M. Tech. Electrical Engineering. / This study proposes a mathematical optimisation approach which invokes Genetic Algorithm (GA) for initialisation and application of Tabu Search (TS) algorithm in finding the sites of node Bs in the network to enable it have the potential to support an increased number of users requiring the increased number of services. The global optimisation can be obtained in terms of great probability as GA is applied to global search and TS is applied to the local search. The particular memory ability of TS can be integrated to GA and the prematurity of GA can be avoided by virtue of the hill-climbing ability of TS. The problem to be addressed is the determination of optimal locations of node Bs in the network based on the user distribution, while improving the QoS. The proposed approach considers the site selection as an integer problem and the site placement as a continuous problem. The two problems are focused on concurrently - finding the optimal number of node Bs that satisfies the capacity requirements in the network and hence QoS improvement. The proposed algorithm combines the strength of Genetic and Tabu Search algorithms in successive elimination of node Bs after their random distribution in the area of study. The results showed that the proposed approach produced fewer number of node Bs sites in the network that provided the required QoS. In addition, it exhibited high fitness function in the simulations meaning that it has the higher ability of achieving the objective function when it was compared to TS and GA.

In our time, it has become easy to contribute to the general pool of knowledge: Tell somebody about events that have just happened and think yourself useful, publish a video of a crime and make history, put up a rumour and ruin someone’s career. My question is: Can we talk about counter-knowledge when it comes to news-contributors who are not journalists but have mobile phones from which they can send messages and photos? I will first outline why the idea of counter-knowledge is attractive, then sketch it as defined by French philosopher Michel Foucault. My third point is about ways of writing which produce counter-knowledge, before finally asking if sending an image can have the same effect.

Modern networks carry a wide range of different data types, each with its own individual requirements. The scheduler plays an important role in enabling a network to meet all these requirements. In wired networks a large amount of research has been performed on various schedulers, most of which belong to the family of General Processor Sharing (GPS) schedulers. In this dissertation we briefly discuss the work that has been done on a range of wired schedulers, which all attempt to differentiate between heterogeneous traffic. In the world of wireless communications the scheduler plays a very important role, since it can take channel conditions into account to further improve the performance of the network. The main focus of this dissertation is to introduce schedulers, which attempt to meet the Quality of Service requirements of various data types in a wireless environment. Examples of schedulers that take channel conditions into account are the Modified Largest Weighted Delay First (M-LWDF), as well as a new scheduler introduced in this dissertation, known as the Wireless Fair Largest Weighted Delay First (WF-LWDF) algorithm. The two schemes are studied in detail and a comparison of their throughput, delay, power, and packet dropping performance is made through a range of simulations. The results are compared to the performance offour other schedulers. The fairness ofM-LWDF and WFLWDF is determined through simulations. The throughput results are used to establish Chernoff bounds of the fairness of these two algorithms. Finally, a summary is given of the published delay bounds of various schedulers, and the tightness of the resultant bounds is discussed. / Thesis (M.Sc. Eng.)-University of Natal, Durban, 2003.

This dissertation exammes two of the rlsing technologies in the world of wireless, cellular communications - CDMA and the software radio. This thesis covers many of the issues related to these two emerging field s of wireless communications, establish ing a theoretical framework for the broader issues of implementation. To this end, the thesis covers many of the basic issues of spread spectrum communications, in addition to establishing the need for, and defining the role of, the software radio. Amalgamation of these two key areas of interest is embellished in a presentation of many of the concerns of implementing a specific CDMA system on a particular type of software radio - the Alcatel Altech Telecomms Flexible Radio Platform. Of primary concern in the research methodology embraced in this thesis is the mastering of a variety of analysis and implementation tools. Once the theoretical background has been substantiated by current expositions, the thesis launches along a highly deterministic route. First, the research issues are tested in a mathematical environment for suitability to the given task. Second, an analysis of the appropriateness of the technique for the software radio environment is undertaken, culminating in the attempted deployment within the hardware environmenl. Rigorous testing of the input/output mapping characteristics of the hardware instantiations created in this manner complements the research methodology with a viability study. This procedure is repeated with many elements of the CDMA system design as they are examined, simu lated, deployed and tested. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

