Demystifying Xiaomi Note2's powerful positioning system, SAP assisted positioning tunnel is not afraid

For the majority of riders, many people like to use mobile phones to do navigation software. At this time, GPS is very important. However, in real life, we often hear friends around us spit out: "How is this navigation so bad, and put me "There is no signal." "Well, there is no road ahead, what should I do?"

The recently released Xiaomi Note 2 has a "black technology" in this regard - SAP assisted positioning. Positioning can be achieved even when there is no satellite signal or tunneling.

So what is the difference between GPS and SAP, and how does SAP achieve signalless positioning? The Xiaomi company technical team conducted a science popularization for us in the official forum:

When we use satellite positioning in the city, the mobile phone can't receive the satellite signal because of the blockage of buildings, trees and viaducts. Sometimes the signal is reflected and reaches the mobile phone. These reflected signals are what we usually call "multiple." Path effect." The inability to receive satellite signals and multipath effects has caused drift in the location of satellite-based mobile phones in urban environments, and sometimes cannot be located.

Since the release of Xiaomi Note 2, everyone has been hotly discussing "what is SAP-assisted positioning?" I have read the introduction of the forum rice noodle and Zhihu users to "SAP assisted positioning", it is not very accurate. Which one is the truth?

For everyone, the two terms "SAP" and "PDR". The full name of "SAP" is "Sensor Assisted PosiTIoning", which means sensor-assisted positioning. The full name of "PDR" is "Pedestrian Dead Reckoning", which means intelligent walking trajectory tracking. Xiaomi Note 2 has both SAP and PDR built in.

Both SAP and PDR built into Xiaomi Note 2 use gyroscopes, accelerometers and geomagnetic sensors in mobile phones to improve positioning performance in urban environments. Gyroscopes and accelerometers are often referred to as inertial devices. The accelerometer can obtain the speed and displacement information of the terminal by integrating, and the gyroscope can sense the rotation angle of the terminal.

This information can be obtained by complicated operations. This technique is also commonly referred to as inertial navigation. The advantage of inertial navigation is that it can navigate autonomously and is free from outside interference. All aircraft, spacecraft and large ships are equipped with inertial navigation systems.

The SAP and PDR functions of Xiaomi Note 2 can be combined with satellite and inertial navigation, which is a combined navigation technology. It will operate according to the current satellite signal quality and inertial navigation error intelligence, so that it can have very accurate position output in various environments, thus ensuring a stable GPS signal when using the mobile phone.