Indoor Positioning System Through Wifi Signal Strength

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A typical infrared based positioning system is the Olivetti Active Badge System: A badge worn by a person emits a unique infrared signal every 10 seconds. Sensors that are placed at known positions receive the unique infrared identifiers and relay them to the locating software [WHF+92]. Other infrared based system are Xerox ParcTab [WSA+96] and Cyberguide project [AAH+97].

2.2.2 Radio Frequency (RF) Based

3D-iD system from Pinpoint [WL98] is a radio frequency based positioning system: Antennas, which are placed around a facility, emit radio signals at 2.4GHz. Tags worn by persons or mobile devices transmit response signals at 5.8GHz with an identifier code. Antennas receive the signals and send the result to cell controllers, which triangulate the reflections and determine the locations of the tags. The Personal Shopping Assistant of AT&T [AGK94] and Pinger near-field tagging system of HP [HNR97] are also radio frequency based systems.

2.2.3 Ultrasonic and Other

Bat System at AT&T Laboratories Cambridge [HHS+99] and the Cricket location-support system [PCB00] from MIT Laboratory make use of Ultrasonic technology.

2.2.4 Signal Footprint

Signal footprint positioning technology, shown in Figure 6, has gained much attention at indoor positioning recently, because it utilizes the existing wireless infrastructure and needs no extra specialized hardware. The research has shown that it could provide acceptable accuracy in indoor positioning with proper algorithms.


Location determination is considered as vital element for producing valuable and inventive location base services. Such services not only increase the network performance but also efficiently improve the user experience. One such system that provides location awareness is Global Positioning System (GPS).The problem with GPS is that it only works outdoors not indoors, and even in outdoors it gives an accuracy of about 20 meters. Therefore, there is a need of a system which can work indoors to provide Location Based Services (LBS).

Out of many Indoor Positioning Systems currently deployed, one such system is WIFI based Indoor Positioning System. It uses the Received Signal Strength Information (RSSI) of WIFI signals from the neighbouring Access Points (APs), to locate a user device inside the building.

Finger Print approach is used to determine user device location. WIFI environment was chosen because of increase in development, ease of use and low cost in deployment of Wireless LAN technology.



Cellular network infrastructure provided the background for the evolution of positioning systems [3]. The enhancement in mobile computing and wireless networking have enabled users to move freely inside an indoor wireless network environment .Location of a user inside this environment will not only help in the management of Networks e.g resource management, load balancing, network planning etc , but will help in providing Location Based Services [2].

All these applications are only possible if the user device is accurately located.

Location Based Services:

Indoor Positioning System can be used for variety of services .Some of the Key Applications are:

Network management and security:

Wireless LAN based Indoor Positioning System can enhance management of networks e.g resource management, assets tracking and load balancing etc.

If a user device location is known then we can enforce location base authentication and authorization [3].such systems are already available in commercial market [5][3].


It is a term derived from Ubiquitous Computing. Context-Awareness systems can change environment based on a certain information such as location .Wireless LAN base Indoor Positioning System can locate a user device

Problem Description and Motivation:

Motivation for the project came from the useful applications as described above. GPS networks best works outdoors but suffer the limitation of indoor tracking because its signals are weak enough to penetrate the walls. The other problem is that it cannot identify a device location based on floor in a building. Therefore a need for Indoor Positioning System was needed.

There are many techniques and systems through which we can deploy Indoor Positioning System, will discuss later. But the optimal reason for choosing Wireless LAn was the low cost, Less Processing and easily availability of WIFI Access Points. No additional hardware is required for implementing Indoor Positioning System based on Wireless LAN.

The goal here is to implement Wireless LAN in Glasgow Caledonian University (GCU) building and check the feasibility of WIFI signals as the mean for locating user device.

Current status and Developments of Research or Technology:

An overview of the current wireless positioning systems with related work is discussed below.

Global Positioning System (GPS):

Global Positioning System provides location awareness in outdoor environment. It is used for many military and commercial applications. It uses triangulation technique to track a receiver. So it requires having at least four satellites with clear line of sight to calculate the distances to GPRS receiver.

In case of obstructed path such as buildings, trees etc the GPRS receiver won't be able to maintain clear line of sight with the satellites, which can make significant impact on its performance.

Location determination is very essential in mobile computing. The wide range of context-aware applications has inspired researchers to design and implement location aware systems specifically in the area where Global Positioning System don't work, Such as indoors and path where there is no clear line of sight [6].

2.2 Indoor Positioning Technologies:

2.2.1 Infra Red ( Indoor positioning System):

Infrared based systems works on the principle that each user device emits a proprietary infrared beacons, which is directed by the receiver and pass it to the locating software. These infrared beacons are unique codes for specific devices. But the problem with it is that infrared signals requires line of sight and does not penetrate through opaque objects such as walls. Therefore a number of receivers are required to efficiently implement this system indoors.

