Faculty of Engineering, Electronics & Telecommunication Engineering

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item: Thesis-Abstract
3-Dimensional spatial channel model for multi-storeyed indoor environments
(2021) Tennakoon TMP; Wavegedara KCB
A three-dimensional (3-D) geometry-based stochastic model (GBSM) is presented for various types of multi-story indoor environments. The proposed model assumed that the scatterers are distributed within a spheroid, where the transmitter and the receiver are located at the focal points of the spheroid. The proposed model provides the probability density functions (PDFs) of the angle of arrival (AoA), the time of arrival (ToA) and the spatial correlation coe cients correspondence with several channel parameters of the channel. By considering non-uniform scatterer distributions, the spheroid GBSM is extended for multistory indoor environments. Closed-form expressions are derived for the joint and marginal PDFs of the AoA in both the elevation and azimuth planes and the ToA. The analytically-derived PDFs of the AoA and ToA obtained for Gaussian and Rayleigh scatterer distributions are compared against those obtained from the ray-tracing simulation of typical indoor environments. The standard deviation values of Gaussian and Rayleigh scatterer distributions are chosen to provide the best possible approximation to the PDFs of the AoA and the ToA obtained from simulation. Our results clearly indicate that the analyticallyderived PDFs of the AOA and the TOA for Gaussian and Rayleigh scatterer distributions are in much closer agreement with those obtained from ray-tracing simulation than for uniform scatterer distribution. However, analytically-derived PDFs of the AOA and the TOA for Gaussian scatterer distribution show closest agreement with those PDFs obtained from the simulations. A generalized 3D channel model with an arbitrator scatterer distribution point is proposed based on the spheroid GBMS. The proposed channel model is assumed that the scatterers to be distributed according to the Gaussian distribution about an arbitrary point within the spheroid. Closed-form expressions are derived for the joint PDFs of the AoA, marginal PDFs in both the elevation and azimuth planes, as well as for the marginal PDF of the ToA. Numerical results are utilized for the veri cation of the derived-closed form mathematical expressions. More-over, the obtained marginal PDFs of AoA and TOA are compared against PDFs obtained from the simulation of an indoor environment using ray-tracing tool. By choosing a proper scatterer distribution center point based on the actual indoor propagation environment and a suitable value for the standard deviation of the scatterer region, the proposed 3-D model of the channel can be exploit the performance of the wireless communication technologies and systems in indoor environments. The spheroid GBSM is extended to a 3D geometry-based spatial correlation model for multiple-input multiple-output (MIMO) communication environments. Approximated closed-form expressions are obtained for the normalized spatial correlation coe cients of frequency non-selective Rician fading channels. As a special case, the normalized spatial coe cients are derived for Gaussian scatterer distribution. Closed-form expressions developed are veri ed by the simulation results obtained using the WINNER Phase II channel model (WIM2). Furthermore, the capacity performance of MIMO channels is investigated using the proposed geometry-based correlation model. Our results have clearly demonstrated that the proposed 3D spatial correlation model can be used to investigate the performance of the frequency non-selective Rician or Rayleigh fading MIMO channels with di erent antenna con gurations accurately.
item: Thesis-Full-text
A 3D models of human ejaclulatory ducts
Gunasekera, CL; Dayananda, N
Benign Prostatic Hyperplasia (BPH) is a common non-malignant ailment effecting in ejaculatory duct of aging men. BPH induces bothersome lower urinary tract symptoms. The standard treatment for BPH is Transurethral Resection of the Prostate (TURP), which mitigate urinary symptoms and enhance urinary flow. Smooth sphincter of the bladder neck accumulates and resides seminal fluid as it reaches the prostatic urethra before it ejects during ejaculation. Retrograde ejaculation occurs due to removal of this smooth sphincter of the bladder neck during TURP. Hence, about 53-77% patients develop retrograde ejaculation after the procedure. The research has shown that preserving the portion of supramontanal prostatic tissue during TURP leads to preserve antegrade ejaculation in about 80% of patients. The accuracy of this surgical procedure could be enhanced by the aid of 3D modelling. A literature survey on the existing procedures for model construction indicated that further improvements could be achieved through reconstructing a 3D model. A 3D model will enhance the understanding of the anatomical relationship of the ejaculatory ducts and prostatic urethra in cross sections of the prostate gland and to determine a safe zone with the prostate to remove without damaging the ejaculatory ducts. We used photographic images of prostates obtained from male cadavers above the age of fifty years. The prostate samples fixed on to a wax block and uniform 2 mm thick slices were removed sequentially while taking photographs with a digital camera. Major steps in constructing a 3D model from the acquired images include: image registration to align series of slices, segmentation of the prostate, urethra and ducts and 3D modelling of the segmented structures. A simple landmark based image registration technique was employed by manually selecting points along the four edges of the wax block and automatically detecting the vertices of the block using intersections. Then rotation, translation and scaling were estimated on individual slices to align all the slices. The prostate was then segmented manually using an existing software tool program. The ejaculatory ducts and the urethra were segmented using a simple active contour based segmentation tool. Finally, a 3D mesh model was developed using boundary points of each of the segmented structure. The following three surgically important measurements calculated using to the model: the angles of the centre of the left duct, to the centre of urethra and to the centre of right duct, perpendicular distance from the centre of urethra to the line joining the two centres of ducts, and width of the prostate. Results showed a large angle both proximally and distally, 3D relationships of ejaculatory ducts and urethra depended on the maximum width of the prostate. During TURP, safe distances to resect the prostate without damaging the ducts are calculated based on the maximum width of the prostate. Depth can be safely resected without damaging the ejaculatory ducts. In the future, it is quite essential to test these results on clinical grounds.
