Publications

• S. Fowler, M. Eberhard, K. Blow and A. Shaikh, Adaptive Sending Rate over Wireless Mesh Networks using SNR, International Journal of Wireless Networks and Broadband Technologies 1 (2011) 30-48
  Abstract: Wireless Mesh Networks (WMNs) have emerged as a key technology for the next generation of wireless networking. Instead of being another type of ad-hoc networking, WMNs diversify the capabilities of ad-hoc networks. Several protocols that work over WMNs include IEEE 802.11a/b/g, 802.15, 802.16 and LTE-Advanced. To bring about a high throughput under varying conditions, these protocols have to adapt their transmission rate. In this paper, we have proposed a scheme to improve channel conditions by performing rate adaptation along with multiple packet transmission using packet loss and physical layer condition. Dynamic monitoring, multiple packet transmission and adaptation to changes in channel quality by adjusting the packet transmission rates according to certain optimization criteria provided greater throughput. The key feature of the proposed method is the combination of the following two factors: 1) detection of intrinsic channel conditions by measuring the fluctuation of noise to signal ratio via the standard deviation, and 2) the detection of packet loss induced through congestion. We have shown that the use of such techniques in a WMN can significantly improve performance in terms of the packet sending rate. The effectiveness of the proposed method was demonstrated in a simulated wireless network testbed via packet-level simulation.
  
  
• M. Eberhard, A. Maruta and M. Faisal, Analytical First Order Comparison of Amplitude and Phase Noise in Single and Dual Mach-Zehnder Interferometer Detection Schemes for DQPSK Transmission Systems, In Techn. Digest Series, Conference on Nonlinear Photonics (NP), page NTuC47, Karlsruhe, Germany, June 2010, Optical Society of America
  Abstract: An analytical first order calculation of the impact of Gaussian white noise on a novel single Mach-Zehnder Interferometer demodulation scheme for DQPSK reveals a constant Q factor ratio to the conventional scheme.
  
  
• S. Fowler, M. Eberhard and K. Blow, Implementing an Adaptive TCP Fairness while exploiting 802.11e over Wireless Mesh Network, International Journal of Pervasive Computing and Communications, Special Issue on Resource Allocation and Management in Wireless Mesh Networks 5 (2009) 272-294
  Abstract: Purpose - The purpose of this paper is to investigate the use of 802.11e MAC to resolve the transmission control protocol (TCP) unfairness. Design/methodology/approach - The paper shows how a TCP sender may adapt its transmission rate using the number of hops and the standard deviation of recently measured round-trip times to address the TCP unfairness. Findings - Simulation results show that the proposed techniques provide even throughput by providing TCP fairness as the number of hops increases over a wireless mesh network (WMN). Research limitations/implications - Future work will examine the performance of TCP over routing protocols, which use different routing metrics. Other future work is scalability over WMNs. Since scalability is a problem with communication in multi-hop, carrier sense multiple access (CSMA) will be compared with time division multiple access (TDMA) and a hybrid of TDMA and code division multiple access (CDMA) will be designed that works with TCP and other traffic. Finally, to further improve network performance and also increase network capacity of TCP for WMNs, the usage of multiple channels instead of only a single fixed channel will be exploited. Practical implications - By allowing the tuning of the 802.11e MAC parameters that have previously been constant in 802.11 MAC, the paper proposes the usage of 802.11e MAC on a per class basis by collecting the TCP ACK into a single class and a novel congestion control method for TCP over a WMN. The key feature of the proposed TCP algorithm is the detection of congestion by measuring the fluctuation of RTT of the TCP ACK samples via the standard deviation, plus the combined the 802.11e AIFS and CWmin allowing the TCP ACK to be prioritised which allows the TCP ACKs will match the volume of the TCP data packets. While 802.11e MAC provides flexibility and flow/congestion control mechanism, the challenge is to take advantage of these features in 802.11e MAC. Originality/value - With 802.11 MAC not having flexibility and flow/congestion control mechanisms implemented with TCP, these contribute to TCP unfairness with competing flows.
  
