Design Based On Software Radio For Digital Frequency-swept Receiver

For the realization of received signal tuning,filtering,attenuation,down.conversion,quadrature demodulation and other functions,conventional radio receivers all adopt analog circuits.However,this solution is confronted with the weakness of the complexity of circuit,difficulty in debug,narrow bandwidth of the receiver,inflexibility,low anti-interference performance and difficulty in standardization and modularization.In addition,once the hardware circuit design is completed,its receive band is fixed and it would be hard to modify the circuit.Through constructing an open and standardized general hardware platform,software radio technology realizes the above described various functions by software programming.Software radio technology can arrange the A/D and D/A converter close to the antenna and shift Radio Frequency(RF)and medium frequency to baseband.Having added the digital receiver,Software Radio Receiver(SRR),the inevitable trend of future,can replace the traditional radio receiver and solve the shortage of traditional receiver.Signal orthogonal transform technique and down-conversion technology involved software radio digital receiver is the key technology of software radio communication research.Firstly,according to the characteristics of the digital receiver,by theoretical analysis and simulation and find the best pulse compression coding,finally adopt 13.bits Barker code to compress.On the basis of in-depth research of digital down conversion working principle,this paper has conducted the principle calculation of cascaded integrator comb(CIC)filter and Half-Band(HB)filter which are the key technologies of digital down converting.In addition,through amplitude frequency response characteristics simulation analysis under different cascade series and delay factors,this paper obtains proper filter design factors by MATLAB.Secondly,this paper designs a digital scanning receiver model based on software radio technology to meet the needs of the ionosphere probe.Through RF front-end,antenna filters a variety of space radio interference and noise in received RF signal and amplifies the weak received useful signal.Improving the receiver front-end SNR,so that the received signals are suited to A/D sampled and then converts the signals into digital signals.Then with the help of software algorithm,this paper processes the digital signal data.In addition,by the way of software design,numerically controlled oscillator is designed to generate local oscillator signal and the system proceeds with digital down-conversion and quadrature demodulation.Efficient digital filter is designed for sampling rate decimation and filtering of signals as well as the adjustment of two way signals amplitude and phase.In order to obtain a more optimized parameter model design of digital scanning SRR,this paper makes use of MATLAB to conduct simulation,the decimation factor,stop-band attenuation,pass-band attenuation and cascading series should be designed rationally.Thirdly,in the Hyman USRP(Universal Software Radio Peripheral)N210 platform,using GNU Radio,an open source software environmental controls the motherboard to conduct BPSK(Binary Phase Shift Keying)modulation in 13.bits Barker pulse compression signals and accomplishes D/A converting,and then transmit modulated signals by the transmitting sub-board(LFTX Low Frequency Transmission).At the receiving terminal,the modulated signals are received by the receiving sub-board(LFRX Low Frequency Reception),and the completion of A/D conversion through the motherboard with the use of C++ and python mixed programming,this paper completes the emitting,receiving,encoding,modulating,and digital down converting,demodulating and decoding functions in GNU Radio software environment.Experimental results show that digital swept frequency SRR can be software based and reconfigurable;modulation-demodulation,digital filtering,decimation,encoding,decoding and other functions can all be realized by utilizing digital signal processing libraries in GNU Radio dynamically to reconfigure part of software on the USRPN210 hardware platform.Finally,in this paper,the software radio platform,constituted by utilizing GNU Radio software environment and USRPN210 hardware platform,is applied to existing ionosphere altimeter.The software radio platform can realize detection by the way of software radio detection and obtain a clear digital ionogram.Implementation of the digital altimeter on SRR verifies the feasibility of ionosphere detection technology based on software radio platform and provides significant technical route for further improvement the ionospheric radio detection and diagnosis technology.In short,this paper systematically introduces the quadrature transform and digital down conversion of signal systematically and derives the design model of digital swept frequency SRR to obtain proper design parameters.With the use of MATLAB simulation and verification of specific design factors spectrum was good compared to the baseband signal amplitude.Then utilizing GNU Radio software environment to conduct experiments on the USRPN210 platform,which realize transmitting and receiving of swept frequency signal,as well as digital down conversion mixers and other digital signal processing.Finally,this paper designs a digital swept frequency SRR and gets a good test results,in addition,it else meets the desired design specifications.