item: Thesis-Full-text
A Study on the use of MPLS-TE in IP core networks
Gajendran, A; Samarasinghe, ATLK
Today's demand for various applications like voice, data and real time video etc., are increasing in the consumer market and stakeholders mostly expect all services from a service provider. The tremendous growth in ICT adds more users and also traffic adds another dimension. NGN is expected to be the emerging IP network to transport converged services and MPLS and MPLS- TE plays an important role in this context. These new applications have increased demand for guaranteed bandwidth in the limited backbone capacity in the provider's network and the challenge is to provide differentiated class of services with required QoS and also to produce SLA performance reports to the end users when requested. Due to numerous benefits such as guaranteed end to end QoS, link protection and efficient use of core bandwidth MPLS- TE is being recognized and becoming popular among service providers. TE enables service providers to route network traffic in such a way that they can offer the best service to their users in terms of throughput and delay. In this research MPLS- TE approach is used to implement end to end QoS for prioritized services and a SLA program is developed using SNMP to produce end to end reports on critical performance metrics like delay, round trip time, jitter and application aware services to customers. The study also investigates the process of steering traffic across the MPLS/IP core backbone to facilitate efficient use of available bandwidth between a pair of backbone routers to ensure the required service levels. Hence in a multilink environment where many links are available for routing we can avoid the shortest paths being congested. Since network can have different types of packets; packets were generated and marked based on DSCP for QoS which were routed in different TE tunnels in a lab environment. The lab results showed that, using, TE tunriels constrained routing can provide explicit paths to required destinations regardless of the paths calculated by the routing protocols thus bandwidth efficiency can be achieved in the core while ensuring end to end QoS for critical applications for a given IP SLA. Also, results obtained by the SLA program from a live operational network were acceptable in providing SLA performance reports.
item: Thesis-Full-text
Activity recognition combined with scene context and action sequence
Ramasinghe, SC; Rodrigo, R
In this study, we investigate the problem of automatic action recognition and classification of videos. First, we present a convolutional neural network architecture, which takes both motion and static information as inputs in a single stream. We show the network is able to treat motion and static information as different feature maps and extract features off them, even though stacked together. By our results, we justify the use of optic flows as the raw information of motion. We demonstrate that our network is able to surpass state-of-the-art hand-engineered feature methods. Furthermore, the effect of providing static information to the network, in the task of action recognition, is also studied and compared here. Then, a novel pipeline is proposed, in order to recognize complex actions. A complex activity is a temporal composition of subevents, and a sub-event typically consists of several low level micro-actions, such as body movement, done by different actors. Extracting these micro actions explicitly is beneficial for complex activity recognition due to actor selectivity, higher discriminative power, and motion clutter suppression. Moreover, considering both static and motion features is vital for activity recognition. However, how to control the contribution from each feature domain optimally still remains uninvestigated. In this work, we extract motion features in micro level, preserving the actor identity, to later obtain a high-level motion descriptor using a probabilistic model. Furthermore, we propose two novel schemas for combining static and motion features: Cholesky transformation based and entropy based. The former allows to control the contribution ratio precisely, while the latter uses the optimal ratio mathematically. The ratio given by an entropy based method matches well with the experimental values obtained by a Choleksy transformation based method. This analysis also provides the ability to characterize a dataset, according to its richness in motion information. Finally, we study the effectiveness of modeling the temporal evolution of sub-event using an LSTM network. Experimental results demonstrate that the proposed technique outperforms state- of-the-art, when tested against two popular datasets.
