In The Cognitive System Research And Implementation Of Orthogonal Multi-carrier Signal Design

The ever growing demand for wireless services has placed enormous burden onvaluable resources such as spectral bandwidth. Cognitive radio arises to be a temptingsolution to spectral crowding problem by introducing the opportunistic usage offrequency bands that are not heavily occupied by licensed users. Hence, cognitive radioshould have the ability to sense and be aware of its operational environment, anddynamically adjust its radio operating parameters accordingly. To achieve this objective,the Physical Layer (PHY) needs to be highly flexible and adaptable. A special case ofmulticarrier transmission known as OFDM is one of the most widely used technologiesin current wireless communications systems and it has the potential of fulfilling theaforementioned requirements of cognitive radios inherently or with minor changes.Because of OFDM signal formation processing, it naturally has a high peak to averagepower ratio and a large sidelobe power, this paper will discuss and study these twoshortcomings and complete the orthogonal multi-carrier signal design, successfullyapplied to cognitive radio communication systems which working frequency is694MHz-806MHz. Combination with our software-defined radio test platform, thework done in this article are as follows:First, for our cognitive radio system, the original signal has a high peak to averagepower. This paper analyze the influencing factors of OFDM signal’s PAPR, study therelated various crest factor reduction technology which has a easy achievement inpractice, give specific steps of the achievement, and compare their performance afteradding them to the data channel link in Matlab simulation.Then, for our cognitive radio system, the original signal has a large sidelobe powerslowly decreased, analyze the factors affecting the OFDM signal sidelobe power, studysome sidelobe suppression technologies as well as the combination of various methods,and compare their performance.Finally, combined with the demand for our cognitive radio system, twocost-effective high technologies are selected in the preceding analysis. After thealgorithm optimization, they have been carried out by using hardware description language in the FPGA. They greatly reduce the system’s complexity in theimplementation process. On the basis of the optimized transmitted signal in the previouswork, I complete the FPGA’s design of the transmit link, combining with self-designedinterface and control module. In addition, I complete the online test of the optimizedOFDM transmit signal. The correctness of its functions is verified by self-loop test.Then, I count the PAPR reducing performance. Though the measurements of the RFsignal, I finish statistics and calculation of some indicators. The experimental resultsshow that it meets the relevant regulations.