Elektronik ve Haberleşme Mühendisliği Bölümü

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/179

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Performance analysis of detection techniques in direct sequence code division multiple access (DS-CDMA) communication systems
(2004) Alat, Gökçen; Bilgisayar Mühendisliği
DS-CDMA is a new technology providing significant progress in wireless communication. Each user is distinguished by a unique spreading code to modulate an information signal. There are two factors limiting a DS- CDMA system: channel noise which is modelled as an additive white Gaussian noise and multiple access interference due to the many user simultaneously sharing the system. Generally, there are three different methods in the detection of user's signal: the single user detection technique, the optimal detection technique and the suboptimal detection technique. m In previous works, conventional detector and the suboptimal multiuser detection techniques are compared using Gold sequence which is produced from the pseudo noise code sequence. In this thesis, conventional single user detection technique is compared against the decorrelating detector and minimum mean square error (MMSE) based on suboptimal linear multiuser detection techniques. Three types of signature waveforms are used in this study: Gold sequence, small set of Kasami and the large set of Kasami. The small set of Kasami displays best BER performance. The large set of Kasami provides better performance than Gold sequence. Finally, in addition to frequently used Gold code sequence on the detection techniques, this thesis makes a comparison according to the usage of different code sequences that have lower cross correlation property
VHF data technology in air traffic services
(2006) Bellikli, Ahmet Eren
In this thesis, we have introduced communication, navigation and surveillance system?s working principles and bottlenecks based on working performances used in Air Traffic Control systems. We investigated the possible system solution to meet current bottlenecks, safety issues and Air Traffic growth handling for today and in the future. Air Traffic Navigation continuation and communication quality regarding safety issues are directly dependent on the chosen technology base. Choosing the right technology to meet requirements is what we have searched in this thesis. The baseline technology of Broadband -VHF project is as in the fourth generation (4G) mobile communications. iv B-VHF approaches communication in two different ways The one from ground stations to aircrafts (forward link) is based on combination of OFDM-CDMA called MC-CDMA and the second link from aircraft to ground (reverse link) is based on combination of OFDM-FDMA. We added Code Division Multiplexing into the reverse link to enhance the link robustness against interferences and data security. In order to realize this, we developed a Matlab code to simulate its performances to observe whether this combination provides robustness against interferences. Using the simulation we have obtained BER results at different cyclic prefix, number of OFDM symbols, code length size and channel settings. BER obtained with the inclusion of CDM are slightly favorable as compared to OFDM only reverse link, however, the performance improvement is not within the expected scale
The application of BDW method to the plane diffraction problem from PEC half plane
(2006) Ali, Aysha
Diffraction is a phenomenon by which wavefronts of propagating waves bend in the neighborhood of obstacles. Diffraction around apertures is described approximately by the diffraction wave method. Diffraction problems are among the difficult encountered in optics, and exact rigorous solutions are quite rare. A new procedure for calculating the scattered fields from a perfectly conducting body is introduced. The boundary diffraction wave method is used to evaluate the scattered field at an observation point after a certain obstacle with an aperture. The scattered field is combination of the diffracted and transmitted fields. The diffracted field is originated from the boundary of the aperture whereas the transmitted field originates from the aperture itself. The boundary diffraction wave method defines a new vector potential which is associated with any incident scalar wave field, and the integral of this vector potential expressing the field scattered by a perfect conducting screen with an aperture whose dimensions are larger than the wavelength. The Helmholtz-Kirchhoff formula is expressed in terms of the new vector potential to evaluate the disturbance, from certain points Q on a surface S, at an observation point. The method demands that the location of the point Q always depends on the location of the observation point
General optical beam formulation and their propagation in atmospheric optical telecommunication links
(2007) Yazıcıoğlu, Canan
In this thesis, we have developed a general source beam to combine many types of different beams such as Bessel, Bessel Gaussian, Laguerre, Laguerre Gaussian, Ince Gaussian, dark hollow, bottle, super Gaussian, Lorentz, flat-topped, Hermite-sinusoidal- Gaussian, sinusoidal-Gaussian like cos-Gaussian, sine-Gaussian, cosh-Gaussian, sinh- Gaussian, annular and their higher order modes with their truncated, elegant and elliptical versions in a single expression. Also we developed a Matlab code to plot intensity distributions at source and receiver. Using this Matlab code and the general source beam formulation, all the mentioned beams? source equations are obtained, compared with their existing forms in the literature and intensity patterns of some of them are plotted at source plane. Using a part of this formulation and the Matlab simulation, intensity is calculated and plotted intensity distributions of Hermite-sinusoidal-Gaussian, sinusoidal- Gaussian, annular and higher-order annular beams at different propagation distances in atmospheric turbulence
Multiuser detection in cdma system and its simulation in Matlab
(2007) Çakır, Burhan
In this thesis, we investigated performance of uncoded and with convolutional coded direct sequence code division multiple access (DS-CDMA) with decorrelating detection communication systems in additive white Gauss noise (AWGN) channel and Rician channel with Rician factors of 1, 10, 100. Rician channel with a high Rician factor will gradually resemble an AWGN channel. But as the Rician factor is made smaller, the error performance degrades, finally approaching the Rayleigh limit. Comparisons of uncoded and convolutional coded system show that: convolutional coded system has much better performance than the uncoded system. Two different convolutional code rates, which are 1/2, and 2/3 are tested. It is observed that for the same bit error rate (BER) value, at the code rate 1/2 has a lower signal-noise ratio (SNR) value than the code rate 2/3.