item: Thesis-Abstract
Adaptive fuzzy systems
De Silva, GLPJ; Jayasingha, JAKS; Samarasiri, BS
Fuzzy sets offer a possibility to formally describe linguistic expressions. An adaptive fuzzy logic system not only adjusts to time or process phased conditions but also changes the supporting system controls. A real time target tracking system has been selected as a situation where an adaptive fuzzy controller can be implemented. The inputs to the system will be the Error, The rate of change of error and the previous velocity of the platform with respect to the target for elevation as well as for the azimuth. The output will be the velocity required for the platform to track the target. Target tracking systems have been designed in various methods, and in the project I have selected to use an adaptive fuzzy system to simulate the target tracking system. Objectives (a) to design a Matlab interface to study the behaviour of a fuzzy system. The inputs, outputs, term sets and the rules to be specified in the system and to be used subsequently to study the system behaviour. (b) to simulate a target tracking system and to design its controller. (c) to test an adaptive technique on the system and to compare the adaptive system with the normal fuzzy system to decide on the optimum controller. The interface was designed using Matlab version 4.00, and the inputs are the number of inputs and outputs, names of inputs and outputs, term sets and the rules. Separate Matlab in files were written to implement the controller. Adaptive techniques can be used in the system with modifications to the controller implementation. The number of rules to be used can also be increased by modifying some of the functions. It can be shown that when an adaptive technique is used the target can be tracked with a minimum error.
item: Thesis-Abstract
Adaptive video streaming for bandwidth variation with optimum quality
(2014-05-31) Medagama, JMW; Dias, D; Fernando, MSD
Bandwidth scarcity is a common problem faced in video transmission over broadband networks, particularly in wireless medium. It is important to find solutions for that since high bandwidth consuming video applications such as video streaming, video conferencing are of high interest to the broadband and mobile users today. This thesis presents adaptive video streaming based methodology to address the given problem. Adaptive streaming is discussed through transcoding. It is a solution that can be adopted to overcome this problem in any network environment. Conversion of video to a form that has less information so that the resulting data volume is appropriate for streaming over a low bandwidth scenario can be done with transcoding. But the video quality drops due to transcoding. A compromise can be made between the video quality and network delay. Effect on video quality and data volume with the variation of transcoding parameters are analyzed in this research, especially with the temporal scaling parameters. A relationship between the transcoding parameters, the data volume reducing factor and the video quality is obtained through numerical methods. Hence a methodology derived from the numerical method is proposed to achieve an adaptive streaming solution. One of the significant outcomes of this thesis is the video quality measurement mechanism proposed that could be used in the presence of spatial and temporal scaling. This solution presents the best transcoding parameters to achieve optimum quality video in a low bandwidth situation. With that, when there is a large number of users are sharing the network, they could watch a video at a lower, but acceptable quality with no interruption. Keywords – Adaptive stream, Transcode, Video quality, Frame Rate, Quantization
item: Thesis-Abstract
Aircraft locating system
Pathirage, RJ
This research project is to design and develop a Centre for the Aircraft data locating system utilizing Air Craft Instruments and GPS with existing voice network belongs to Sri Lanka Air Force. Currently, Air Traffic Controllers of the Sri Lanka Air Force do not have an automated system (our own system) to monitor the air craft movements within their field of range. Hence, implementation of our (SLAF) owns system was a long felt need .Availability of separate IFF radar systems will be a solution; however it will be an expensive option for the government of Sri Lanka at this juncture. The main reason is that it is not only the Radar, but the entire fleet of the Sri Lanka Air Force Air Craft that are required to be equipped with IFF transponders. Hence this project is to develop a dynamic solution which is effective, efficient and affordable in the present context. The outcome of the research would provide an aircraft location on a corresponding ground map in a viewing terminal available in front of the Air Traffic Controller. This timely information to the air traffic controller will be useful to establish a proper accurate air traffic controlling. Also, this will be a good source for the Sri Lanka Air Force to track whether the air craft movements are in accordance with the flight plans. This project consists of three main subsystems such as Onboard processing sub system. Onboard sensor subsystem and Ground Monitoring Station. In here Sensor information of the air craft have been gathered by using On board sensor subsystems and gathered information have been processed and taken decisions by using onboard processing subsystem. Finally all the gathered information have been transferred to the Ground Monitoring Station by using existing secure voice communication network available at Sri Lanka Air Force. It provides a very user friendly display provisioning Air Craft speed. Height and Location.