  
• N. Johnson, S. M. Nissanka, T. Nakamura, M. Eberhard, A. Maruta and K. Blow, Simultaneous dibit recovery of a DQPSK signal using a single Mach-Zehnder Interferometer, Elec. Lett. 45 (2009) 321-322
  Abstract: The dibit recovery of a DQPSK signal will be demonstrated using a single Mach Zehnder Interferometer, containing a 1-bit delay, and a single balanced receiver. The electrical output levels of the balanced receiver are dependent upon the relative phase delay between the arms of the Mach Zehnder Interferometer. This paper will investigate this characteristic when the input signal is DQPSK modulated. It will also be shown that with a certain amount of phase shift the DQPSK signal can be converted into four different equally spaced electrical signal levels. With each decoded level representing one of the four possible dibits.
  
  
• M. Eberhard and A. Maruta, Single Mach-Zehnder Interferometer Detection Scheme for Differential Quadrature Phase Shift Keying Transmission Systems, In 2nd Global COE International Symposium Electronic Devices Innovation (EDIS2009), page 103-106, Suita, Osaka, Japan, December 2009, Osaka University
  Abstract: The performance of the conventional Differential Quadrature Phase Shift Keying (DQPSK) demodulation scheme using two Mach-Zehnder Interferometers (MZIs) is compared with a novel single MZI demodulation scheme by numerical simulation. It is shown that both schemes require dispersion compensation for transmission distances in excess of 30 km and that both schemes perform well for longer distances with dispersion compensation added.
  
  
• S. Fowler, M. Eberhard, K. Blow and A. Shaikh, Implementing an Adaptive Sending Rate by exploiting SNR in relation to throughput over Wireless Mesh Networks, In Networking and Electronic Commerce Research Conference (NAEC2008), page 288-304, Lake Garda, Italy, September 2008, International Federation for Information Processing (IFIP)
  Abstract: Wireless Mesh Networks (WMNs) have emerged as a key technology for the next generation of wireless networking. Instead of being another type of ad-hoc networking, WMNs diversify the capabilities of ad-hoc networks. There are many kinds of protocols that work over WMNs, such as IEEE 802.11a/b/g, 802.15 and 802.16. To bring about a high throughput under varying conditions, these protocols have to adapt their transmission rate. While transmission rate is a significant part, only a few algorithms such as Auto Rate Fallback (ARF) or Receiver Based Auto Rate (RBAR) have been published. In this paper we will show MAC, packet loss and physical layer conditions play important role for having good channel condition. Also we perform rate adaption along with multiple packet transmission for better throughput. By allowing for dynamically monitored, multiple packet transmission and adaptation to changes in channel quality by adjusting the packet transmission rates according to certain optimization criteria improvements in performance can be obtained. The proposed method is the detection of channel congestion by measuring the fluctuation of signal to the standard deviation of and the detection of packet loss before channel performance diminishes. We will show that the use of such techniques in WMN can significantly improve performance. The effectiveness of the proposed method is presented in an experimental wireless network testbed via packet-level simulation. Our simulation results show that regardless of the channel condition we were to improve the performance in the throughput.
  
  
• M. Eberhard and S. Fowler, Integration of the Manakov-PMD Equation with Precomputed M(w) Matrices for PMD Simulation, Journal of Scientific and Practical Computing 2 (2008) 3-12
  Abstract: A novel direct integration technique of the Manakov-PMD equation for the simulation of polarisation mode dispersion (PMD) in optical communication systems is demonstrated and shown to be numerically as efficient as the commonly used coarse-step method. The main advantage of using a direct integration of the Manakov-PMD equation over the coarse-step method is a higher accuracy of the PMD model. The new algorithm uses precomputed M(w) matrices to increase the computational speed compared to a full integration without loss of accuracy. The simulation results for the probability distribution function (PDF) of the differential group delay (DGD) and the autocorrelation function (ACF) of the polarisation dispersion vector for varying numbers of precomputed M(w) matrices are compared to analytical models and results from the coarse-step method. It is shown that the coarse-step method achieves a significantly inferior reproduction of the statistical properties of PMD in optical fibres compared to a direct integration of the Manakov-PMD equation.
  
