A low-cost displacement monitoring system with sub-millimeter resolution based on software-defined radio platform

In this paper, a displacement monitoring system is developed for regional high-precision monitoring tasks. This system locates the positions of target points by using hyperbolic positioning principle, and monitors displacements by continuously locating. To form the hyperbolas, the system works as a microwave interferometer to solve the phase difference of arrival. Composed by software defined radio platforms, the configuration of this system can be easily set and adjusted. Experiments performed under a prototype system shows a measuring error within ±0.2mm at a monitoring coverage of 5m when carrier frequency is configured at 433MHz, which shows a relative uncertainty about 0.03% when normalizing to wavelength. By applying simplified beacons, average cost for each test point can be minimized. More works are done to compensate phase drift in microwave cables used. This system has great applications in regional high-precision monitoring and positioning tasks, especially when test points are required in large scale.