Marios Hadjinicolaou

Brunel University, अक्सब्रिज, England, United Kingdom

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Publications (27)7.57 Total impact

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    ABSTRACT: This work presents applications of an inductive topological approach in the calculation of the transfer function of a cascading network control system. The method provides a very versatile and effective way of counting all the graphs that contribute and of translating them into their algebraic contribution. The contributing graphs are very simple and reflect the morphology of the original control system signal flow graph. Application of the method and results are presented for an n-cell RC network. We derive an analytical formula relating ω(3 dB) to the filter size (n) and R j C j (j=1,2,…,n). This formula can be used for designing preset frequency range self-loaded LP filters by varying their size. We also derive general expressions for the sensitivities which we use to observe a sensitivity-insensitivity filter transition for various frequency ranges, relaxation times, and, most importantly, filter sizes.
    Circuits Systems and Signal Processing 01/2013; · 0.98 Impact Factor
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    C. Zarakovitis, Qiang Ni, D. Skordoulis, M. Hadjinicolaou
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    ABSTRACT: Reducing power consumption subject to quality-ofservice (QoS) provisions is a critical task for next-generation networking. Recent research in resource management for orthogonal frequency-division multiple-access (OFDMA) systems has generally assumed the availability of perfect channel state information at the transmitter (CSIT) or imperfect CSIT with small uncertainty. Nevertheless, such approaches deliver resource scheduling strategies with high transmitting power because, in real environments, large channel feedback delays and estimation errors cause high CSIT imperfectness. Furthermore, most existing works treat various QoS requirements frommobile users as homogenous, although they are heterogeneous in nature. In this paper, we address these issues by proposing a new power-efficient adaptive error-tolerant cross-layer scheduling scheme for OFDMA systems (PE-AETS). Our target is to minimize the transmitting power by considering heterogeneous QoS requirements and data outage due to imperfect CSIT. The proposed scheme adopts a robust power-bit loading (PBL) method that adjusts power and data rates across subcarriers with increased system resilience to channel errors.We develop a statistical queuing model to express the delay limitation of each user with an equivalent cross-layer constraint, and we apply subcarrier time-sharing relaxation to formulate a convex optimization problem. Finally, we utilize Lagrangian optimization to propose a joint power and subcarrier allocation policy with guaranteed convergence to optimal solutions and linear complexity. Various simulation scenarios confirm the superior performance of the proposed PE-AETS over relevant cross-layer approaches.
    IEEE Transactions on Vehicular Technology 02/2012; 61(2):781-798. · 2.06 Impact Factor
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    Qiang Ni, Ling Hu, A. Vinel, Yang Xiao, M. Hadjinicolaou
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    ABSTRACT: WiMAX networks have received wide attention as they support high data rate access and amazing ubiquitous connectivity with great quality-of-service (QoS) capabilities. In order to support QoS, bandwidth request (BW-REQ) mechanisms are suggested in the WiMAX standard for resource reservation, in which subscriber stations send BW-REQs to a base station which can grant or reject the requests according to the available radio resources. In this paper we propose a new analytical model for the performance analysis of various contention based bandwidth request mechanisms, including grouping and no-grouping schemes, as suggested in the WiMAX standard. Our analytical model covers both unsaturated and saturated traffic load conditions in both error-free and error-prone wireless channels. The accuracy of this model is verified by various simulation results. Our results show that the grouping mechanism outperforms the no-grouping mechanism when the system load is high, but it is not preferable when the system load is light. The channel noise degrades the performance of both throughput and delay.
    IEEE Systems Journal 01/2011; · 1.27 Impact Factor
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    ABSTRACT: This paper presents an inductive topological ap- proach in the calculation of the transfer function of a cascading network control system. The method provides a very versatile and effective way of counting all the graphs that contribute and of translating them into their algebraic contribution. The contributing graphs are very simple and reflect the morphology of the original control system signal flow graph. Application of the method and results are presented for an n-cell RC-network.
    01/2011;
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    ABSTRACT: In this paper, a queue aware game theoretic cross-layer scheme is introduced for multiuser orthogonal frequency division multiple access (OFDMA) wireless systems. A joint scheduling process that combines an adaptive modulation (AM) at the physical layer (PHYL) along with a discrete Markov modulated Poisson process (dMMPP) at the medium access control (MAC) layer, is devised. Moreover, relied on this cooperative game theoretic architecture, we formulate an optimization problem on a Nash bargaining solution (NBS) basis. Finally, the allocation policies result an optimal tradeoff between proportional fairness and throughput maximization that fits in realistic wireless networks scenarios.
    Computer and Information Technology (CIT), 2010 IEEE 10th International Conference on; 08/2010
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    ABSTRACT: The key issues in the design of a cross-layer optimization scheme for multiuser orthogonal frequency multiple access (OFDMA) systems are the optimal subcarrier, bit and rate distribution policies. In many recent researches, these allocation strategies are derived either through dynamic programming or via mathematical analysis. When the latter option is available, an additional iterative process is needed for the final solution to be obtained. This paper includes performance comparisons between the analytical and the numerical techniques as well as assessments on which of the existing iterative methods exhibits the highest effectiveness. Deductively, relying on system's evaluations, the semi-implicit root (SIR) mechanism produces the highest rapidity, precision and stability, in terms of convergence rate, root's accuracy and number of iterations.