  
• M. Eberhard, Polarisation Mode Dispersion Induced Transmission Penalties for Long-Haul High Speed Optical Communication Systems, In 1st Global COE Student Conference on Innovative Electronic Topics (SCIENT2008), page I-2, Suita, Osaka, Japan, August 2008, Osaka University
  Abstract: Results of full numerical simulations of a guiding-centre soliton system with randomly birefringent SMF fibre are shown and analysed. It emerges that the soliton system becomes unstable even for small amounts of PMD.
  
  
• N. Johnson, S. M. Nissanka, M. Eberhard and A. Maruta, Recovery of multiple amplitude levels from a DQPSK NRZ signal using a single Mach-Zehnder Interferometer, In 1st Global COE Student Conference on Innovative Electronic Topics (SCIENT2008), page AMP-14, Suita, Osaka, Japan, August 2008, Osaka University
  Abstract: In this research the recovery of a DQPSK signal will be demonstrated using a single Mach-Zehnder Interferometer (MZI). By changing the phase delay in one of the arms it will be shown that different delays will produce different output levels. It will also be shown that with a certain level of phase shift the DQPSK signal can be converted into four different equally spaced optical power levels. With each decoded level representing one of the four possible bit permutations. By using this additional phase shift in one of the arms the number of MZIs required for decoding can be reduced from two to one.
  
  
• A. D. Shaikh, M. Eberhard, K. J. Blow and S. A. Fowler, Statistical Study of Talk Spurts and Silence Lengths with relation to various Languages and Speakers for Advanced Silence Suppression in Next Generation Wireless Communication Devices, In 1st Global COE Student Conference on Innovative Electronic Topics (SCIENT2008), page P-2, Suita, Osaka, Japan, August 2008, Osaka University
  Abstract: As wireless network technologies evolve towards an All-IP framework, Next Generation Wireless Communication Devices demand better use of spectral resources by employing advanced techniques of silence suppression. This paper presents an analysis of VoIP call data and compares the statistical results based on observed patterns of talk spurts and silence lengths to those achieved by a modified on-off voice model for silence suppression in wireless networks. As talk spurts and silence lengths are sensitive to varying word lengths, temporal structure and other prosodic aspects of speech, the impact of the use of various languages, dialects and gender of speakers on these results is also assessed.
  
  
• M. Eberhard and K. J. Blow, Simulation of guiding-centre soliton transmission system stability in the presence of polarisation mode dispersion, In Techn. Digest Series, Conference on Nonlinear Photonics (NP), page JWA24, Quebec, Canada, September 2007, Optical Society of America
  Abstract: Results of full numerical simulations of a guiding-centre soliton system with randomly birefringent SMF fibre are shown and analysed. It emerges that the soliton system becomes unstable even for small amounts of PMD.
  
  
• C. Braimiotis, M. Eberhard and K. Blow, Polarisation mode dispersion correlations with the coarse-step method, Opt. Comm. 262 (2006) 135-139
  Abstract: Having a fixed differential-group delay (DGD) term b' in the coarse-step method results in a repetitive pattern in the autocorrelation function (ACF). We solve this problem by inserting a varying DGD term at each integration step. Furthermore we compute the range of values needed for b' and simulate the phenomenon of polarisation mode dispersion for different statistical distributions of b'. We examine systematically the modified coarse-step method compared to the analytical model, through our simulation results.
  
  
• M. Eberhard and K. J. Blow, Q parameter estimation using numerical simulations for linear and nonlinear transmission systems, Opt. Comm. 265 (2006) 73-78
  Abstract: We compare the Q parameter obtained from scalar, semi-analytical and full vector models for realistic transmission systems. One set of systems is operated in the linear regime, while another is using solitons at high peak power. We report in detail on the different results obtained for the same system using different models. Polarisation mode dispersion (PMD) is also taken into account and a novel method to average Q parameters over several independent simulation runs is described.
  