WCDMA promises to achieve high-speed internet, high quality image transmission and high-speed data services with larger system capacity. However, Multiple Access Interference is one of the major causes of transmission impairment, which reduces the link capacity in WCDMA systems. The Adaptive Antenna Array (AAA) technique reduces multiple access interference by directing antenna beam nulls towards the interfering signals by weighting the received signals from all antennas before combining the signals. With the very rapid advancement of wireless personal communications services, a new challenge to the cellular industry is the integration of multiple systems and applications on a single device. A software radio technique offers a possible solution to achieve this goal including international roaming and multiple standard operations within the same geographical area. The main attraction of a software radio is it's flexibility, in that it can be programmed for emerging cellular standards allowing it to be updated with new software without any changes in the hardware infrastructure. A software radio incorporating adaptive array beamforming at the receiver can increase the total carried traffic in a system and transmit power while the probability of call blocking and forced termination can also be decreased. This dissertation examines WCDMA, AAA, power control and software radio techniques in the world of wireless communication systems. Once the theoretical background of CDMA and AAA has been substantiated, the thesis establishes the need for power control in mobile systems by examining simulation results. An AAA receiver with six antenna elements is proposed and evaluated in different environments as a precursor to implementation. It can be inferred that when the link is interference limited, the link capacity can be increased and it has been shown that the AAA receiver with six antenna elements increases the link capacity to about 2.9 times that of the single antenna RAKE receiver. This thesis also examines the basic concepts of VHDL and considers this as the principle means to program reconfigurable core FPGA's in the software radio. A three-layered (PC/DSP/FPGA) software radio test bed is used to implement an AAA receiver. The architecture of the test bed is designed in such a way that it can be used to evaluate the performance of various FPGA based transceivers and coding schemes etc. Many of the desirable features and flexibilities inherent in the software radio concept are available on this test bed and the system has proved to be capable of high speed digital processing and is ideally suited to the development of time critical system components. The bit error rate achieved using the implemented receiver is assessed and compared to simulation results in an environment incorporating Rayleigh fading and AWGN. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.

An ad-hoc network is a collection of mobile nodes (wireless communication devices) that transmit data over systems that do not require any centralized control, such as that found in cellular networks. This makes ad-hoc networks suitable for military type applications, since there is no need for an established backbone infrastructure and hence no single-point-of-failure. However, other uses of ad-hoc systems include search and rescue missions, law enforcement operations, commercial and educational communication of laptop (and other handheld device) data, as well as in the transmission of environmental sensor information. The mobile ad-hoc concept brings many design challenges. The dynamic freedom of movement from mobile nodes causes random, sometimes rapidly time changing topologies, which are inappropriate for use through traditional wired protocols. In addition, wireless networks generally contain greater bandwidth, processing and power constraints than their wired counterparts, since they are implemented on embedded mobile, handheld devices. Thus, a different approach is needed in the wireless network domain. This has resulted in wireless routing protocols employing adaptive, multi-hop, distributed methodologies in which each node additionally acts as a router for each of its neighbouring nodes, in order to achieve a large degree of network connectivity. However, due to the broadcast nature of wireless transmissions, ad-hoc systems contain a point-to- multipoint communication architecture, making it well suited to multi-path traffic. One such application is in multicasting, which sends data from one source to two (or more) destinations. But, due to the shared characteristics of the communication channel, such traffic may cause multiple contentions and collisions to occur, which will degrade the efficiency and performance of a protocol. This dissertation examines these different design tradeoffs through the use of a freely available simulation package, known as NS-2 (Network Simulator - version 2). In addition, a novel routing protocol, known as LAMP (Location Aided Multicasting Protocol), is developed to handle time-bounded audio information, which is employed in a network that consists of sixteen commercial handheld devices. LAMP utilizes a destination-sequenced, next-hop routing table to forward multicast data. Since mobility causes neighbouring nodes to continually change, next-hop links need to be periodically updated. But, between each update period, a next-hop link may become broken. Thus, if a packet is required to be routed, for which its' next-hop link is unknown, LAMP reverts to a localized location aided flood to find a path to that destination. However, since flooding causes network congestion, it is only employed when its' table forwarding scheme fails. Results have shown that LAMP improves packet delivery ratios by up to 5% over exisiting flood-limiting schemes: Furthermore, LAMP has been shown to be comparable to leading schemes, even when employed to route data to a single source-destination pair. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

Quality-of-service (QoS) guarantees have become critically important for the transmission of real-time multimedia traffic in next generation mobile wireless networks. The aim of this dissertation is to investigate the cross-layer design for support of delay bound QoS guarantees over fading channels. Providing diverse QoS guarantees presents a challenge due to the time-varying fading nature of wireless channels. Existing physical layer modelling is inadequate in supporting real time QoS metrics such as delay, hence adaptive techniques need to be extended to the upper-protocol layers. The first objective of this dissertation is to introduce a cross-layer design framework which investigates the impact of the physical layer on the data link delay bound QoS performance. At the physical layer, adaptive modulation and coding (AMC) is utilized for transmission over block fading channels. At the data link layer, the effective capacity approach is used to model the delay bound QoS performance subject to physical layer variations. The effects of varying physical layer parameters, such as average signal-to-noise ratio (SNR), the fading parameter for the kagami- model, and target packet-error rate (PER), on the analytical delay bound performance are investigated and then validated by the simulation of a queuing system. Due to the cross-layer design framework, the system’s throughput has a significant impact on bounded delay at the data link layer. The switching levels of the conventional AMC scheme used in the first objective were fixed, subject to a target PER. However, fixed switching levels results in the system’s throughput limiting the delay bound performance. The second objective of this dissertation is to optimize the switching levels of the AMC scheme employed at the physical layer, by maximizing the average throughput, while maintaining the target PER constraint. The analytical and simulated results show that by optimizing the switching levels, a superior delay bound performance is achieved, when compared to the deterministic switching levels of the conventional AMC scheme used in the first objective. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

