In this thesis, multiuser receivers for code division multiple-access (CDMA) downlink are studied under frequency selective fading channel conditions. The receivers investigated in this thesis attempt to estimate desired symbol as a linear combination of chip-rate sampled received signal sequence. A common matrix-vector representation of signals, which is similar to the model given by Paulraj et. al. is constructed in order to analyze the receivers studied in this thesis. Two receivers already well known in the literature are introduced and derived by using the common signal model. One of the receivers uses traditional matched filter and the other uses symbol-level linear minimum mean square error (MMSE) estimation. The receiver that uses traditional matched filter, also known as the conventional RAKE receiver, benefits from time diversity by combining the signal energy from multiple paths. The conventional RAKE receiver is optimal when multiple-access interference (MAI) is absent. Linear MMSE based receivers are known to suppress MAI and to be more robust to noise enhancement. The optimal symbol-level linear MMSE based receiver requires inversion of large matrices whose size is determined by either number of active users or spreading factor. These two parameters can be quite large in many practical systems and hence the computational load of this receiver can be a problem. In this thesis, two alternative low-complexity receivers, which are chip-level linear MMSE equalizer proposed by Krauss et. al. and interference-suppressing RAKE receiver proposed by Paulraj et. al., are compared with the linear full-rank MMSE based receiver and with the conventional RAKE receiver in terms of bit-error-rate performance. Various simulations are performed to evaluate the performance of the receivers and the parameters affecting the receiver performance are investigated.

Wireless sensor networks (WSN) have thus far been used for detection and tracking of static and mobile targets for surveillance and security applications. However, detection and tracking do not suffice for a complete satisfaction of these applications and an accurate target classification. To address this need, among various target classification methods, imaging of target yields the most valuable information. Nevertheless, imaging of mobile targets moving over an area requires networked and collaborative detection, tracking and imaging capabilities. With this regard, ultra-wideband (UWB) radar technology stands as a promising approach for networked target imaging over an area due to its unique features such as having no line-of-sight (LoS). However, the UWB wireless radar sensor network (WRSN) is yet to be developed for high quality imaging of mobile targets. In this thesis, an architecture for UWB wireless radar sensor network and a new collaborative mobile target imaging (CMTI) algorithm for UWB wireless radar sensor networks (WRSN) are presented. It is intended to accurately and efficiently obtain an image of mobile targets based on the collaborative eort of deployed UWB wireless radar sensor nodes. CMTI enables detection, tracking and imaging of mobile targets with a complete WRSN solution. CMTI exploits mobility of the target in the sensor field to build its own multi-static radar aperture. Performance evaluations reveal that CMTI obtains high quality radar image of mobile targets in WRSN with very low communication overhead and energy expenditure.

In this study, an automatic video segmentation and classification system based on audio features has been presented. Video sequences are classified such as videos with &ldquo / speech&rdquo / , &ldquo / music&rdquo / , &ldquo / crowd&rdquo / and &ldquo / silence&rdquo / . The segments that do not belong to these regions are left as &ldquo / unclassified&rdquo / . For the silence segment detection, a simple threshold comparison method has been done on the short time energy feature of the embedded audio sequence. For the &ldquo / speech&rdquo / , &ldquo / music&rdquo / and &ldquo / crowd&rdquo / segment detection a multiclass classification scheme has been applied. For this purpose, three audio feature set have been formed, one of them is purely MPEG-7 audio features, other is the audio features that is used in [31] the last one is the combination of these two feature sets. For choosing the best feature a histogram comparison method has been used. Audio segmentation system was trained and tested with these feature sets. The evaluation results show that the Feature Set 3 that is the combination of other two feature sets gives better performance for the audio classification system. The output of the classification system is an XML file which contains MPEG-7 audio segment descriptors for the video sequence. An application scenario is given by combining the audio segmentation results with visual analysis results for getting audio-visual video segments.

Multiple-input multiple-output (MIMO) systems have received much attention due to their multiplexing and diversity capabilities. It is possible to obtain remarkable improvement in spectral efficiency for wireless systems by using MIMO based schemes. However, sophisticated equalization and decoding structures are required for reliable communication at high rates. In this thesis, capacity achieving practical transceiver structures are proposed for MIMO wireless channels depending on the availability of channel state information at the transmitter (CSIT). First, an adaptive MIMO scheme based on the use of quantized CSIT and reduced precoding idea is proposed. With the help of a very tight analytical upper bound obtained for limited rate feedback (LRF) MIMO capacity, it is possible to construct an adaptive scheme varying the number of beamformers used according to the average SNR value. It is shown that this strategy always results in a significantly higher achievable rate than that of the schemes which does not use CSIT, if the number of transmit antennas is greater than that of receive antennas. Secondly, it is known that the use of CSIT does not bring significant improvement over capacity, when similar number of transmit and receive antennas are used / on the other hand, it reduces the complexity of demodulation at the receiver by converting the channel into noninterfering subchannels. However, it is shown in this thesis that it is still possible to achieve a performance very close to the outage probability and exploit the space-frequency diversity benefits of the wireless fading channel without compromising the receiver complexity, even if the CSIT is not used. The proposed receiver structure is based on iterative forward and backward filtering to suppress the interference both in time and space followed by a spacetime decoder. The rotation of multidimensional constellations for block fading channels and the single-carrier frequency domain equalization (SC-FDE) technique for wideband MIMO channels are studied as example applications.

