The ever-increasing demand for broadband services by end-user devices utilising 3G/4G/LTE and the projected 5G in the last mile will require sustaining broadband supply from fibre-linked terminals. The eventual outcome of the high demand for broadband is strained optical and electronic devices. The backbone optical fibre transport systems and techniques such as dense wavelength division multiplexing (DWDM), higher modulation formats, coherent detection and signal amplification have increased both fibre capacity and spectrum efficiency. A major challenge to fibre capacity and spectrum efficiency is fibre-faults and optical impairments, network management, routing and wavelength assignment (RWA). In this study, DWDM and flexible spectrum techniques such as wavelength assignment and adjustment, wavelength conversion and switching, optical add and drop multiplexing (OADM) and bitrate variable transmission have been experimentally optimized in a laboratory testbed for short- and long-haul optical fibre networks. This work starts by experimentally optimising different transmitters, fibre-types and receivers suitable for implementing cost effective and energy efficient flexible spectrum networks. Vertical cavity surface-emitting lasers (VCSELs) and distributed feedback (DFB) lasers have been studied to provide up to 10 Gb/s per channel in 1310 nm and 1550 nm transmission windows. VCSELs provide wavelength assignment and adjustment. This work utilises the non-return-to-zero (NRZ) on-off keying (OOK) modulation technique and direct detection due to their cost and simplicity. By using positive intrinsic negative (PIN) photo-receivers with error-free BER sensitivity of -18±1 dBm at the acceptable 10-9-bit error rate (BER) threshold level, unamplified transmission distances between 6 km and 76 km have been demonstrated using G.652 and G.655 single mode fibres (SMFs). For the first time, an all optical VCSEL to VCSEL wavelength conversion, switching, transmission at the 1550 nm window and BER evaluation of a NRZ data signal is experimentally demonstrated. With VCSEL wavelength conversion and switching, wavelength adjustments to a spectrum width of 4.8 nm (600 GHz) can be achieved to provide alternative routes to signals when fibre-cuts and wavelength collision occurs therefore enhancing signal continuity. This work also demonstrates a technique of removing and adding a wavelength in a bundle of DWDM and flexible channels using an OADM. This has been implemented using a VCSEL and a fibre Bragg grating (FBG) providing a wavelength isolation ratio of 31.4 dB and ~0.3 𝑑𝐵 add/drop penalty of 8.5 Gb/s signal. As a result, an OADM improves spectrum efficiency by offering wavelength re-use. Optical impairments such as crosstalk, chromatic dispersion (CD) and effects of polarization mode dispersion (PMD) have been experimentally investigated and mitigated. This work showed that crosstalk penalty increased with fibre-length, bitrate, interfering signal power and reduced channel spacing and as a result, a crosstalk-penalty trade-off is required. Effects of CD on a transmitted 10 Gb/s signal were also investigated and its mitigation techniques used to increase the fibre-reach. This work uses the negative dispersion fibres to mitigate the accumulated dispersion over the distance of transmission. A 5 dB sensitivity improvement is reported for an unamplified 76 km using DFB transmitters and combination of NZDSF true-wave reduced slope (TW-RS) and submarine reduced slope (TW-SRS) with + and – dispersion coefficients respectively. We have also demonstrated up to 52 km 10 Gb/s per channel VCSEL-based transmission and reduced net dispersion. Experimental demonstration of forward Raman amplification has achieved a 4.7 dB on-off gain distributed over a 4.8 nm spectral width and a 1.7 dB improvement of receiver sensitivity in Raman-aided 10 Gb/s per wavelength VCSEL transmission. Finally, 4.25-10 Gb/s PON-based point to point (P2P) and point to multipoint (P2MP) broadcast transmission have been experimentally demonstrated. A 10 Gb/s with a 1:8 passive splitter incurred a 3.7 dB penalty for a 24.7 km fibre-link. In summary, this work has demonstrated cost effective and energy efficient potential flexible spectrum techniques for high speed signal transmission. With the optimized network parameters, flexible spectrum is therefore relevant in short-reach, metro-access and long-haul applications for national broadband networks and the Square Kilometre Array (SKA) fibre-based signal and data transmission.