item: Thesis-Abstract
Analysis of early dropping mechanism for optical burst switched networks
Amarasinghe, T; Thilakumara, P
Quality of Service in Optical Burst Switched Networks using Early Dropping Mechanism with Different Network Characteristics Keywords: Optical Burst Switching (OBS), Absolute Quality of Service (QoS), Early Dropping Mechanism, Dense Wave Length Division Multiplexing (DWDM). Optical Burst Switching is a promising bufferless DWDM switching technology that can potentially provide high wavelength utilization. Quality of Service support has become an important issue in OBS networks. There are two models to guarantee QoS in OBS networks. Those are relative QoS guarantee and absolute QoS guarantee. Most existing schemes are based on relative QoS model and in those models the service levels can be defined relative to the service requirements of another class of traffic. In absolute QoS model it provides a bound for loss probability of the guaranteed traffic. This kind of hard guarantee is essential to support applications with bandwidth constraints. Further efficient admission control and recourse provisioning mechanisms will enhance the service of absolute QoS model to guarantee the service requirements in the OBS networks. Early dropping mechanism is proposed to maintain the dropping probability in Absolute QoS model in OBS networks. Due to the bufferless nature of the OBS core nodes, the early dropping mechanism computes the intentional dropping probability based on measured , online loss probability. In early dropping mechanism it can be simply implemented by using a threshold value which is responsible to maintain the maximum acceptable loss probability. But in this mechanism the lower priority class of traffic suffers from high loss probability when higher priority Glasses exceed its threshold vales of loss probability. Early dropping by Span mechanism introduces a span of acceptable loss probabilities rather than using one threshold value andthis mechanism has improved QoS guarantee in higher priority classes of traffic while reducing the loss probability of lower priority classes as well. Further the performance of this mechanism can be applied in a dynamic wave length assigning network in order to guarantee the absolute QoS with efficient recourse provisioning
item: Thesis-Abstract
Analysis of pairwise error probability bounds for space-time coded mimo systems
Dharmawansa, KDP
Space-time codes have attracted considerable attention in the area of wireless communications due to their ability to exploit the enormous capacity promised by the multiple-input multiple-output(MIMO) antenna system in comparison with a single antenna system. The main idea behind MIOMO is to establish independent parallel channels between multiple transmit and receive antennas. But in reality, the spatial correlation and the tap correlation in the case of frequency selective channel degrade the performance of space -time codes. For that reason, analytically derived pair wise error probability (PEP) expressions or bounds are of great importance in analyzing the performance of space-time codes over different fading environments. The main contribution of this thesis is to provide a broad mathematical framework to derive PEP bounds, which ultimately pave the way to design good codes. A new analytical PEP upper bound is derived in this thesis for frequency selective Rician fading channels with dependent fading coefficients and tap coefficients. The mathematical analysis presented in this thesis in deriving the former bound is sufficiently general to handle any form of fading environment except Nakagami-m fading model. With this bound the impact of correlation towards the code performance is also discussed. An exact PEP expression is also presented in the form of a definite integral, which doesn't have a closed form while the closed form is presented when the codewords are taken from orthogonal designs. Since the exact PEP expressions have complicated closed forms, an approximate expression is presented which is valid for sufficiently high signal-to-noise ratios. Although the Nakagami-m fading model is of practical importance compared to the other models, the mathematical complexity is very high if one follows the same classical approach, due to the unavailability of probability density function for a linear sum of several Nakagamim random variables. There is not much literature available related to the properties of spacetime codes due to this complexity. The thesis provides a new way of approach to the PEP upper bound derivation in the case of Nakagami-m fading channels employing two transmit antennas and subsequently it is extended to a more general case. Furthermore, exact PEP expressions are also derived in the case of orthogonal designs. Validity of the bounds is verified by the simulations at the latter part of the thesis.
