Sharif Digital Repository

In this work we have investigated the methods of providing quality of service in cognitive radio networks. At first, we have explained the various algorithms of providing BER quality of service in wireless networks. Especially we have explained those algorithms which are known as the distributed power control algorithms. Then we have introduced methods of using adaptive modulation and we have used this kind of modulation to provide delay quality of service in cognitive radio networks. We have done this by maximizing the sum of effective capacities of secondary links under the power constraints and also the interference constraints set by the primary receivers. Finally, we have introduced... 

Nowadays, swift development of cellular network with the increased penetration rate, have made mobile voice channels widely available almost everywhere with higher priority comparing to the other conventional channels, e.g., GPRS, EDGE, HSDPA and etc. Leveraging on this fact two important utilization can be considered. The first one is related to urgent transmitting of vital data. As mentioned earlier, since this channel deems to be available everywhere and, recalling its priority, it is even accessible in congestion condition, it can be exploited as an efficient way to transmit small volume of emergence data urgently. Transforming the crash data on the road is an example of utilizing such... 

Research on target localization in multiple-input multiple-output (MIMO) radars, has seen significant growth in recent years. In general, localization methods in these radars can be classified as direct and indirect methods. In the former, the cinematic specifications of target is directly extracted from the received signals, whereas in the indirect methods, different measurements are calculated from the received signals and then, the target position is estimated using the acquired measurements. In this thesis, by concentrating on indirect target localization methods and by taking practical problems, such as uncertainties in sensors position and velocity, asynchronous sensor clocks and... 

MIMO (Multi Input Multi Output) Radars issue is a new topic in Radar systems field and power allocation in these systems is very important to improve their performance.In this thesis, at first, two optimum detectors for MIMO radars with widely separated antennas are designed. In the first one, received signal in all receivers is gathered in a central processor and centralized detection is performed. This type of detection needs too much process power and is complex. Because of complexity of detector, probability of detection is very difficult to derive and deflection criterion is used for evaluating system performance. In the second one, each receiver processes received signals from all... 

Next generation wireless networks support high data rates and QoS parameters of various users. OFMDA is a popular transmission technique to support high rate transmission, however in multi-access environments, it relies on careful resource allocation to guarantee the desired QoS parameters. While resource allocation in centralized scenarios such as cellular networks is relatively straightforward, the problem becomes quite complex in distributed scheduling of multiple access environments. One key resource is power assigned to each sub-channel which determines the overall transmission capacity.In this dissertation, firstly we introduce some cross layer QoS provisioning or power efficient QoS... 

Estimating direction of arrival (DOA) is one of the most important problems in array signal processing to solve which various methods have been proposed. The older methods for estimating signal DOA were divided into three main groups: beamforming, maximum likelihood-based and subspace-based methods. By applying sparse representation techniques to the DOA estimation problem, a new group of methods for solving this problem are introduced. In this thesis, two grid-based methods, which are tow sub groups of sparse methods for estimation of DOA, are proposed. Each of these methods uses singular value decomposition to reduce the power of noise. Also proposed methods are compared with the multiple... 

Waveform design for Target identification and classification in MIMO radar systems has been studied in several recent works. While the previous works considered signal independent noise and found optimal signals for an estimation algorithm, here we extend the results to the case where clutter is also present and then we will find the optimum waveform for several estimators differing in the assumptions on the given statistics. Several different approaches to the optimal waveform design are proposed, including minimizing the error of MMSE estimator, minimizing the maximum error of the covariance shaping least square (CSLS) estimator and minimizing the MSE error of scaled least square (SLS)... 

There are a wide variety of radar systems that one of them is MIMO Radars. After a spark in communication in 1998 that developed MIMO communication, recently there has been a great attention towards MIMO radar systems. Researchers have studied this topic from several points of view. Generally, MIMO radar systems are divided into two categories: MIMO radars widely separated antennas and MIMO radars with collocated antennas. One of the important issues of widely separated MIMO radars, is the placement manner of receivers in the geometrical area. This radar’s performance is very dependent to placement of the antennas, because the performance is dependent to relative position of... 

Passive radars using illuminators of opportunity have attracted much attention in recent years. The worldwide inter-operability for microwave access (WiMAX) signal is a new illumination source for passive radar. This paper presents a study to understand and to demonstrate the feasibility of using WiMAX signals for passive radar. The study includes WiMAX signal analysis, the design and implementation of a WiMAX-based passive radar demonstrator, the associated radar signal processing scheme, and some approaches to yield an effective removal of the undesired peaks in WiMAX ACF  

Passive source localization accounts for the identification of the position and velocity of an object that emits electromagnetic/sound waves. This concept suggests various civil and military applications such as localization of the cellular phone users for emergency services, navigation, localizing radar and sonar sources. Received Signal Strength (RSS), Time of Arrival (TOA), Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) of the emitted signals are commonly used for position finding. Among all these measurement methods, localization using TDOA and FDOA is highly accurate and needless of any time synchronization between the source and the sensors. Common methods... 

