How did the signal interference come about?
According to the frequency band: uplink interference and downlink interference
Uplink interference is defined as the interference of the interference signal in the uplink frequency band of the mobile network, and the interference of the external radio frequency interference source to the base station. Uplink interference will reduce the coverage of the base station. Under the condition of no uplink interference, the base station can receive mobile phone signals from far away. When uplink interference occurs, the mobile phone signal needs to be stronger than the interference signal in order to communicate with the base station. Therefore, the mobile phone must be closer to the base station. Signal Jammer
Downlink interference means that the interference signal sent by the interference source is in the downlink frequency band of the mobile network, and the mobile phone receives the interference signal and cannot distinguish the normal base station signal, so that the communication between the mobile phone and the base station is interrupted, resulting in dropped calls or failure to register.
Co-channel interference refers to the interference of all unwanted signals with the same frequency as the useful signal that fall within the passband of the receiver, also known as co-channel interference. These useless signals are the same as useful signals. They are expanded in the receiver and converted to frequency to fall within the intermediate frequency passband. Therefore, as long as there is co-channel interference at the receiver input, the receiver system cannot filter and suppress it.
Non-co-channel interference mainly includes adjacent frequency interference, intermodulation interference, blocking interference, and spurious interference
adjacent channel interference
Adjacent frequency interference refers to signal interference from frequencies adjacent to the applied signal frequency. Adjacent frequency interference is caused by the unsatisfactory reception filter, which causes the signal of adjacent frequency to leak into the transmission bandwidth. Adjacent channel interference can be minimized through precise filtering and channel assignment.
Near-far effect: If the base station of the adjacent channel transmits in a range very close to the receiver of the user, and the receiver uses the signal of the base station of the preset channel, this problem will become very serious, which is called the near-far effect. The near-far effect also occurs when the channel used by a mobile station very close to the base station and the channel used by a weak signal mobile station are adjacent channels. (In the UMTS system, because all mobile stations use the same frequency band, the effect of the near-far effect is more significant, but the UMTS system uses excellent power control to eliminate the effect of the near-far effect).
Intermodulation interference
When two or more different frequency signals act on a nonlinear circuit, they will modulate each other to generate a new frequency signal output. If the frequency falls within the operating channel bandwidth of the receiver, it will interfere with the receiver and become intermodulation interference. .
jam interference
Any receiver has a certain reception dynamic range. When the out-of-band interference signal is strong to a certain extent, and the reception power exceeds the maximum power level allowed by the reception dynamics, it will cause the receiver to be fully blocked, thereby affecting the reception performance of the system. This kind of interference called jamming. Blockage will cause the receiving machine to fail to work normally, and long-term blockage may also cause permanent performance degradation of the receiving machine.
spurious interference
Because of the roll-off characteristics of the transmit filter (no filter can be an ideal step method),
As a result, there is always a certain amount of out-of-band radiation, which is what we generally call emission spurs. The interference caused by the transmission spurs is called spurious interference.
Interference between mobile communication systems
In-band interference: The CDMA transmitting signal directly acts on the GSM receiver as in-band noise through methods such as intermodulation, resulting in a decrease in the sensitivity of the GSM receiver. This type of interference is further divided into transmitted spurious interference and intermodulation interference;
Out-of-band interference: When the out-of-band interference is strong to a certain extent, it will cause the receiver to be fully blocked, thereby affecting the reception function of the GSM system. This type of interference is also called blocking interference.
