Theoretical and Experimental Analysis of WiFi Location Fingerprint Sampling Period

Indoor positioning with smartphones is of great importance for a lot of applications and has attracted many researchers' interests these years. Received Signal Strength (RSS) fingerprinting has been considered as an efficient method for indoor positioning. Numerous systems have been developed based on it. Location fingerprint sampling is the first step of the RSS fingerprinting method. Slow sampling speed will delay the positioning speed and will reduce the accuracy if the tracking object is moving. Theoretically, the sampling period is about one fingerprint per second. However, our experiments on some Android phones/pads show that it may even take more than 10s to sample a fingerprint occasionally. By analyzing the Android WiFi scanning framework, it is easy to find which part of the fingerprint sampling process costs more time. After theoretically analysis and experimental measurement, we provide some suggestions on how to improve sampling speed on some practical WiFi positioning system architectures. To contribute to the research community of WiFi positioning, we make all our measurement codes and our data sets available as open source.