ip-com:20000364 · 0.79 Impact Factor
  • Ioannis S. Barbounakis, Peter Stavroulakis, John Gardiner
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    ABSTRACT: Wireless local loop (WLL) denotes an access system that uses a wireless link to connect a subscriber's terminal station to the line terminating equipment (local exchange or distribution node) in place of conventional copper cable. Many technical advances in transceiver component design have managed to cut down the overall cost and increase the efficiency of wireless systems making them competitive for the local loop. The technical requirements of a WLL system vary according to the market segment, geographical area and services available or scheduled by the wireline counterpart. Hence, WLL is not described exclusively by a single technology but many technologies have been utilized as wireless local loop systems. These are cellular, cordless, satellite broadcasting or terrestrial microwave distribution technologies that were conceptualized for different market needs. The competition is going to be in service quality, data rate per channel and supplementary services such as videoconference, teleshopping, teleworking, Internet access, etc. However, given the availability of radio frequency spectrum, the declining cost, the speed of installation and the flexibility of technology, wireless local loop tends to become the prevalent solution in telephone network access provision. In this paper, we review the requirements of WLL systems and the technological innovations applicable to wireless transceivers. We also cover various multiple-access systems already implemented in other applications as candidates to offer WLL services. Copyright © 2000 John Wiley & Sons, Ltd.
    International Journal of Communication Systems 05/2000; 13(3):187-206. DOI:10.1002/1099-1131(200005)13:33.0.CO;2-C · 1.11 Impact Factor
  • I.S. Barbounakis, P. Stavroulakis, J.G. Gardiner
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    ABSTRACT: Cellular systems are characterized both by a great subscriber base and very limited frequency spectrum resources. Techniques such as frequency reuse, directional antennas, advanced speech and channel coding, power control etc. have been studied and proposed as solutions to increase the capacity. Modulations other than binary (GMSK) and quaternary (π/4-DQPSK) have not been widely adopted until lately. The most important reasons for this are the low signal-to-noise ratios encountered in the macrocells and the multipath fading, which may prove completely destructive for the signal. The receiver is consequently obstructed from recovering reliable amplitude and phase references resulting in irreducible error rates for highly efficient modulations such as QAM. With this paper, we attempt to introduce star QAM properly encoded at the transmitter. In addition, the adaptation of the star QAM to the requirements of the NEC receivers, already tested with MPSK modulations, opens new areas of applications that need higher efficiency. The performance improvement derived from Monte-Carlo simulations is a strong indication of what it is going to follow in the area
    Vehicular Technology Conference Proceedings, 2000. VTC 2000-Spring Tokyo. 2000 IEEE 51st; 02/2000
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    ABSTRACT: An efficient model for ATM routing in the IRIDIUM system is presented in this paper. The model tries to be as realistic as possible. A proper energy function is constructed from the constraints of the ATM routing concept which are clearly indicated. The combinatorial nature of the problem is clearly shown and a properly modified Hopfield neural network can be easily applied and give adequate solutions
    Vehicular Technology Conference Proceedings, 2000. VTC 2000-Spring Tokyo. 2000 IEEE 51st; 02/2000
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    ABSTRACT: Channel allocation schemes in a cellular network can be modeled as combinatorial optimization problems. Genetic algorithms (GAs) have been shown to be effective and robust tools in providing adequate solutions of such problems. This paper investigates the application of GAs to two common assignment strategies from the field of cellular communications: the dynamic (DCA) and the borrowing channel assignment (BCA). In both schemes, channel allocation is formulated as a discrete energy minimization problem and can be put in proper genetic representation. A computer simulation model examines the performance of the proposed GA-DCA and GA-BCA schemes for uniform and non-uniform traffic distributions under the effect of cochannel and adjacent channel interference constraints.
    Mathematics and Computers in Simulation 01/2000; 51(3):273-286. DOI:10.1016/S0378-4754(99)00123-8 · 0.86 Impact Factor
  • P. Stavroulakis, C.P. Kakkavas, H.G. Sandalidis
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    ABSTRACT: The study of image compression has been risen dramatically. Many new ideas have come out with impressive results. Since images can be regarded as two-dimensional signals with the independent variables being the coordinates of two-dimensional space, many digital compression techniques can be extended, for instance from one-dimensional signals. This paper presents the most used still and video image compression techniques
    Signal Processing Proceedings, 2000. WCCC-ICSP 2000. 5th International Conference on; 01/2000
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    ABSTRACT: Three established channel allocation schemes for cellular networks are compared using some commonly acceptable quality-of-service measures. These schemes assign channels on an efficient and robust heuristic technique, derived from the well known family of evolutionary algorithms, called combinatorial evolution strategy. Their performance is examined through a simulation using a realistic cellular network model
    IEE Proceedings - Communications 11/1999; DOI:10.1049/ip-com:19990434 · 0.79 Impact Factor
  • H G Sandalidis, P P Stavroulakis, J Rodriguez-Tellez
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    ABSTRACT: The demand for more efficient and fast channel allocation techniques in cellular systems increases day by day. Borrowing channel assignment (BCA) was introduced in the literature as a compromise between the classic fixed and dynamic channel allocation schemes. This paper examines the behavior of three heuristic BCA techniques based alternatively on a Hopfield neural network, an efficient evolutionary algorithm named combinatorial evolution strategy (CES) and a third heuristic which combines the basic advantages of the two above computational intelligence methods. By considering some specific assumptions that follows an ideal cellular mobile model, BCA is formulated as a combinatorial optimization problem. The above heuristics have been extensively applied to solve efficiently such problems in the past. Simulation results, derived for uniform and nonuniform traffic load conditions, are used to compare these BCA schemes each other as also with other well-established allocation techniques.
    IEEE Transactions on Neural Networks 02/1999; 10(1):176-81. DOI:10.1109/72.737504 · 2.95 Impact Factor