item: Thesis-Full-text
Analysis of the performance of MQTT with shared dictionary compression (SDC) in IOT networks
(2019) Vinyagamany S; Samarawickrama JG
The Internet of Things or IOT is a set of organized computing devices that are provided with exclusive identifiers and the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction. The Internet of Things spreads internet connectivity beyond traditional devices like desktop and laptop computers, smartphones and tablets to a range of devices and everyday things that use embedded technology to connect and interact with the outside environment, all via the Internet. The architecture of IOT will greatly grow in the next few years and there will a big demand in the field of IOT devices performances. IHS forecasts that the IoT market will grow from an installed base of 15.4 billion devices in 2015 to 30.7 billion devices in 2020 and 75.4 billion in 2025 as shown in the Figure 1 - [2]. In order to cope up with the impending needs, we have to improve the current application protocols used in the internet of things. One of the most popular application protocols for IOT would be MQTT - Message Queue Telemetry Transport). As the Internet of Things ' growth explodes, the underlying fundamental protocols are changing. In particular, MQTT, or Message Queue Telemetry Transport, is now the dominant protocol for IoT globally. MQTT is a machine-to-machine (M2M)/"Internet of Things" connectivity protocol. It has been designed as an extremely lightweight messaging protocol packaged as publish / subscribe. MQTT is alright equipped with compression technologies like deflate. However, our goal is to further enhance compression by introducing Shared Dictionary Compression. Shared Dictionary Compression is tool which uses the redundancies in the messages to form dictionaries for frequently occurring key strings. These dictionaries are distributed among the iv devices and for compression and decommission. This could greatly in terms of the compression and hence the bandwidth. However, it must be noted that enabling Shared Dictionary Analysis would require detecting frequency of repeating keywords among the messages. This could induce additional computation on top of MQTT. Moreover, the distribution of dictionary might have adverse effects on the bandwidth. So, we will need to find the right balance between the achievable bandwidth reduction and computation complexity. In order to find the right tradeoff between computational costs and bandwidth reduction. We will need to implement an algorithm to assess the performance and determine the right settings for the SDC to function. This could be called as the adaptive algorithm, as the settings would greatly depend on the dataset used. In terms of our research, we will initially evaluate the Compression Potential of SDC + MQTT. After confirming the potential of SDC, we will evaluate the same with adaptive algorithm. Consequently, using the adaptive algorithm, we will find the right balance between the performance and compression, by evaluating the compression potential and computational costs of SDC-MQTT. Finally, to further optimize, we will need to analysis the ideal data format for SDC-MQTT for fully optimized performance of SDC-MQTT.
item: Thesis-Abstract
Analysis on business to business (B2B) e-commerce infrastructure of Sri Lanka
Rodrigo, DNR
This thesis presents the findings from a comprehensive survey done to find out to how far the Sri Lankan Industries have adapted E Commerce technology and also the bottlenecks faced by them in adapting E Commerce" This research has three main Objectives:  To identify the obstacles faced by the Sri Lankan industry to enter into  132B E-commerce through a comprehensive survey To investigate the possibility of B2B Framework specifically suitable for  Sri Lanka and also investigate the services expected by the participants, To propose a suitable framework according to the findings of the survey A general questionnaire was used to gather information of Companies* current use of Internet, their website status and barrier and drivers in adapting E Commerce: and a System Integration questionnaire was designed to feed core indicators on the usage of ICT in those enterprises. At the Pilot Analysis stage population for the direct interviews was selected among the major Companies in Sri Lanka. The research survey covered only the private sector organizations, due to their ability for quick implementation possibility of theB2B e-commerce trading, as they have the potential in entering into L-Commerce. A comprehensive survey was administered by Postal mail, Internet, e-mail and personal interviews. The questionnaire was web enabled to reach larger population, so that the si/e of the sample, together with its geographical dispersion, has a significant bearing on the research. The comprehensive study showed the current situation of B2B E Commerce Infrastructure in the Sri Lankan Industries have barriers and drivers, where recommendations are made to rectify those barriers and make advantages of the drivers, so that they can be in par with the global E commerce. One of the major findings was that the current E commerce regulatory factors in SriLanka do not support the Companies doing B2B E Business. Companies who have technical facilities up to some standards should be encouraged to upgrade their systems to venture into E Business. The available data shows that Sri Lanka Telecommunication Infrastructure availability is not a problem for companies to commence E Business. It is the reliability, running cost and connection cost that mainly affect the businesses* confidence to venture into E business. E commerce solution providers in Sri Lanka are competent in developing Ecommerce solutions but again it is clear that insufficient in-house skills and training and non-availability of in-house technology arise among the organisations which do not engage in E Business. It was revealed that even an enterprise with a single person can practice E Commerce. This is an encouragement to new businessmen in Small and Medium Scale Enterprises to use the advantages in E Commerce.
