R. Nilavalan

Brunel University, अक्सब्रिज, England, United Kingdom

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Publications (96)33.17 Total impact

  • Source
    T Peter · R Nilavalan · S W Cheung
    Full-text · Dataset · Nov 2015
  • Source
    T. Peter · T. I. Yuk · R. Nilavalan · S. W. Cheung
    Full-text · Dataset · Nov 2015
  • [Show abstract] [Hide abstract] ABSTRACT: AODV and DSR are normally taken as a standard in reactive routing protocols for Mobile Ad-Hoc Network (MANETs). Both of these protocols are widely used in different applications of MANET because of their simple design and better performance. AODV does not provide optimal results in the scenarios where we have heavy traffic with large number of connections and higher routing load. In this paper, we have introduced a novel idea of “Reliability Factor” to determine reliable links between the intermediate nodes; based on this factor a reactive routing protocol is proposed, the simulation results of Reliability Factor Based Routing Protocol show that it outperforms AODV and SP-AODV in terms of better packet delivery fraction, routing load and end-to-end delay.
    No preview · Article · Mar 2015 · Wireless Personal Communications
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    [Show abstract] [Hide abstract] ABSTRACT: Long term evolution (LTE)-advanced was introduced as real fourth generation (4G) with its new features and additional functions, satisfying the growing demands of quality and network coverage for the network operators’ subscribers. The term muti-tier has also been recently used with respect to the heterogeneity of the network by applying the various sub-network cooperative systems and functionalities with self-organising capabilities. Using indoor short-range low-power cellular base stations, for example, femtocells, in cooperation with existing long-range macrocells are considered as the key technical challenge of this multi-tier configuration. Furthermore, shortage of network spectrum is a major concern for network operators which forces them to spend additional attentions to overcome the degradation in performance and quality of services in 4G HetNets. This study investigates handover between the different layers of a heterogeneous LTE-advanced system, as a critical attribute to plan the best way of interactive coordination within the network for the proposed HetNet. The proposed comprehensive handover algorithm takes multiple factors in both handover sensing and decision stages, based on signal power reception, resource availability and handover optimisation, as well as prioritisation among macro and femto stations, to obtain maximum signal quality while avoiding unnecessary handovers.
    Full-text · Article · Sep 2014 · IET Science, Measurement and Technology
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    Christos Chousidis · Rajagopal Nilavalan · Laurentiu Lipan
    [Show abstract] [Hide abstract] ABSTRACT: The growing need for multimedia applications within wireless Local Area Networks (LAN) demands reliable and efficient broadcasting and multicasting transmission of throughput sensitive data, like audio and video. IEEE 802.11 standard which is the primary technology in wireless LANs was not initially designed to handle heavy broadcasting traffic. However, this raises a series of reliability problems mainly related to the lack of an effective feedback mechanism for multicasting and broadcasting transmission. This inherited drawback does not allow the standard to take full advantage of the bandwidth offered by its latest amendments. The main aim of this work is to offer an alternative congestion control mechanism especially for broadcasting. For this, the expanding use of the CTS-to-Self protection mechanism is proposed. The Medium Access Control (MAC) algorithm is appropriately modified and tested under various data traffic conditions. The simulation shows that the use of this amended MAC method in conjunction with the suitable data packet size can significantly improve throughput, in multimedia type data broadcasting over wireless ad-hoc networks.
    Full-text · Conference Paper · Aug 2014
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    [Show abstract] [Hide abstract] ABSTRACT: A novel transparent ultra-wideband antenna for photovoltaic solar-panel integration and RF energy harvesting is proposed in this paper. Since the approval by the Federal Communications Committee (FCC) in 2002, much research has been undertaken on UWB technology, especially for wireless communications. However, in the last decade, UWB has also been proposed as a power harvester. In this paper, a transparent cone-top-tapered slot antenna covering the frequency range from 2.2 to 12.1 GHz is designed and fabricated to provide UWB communications whilst integrated onto solar panels as well as harvest electromagnetic waves from free space and convert them into electrical energy. The antenna when sandwiched between an a-Si solar panel and glass is able to demonstrate a quasi omni-directional pattern that is characteristic of a UWB. The antenna when connected to a 2.55-GHz rectifier is able to produce 18-mV dc in free space and 4.4-mV dc on glass for an input power of 10 dBm at a distance of 5 cm. Although the antenna presented in this paper is a UWB antenna, only an operating range of 2.49 to 2.58 GHz for power scavenging is possible due to the limitation of the narrowband rectifier used for the study.
