Study On The Key Technology Of Ransmission Link Adaptive Based On Cognitive Radio

According to transmission characteristic of work environmental, cognitive radio can adaptively select different means of communication, modulation, frequency. It is expected to completely change the existing radio resource allocation policy. In cognitive radio system, as long as there are no user in a band, any other user can occupy the frequency resources, without a fixed frequency allocation strategy, therefore, the cognitive radio is the solution to the current tension of frequency resources in one of the effective ways.In the system of cognitive radio, the transmitted link adaptive technology plays a crucial role in the high-effect and reliable signal communication. The cognitive radio system demands data transmission having the behavior of adapt the transmitting channel shift with good flexibility. In this article, we have the deep research about the transmitted link adaptation, which is the key technology of the system of cognitive radio. This essay contains 3 points to research:(1)Introduce the origin background,fundamentals,system model,key technology and the system structure of cognitive radio in brief; provide a kind of cognitive radio system structure based on the transmission of OFDM in addition of making a rationale of its operation fundamentals.(2)The prerequisite of the Wireless link adaptive is channel estimation. According to the demand of cognitive radio system of MIMO-OFDM, and at the point of the view for gives consideration to both sides of enhancing the performance of channel estimation and debating the complexity of algorithm, we provide a kind of channel estimation algorithm on account of Pre-linear non-redundant coding and Second-Order Statistics, and take an analysis with simulation. The result shows that this algorithm can enhance the performance of channel estimation and debate the complexity of algorithm to compare with those based on pilot estimation and traditional blind channel estimation.(3)Research the OFDM adaptive technology based on cognitive radio, to provide an adaptive bit distribution algorithm on the basis of analyzing the performance of constant bit rate distribution algorithm, and take an analysis with simulation. The result shows that this algorithm is better than that of constant bit rate distribution on the performance of error rate in the addition of reducing the transmission power of system.