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An ever increasing number of wirelessly-enabled applications places a very high demand on stringent spectral resources. Cognitive radios have the potential of enhancing spectral efficiency by improving the usage of channels that are already licensed for a specific purpose. Research on cognitive radios involves answering questions such as: how can a cognitive radio transmit at a high data rate while maintaining the same quality of service for the licensed user? There are multiple forms of cognition studied in literature, and each of these models must be studied in detail to understand its impact on the overall system performance. Specifically, the information-theoretic capacity of such systems is of great interest. Also, the design of cognitive radio is necessary to achieve those capacities in real applications. In this dissertation, we formulate different problems that relate to the performance of such systems and methods to increase their efficiency. This dissertation discusses, firstly, the means of "sensing" in cognitive systems, secondly, the optimal resource allocation algorithms for interweave cognitive radio, and finally, the fundamental limits of partially and overly cognitive overlay systems. / text

Darbe apžvelgiamas, išanalizuojamas IEEE 802.11 standartas, jo architektūra, fizinis lygmuo, kanalinis lygmuo. Aprašoma tyrime naudojama aparatinė ir programinė įranga, tyrimo vykdymo eiga, metodika. Eksperimentiškai ištirtos bevielių lokalių tinklų IEEE 802.11 standarto kokybinės charakteristikos. Pateikiamas kokybinių charakteristikų teorinis įvertinimas. Naudojantis tyrimo rezultatais ir surinkta informacija, sukuriama programinė įranga, skirta bevielių lokalių tinklų laidumo, vėlinimo laiko, aprėpties zonos nustatymui, radimui, skaičiavimui, įvertinimui. Aptariami, pateikiami programinės įrangos kūrimo etapai: reikalavimų specifikacija, architektūros projektavimas, programavimas, testavimas; apibendrinami gauti rezultatai, pateikiamos išvados. / The aim of project work is to research of wireless local network qualitative characteristics: throughput, maximum range, delay. The standart IEEE 802.11, its architecture, physical layer, MAC layer is analysed. Hardware and software, used in research, the methods of research are discribed. Research of qualitative characteristics of wireless local network is done. On the basis of research results the software intended for calculation, determination of value of qualitative characteristics of wireless local network, software is created. The main stages of software creation: specification, designing of architecture, programming, testing are analysed. Obtained results are discussed. Practical, experimental researches are carried out according to recommendations of IEEE 802.11, IEEE 802.3 standarts.

Temporal data is common in real-world datasets. Analysis of such data, for example by means of clustering algorithms, can be difficult due to its dynamic behaviour. There are various types of changes that may occur to clusters in a dataset. Firstly, data patterns can migrate between clusters, shrinking or expanding the clusters. Additionally, entire clusters may move around the search space. Lastly, clusters can split and merge. Data clustering, which is the process of grouping similar objects, is one approach to determine relationships among data patterns, but data clustering approaches can face limitations when applied to temporal data, such as difficulty tracking the moving clusters. This research aims to analyse the ability of particle swarm optimisation (PSO) and differential evolution (DE) algorithms to cluster temporal data. These algorithms experience two weaknesses when applied to temporal data. The first weakness is the loss of diversity, which refers to the fact that the population of the algorithm converges, becoming less diverse and, therefore, limiting the algorithm’s exploration capabilities. The second weakness, outdated memory, is only experienced by the PSO and refers to the previous personal best solutions found by the particles becoming obsolete as the environment changes. A data clustering algorithm that addresses these two weaknesses is necessary to cluster temporal data. This research describes various adaptations of PSO and DE algorithms for the purpose of clustering temporal data. The algorithms proposed aim to address the loss of diversity and outdated memory problems experienced by PSO and DE algorithms. These problems are addressed by combining approaches previously used for the purpose of dealing with temporal or dynamic data, such as repulsion and anti-convergence, with PSO and DE approaches used to cluster data. Six PSO algorithms are introduced in this research, namely the data clustering particle swarm optimisation (DCPSO), reinitialising data clustering particle swarm optimisation (RDCPSO), cooperative data clustering particle swarm optimisation (CDCPSO), multi-swarm data clustering particle swarm optimisation (MDCPSO), cooperative multi-swarm data clustering particle swarm optimisation (CMDCPSO), and elitist cooperative multi-swarm data clustering particle swarm optimisation (eCMDCPSO). Additionally, four DE algorithms are introduced, namely the data clustering differential evolution (DCDE), re-initialising data clustering differential evolution (RDCDE), dynamic data clustering differential evolution (DCDynDE), and cooperative dynamic data clustering differential evolution (CDCDynDE). The PSO and DE algorithms introduced require prior knowledge of the total number of clusters in the dataset. The total number of clusters in a real-world dataset, however, is not always known. For this reason, the best performing PSO and best performing DE are compared. The CDCDynDE is selected as the winning algorithm, which is then adapted to determine the optimal number of clusters dynamically. The resulting algorithm is the k-independent cooperative data clustering differential evolution (KCDCDynDE) algorithm, which was compared against the local network neighbourhood artificial immune system (LNNAIS) algorithm, which is an artificial immune system (AIS) designed to cluster temporal data and determine the total number of clusters dynamically. It was determined that the KCDCDynDE performed the clustering task well for problems with frequently changing data, high-dimensions, and pattern and cluster data migration types. / Dissertation (MSc)--University of Pretoria, 2015. / Computer Science / Unrestricted

