Design And Research Of Transmission Scheme In Rateless Coded Cognitive Radio System

In 21th century, cognitive radio has become a key research direction in wireless communication. It's an intelligent spectrum sharing technology, which allows the unlicensed user to opportunistically occupy the licensed spectrum. Cognitive radio can make the usage of spectrum more efficient, and relief the crisis of spectrum resource scarcity. Rateless codes are exploited in cognitive radio systems with promising virtue of high resilience and adaptivity in link transmission. By making use of rateless codes'adaptivity with the dynamic channel environment, the unlicensed user can confront the unpredictable channel occupancies by the licensed user. In this dissertation, we first introduce the concept and the feature of cognitive radio and rateless codes, then propose a scenario of cognitive radio system with the employment of rateless codes and investigate the problem of system design and frame structure. In addition, we discuss the thoughput optimization and energy allocation of rateless coded cognitive radio system. Finally, the design and implementation of software defined radio platform has been fully researched.Firstly, we investigate how to make a design of the transmission scheme in rateless coded cognitive radio system, and propose a scenario of transmitting and receiving. We choose Raptor code as the channel coding scheme of our cognitive radio system. Based on the simulation results of the performance of Raptor code with different code length under different decoding algorithms, we choose proper code length for cognitive radio system. Then we design two kinds of frame structures for different decoding algorithms, and discuss the problem of modulation and demodulation in an OFDM system. The date streams of frames are parallel, then the scenario of transmitting and receiving is complete.Secondly, we research the optimization algorithm of rateless coded cognitive radio system. We set up a numerical model for the cognitive system which has one secondary user and a group of primary users. The secondary user transmits encoded packets through detected available channels using rateless codes. With the employment of periodical spectrum sensing we analyze the interference to primary users. Then we investigate the thoughput of secondary user and analyze the relationship between the thoughput and the number of time slots for transmission. We optimize the thoughput, meanwhile guaranteeing the constraint of interference to primary users. The energy consumption of the secondary user has also been analyzed. The proposed energy allocation algorithm can allocate the sensing energy and transmission energy of the secondary user to minimize the energy consumption, taking into account both channel and system characteristics.Finally, the system is based on software defined radio. Based on the Sora SDR released by Microsoft, a cognitive radio system is implemented with Raptor code in application layer. And another cognitive radio system is implemented with Raptor code in physical layer based on a self-design software defined radio platform.