    10th IEEE International Conference on Computer and Information Technology, CIT 2010, Bradford, West Yorkshire, UK, June 29-July 1, 2010; 01/2010
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    Vijay Sahota, Maozhen Li, Marios G. Hadjinicolaou
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    ABSTRACT: Information services play a crucial role in grid computing environments in that the state information of a grid system can be used to facilitate the discovery of resources and services available to meet user requirements and help tune the performance of the grid. This article models PIndex, which is a grouped peer-to-peer network with Colored Petri Nets CPNs for scalable grid information services. Based on the CPN model, a simulator is implemented for PIndex simulation and performance evaluation. The correctness of the simulator is further verified by comparing the results computed from the CPN model with the results generated by the PIndex simulator.
    IJGHPC. 01/2010; 2:51-68.
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    ABSTRACT: For the first time, a complete wireless and mobile emergency TeleOrthoPaedics system with field trials and expert opinion is presented. The system enables doctors in a remote area to obtain a second opinion from doctors in the hospital using secured wireless telecommunication networks. Doctors can exchange securely medical images and video as well as other important data, and thus perform remote consultations, fast and accurately using a user friendly interface, via a reliable and secure telemedicine system of low cost. The quality of the transmitted compressed (JPEG2000) images was measured using different metrics and doctors opinions. The results have shown that all metrics were within acceptable limits. The performance of the system was evaluated successfully under different wireless communication links based on real data.
    IET Communications 09/2009; · 0.72 Impact Factor
  • Maozhen Li, Marios Hadjinicolaou
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    ABSTRACT: Collaborative learning an educational strategies that should be incorpored in all plan of studies in the university careers. It is considered as one of the main learning strategies in the Bologna process. In collaborative practices students are divided ...
    Proceedings of the 5th WSEAS/IASME international conference on Engineering education; 07/2008
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    A Gravalos, M Hadjinicolaou, Q Ni, R Nilavalan
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    ABSTRACT: A novel scheme using spatial data stream multiplexing (SDSM) in the upcoming multiple-input multipleoutput (MIMO)-based IEEE 802.11n physical layer is proposed. It is shown that with SDSM, the same data rate can be achieved by using less number of transmit and receive antennas and therefore this scheme can reduce the number of antennas which results in reducing mutual coupling effects, hardware costs and implementation complexities. The maximum data rates that can be achieved using a 2 * 2 MIMO system is 270 Mbps and for a 4 * 4 MIMO system is 540 Mbps. The same data rates can be achieved using the SDSM technique which reduces the 2 * 2 MIMO system to 1 * 1 SISO system and the 4 * 4 MIMO system to a 2 * 2 MIMO system.
    IET Communications 01/2008; · 0.72 Impact Factor
  • Marios G. Hadjinicolaou, Kostas E. Psannis, Yutaka Ishibashi
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    ABSTRACT: This paper presents an efficient approach for supporting wireless video full interactive services. One of the main goals of wireless video multicast services is to provide priority including dedicated bandwidth, controlled jitter (required by some real-time and interactive traffic), and improved loss characteristics. The proposed method is based on storing multiple differently encoded versions of the normal/interactive video streams at the server. The corresponding video streams are obtained by encoding the original uncompressed video file as a sequence of I-P(I) frames and I-P(M) frames using different GOP (Group Of Pictures) pattern. Mechanisms for controlling the normal/interactive request are also presented and their effectiveness is assessed through extensive simulations. Wireless normal/interactive video services are supported with considerably reduced additional delay and acceptable visual quality at the wireless client-end.
    Proc SPIE 09/2007;
  • Kostas Psannis, Marios Hadjinicolaou, Yutaka Ishibashi
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    ABSTRACT: In this paper, we present an efficient method for supporting wireless video multicast services. The method is based on storing multiple differently encoded versions of the video stream at the server. The corresponding video streams are obtained by encoding the original uncompressed video file as a sequence of I-P(I) frames using different GOP pattern. Mechanisms for controlling the multicast service request are also presented and their effectiveness is assessed through simulations. Wireless multicast video services are supported with considerably reduced additional delay and acceptable visual quality at the wireless client –end.
    06/2007: pages 205-210;
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    A.G. Gravalos, M.G. Hadjinicolaou, Qiang Ni
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    ABSTRACT: The main focus of current research and development for the next-generation wireless local area network (WLAN) communication systems is to enhance the link throughput and channel capacity. In this paper, the performance analysis of the ongoing next-generation WLAN standard, IEEE 802.11n high throughput WLAN PHY layer is presented. The design criteria is based on a 4times4 MIMO-OFDM scheme using 64-QAM (quadrature amplitude modulation) technique under Rayleigh frequency-selective fading and flat fading channels. Simulation results show that a significant performance gain, 4-7 dB, depending on the channel selection, can be achieved when 1/2 space-time block code (STBC) rate is applied with respect to bit-error-rate (BER). Furthermore, performance gain of 7 dB is achieved when the 4times4 system using 1/2 STBC is compared with a 2times2 system using STBC code rate 1.
