Research On Multi-target Spread Spectrum Ranging System And The Digital Implementation

Spread spectrum ranging measures the distance through the propagation delay ofthe spread spectrum code in the space, which is calculated by the correlativeperformance of spread spectrum code sequence. Spread spectrum ranging withadvantages of high precision, good anti-interference performance and strongadaptability is mainly used in the systems of navigation and positioning, satelliteTracking Telemetering&Command and so on.As the set of spread spectrum ranging code is not completely orthogonal, theintercorrelation of chips will cause interference between users called multiple accessinterference(MAI), which can seriously affect the capacity and performance of theranging system. Multi-user detection (MUD) is a kind of technology used to do jointdetection or subtract interference from the received signal, which can effectivelyeliminate the MAI, and improve the capacity and performance of ranging system.The multi-target spread spectrum ranging system is studied deeply and anall-digital system is realized with FPGA in this thesis. The main contents are asfollows：Firstly, the paper introduced the theory of spread spectrum communication and thebasic principle of spread spectrum ranging. The simulation modules of transmitter andreceiver of spread spectrum ranging system in MATLAB were given, and the feasibilityof the designed system was verified.Secondly, the paper introduced the generation of MAI and analyzed the effect ofMAI in the probability of detection and false alarm probability of the spread spectrumranging system and near-far effect in the multi-targets spread spectrum ranging. It alsointroduced a variety of MUD techniques, simply analyzed the advantages anddisadvantages of them and chose the parallel interference cancellation detector (PIC) asthe realization of the algorithm, which is simple and superior of performance. Then thepaper focused on the improvement of the PIC in the detection probability and falsealarm probability of spread spectrum ranging system, and the performance ofanti-near-far affect. The system simulation platform of the multi-targets spread spectrumranging modem in MATLAB was built and simulation waveforms were given.Finally, various modules of the multi-targets spread spectrum ranging system weredesigned, simulated and implemented in QuartusII environment, including the keymodules such as spread spectrum code generator, raised cosine filter, digital upward frequency conversion (DUC), digital down conversion (DDC), Cascaded integratorcomb filter(CIC), digital matched filter (DMF) and so on, whose simulation waveformswere given. Then the hardware circuit was designed with Protel99, and the program wasdownloaded to the board, the waveform can be observed using the oscilloscope. Theranging waveforms showed that the design of spread spectrum ranging system in thispaper completely met the design requirements and achieved the purpose of ranging.