R.M.A.P. Rajatheva

Asian Institute of Technology, Bangkok, Bangkok, Thailand

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Publications (72)12.11 Total impact

  • T. Sanguanpuak, R.M.A.P. Rajatheva
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    ABSTRACT: We consider a system of two user terminals, both of which are capable of acting as relay stations for each others. We consider a simple scenario where the user equipment that acts as an amplify-and-forward relay station tries to sell its data rate at some fixed price to the user equipment that acts as a source station. The benefit the source station receives is equal to the difference between the maximal ratio combining rate and the data rate it buys from the relay station, converted into a monetary value. The cost of cooperation for both the stations is reflected by their power consumption, which both of them want to reduce. This conflicting goal of increasing the revenue, while at the same time, decreasing the cost, by both the users, is studied using game theoretical modeling. The situation is modeled as a symmetric, two person bargaining game. The solution of such a game is unique and Pareto optimal. We derive the necessary and sufficient conditions for the bargaining solution, and obtain explicit solutions for the source and the relay transmit power. Lastly, we plot a graph of the dependence of transmit power on the pricing factor.
    Communications and Networking in China, 2009. ChinaCOM 2009. Fourth International Conference on; 09/2009
  • S. Guruacharya, R.M.A.P. Rajatheva
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    ABSTRACT: It is well known that, when the channel state information and noise power is perfectly known, the optimal power allocation policy is given by waterfilling procedure. In this paper, we derive the necessary and sufficient conditions for optimal power allocation policy under noise power uncertainty, and express it in terms of Hilbert transformation. A two step algorithm is developed to allocate power in such a case. We then examine the consequences of such a policy in multi user power allocation problem using non-cooperative game theory and show the existence of a unique, pure, and stable Nash equilibrium. For multi user case, an iterative approach is used to allocate power to each user in a distributive manner.
    Communications and Networking in China, 2009. ChinaCOM 2009. Fourth International Conference on; 01/2009
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    Y. Li, H. Minn, R.M.A. Rajatheva
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    ABSTRACT: This paper addresses preamble-based low complexity synchronization, channel estimation and equalization for Zero-padded (ZP) MB-OFDM based UWB systems. The proposed synchronization method consists of sync detection, coarse timing estimation, fine timing estimation, and oscillator frequency offset estimation. The distinctive features of MB-OFDM systems and the interplay between the timing and carrier frequency hopping at the receiver are judiciously incorporated in the proposed synchronization method. In order to apply the low complexity one-tap frequency-domain equalizer, the required circular convolution property of the received signal is obtained by means of an overlap-add method after the frequency offset compensation. The proposed low complexity channel estimator for each band is developed by first averaging the over-lapadded received preamble symbols within the same band and then applying time-domain least-squares method followed by the discrete Fourier transform. We develop an MMSE equalizer and its approximate version with low complexity. We also derive the probability density functions of the UWB channel path delays, and using them we present several optimization criteria for our proposed synchronization, channel estimation, and equalization. The effectiveness of our proposed methods and optimization criteria are confirmed by computer simulation results.
    IEEE Transactions on Wireless Communications 12/2008; · 2.42 Impact Factor
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    P. Chaturanga Weeraddana, R. M. A. P. Rajatheva, Hlaing Minn
    Proceedings of the 68th IEEE Vehicular Technology Conference, VTC Fall 2008, 21-24 September 2008, Calgary, Alberta, Canada; 01/2008
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    T. Jacobs, Y. Li, H. Minn, R.M.A.P. Rajatheva
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    ABSTRACT: This paper presents a preamble-based low complexity synchronization method for MB-OFDM based UWB systems. The proposed synchronization method consists of sync detection, coarse timing estimation, fine timing estimation, and oscillator frequency offset estimation. The distinctive features of MB-OFDM systems and the interplay between the timing and carrier frequency hopping at the receiver are judiciously incorporated in the proposed synchronization method. We also derive the probability density functions (pdfs) of the delays of the UWB channel paths which are used in optimizing our synchronization method. These pdfs are also useful in evaluating or optimizing the energy capture of other UWB systems. The effectiveness of our proposed synchronization method and optimization criteria are confirmed by computer simulation results.
    Communications, 2007. ICC '07. IEEE International Conference on; 07/2007
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    ABSTRACT: The research on distributed video coding (DVC) has been increasingly popular in recent times due to its promising features. DVC primarily has a modified complexity balance between the encoder and decoder, in contrast to conventional video codecs. In video communications over wireless channels, the noise and multipath fading effects have a significant effect on the perceptual video quality experienced at the decoder. However, it is noted that in all the research literature on DVC, an error-free ideal communication channel is assumed between the encoder and decoder. In this paper, we take into account the effects of noise and fading in a wireless channel on the performance of a DVC codec with necessary modifications to the decoding algorithm while proposing a higher order (4x4) MIMO based diversity scheme to take advantage of the multipath propagation effects to improve the performance. Simulation results show that the proposed DVC system outperform the state of the art H.264 video codec at low SNR levels.
