INTRODUCTION:

MOBILE TECHNOLOGY

The whole cellular communication is divided into various zones having their own base station (BS).Each BS related zone is referred to as "cell”. The frequency range assigned to each BS varies from 450-950 MHz’s There could be BSs that Operating at same frequency but it is seen that they are not adjacent to each other if they are adjacent it would result in interference. All BSs are controlled and monitored by MTSO so that subscriber could keep on his call while moving between cells. Emergency based calls in case of fire, or patient needs first aid there is a need to locate the position in a particular cell called as "location based services”. The main two functions of mobile technology are call fixing and hands-off process. Whenever a call is made request for call is accepted by BS and sent to BSC and MTSO. Then MTSO searches for cell where the call has to be forwarded and fixes the call to particular subscriber. Whenever the user movement occurs between the cells MTSO will change the frequency allocated to it and assigns the frequency of new BS. For these functions to be operated we need GEOLOCATION of mobile.

Figure: Architectural setup of mobile communication

As shown in Figure, the mobile telecommunication network includes a several base stations (BSs) B 1 to B N for providing mobile telecommunication service to a mobile subscriber through a mobile telephone M1, a base station controller (BSC) for controlling the BSs B 1 to B N, and a mobile telephone switching office (MTSO) for connecting the BSC to another BTS or a PSTN (Public Switched Telephone Network).

DISTANCE CALCULATION:

The service provider often maintains the log history of all the mobiles in particular cellular area so that they can be used for handshaking. So when a particular mobile needs to be tracked we are going to emit a signal in a cellular area where a particular mobile is present so based on the time taken by the signal transmission and acknowledgement the distance between the mobile from a base station is calculated

MATHEMATICAL EXPRESSION:

When RF signal is emitted by the base station the mobile (receiver) receives it and sends back the acknowledgement

The total distance travelled will be 2d where d is distance between base station and receiver.

The speed of radio signal is speed of light (3*10^8) m/s

Applying in formula

Distance=speed*time

2d=s*t

d=(s*t)/2

Where t=time taken for both receiving and acknowledgement, s=speed of RF signal

Based on this expression we are going to find out the distance between transmitter and receiver but we will be left with a numerous points with the same distance .so the methods to be referred are often used to restrict the position of receiver to a single point.

DISTANCE ANALYSIS THROUGH OPERATOR TIME:

Whenever there is need for position tracking of handset signal is transmitted along with the time at which it is generated, so a network time will record the time at which the signal is received depending upon the sending and receiving time the distance is calculated, a standard time is used in order to record the time difference which results in determining the distance between the handset and substation. IN the same way substation evaluates the distance between base station and handset.

Mathematical expression:

Distance=speed*time

Where time is the time difference between the sending and receiving time based on the standard reference time.

Time=time at which it is received-time at which it is transmitted.

METHODS FOR TRACKING

1) SIMPLE GEOMETRIC LOCATION TRACKING

Based upon the distance calculated from both the base stations (t1,t2) to the point(m1) two circles c1,c2 are drawn taking t1 and t2 as centres and distance calculated as the radius , these circles intersect at two points(m1,m2) restricting the position of points to two.

So together with this we are going to calculate the angle of arrival by taking a reference line this in turn will reduce the position of the mobile to one point.

Even though AOA calculation is affected by various external points it results in good results. AS we only need a minute variation with horizontal reference line.

If point is on the line connecting centres we will get only one point.

2) LOCATION TRACKING THROUGH FAMILY OF CIRCLES

Figure 2. Determines how position is found

Whenever a request for location is sent to mobile station it actually checks the distance between the sender and receiver by distance calculated method after that depending on the distance it forms a circle with radius for bs1 so there will be so many points possible With the distance calculated then it is in turn minimized to two points by forming another circle with radius as the distance calculated from the adjacent base station bs2 .These two points in turn formed is minimized to one point by fallowing the same process by another base station adjacent two it.

The process is demonstrated with diagrams as:

Step-1 Imaginary circle is drawn

Figure 2.1

Step-2

Points minimized to two by forming another imaginary circle with adjacent base station (m1 position of mobile)

Figure 2.2

Step-3

The point is in turn minimised to one by another adjacent base station the intersection of three imaginary circles forms the position of mobile which is m1.

