Published on Apr 02, 2024
The sniffer is a small base station, it includes transceiver section. It should operate at a frequency that is much different from the frequency of the current cell in which the operation of detection is being carried out. Some of the main important things are the frequency that has to be generated by the transceiver section is around 900MHz range which is a VHF range and it is necessarily to design the oscillator circuit for that frequency range .Another important is the cooling that has to be provided to the circuit while designing the circuit that is to be operated at 900MHz range of frequency.
Hence proper design of base station is an important thing in the design of the sniffer. Mobile phones as well as the base station has low power transmitter is also transmitting at low power. The transmitter of the sniffer has to be a low power transmitter. This helps in the process of reducing the interference of the device with the devices that are in the other cells.
One of the most interesting things about cell phone is that it is really a radio an extremely sophisticated radio, which uses some band of frequency that has the basic working similar to the ordinary cordless phone. The mobile cellular communication has been appreciated since its birth in the eary 70’s and the advancement in the field of VLSI has helped in designing less power, smaller size but efficient transceiver for the purpose of communication. But however the technology has not yet answered the loss or misplacement of the lost mobile phone which is significantly increasing. In this paper we discuss the problem and the probable solution that could be done. The IMEI number is a unique number that is embedded in the mobile phone the main purpose of which is the blocking of calls that is made by unauthorized person once the mobile is reported as stolen but here we use it effectively for the purpose of detection.
As stated this proposal is about the detection of lost mobile phone and for this purpose we are designing a new device called the Sniffer. The sniffer device has to be designed precisely and size should be reduced for easy mobility for the purpose of detection. The device can be called as a mobile base station that includes the following important components:
1. Sniffer base station
2 .Unidirectional antenna
3 .Tracking software
The sniffer is a small base station, it includes transceiver section. It should operate at a frequency that is much different from the frequency of the current cell in which the operation of detection is being carried out. Some of the main important things are the frequency that has to be generated by the transceiver section is around 900MHz range which is a VHF range and it is necessarily to design the oscillator circuit for that frequency range .Another important is the cooling that has to be provided to the circuit while designing the circuit that is to be operated at 900MHz range of frequency. Hence proper design of base station is an important thing in the design of the sniffer. Mobile phones as well as the base station has low power transmitter is also transmitting at low power. The transmitter of the sniffer has to be a low power transmitter. This helps in the process of reducing the interference of the device with the devices that are in the other cells.
Though the transceiver in a sniffer plays an important role in the detection of the mobile phone but however it is the directional antenna that has a major role in the design of the transmitter. The directional antenna acts as the eyes for the sniffer for the purpose of the detecting the lost mobile phones. Hence the proper design of the directional antenna is required. Antenna is a device which works at specified frequencies range for transmitting or receiving the data signal. In general, antennas transmit power depending on lobe pattern which varies from one antenna to the other. The lobe pattern is a two dimensional diagrams that is used to show radiation pattern. Radiation pattern of directional antenna is shown in fig1.
In addition to this it is necessary that the transmitter should be a low power transmitter. The Gain and directivity are intimately related in antennas. The directivity of an antenna is a statement of how the RF energy is focused in one or two directions. Because the amount of RF energy remains the same, but is distributed over less area, the apparent signal strength is higher. This apparent increase in signal strength is the antenna gain. The gain is measured in decibels over either a dipole (dBd) or a theoretical construct called an Isotropic radiator (dBi).
The isotropic radiator is a spherical signal source that radiates equally well in all directions. One way to view the omni directional pattern is that it is a slice taken horizontally through the three dimensional sphere. The graphical representation of Radiation pattern of the unidirectional antenna is shown in figure. The spherical co-ordination system has three main components for the pattern representation and they are (R, _ , _ ) .The shape of the radiation system is independent of R, as long R is chosen to be sufficiently large and much greater than the wavelength as the largest dimension of the antenna. The magnitude of the field strength in any direction varies inversely with R. A complete radiation pattern requires the three dimensional representation.
The other factors that are to be taken into account during the development of the antenna for the sniffer should be the gain and the directivity .As these features have a greater effect while designing the antenna. The gain of the antenna is defined as the ability of the antenna to radiate the power in a particular direction. The power radiated per unit area in sany direction is given by the pointing vector and is equivalent to E2/_2 W/m2
Total of the power that is being radiated by the antenna is given as
W=__d_
The average power that gets radiated is given as _(avg)=W/4_ (watts per steradian) The Directivity of the antenna is the direction in which there is maximum gain for the radiation that is being radiated, the gain of the antenna is given as a function of the angles. The directivity value is constant for a particular direction. In addition to the directivity and the gain of the antenna the other important thing that has to be taken into account is the power that is being radiated by the antenna. The total power is given as W and is the summation of the radiated power and the ohmic loss of the antenna. Here the Wl represents the ohmic losses of the antenna.
