Device-free indoor localisation using radio tomography imaging in 800/900 MHz band

Radio tomographic imaging (RTI) can be used as a method for device free localisation of persons in rooms. By measuring the signal strength of all links of a network of sensor nodes, one can estimate the position of an attenuating object with reasonable precision. The sub-GHz is shown to be suitable for an implementation. Such a design is more energy efficient than a 2.4 GHz implementation. We adapt, evaluate, and improve the device-free localization method of Wilson and Patwari to indoor environments using the 800/900 MHz band. The advantage of using 800/900 MHz is reduced reflections compared to 2.4 GHz. At the same time, the signal is attenuated less by objects in its path. Thus, the methods of Wilson and Patwari needed to be refined and parameters needed to be adapted. We evaluate some combinations of the most common choices of norms to perform a Tikhonov regularisation. The first difference gradient operator with H1 norm works best. We equipped a 5 m×5 m room with 20 wireless sensor nodes. We evaluated the influence of the distance to walls and the height of nodes. The radio tomographic image are post-processed by filters to make likely positions of objects more apparent. Additional parameters values suggested by Wilson and Patwari could not be used for the new frequency and hardware. For example, the ellipse excess path length has been experimentally determined to be close to 20 cm instead of 2 cm. In our experiments-up, we achieve an a maximum average localisation error below of 78 cm. With this work, we have reproduced the results of Wilson and Patwari, adapted it to a different frequency in the 800/900 MHz band and developed improvements to the original algorithms.