Wi-Fi based Indoor Positioning System--GROUP-11

Indoor Positioning System Using Wi-Fi

Abstract 

Positioning is the most attractive Technology today. Various technologies are used nowadays for positioning purposes. GPS is the most commonly used positioning technology, but it is strictly restricted only for outdoor environment, Non-suitability of GPS in an indoor environment is because of its NO LINE OF SIGHT conditions and signal attenuation has to lead to several other techniques of indoor positioning. The document below compares a few of the efficient and reliable indoor positioning methods and proposes an indoor positioning system using the trilateration method.

Introduction 

Positioning finds its applications in locating a person in an area, helping the user navigate, etc.GPS positioning system requires a line of sight and hence it is not suitable for indoor positioning The primary motive of this project is to develop a general understanding of indoor positioning systems. Various technologies and methodologies have been used in indoor positioning systems based on cellular signals. In this project, we tried establishing an indoor positioning system using the trilateration method which uses RSS data from WIFI access points to do localization in an indoor environment. For this project, we have referred to various academic journals and online webpages. Few of them includes - 

1)https://behrtech.com/blog/large-scale-indoor-localization/ 

2)https://www.talentica.com/assets/white-papers/wifi-indoor-positioning-using-smartphones.pdf  
3)https://www.favendo.com/wayfinding/indoor-positioning-is-everything

Indoor Positioning Systems

Indoor Positioning has always been the topic of interest in wireless technologies. These systems employ a wide range of different technologies; these Systems could use any combination of the following :

• Ultra-wideband (UWB)
• Infrared
• Radiofrequency identification (RFID)
• Inertial sensors, magnetic sensors, etc.
• Sound (ultra-sound or audible)
• Wi-Fi
• Camera

The first five positioning systems in the above listings can locate users with very high accuracies, however, these systems require installation of different hardware systems and hence they lead to a high budget and labor cost, preventing them from having large-scale deployments. And hence for a low budget system Wi-Fi is used.

Wi-fi Indoor Positioning System 

These are the few terms we need to understand about Wi-Fi Positioning techniques 

• Access points ( AP’s )

• It is a networking device that allows a Wi-Fi enabled device to connect to a wired network, For e.g, Wi-Fi routers      

• Received Signal Strength ( RSS )

• It is a measurement of how well your device is connected to an access point or router.

• Wireless Local Area Network ( WLAN )

• It is a wireless Computer network that links two or more devices using wireless communication within a limited area such as a home, school, or office building 

Our Indoor Positioning system consists of three components :

• Client device
• At least 3 wifi access points (AP’s)
• Server

Methodology 
The client device is capable of wifi access and receiving wifi signals from all access points in the vicinity. The key purpose of the client is to record the wifi signals strength data i.e RSS
And the network of wifi access points acts as a communication channel between client and server.
The main task of the server is positioning and navigation system. An android application is used to scan the wifi AP's in the vicinity and collects data like signal strength from respective AP's. The android device then sends this RSS data to the server.
The server then runs the positioning algorithms and calculates the location coordinates of the user.

The server runs two types of algorithms:
            a)Distance calculation from AP
            b)Tri-Lateration Algorithm
The server then sends the calculated location co-ordinates back to the client device. Android has the front-end application showing the indoor map and the location co-ordinates calculated by the server are shown in the indoor map as user position.


Trilateration Algorithm


The trilateration algorithm calculates the exact location of the user given the exact location of access points and distances from each access points to the user. This algorithm requires a minimum of 3 wifi AP's in indoor to calculate location coordinates.

RSS values from these AP's are used to calculate the spatial distances and are used as radii of circles i.e d1,d2,d3. The point of intersection of these three circles is the position of the receiver.
Now, knowing d1,d2,d3 and center coordinates of access points location is calculated using the following set of equations.

These set linear sets of simultaneous equations can be easily solved using matrices and the system gives the unique solution (x,y,z) which is the required position of the user in an indoor environment.



Future work
The future scope of the system lies there in the efficient indoor navigation system which can be used in many places.
Accuracy in positioning can be improved using the Fingerprinting method.

FINGERPRINT METHOD

The main advantage of this method compared to trilateration is that this method results in higher accuracy and gives continuous positioning and even environmental effects are considered in the calibration phase of this method

This method points with a certain minimum distance between them is spread over the indoor environment and they possess a unique set of RSS readings from AP's and it is the fingerprint for the location. And then distances from these fingerprints to the user are calculated and using the trilateration method the location is calculated.

In this method, the Machine Learning Algorithm like Nearest Neighbour (NN) Algorithm is used for minimum distance calculation from the fingerprints or the reference points.

Summary

On the above page, we got to know the difference between GPS based positioning and wi-fi based positioning, we also discussed indoor positioning technology; including the process of Wi-Fi trilateration technology. We also summarised a few terms related to wireless networks. The above page also suggests work related to the Fingerprint method for indoor positioning using Wi-Fi. Hence from all the above discussions from the page, we can also conclude about indoor positioning systems that the complex nature of the indoor environment could be a big hurdle for doing positioning in indoor systems. Obstacles like walls, glass, metal objects, moving objects need to be handled and assessed very carefully while using the Wi-Fi positioning system.

The End