Department Publications

Industrial automation is undergoing an increased use of wireless networks due to high flexibility and ease of deployment. However, despite the benefits, wireless networks have their inherent problems and vulnerabilities. This paper investigates the feasibility of using anomaly detection using possibility theory for network traffic. This is then used as a lightweight hostbased intrusion detection system for single board computer or embedded devices of an IEEE 802.11 based wireless industrial automation network. Traffic data is collected for genuine browsing and simulated attacks. It is then subjected to cluster analysis and tested using standard classifiers. The logarithmic histogram of the interpacket delay is used as the feature for classification. Subsequently it is used for training and testing a possiblisitic anomaly detector. The performance is then compared with a statistical outlier detector.

Multivariate statistics play an important role in performance analysis of wireless communication systems in correlated fading channels. This thesis presents a framework which can be used to derive easily computable mathematical representations for some multivariate statistical distributions, which are derivatives of the Gaussian distribution, and which have a particular correlation structure. The new multivariate distribution representations are given as single integral solutions of familiar mathematical functions which can be evaluated using common mathematical software packages. The new approach can be used to obtain single integral representations for the multivariate probability density function, cumulative distribution function, and joint moments of some widely used statistical distributions in wireless communication theory, under an assumed correlation structure. The remarkable advantage of the new …

Scintillation effect is a dominant atmospheric impairment among the various contributing factors for low fade margin communication systems operating on high frequency bands such as Ku. Empirical analysis of scintillations can be done using signal strength measurements which can be treated as a time series prediction problem in forecasting the short-term scintillation effect. This paper discusses the time series based statistical prediction analysis of tropospheric scintillation effect. The experiment was performed under clear sky conditions where the other attenuation contributions such as rain, dense clouds is minimum. The experiment was setup at the University of Moratuwa, Sri Lanka using a Ku band satellite downlink operating on a moderately high elevation angle of 45 degrees. The time series analysis was performed using linear, non-linear, fuzzy and neural prediction techniques. The results show that …

The study of empirical propagation models for mobile channels has been done extensively, but the applicability of those models to a Fixed Wireless Access (FWA) System is not appropriately tested. The candidate models include Hata - Okumura, COST 231 Hata, COST-Walfisch-Ikegami and Erceg. From those models Erceg model seems to be the most suitable. In this paper field measurements are taken for the 3.5GHz Fixed WiMAX network in Katubedda, Sri Lanka. Those are used to validate the applicability of the above mentioned propagation models in a sub urban environment in Sri Lanka.

Testing of wireless sensor network protocols can be tedious for large networks when mobility is added. Mainly because these networks involve a large number of nodes scattered in an ad-hoc configuration. Although there are several publicly available static sensor network testbeds, testbeds where mobility is facilitated are very rare. One of the main objectives of this work is to provide a general hardware platform, which supports to implement different protocols for mobile sensor networks. The testbed is implemented with one base station node, one mule and five sensor nodes, where data mules move in a random manner through a community of fixed sensor nodes. As the mule comes within range of each sensor node, it collects the available data. After collecting data from all the sensor nodes, the mule returns to a central node, where it uploads all the data collected. The motes are connected to the central node …

Wireless sensor networks are an emerging area of interest among embedded and wireless research groups around the globe. It is envisioned that these low power computers will become the enabling technology in pervasive computing and bring about the next paradigm shift in computing. We present a new type of MAC protocol that is applicable to a special type of mobile wireless sensor network. In this network, mobile sensor nodes will sense the environment, and buffer the measured data for later retrieval. Once within range of the base station, the mobile mote will have a considerable amount of data to upload to the base station. Such a system could be used in different applications such as analyzing migration patterns of animals (ex. elephants) or offline monitoring of vehicle fleets. We present a MAC protocol that will maximize the throughput of the said network, and thereby ensure that the maximum amount of …

Abstract œ The paper describes the design and development of an emergency warning network that can disseminate disaster early warnings in three languages, to vulnerable communities over the GSM network. The Disaster Early Warning Network (DEWN) is a last-mile solution for early warning of disasters, and consists of a server at a warning dissemination centre, the GSM network and user terminals. The user terminals are mobile phones with the DEWN application and electronic alarm devices capable of generating audible, high-volume alarms and flashlights. The user devices generate alarms in response to a warning message from an authorized entity via GSM‘s short message service (SMS) or cell broadcast (CB). The design of DEWN follows international guidelines on emergency communications, such as the ability to reach a large number of people very fast, awaken sleeping communities, and be able to acknowledge warning messages.

In a very high noise environment, conventional communication means suffer from significant degradation due to the external noise which can drown out the desired speech signal. Environments such as industrial complexes, manufacturing plants, battle fields are examples of extremely noisy environments. Mobility is also crucial requirement for communication in such environments frequently. The paper describes the design and implementation of a mobile wireless communication system which can operate in such an environment using effective noise cancellation techniques.