Effects of beam types in the performance of free space optics systems
(2008) Tatgin, Deniz
In this thesis, a general light source beam formula is developed which combines many beam types. Using different parameter sets in the general source beam formula, we obtained different beam’s source equations. Using Matlab, intensity distributions at the source plane for various beam types are plotted. Received average intensity in atmospheric turbulence is calculated for the general source beam and numerical evaluations are made and the received average intensities are plotted for certain specific beams such as Dark Hollow, Flat-topped, Bottle, Lorentz and Super Gaussian beams.
Public safety communication services requirement and their applications in the Turkish geographic structure
(2008) Usta, Mesut Bedri
Türkiye is a country which may face with many natural and social disasters due to the geography surrounding it. In this context, fast and effectual intrusion to the disasters is vital for the comfort and prosperity of the country. Certainly, such an intrusion demands a widespread, advanced, and cost-effective communications system which provides interoperability among different foundations like army, police, civil defence, fire brigade, ambulance, and some civil society organizations. At this point two systems come to front as the solution: APCO25 widely used in North America and TETRA widely used in Europe. In the studies of this thesis the aforermentioned two systems are compared with respect to their technical specifications especially the coverage areas; the results obtained are investigated in detail; and finally, by depending on a technology selection model in the literature, one of the systems is proposed as a solution. The coverage analyses are implemented using the computer program National Spectrum Management System (NSMS) developed by TÜBİTAK for the base stations of two alternative systems placed on several certain locations in Ankara province and the results are submitted in a visual manner. Analyses are divided into two classes to compare the coverage area of a single base station and the total coverage area of a group of base stations.
Analysis and observation on quality of service for data networks of turkish telecommunication infrastructure
(2008) Demirel, Mustafa
In this thesis, Jitter, Delay and Packet Loss values are measured for different points on TT IP/MPLS Backbone and compared with acceptable values. Measurements are made by using TT’s Alcatel 7750-SR12 devices which run in Ankara, Konya, Kahramanmaraş and Van. During measurements the device running in Ankara is always used as resource.Each of the other points are used as targets.The transmission distances between the devices measurements are as Ankara-Dikmen distance 10 Km and Ankara-Konya 300 Km, Ankara-Kahramanmaraş 602 Km and finally Ankara-Van 1248 Km. In this way, the connection between Jitter, Packet Loss and Delay Values and transmission distance is determined During tests every measurement is performed using 1500 and 4000 Bytes divided packets.The measurement values are taken using ping command on a software called SMART which can reach all devices on TT IP/MPLS Backbone. Measurements made are calculated in a day time zone. The connection of the software by which we perform measurements to the backbone is 100 Mbps. In the measurements taken, increase in Jitter and Delay value is observed when there is an increase in packet size. At the same time, increase in Jitter and Delay value is observed when there is an increase in transmisson distance. The packet loss value is evaluated as %0 in all of the tests made on TT IP/MPLS Backbone.
Diffraction of electromagnetic waves by impedance slits and strips
(2008) Coşkun, Galip Çağlar
In this thesis, diffraction process of electromagnetic waves by strips and slits will be examined by using the methods of the physical optics (PO) and modified theory of physical optics (MTPO) that have impedance boundary conditions on them. The integral will be evaluated by using the methods of stationary phase and edge point. The obtained solutions will be compared plotted numerically by using MATLAB.
Effects of beam types in the performance of free space optics systems
(2008) Tatgın, Deniz
Bu tezde, birçok hüzme tipini birleştiren bir genel ışık kaynağı formülü geliştirildi. Genel kaynak ışık hüzmesi formulünde farklı paremetre setleri kullanılarak, farklı ışık hüzmelerinin kaynak denklemleri elde edildi. Matlab kullanılarak, çeşitli hüzme tipleri için kaynak düzleminde ışık şiddeti dağılımları çizildi. Genel kaynak hüzmesi için türbülanslı atmosferde alıcıdaki ortalama ışık şiddeti hesaplandı ve Dark Hollow, Flat-topped, Bottle, Lorentz ve Süper Gauss gibi bazı spesifik hüzmelerin alıcı düzleminde oluşturduğu ışık şiddeti dağılımları nümerik hesaplanarak çizdirildi.
Diffraction of the packet-like and nondiffracting propagating beams by an obstacle in the atmosphere
(2008) Kara, Mustafa
This thesis takes two different solutions of homogenous wave equation into consideration. These solutions are named as packet-like solution and non-diffracting beam.First of all the propagation of these waves in the atmosphere is investigated. As a second step, an obstacle (a knife edge) is located on the propagation path of the diffracting beam and the diffraction effects are examined. The results are plotted numerically by using MATLAB
Regulation and competition aspects of wimax services in Turkey
(2009) Tilkioğlu, Ahmet Kerem
In recent years, especially the last decade, Broadband Wireless Access (BWA) Services have been rapidly developed and deployed to the world step by step. Nowadays, this development leads authorities to the field of telecommunication regulation strategies. This thesis study will examine the market share and competition case, test the system performance of WiMAX (Worldwide Interoperability for Microwave Access) services and investigate the required conditions for authorization process in Turkey.
