Master of Science in Telecommunications

Permanent URI for this collectionhttp://192.248.9.226/handle/123/60

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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
Cross-relation-based frequency domain blind channel estimation for MIMO communication systems
Rathnasiri, HHS; Wavegedara, C
Blind channel estimation is attractive for the application of in high-speed wireless communication systems due to its high spectral efficiency. Most of the conventional blind channel identification algorithms are based on the statistical properties of the transmitted signals. However, in practical communication systems, the statistical model of the transmitted signals may not be known or there may not be sufficient data to estimate the statistical properties. Alternatively, we can use Cross Relation (CR) principle for computationally-efficient blind channel estimation. CR principlebased frequency domain blind channel estimation schemes offer good performance when the data length is inevitably short. In this thesis, a frequency-domain CR-based blind channel estimation schemes are developed for both single-carrier and multicarrier multiple-input multiple-output (MIMO) systems. The proposed channel estimation scheme is able to identify the channel using a single received signal block. This channel estimation scheme is accompanied by a simple block pre-coding scheme. The channel is assumed time invariant within the signal block period which depends on the antenna configuration ofthe system. The numerical simulation shows that the proposed methods perform satisfactorily with only one or very few received signal blocks, with compared to existing correlation based methods which require more data blocks.
item: Thesis-Abstract
Developing a strategy and an open module for N-SBC to eliminate DDOS attacks from sip based NGN IP interconnections
(2015-09-18) Weerasinghe, SN; Samarasinghe, K
The Session Initiation Protocol (SIP) is the communication protocol of the future. Used for Voice-over-IP (VoIP), Internet Multimedia Subsystem (IMS) and Internet Protocol Television (IPTV), SIP's concepts are based on mature and open standards and it is usage is increasing rapidly. However, with its acceptance as a mainstream communication platform, security concerns become ever more important for users and service providers. Usage of SIP for communication is currently spreading into the last mile of mobile and fixed line carriers making then very much vulnerable to the protocols ofthe internet domain. The posed threat can be understood by the increasing number of calls being initiated from the internet to mobile and fixed line devices. At the crust, in order to manage the threats coming in from the internet, operators usually go for tighter Security in the Session Boarder Gateway (SBC), the interface between internet and the operator's domain. Furthermore, rogue attempts to infiltrate the Operator's domain is now becoming a common occurrence and leading to losses beyond billions of dollars of revenue. Irony is that Operator's sometimes does not understand the scale of the exploitation until much later in the billing cycle. This thesis identifies the probable modes of attacks including DoS and DDoS, and provides a strategy and an implementation plan to identify these threats via pattern matching and heuristic logic which is built on leaning algorithms. Target is to introduce a solution capable of learning and identifying patterns which leads to DoS, DDoS attacks and eliminate the rogue communication threads from ever entering the realms of the operator. With this solution, general VOIP communications with Operators shall be more robust against DoS and Distributed DoS attacks and many other threats looming at the N-SBS level of an NGN network.
item: Thesis-Full-text
Development of a quality of service (QOS) policy framework for mobile broadband services in Sri Lanka
(2016-09-17) Konara, DG; Samarasinghe, K
Development of a QoS Policy Framework for Mobile Broadband Services in Sri Lanka Quality of Service (QoS) has become an important aspect of regulation as part of industry monitoring and consumer protection objectives. The statutory framework that exists currently in Sri Lanka for mobile broadband QoS regulation is elementary, outdated and no proper monitoring mechanism in relation to the telecommunications environment today. Therefore, the current regulations falls short of driving improvements in quality of service in the telecommunications industry, promoting investment and innovation in the provision of services, and empowering consumers to make informed decisions about the choice of services and service providers. This research is mainly focused to identify the most suitable parameters required to measure the broadband QoS in mobile telecommunication; define target values for those parameters; define the procedures to get the measurements and define the auditing procedures for the regulator. There are few steps used to gather information for the policy framework. A survey was conducted among the professional in mobile telecommunication industry in Sri Lanka as the premier step. Then a study was done about the already implemented broadband policy frameworks in other countries. And also, it was thoroughly followed the definitions and standard introduced by ITU and ETSI. Finally seven QoS parameters were identified which are suitable for the proposed QoS policy framework and defined their target values. The measurements for three parameters have to get from live tests and remaining four can be calculated from the network tools already used by the operators. Therefore first three measurements should be taken by the regulator and remainings should be taken by the operator and required to send them to the regulator. It is proposed to do these testings once a month and the regulator should do an audit once a quarter for each and every operator.