The advantage is that it won't interfere with other frequencies. The disadvantage here is the cost and complexity of implementation. As many Infrared reader is required, especially around the corners of the building and if the asset itself is blocking the line of sight to the Infrared reader.

Systems that based on Infrared are Xerox Parc Tab[4] and Olivetti Active Badge System [7].

2.2.2 Radio Frequency (RFID) Identification:

To implement RFID,RFID scanners are installed inside the building. These scanners actively detect active and passive tags that are attached to the objects (user device to be detected). These transceivers (tags) are identified based on its unique electronic code. The difference between the two is that active tag uses batteries and can be identified by a scanner from a maximum of 20 feet , while positive tag receive power from the RFID scanner and it has to be in close proximity of RFID scanner.

The disadvantage here is again the cost and complexity of implementation and it interference with other wireless technologies, such as WIFI. So if a client wants to implement wireless technology to be implemented in the facility, then the performance of RFID base location determination can be degraded.

One of the system that is based in RFID is 3D-ID from PinPoint [8]. Scanners are installed around the facility which transmit signals of 2.4 GHZ. Active or passive tags that are attached to devices emit signals 5.8 GHZ. Each active tag is identified by unique electronic code, RFID detects it and send it to centralized station. Where all the tag information is stored. Another system that RFID base system is Personal Shopping Assistant by AT&T [9].

2.2.3: Location based on UltraSonic

Location determination based on Ultrasonic are used by BAT System at AT&T laboratories Cambridge [10].

2.2.4 Sensor Fusion:

As indoor environment is very complex in nature. It is very difficult to implement a single system solution for location awareness applications. One such solution is to use Sensor Fusion to improve accuracy of user device location.

Sensor Fusion is define as "The process of combining multiple and independent observations to obtain improved accuracy and robustness".[11][12]

[11] proposes an algorithm for fusion. It is explained in the figure below.

Sensor fusion, source [11]

2.2.5 Finger Print Approch:

There are many techniques to implement indoor positioning system using Wireless LAN. Such as Baysen method , Triangulation and finger Print approach. Finger Print approach uses the existing Wireless LAN infrastructure to find the location of a device.

Project Aim:

The main aim of the project is to implement indoor positioning system inside GCU building. Investigate and evaluate the feasibility of WIFI signals as a mean for location determination.

Project objectives:

Objectives that are setup in achieving this aim;

To study the literature review for understanding the WIFI positioning system in location determination based on WIFI signal strength and Java as a simulation software.

To study the indoor propagation environment and the effect of environment on radio wave propagation.

To create a test bed for the implementation in one of the floor in GCU building with at least four rooms.

To design and implement the software, which will be used in location determination of user device.

To check the feasibility of WIFI signals as a mean of locating user device by determining the level of acceptable accuracy and validate it with known results.

Try to improve the accuracy of system, if possible using extra hardware or through location determination algorithms.

Expected Outcomes/Deliverables:

The following outcomes are expected at the end of achieving the above objectives.

Understanding the creditability of WIFI signal strength as a mean of location determination.

Understanding Java (J2ME) software tool.

Practical implementation of the system and its limitations.

Critical analysis on the accuracy of the system.

Comprehensive and structured documentation of the work done.

The Project Method:

WLAN (Wireless Local Area Network):"Using radio frequency (RF) technology, WLAN transmit and receive data over the air, minimizing the need for wired connections. Thus, wireless combine data connectivity with user mobility. WLAN's are essential networks that allow the transmission of data and the ability to share resources, such as printers without the need to physically connect each node, or computer wit wires. Wireless LAN offer the productivity, convenience and cost advantages over traditional wired networks. "[13]

The method to be employed by the project:

Wireless LAN location determination can be define as "The process of locating mobile network devices , such as laptops or personal digital assistants, using a wireless local area network (WLAN) infrastructure. Positioning is carried out by exploiting the dependency between the location of a mobile device (MD) and characteristics of signals transmitted between the MD and a set of WLAN Access Points (AP's).These characteristics are generally the Time Of Arrival (ToA), Time Difference of Arrival (TDoA) Angle of Arrival (AoA) and Receive Signal Strength (RSS) is the feature of choice in WLAN positioning systems as it can be obtained directly from Network Interface Card (NIC) that are available on most handheld computers. This allow the implementation of positioning algorithms on top of existing WLAN infrastructures without the need for any additional hardware".[3]