  
• S. Oda, M. Eberhard and A. Maruta, All-optical digital-to-analog conversion using nonlinear optical loop mirrors, In Proc. of IEICE Autumn Conference, page B-10-27, Hokkaido, Japan, September 2005, Institute of Electronics, Information and Communication Engineers (IEICE)
  Abstract: While all-optical analog-to-digital conversion (ADC) has been extensively studied [1], there are only a few works on all-optical digital-to-analog conversion (DAC) [2-5]. In this paper, we propose a novel all-optical DAC scheme using nonlinear optical loop mirrors (NOLMs). The feasibility of the proposed scheme is confirmed by numerical simulations.
  
  
• C. Braimiotis and M. Eberhard, Application of the Manakov-PMD equation to a computational investigation of low-PMD fibres, In Techn. Digest Series, Conference on Nonlinear Guided Waves and Their Applications (NLGW), page ThB8, Dresden, Germany, September 2005, Optical Society of America
  Abstract: The phenomenon of low-PMD fibres is examined through numerical simulations. Instead of the coarse-step method we are using an algorithm developed through the Manakov- PMD equation. With the integration of the Manakov-PMD equation we have access to the fibre spin which relates to the orientation of the birefringence. The simulation results produced correspond to the behaviour of a low-PMD spun fibre. Furthermore we provide an analytical approximation compared to the numerical data.
  
  
• M. Eberhard and K. J. Blow, Numerical Q parameter estimates for scalar and vector models in optical communication system simulations, Opt. Comm. 249 (2005) 421-429
  Abstract: The Q parameter scales differently with the noise power for the signal-noise and the noise-noise beating terms in scalar and vector models. Some procedures for including noise in the scalar model largely under-estimate the Q parameter. We propose a simple method for including noise within a scalar model which will allow both the noise-noise dominated limit and the signal-noise dominated limit to be treated consistently.
  
  
• C. Braimiotis and M. Eberhard, Numerical implementation of low-PMD spun fibres with precomputed M(w) matrices, In Proc. Postgraduate Research Conference in Electronics, Photonics, Communications and Networks, and Computing Science (PREP), page 100-101, Lancaster, UK, March 2005, University of Lancaster
  Abstract: With the use of the coarse-step method for simulating the phenomenon of PMD the fibre-twist as not included into the equations. This was an obstacle in representing low-PMD spun fibres numerially.
  
  
• M. Eberhard and K. J. Blow, Semi-analytical Q parameter estimate in linear and nonlinear transmission systems, In Techn. Digest Series, Conference on Nonlinear Guided Waves and Their Applications (NLGW), page ThB4, Dresden, Germany, September 2005, Optical Society of America
  Abstract: We compare the Q parameter obtained from the semi-analytical model with scalar and vector models for two realistic transmission systems. First a linear system with a compensated dispersion map and second a soliton transmission system.
  
  
• M. Eberhard, Symmetric and asymmetric evaluation of the Tokamap in comparison with direct symplectic integration, Phys. Rev. E 71 (2005) 026411
  Abstract: Comparing the Poincare plots of the Tokamap and the underlying Hamiltonian system reveals large differences. This stems from the particular choice of evaluation of the singular perturbations present in the system (a series of delta-functions). A symmetric evaluation approach is proposed and shown to yield results which almost perfectly match the Hamiltonian system.
  
  
• M. Eberhard and C. Braimiotis, Numerical implementation of the Manakov-PMD equation with precomputed M(w) matrices, In Techn. Digest Series, Conference on Nonlinear Guided Waves and Their Applications (NLGW), page MC3, Toronto, Canada, March 2004, Optical Society of America
  Abstract: The Manakov-PMD equation can be integrated with the same numerical efficiency as the coarse-step method by using precomputed M(w) matrices, which entirely avoids the somewhat ad-hoc rescaling of coefficients necessary in the coarse-step method.
  
