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Υλοποίηση κατανεμημένου αλγορίθμου Alamouti σε OFDM σύστημα χρησιμοποιώντας USRP N200

Karamolegos Nikolaos

Πλήρης Εγγραφή

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Περίληψη

Orthogonal frequency division multiplexing (OFDM) is a modulation techniquewhich is now used in most wired and wireless communication systems, because it isan effective solution to cope with intersymbol interference caused by the channel.In wireless communication, the concept of parallel transmission of symbols is usedto achieve high throughput and better transmission quality. OFDM is one of thetechniques for parallel transmission. OFDM splits the total transmission band-width into a number of orthogonal subcarriers in order to transmit the symbolsusing these subcarriers in parallel. It is a widely used modulation and multiplexingtechnology, 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 antennascan be used for increasing bit rates through spatial multiplexing or for improveddiversity order through space-time coding techniques.In this thesis, we combine OFDM and MIMO systems. Specifically, we designand implement an OFDM system with two transmitters and one receiver withAlamouti space time code (STC) using USRP. At the beginning, we create anOFDM transmitter and receiver with N subcarriers in Matlab and GNU radio andthen we build it using C++ for real time processing. The two transmitters modifythe data, as described, by Alamouti STC and they send them simultaneously. Thereceiver has to receive and process the data in order to detect the transmittedsymbols. Time synchronization, CFO cancellation and channel estimation are suchprocesses. The transmitters are two USRPs N200, which were synchronized to sendthe Alamouti symbols at the same time. Also, the receiver is a USRP N200. Beforethe Alamouti scheme, we implemented an OFDM system with one transmitter andone receiver. Finally, we measure some performance metrics, like SNR and BER.

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