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Yayın Design and performance analysis of a novel trellis coded space-time-frequency transmission scheme(Işık Üniversitesi, 2004-07) Oğuz, Onur; Panayırcı, Erdal; Aygölü, Hasan Ümit; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Elektronik Mühendisliği Yüksek Lisans ProgramıThis work is concerned with a transmitter diversity technique for wireless communications over frequency selective fading channels. The proposed technique utilizes orthogonal frequency division multiplexing (OFDM) to transform a frequency selective fading channel into multiple flat fading sub channels on which space-frequency processing is applied and then additional space-time coding is applied in order to increase the diversity. In order to improve the performance of the system, a convenient trellis coding scheme is investigated and design criteria are established. Performance of proposed space-time-frequency OFDM (STF-OFDM) transmitter diversity technique has been examined by computer simulations.Yayın Ultra wideband indoor communication(Işık Üniversitesi, 2005-07) Yirmibeş, Elif; Panayırcı, Erdal; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Elektronik Mühendisliği Yüksek Lisans ProgramıUltra-wideband communication with its attractive features has received great interest from the industry and the research community. It has the potential for very high data rates with low processing powers. With its extremely wide bandwidth, multiple access capability, enhanced capability to penetrate through obstacles and its robustness to fading invites major advances in wireless communications. However, many important aspects of UWB-based communication systems have not yet been thoroughly examined. The propagation of UWB signals in indoor environments is one of the important issues with significant impacts . The amount of available UWB measurement data is very limited and more information is needed to support a comprehensive channel modeling. This paper describes the time-domain characterization of ultra-wideband propagation in indoor environments and introduces the recent proposed channel models with their effectiveness for indoor communications.Yayın Performance analysis of space time transmit diversity in UMTS under presence of carrier phase offset(Işık Üniversitesi, 2003-12) Toplu, Mehmet İlker; Panayırcı, Erdal; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Elektronik Mühendisliği Yüksek Lisans ProgramıThe reguirements for the next generation of mobile communication systems are primarily driven by the explosive growth of worldwide mobile communication subscribers. Additionaly, 3G systems will allow various of new services including wireless Internet acess, high -speed mobile data services and other multimedia applications. The expected growth of subscibers and the provided services indicate the need for increased system capacity of the future mobile communication systems. This thesis deals with Transmit Diversity techniques used for capacity enhancement in the downlink. The principle of Transmit Diversity is to send the same information with two antennas at the base station. If the signals from the different antennas fade independently, diversity at the receiver is achieved. Therefore, the ratio between the desired signal and the noise plus interference from other base stations can be enhanced. This means that there is less transmission power required to meet the same signal quality as in the single antenna case. The investigations within the scope of this work focus on Space-Time Transmit Diversity concept specified in the UMTS standard. I consider the application of Alamouti's Space-Time Transmit Diversity tevhniques in different scenarios. It's performance is evaluated by the calculation of the Average Error at the receiver depentent on the Signal to Noise Ratio. The performance of this method is compared by means MATLAB simulations.Yayın A novel channel estimation algorithm for ultra wideband communication systems(Işık Üniversitesi, 2005) Çağlar, Ekrem; Panayırcı, Erdal; Işık Üniversitesi, Fen Bilimleri Enstitüsü, Elektronik Mühendisliği Yüksek Lisans ProgramıUltra WideBand (UWB) is an emerging technology that is currently investigated as one viable solution for high capacity, short range wireless indoor systems. Its robustness in dense multipath environments, low cost and low power implementation together with high bit rates achievable are its unique promising features. However UWB signals occupy extremely large bandwidth and experience different propagation characteristics than conventional narrowband signals. Thus to evaluate the performance of UWB systems, an innotive channel model and corresponding channel estimation algorithm is required. This work is concerned with channel models developed so far for the UWB systems and appropriate channel estimation techniques. In this work the IEEE 802.15.3a channel model which best decribes the propagation of UWB signals is chosen as working model and a novel channel estimation method based on sequence estimation via EM algorithm is derived.