  
• M. Eberhard and C. Braimiotis, Numerical implementation of the coarse step method with a varying differential group delay, In Proc. of Conference on Optical Networks and Technologies (OpNeTec), page 530-534, Pisa, Italy, October 2004, Consorzio Nazionale Interuniversitario per le Telecomunicazioni (CNIT)
  Abstract: The effect of having a fixed differential group delay term in the coarse step method results in a periodic pattern in the autocorrelation function. We solve this problem by inserting a varying DGD term at each integration step, according to a Gaussian distribution. Simulation results are given to illustrate the phenomenon and provide some evidence about its statistical nature.
  
  
• M. Eberhard and K. J. Blow, Q parameter scaling in scalar and vector models with dominant signal-noise and noise-noise beating terms, In Techn. Digest Series, Conference on Nonlinear Guided Waves and Their Applications (NLGW), page MC11, Toronto, Canada, March 2004, Optical Society of America
  Abstract: The Q parameter scales differently with the noise power for the signal-noise and the noise-noise beating terms in scalar and vector models. Some procedures for including noise in the scalar model largely under-estimate the Q parameter.
  
  
• M. Eberhard, Vergleich von Transportmodellen für Feldlinien und Teilchen in stochastischen Magnetfeldern mittels symplektischer Abbildungen, PhD thesis, Heinrich-Heine-Universität Düsseldorf, May 2000
  Abstract: The thesis investigates transport properties in high temperature plasmas with symplectic mappings. A formalism is developed to derive such maps from symplectic integrators. Concrete maps are given and analyzed.
  
  
• M. Eberhard, Transition from time-continuous systems to discrete mappings, In Europhysics Conference Abstracts: EPS Conference on Controlled Fusion and Plasma Physics, volume 23J, page 781-784, Maastricht, The Netherlands, June 1999, European Physical Society
  Abstract: Detailed transport studies in plasmas require the solution of the time evolution of many different initial positions of test particles in the phase space of the systems to be investigated. To reduce this amount of numerical work, one would like to replace the integration of the time-continues system with a mapping.
  
  
• K. H. Spatschek, M. Eberhard and H. Friedel, On models for magnetic field line diffusion, Physicalia Mag. 20 (1998) 85-93
  Abstract: In this contribution, certain aspects of the nonlinear dynamics of magnetic field lines are reviewed. First, the basic facts (known from literature) concerning the Hamiltonian structure are briefly summarized. The paper then concentrates on the following subjects: (i) Transition from the continuous description to discrete maps; (ii) Characteristics of incomplete chaos; (iii) Control of chaos. The presentation is concluded by some remarks on the motion of particles in stochastic magnetic fields.
  
  
• M. Eberhard, Niedrigfeld Magnetowiderstand inhomogener Halbleiterschichten, Master's thesis, Technische Universität München, March 1996
  Abstract: The resistance of semiconductor superlattices under weak magnetic fields is modelled with a classical approach. It is shown, that this is sufficient to explain the experimental features of these systems and that a quantum-mechanical approach will only be needed for significantly smaller lattice structures.
  
  
• M. Ben-Chorin, F. Möller, F. Koch, W. Schirmacher and M. Eberhard, Hopping transport on a fractal: ac conductivity of porous silicon, Phys. Rev. B 51 (1995) 2199-2213
  Abstract: We have measured the frequency dependence of the conductivity and the dielectric constant of various samples of porous Si in the regime 1 Hz-100 kHz at different temperatures. The conductivity data exhibit a strong frequency dependence. When normalized to the dc conductivity, our data obey a universal scaling law, with a well-defined crossover, in which the real part of the conductivity sigma' changes from an sqrt(omega) dependence to being proportional to omega. We explain this in terms of activated hopping in a fractal network. The low-frequency regime is governed by the fractal properties of porous Si, whereas the high-frequency dispersion comes from a broad distribution of activation energies. Calculations using the effective-medium approximation for activated hopping on a percolating lattice give fair agreement with the data.