The Adaptive OFDM Modulation Technology Of Research And Implementation Based On CRAHN

During all kinds of disasters, communication facilities and base stations will be easily damaged. At the same time, the data traffic usually increases obviously, this increase the difficulty of the rescue work. Quick and effective means of communication has already become a key factor in order to reduce disaster damage. Traditional division of frequency spectrum has a poor efficiency, in emergency circumstances, which is a tremendous waste. CRAHN technology can solve this problem, this kind of network technology can build ad-hoc network whose nodes have the ability to perceive the spectrum and use the available spectrum resources for emergency communications. In a word, the CRAHN technology can not only effectively improve the efficiency of the radio spectrum, and can easily deal with explosive growth of communication traffic.At the beginning of this paper, we introduce the significance of CRAHN technology including cognitive radio and Ad hoc networks. At the same time, we discuss the advantages and challenges of adaptive OFDM based CRAHN technology, this will make a preparation for the follow-up parts.This paper consists of three main parts. Firstly, we discuss the principle and key techniques of adaptive OFDM modulation and demodulation, as well as the technical difficulties of the adaptive OFDM modulation system. Secondly, we come up with the framework of adaptive OFDM modulator system under the guide of cross-layer control method and improved adaptive resource allocation algorithm. We define the MAAC frames and PPDU format as well as refine the relevant parameters. According to overall framework, we analyze the principle and implementation of channel coding, interleaving, mapping, etc. Finally, we use Verilog HDL language to implement the adaptive OFDM system based on Quartus II software platform.The innovation point of this paper is that each module can change modulation according to MAC frame in order to different environment. This solution really achieves the adaptive OFDM modulation. In addition, we choose “Call-Answer” control mode to make the response of each module more quickly when the control parameters are more. Benefit from the separation between controls and data & parameterized module, my adaptive OFDM system can be applied to complex CRAHN environment, thus having strong theoretical and practical significance.