item: Thesis-Abstract
Analyzing traffic behavior and treatment in NGN IP core networks
Karunaratne, MAIK; Samarasinghe, K
Today Internet Protocol has taken over the entire communication. With the advancements in the new technologies cost of the IP related equipments has come down which has helped this exponential growth. with the increase of the usage the telecommunication service providers are expanding their infrastructure to cater the growth. Entire world is expanding their infrastructure mainly on IP equipments. Integrating the legacy infrastructure to the IP Network has lot of challenges. The real challenges are the transporting delay sensitive traffic like voice over the IP Network, IP node failures, IP link failure detections, delay variations. There are proprietary systems being developed between the IP vendors and the others in order to over come these challenges which can sometime be not flexible to the telecom service provider. In this research an open standard based approach is used to integrate media gateways to an IP/MPLS Network. The challenges of the integration are discussed in this thesis. A lab setup and a live network test were performed in order to measure the quality of the integration work. The interconnection methods were analyzed after going through the theories related to the media gateways and IP/MPLS technologies. Also since there. can be different type of traffic in an IP/MPLS network a traffic treatment method should also be developed The major results of the research was that using open standards methods the Essential parameters for the Media gateway integration of the IP core networks can be achieved. Also the model that was developed for the traffic treatments was successful. Media gateways interconnections with IP. networks are successful on open standards IP protocols. Fast convergence requirements, QoS requirements and jitter and delay requirements can be addressed using open standards IP protocols
item: Thesis-Abstract
Beamforming techniques for the downlink of space-frequency coded decode-and-forward MIMO-OFDM relay systems
Suraweera, ND; Wavegedara, Dr. KCB; Ekanayake, Prof. EMN
Multiple-input multiple-output (MIMO) techniques can be used to achieve diversity gain, multiplexing gain and/or array gain. Particularly, diversity cod- ing techniques (e.g. Space-Time (ST), Space-Frequency (SF) coding) have re- ceived tremendous attention as e ective means of achieving spatial diversity gain in MIMO systems. However, in the presence of spatial correlations the diversity gain of ST/SF coding diminishes. Beamforming techniques can be used to achieve array gains in MIMO systems. Hence, in correlated channels beamforming tech- niques can be combined with ST/SF coding to further improve the performance. In this thesis, we develop beamforming techniques relying on statistical channel state information at the transmitter (CSIT) for space-time (ST) / space-frequency (SF) coded MIMO systems to minimize the pair-wise error probability. We pro- pose beamforming techniques for SF coded MIMO-OFDM systems in correlated frequency-selective Rician fading channels. We propose two novel beamforming techniques for this channel model. Furthermore, distributed beamforming techniques are developed for correlated Rayleigh at-fading channels, relying on full-instantaneous CSIT as well as sta- tistical CSIT. Moreover, we extend these techniques for SF coded MIMO-OFDM relay networks in correlated Rician fading channels and propose optimal beam- forming techniques relying on full-instantaneous CSIT. Also, suboptimal beam- forming techniques relying on statistical CSIT are developed. The variation of error performance is thoroughly investigated and the simulation results con rm that all the proposed beamforming techniques achieve signi cant performance ad- vantages over MIMO systems using ST or SF coding only.
item: Thesis-Abstract
Blind frequency-offset estimation for OFDM systems operating in frequency selective fading channels
Patabandi, KPCS
Orthogonal frequency division multiplexing (OFDM) is successfully used in many wireless digital communications systems. It is used in Digital Audio/ video broadcasting, Wireless Local Area Networks (LAN) and related discrete multi-tone (DMT) is use in wired digital communications. Power of OFDM lies in dividing wideband channels into narrow band sub cannels while keeping the bandwidth efficiency. When channels are narrow band, they can be considered as frequency flat even in harsh conditions such as mobile communications. It also possesses some disadvantages. Sensitivity of OFDM to carrier frequency offsets and the degradation due to that in performance is one of the main disadvantages. This research work is focused on estimating unknown frequency offsets which cause intercarrier interference (ICI), while maintaining the bandwidth efficiency. There are numerous methods that have been proposed to overcome frequency offset problem in OFDM. Some adversely affect on the bandwidth efficiency by repeatedly transmitting data symbols or by overloading system with synchronization aided data. But there are methods which use inherent properties of OFDM signals to estimate the carrier offset while not lowering the bandwidth efficiency. The technique proposed in this thesis uses a concept which has been published by Mounir Ghogho and Anantharam Swami. But their algorithm has been modified so that a relatively efficient combined quadrature amplitude modulation (QAM) scheme can be used for transmissions. This new combined modulation scheme, which is referred to as pseudo QAM in this thesis, uses full QAM constellation for modulating part of the sub carriers in the OFDM symbol while other sub carriers are modulated using a sub constellation of the full QAM constellation. The sub constellation is selected so that all the symbols in the constellation have the same modulus. The estimation algorithm is based on virtual sub carrier property and the constant modulus property of the pseudo QAM sub carriers. To compare the performance improvement of the proposed scheme, computer simulations have been carried out for multi path fading channel with additive white Gaussian noise (AWGN). Simulation results indicate very good improvement of the accuracy of the estimation relative to the estimation based on virtual sub carriers alone. Few bit error rate (BER) simulations have also been carried out and the results are included to verify performance in terms of BER. The bandwidth efficiency has been improved in proposed scheme since part of the sub carriers can be modulated with full QAM constellations. Hardware required for this new modulation scheme is the same as that for general QAM schemes. Required changes can be carried out in software. System can be made such that it goes for pseudo QAM scheme only when the estimation accuracy obtained with virtual carriers alone is not enough. ii
