This document gives a short overview to indoor positioning systems (IPS). IPSs are under development in order to localize targets inside buildings, where it is not possible to use Global Positioning System (GPS). Techniques and used methods for indoor localization are discussed.
This work focused on antenna array receivers, which is a promising way for reliable indoor positioning systems. The proposed technology was Wireless LAN, therefore WLAN synchronization methods have been studied. Discussion has been made for the switching receiver timing synchronization. This technique can be a key idea to decrease the number of used receivers in the hardware. Small amount of receivers cause reduction of needed power, storage place and weight. It allows the indoor positioning system to be implemented in handheld devices, such as smart phones and tablets.
Then two algorithms for the switching receiver timing synchronization have been developed and have been evaluated using MATLAB software. The first algorithm uses simple synchronization technique, while the second one advances in the adjustment of the switching timings. Therefore the simpler algorithm is beneficial in systems, where lower hardware complexity has high priority. The advanced algorithm requires more complex hardware than the simpler one. However, it is more tolerant to errors, such as carrier frequency offset and wrong measurement of the frame start. SIMULINK models have been made to visualize the critical parts of the algorithm and to make the realization easier. The main goal of this work was to implement those algorithms in VHDL and to test it in an FPGA board. It has been achieved and both algorithms were working in a real-time environment. The proofs of the working hardware were measurements of WLAN signals received from different antennas.