item: Thesis-Abstract
Effect of polarization deviation in OTDM de-multiplexing using nonlinear optical loop mirror
Kumaran, K.; Thilakumara, P
Today, the optical communication is of great interest in developing extensive, high-speed networking infrastructures in all optical domains. High speed data rates are achieved in optical domain using different multiplexing techniques, mainly WDM and OTDM. WDM systems are somewhat matured today and are commercially deployed. OTDM systems are still in the research level and a promising technology for the future. Multiplexing and demultiplexing in optical domain is still a challenge mainly due to immaturity of all optical devices. All optical switching devices, which can potentially operate at very high speeds and much faster than electronic devices, are expected to play important role in the future optical communication systems. The large nonlinearity offered by the optical fibers demonstrates the potential for all optical switching. In this thesis, Demultiplexing of OTDM signal using NOLM is studied. The NOLM, whose operation principle is based on the fiber nonlinear effects, has been identified as the suitable best candidate for the demultiplexing of OTDM signal due to its simple configuration, low switching power operation and over Tb/s switching potentiality. This thesis investigates theoretically a dominant issue on NOLM demultiplexer. The impact of polarization deviation between the signal and control pulses and the switching efficiency of the NOLM demultiplexer for various power levels are studied. A complete set of equations concerning the different states of polarization and considering the SPM and XPM as the nonlinear effect of the fiber are established and simulated using MATLAB software.
item: Thesis-Full-text
An Energy efficient D2D communication model with guaranteed QoS for cloud radio access networks
(2020) Ranawaka IJ; Samarasinghe T; Hemachandra K
This work proposes a spectrum selection scheme and a transmit power minimization scheme for a device-to-device (D2D) network cross-laid with a cloud radio access network (CRAN). The D2D communications are allowed as an overlay to the CRAN as well as in the unlicensed industrial, scienti c and medical radio (ISM) band. A link distance based spectrum selection scheme is proposed and closed-form approximations are derived for the link distance thresh- olds to select the operating band of the D2D users. Furthermore, analytical expressions are derived to calculate the minimum required transmit power to achieve a guaranteed level of quality of service in each operating band. The results demonstrate that the proposed scheme achieves nearly 50% power saving compared to a monolithic (purely overlay or purely ISM band) D2D network. Moreover, this work creates an immense space for communication tech- nologies to be wisely managed and utilized by application layer requirements through CRAN architecture. Caching strategies for content replication across end user devices and e ective content delivery strategies can be implemented for forthcoming video streaming applications.
item: Thesis-Abstract
Evaluation of EM exposure from wireless communication devices in a household environmnt
(2016-05-30) Ariyaratne, TRCO; Samarasinghe, ATLK
With the increasing usage of wireless devices in households, the magnitude of exposure is explored when multiple such devices are used simultaneously. Out of many wireless devices found in a typical house, the study is limited to three common applications: Mobile Communication (GSM 900 MHz, GSM 1800 MHz and WCDMA 2100 MHz), Wi-Fi Communication (2400 MHz) and Cordless System Communication (1900 MHz). The necessary data samples were collected from a household environment and SAR calculations were performed. An indoor wireless propagation simulation was carried out to visualize the existing radio environment under wireless transmission. It is shown that effects of simultaneous exposure can increase the level of harmfulness.
item: Thesis-Full-text
Feasibility study on mobile number portability implementation in Sri Lanka
(2016-09-17) Hatharaliyadda, CB; Samarasinghe, ATLK
Mobile telephone number is considered as a great asset to a mobile telephone user. Generally subscribers are reluctant to change their mobile telephone number as it requires him to communicate about his movement to each and every potential person that is trying to reach him via his mobile telephone. Mobile number portability is a network function that allows mobile subscriber to switch service provider while retaining the mobile telephone number. Many countries have implemented MNP services in their telecommunication network to date. In this research study the necessity and subscriber willingness to accept MNP services implemented in Sri Lankan telecommunication market was tested through a mobile subscriber survey. In addition statistics on reasons for subscriber churn and some demographic aspects of subscribers those are willing to accept MNP services also analyzed through the responses collected on survey. Different MNP implementation architectures were analyzed in detailed with call flows. Advantages and disadvantages of each implementation architectures was identified and compared. The list of modification required in mobile service provider’s core network under each architecture was identified and feasibility of implementing each architecture was discussed with mobile telecom service providers in Sri Lanka. Analysis and comparison of costs involved in each different MNP implementation architecture was performed. The recommendations on implementable MNP architecture was given based on the feasibility and cost analysis using the statistics prediction made through subscriber survey.