This thesis is aimed to the problems of virtual local networks. In the first chapters are explained both basic and advanced methods of designing and management of virtual LAN networks. The following chapters are dedicated to the methods of effective management VLAN networks and to the protocol Spanning Tree, preventing formation of loops in redundant networks, and their exploitation in VLANs. The practical part describes the application of the implementation of the technology of virtual local networks in experimental network, containing various types of devices. Based on this theory, a laboratory assignment has been designed for the training of the students in solving such problems. The scope of the laboratory assignment is divided into simpler partial tasks, which even a less advanced student should be able to configure and test.

The network externality function plays a very important role in the study of economic network industries. Moreover, the consumer group dynamic interactions coupled with network externality concept is going to play a dominant role in the network goods in the 21st century. The existing literature is stemmed on a choice of externality function with certain quantitative properties. The utility function coupled with the network externality function is used to investigate static properties of rational equilibrium. The aim of this work is to systematically initiate a development of quantitative effects of the concept of network externality and its influence on the characteristics of network market equilibrium. We introduce several basic concepts, notably, network externality process and network goods. Formulating a principle of network externality, we developed a mathematical dynamic model (1) for the network externality process. A closed form solution of the mathematical model was determined and analyzed (2). The presented qualitative and quantitative analysis provides a systematic and unified way of constructing the existing network externality function. The solution process is called "Generalized Network Externality Function (GNEF)". Moreover, our study of quantitative description, parametric representation of attributes and sensitivity analysis of network externality process provides a tool for planning, policy and performance for network goods (3). In the absence of desired data set, we presented an illustration to exhibit the significance of GNEF. We used two types of data sets on the US banking asset and deposit. Employing nonlinear regression methods and data sets, we developed statistical models for the US banking asset and deposit, and constructed two normalized the US banking deposit models (4). Finally, using the concept of theory of relative growth and GNEF (4), we developed two dynamic models for the network externality for the US banking asset with respect to the US banking deposit as a financial market share (5). Incorporating the GNEF (2) in the consumer utility function, a concept of market share adjustment function is introduced and utilized to develop dynamic models for existing rational and static expectation processes (6). In fact, the role and scope of dynamic models of market share adjustment process are extended to the well-known adaptive expectation and its extension process (7). Using a fixed point theorem and the method of upper and lower solutions of discrete time processes, the existence of equilibrium states of developed dynamic models of market share adjustment processes are established in a systematic way (8). Furthermore, the qualitative properties (stability and oscillatory) of equilibrium states are investigated in terms of model and speed of adjustment parameters. Moreover, the system parameter space is decomposed according to qualitative properties (stability, instability and oscillatory) and the type of expectation processes. Very recently, the idea of local network externality is utilized to characterize the rational equilibrium (under fulfilled expectation assumptions). From the study on two-scale network dynamic model of human mobility process an eco-socio-culture interactions, we note that heterogeneity in the network goods consumer community generates a local network externality. Furthermore, dynamic models of adaptive expectation processes (6,7) for network goods provide tool to extend the characterization of rational equilibrium study to static, current and lagged adaptive types equilibriums. Here, we treat the consumer decision to be a dynamic process. We formulate a dynamic structural representation of a consumer network structure, structure of utility function and decision rule under the influence of local network externality concept (9). For the consumer network structure, we generalize the one-dimensional Hotelling location line model to multi-dimensional location (10). This formulation generates a mathematical model for a consumer decision dynamic process (11). The byproduct of the dynamic model leads to an agent-based simulation model (12). The simulation model is employed to investigate different types of consumer decision dynamic market equilibriums. Moreover, prototype illustrations are given to exhibit the association between network attributes and its market equilibriums. We extend the work of two firms (duopoly) into multi-firms (oligopoly and monopolistic competition). This work shed light on the policies for manager to meet performance goal of their firm in network goods industry. In future, we propose to extend this work to incorporate random fluctuations, to remove restrictions and the local and global economic framework in the 21st century.