Figure 2.3

3) NATURE OF TRANSMITTED WAVE

Figure 3. Communication setup

In this method we are going to determine the position based on the parabolic structure of received wave.

Two methods to determine the position

a) Determining the edges of received wave.

b) Time gap and distance

a) Determining the edges of received wave

Process is to determine the end points of the received parabolic wave at the receiver together with the time difference/time gap which helps to determine the distance between transmitting and receiving edges.

The wave transmitted contains information and the time of generation.

Once the time gap is known distance is determined as mentioned above in the distance calculation methods with this distance a sector is drawn passing through two points and the sector angle determines the position of transmitter.

Figure 3.1 Parabolic form of wave

Edges E1 and E2 determined at the receiver end.

Here the radius is the distance between transmitting and receiving end and sector angle is to determine the position.

b) Time gap and distance

Figure 3.2 Parabolic transmission of waves

Experimental evaluation should be carried out to determine the expanded or the formed new parabolic wave that varies with either time or distance. A parabolic equation based on time or distance as parameter should be determined so that it can be used in knowing the position of the transmitter.

Process Transmitter: sends the parabolic electromagnetic waves along with time of generation Receiver: receives the transmitted wave determines the shape of the parabolic form with its newly formed parameters it is used to find the initial position of the transmitter.

On what basis should the parabolic equation should be formed?

1) Distance

2) Time

And new parabolic equation that varies with either time/distance

4) IMAGINARY CIRCLE METHOD

From the above method, we’ve seen that from the distance and time we could find an equation which would imply the exact location of handset. But as the distance increases between the tower and the handset, distance between waves increases and time delay may occur when we use the equation. So, we use another method namely “imaginary circle method”.

In this method we imagine an imaginary circle equation with base station as centre. Depending on the analysis of the incoming parabolic wave we find the equation of parabola. Now the incoming wave is assumed cut that imaginary circle at two points. We imagine a line joining those two points forming a chord. Now imagine a line which cuts that chord exactly at the middle and extended with handset being a point on this line. Since we know the time of waves reaching the base station and velocity of the waves, we can find the distance of the handset from the base station as we already know the position that it lies on the chord.

Figure 4. Intersection of parabolic waves with imaginary circle

5) RELATIVE WIFI BASED TRACKING

The distance calculated might actually vary with the various factors like environmental issues, signal interference due to Frequencies of other signals, or due to thick concentric walls in environment these will result in actually wrong approximations of the mobile that is being tracked .so in order to make through all these distance calculated technologies we actually adopt this method.

These factors usually cause the delay of signal so delay might result in location of phone far away from base station so increased time is actually a trigger to wrong approximation of phone that is being tracked.

Figure 5. Usage of router and Wi-Fi connection for positioning mobile

In this method we are actually going to restrict the area of tracked phone by using the routers.

Usage of LAN technologies and routers are pacing up in the current internet usage. in this method we are going to introduce a separate module along with the routers for providing location based services through Wi-Fi which is made available to all those handsets in any Wi-Fi zone .So whenever a handset comes in Wi-Fi zone it actually uses the Wi-Fi for navigation or so. As the routers position is fixed we could easily track down the position of handset with respect to the router. This Wi-Fi is made available to all the handsets in its range making it public and internet usage is based on the private user. And the position calculation is based on the angle of signal arrival to router where a separate antenna is used to make computation regarding the signal arrival for its position tracking.

CONCLUSION:

Thus, we can conclude that above methods can be used to track the location of the hand set in case of emergencies or any other reasons. The relative Wi-Fi based tracking being the most efficient method can track the mobile subscriber precisely. But the backdrop of this type is that, users using Wi-Fi are limited in the present situation. But in the coming future this type of tracking is the most efficient. So, at present conditions, imaginary circle method can be trusted the most.

REFERENCE:

Sourabh Pawade, Pushkar Masodkar, Pankaj Hedaoo. Tracking and Positioning of Mobile Systems in Telecommunication Networks. International Journal of Engineering Research and Applications. 201; 1(3) 1080-1087 -1080.

Received on 15.09.2015 Accepted on 29.01.2016

Int. J. Tech. 2016; 6(1): 17-22

DOI: 10.5958/2231-3915.2016.00005.5