    Full-text · Article · Mar 2014 · IEEE Transactions on Antennas and Propagation
  • M. Spasos · R. Nilavalan
    [Show abstract] [Hide abstract] ABSTRACT: This paper presents in detail the entire procedure of calculating the bias resistance of an ohmic RF-MEMS switch, controlled under resistive damping (charge drive technique). In case of a very stiff device, like the North Eastern University switch, the actuation control under resistive damping is the only way to achieve controllability. Due to the short switching time as well as the high actuation voltage, it is not practical to apply a tailored control pulse (voltage drive control technique). Implementing a bias resistor of 33 MΩ in series with the voltage source, the impact velocity of the cantilever has been reduced 80 % (13.2 from 65.9 cm/s), eliminating bouncing and high initial impact force during the pull-down phase. However, this results in an affordable cost of switching time increase from 2.38 to 4.34 μs. During the release phase the amplitude of bouncing has also been reduced 34 % (174 from 255 nm), providing significant improvement in both switching operation phases of the switch.
    No preview · Article · Dec 2013 · Microsystem Technologies
  • Christos Chousidis · Rajagopal Nilavalan
    [Show abstract] [Hide abstract] ABSTRACT: The increasing use of multimedia streaming applications in addition with advent of internet television and radio, demands from today's wireless networks to handle with reliability multiple broadcasting and multicasting sources. However, the way that 802.11 standard, which is the primary technology in wireless networking, handle this type of traffic raises a series of problems mainly related to the lack of an effective feedback mechanism [1]. This lack in turn, limits the capability of random backoff process to eliminate collisions and reduce reliability and fairness. This inherited drawback of the standard is affecting the way broadcast [2] and multicast traffic is transmitted as well as the overall performance of the network. In this paper initially we are highlighting the drawback of the IEEE 802.11 MAC algorithm in handling multiple stations “media type” data broadcasting in an ad-hoc wireless network [3]. Then, we propose two different approaches in alleviating these problems. The first approach is the simple linear increase of the contention window (CW) while the second propose a linear increase of the CW implementing an exclusive backoff number allocation (EBNA) algorithm. In addition we are modifying the 802.11 medium access control (MAC) algorithm to use the clear to send to self (CTS-to-Self) protection mechanism prior to every transmission. Both the above techniques are simulated and compared with the classic 802.11 MAC. The result sows that the overall performance of the network can be improved using these alternative MAC methods.
    No preview · Conference Paper · Oct 2013
  • Source
    Mohammadreza Behjati · John Paul Cosmas · Rajagopal Nilavalan
    Full-text · Conference Paper · Jun 2013
  • [Show abstract] [Hide abstract] ABSTRACT: An Electron Beam Welding power-source was analyzed using system modeling techniques for implementing hardware changes. Fault recovery control circuits for flashover detection and system stability were analyzed. Simulation results obtained revealed the possibility of enhancing the system and further work is required to implement the identified parameters in the real hardware for welding trials.
    No preview · Conference Paper · May 2013
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    Christos Chousidis · Rajagopal Nilavalan
    [Show abstract] [Hide abstract] ABSTRACT: Multimedia applications over wireless networks have dramatically increased over the past years. Numerous new devices and applications that distribute audio and video over wireless networks are introduced every day and all of them demands a reliable and efficient wireless standard. Either operating as independent ad-hoc networks or as terminal parts of wired networks or the internet, wireless networks are frequently facing the need to broadcast multimedia data from multiple sources to multiple users. IEEE 802.11 standard (Wi-Fi) is the primary technology in wireless networking today. However, it has some inherited problems when it comes to broadcasting caused mainly by the lack of an acknowledgment mechanism. These problems do not allow the standard to take full advantage of the bandwidth offered by its latest amendments. In this paper two independent modifications of the medium access control (MAC) mechanism of the standard, are proposed along with the expanded use of the CTS-to-Self protection mechanism. The main objective of this study is to explore the ability of the modified MAC mechanisms to improve broadcasting performance while are operating in conjunction with a regular wireless network, and also to define the cases were the use of CTS-to-Self-protection mechanism can improve the overall performance of the network. The results show that the overall performance can be improved using these alternative MAC methods. Also, the cases where the CTS-to-Self technique can additionally contribute to the network performance are defined and analyzed.
    Full-text · Article · Jan 2013 · International Journal of Computer Science and Applications
