A test-bed implementation of an acquisition system for indoor positioning

Indoor GNSS signals are typically received with poor signal-to-noise ratio, which impairs the acquisition stage of common global positioning system (GPS) receivers. Extending the coherent integration time increases the acquisition sensitivity, but the data-bit-rate limits the maximum achievable performance. Non-coherent processing also improves the detection performance, but indoor signals require a large amount of accumulations resulting in significant squaring loss. Moreover, both strategies have high computational complexity which fixes demanding requirements for stand alone mass-market terminals operating in real time. A sensitivity-complexity trade-off is therefore mandatory. Assisted-GPS, which is included in 3GPP specifications, reduces the overall acquisition complexity and enhances sensitivity. In this paper we describe a low-complexity-assisted data-wipe-off technique that enables the high-sensitivity acquisition of GPS signals. The method is based on the acquisition of the strongest signal in order to obtain information that eases the acquisition of the weaker ones. The analysis also addresses sources of sensitivity loss, such as Doppler effects and local oscillator inaccuracies. A test campaign with real signals and integration times up to 2 s validates the method, demonstrating the effectiveness of the proposed technique in indoor environments.