| In passive radar systerms,in order to improve detection performance,the method of direct wave reconstruction is often used.LTE uplink signal processing uses SC-FDMA,and the downlink signal processing uses OFDMA.As the passive radar only uses the downlink waveform,so to reconstruct the high-quality direct wave signal,the things we only need to do is that,demodulating and decoding in accordance with the mode of the mobile station to receive downlink channel signals firstly,and then coding and modulating in accordance with the mode of the base station to send the downlink signals.The contents of this paper include the receiving and transmitting of downlink.The receiving portion comprises: 1)downlink signal receiving,down-conversion,ADC sampling,getting the complex baseband signals;2)Synchronization signal detection;3)frequency offset estimation and correction;4)OFDM demodulation,Channel estimation and equalization,receiving the channel of PBCH to get the system antenna configurations,bandwidth,and other information;5)receiving the channel of PCFICH to obtain the configuration information of the PDCCH;6)receiving the channel of PDCCH to obtain the configuration information of PDSCH;7)resolve the configuration information of the PDSCH,according to this to demodulate and decode the information of the channel of PDSCH to obtain the user data.The transmitting portion comprises the following things.User data channel coding again,scrambling,digital modulation,layer mapping,pre-coding,resource mapping,generating the OFDM symbol,so we can get the high-quality reconstructed baseband signal.In the simulation and verification,I got the LTE downlink signals from the signal generator,then obtained the digital baseband signal by downconversion and sampling through the receiving circuit board,and completed the downlink receive-transmit reconstruction process of the baseband signals In MATLAB,finally verified the reconstruction method of the passive radar high quality reference signals. |
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