The paper describes the design and development of an emergency warning network that can disseminate disaster early warnings in three languages, to vulnerable communities over the GSM network. The Disaster Early Warning Network (DEWN) is a last-mile solution for early warning of disasters, and consists of a server at a warning dissemination centre, the GSM network and user terminals. The user terminals are mobile phones with the DEWN application and electronic alarm devices capable of generating audible, high-volume alarms and flashlights. The user devices generate alarms in response to a warning message from an authorized entity via GSM’s short message service (SMS) or cell broadcast (CB). The design of DEWN follows international guidelines on emergency communications, such as the ability to reach a large number of people very fast, awaken sleeping communities, and be able to acknowledge warning messages.

This paper presents a coherent demodulation scheme that reduces the multiple-access interference (MAI) considerably in a band-limited direct-sequence code-division multiple-access system. The despreading signal is obtained from a combination of the conventional despreading signal and its weighted early and late versions that are used in the delay-locked loop (DLL). It is shown that with appropriate choice of the weighting parameter of the early-late signals of the DLL, the signal-to-interference-plus-noise ratio of the decision variable is increased, which leads to improvement in the bit-error performance and hence the potential increase in the system capacity by about 25%. The analyses are performed in the frequency domain. The effect of imperfect synchronization on the system performance is also analyzed.

In today's competitive and fast-changing telecom industry, most professionals find themselves in the difficult situation of having to sacrifice keeping on top of the latest technology because they are striving to meet another round of high-pressure deadlines. Essentials of Modern Telecommunications Systems offers you a solution to this problem, helping you quickly coming up to speed with the latest advances in your field. By cutting out arcane mathematics and management-speak jargon, it focuses on the essentials you need for rapidly understanding and mastering the latest implementation and development techniques. It provides the complete systems picture from semiconductors to end-to-end networking.

The thesis presents the development of a simple technique for remote reading of utility meters using the low voltage power distribution network. Remotely reading electricity, gas and water meters have distinct advantages over traditional metering methods. Several communication technologies have been designed and implemented for this purpose using wireless techniques, telephone lines, power transmission and distribution lines. In this study, the last one has been selected as the basis for the development of a remote meter reading system applicable to Sri Lanka.

The performance of a coherent delay-locked tracking scheme for direct-sequence/spread-spectrum systems using half-sine or triangular chip waveforms for early and late despreading sequences is analyzed. The effect of band-limiting on the received signals is considered. Mean time to lose lock (MTLL) and root mean square (rms) tracking error of the delay-locked loop (DLL) are compared with that of a conventional DLL which uses rectangular chip despreading waveforms. Linear and nonlinear (based on the renewal process approach) analyses are employed to evaluate the performance of the DLL. Results show that the use of either the half-sine or triangular chip waveform reduces the rms tracking error and increases the MTLL considerably when the early-late spacing is approximately between 0.7-1.3 chip times. The results apply in particular to the commonly used DLL using one chip early-late spacing …

HKU Scholars Hub: Delay-locked loop techniques in direct sequence spread-spectrum receivers Skip navigation HKU Login Guest Login Home Publications Researchers Staff Research Postgraduates Organizations Grants Datasets Deposit Data HKUL Research Data Management Theses Patents Community Service File Download FullText.pdf Links for fulltext (May Require Subscription) DOI: 10.5353/th_b3124104 Supplementary Appears in Collections: HKU Theses Online Electrical & Electronic Engineering: Theses postgraduate thesis: Delay-locked loop techniques in direct sequence spread-spectrum receivers Show simple item record Show full item record Export item record Title Delay-locked loop techniques in direct sequence spread-spectrum receivers Authors Thayaparan, Subramaniam. Issue Date 1999 Publisher The University of Hong Kong (Pokfulam, Hong Kong) Citation Thayaparan, S.. (1999). Delay-…

HKU Scholars Hub: Gaussian Despreading Chip Waveform for Coherent Code Tracking in DS/CDMA Systems Skip navigation HKU Login Guest Login Home Publications Researchers Staff Research Postgraduates Organizations Grants Datasets Deposit Data HKUL Research Data Management Theses Patents Community Service File Download There are no files associated with this item. Supplementary Appears in Collections: Electrical & Electronic Engineering: Conference papers Conference Paper: Gaussian Despreading Chip Waveform for Coherent Code Tracking in DS/CDMA Systems Show simple item record Show full item record Export item record Title Gaussian Despreading Chip Waveform for Coherent Code Tracking in DS/CDMA Systems Authors Thayaparan, SWang, JNg, TS Issue Date 1999 Citation Proc. International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC'99, …

This paper presents the code tracking performance on the use of weighted chip despreading PN sequence in a coherent delay locked tracking scheme for direct-sequence spread-spectrum (DS/SS) systems. In the delay locked loop (DLL), the conventional rectangular chip waveform for early and late despreading PN sequences is replaced by a weighted exponential chip waveform. The chip weight (/spl gamma/) is tuned to optimise the DLL performance. The early-late spacing is considered as one chip time. This scheme is analysed for both ideal and band limited received signals in the presence of additive white Gaussian noise.