    Electrical and Computer Engineering, 2007. CCECE 2007. Canadian Conference on; 05/2007
  • P.C. Weeraddana, R.M.A.P. Rajatheva
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    ABSTRACT: In this paper, we derive closed form bit error rate (BER) expressions for orthogonal frequency division multiplexing (OFDM) systems with residual carrier frequency offset (CFO). Several papers have been written treating CFO as a nonrandom parameter where as we consider it as a random variable in this study. The BER performance of binary phase shift keying (BPSK) OFDM system is analyzed in the cases of additive white Gaussian noise (AWGN), frequency flat and frequency selective channels. We further derive an expression for the BER in flat fading Rayleigh channels without the perfect channel state information (CSI) at the receiver. The simulation results are provided to verify the accuracy of the new BER expressions.
    Vehicular Technology Conference, 2007. VTC2007-Spring. IEEE 65th; 05/2007
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    K.D.P. Dharmawansa, R.M.A.P. Rajatheva, C. Tellambura
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    ABSTRACT: In this paper, we derive a new infinite series representation for the trivariate non-central chi-squared distribution when the underlying correlated Gaussian variables have tridiagonal form of inverse covariance matrix. We make use of the Miller's approach and the Dougall's identity to derive the joint density function. Moreover, the trivariate cumulative distribution function (cdf) and characteristic function (chf) are also derived. Finally, bivariate noncentral chi-squared distribution and some known forms are shown to be special cases of the more general distribution. However, non-central chi-squared distribution for an arbitrary covariance matrix seems intractable with the Miller's approach.
    Vehicular Technology Conference, 2007. VTC2007-Spring. IEEE 65th; 05/2007
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    ABSTRACT: In this paper, we derive new infinite series representations for the quadrivariate Nakagami-m distribution and cumulative distribution functions (cdf). we make use of the Miller's approach and the Dougall's identity to derive the joint density function. The classical joint density function of exponentially correlated Nakagami-m variables can be identified as a special case of our joint density function. Our results are based on the most general arbitrary correlation matrix possible. Moreover, the trivariate density function and cdf for an arbitrary correlation matrix is also derived from our main result. Bounds on the error resulting from truncation of the infinite series are also presented. Finally, numerical results are presented to verify the accuracy of our formulation.
    IEEE Transactions on Wireless Communications 01/2007; 6:4320-4328. · 2.42 Impact Factor
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    ABSTRACT: In this paper, we present a novel distributed video coding algorithm based on turbo trellis coded modulation (TTCM). As in the conventional turbo based Slepian-Wolf encoder, quantised information is applied to the TTCM encoder and parity bits are generated from both constituent encoders. However, TTCM symbols are not generated at the encoder since they are not sent to the decoder. Parity bits produced by the TTCM encoder are stored in a buffer and transmitted to the decoder upon request. TTCM symbols are generated at the decoder and these symbols are passed to the TTCM decoder for demodulation. Experimental results show that the proposed TTCM based codec can improve the PSNR by up to 6 dB at the same bit rate with less memory compared to the turbo coded distributed video codecs
    Image Processing, 2006 IEEE International Conference on; 11/2006
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    P. Kocharoen, K.M. Ahmed, R.M.A.P. Rajatheva, W.A.C. Fernando
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    ABSTRACT: In this paper, a new method for low bit-rate content-adaptive mesh-based video coding is proposed. Intra-frame coding of this method employs feature map extraction for node distribution at specific threshold levels to achieve higher density placement of initial nodes for regions that contain high frequency features and conversely sparse placement of initial nodes for smooth regions. Insignificant nodes are largely removed using a subsequent node elimination scheme. The Hilbert scan is then applied before quantization and entropy coding to reduce amount of transmitted information. For moving images, both node position and color parameters of only a subset of nodes may change from frame to frame. It is sufficient to transmit only these changed parameters. The proposed method is well-suited for video coding at very low bit rates, as processing results demonstrate that it provides good subjective and objective image quality at a lower number of required bits.
    IEEE Transactions on Consumer Electronics 06/2006; · 1.09 Impact Factor
  • C. Jittilertwirun, K.M. Ahmed, R.M.A. Premanandana Rajatheva
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    ABSTRACT: Bit error rate of two-user cooperation over the uplink scheme frequency selective Rayleigh fading channel is presented in this paper. The time division multiple access (TDMA) scheme and the half-duplex mode of transmission are assumed. The network architecture is defined as symmetrical structure. We analyze the bit error rate of BPSK two-user cooperation in various relaying protocols where the perfect channel state information is available at the receiver. The relaying protocols are considered as amplify-and-forward, decode-and-forward, selection, and incremental relaying. We investigated the effects of various interuser SNRs on the performance. The result shows that the higher interuser SNRs, the better bit error rate performance. From the bit error rate performance comparison of all relaying protocols illustrates that the incremental relaying protocol give the best performance. This is the result of limited feedback in the incremental relaying from the destination yield a great improvement on the system performance