M.Ing. / The transmission of digital data at higher data rates and greater reliabilities is becoming increasingly more important in the society of today. The usage of, especially wireless digital data, is increasing at an alarming rate, and the need arises for more bandwidth to be made available for this purpose. Hence, the need arises to optimise and expand the usage of bandwidth currently under use. Existing wireless channels, such as the commercial FM service, need to be re-evaluated and unused bandwidth needs to be developed and used as close to capacity as possible. In this dissertation, a study was launched to develop the FM SST (Supplementary Signal Transmission) commercial analog service as a simplex digital channel that can commercially be used to transmit a myriad of digital data. With the help of a commercial FM radio channel, digital data was transmitted using a number of different modulation schemes to obtain channel measurements for the FM SST channel. The modulation scheme that performed the best, given certain criteria, was GMSK. This raw information was then used to extract first and higher order statistical information from the channel, in order to parameterise discrete channel models, based on a Markov process. The channel models that were used were the Gilbert, GilbertElliott and Fritchman channel models. These channel models were then tested according to their iirst and higher order statistical data to evaluate their effectiveness in modelling the error process on the FM SST channel. It was found that the channel model best approximating the real channels was the Gilbert channel. Once satisfactory results were obtained, these discrete channel models were then used to evaluate various error correction schemes for their ability to correct burst errors on the FM SST channel. From the various schemes evaluated, a (63,39) BCH with an interleaver of index 4 was found to perform the best. The purpose of which is to transmit digital data at the highest data rate possible and at the same time having a bit error rate less than lxl0-6.

An automatic repeat request (ARQ) scheme with memory and soft error detectors has been recently proposed by Benelli. Its performance was studied mainly through computer simulation. In this thesis, a generalized version of this ARQ scheme is examined. The selection of certain thresholds and weights to minimize the bit error rate in systems using a fixed number of packet repeats is considered. The evaluation of the average number of transmissions per packet in systems in which negatively acknowledged packets are retransmitted until successfully received is described. Finally, the performance of the memory ARQ scheme with forward error correction is analyzed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

M.Phil. / The advantages offered by power line communications (hereon after called PLC) cannot be over-emphasized neither can the inherent problems affecting its commercial takeover be underestimated. This research work creates a background study for experimental measurement and eventual implementations on power lines. It explains those salient aspects of commercially available communication modules that are rather not straight forward to understand from reading the Comblocks user manual. Especially, addressing those shortcomings of Comblocks that were not indicated in the documentation, we o er solutions to those we could nd our way around. M-ary frequency shift keying was implemented. This implementation tested the ro- bustness of the scheme against noises, attenuation and other power line channel char- acteristics as encountered practically. Based on our results, we nally recommend an optimal set of frequencies; we believe to be good for use in most PLC application pur- poses. Pseudo random bits of information were generated, encoded and modulated; the signals were transmitted over power line channels. The impact of noise sources, impulse noise especially was observed at di erent distances along the channel. Coupling and decoupling circuits used for this research, with associated issues sur- rounding the use of coupling circuitry are also presented. The CENELEC norm for PLC communication was adhered to, hence only frequencies that fall within the CENELEC speci cation for low voltage power distribution network were considered for MFSK use. Signal-to-noise ratio and other factors that a ect signal transmission over PLC was also measured. A complete communication system comprises of the transmitter, the channel and the receiver. This work however did not cover the receiver part of the system. Future work can now be done on this aspect which amongst others can take care of synchronization issues, in which a coding system as well as bit error rates can be determined.

