GSM JAMMER

GSM Jammer

ProposalFinal Year Project

Fall 2006Project Advisor_________________ Dr. Pervaiz Akhtar

Group Members

Syed Absar Ahmed Shah

Sohaib Zafar

Syed Ali Wajahat Jafri

OverviewGSM Communication Basic Structure

The GSM communication network works on airwave frequency band 890-960MHz, with two banks the uplink band (935-960MHz), and the downlink band (890-915MHz). Each band is 200kHz wide. Each uplink frequency is coupled with a downlink frequency. Together, this pair of frequencies is known as an ARFCN (Absolute Radio Frequency Number). By using TDMA (Time Division Multiple Access) technology, each ARFCS accommodates eight timeslots, which can be (at a very basic level), seen as a separate channel (although this is not the case). This binding of eight timeslots on a single ARFCN is also known as a TDMA frame.

The MS (Mobile Set) is a dumb device, which only communicates with the BTS (Base Transceiver Station), which carries out the rest of the operations necessary for proper communication. The MS-BTS communication is carried out over two types of channels:

1. TCH (Transmission Channels)

2. And three control channels:

a. BCCH (Broadcast control channel)

b. CCCH (Common control channel)

c. DCCH (Dedicated control channel)

Each channel is assigned a fixed timeslot on a TDMA frame.

Approach

The basic approach to prohibiting the use of cell phones in an area is to add interference to the frequencies that accommodate GSM communications. If this interference signal is produced on the uplink frequencies, the results can be disastrous.

Consider a BTS, serving a radius of 2km. If a GSM device lies in that radius, it will tend to communicate with the BTS at all times at the assigned frequencies, completely consuming the limited capacity of the BTS. Therefore, no other cell phone in the service area of the BTS will be able to make or receive a call. This is unfair to people outside the intended, legal area of jamming (such as banks, which are PTA authorized to use jammers for security purposes).

A more civilized, and technically feasible approach would be to produce interference only on downlink frequencies. In this manner, only phones in the service area of the Jammer will be disrupted, since their incoming transmission would be junk, because of the interference. Phones outside the power range of the jammer will be able to make and receive calls as usual.

Project Breakup

Equipment Required

To test the equipment during development stages, a CRO (Cathode Ray Oscilloscope) and a frequency generator, capable of recording and producing, respectively, frequencies of up to 450MHz would be required. A spectrum analyzer capable of measuring GSM frequencies would suffice.Proposal

We propose a device that would disrupt downlink frequencies only in the GSM band, due to testing limitations for the higher DCS and PCS frequencies. The power level would be fixed at a nominal value.

DeviceThe, according to our understanding at this point, will consist of three major, definitive parts:1. The Power Section

2. The RF Section

3. The Transmission Section

A basic analysis of each section follows.

Basic Analysis

The Power Section of the device will make the device wall-socket-pluggable in a 220V environment. It will transform input power into the form preferred by the RF Section. It will make sure that the output power of the device only affects the desired area, and does not contain overshoots. The RF Section will generate the waveform necessary to disrupt the GSM communication service in the uplink frequency range. The Transmission Section will consist of a suitable antenna, and an amplifier/attenuator, to control the region of interference, and to effectuate suitable jamming.

ExpansionIf need may arise in the future, the device would be modified to incorporate jamming capabilities for DCS and PCS bands, employing the same principle as in the project. The power levels may also be made adjustable by the use of appropriate amplifiers/attenuators.

However, this shall not be under the scope of our current proposed project.