    Systems and Control in Aerospace and Astronautics, 2006. ISSCAA 2006. 1st International Symposium on; 02/2006
  • A. H. M. Rezaul Karim, R. M. A. P. Rajatheva, Kazi M. Ahmed
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    ABSTRACT: Mobile Ad hoc networks (MANETs) are susceptible to several attacks due to their general infrastructureless scenario, dynamic topology and other characteristics. General security mechanisms that exist in wired network cannot be applied efficiently in MANET. In the current literature, there are many proposals for intrusion detection system (IDS) in MANET as a second defense. However, all such IDS suffer from performance penalties and high false alarm rates. In this paper we propose a collaborative IDS for MANET using Bayesian method. We use a set of very useful features which guarantee the effectiveness of the IDS and the Bayesian method improves the efficiency in the detection procedure. We expect it to be more versatile than other existing collaborative methods. Considering the protocol-independence of our method, it may be applied in any Ad hoc scenario.
    Proceedings of the 9th International Symposium on Modeling Analysis and Simulation of Wireless and Mobile Systems, MSWiM 2006, Terromolinos, Spain, October 2-6, 2006; 01/2006
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    ABSTRACT: Exact expression for the joint density of the trivariate Rician variables is not available in the open literature. In this paper, we derive new infinite series representations for the joint probability density function (pdf) and the joint cumulative distribution function (cdf) of three correlated Rician random variables. The cdf and chf of bivariate Rician density are also derived as special cases of the trivariate case. The most celebrated Millers approach is used here in deriving the trivariate Rician distribution . Bounds on the error resulting from truncating the infinite series are also presented.
    Proceedings of the 64th IEEE Vehicular Technology Conference, VTC Fall 2006, 25-28 September 2006, Montréal, Québec, Canada; 01/2006
  • Ieice Electronic Express. 01/2006; 3(8):178-183.
  • Vien Hoai Nam, R. M. A. P. Rajatheva
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    ABSTRACT: Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) techniques are applied to multiband ultrawideband (UWB) systems to obtain high rate communications over indoor wireless channels. In this paper, we setup a general scenario to investigate the performance of MIMO-OFDM multiband UWB systems without specific coding schemes. We also derive a lower bound of pairwise-error probability (PEP) of an (KNtNrL) system (K bandhopping, Nt transmit antennas, Nr receive antennas and L paths combined) in case of lognormal fading channel.
    Proceedings of the 64th IEEE Vehicular Technology Conference, VTC Fall 2006, 25-28 September 2006, Montréal, Québec, Canada; 01/2006
  • A. Rahman, K. M. Ahmed, R. M. A. P. Rajatheva
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    ABSTRACT: Waterways play a very important role in the transportation of any riverine country like Bangladesh. A safe and well-organized riverine transportation system can commence some significant impact of the economy of the country. In virtual cellular architecture more than one base station with antennas of different polarizations are placed under one control base station. Dedicated short range communications (DSRC) is a very well known technology for the communications between the moving vehicles and roadside fixed antennas. The validity of DSRC for the riverine communication environment in a cellular architecture gives some interesting outcomes. This paper represents the application of DSRC in a three-tier virtual cellular architecture to determine the optimum cell size for transport to riverside communication in riverine transport navigation systems.
    01/2006;
  • M.G.S. Sriyananda, R.M.A.P. Rajatheva
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    ABSTRACT: Not Available
    Vehicular Technology Conference, 2005. VTC-2005-Fall. 2005 IEEE 62nd; 10/2005
  • P. Dharmawansa, R.M.A.P. Rajatheva
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    ABSTRACT: Not Available
    Vehicular Technology Conference, 2005. VTC-2005-Fall. 2005 IEEE 62nd; 10/2005
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    P. Kocharoen, K.M. Ahmed, R.M.A.P. Rajatheva, W.A.C. Fernando
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    ABSTRACT: In this paper, a new procedure for generating a mesh structure of image representation has been proposed. The proposed algorithm employs a feature map extraction with a specific threshold level to place initial nodes densely in regions that contain high frequency features and nodes are placed coarsely in smooth regions. After that, many insignificant nodes are removed using node elimination scheme. The proposed algorithm is well suited for usage at very low bit-rate image and video coding as processing results have demonstrated that it provides a good subjective and objective image quality at a lower number of required nodes. Moreover, comparison shows that the proposed method provides comparable image quality while requiring fewer mesh nodes than the several existing methods.
    Communications, 2005. ICC 2005. 2005 IEEE International Conference on; 06/2005

Publication Stats

239 Citations
12.11 Total Impact Points

Institutions

  • 1998–2009
    • Asian Institute of Technology
      • School of Engineering and Technology (SET)
      Bangkok, Bangkok, Thailand
  • 2007–2008
    • University of Texas at Dallas
      • Department of Electrical Engineering
      Dallas, TX, United States
  • 2006
    • Brunel University
      • School of Engineering and Design
      London, ENG, United Kingdom
  • 2004–2005
    • University of Moratuwa
      • Department of Electronic and Telecommunication Engineering
      Moratuwa, Western Province, Sri Lanka
  • 2003
    • University of Saskatchewan
      • Department of Electrical and Computer Engineering
      Saskatoon, Saskatchewan, Canada
  • 1991–1999
    • University of Manitoba
      • Department of Electrical and Computer Engineering
      Winnipeg, Manitoba, Canada