This paper presents the performance comparison on the use of general non-linear dectors in a non-coherent delay locked tracking scheme for direct-seuence spreqd-spectrum systems. In the dalay locked loop (DLL), the square law-enevelope detectors are replaced by a full wave (even) nth - law detectors and this scheme is analysed in the presence of additive white gaussian noise. The tracking error of the DLL is compared for different values of n (n=0.5, 1, 2, 3, respectively). The results shows that the tracking error of the DLL can be reduced further in low signal to nose power ratio region by using the full wave (even) nth -law detectors for n<2 when compare with using the square law enevelope detectors (n=2).

An adaptive Viterbi algorithm, derived from a dynamic estimate of the fading channel is used for the decoding of a convolutional coded 16 QAM system in a mobile environment. The estimates are obtained by a sequence of known pilot symbols embedded in the data stream, and perform compensation for Rayleigh fading. The likelihood criterion in the Viterbi decoder is also modified by these channel estimates through a metric weighting function. We demonstrate through computer simulations, that our new technique achieves a BER improvement of 7-10 dB at P/sub e/=10/sup -3/ in a fast flat Rayleigh fading environment compared to an uncoded system. The BER performance of our new technique in a co-channel interference (CCI) controlled environment is also studied, and the results show that it may achieve a 40% to 85% improvement in capacity over the standard modem scheme for the new US digital cellular …

We apply baseband pulse shaping techniques for /spl pi//4 QPSK in order to reduce the spectral regeneration of the bandlimited carrier after nonlinear amplification. These Feher's patented techniques, namely, /spl pi//4 FQPSK (superposed QPSK) and /spl pi//4 CTPSK (controlled transition PSK), may also be noncoherently demodulated. Application of these techniques is in fast fading, power efficient channels, typical of the mobile radio environment. Computer simulation and experimental studies demonstrate that with these baseband waveshaping techniques, carrier envelope fluctuations are significantly reduced, and the out-of-band power after nonlinear amplification is suppressed by up to 20 dB compared to /spl pi//4 QPSK. In frequency noninterleaved land or satellite mobile radio systems operating in a nonlinear, fading and ACI (adjacent channel interference) environment, these techniques may achieve 20 …

An adaptive Viterbi algorithm, derived from a dynamic estimate of the fading channel, is used for the decoding of a convolutional coded 16-QAM system in a mobile environment. The estimates are obtained by a sequence of known pilot symbols embedded in the data stream, and perform compensation for Rayleigh fading. The likelihood criterion in the Viterbi decoder is also modified by these channel estimates through a metric weighting function. We demonstrate, through computer simulations, that our new technique achieves a BER improvement of 7-10 dB at P,= 10-’in a fast flat Rayleigh fading environment compared to an uncoded system. The BER performance of our new technique in a CCI controlled environment is also studied, and the results show that it may achieve an 80 percent improvement in spectral utilization over the standard modem scheme for the new US. digital cellular system, ii/l-DQPSK.

New methods for generating additional capacity from the limited available spectrum for digital mobile, cellular and personal communications systems are introduced. Techniques for the improvement of spectral efficiency and capacity with modulation schemes currently in use are first investigated. The adoption of more spectrally efficient multilevel modulation formats to yield further improvements in capacity is then undertaken.

A coded 16-quadrature amplitude modulation (QAM) scheme with digital channel sounding, convolutional coding, and space diversity is introduced for improving the spectral utilization of digital cellular systems. A combined estimate of channel reliability is obtained from the diversity branches, and is used to modify the likelihood criterion of the Viterbi decoder. This is an extension of the authors previous decoding techniques to include multiple diversity paths. They investigate the bit error rate performance of this scheme in fast fading channels corrupted by additive white Gaussian noise and cochannel interference through computer simulations. The results show that in a cellular environment, this scheme may achieve an improvement in capacity of 30% compared to the pi /4-DQPSK method with diversity reception.<>

The application of two baseband pulse shaping techniques to improve the spectral efficiency obtained by pi /4-DQPSK (differential quadrature phase shift keying) in a nonlinearly amplified land mobile environment is examined. The spectral and bit error rate (BER) performance of these techniques is studied through computer-aided design techniques. It is demonstrated that, by using the shaping methods considered. pi /4-QORC (quadrature overlapped raised cosine) and pi /4-CTPSK (controlled transition PSK), the spectral regeneration after nonlinear amplification can be reduced significantly. Thus, the schemes studied allow closer channel spacing compared to pi /4-DQPSK, the current standard modem scheme for the US digital mobile communications system.<>

The spectral/power efficiency and performance of the pi /4-quadrature phase-shift keying (QPSK) modems (American and Japanese digital cellular emerging standards) are studied and briefly compared to GMSK modems (proposed for European Digital European Cordless Telephone System) (DECT) and Group Special Mobile System (GSM) cellular standards). Improved filtering strategies and digital pilot aided (digital channel sounding) techniques are considered for pi /4-QPSK and for other digital modems. More spectrally efficient modem trends and some research results for future cellular/mobile (land mobile) and satellite communication systems applications are also highlighted.<>