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    [Show abstract] [Hide abstract] ABSTRACT: In this letter, the design of a compact monopole antenna for multiband and wideband operations is proposed. The antenna has three distinct frequency bands, centered at 0.94, 2.7, and 4.75 GHz. The antenna has a compact size of only 30$\,\times \,$ 40$\,\times \,$ 1.57 mm$^{3}$ including the ground plane. The multiband and wideband operations are achieved by using an E-shaped slot on the ground plane. The design procedure is also discussed. The frequency bands can be independently controlled by using the parameters of the E-slot. The impedance bandwidth, current distributions, radiation patterns, gain, and efficiency of the antenna are studied by computer simulation and measurements.
    Full-text · Article · Dec 2012 · IEEE Antennas and Wireless Propagation Letters
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    [Show abstract] [Hide abstract] ABSTRACT: This paper presents the design of a low-profile compact printed antenna for fixed frequency and reconfigurable frequency bands. The antenna consists of a main patch, four sub-patches, and a ground plane to generate five frequency bands, at 0.92, 1.73, 1.98, 2.4, and 2.9 GHz, for different wireless systems. For the fixed-frequency design, the five individual frequency bands can be adjusted and set independently over the wide ranges of 18.78%, 22.75%, 4.51%, 11%, and 8.21%, respectively, using just one parameter of the antenna. By putting a varactor (diode) at each of the sub-patch inputs, four of the frequency bands can be controlled independently over wide ranges and the antenna has a reconfigurable design. The tunability ranges for the four bands of 0.92, 1.73, 1.98, and 2.9 GHz are 23.5%, 10.30%, 13.5%, and 3%, respectively. The fixed and reconfigurable designs are studied using computer simulation. For verification of simulation results, the two designs are fabricated and the prototypes are measured. The results show a good agreement between simulated and measured results.
    Full-text · Article · Aug 2012 · IEEE Transactions on Antennas and Propagation
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    M. Spasos · N. Charalampidis · K. Tsiakmakis · R. Nilavalan
    [Show abstract] [Hide abstract] ABSTRACT: The analysis, design and simulation of a novel easy to control all-metal in-line-series ohmic RF MEMS switch is presented, for applications where the operating frequency ranges from DC to 4GHz. The proposed switch, due to its unique shape and size, assures high isolation and great linearity fulfilling the necessary requirements as concerns loss, power handling and power consumption. Simplicity has been set as the key success factor implying robustness and high fabrication yield. On the other hand, the specially designed cantilever-shape (hammerhead) allows distributed actuation force ensuring high controllability as well as reliability making the presented RF MEMS switch one of its kind. KeywordsOhmic RF MEMS switch–Simplicity–Controllability–Reliability
    Full-text · Article · Apr 2012 · Analog Integrated Circuits and Signal Processing
  • [Show abstract] [Hide abstract] ABSTRACT: AbstractA small ultra‐thin planar inverted‐F antenna (PIFA) which can be switchable or tunable using PIN or varactor diodes, respectively, is proposed. The antenna consists of two radiators and connected together using two PIN or varactors diodes. Frequency reconfigurability is obtained by (i) tuning using varactor diodes or (ii) switching using PIN diodes. In the study, when varactors are used, the PIFA is optimized to operate in five frequency bands centered at 0.72, 1.35, 1.98, 3.6, and 5 GHz. Varying the voltages across the varactors can tune these five bands over the range of 45.33% (0.58–0.92 GHz), 17.77% (1.23–1.47 GHz), 26% (1.57–2.04 GHz), 6.66% (3.48–3.72 GHz), and 0.97% (4.99–5.04 MHz), covering the DVB‐H, GSM 800/900, GPS, PCS, DCS, UMTS, Wibro phase III, WiMAX, WLAN systems, etc. If PIN diode switches are used instead, the frequency bands can be switched among different standards, including the DVB‐H, GSM, UMTS, DCS, GPS, WiMAX, and WLAN systems, depending on the switching states. The two radiators are supported using a shorting wall and a shorting pin connected to a small ground plane. Results of intensive investigations using computer simulations and measurements show that the ground plane size has little effects on the performance of the antenna. The effects of user's hand on the S11, radiation patterns and efficiency are also characterized. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:725–729, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26640
    No preview · Article · Mar 2012 · Microwave and Optical Technology Letters
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    [Show abstract] [Hide abstract] ABSTRACT: A reconfigurable wideband and multiband C-Slot patch antenna with dual-patch elements is proposed and studied. It occupies a compact volume of 50 × 50 × 1.57 (3925 mm<sup>3</sup>), including the ground plane. The antenna can operate in two dual-band modes and a wideband mode from 5 to 7 GHz. Two parallel C-Slots on the patch elements are employed to perturb the surface current paths for excitation of the dual-band and the wideband modes. Two switches, implemented using PIN diodes, are placed on the connecting lines of a simple feed network to the patch elements. Dual-band modes are achieved by switching “ON” either one of the two patch elements, while the wideband mode with an impedance bandwidth of 33.52% is obtained by switching “ON” both patch elements. The frequencies in the dual-band modes can be independently controlled using positions and dimensions of the C-Slots without affecting the wideband mode. The advantage of the proposed antenna is that two dual-band operations and one wideband operation can be achieved using the same dimensions. This overcomes the need for increasing the surface area normally incurred when designing wideband patch antennas. Simulation results are validated experimentally through prototypes. The measured radiation patterns and peak gains show stable responses and are in good agreements. Coupling between the two patch elements plays a major role for achieving the wide bandwidth and the effects of mutual coupling between the patch elements are also studied.