Campus Area Networks (CANs) are a subset of enterprise networks, comprised of a network core connecting multiple Local Area Networks (LANs) across a college campus. Traditionally, hosts connect to the CAN via a single point of attachment; however, the past decade has seen the employment of mobile computing rise dramatically. Mobile devices must obtain new Internet Protocol (IP) addresses at each LAN as they migrate, wasting address space and disrupting host services. To prevent these issues, modern CANs should support IP mobility: allowing devices to keep a single IP address as they migrate between LANs with low-latency handoffs. Traditional approaches to mobility may be difficult to deploy and often lead to inefficient routing, but Software-Defined Networking (SDN) provides an intriguing alternative. This thesis identifies necessary requirements for a software-defined IP mobility system and then proposes one such system, the Software-Defined Mobile Campus Area Network (SD-MCAN) architecture. SD-MCAN employs an OpenFlow-based hybrid, label-switched routing scheme to efficiently route traffic flows between mobile hosts on the CAN. The proposed architecture is then implemented as an application on the existing POX controller and evaluated on virtual and hardware testbeds. Experimental results show that SD-MCAN can process handoffs with less than 90 ms latency, suggesting that the system can support data-intensive services on mobile host devices. Finally, the POX prototype is open-sourced to aid in future research.

The General Direction Routing Protocol (GDRP) is a Wireless Sensor Network (WSN) multi-path routing protocol which abstracts localization information (commonly GPS coordinates) into relative direction information in order to perform routing decisions. By generating relative direction information GDRP is able to operate with fewer precision requirements than other protocols. This abstraction also allows the integration of other emerging hardware-based localization techniques, for example, Beamforming Sensor Arrays. GDRP does not specifically address the next hop a packet should take, but instead specifies a direction it should travel. This direction abstraction allows for multiple paths to be taken through the network thus enhancing network robustness to node mobility and failures. This indirect addressing scheme also provides a solution to sensor node unique identification. GDRP is simulated in a custom simulator written in Java. This simulator supports interfaces for multiple protocols for layers 1, 2, 3, and 7 of the OSI model. For performance comparisons, GDRP is compared against multiple WSN routing protocols. GDRP operates with a significantly lower setup cost in terms of bytes transmitted and a lower setup latency for networks of varying sizes. It also demonstrates an exponentially lower routing cost when compared to another multi- path routing protocol due to a more efficient packet propagation in the network.

Recent advancements in Large Scale Integration Technology have made available devices, such as microprocessors, analog gates and “three state” logic, that provide the designer with a wide range of possibilities in the design of telecommunication systems. A microprocessor and analog gates are utilized in this design to demonstrate the feasibility of implementing a flexible Telecommunication System. The microprocessor is programmed to control, through software, the system functions. The feasibility of systems highly adaptable to the needs of individual subscribers is thus demonstrated.

Mobile devices have advanced tremendously during the last ten years and have changed our daily life in various ways. Secure pairing of mobile devices has become a significant issue considering the huge quantity of active mobile device connections and mobile traffic. However, current commonly used file sharing mobile applications rely on servers completely that are always targeted by attackers. In this thesis work, an innovative mechanism is proposed to generate symmetric keys on both mobile devices independently from a shared movement in arbitrary pattern, which means no server needs to be involved and no data exchange needed. A secret wireless-communication channel can then be established with a particular network strategy.

No description available.

As the functionality that current computer network can provide is becoming complicated, a traditional router with application-specific integrated circuit (ASIC) implementation can't satisfy the flexibility requirements. Instead, a programmable packet forward system based on a general-purpose processor could provide the flexibility. While this system provides flexibility, a new potential security issue arises. Usually, software is involved as the packet forward system is programmable. The software's potential vulnerability, especially as to the remote exploits, becomes an issue of network security. In this thesis work, we proposed a software stack overflow vulnerability on click modular router and show how a disastrous denial-of-service attack on click modular router could be triggered by a single packet. In our research work, click modular router runs on Linux operating system based on general-purpose hardware. We actually showed that even a software router run within a modern operating system's protection is vulnerable by elaborate attack. And we checked the possible stack protection mechanisms on modern OS based on general-purpose hardware and proposed a possible stack protection mechanism for embedded OS.