item: Thesis-Full-text
Geo based routing for border gateway protocol in ISP multi-homing environment
Thilakarathne, D; Pasqual, A
BGP is the one and only protocol used by ISPs to exchange routing information between Autonomous Systems. An Autonomous System is an IP network or group of IP networks under a common administration with common routing policies. Internet Service Providers (ISP) connects to each other to facilitate reachability among Autonomous Systems using BGP protocol. Many ISPs setup multiple upstream connections to achieve global connectivity, redundancy, and a better quality of service. Multiple upstream connectivity results multiple paths to destinations. ISPs need to apply complex route policies to select the best outgoing interface to destination among multiple paths since BGP protocol does not consider link congestion, and distance to destination during the route selection process. Incorrect path selection leads to unnecessary traffic route between autonomous systems, high latency and low quality of service. Most prevailing issue for the South Asian internet users is that Internet content is not hosted within the region but in Singapore, Europe, and USA data centers. BGP protocol does not select shortest distance always when multiple upstream connections are available to ISP. This results in high latency to the end users. We can simulate different ISP path delays by introducing delay element between end server and client terminal. This proposal provides experimental results on how end user experience varies when delay to end server varies. Delay is proportional to distance between user terminal and end server. Therefore, this proposal considers distance to end server when solution is proposed to optimize end user delay. Traditional BGP does not consider geographical distance to end server when selecting outgoing interface. BGP has thirteen criteria to select best outgoing interface but most dominant criteria is the AS-PATH length. This research focuses on equal AS path length occurrences of current full BGP routing table in multi-homing environment. Equal AS-PATH length results BGP protocol to select outgoing interface randomly based on lowest router ID or lowest interface ID. The proposal suggests using geo graphic distance to destination as tiebreak condition for equal AS-PATH. This enables BGP itself to calculate best path without using complex routing policies. BGP is a heavily adopted protocol in the internet domain. It is hard to change such a stable implementation to achieve proposed geo based routing. SDN based implementation proposes in this proposal since SDN implementation is becoming popular in IP networking domain. New route selection criteria for BGP can easily implement using SDN controller. Simulation results reveal approximately 50 percent of the routing decisions are based on equal AS-PATH length if special routing policies are not applied. Further, simulation result justifies a relationship between latency and web page browsing user experience.
item: Thesis-Abstract
High data rate optical soliton communication systems
Athuraliya, JPDS; Thilakumara, RP; Dayawansa, J
Optical solitons are attractive at very high bit rates as linear systems are impossible at such high bit rates due to dispersion effect. In a solitor propagation system no dispersion compensation fibers are used. The pulses propagate partly as a soliton between repeaters, and at the latter part as the power decreases the system exhibits linear properties. As the system exhibits quasi -soliton propagation effects the system cannot be evaluated by soliton equations. Such a system can only be evaluated using modeling.// As the optical soliton is of the envelope of light waves whose fundamental properties are described by the Nonlinear Schrc dinger Equation (NLSE), the NLSE can be used to present the soliton concept for application to communications. The NLSE is solved using one of the numerical modeling, split step Fourier method.// Therefore the solution of the NLSE is used to present the solitor concept for application to communications. In this research, Short laser pulses are used to make the soliton communication system. The simulated results of 40Gbps single channel transmission of standard fiber and LEAF fiber are compared.// The results of the 4CGbps single channel transmission of standard fiber indicate that the maximum distance the pulse could travel is about 500km with a repeater spacing of 50km and the results o f the 40Gbps single channel transmission of LEAF fiber indicate that the maximum distance the pulse could travel is about 1250km with a repeater spacing of 50km.
