Implementation of distributed Alamouti space time code in orthogonal frequency-division multiplexing (OFDM) system using USRP N200Implementation of distributed Alamouti space time code in orthogonal frequency-division multiplexing (OFDM) system using USRP N200Υλοποίηση κατανεμημένου αλγορίθμου Alamouti σε OFDM σύστημα χρησιμοποιώντας USRP N200 Διπλωματική Εργασία Diploma Work 2015-12-022015enOrthogonal frequency division multiplexing (OFDM) is a modulation technique which is now used in most wired and wireless communication systems, because it is an effective solution to cope with intersymbol interference caused by the channel. In wireless communication, the concept of parallel transmission of symbols is used to achieve high throughput and better transmission quality. OFDM is one of the techniques for parallel transmission. OFDM splits the total transmission band- width into a number of orthogonal subcarriers in order to transmit the symbols using these subcarriers in parallel. It is a widely used modulation and multiplexing technology, which has become the basis of many telecommunications standards in- cluding 4G, wireless local area networks (LANs), digital terrestrial television (DTT) and digital radio broadcasting in much of the world. Multiple-input multiple-output (MIMO) technology significantly enhances sys- tem performance. The extra degrees of freedom afforded by the multiple antennas can be used for increasing bit rates through spatial multiplexing or for improved diversity order through space-time coding techniques. In this thesis, we combine OFDM and MIMO systems. Specifically, we design and implement an OFDM system with two transmitters and one receiver with Alamouti space time code (STC) using USRP. At the beginning, we create an OFDM transmitter and receiver with N subcarriers in Matlab and GNU radio and then we build it using C++ for real time processing. The two transmitters modify the data, as described, by Alamouti STC and they send them simultaneously. The receiver has to receive and process the data in order to detect the transmitted symbols. Time synchronization, CFO cancellation and channel estimation are such processes. The transmitters are two USRPs N200, which were synchronized to send the Alamouti symbols at the same time. Also, the receiver is a USRP N200. Before the Alamouti scheme, we implemented an OFDM system with one transmitter and one receiver. Finally, we measure some performance metrics, like SNR and BER. Διπλωματική εργασία που υποβλήθηκε στη σχολή ΗΜΜΥ του Πολυτεχνείου Κρήτης για την πλήρωση προϋποθέσεων λήψης του Διπλώματος Ηλεκτρονικού μηχανικού και μηχανικού ηλεκτρονικών Υπολογιστώνhttp://creativecommons.org/licenses/by/4.0/Πολυτεχνείο Κρήτης::Σχολή Ηλεκτρονικών Μηχανικών και Μηχανικών ΥπολογιστώνKaramolegos_Nikolaos_Dip_2015.pdfChania [Greece]Library of TUC2015-12-02application/pdf2.3 MBfree Karamolegos Nikolaos Καραμολεγκος Νικολαος Liavas Athanasios Λιαβας Αθανασιος Paterakis Michalis Πατερακης Μιχαλης Karystinos Georgios Καρυστινος Γεωργιος Πολυτεχνείο Κρήτης Technical University of Crete OFDM systems Telecommunication OFDM Orthogonal frequency division multiplexing OFDM in SDR