When using a wireless repeater in a network, an overlap zone between the repeater and the primary access point that holds the internet connection is created. The theoretical throughput for connections through the repeater is reduced by half since the repeater can’t send and receive data at the same time when using only one channel which was the case in this thesis. To solve the problem with the overlap zone, an algorithm that runs in the form of a bash script on two openWRT-based access points where one acts as a repeater and the other one is a gateway with an internet connection was developed. The script uses the signal strength value (RSSI) to decide whether a wireless device is located within the overlap zone by comparing the measured value against a set threshold where the gateway still delivers higher throughput than the repeater. Wireless devices in the overlap zone are blocked on the repeater and will then connect to the gateway instead. Wireless devices that are located outside the overlap zone will connect to the access point that yields the strongest signal strength. The throughput to the gateway was measured at several locations with different signal strengths to both the gateway and the repeater. Wireless devices within the overlap zone that were connected to the repeater before the script was run gained a higher throughput after the script was run and made it connect directly to the gateway instead. / Vid användning av en trådlös repeater i ett nätverk skapas en överlappningszon mellan repeatern och den primära anslutningspunkten som har uppkopplingen mot internet. Den möjliga datagenomströmningshastigheten för uppkopplingar via repeatern halveras eftersom repeatern inte kan sända och ta emot samtidigt på samma kanal. För detta examensarbete fanns inte möjligheten att använda fler kanaler. För att lösa problemet med överlappningszonen utvecklades en algoritm som körs i form av ett bash-skript på två openWRT-baserade anslutningspunkter där den ena agerar som repeater och den andra är en gateway med internetuppkoppling. Skriptet använder värdet på signalstyrka (RSSI) för att avgöra om en trådlös enhet befinner sig i överlappningszonen genom att kontrollera uppmätt värde mot ett tröskelvärde där gatewayen fortfarande ger högre datagenomströmningshastighet än repeatern. Trådlösa enheter i överlappningszonen blockeras på repeatern och kopplar då upp till gatewayen istället. Utanför överlappningszonen kopplas enheter upp till den anslutningspunkt som har starkast signalstyrka. Datagenomströmningen till gatewayen mättes på flera platser med olika signalstyrkor till både gatewayen och repeatern. Trådlösa enheter i överlappningszonen som var uppkopplade till repeatern innan skriptet kördes fick en högre datagenomströmningshastighet efter att skriptet kört och styrt om anslutningen direkt till gatewayen istället.

The subject of the “The Computer Network Design” thesis is the analysis of the current company status and a detailed analysis of its possible improvement. The present status, company demands and the brief summary of available technologies for proposed solution have been described. The optimal option for the company has been chosen. Current company costs have been analyzed and savings solution for both monthly costs for maintaining the network and purchasing cost for computer technology itself.