item: Thesis-Abstract
Integration of fingerprinting and trilateration algorithms for improved indoor localization
(2014-08-22) Kodippili, NS; Dias, D
Many useful commercial, educational, security and health-care applications of location-awareness related to navigation, tracking and detection of people and objects have been developed throughout the history. However the demand for the location information has been limited to outdoor applications until many indoor localization requirements appeared recently with the emergence of ubiquitous computing. The indoor applications inherently call for higher positioning accuracy than those of outdoor. The existing sophisticated outdoor localization techniques like A-GPS do not perform satisfactorily in indoors due to the poor satellite signal coverage and the signal propagation complexities in indoor environments. On the other hand, though a number of different indoor techniques have been implemented and tested hitherto, none of those techniques have displayed satisfactory overall performance adequate for large scale deployment of commercial applications. The key performance indicator of positioning techniques is the positioning accuracy, which is quantified in terms of error distance. This research was focused on integrating two existing basic positioning algorithms, fingerprinting and trilateration, with a view to improving the performance with respect to positioning accuracy as well as cost, complexity, response time and implementation aspects etc. The fingerprinting has been used to identify few locations of known coordinates and signal strengths, closer to the target location. The final position estimation is done by applying the trilateration technique over the range between the selected known locations and the target location. The signal propagation model employed in this technique reproduces the real signal propagation behavior accurately since it is being applied over a short range and hence the distances calculated using the signal propagation model are fairly accurate. Consequently a better estimation of the location can be derived without getting affected by typical practical problems associated with unpredictable nature inherent to the radio signal propagation. This research thesis describes the design and implementation of the proposed integrated algorithm in an indoor WLAN environment to evaluate its performance in comparison with the basic techniques it is derived from. The proposed technique estimates the location of an object accurately within 1.1 m in less than a second with manageable training grid size at almost no additional cost. The overall satisfactory performance suitable for generic commercial applications demonstrated by the proposed technique could be a good foundation for ubiquitous deployment of indoor localization applications.
item: Thesis-Abstract
Intelligent browser agent
Ratnayake, A; Pasqual, A
In today's information technology era IT infra structure and solutions provide a solid base for us to carry out our day to day work. Yet the computers themselves are unable to stand on their own with complete independence. Information technology has always been a combination of intelligent human beings and computationally efficient machines. The objective of the research is to develop an automated internet browser module which assists the user in searching content in the internet. In that sense the research attempts to pass on human intelligence as much as possible to the software such that the actions of the agent resemble those of a human being. The independent nature of the agent is focused at an agent actions and behaviors are made not to interfere with end user activities. The research begins with a literature survey on aspects of Artificial Intelligent (AI) and its evolutions. Selected AI theories are then used in designing the prototype of the agent. The prototype focused on key findings of the literature survey and key AI areas such as modeling the environment, building domain knowledge, searching and sorting, agent learning, handling uncertainty and adaptability. Areas of improvements of the initial version were identified and were implemented as an extended version of prototype. The agent monitors the end user actions and identifies the web content he browses. It then decides on the possible areas of interest of the user and tries to predict search terms and searches for targeted sites in the internet. If the user has opted for the agent to load the predicted sites the agent would open them in separate browser windows. The agent is designed to resemble a typical user such that it would monitor the traffic levels and patterns of the user and would take actions only if they won't interfere with user's actions. Observations indicate that level of end user experience improves in various aspects. The agent makes use of only idle bandwidth thus users will not feel any overloading of traffic. Also the agent predicts sites most relevant to the immediate content being browsed thus targets the immediate requirements of the user. The agent highly depends on the relevancy of a web site's Meta tags to its actual contents. Thus if it encounters a site with poorly formatted Meta tags it could fail to achieve the level of appropriateness of the predicted sites to users actual requirements. Observations of TCP/IP traffic traces prove that when the agent is active the search traffic originated by it is below 20 packets per second where as user originated traffic is in the range of 150 - 175 packets per second. Due to the back end packet tracing and analysis the CPU load is around 45% with few +/- variations.