    Wireless Pervasive Computing, 2007. ISWPC '07. 2nd International Symposium on; 03/2007
  • Kostas E. Psannis, Yutaka Ishibashi, Marios G. Hadjinicolaou
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    ABSTRACT: This paper presents an efficient approach for supporting wireless interactive multimedia streaming services. One of the main goals of wireless video interactive services is to provide priority including dedicated bandwidth, controlled jitter (required by some real-time and interactive traffic), and minimum additional resources on the load on the server and the decoder complexity. The proposed method is based on storing multiple differently encoded versions of interactive video streams at the server. The corresponding video streams are obtained by encoding the original uncompressed video file as a sequence of I-P(M) frames using different GOP pattern. Mechanisms for controlling the interactive request are also presented and their effectiveness is assessed through extensive simulations. Wireless interactive video services are supported with a minimum of additional resources on the server load, network bandwidth, decoder complexity and acceptable visual quality at the wireless client end.
    Q2SWinet'07 - Proceedings of the Third ACM Workshop on Q2S and Security for Wireless and Mobile Networks, Chania, Crete Island, Greece, October 22, 2007; 01/2007
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    K.E. Psannis, M.G. Hadjinicolaou, A. Krikelis
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    ABSTRACT: In this paper, we present an efficient method for supporting full interactive functions of MPEG-2 video streaming. The method is based on storing multiple differently encoded versions of the video stream at the server. A normal version is used for normal playback, while several other versions are used for fast/slow/jump forward (rewind)/rewind at variable speedups. Full interactive functions are produced by encoding every Nth frame of the original uncompressed movie as a sequence of I-P(M) frames. Mechanisms for controlling the interactive streams are also presented and their effectiveness is assessed through extensive simulations. Traditional interactive functions are supported with a minimum of additional resources on the server/network bandwidth and decoder complexity.
    IEEE Transactions on Circuits and Systems for Video Technology 03/2006; · 1.82 Impact Factor
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    Kostas E. Psannis, Marios G. Hadjinicolaou
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    ABSTRACT: This paper presents an efficient method for supporting interactive media streaming in High Speed Downlink Packet Access (HSDPA) wireless channel. The corresponding normal/interactive video streams are obtained by encoding the original uncompressed video file as a sequence of I-P(I)-B(I) frames and I-P(I) frames respectively. Mechanisms for controlling the normal/interactive request are also presented and their effectiveness is assessed through simulations. Wireless media services are supported with acceptable visual quality at the wireless client - end
    01/2006;
  • Kostas Psannis, Marios Hadjinicolaou, Yutaka Ishibashi
    01/2006;
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    ABSTRACT: Many times there are refrigerators and chambers that need to be monitored from a distance. Many reasons may prevent the proper operation of the refrigerator and damage may be caused. A remotely configured, supervisory and data acquisition system for refrigerators is proposed. The design is based on an inexpensive, ultra low power 16-bit RISC microcontroller that implements as many as possible functionalities of the supervisory and data acquisition system. Different type of sensors to monitor the condition of the refrigerator and their interfaces are presented. Communication techniques are analyzed and different designs are presented for data transmission through the telephone line. A microprocessor based design, including hardware and algorithms, is explained. Efficient algorithms were elaborated and their running time on the processor is estimated. The design targets for a reliable and accurate system with reduced power consumption.
    01/2006;
  • I. Papadakis, H. Rigakis, M. Hadjinicolaou, E. Antonidakis
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    ABSTRACT: Vehicles need to monitor different parameters while traveling and report them to a Base Station. Many parameters do not have to be presented to the Base real time. This information can be communicated with RF when vehicle is in proximity with the Base. A protocol was designed targeted for this purpose and was mplemented using polling mechanism. Analysis and performance on the protocol is presented.
    Proceedings of the 9th WSEAS International Conference on Communications; 07/2005
  • K. Psannis, M. Hadjinicolaou
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    ABSTRACT: We address the problem of supporting interactive playout, both forward and backward, of MPEG-2 encoded video stream. Typically, the forward and backward operations are used mainly in the form of fast forward (FF) and fast backward or fast rewind (FR). The proposed approach is based on transmitting additional data of the same movie from the server to the digital storage device (DSD) in a client station. The server responses to FF/FR request by switching via the digital device from normal version to appropriate FF/FR version. The special additional data consists solely of I frames by removing the P and B frames and showing only the I frames. The alternative “interactive” data is generated from the storage at the server every n-th frame from the original MPEG-2 compressed video. Interactive operations are supported using extra network bandwidth than that is already allocated for normal playback. Specifically the server can decide the bit rate of the additional data, required for transmission to the digital device by varying the frame rate (number of I frames/sec), depending on the availability of the network bandwidth
    Intelligent Multimedia, Video and Speech Processing, 2001. Proceedings of 2001 International Symposium on; 02/2001