| With the rapid development of social economy, science and technology, manycountries across the world have built a lot of skyscrapers, ultra-high pressure towersover the river, large bridges, large dams and other tall buildings. These tall buildingsexposed in the air for a long time may occur micro-deformation or micro-displacementbecause of suffering from temperature, humidity, climate and other environmentalfactors. Deformation is allowed below a certain level. But once beyond this range, it islikely to trigger disasters, which would bring immeasurable loss to public safety andeconomy. Therefore, the deformation monitoring of these tall buildings is verynecessary. In order to implement the structural health monitoring of these tall buildings,a novel deformation monitoring system based on pseudolite is studied in this paper. Themain issues are as follows:(1) The working principle and system structure of the deformation monitoringsystem based on pseudolite technology is discussed.The basic principle is as follow: a pseudolite reference base station generates twodifferent frequency spread spectrum signal. One is radiated to the observation stationdirectly. The other one is received, delayed and amplified and then re-transmitted theobservation station by each repeater pseudolite. Observation station receives mixedsignal coming from the reference base station and the other three repearter pseudolites,and then recover the pseudo random code of the reference base station.This pseudorandom code is used to despread the mixed multi-channel spread spectrum signal torecover the carrier signals of the reference base station and other three repeaterpseudolites. The phase difference between the carrier signals can be calculated. We canconstruct one linear equation group to get the three dimensional deformation ofobservation station from these phase difference variations. Characteristics，constructionmethod and its application in deformation monitoring system of m sequence spreadspectrum code is analyzed. The circuit principle diagram of pseudolite reference station,repeater pseudolite and observation station is given. Each module is simulated by theMATLAB tool to verify the correctness of system design.(2) Each module of the system is designed using hardware description language,and simulated by ISE and Modelsim simulation tools.The following modules are designed and implemented: Pseudo satellite reference base station module, repeater pseudolite module, pseudo code synchronization modulein observation, phase discriminator module and so on. Among them, PN codeacquisition circuit is implemented using sliding correlation method, and the pseudorandom code tracking is implemented using non-coherent delay locked loop. Thesimulation waveform of each module has verified the correctness of system design, andit is indicated that the design can be implemented in FPGA chips.This paper studies a deformation monitoring system and method based onpseudolite, and the system simulation is accomplished. This paper makes a usefulexploration to develop novel micro-deformation monitoring instrument. |
