Research On The Key Technology Of Cognitive Radio Based RF Transmitter Front End

With the development of wireless communication technology, wireless spectrumresources is becoming scarce. In the premise of not affect the quality of communication ofauthorized users, cognitive radio realizes the dynamic spectrum sharing and improves theutilization of spectrum by sensing “spectrum hole” in the electromagnetic environment.Cognitive radio transmitter should be able to adjust the operating parameters such asfrequency, modulation, transmission power and communication protocol without changinghardware components, while the frequency and transmission power of traditional RFtransmitter is fixed. Therefore, it is necessary to carry out the research of cognitive radiobased RF transmitter.This paper’s work and research content is divided into the following three aspects:(1) This paper analyses the main types of CR transmitter RF front-end and theiradvantages and disadvantages. Based on the simulation of each structure, the low IFtransmitter scheme has been proposed.(2) The key modules of the transmitter have been designed. Using quadrature modulatorAD8345and tunable filter, the frequency reconstruction and the problem of LO leakage andLO traction have been solved. The transmission power is controlled by RF detector AD8314and variable gain amplifier HMC681. Finally, two power amplifier HMC482and HMC453have been used to provide sufficient output power.(3) The system performance of RF transmitter front-end has been tested. This transmitteris able to work on14channel in694-806MHz, and the maximum output power reaches30dBm. The power range of the transmitter is more than45dB. While the output power is30dBm, ACPR is lower than-32dBc and Spur suppression ratio is larger than35dB. Theseresults verified the feasibility of the low IF cognitive radio transmitter.