RF and acoustic communications are widely used in terrestrial and underwater environments, respectively. This thesis examines the use of ultrasonic communication alternately in terrestrial applications. We first investigate the ultrasonic channel in order to observe whether reliable communication is possible among the ultrasonic nodes as an alternative to RF-based communications. Some key characteristics of the single-input-single-output (SISO) and single-inputmultiple- output (SIMO) ultrasonic channel are inspected with extensive experiments utilizing ultrasonic transmitters and receivers. Well known receiver diversity techniques are employed to combine the observations of multiple receiving ultrasonic transducers in a SIMO scheme and receiver diversity gain is attained. The thesis also covers the implementation of a receiver node by using a low-cost microcontroller.

With the developing radar technology, radars have been started to be used in the airborne platforms due to the need of fast, accurate and reliable information about the enemies. The most important and tactically needed information is the movements in an observation area. The detection of a ground moving target buried in a dense clutter environment from a moving air platform is a very challenging problem even today. The geometry of the operation, the course of the flight and structure of the clutter are the most effective parameters of this problem. There are some &ldquo / Ground Moving Target Indication&rdquo / (GMTI) techniques that have been studied for the last twenty years to overcome this problem. In this thesis, the simulation of some of these techniques in a realistic environment and the comparison of their performances are discussed. In this work, a GMTI simulator is developed to generate the environment containing the clutter and the noise signals, to locate and simulate the targets in this environment and to apply the GMTI techniques on the raw data generated by the simulator. The generation of the clutter signals including the internal clutter motion (ICM) for different types of clutter distributions is one of the most important parts of this thesis. The GMTI techniques being investigated throughout this thesis are &ldquo / Displaced Phase Center Antenna&rdquo / (DPCA), &ldquo / Along-Track Interferometry&rdquo / (ATI), &ldquo / Adaptive DPCA&rdquo / , &ldquo / Pre-Doppler Sigma-Delta STAP&rdquo / and &ldquo / Post-Doppler Sigma-Delta STAP&rdquo / techniques. These techniques are compared according to their clutter suppression and target detection performances under different environmental conditions.

In this thesis work, importance of radome structures for antenna systems is emphasized. Structural and electromagnetic requirements of various types of radome structures are analyzed and specific properties are given. Electromagnetic scattering analysis of sandwich type radome seams has been done. Total antenna system far electromagnetic field expression, which is the combination of original antenna far electromagnetic field and the scattered electromagnetic field of the framework of the sandwich radome structure has been found and simulated. To enhance electromagnetic transparency of sandwich type radomes two sandwich radome design methods are proposed which are expressed as Geometrical Randomization and Tuning the Seams. Electromagnetic scattering level minimizations advanced by these design methods are presented with related simulations.

Fractal is a recursively-generated object describing a family of complex shapes that possess an inherent self-similarity in their geometrical structure. When used in antenna engineering, fractal geometries provide multi-band characteristics and lowering resonance frequencies by enhancing the space filling property. Moreover, utilizing fractal arrays, controlling side lobe-levels and radiation patterns can be realized. In this thesis, the performance of Koch curve as antenna is investigated. Since fractals are complex shapes, there is no well&ndash / established for mathematical formulation to obtain the radiation properties and frequency response of Koch Curve antennas directly. The Koch curve antennas became famous since they exhibit better frequency response than their Euclidean counterparts. The effect of the parameters of Koch geometry to antenna performance is studied in this thesis. Moreover, modified Koch geometries are generated to obtain the relation between fractal properties and antenna radiation and frequency characteristics.

In this thesis, we analyze allocation of two separate resources in wireless networks: transmit power and buffer space. Controlled allocation of power can provide good performance for both users and the network. Although centralized mechanisms are possible, distributed power control algorithms are preferable for efficient operation of the network. Viewing distributed power allocation as the collection of rational decisions of each user, we make game theoretic problem formulations, devise distributed algorithms and analyze them. First, equilibrium analysis of a vector power control game based on network energy efficiency in a multiple access point wireless network is presented. Then, a distributed mechanism is proposed that can smooth admission control type power control so that every user can stay in the system. Introducing a new externality into utility function, a game theoretic formulation that results in desired distributed actions is made. Next, the proposed externality is investigated in a control theoretic framework. Convergence of gradient based iterative power updates are investigated and stability of corresponding continuous time dynamical system is established. In the final part of the thesis, allocation of buffer space is addressed in a wireless downlink using a queueing theoretic framework. An efficient algorithm that finds optimal buffer partitioning is proposed and applications of the algorithm for different scenarios are illustrated. Implications of the results about cross layer design and multiuser diversity are discussed.

In this study, we considered a heterogeneous, clustered WSN, which consists of two types of nodes (clusterheads and sensor nodes) deployed randomly over a sensing field. We investigated two cases based on how clusterheads can reach the sink: direct and multi-hop communication cases. Network dimensioning problems in randomly deployed WSNs are among the most challenging ones as the attributes of these networks are mostly non-deterministic. We focused on a number of network dimensioning problems based on the connected coverage concept, which is the degree of coverage achieved by only the connected devices. To evaluate connected coverage, we introduced the term cluster size, which is the expected value of the area covered by a clusterhead together with sensor nodes connected to it. We derived formulas for the cluster size and validated them by computer simulations. By using the cluster size formulas, we proposed a method to dimension a WSN for given targeted connected coverage. Furthermore, we formulated cost optimization problems for direct and multi-hop communication cases. These formulations utilize not only cluster size formulas but also the well-connectivity concept. We suggested some search heuristics to solve these optimization problems. Additionally, we justified that, in practical cases, node heterogeneity can provide lower cost solutions. We also investigated the lifetime of WSNs and for mulated a cost optimization problem with connected coverage and lifetime constraints. By solving this optimization problem, one can determine the number of nodes of each type and the initial energies of each type of node that leads to lowest cost solution while satisfying the minimum connected coverage and minimum lifetime requirements.