Working principle of mobile phone jammer is as follows: depress the signal of communication system by transmitting high-power electromagnetic signal in the whole working frequency range of cell phone so that communication between the cell phone and base station can be cut off.
Although this kind of method is easy and can cut off inter-cell phone communication, it is hard to control the covering range, high-power electromagnetic radiation is harmful to people?s health and the cell phone jammer may interfere with the mobile communication base station and even palsy the communication base nearby so that the cell phones in the specific area can not be connected.
Take the GSM system for example in this text. Based on the actual measurement and emulational analysis, perform the quantitative analysis for effective shielding range of the cell phone jammer and its influence on the mobile communication system according to related standards of the communication industry.
1 Working principle of cell phone jammer
1.1 Working principle of cell phone jammerThe cell phone jammer interferes with the digital signal in different frequency ranges by transmitting high-power triangular wave. Different cell phones have different frequency ranges used for interference. GSM contains 900 MHz and 1800 MHz (also known as DCS). The uplink frequency of narrow-range CDMA is 824-849MHz and the downlink is 869-894 MHz. The frequency range of PHS is 2 GHz.
In the circuit of cell phone jammer, 220V AC will output 5V DC voltage via transformation rectifier and generate low-frequency signal of triangular wave created by the wave generation circuit. And then the triangular wave will output high-frequency sinusoid signal via Voltage Control Oscillator (VCO), which will be transmitted to the emission antenna after being magnified by power amplifier module on the circuit board and then radiated to the space by the antenna.??
When the cell phone is in the normal condition that it is not interfered by the jammer and it enters a certain cell for the first time, the local cell base station will perform the position updating management for the travelling carriage and allocate such temporary user information as the new temporary mobile user identifier to the travelling carriage.
The travelling carriage can determine its cell location after receiving the information from the base station. The travelling carriage only receives BCH from the base station in the cell in the condition without communication. The interference signal sent by the cell phone jammer will interfere with effective signal in the BCH frequency range of the base station.
The interference signal increases the error rate of mobile communication channel and reduces signal-to-noise ratio of the channel in order to influence the travelling carriage effectively receiving the signal from base station.
When signal-to-noise ratio reduces to +9dB (GSM network), the travelling carriage cannot correctly decode broadcast information from base station so that connection with base station will be lost. After the travelling carriage fails in searching BCH for several times and cannot determine its service area, therefore the cell phone in the interfered area displays no signal, out of service area, no text and call sending and receiving.
Abstract: Recently, the Cellular Phone Jammer? is used more and more widely. Although this kind of equipment realizes forbidding using the cell phone, it also will seriously interfere with the mobile communication system.
To normalize use of cell phone jammer, do the quantitative analysis of effective shielding range of cell phone jammer and influence on mobile communication system outside shielding range, the cell phone jammer has been analyzed according to related standards of communication industry and radio transmission model, starting from working principle of cell phone jammer and dissipation analysis of signal in transmission.
Finally, verify that the calculation way of the model is correct and feasible through comparison and analysis of calculated data and actual measurement data.
Key words: cell phone jammer; transmission dissipation; radio transmission model; carrier frequency of control channel.
Source: http://democracyroad.com/mrbobama/?q=node/15201
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