Indoor Positioning System Based on Global Positioning System Signals with Down- and Up-Converters in 433 MHz ISM Band

Area of Science:

• Electrical Engineering
• Navigation Systems
• Signal Processing

Background:

• Global Navigation Satellite Systems (GNSS) like GPS are restricted indoors.
• Existing indoor positioning systems often lack accuracy or are complex.
• Repurposing GPS signals for indoor use presents a viable alternative.

Purpose of the Study:

• To propose and demonstrate an indoor positioning system utilizing repurposed GPS signals.
• To evaluate the system's performance under both line-of-sight (LOS) and non-line-of-sight (NLOS) conditions.
• To achieve sub-meter accuracy for indoor location estimation.

Main Methods:

• Utilized down-converting (DC) repeaters to shift outdoor GPS L1 signals (1575.42 MHz) to the 433 MHz Industrial Scientific Medical (ISM) band.
• Employed an up-converting (UC) receiver to shift 433 MHz signals back to L1 for an off-the-shelf GPS receiver.
• Integrated an attenuator in repeaters to equalize signal transmission and prevent jamming, with data processed via Wi-Fi.

Main Results:

• Achieved sub-meter accuracy for indoor positioning under both LOS and NLOS conditions.
• Demonstrated average position errors of 54 cm (LOS) and 98 cm (NLOS).
• Reported a 50% circular error probable (CEP) radius of 3.3 m (LOS) and 4 m (NLOS).

Conclusions:

• The proposed GPS-based indoor positioning system offers a practical solution for accurate indoor navigation.
• The DC/UC repeater architecture effectively overcomes GNSS indoor limitations and signal path loss.
• The system demonstrates robust performance, providing reliable sub-meter positioning in diverse indoor environments.