item: Thesis-Abstract
Intuitive reasoning for epistemic uncertainty
(2016-05-25) Senaratne, DN; Pasqual, AA; Jayasinghe, JAKS; Kulasekera, EC
Epistemic uncertainty, characterized by subjectiveness and partial availability of information, is associated with the domains of multi-sensor fusion, evidence processing, etc. Mathernatical Theory of Evidence, pioneered by Glenn Shafer [1], is a branch of study seeking to analytically model and manipulate the epistemic uncertainty entertained by an agent. The field is relatively young and cluttered with schemes that are used non-cohesively and often counter-intuitively. Further the issue is made worse as none of the schemes seems to be capable of modeling fully the uncertainty met in practice. Interestingly, humans are capable of intuitively handling such uncertainty in statements in their day-to-day activities. It is apparent that the reasons for deficiencies in existing models is the unjustified nature of their application approaches. This research seeks to enhance the intuitiveness and flexibility in mathematical modeling of epistemic uncertainty. It identifies three aspects, which any model should address cautiously. Namely, the manner in which real world propositions are mathematically represented, the manner in which uncertainty entertained by an agent is conveyed as a number assignment, and the manner in which expressed uncertainty is combined and conditioned. Novel strategies that parallels the way humans reason and hence enhance the intuitiveness, are introduced to overcome shortcomings in the existing mathematical representation. Further it proposes representing support as functions of propositions which are formed using a Boolean algebra on a set of hypotheses representing the context. Handling of some complicated propositions is simplified by introducing N-of, a logical operator formalizing the human notion 'N of n'. The research also proposes methods that can be used to select an appropriate combination strategy based on the contextual relationships between the frames, for a given evidence. It is further noted that the counter intuitive results obtained using the existing combination function's is a direct consequence of one being unaware of this relationship. Latter part of the research focuses on the concept of pre-conditioning, where evidence is conditioned based on external information one deems as certain. It also examines how comparable evidence may be averaged based on pre-determined weights. Although, a couple of novel concepts are introduced, the concepts retains backward compatibility with what is already established in this domain. Being modular, the proposed schemes can be selectively integrated with the existing techniques.
item: Thesis-Abstract
Investigation of methods to develop a system for human psychological state detection
(2015-09-18) Ranathunga, RAMP; Samarasinghe, ATLK
Stress is considered a major concern of the modem world as it negatively impacts social stability by hindering performance, efficiency and overall health of people. It is the leading cause of serious life threatening diseases such as heart disease, stroke, high blood pressure, cancer and many psychological disorders. Therefore solutions are constantly researched as it has become a severe issue in the fast paced world especially western nations where they have encountered drastic consequences. The only solution that can counteract stress is relaxation. The western approach to stress management is mainly through psychotherapy and external stimuli such as brain synchronous music, while the eastern approach tends to go into deeper relaxation through meditation. It's not possible to detect stressed/relaxed psychological states directly, it is essential to study the physiological cues through which it manifest in order to detect it. According to literature different research studies have used cues Heart Rate Variation (HRV), skin temperature, Galvanic skin response, Respiration patterns, Electroencephalography (EEG) as physiological cues, however very few research studies have been carried out focusing on physiological effects of eastern relaxation techniques. Heart rate and Electroencephalography (EEG) were selected as physiological variables during this research and most importantly both western and eastern approaches to relaxation have been analysed together with counterpart stress. Stressed state triggered using arithmetic stressors and stressful videos while relaxed state generated by meditation and relaxation music. Nonin 4100 pulse oxymeter and Emotiv EEG headset were respectively used for capturing raw heart rate and EEG signals. Fourier techniques have been widely used while wavelet techniques have been occasionally used for Heart rate and EEG data processing as per the literature, decided to proceed with wavelet packet decomposition as it allowed both frequency and time localization of the signal with much reasonable accuracy. Matlab together with EEGLAB was used as the data processing tool during entire research. Heart Rate signals' Power characteristics of Low Frequency (0.04 - O.1S Hz) and High Frequency (O.lS - O.S Hz) bands, which correspond to sympathetic and parasympathetic activities were analyzed. Further power characteristics of Delta, Alpha, Beta and Gamma rhythms of EEG singals were analyzed for each test case, each channel. The results of the experiments were in par with the results suggested by current literature for common stress and relaxation test cases, importantly additional test case meditation triggered high power in Alpha EEG rhythm and high frequency band of Heart rate signals. It was possible to identify that db2 (sym2), dbS, sym7, coiflets4 and coifletsS wavelets can be used for heart rate based analysis, in addition to db4 & dbS which were used in literature. Noticed that the EEG channels corresponding to occipital regions are the best channel locations that have to be analyzed to identify psychological state, while it's possible to use db6, db7, dbS coif2, coif3, coif4, coifS, symS, sym6, sym7 and symS wavelets in addition to db4 and dbS which were generally used in literature for EEG related analysis. Accuracy of the test setup can be further improved by incorporating more physiological cues and by identifying best techniques for filtering, rejecting artifacts of EEG signals. Further, state identification process needs to be automated while integrating a data mining tool to convert setup to a real-time psychological state detection and management tool. Abstract
