Time-Division Micro Deformation Telemetry For Multi-Target And Its FPGA-based Implementation

With the development of technology and the growing requirements of people, there are more and more large-scale buildings such as long-span bridges, dams and high-rise flats appearing in our lives. However, because of the factors like building material aging, disastrous weather and accidents, most buildings have potential problems which are directly related to safety of people’s life and property. As a result, it is important to monitor the micro deformation of these buildings in real time.Firstly, the existing deformation monitoring technologies are analysed and compared. A brief introduction on the micro deformation measuring method based on spreading spectrum technology and carrier phase discrimination is given. The structure of circuits and operating principle are also illustrated by block diagram and schematic diagram.Secondly, time-division telemetry is proposed to overcome the multiple access interference in the system of micro deformation monitoring mentioned above. The reference antenna transmits the wireless reference signal continuously, while the other antennas at each observation point share the same beacon transmitter circuit and transmit the wireless telemetry signals at different time divisions. So there are only two signals arrive at the receiver simultaneously. The displacement of each observation point is measured in turn by calculating the relative phase difference between the reference and telemetry signals. The advantage of time-division technology is reducing the number of PN-codes required, which contributes to the decreased multiple access interference, simplified PN-code generating circuit and saving of expense. The key of time-division deformation monitoring is the technology of obtaining timing information, which is critical to determine which observation point the spread spectrum signal comes from. This paper presents three implementations of time-division telemetry, and analyses the advantages and disadvantages of each implementation.Based on the principle of Time-Division Micro Deformation Monitoring for Multi-Target, the circuits of beacon transmitter and receiver are designed in FPGA chip, which include PN-code generator, modulator and demodulator of switch and logical signals, spreading and de-spreading modules, PN-code synchronizer, carrier separator and phase detector, etc. The circuits are simulated by ISE and Modelsim, and the result shows the validity of time-division telemetry and establishes the foundation for its practical application.