    Full-text · Article · Feb 2012 · IEEE Transactions on Antennas and Propagation
  • H.F. Abutarboush · R. Nilavalan
    [Show abstract] [Hide abstract] ABSTRACT: A reconfigurable antenna based on E-shaped structure with bandwidth controlled is proposed in this paper. The bandwidth of the antenna can be increased and controlled from 3.4% to 23% by varying the capacitance of the varactor diodes. The bandwidth can cover the frequency range from 1.85 GHz-2.33 GHz. The antenna consists of four E-Shaped connected to 50 ohm GCPW line, varactor diodes and 10 pF ship capacitances. The total size of the antenna is 80×80mm2. The performances of the proposed antenna, in terms of return losses and radiation patterns, with different DC bias voltages across the varactor diode, have been studied using computer simulation and measurement. Simulated and measured results are in good agreements.
    No preview · Article · Jan 2012
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    T Peter · R Nilavalan · S W Cheung
    [Show abstract] [Hide abstract] ABSTRACT: A novel transparent Tapered Slot Antenna is proposed in this paper. Since the approval by the FCC in 2002, much research has been undertaken on UWB especially for wireless communications. Often times especially for devices where internet services are required, UWB is complemented with the 2.4 GHz WLAN service like in Laptops or notebooks instead of being filtered out. In this paper, a transparent Tapered Slot Antenna (TSA) covering the frequency range from 2.1 GHz to 10.8 GHz is designed and fabricated using AgHT-8 for use in Laptop applications. The antenna provides sufficient gain, reasonable efficiency and a good return loss.
    Full-text · Article · Jan 2012
  • [Show abstract] [Hide abstract] ABSTRACT: Radio over Fiber (RoF) technology uses optical fiber links to distribute RF signals from a central station to multiple remote access units due to its ability to provide simple antenna front ends, increased capacity, and multi radio wireless access coverage. In this paper, an All-photonic Digital Radio over Fiber (DRoF) architecture is proposed and its performance is individually investigated in a dedicated and an integrated fiber link and compared with an Analog Radio over Fiber (ARoF) and Baseband over Fiber communication systems. Link's performance is investigated in the presence of other channels interference and Mode-locked Laser Diode pulse trains with about overall 1 picoseconds timing jitter. Simulation results proved that the proposed All-Photonic DROF is a suitable candidate for very high sampling rate of the digital optical links and is more robust against channel interferences than Analog Radio over Fiber (ARoF).
    No preview · Conference Paper · Nov 2011
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    [Show abstract] [Hide abstract] ABSTRACT: This study presents an H-shaped reconfigurable antenna for wireless applications. The antenna consists of an H-shape radiator and a CPW printed on a circuit board and a varactor diode connecting the upper and lower arms of the H-shape radiator for reconfigurability. The uniqueness of the antenna lies on the ability to select the operating mode and frequencies electronically using a varactor diode. By selecting the DC-bias voltages of 11.5, 10 and 8 V across the varactor diode, which in turn selects the corresponding varactor capacitances of 2, 4 and 6 pF, the antenna can be controlled to operate in three different modes, namely a single-band mode to cover the GSM1900, a dual-band mode at 1.88 and 2.4 GHz to cover the GSM1900 and Bluetooth/WLAN, respectively and a tri-band mode at 1.57, 1.88 and 2.4 GHz to cover the GSM1900, WLAN and GPS, respectively. Furthermore, by varying the varactor capacitance from 7 to 13 pF, the GPS and WLAN bands can be tuned by 11.44% (1.57-1.4 GHz) and 6.46% (2.4-2.25 GHz), respectively, yet keeping the 1.88-GHz band unchanged. Detailed studies on the antenna's performance are carried out to investigate the behaviour of the antenna at each resonant frequency in each operating mode.
    Full-text · Article · Nov 2011 · IET Microwaves Antennas & Propagation

Publication Stats

697 Citations
33.17 Total Impact Points

Institutions

  • 2006-2014
    • Brunel University
      • • School of Engineering and Design
      • • Department of Electronic and Computer Engineering
      अक्सब्रिज, England, United Kingdom
  • 2011
    • The University of Hong Kong
      • Department of Electrical and Electronic Engineering
      Hong Kong, Hong Kong
  • 1998-2007
    • University of Bristol
      • Department of Electrical and Electronic Engineering
      Bristol, England, United Kingdom
  • 2005
    • Technical University of Denmark
      København, Capital Region, Denmark