過去對於台灣單一廠商朝向大型集中化的企業集團發展及其在地交易治理模式的現象較少涉及，本研究由網絡理論出發，扣連華碩集團作為研究場域，援引Håkanson企業全球擴張模式，企圖論證華碩企業集團化過程中，如何透過獨資或合資之進入模式，佈局全球在地網絡關係，進而運用Powell組織治理模式，探討企業集團在地網絡治理模式。有別於過去文獻單從政治經濟學詮釋企業集團介入不同產業時，強調國家角色的重要性；或者從經濟地理學探討單一產業之廠商全球佈局或跨界生產網絡建構與在地鑲嵌實證研究，期能補充過去文獻之不足。經研究後發現： 一、Håkanson於1979年所提出之企業集團全球擴張模式，無法適用於華碩全球網絡擴張模式。 經本研究分析，Håkanson所提出的企業集團全球擴張模式，無法適用於華碩企業集團的全球網絡擴張模式，就其原因，應與現今之企業集團受全球網絡接軌、資訊技術的進步、市場全球化、專業技術的研發及台灣中小企業的靈活性等因素影響。故本研究依華碩案例，整理出企業集團全球擴張模式的三階段，1.單一廠商及採用海外銷售代理商階段；2.滲透到個國內外市場階段；3.產生跨國產業的公司。 二、Powell的組織交易治理模式，可以解釋華碩企業集團全球網絡下各公司在地網絡治理行為。 Powell強調網絡是一個重要的組織交易治理模式，相關研究亦指出華人企業比較重視「網絡」，透過華碩企業集團案例分析，顯示研發活動受到確保關鍵技術的限制而採用層級型；在製造活動上，受到控制產品品質及降低成本的需求，初期會採用層級型，然後隨着產品多樣化而採用網絡層級型；行銷活動為了獲取最大的銷售利益，在單一技術多角化經營期間採用市場網絡型，隨着產品多樣化而採用市場型。 三、本研究所選擇的四個影響在地組織交易治理模式因素，僅有企業價值活動具解釋性。 透過企業發展階段、各公司設立時間、進入模式及企業價值活動等四個選擇因素的迴歸分析，發現各分、子公司所從事的企業價值活動對在地組織交易治理模式有顯著影響。 / There are few researches on how a Taiwanese single manufacturer developing into a hyper-centralized group and what its localized business and management model is. Hence this paper is employed the network theory to Asus as studied case and applied Håkanson’s Corporate Global Expansion Model for Asus’ group developing process to try to explain how employ solely or joint investment entering model to layout global localized network. Furthermore, employ Powell’s organization management model to explore corporate group’s local management network. This dissertation is different from most papers focus on the role of country when interpreting from political economy view that how corporate group enters various industry. It is also different from economic geography view to explore how one single manufacturer layout globally or across industry to setup and localize completely production. I hope the approach of this paper can fill the gap. Findings: 1. Håkanson’s Corporate Global Expansion Model submitted in 1979 can not be applied for Asus’ global network expansion model. The reason why Håkanson’s Corporate Global Expansion Model can not be applied for Asus’ global network expansion model is modern corporate group is highly influenced by global network, information technology, market globalized, and the development of professional skills, and the flexibility for Taiwanese middle and small companies. It can be concluded that there are three stages for the corporate group to expand globally based on case Asus. First is one single producer and oversea sales agent, the next step is penetrating to foreign market, and the third phase is one cross-country manufacturer is born. 2. Powell’s organization management model can explain how Asus’ individual company’s local managing behavior under the global umbrella of Asus Corporate Group. Powell emphasizes the network is a very important organization business management model. All the relative researches also point out that Chinese enterprises consider “network” more important than the others. Base on the stud of Asus, this paper indicates R & D development is restricted for protecting critical technology so as to employ ranking mode. As in production, by the request of controlling product quality and lowering down cost, at first, the ranking mode is required, then, along with product variety increasing, the network mode is employed. Marketing activity aims to maximize selling profit. Asus employs market network mode for a single technology with diversified managing phase while market mode for product variety situation. 3. Researching four chosen factors of influencing local organization business managing model, enterprise value activity only is explainable. Based on the regression analysis for four chosen factors as enterprise developing stages, the setup date of each subsidiary or branch office, entering models, and enterprise value activity, the enterprise value activity of each subsidiary or branch office does significant influence on local organization business managing model.

The aim of this master's thesis is suggestion and following realization of voice transmission over the local network equipment and a description of used circuits and solutions in terms of hardware and software. This thesis deals with digitization of low-frequency signals, the structure of IP and UDP protocols, implementation of TCP/IP stack cIPS