item: Thesis-Abstract
Broadband connectivity using optical Access for the eastern province of Sri lanka
(2015-08-27) Alakurajah, B; Samarasinghe, ATLK
In Sri Lanka the widely used wired technology for broadband access is Asymmetric Digital Subscriber Line (ADSL).Fiber access is available in the Western Province with limited usage such as for business purposes. The Eastern Province is the focus for this research because it is one of the affected areas during the last two decades ofwar and therefore has limited facilities for the people living in that part of the country.The development work in the Eastern Province is in progress at present and it also includes facilities for broadband access. ADSL broadband usage within Eastern Province is available but limited to city areas only. This work focuses on a system to implement Fiber to the Home (FTTH) for the Eastern Province and thus provide efficient broadband access for its people. The available Fiber Access technologies are analyzed and the most suitable one is selected for implementation. The thesis proposes a network based on Passive Optical Network (PON) technology to be employed with Gigabit PON (GPON) in order to provide FTTH to a wider area of the Eastern Province. The GPON technology includes Coarse Wavelength Division Multiplexing (CWDM) with Time Division Multiple Access (TDMA); known as Hybrid PON. For the selected four cities Optical Line Terminal (OLT) locations are identified and Ring topology access is used with Remote Nodes which can be expandable when customer number increased. A cost estimate using the current equipment prices and the payback of the capital are calculated and presented in the thesis. The performance of the proposed network is analyzed which includes the Link Power Budget and the Bit Error Rate(BER). The performance analysis shows that the proposed Optical Access Network using GPON is feasible for implementation in the Eastern Province.
item: Thesis-Abstract
Broadband connectivity using optical access for the eastern province of Sril Lanka
Alakurajah, B; Samarasinghe, ATLK
In Sri Lanka the widely used wired technology for broadband access is Asymmetric Digital Subscriber Line (ADSL). Fiber access is available in the Western Province with limited usage such as for business purposes. The Eastern Province is the focus for this research because it is one ofthe affected areas during the last two decades of war and therefore has limited facilities for the people living in that part of the country. The development work in the Eastern Province is in progress at present and it also includes facilities for broadband access. ADSL broadband usage within Eastern Province is available but limited to city areas only. This work focuses on a system to implement Fiber to the Home (FTTH) for the Eastern Province and thus provide efficient broadband access for its people. The available Fiber Access technologies are analyzed and the most suitable one is selected for implementation. The thesis proposes a network based on Passive Optical Network (PON) technology to be employed with Gigabit PON (GPON) in order to provide FTTH to a wider area of the Eastern Province. The GPON technology includes Coarse Wavelength Division Multiplexing (CWDM) with Time Division Multiple Access (TDMA); known as Hybrid PON. For the selected four cities Optical Line Terminal (OLT) locations are identified and Ring topology access is used with Remote Nodes which can be expandable when customer number increased. A cost estimate using the current equipment prices and the payback of the capital are calculated and presented in the thesis. The performance of the proposed network is analyzed which includes the Link Power Budget and the Bit Error Rate (BER). The performance analysis shows that the proposed Optical Access Network using GPON is feasible for implementation in the Eastern Province.
item: Thesis-Abstract
Capacity improvement of CDMA systems by adaptive beam forming using GRNN techniques
Jayawardena, C.S.
The objective of this work is to demonstrate a method of improving the capacity of a Code Division Multiple Access (CDMA) system by employing Neural Network based Adaptive Beam forming. A Generalized Regression Neural Network was used for this purpose. First, the Neural Network was designed, which could accurately predict the phase angle of the feed current to a ten-element antenna array in order to form a directional beam towards a given signal source direction while forming a null towards a given interfering source. Then, the model was developed to form multiple beams to wards different signal sources. Next, using the multiple beam forming technique, a new Space Division Multiple Access (SDMA) model was developed to improve the capacity of an existing CDMA system that has already become saturated. This SDMA model is based on the statistical distribution of the mobile users within a sector. It assumes that the user distribution within a sector is non-uniform. More densely populated areas within a sector are identified and the users in a particular area are grouped together. One such group is called a cluster. Similarly, a number of clusters are selected and the three most populated clusters are served with three isolated directional beams operating on the same frequency achieving SDMA. It was observed that this new SDMA model could improve the capacity of existing CDMA systems up to a maximum of 20% with three directional beams.
