Software Radio Modem Design

The key idea of software radio is to construct an open, standardized, modularized and general hardware platform using software to realize the wireless function instead of hardware, which greatly increases the flexibility of the communication system. The software radio plays an important role in the development of mobile communications. In the current design of software radio,it's impossible to sample the radio-frequency signal due to the performance limitation of current DSP processor and AD converter, instead, it's common to sample the intermediate frequency signal in most designs, thus intermediate frequency modulation/demodulation technology becomes a key point in the design of software radio.This thesis mainly studies the digital up convert (DUC) and digital down convert (DDC) based on intermediate frequency modulation/demodulation technology in software radio.It constructs a basic hardware platform composed of FPGA, AVR MCU, AD converter and so on. In DDC,the sampled signal from AD and the two orthogonal local oscillated signal which generated by direct digital synthetic technology mixed to move the signal from intermediate frequency to baseband, then through down-sampling and lowpass filtering we change the fast intermediate frequency signal into low baseband signal. When it comes to the DUC, we do the inverse operation. That is mixing the baseband signal (linear frequency modulation signal and sinusoid signal) with two orthogonal local oscillated signal generated using direct digital synthetic technology to move the baseband signal to intermediate frequency band. Under the control of AVR MCU, based on QuartusⅡ8.1,using VHDL and the IP core in FPGA, the designed software radio DDC module can realize bypassable, variable sampling rate, variable truncation output of CIC filter; bypassable, variable truncation output of HB filter; reconfigurable coefficient,variable truncation output of FIR filter. Besides, there are LCD display and keyboard input providing good human-machine interaction with the help of AVR MCU.