1 Cell phone shielding of cell phone jammer and cell phone jammer system
1.1 Shielding and cell phone shielding
The shielding literally means shading and blocking. The shielding on the internet means deleting information containing some specific contents. It means isolating and sealing in the electromagnetism. Normally, the good electrical conductor and magnetic conductor will be adopted to wrap up the part needed to be isolated, blocked and sealed to prevent radiation of the inside energy entering outside and prevent the outside energy from interfering with the inside. The practical products in the real life and production contain the shielding shell, case, cover and net; shielding cabinet; shielding house and shielding clothing and so on.
Cell phone shielding of cell phone jammer and cell phone jammer system is the signal (fake data code) sent by the cell phone jammer or cell phone shielding system, which can interfere with several data codes in the communication link of cell phone registering the network. Therefore, cell phone cannot identify the network instruction or register the network so that the cell phone cannot normally communicate.
The cell phone connects with the base station within the specified frequency range through the radio wave when it works to finish transmission of data and voice with the specific baud rate and modulation mode.
When environment at site requires the signal shielding, the mobile phone jammer or cell phone shielding system will interfere with the electromagnetic wave signal transmission between the transmission station of mobile communication base station and the cell phone so that the cell phone cannot receive the signal sent by the base station and communication cannot be performed.
1.2 Interference mode of cell phone shielding
1.2.1 Pilot frequency interference method
The pilot signal is the direct-sequence spread-spectrum signal continuously transmitted by the base station which hasn?t been modulated. It can enable the cell phone to have multiple-access channel time limit of the forward code, provide related demodulation phase reference and provide signal strength comparison for every base station so that the cell phone can confirm when to switch. The pilot signal channel can enable the subscriber station to get multiple-access channel time limit of the forward code, provide related demodulation phase reference and provide signal strength comparison means for every base station to confirm when to switch. The pilot signal is used in the WCDMA system as: soft switch, cell reselection, open loop power control and so on. It doesn?t have the corresponding logic, transmission channel and exists in the physical channel.
1.2.2 Frequency hopping interference method of dot frequency
Frequency hopping is one of the most common spread spectrum methods. Its working principle is that carrier frequency of transmission signal of sending and receiving parties changes discretely as per the predetermined discipline, i.e. the carrier frequency used in communication randomly hops because of being controlled by the fake random changing code. In the realizing method of communication technology, frequency hopping is the communication method to perform key control of multifrequency shift using the code sequence. It is also a kind of communication system of code-control carrier frequency hopping. Judging from the time domain, the frequency-hopping signal is the multiple-frequency frequency shift key control signal; from the frequency domain, the frequency spectrum of the frequency-hopping signal randomly hops with uneven interval in a wide frequency band.
1.2.3 White noise pressure interference method
In communication system, white noise means its power spectrum density function is the constant in the whole frequency domain, i.e. it obeys the uniform distribution. The reason why it is called white noise is that it is similar to the white light including all visible light frequencies in the optics. The noise which doesn?t conform to the above condition is called color noise. Actually, the absolutely ideal white noise doesn?t exist. Normally, if the frequency range of uniform distribution of noise power spectrum density function is far bigger than the working frequency range of communication system, it can be approximately considered as the white noise.
1.3 Typical products of cell phone shielding
The product for cell phone shielding in the current market includes such main two types as the Cellular Phone Jammer and cell phone jammer system.
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