Wt=Wr+Wl
The power gain of the antenna is given as
gp=4__/wt
The ratio of power to the directivity is referred as a measure of efficiency of the antenna
gp/gd=Wr/(Wr+Wl)
The power radiated by the antenna should be properly designed as this causes more penetration of the electromagnetic radiation and thus it might have some effect in the near by cells. The effective area of the antenna is another important factor that is mainly required in the receiving antenna and it may be referred as the effective aperture or capture area and is related to the directive gain of the antenna through the relation A=gd_2/4
Since the sniffer device that is constructed is a device that has both the transmitting and the receiving antenna. Effective gain has to be taken into account and this shows the ability of the antenna to capture the signal that the lost mobileis transmitting.
The software part plays a major role in the tracking of the lost mobile phone It is the base for the antenna to track the lost mobile the main feature of this software is that it helps in the process of creation of the data base and this is mainly done using a Random Access Memory. The mobile phone that is lost has certain IMEI number that is embedded in the chip. This RAM of the sniffer device stores the IMEI number of the lost mobile phone. Thus this acts as a data base or the directory of the lost mobile phone number/The software that is to be designed in such a way that the software has the input as the IMEI number of the lost mobile phone from the RAM and this ID done using the SQL query that fetches the IMEI number.
After getting the input of the lost mobile phones IMEI number it checks the comport for getting the information whether it obtains any signaling information from the lost device that might respond to the signal sent by the sniffer The programming is done with C or Java. However the C is most preferred as it is easily embedded with the chips. With VB the front end is designed. The oracle SQL is the back end as it helps in retrieving the input data from the RAM using the query. But however the sample program that we have designed does not use the oracle it takes the input directly from the keyboard and this is an example and a dummy program that has been created that helps in the understanding of how the device would work.
The sniffer is basically a transceiver that works in the frequency which is in the special unused range that is operated by the service provided or it can designed to operate at a frequency that is of much different frequency than the one that is being used by the nearby cells as there may be possibility of interference by the device with the devices in the nearby cells. The working for the device is as follows. The fig 2 &3 shows the working of the sniffer ; as given in the fig2 it gives the normal operation of the mobile with the base station and there is a BTS that acts as a middle man in the process of communication between the mobile and the MTSO which is popularly known as MSC or Mobile Switching Centre .
There is always a two way communication between devices and before the establishment of the communication the authentication of the SIM card that has the IMSI or the International Mobile Subscriber Identifier .This IMSI number helps in the authorization of the user. The second authentication is the authentication of the handset, which is done in EIR or the Equipment Identifier Register. This register is located at the MSC and it contains the IMEI number of the lost handset and if the signal is obtained from the normal one then the two way communication is established. The IMEI of the lost mobile phone number once has been reported to the service provider, who keeps in track of the record of lost mobile phones.
The MTSO or the MSC which keeps in track of all the mobile phones with IMEI number and the IMSI number has the information of the lost mobile phones location which means the location of the cell where the lost device is because of the two way communication with the device the BTS of the lost device is known to MSC. From this information regarding the cell in which the device is located the sniffer device is introduced.
After the information regarding the IMEI number of the lost device is provided by the MTSO or MSC .This is then fed into the sniffers main memory the sniffer's located in particular cell gets into action of detecting the lost device. The sniffer uses a frequency that is different from the one that is being used by the base station and the located nearby cells .The base station disconnects the connection with the lost mobile phone, as there is a request regarding this action from the EIR part of the MSC. This causes the lost device to search the BTS to get locked with since each base station does not have authorization capability the lost device send appropriate connection request signal. Now when the sniffer device is being deployed and this device has in built authorization capability the lost device finds the sniffer to get itself locked to the frequency of the sniffer .
Since the boom of the mobile phone for the purpose of the communication there has been a large no. of complaints regarding the mobile phone that is being lost and there has been no effective method developed for detecting the lost device. The given paper dealt about the idea of development "Sniffer for the detection of lost Mobile phones" paves a way by means of which the lost mobile phones can be recovered. But the process of detection is yet to be developed through the software and demo has been developed and is with the authors.
The demo has been written in VB that gives the over view of how the lost mobile is being detected and the software has been written in C. The SQL has to be used for the purpose of querying and the internal architecture is of lesser complexity compared to the base station as this mainly involves the control signal and there is no need for the voice process. The design involved the following: Design of the sniffer base station design of unidirectional l antenna, development of software for tracking. Though this method appears to be a little bit complex involving the design of the sniffer but however for large scale detection the overall effective cost of the design and the detection scales down.
There are certain boundary conditions or criteria that have to be qualified for the identification of the lost mobile like the power of the mobile should be good enough , the mobile phone should not be in the shadow region etc., but however this method can be improved by using modern technologies and devices.
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