Wednesday, August 19, 2015

Session 5 Paper 2: SpotFi: Decimeter Level Localization Using WiFi

Authors: Manikanta Kotaru (Stanford), Kiran Joshi (Stanford), Dinesh Bharadia (Stanford), Sachin Katti (Stanford)

Presenter: Manikanta Kotaru

Link to the paper
Link to the public review

This talk presents the design and implementation of an indoor WiFi localization system - SpotFi. The presenter first illustrates several indoor applications that can benefit from accurate indoor localization. A good solution should consider both the deployment, universal, and accuracy. The key idea of this paper is also to exploit the angle-of-arrival (AoA) of signals, together with the time-of-flight signals. Compared to other existing works on indoor WiFi localization, this work does not need to modify the AP firmware. SpotFi only needs information that is already exposed by commodity WiFi devices.

As presented in the talk, this work has two major contributions:

1) Different from previous work that needs half dozen antennas at the AP, SpotFi is able to compute the angle of arrival of multipath signals accurately with only three antennas. This will be very useful in practice because most of the existing APs in use by people only have three or less antennas.

2)  Furthermore, advanced estimation and filtering techniques are adopted to identify the angle-of-arrival of the path between AP and targeted object. Existing works only consider the angle-of-arrival. The technique proposed in this paper also consider the time-of-flight. The analytical model includes both signals at the antenna as well as signals from different subcarrier, to compensate the few antennas it uses.

The proposed SpotFi has been implemented using the off-the-shelf Intel 5300 WiFi NICs. Experiments are carried out in 55 different positions of a building. Experimental results show that with only three antennas at the AP, the SpotFi can achieve median localization error of 0.4 m, which is similar to those famous existing work ArrayTrack  and Ubicarse.

Q: The median localization error is 0.5m, and the maximal is up to 5m. Is this practical?
A: Yes, the median value is 0.4m. About 80% of the localization error is below 1.5m.

Q: It is a nice work. Have you considered the impact of light of sight? In reality, the target object can move and may stay in an environment of dense APs. Can you comment on this?
A: The system can still work in dense layout of APs.
Q: The localization is in a passive way and may cause privacy problems to the targeted devices.
A: We can allow users to decide. Users can enable/disable to use this technique.