When a user with wireless LAN device driver enter an area occupied by Access Points, it receive beacon messages, which is broadcasted by all the Access Points in that area. These beacons messages helps the client to select the best Access Point in that area. This process is also called Passive scanning. Best Access Point means which have the better Signal to Noise Ratio (SNR) compare to other Access Points. These also helps in handsoff. In Active scanning phase the WLAN driver sends out probe request to all Access Point's in that area. The Access Point's respond with probe response frame. Mac-address of all the Access Point's are advertised in the beacon and probe response frame . The signal strength from each Access Point can be calculated through the service provided by WLAN-MAC Layer .[15] In this way Signal Strength (SS) from all the Access Point's is calculated with respect to the current position. It is the key parameter on which location determination calculation is based upon [14]

Offline Phase (Data Calculation):

WLAN positioning system consists of two phases. Online and Offline phase. In Offline phase ,the Signal Strength Received Indicator (RSSI) from all visible Access Point's is obtained on specific locations inside the building. The location are also called calibration points. A Radio Map of the building is composed based on these calibration points. The process of collecting RSSI on all the calibration points is called fingerprinting.[14][1]

As Signal Strength degrades because of opaque objects such as walls, furniture and even user blocking the line of sight between Access Point and WLAN device driver. The difference between a user blocking line of sight and non blocking is reported as 5db[14][1]

Online Phase:

In the online phase a user scan the Area for Active Access Point's and measure the RSSI. This real time Signal Strength(SS) Finger Print is then compared with the Radio Map Finger Print already obtained in Offline Phase, using positioning algorithm. In the last step the user device location is estimated, based on the known location from Radio Map entries [2][1]

Positioning Process Overview, source [2]

Project Method Illustration, Validation and Evaluation:

A real world scenario will be implemented by using Access Point's. The whole project will be implemented using Java (J2ME). This projected will be physically implemented inside GCU Building. The main focus will be a single floor with around four rooms due to time restraints. This setup will require two or three Access Point's located in a fix position.

As discussed earlier for receiving the signal strength (RSSI) from the Access Point's, a software will be written using J2ME. The software will consist of

User Interface

Offline And Online data Collection

Radio Map (Signal Strength Database)

Positioning Algorithm

User interface will help the users to operate the software. First of all, Offline Data will be collected on various locations of floor and rooms and will be store in the Database. In Online Phase, when a user collects Signal Strength (SS) from the Access Point's in real time, will be store in the Database. User device will be located by applying Positioning Algorithm on the Offline and Online data collected.

The results obtained can be validated with the previous work done in this area .[1] The main focus will be on the accuracy of this system based on the WIFI Signal Strength and can its accuracy be further improved.

5. Project Plan:

5.1 Project Schedule

The following schedule will be followed throughout the course of project. Contains all the phases of project planning, development, implementation, validation, analysis and reporting in 12 week period.

Research Phase:

1.1) Meeting with supervisor

1.2) Research and comprehensive study of Indoor positioning System using WFI Signal Strength.

1.3) Study and understanding of JAVA (J2ME).

1.4) 2nd meeting with project supervisor, discussion about the test bed setup for the implantation.

Implementation Phase:

2.1) Designing the software for Indoor Positioning system.

2.2) Implementing the design in software (JAVA, J2ME)

2.3) Setting up test bed for the implementation of the system, placing Access Point's in fixed locations.

2.4) Offline data gathering for building Radio Map.

2.5) Online data gathering, analysis.

2.6) Interim report.

2.7) Third meeting with project supervisor - discussion of simulation results.

3 Documentation Phase:

3.1) Documentation of the project.

3.2) Final meeting with supervisor , discussion of Thesis documents.

3.3) Compilation of the Project documents.

3.4) Submission of draft project report to supervisor for review.

3.5) Presentation and submission dissertation report.

5.2 Resource requirements:

Resources required for Research;

Unlimited access to GCU library.

Access to internet

Access to online resources such as Athens and IEEE Xplore.

Hardware resources required are;

A laptop with window 7 operating system installed.

Microsoft Office Suite along with Microsoft Office project.

Two to Three Access Point's (CISCO preferred)

5.3 Risk Management:

Limited Time:

Completion of the project in 12 weeks poses a lower risk. But its consequences can be vital. This risk can be mitigated by project management techniques, and a week is reserved in the project schedule on the occurrence of such risk.

Development of Software using Java:

Less experience in Java can cause medium level risk. This is due to the limited knowledge about the software and may result in not developing the required software in time. So a lot of time is reserved for extensive study of tutorials and related documents to overcome this risk.

Loss of Data:

The unpredictable nature of software and hardware may cause loss of data. Although the occurrence of this risk is low but can be very daunting if this happens. This can be avoided by creating multiple backups of the data and excessive documentation.

5.4 Ethical Issues:

Separate test bed environment will be setup for the implementation of the project with separate Access Points, rather than using GCU Access Points. So no ethical approval is required.