| With the adventure of new technologies and booming of wireless devices, spectrum resources become increasing intense. Therefore how to enhance spectrum efficiency comes out to be one of the most urgent problems. Cognitive radio, a very effective technical approach to address the problem, is defined as an intelligent wireless communication system which is able to obtain the spectrum diagram in the surroundings through spectrum sensing and plans spectrum allocation and accessing based on the information obtained. According to the above, cognitive radio need to dynamically adjust the operational parameters of its wireless system, which requires its physical layer to possess high flexibility and adaptability. In the use of spectrum chance, effective physical transmission technologies become quite an important issue. First of all, how to generate signals with no interference to primary users and realize spectrum sharing with them is the primary concern in cognitive physical transmission technologies. Secondly, owing to that time and frequency of primary users’adventure are uncertain, cognitive users will suffer degradation in communication link quality and data transmission. Thus effective channel coding should be provided to cognitive radio system. In order to solve all the above problems, this thesis concentrates on the physical transmission technologies for cognitive radio and proposes two brand new ideas in multicarrier sharing and channel coding separately. Exhaustive theoretical analysis and performance simulations are also given in the thesis.Firstly, a new scheme named Overlapped OFDMA is proposed, under which, secondary users’ subcarrier bandwidth can be 1/2 of those used by primary users. The spectrum between them is allowed to be overlapped. If primary and secondary users’ time-domain signals are quasi-synchronized and secondary users’ subcarrier assignment complies with certain constraint, primary users will not be interfered. Moreover, overlapping interference in any subcarrier contains information about other subcarriers, thus desired information could be drawn by well-designed signal recovery algorithm. Quasi-synchronized mechanism, subcarriers assignment constraint and the signal recovery algorithm will be fully illustrated. Communication diagram, transceiver and receiver structure and feasibility of the system will be shown. Simulation results illustrate that Overlapped OFDMA have better throughput performance than NC-OFDM cognitive system. The new scheme provides a new possible approach for spectrum sharing system design.Secondly, the thesis proposes a new unequal error protection rateless codes based on channel state information. In the wireless communication scenes where CSI could be obtained, it could be used in packets scheduling for rateless codes and assign the best accessed channel for each encoded packet, resulting a performance rise of rateless codes. We apply UEP-CSI rateless codes into cognitive radio system and adopt overlay spectrum sharing with primary users. The simulation outcomes demonstrate that the new approach could enhance the throughput performance of cognitive users in a certain degree.Finally, hardware and software realization of cognitive OFDMA physical transmission technologies are illustrated. In the first place, hardware, system structure and software of Microsoft’s SORA platform are shown. Then physical layer algorithms of cognitive OFDMA system, which are based on SORA platform, are demonstrated. These algorithms are able to make cognitive users take advantage of spectrum holes effectively and generate no harm to primary users. In the last we will shown the actual performance tests of these algorithms using SORA platform. |
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