The Design And Implementation Of The Complex Signal Source Based On GNU Radio

Software Defined Radio(SDR) is essentially used to process digitized RF signal by software. This method can transfer an amount of hardware problems into software problems with a strong flexibility. In fact, traditional radio signal generation and processing are basically done by hardware equipment. However, Software Defined Radio can be used to achieve the function which can be implemented by the hardware. Operate on a certain hardware platform, this method modify and add the system function by modifying and adding the software features. As a result, this not only can reduce the modification cost and complexity of hardware, but also reduce the difficulty in system development. In addition, it will increase the flexibility of system as well. Thus, this paper will present a complex signal source design which is based on the GNU Radio.With the development of chip technology and the advent of mobile Internet era, ARM processor especially the multi-core ARM processor has been widely used and it might replace the x86 processor. In this paper, the single-board computer with Raspberry Pi board, which is based on the ARM architecture, is used to be upper computer processing platform. And the GNU Radio of open-source radio development suites is operated on this platform as parts of various complex modulated signal of baseband processing. The single-board computer with Raspberry Pi board communicate with core signal generating unit designed in this paper by using SPI interface and GPIO to transfer the original baseband IQ data and control order. The core signal generating unit is composed of FPGA with high-speed TxDAC. It can receive the baseband IQ data from upper computer and then modulate two orthogonal zero frequency signal of high-speed IQ to digital intermediate frequency and also send to high-speed TxDAC to output various modulating signal. In the end, Intermediate frequency signal, which is output by the core signal generating unit is sent to analog up converter. After mixing to specific frequencies and then magnifying, it will be sent out by antenna.Firstly, this paper will introduce the significance and functions of complex signal source on the role of radio monitoring network planning platform. Secondly, it will present the schematic diagram and print circuit board of core signal generating unit and upper converter. Thirdly, the hardware circuit debugging of core signal generating unit and the testing of software code module is introduced. At last, the designed core signal generating unit was connected to the single-board computer with Raspberry Pi, where various function modules of modulation signal are used to do joint debugging by using the GNU Radio of open-source radio development toolset. The complex signal source designed in this paper can output many modulating signals, and the range of output frequency is 20MHz~3000MHz. Debugging and testing results about the designed complex signal source, and analysis of various index of the output signal was presented at the end of this paper. The result turns out that the core signal generating unit designed in this paper can work normally. Also, the device module designed on gnuradio-companion can communicate with FPGA successfully.