Passive Location is to obtain the location and velocity of a radio source using a source-generated signal in the environment and extract its parameters, which today have many applications in controlling security activities, tracking people and vehicles, emergency services, radar, Sonar, electronic warfare, and etc. . The location of a source is obtained by using a variety of methods such as received signal strength (RSS), signal angle of arrival (AOA), signal time of arrival (TOA), time difference of arrival (TDOA), and frequency difference of arrival (FDOA) of received signals. Many studies have been done in measuring and extracting data and solving the equations. However, little research... 

Target localization using positioning systems has long been considered by researchers in various fields.One of the important issues in localizing a target is the accuracy of its determined position. There are several parameters in the accuracy of position estimation. In a comprehensive view, these parameters can be divided into three general factors,including the relative geometry of the transmitters/receivers with respect to the target, the accuracy of measurements, and the type of target position estimator.The first factor, i.e. the relative geometry between the target and the transmit/receive antennas, plays an important role in localization accuracy. In the first part of this thesis, the... 

In this thesis, Particle Filter Methods are investigated in the context of moving targets tracking and the associated performance analysis. The application scope of this algorithm which is a particular case of Sequential Monte Carlo Method is far broader than tracking of moving targets. This algorithm can be used for mathematical calculations such as estimation of mathematical expectations, integrals, surface area of curves and many other mathematical calculations. In addition, it has applications in other branches of science like genetics. This algorithm is based on random sampling of a probability density function and resampling from the extracted samples. We change this algorithm in... 

Passive wideband reconnaissance receivers, listen to the radio and radar signals in the environment and estimate their important parameters such as direction of arrival (DOA). The wideband attribute for these receivers is to refer to their ability to receive wideband signals.Due to the use of processing gain, LPI radars reduce their transmitted signal power to see and not to be seen. On the other hand reconnaissance receivers can not have much processing gain, because they do not know the nature of the transmitted signal; Therefore, to increase the operational range of these systems, it is necessary to increase the signal to noise power ratio (SNR). This thesis examines the use of antenna... 

In general, multi-target tracking consists of estimation of the posterior density function of present targets at each scan in the observation area. These targets may have unknown and time varying number of targets. It is a tough job due to misdetections, false alarms, data association ambiguity, and nonlinear equations-non Gaussian noises. These all make it difficult to apply Kalman filter and its extensions such as extended Kalman filter and unscented Kalman filter. Monte Carlo methods, particularly particle filters, have recently aroused the interest of designers and enjoyed a lot of success to deal with multi-target tracking difficulties. In addition, they can handle nonthresholded data... 

In-fiber and all-optical wavelength-selective signal processing are key aspects of fiber Bragg grating (FBG)-based devices in optical communication systems. FBGs with sharp filtering properties have already been used in fiber optic communication networks as dispersion compensators, optical add–drop multiplexers, fiber lasers, and optical label switching modules. We have developed an in-fiber wavelength-selective optical intensity modulator to superimpose low rate overhead data on the transit high-speed payload signals. The tunable fiber Bragg grating (FBG), as the heart of a wavelength-selective modulator (WSM), is designed and properly biased to implement the desired modulation... 

This work is mostly about the analysis of direct position determination (DPD) approach as an emerging approach in source localization. Different aspects of this localization has been considered and some improvement techniques has been addressed. DPD is known as a replacement for the conventional 2-step localization approach in which the location of the target is estimated via the estimation of some interface parameters such as time of arrival, angle of arrival and etc. The main focus of this thesis is on the sensor placement problem in DPD in order to find an optimal configuration for the sensors to achieve the best accuracy in the estimation process. In this regard, the formulas of the... 

Modulation Recognition of communication signals has been an important theme in the field of wireless communication. Modulation Recognition has various applications for both military and civil purposes. Recently there has been considerable attention to Digital Modulation Recognition, due to the vast application of this kind of Modulation Recognition tasks. In this thesis, we proposed a Digital Modulation Recognition Algorithm, which is able to identify various types of digital modulations in low SNRs. These include BASK, BFSK, BPSK, 4-ASK, 4-FSK, 4-PSK, 8-FSK, 8-PSK, MQAM (M=16, 32, 64). The proposed method uses a general pattern recognition scheme, consisting of a feature extraction phase... 

Nowadays, with the increased penetration of wireless mobile networks (e.g. GSM, 3G, etc.), voice channels are widely available ubiquitously. This availability and wide coverage encourages utilization of such channels as a valuable available infrastructure for point to point secure data communication. This can be done either by using steganography and hiding the secure message in the voice passing through the channel or by ciphering and transmitting it through the voice channel as a speech-like signal. The proposed method for data communication or steganography through voice channels should be robust against lossy compression techniques applied by the vocoder block present in such channels.... 

The endothelial (the artery inner lumen cells) function is associated with cardiovascular risk factors. Its assessment methods can be classified into the two groups of invasive and noninvasive ones. The most widely used method among the current non-invasive tests employed in research settings is flow-mediated dilation (FMD). This technique measures endothelial function by inducing reactive hyperemia via the temporary arterial occlusion and measuring the resultant relative increase in the blood vessel diameter via ultrasound. The high price and large size of the device, and being operator dependent are the limitation of this method. In this work, we propose using the photoplethysmogram (PPG)...