Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Access type: Open accessAuthor: search.filters.author.Altınkaya, Mustafa Aziz

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Now showing 1 - 4 of 4
  • Master Thesis
    Space-Time Coding for Cdma-Based Wireless Communication Systems
    (Izmir Institute of Technology, 2002) Taban, Alper; Altınkaya, Mustafa Aziz
    Multiple transmit antennas giving rise to diversity (transmit diversity) have been shown to increase downlink (base station to the mobile) capacity in cellular systems.The third generation partnership project (3GPP) for WCDMA has chosen space time transmit diversity (STTD) as the open loop transmit diversity technique for two transmit antennas.On the other hand, the CDMA 2000 has chosen space time spreading (STS) and orthogonal transmit diversity (OTD) as the open loop transmit diversity.In addition to all the standardization aspects, proposed contributions such as space time coding assisted double spread rake receiver (STC-DS-RR) are exist.In this thesis, open loop transmit diversity techniques of 3GPP, CDMA 2000 and existing contributions are investigated.Their performances are compared as a means of biterror- rate (BER) versus signal-to-noise ratio (SNR).
  • Master Thesis
    Multiuser Detection in Cdma Using Blind Techniques
    (Izmir Institute of Technology, 2004) Altınsoy, Eşref Olgu; Altınkaya, Mustafa Aziz
    In code division multiple access (CDMA) systems, blind multiuser detection (MUD) techniques are of great importance, especially for downlinks, since in practice, it may be unrealistic for a mobile user to know the spreading codes of other active users in the channel. Furthermore, blind methods remove the need for training sequences which leads to a gain in the channel bandwidth. Subspace concept in blind MUD is an alternative process to classical and batch blind MUD techniques based on principle component analysis, or independent component analysis (ICA) and ICA-like algorithms, such as joint approximate diagonalization of eigen-matrices (JADE), blind source separation algorithm with reference system, etc. Briefly, the desired signal is searched in the signal subspace instead of the whole space, in this type of detectors. A variation of the subspace-based MUD is reduced-rank MUD in which a smaller subspace of the signal subspace is tracked where the desired signal is contained in. This latter method leads to a performance gain compared to a standard subspace method. In this thesis, blind signal subspace and reduced-rank MUD techniques are investigated, and applied to minimum mean square error (MMSE) detectors with two different iterative subspace tracking algorithms. The performances of these detectors are compared in different scenarios for additive white Gaussian noise and for multipath fading channels as well. With simulation results the superiority of the reduced-rank detector to the signal subspace detector is shown. Additionally, as a new remark for both detectors, it is shown that, using minimum description length criterion in subspace tracking algorithm results in an increase in rank-tracking ability and correspondingly in the final performance. Finally, the performances of these two detectors are compared with MMSE, adaptive MMSE and JADE detectors.
  • Master Thesis
    Acoustic Indoor Localization Employing Code Division Multiple Access
    (Izmir Institute of Technology, 2010) Sertatıl, Cem; Altınkaya, Mustafa Aziz
    Indoor localization becomes a demand that comes into prominence day by day. Although extensively used outdoor location systems have been proposed, they can not operate in indoor applications. Hence new investigations have been carried on for accurate indoor localization in the last decade. In this thesis, a new indoor location system, that aims to locate an entity within an accuracy of about 2 cm using ordinary and inexpensive off-the-shelf devices, has been proposed and an implementation has been applied to evaluate the system performance. Therefore, time of arrival measurements of acoustic signals, which are binary phase shift keying modulated Gold code sequences using direct sequence spread spectrum technique, are done. Direct sequence-code division multiple access is applied to perform simultaneous accurate distance measurements and provides immunity to noise and interference. Two methods have been proposed for the location estimation. The first method takes the average of four location estimates obtained by trilateration technique. In the second method, only a single robust position estimate is obtained using three distances while the least reliable fourth distance measurement is not taken into account. The system performance is evaluated at positions from two height levels using two sets of variables determined by experimental results. The precision distributions in the work area and the precision versus accuracy plots depict the system performance for different sets of variables. The proposed system provides location estimates of better than 2 cm accuracy within 99% precision. Eventually, created graphical user interface provides a user friendly environment to adjust the parameters.
  • Master Thesis
    Differential and Coherent Detection Schemes for Space-Time Block Codes
    (Izmir Institute of Technology, 2002) Oruç, Özgür; Altınkaya, Mustafa Aziz
    The single most important technique providing reliable communication over wireless channels is diversity. One of the diversity techniques is space diversity. Typical examples of space diversity are multiple transmit and/or receive antenna communications. By employing multiple antennas either at the transmitter or at the receiver, multiple antenna communications introduce a space diversity to combat fading without necessarily sacrificing bandwidth resources; thus they become attractive solutions for broadband wireless applications.Space-time coding is a new diversity method for communication over wireless channels using multiple transmit antennas. Two types of space-time coding have been studied for a few years: trellis and block coding. Space.time trellis codes perform extremely well at the cost of relatively high complexity. Owing to this, in this thesis, space-time block codes are investigated in detail. Not only these codes support an extremely simple maximum likelihood detection algorithm based only on linear processing at the receiver, but also they can be used for multiple transmit antenna differential detection.In this thesis, coherent and differential detection schemes for space-time block coding are investigated in detail over non-dispersive Rayleigh fading channels. In coherent detection systems, Alamouti's and Tarokh's codes with two, three and four transmit antennas are simulated for BPSK and QPSK modulation. Furthermore, Tarokh's and Hughes' differential detection schemes with two transmit antennas are investigated and a unifying approach to these structures is developed with a new design criteria for optimal unitary group codes. Then, the codes chosen by Tarokh and Hughes are simulated using a generalized differential detection scheme for BPSK and QPSK modulation. Moreover, codes of Hochwald are also simulated in order to compare them to the codes of Tarokh.