item: Thesis-Full-text
An Iterative capacity dimensioning scheme for an LTE advanced network under resource constraints
(2019) Chandimal KGN; Wavegedara C; Samarasinghe T
Since the need for high-speed broadband services is growing exponentially, legacy voice oriented networks are now becoming obsolete. Due to the unceasing demand for data, investors of mobile service providing companies are also keener on investing new technologies other than GSM, which ultimately improves spectrum efficiency and speeds up the access. Long Term Evolution (LTE) is the fastest and latest broadband technology with widespread global development of commercial networks. Until now, scientists are working to improve the communication capabilities while evolving from basic voice services to high definition video streaming and real time video game playing. However, every operator has a limited investment capacity and are highly concerned about the maximum utilization of resources with a higher ROI. As a result, it is imperative to have a properly dimensioned and well-optimized network. However, LTE network dimensioning is not as easy as legacy pure voice-only networks (circuit switched), which can be easily modeled by Erlang formulae. LTE networks are evolving from circuit switching to packet switching; therefore, both voice and data will be transferred as packets. There can be combinations of different data service requirements such as streaming, browsing, interactive video, gaming etc. with voice. In fact, different types of traffic, which require different QoS are inherent. With the new releases of LTE standards, researchers all over the world are interested in finding most optimum ways of dimensioning LTE networks. Several perspectives have looked at calculating the required number of 4G sites in the initial network-planning phase. Even though there are quality-based models, coverage based models, capacity based models and hybrid models already, due to the complexity of both UL and DL throughput calculations, each model has its own advantages and disadvantages. None of the approaches are discussing about an iterative capacity dimensioning solution to fine tune the required site count. Therefore, in this research thesis author proposes an iterative method under constraints to find the minimum site count while achieving given UL/DL speed requirements for LTE network rollouts. This method will be based on iterations, and varying parameters will be heavily significant in the context of DL and UL throughput.
item: Thesis-Full-text
K-best sphere detector based receiver for mimo non-orthogonal multiple access systems
(2019) Ranaweera NNS; Wavegedara KCB; Samarasinghe T
Non-Orthogonal Multiple Access (NOMA) is a promising radio access technology, which improves the spectrum efficiency and system throughput considerably over conventional Orthogonal Multiple Access (OMA) techniques and also enables massive connectivity. NOMA is currently being considered extensively as a key enabling technology for 5G wireless networks. However, in NOMA, one of the key technical challenges is to develop efficient receivers due to the presence of Multiple-Access Interference (MAI) caused by non-orthogonal resource allocation. Minimum Mean Square Error (MMSE) based Successive Interference Cancellation (SIC) receivers have widely been discussed in the literature for power-domain NOMA systems. However MMSE detector is a linear detector with poor error performance. In this research, a K-Best sphere detector based SIC receiver is discussed for the downlink of power-domain MIMO-NOMA systems. The BER performance of the proposed receiver is investigated for different power allocation ratios and for different K values of the K-Best detector. Link level simulation results demonstrate that our proposed K-Best detector based receiver offers much superior performance over the MMSE-SIC based receiver.
item: Thesis-Full-text
Knowledge management framework for mobile telecommunication sector in Sri Lanka
Nadeera, J; Samarasinghe, K
Sri Lankan mobile telecommunication industry is a fiercely competitive market space where five key mobile service companies operate. Most operators provide their services island wide; therefore the coverage footprint is no longer a differentiating factor. On the other hand, knowledge is a tool, which companies can use to provide a better service quality, which is now in demand with customers. Due to globalization and increasing opportunities for individuals, companies face a challenge to retain best employees within the organization. Now the focus has shifted to keep the knowledge within the organization even with the movement of skilled labor. Therefore, knowledge management systems are necessary than ever before, but a most suitable knowledge management framework is yet to be identified. The objective of this study was to determine a most appropriate Knowledge Management Framework for Mobile telecommunication sector in Sri Lanka. To realize this goal, initially, a literature survey was performed. The Author analyzed various knowledge management models available and best global practices of knowledge management aspects. It revealed six key concept variables, i.e. socialization, externalization, combination, internalization, knowledge sharing culture, and leadership. Next, an online survey tested these concepts to find the importance and current practices in the mobile telecommunication industry in Sri Lanka. This study identified that all the six concept variables were relevant to Sri Lankan context, while externalization, combination, and internalization practices were at a lower level. Finally, a knowledge management framework suitable for mobile telecommunication industry in Sri Lanka was developed.
