Research On Adaptive Wideband Digital Receiver Technology

With the increasing complexity of the electromagnetic environment,radar signals appearing in the battlefield generally begin to adopt low probability intercept(LPI)signals with large bandwidth in low SNR.The traditional wideband receivers which in the battlefiled have some shortcomings,such as the problem of cross-channel signal,poor ability of processing simultaneously arrived signals,and poor signal detection when receiving wideband radar signals under low signal-to-noise ratios(SNRs),because the sub-bands' bandwidth of uniform channelization digital receivers which cannot receive signals adaptively is fixed.Therefore,this paper proposes some feasible solutions including the new recognition algorithm,new receiver architecture and new receiver reconfiguration from the view of software arithmetic and hardware implementation.The main contents and innovations of this paper are as follows.At first,aiming at the large-bandwidth radar signals which have appeared in the electronic battlefield in recent years,this paper studies a signal detection method based on the traditional multiphase filtering DFT structure wideband digital channelized receiver architecture,which can identify the linear frequency modulation(LFM)signals and nonlinear frequency modulation(NLFM)signals at instantaneous bandwidths above GHz based on the method of channel splicing and phase difference frequency measurement from the view of new recognition algorithm.The simulation verified effectiveness of this algorithm.But the algorithm requires the high SNRs with the low flexibility.Therefore,two adaptive digital receiver structures are further proposed in this paper.The first one is the novel wideband digital receiver based on pulse compression,which is extended from the analog domain to the digital domain,and the discrete form of the signals through the compressive receiver is derived.In this novel architecture,the received signals are mixed with the linear frequency modulation signal,and the convolution operation is performed in the digital delay module to obtain the pulse spike.The novel receiver can effectively process signals in low SNR conditions as well as process simultaneously arrived signals,and it does not generate the problem of cross-channel signal.Experimental results show the respective constraint relations between the frequency of input signals and the bandwidths of sweep and digital delay signals.Furthermore,the formula for measuring the PDW information,which includes frequency,bandwidth,pulse width,and amplitude after the radar signals pass through the new wideband digital receiver,is given.The other one is the MWC wideband digital receiver based on the multiphase architecture.The MWC wideband digital receiver based on cyclic pseudo-random sequences can solve the problem of cross-channel signal with mixing the whole sub-band signals into baseband.But the whole architecture works under the high data rate which cannot implement on FPGA easily.Therefore,this paper proposes the MWC wideband digital receiver based on the multiphase architecture with moving forward the extraction module into the forefront of the architecture.Under the condition of using a same multiplication source,the data rate of the new receiver structure is much lower than the existing MWC structure.The proposed design establish the foundation of the MWC discrete compressed sampling digital receiver implementation on FPGA,which makes a more valuable practical engineering application.At last,aiming at the problem that the existing adaptive filters cannot be truly adaptive with the complex architecture,this paper proposes a matched filter module behind the traditional channelization receiver architecture with the technology of FPGA dynamic reconfiguration.For different bandwidth of input signals,a matched filter is constructed and dynamically reconstructed into the overall structure,so as to enhance the sensitivity of the overall receiver structure.At the same time,the correctness and validity of the dynamic reconfigurable technology of the FPGA are verified by simulation,which provides a new solution for the improvement of the digital receiver.