Cognitive Radio (CR) aims to access the wireless spectrum in an opportunistic manner while the licensed user is not using it. To accurately determine the licensed user's existence, spectrum sensing procedure is vital to CR system. Energy detection-based spectrum sensing techniques is favourable due to its simplicity and low complexity. In addition, to improve the detection performance, cooperative spectrum sensing technique exploits multi-user diversity and mitigates detection uncertainty. In this thesis, we investigate several energy detection based cooperative spectrum sensing techniques.First, the closed-form analysis for the Equal Gain Combining based Soft Decision Combining (EGC-SDC) scheme, in which all CR users forward its observation to the fusion center, is derived. In order to reduce the communication overhead between CR users and the fusion center, we proposed quantized cooperative spectrum sensing technique, in which CR users quantize its local observation before forwarding to the fusion center. Next, the Double Threshold scheme, where some users only forward its local decision while other users forward its observation, is considered and analyzed. To further reduce the communication overhead, we also proposed that quantization is applied to the users who forward its observation. Later on, three sequential cooperative spectrum sensing schemes in time-varying channel are considered. By aggregating past local observations from previous sensing slots, CR users can improve the detection performance. The Weighted Sequential Energy Detector (SED) scheme simply takes fixed number of past local observations, while the other two schemes, Two-Stage SED and Differential SED, adaptively determine the number of observations, based on its decision towards primary user's existence.Simulation results show that the analysis on EGC-SDC scheme is accurate and the quantized cooperative spectrum sensing technique can improve the performance and approach the detection performance of EGC-SDC scheme with much less bandwidth requirement. Also, the Double Threshold scheme can help improve the detection performance over the conventional technique. Furthermore, the analysis on Double Threshold provides a closed-form for the probability of false alarm and detection. Additionally, the sequential spectrum sensing schemes are shown to improve the detection performance and enable CR system to work in scenarios that the conventional technique can not accommodate.

In this dissertation we consider the problem of cooperative sensing for secondary user access to primary user spectrum in cognitive radio systems. Using a fusion center or an access point, the cooperative users decide on the availability of spectrum for their use. Both Neyman-Pearson and Bayes criterion are considered for performance assessment. Our work on the asymptotic performance of counting rules with a very large number of sensors in decentralized detection problem shows that majority logic fusion rule has the same order of performance when compared to the best fusion rule based on the binary decisions received from the observing sensors in a network. In cognitive radio context, very large number of sensors may not be realistic and hence we would like to examine the performance of majority logic and counting rules involving a finite and small number of sensors. Uniformly most powerful test for decentralized detection for testing parameter θ when the observation is a sample from uniform (0,θ) distribution is investigated and it is shown that OR rule has the best performance among all counting rules in error free channel. The numerical study for reporting channel as a binary symmetric channel (BSC) with probability of bit error is also investigated and the results show that 2-out-of-5 or 2-out-of-10 has better performance among other k-out-of-n rules, whenever OR rule is not able to provide a probability of false alarm at the sensor, that lies over (0,1) at a given probability of bit error.

Although sensor planning in computer vision has been a subject of research for over two decades, a vast majority of the research seems to concentrate on two particular applications in a rather limited context of laboratory and industrial workbenches, namely 3D object reconstruction and robotic arm manipulation. Recently, increasing interest is engaged in research to come up with solutions that provide wide-area autonomous surveillance systems for object characterization and situation awareness, which involves portable, wireless, and/or Internet connected radar, digital video, and/or infrared sensors. The prominent research problems associated with multisensor integration for wide-area surveillance are modality selection, sensor planning, data fusion, and data exchange (communication) among multiple sensors. Thus, the requirements and constraints to be addressed include far-field view, wide coverage, high resolution, cooperative sensors, adaptive sensing modalities, dynamic objects, and uncontrolled environments. This article summarizes a new survey and analysis conducted in light of these challenging requirements and constraints. It involves techniques and strategies from work done in the areas of sensor fusion, sensor networks, smart sensing, Geographic Information Systems (GIS), photogrammetry, and other intelligent systems where finding optimal solutions to the placement and deployment of multimodal sensors covering a wide area is important. While techniques covered in this survey are applicable to many wide-area environments such as traffic monitoring, airport terminal surveillance, parking lot surveillance, etc., our examples will be drawn mainly from such applications as harbor security and long-range face recognition.

Tato práce je rozdělena do šesti kapitol. První kapitola vysvětluje rozdíly mezi fyzickou vrstvou uplinků systémů LTE a LTE Advanced, zkoumá charakteristiky kanálu komunikace D2D v rámci sítě LTE Advanced, a navrhuje mechanismy optimalizace interferencí. Rovněž je v práci prezentována struktura softwarově definované rádiové platformy, která může být využita pro vyhodnocení rádiových kanálů. Druhá kapitola hodnotí a porovnává výkony uplinkové části fyzické vrstvy systému LTE a LTE Advanced. V prostředí MATLAB je implementována struktura LTE Advanced vysílače a přijímače se všemi stupni zpracování signálu. Generované signály obou výše uvedených systémů jsou přenášeny přes různé modely kanálu ITU-R. Byly používány různé techniky odhadu kanálů a detekce signálu pro obnovení vysílaného signálu. Výsledky jsou prezentovány formou křivek BER a křivek datové prostupnosti. Třetí kapitola navrhuje způsob opakování frekvencí v celulární síti (frequency-reuse) se třemi úrovněmi výkonu, který se využívá jako typ pokročilé metody snižování interferencí. Jsou ukázány normalizované kapacitní hustoty buněk a jejich podoblastí se třemi různými případy distribuce uživatelů uvnitř buněk. Je zobrazena korelace mezi celkovou kapacitou a poloměrem každého regionu. Dosažené výsledky navrhovaného schématu jsou porovnávány s tradiční technikou opakovaného použití frekvence (Reuse-3). Čtvrtá kapitola se zabývá výzkumem alternativní metody optimalizace interferencí. Bylo provedeno ověření kooperačních metod snímání rádiového spektra ve čtyřech různých reálných prostředích: venkovní-interiérové, vnitřní-venkovní, venkovní-vnitřní a venkovní-venkovní. Navržený systém je testován pomocí zařízení Universal Software Radio Peripheral (USRP) a obsahuje dva typy detektorů; energetický detektor a statistický detektor založený na Kolmogorově-Smirnovově testu, které byly implementovány na přijímací straně. Jedním z hlavních požadavků komunikace D2D je znalost charakteristik impulzních odezev rádiového kanálu. Pátá kapitola proto představuje metodu měření kanálu pomocí Zadoff-Chu sekvencí ve frekvenční oblasti jako alternativní techniku k měření kanálu v časové nebo frekvenční doméně. Pomocí navržené metody se základní charakteristiky kanálu, jako je časové rozšíření kanálu (RMS delay spread, mean excess delay), útlum šířením a koherenční šířka pásma extrahují v (až 20x) kratším čase ve srovnání s klasickou metodou měření kanálu ve frekvenční doméně. Jsou také zkoumány charakteristiky venkovních statických rádiových kanálů na vzdálenost několika kilometrů pro pásma UHF a SHF s ko-polarizovanou horizontální a vertikální konfigurací antény. Šestá kapitola uzavírá tezi a shrnuje závěry.