item: Thesis-Abstract
CCTV Based sensing techniques for adaptive control of traffic signals in multiprocessor architectures
Nishantha, GGD; Jayasinghe, JAKS
As the problem of urban traffic congestion spreads, there is a pressing need for the introduction of advanced technology and equipment to improve the state of the art of traffic control. In this context, the techniques used for sensing traffic flow information plays a vital role, ensuring accurate real time controllability. Closed Circuit Television (CCTV) has gained popularity because of its ability to provide diverse information on relatively large regions leading to opportunities for performing substantially more complex tasks than conventional detection schemes. By processing these video images, traffic parameters such as speed, traffic composition, queue length etc. can be extracted. In addition CCTV images can be further processed for other useful information such as detection of vehicle shapes, vehicle types, occurrence of traffic violations and vehicle identification numbers etc. To introduce CCTV based vehicle detection for automation of road traffic control in Sri Lanka involves an unaffordable investment cost to purchase foreign technology and equipment unless some locally developed system is introduced. This thesis presents complete design of a CCTV system, which involves multitude of design and implementational aspects. It involves development of an image grabber, a remote communication interface and detection algorithms. In addition to visual monitoring of remote road traffic scenes, the designed system is capable of assessing many different traffic parameters, which can be used for adaptive control of road traffic. The underlined project is an attempt to seek the possibility of introducing image based traffic sensing technology to Sri Lanka. Significant attention has given to reduce the cost of development throughout the project to ensure that the concept of CCTV can be realized in practice in Sri Lanka for road traffic control.
item: Thesis-Full-text
Cellular positioning by location fingerprinting with the aid of propagation models
Wijesinghe, WHMP; Dias, D
The Fingerprinting method or the Database Correlation Method (DCM) is a network based positioning technique which has shown superior accuracy. DCM is based on a pre-measured database of location dependent variables such as Received Signal Strength (RSS). The major challenge of the technique is the effort involved in forming the database, which prevents it being deployed in large, dynamic networks. The work presented in this thesis investigates the possibility of using network planning tool predictions instead of field measurements to create the fingerprint database for DCM. While the accuracy of this approach is lower than the DCM method with field measurements, further tuning of the predictions in order to improve the performance is proposed. The tuning method is defined as cell-wise calibration, which calibrates the predictions by using a lesser number of field measurements in a cell-by-cell basis. In addition, a novel fingerprint filtering approach and a fingerprint matching technique (a cost function) are proposed. The trial results show that, the performance of DCM using the proposed database is inferior to that using a measured database. However, the application of calibration process for predictions improves the performance up to an acceptable level. The calibration method, designed for the bad urban scenario is based on curve fitting whereas that for urban, suburban and rural environments is based on neural networks. In addition, the novel fingerprint filtering approach is robust for the bad urban environment while the novel cost function shows higher performance with the proposed database. The best positioning accuracy for the. bad urban environment is 200m in 80% of the estimates and that for the urban environment is 125m (80%). Remarkable performance improvement can be observed in the rural environment giving a positioning error less than 385m in 80% of the estimates. The performance in suburban environment is inferior to that-in both urban and rural, with an error less than 550m in 80% of the time. The proposed solution for positioning is best suited for the deployment in large dynamic networks as a network-based method to provide basic information services, such as nearest ATM machine, petrol. station or hospital, traffic information and location based advertising.
item: Thesis-Full-text
CMOS leakage power reduction and data retention
(2019) Udayanga GWGKN; Thayaparan S
As silicon technology scaling, leakage power dissipation has become the most significant component from all CMOS power dissipation mechanisms. Minimum Leakage Vector(MLV) is used as a combinational logic leakage power reduction technique when a system is in standby mode. Compared to MLV, though an excellent leakage power reduction can be achieved with power gating technique it has some drawbacks like higher retention time and system state loss. In this thesis we combine MLV and power gating techniques to achieve more leakage power reduction compared to MLV while mitigating prior mentioned drawbacks of power gating. Instead of full chip power gating, we developed a simple algorithm which runs in linear time to identify the prospective locations for power gating once combination logic is fed with its MLV. The algorithm was implemented in tcl language and run on top of design compiler shell for a synthesized netlist. Flip flops and input ports were modified to feed MLV in standby mode while facilitating for partial power gating within the flops without losing flop state to retain the system state back in active mode. Flop modifications were extended to feed MLV in scan mode also so that scan mode leakage reduction can also be achieved while successful scan shifting carrying out. Our implementations were tested with four selected ISCAS89 benchmarks using fast spice simulations with synopsys XA. We were able to achieve 30%-40% additional leakage power reduction compared to standalone MLV. The measured wake up time was always less than 0.25ns for all benchmarks while with standalone power gating this is more than a nano second or couple of nano seconds . Successful operation in scan mode and state retention of flops after standby mode were also verified. Rough estimate in area increment due to newly added infrastructure was also carried out.