500MHz-2GHz broadband power amplifier design by non-linear modeling methods
(2009) Ünal, Gökalp
This thesis presents the design methods of 500MHz-2GHz broadband RF power amplifier. First of all, RF power transistor technologies are searched and the most suitable one is chosen according to its operation of frequency band, maximum output power, efficiency and cost features. The amplifier is designed as it has two stages, and in both stages LDMOS transistor technology is used as RF power transistors. Large signal models for the LDMOS devices are used in simulation, and according to the measurement results, the circuitry in simulation is tried to model at nonlinear conditions. A broadband RF-Choke structure with a new technique is developed to obtain high DC isolation and low RF loss over the desired bandwidth. Input and output matching networks and shunt feedback topology are introduced to fulfill the bandwidth requirements. Typical values of 20dB power gain, 37dBm output power, have been achieved at the most part of the frequency band of 500MHz-2GHz.
Design of mobile DVB-T single frequency network(SFN) to cover İstanbul-Ankara highway
(2009) Özgün, Hüseyin
In this thesis, it is aimed to implement a DVB-T Single Frequency Network (SFN) for mobile reception which will cover the populated area of İstanbul, the İstanbul-to-Ankara-Highway, E-5 Road and the populated area of Ankara which is surrounded by the Ankara-Ring Highway. In this thesis, it will be designed DVB-T SFN Networks for mobile reception in two different DVB-T modes which are 2k and 8k modes. According to results of the SFN networks, the more suitable one for mobile reception will be obtained. A simulation software with a name of RTVplan is used to show the results and obtain the optimum design
Use of leds as future light sources
(2009) Demirel, K. Volkan
LEDS are conventionally used as indicators in control panels, and also for light sources in low power optic communication applications. Recently, high power and more efficient LEDs have appeared on the market. This study will investigate the use of LEDs for illumination purposes taking into account historical developments and future trends.
Field measurement of 3g base station
(2010) Has, Ahmet Can
3G mobile communication systems launched after some hardware and software changes on existing systems. After these changes operators have new services for subscribers. In this thesis, our target is to find problems, which faced by subscribers, with field measurements. Along these field measurements there were drop, congestion, and low data rate problems. After analyzing these problems we did some hardware and software changes. In this thesis you will find information about these hardware and software changes and the result graphs, which contains comparison for before and after these changes. These results verified by verification tests, if needed the problems re-analyzed and tried to optimize the system.
Analysis on link-16 tactical digital information link (tadil) system networks
(2010) Kir, Kaan
Link-16 Joint Tactical Information Distribution System (JTIDS) allows a tactical information exchange between air, ground and naval units near real time in the presence of adversary units. Link-16 employs the Time Division Multiple Access (TDMA) technique for data communication, and at the same time by using frequency hopping capability and encryption properties interconnects various units simultaneously in synchronized nets concurrently near real time in accordance with the mission requirements. In this study, a network design and management tool is developed that designs, programs and manages the Link-16 Network. This tool’s objective is to effectively and reliably distribute the time slots among the tactical participants based on the mission requirements and scenario.
Iterative decoding of block codes
(2010) Genç, Fatih
Error control coding is vital for digital communication. With the advent of turbo codes a huge interest on iterative decoding aroused recently. Although iterative decoding reduces bit error rate (BER) significantly, it brings new challenges such as increased complexity and large decoding delays. Turbo like codes can be constructed either using convolutional codes or block codes. In this thesis we construct classical turbo codes with both convolutional codes and block Bose Chaudhuri and Hocquenghem (BCH) codes, and simulate their performances and discuss their advantages and disadvantages.
Heating effect of electromagnetic fields on human head at gsm frequencies
(2010) Türk, Afşar
This thesis investigates the heating effect of electromagnetic fields on human head at GSM (Global System for Mobile Communications) frequencies. First of all, existing structure was studied. In this work, the existing spherical head models of head are searched and the head is modelled with different concentric spheres (brain, bone, skin) that have different permittivity and conductivity. The radiation is assumed to be generated by a loop antenna located near the head. The results are obtained at two different frequencies, 900 MHz and 1800 MHz that are widely used in GSM systems. To investigate relations between permittivity, conductivity and heating potential, the numerical results are found on any sphere that has different radius, permittivity and conductivity.
Radar cross section of a conducting flat plate by the method of modified theory of physical optics
(2010) Çınar, Ayşe Tila
In this thesis, reflected scattered fields from a conducting rectangular flat plate, and its edges and corners are observed, calculated and analyzed by using the Method of Modified Theory of Physical Optics. In the calculations, two methods, named “Stationary Phase Point Method” and “Edge Point Method”, are used to solve scattering integrals manually. Numerical results of the calculations are evaluated by plotting them in the MATLAB tool.

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