The Demodulating And Receiving Of FM Broadcast Based On GNU Radio And RTLSDR Software Defined Radio

Nowadays, the wireless communication system develops towards multi-standard and multi-system, but the conventional radio systems are too highly dependent on hardware to adapt to the development of communication system needs. In order to solve the above problems, conventional radio system develops toward software defined radio step by step Software defined radio proposed a concept of realizing radio applications in a standardized, modular, general-purpose, open and expandable way, it has the advantages of software-programmable, expandable, easy to modify and low-cost, through combining a standardized, modular hardware platform with the signal processing software such as GNU Radio, it upgrades the communication technology from the traditional fixed circuits and hardware-dependent limitations to software and expandable in height.In the thesis, the concept, development and application of software defined radio was introduced, further discussed the basic structure and key technologies of software defined radio was analyzed, then a detailed introduction on the structure and working principle of the software GNU Radio and hardware RTLSDR was discussed respectively. Last a FM broadcast demodulation based on GNU Radio and RTLSDR was designed by creating signal processing flow diagram.This thesis focuses on the research and design of FM broadcast signal’s demodulation and receiving which based on GNU Radio and RTLSDR software defined radio platform. The design was based on the idea of software defined radio, which used the tuner R820T of RTLSDR to receive the radio signal and converted it down to low intermediate frequency through twice down-converting, the low intermediate frequency signal was converted from analog to digital and further converted to quadrate baseband IQ signal in the RTL2832U chip of RTLSDR. The baseband IQ signal is fed into the computer signal processing software platform GNU Radio to be demodulated, filtered, amplified In GNU Radio, the signal was demodulated, filtered and amplified by creating signal processing flow chart in the Graphical User Interface GNU Radio-Companion.The important work in the design is the demodulation of the FM broadcast in GNU Radio, which was done in GNU Radio-Companion by creating signal processing flow diagram. In the thesis, the algorithm of calculating arctangent of signal’s phase then difference was used to demodulate the FM radio signal. The source and header code files based on the algorithm was edited to generate a custom signal processing block WBFM block, which was generated and added by gr-modtool (a tool that builds GNU Radio custom signal block). The FM demodulation was done in the WBFM block. A FM broadcast demodulation signal processing flow diagram was created by calling and connecting the necessary blocks, finally ran the flow diagram to demodulate the signal, the FM broadcast was heard from the loudspeaker.