item: Thesis-Abstract
An MMSE-based MCI and MAI cancellation receiver for MIMO OVSF-OFCDMA systems
Kumara, NK; Wevagedara, KCB
Broadband orthogonal frequency code division multiple access (OFCDMA) with two dimensional spreading is a promising candidate for Beyond fourth Generation (B4G) networks. Since wideband channels are highly frequency-selective, orthogonality among orthogonal spreading codes are no longer maintained. Therefore, multiple code interference (MCI) is inevitable in OFCDMA-based systems. Multiple-Input Multiple-Output (MIMO) will be a key technology of future wireless communication systems. In MIMO-OFCDMA systems, in addition to MCI, inter-spatial stream interference (ISSI) will also exist. Even though maximum a posteriori probability (MAP)-based detectors provide the best performance, their computational complexity is high. Alternatively, minimum mean-square error (MMSE) detectors can be used to obtain a better tradeoff between the complexity and the performance. ; Several interference cancellation techniques were proposed under LTE Advanced, B4G standardizations and corresponding literature. One such technique is zero-forcing MAI nulling and cancellation based on QR decomposition (ZF-QRD). That can be used to cancel the MAI separately. But we are proposing a combined ISSI and MCI cancellation technique. We also compare the performance of MIMO VSFOFCDMA recursive ISSI and MCI cancellation scheme with conventional MC-CDMA, MC-DS-CDMA, MT-CDMA and OFCDMA.
item: Thesis-Abstract
Modeling of multimode fiber systems
Maheswaran, M; Priyantha, T
The optical communication is of great interest in developing extensive, highspeed networking infrastructures. Optical fibers provide many advantages over traditional copper cables and wireless links. Among these advantages are high security, low electromagnetic interference, extremely low loss, very high ban dwidths, and highly manageable cabling. However, the very small wavelengths associated with optical radiation require very small waveguide dimensions. Waveguide dimension of single mode fiber (SMF) are < 10um, resulting in relatively poor yield in device manufacturing. For most of the last-mile networks topologies, cost constraints limit the appeal of SMF. Large core fibers allow for less restrictive manufacturing tolerances; however, they also results in multi mode propagation that exhibit distortion from the dispersion in propagation among the many modes. The distortion can be prohibitively large for data rates approaching and exceeding i Gb/s.// Improvement of the de ployability of these multi mode fibers depends on the proper design of the multi mode fiber link parameters for the reduction of the over estimation. Conventional multi mode fiber model ignores all the effects of the different laser mode profiles in the link simulation and over estimates the penalty. Proposed modified model for vertical cavity surface emitting laser (VCSEL) based mult imode fiber (MMF) links considers all effects of different laser mode profiles and compare the transmitted eye diagrams and Q- Factors with the conventional model.// Significant differences observed in the eye diagrams and the Q- factors of the modified model compared to the conventional model with various kinds of graded index mult imode fibers and VCSEL. 29 % of Q- factor improvement observed in laser optimized MMF link with rate of 10 Gb/s and distance of 300 m.
item: Thesis-Full-text
National broadband strategies for Sri Lanka
Jayalath, MB; Samarasinghe, K
Objective of this study was to propose a set of national broadband strategies that suits to Sri Lankan context. Strategic planning process is used as the model to build up national broadband strategies. Initial step of the model is to set some strategic objectives. Therefore, set of strategic objectives, goals, targets for broadband were proposed. It is required to conduct an environmental scanning process which can be used to identify internal and external factors of the broadband environment. Environmental scanning process was done by a questionnaire which was administered among industry personnel and also the face to face interviews were carried out with government body personnel which represented from TRCSL and ICTA. Interviews which were carried out, revealed about existing broadband strategies and also the national broadband policy which has been drafted by a committee of broadband experts. Then the set of broadband plans were formulated and proposed and output of literature was used a platform to build up broadband plans. Literature survey was carried as an analysis of approaches that leading countries have taken in expanding their broadband markets, with a focus on the Republic of Korea. In addition, case studies covered Finland, France, Japan and the United States. Another case study of broadband implementation of Nigeria was also discussed in literature survey. Then this study revealed some set of broadband initiatives and policies that can be aligned with broadband plans. Those initiatives and policies are validated by the outcome of the literature survey and the discussion which had with government body personnel.