RF Interference

Radio frequency(RF) interference is the interference caused by one RF signal to the other RF signal.There are major types such as inter symbol interference, co-channel interference and adjacent channel interference.

RF interference is more predominant now-a-days as more and more cellular standards are operating in one region for example, GSM, WCDMA, WiMAX, LTE cells are available in one location area/ region.

Systems or multi-mode modems are designed to mitigate or reduce the effects of RF interference from one system/RAT to the other RAT (radio access technology). As mentioned RAT can be any technology as mentioned such as wimax,wlan,zigbee,gsm,CDMA,HSPA,LTE etc.

Following are some of the major types of interference.

Inter-Symbol Interference(ISI)

Inter-symbol interference

Due to delay spread transmitted symbol get spread across in time domain. Due to this two consecutive symbols will spread energy to each other and so on, which leads to ISI (Inter Symbol Interference).

Co-Channel RF Interference

RF Interference, co-channel, adjacent channel

It is caused by two users operating at the same frequency but located at some distance away. This is due to use of same frequency in two GSM or WCDMA or LTE cells at some distance away. This re-use of same frequency will cause interference to another mobile of distant cell. This is how co-channel interference occurs. In order to make re-use of the precious frequency spectrum telecom operators do RF planning and keep the power levels such that one cell's signal will not interfere another cell's signal in the same band. If the levels are not properly maintained it will create problem as the signal pass through RF filters easily as it is in the pass band of the designed filter.

Adjacent Channel RF Interference

It is caused by adjacent channel frequency at some distance from the wanted carrier frequency. Let's see how this happens. Assume that two frequencies are allocated to two different mobiles. Due to poor filtering and non linearity one frequency radiates into another frequency's spectrum and hence cause adjacent channel interference . In order to avoid this situation, proper radio frequency planning with appropriate guard bands between the carriers need to be adopted.

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