The Internet Engineering Task Force (IETF) has recently released routing standards that allow deployment of TCP/IP local area networks (LANs) onboard a moving vehicle and yet maintain permanent connectivity of the onboard LAN to the Internet via a vehicular mobile router. This recent development opens up new opportunities for providing efficient mobile computing for users on the move, especially for commuters traveling on public transports. Supporting real-time communications, e.g. IP Telephony, on-line video on demand, etc., over such onboard mobile networks is the main motivation of this thesis. Due to the volatility of the wireless bandwidth available to connect the moving LAN to the Internet at different locations of the trip, supporting on-line services that require bandwidth guarantees becomes a challenging task. The main problem investigated is how to provide bandwidth guarantee efficiently, effectively, and in a scalable manner in the context of moving onboard networks. To achieve the goal, a systematic approach is taken that involves (i) designing a signalling protocol that allows transparent bandwidth reservation for the aggregate demand of all onboard users in the vehicle, and (ii) proposing effective aggregation and bandwidth reservation policies that aim to maximize the chances of successful reservation and minimize the bandwidth and processing overhead in critical network elements. Mathematical models are derived to evaluate the performance of proposed solutions. These models are validated using discrete event simulation. One important conclusion reached is that onboard mobile communication provides significant aggregation and centralized management opportunities that must be exploited to provide a scalable solution to the bandwidth guarantee problem in mobile communications. The techniques proposed and analyzed in this thesis to exploit such aggregation opportunities constitute the original contribution to knowledge.

In the first part of this thesis, the information capacity of time-varying fading channels is analysed using finite-state Markov channel (FSMC) models. Both fading channel amplitude and fading channel phase are modelled as finite-state Markov processes. The effect of the number of fading channel gain partitions on the capacity is studied (from 2 to 128 partitions). It is observed that the FSMC capacity is saturated when the number of fading channel gain partitions is larger than 4 to 8 times the number of channel input levels. The rapid FSMC capacity saturation with a small number of fading channel gain partitions can be used for the design of computationally simple receivers, with a negligible loss in the capacity. Furthermore, the effect of fading channel memory order on the capacity is studied (from first- to fourth-order). It is observed that low-order FSMC models can provide higher capacity estimates for fading channels than high-order FSMC models, especially when channel states are poorly observable in the presence of channel noise. To explain the effect of memory order on the FSMC capacity, the capacities of high-order and low-order FSMC models are analytically compared. It is shown that the capacity difference is caused by two factors: 1) the channel entropy difference, and 2) the channel observability difference between the high-order and low-order FSMC models. Due to the existence of the second factor, the capacity of high-order FSMC models can be lower than the capacity of low-order FSMC models. Two sufficient conditions are proven to predict when the low-order FSMC capacity is higher or lower than the high-order FSMC capacity. In the second part of this thesis, a new implicit (blind) channel estimation method in time- varying fading channels is proposed. The information source emits bits ???0??? and ???1??? with unequal probabilities. The unbalanced source distribution is used as a priori known signal structure at the receiver for channel estimation. Compared to pilot-symbol-assisted channel estimation, the proposed channel estimation technique can achieve a superior receiver bit error rate performance, especially at low signal to noise ratio conditions.

Wireless Sensor Networks (WSNs) comprise a large number of sensor nodes, which are spread out within a region and communicate using wireless links. In some WSN applications, recognizing boundary nodes is important for topology discovery, geographic routing and tracking. In this thesis, we study the problem of identifying the boundary nodes of a WSN. In a WSN, close-by nodes can communicate with their neighbors and have the ability to estimate distances to nearby nodes, but not necessarily the true distances. Our objective is to find the boundary nodes by using the connectivity relation and neighbor distance information without any knowledge of node locations. Moreover, our main aim is to design a distributed algorithm that works even when the average degree is low. We propose a heuristic algorithm to find the boundary nodes which are connected in a boundary cycle of a location-free, low density, randomly deployed WSN. We develop the key ideas of our boundary detection algorithm in the centralized scenario and extend these ideas to the distributed scenario. Then, we show by simulation experiments that the distributed implementation outperforms the centralized one. The centralized implementation relies on the connectivity of the network to the base station. Therefore, for low density disconnected networks, the algorithm cannot find boundaries in partitions of the network that cannot establish connection to the base station. This condition leads to a low quality of boundary discovery. In contrast, the distributed implementation is more realistic for real WSNs, especially for relatively sparse networks when all local information cannot be collected very well due to sparse connectivity. In low-degree disconnected networks, the simulation results show that the distributed implementation has a higher quality of boundaries compared to the centralized implementation.