The Wireless Indoor Positioning System Based On GPS Pseudolite

Global Positioning System (GPS) is famous for its high positioning accuracy and wide positioning range, but the effect depends on the number of satellite traced and its distribution. Therefore, the effect is satisfactory in the way of outdoor positioning. However, when the satellite is blocked, for example indoors, underground and in other places, the GPS receivers cannot work. Pseudolite provides a new way to solve these problems.In this paper, the solution of pseudolite indoor positioning system is come up with. The pseudolite launches the same signal as the GPS navigational satellite, it uses the C/A code to spread the spectrum of navigation message, D codes, realizes BPSK modulation in the L1carrier frequency bands, and launches the L1band signal. It can be used as a satellite indoors, where GPS signal can't be received. Users can implement indoor positioning through existing GPS receivers.In order to meet the need of indoor positioning precision, the system uses the method of double difference carrier phase measurement. Through double difference between the receivers and pseudolites, the errors can be greatly eliminated, such as clock errors, noises and indoor multi-path interference and other factors which impact the precision. In the meantime, how the pseudolites layout affects the positioning accuracy is discussed and the best layout of the four pseudolites is put forward.Baseband part is designed by FPGA, including the functions of clock frequency divider, C/A code generator, D code generator and code combination module. The accuracy and feasibility of the design is verified by simulation and on the development board. To meet the requirements of the following BPSK modulation chip in RF band, the single-ended FPGA output is conversed to differential in the end.The RF part of the system uses the scheme of PLL+BPSK, which simplifies the hardware design. L1carrier is produced by PLL circuit whose control words are written through FPGA. BPSK modulation is completed by a double-balanced mixer. The signal is purified after the band-pass filter and the transmit power is adjusted through an amplifier.The system is simple and low cost. It achieves the demand for indoor positioning.