Views:41 Author:James Wu Publish Time: 2020-09-23 Origin:Site
Just as the literal meaning of "Internet of Things = Things + Internet", data transmission is required to connect to the Internet. The non-contact data transmission is the application scenario of radio frequency. It means almost all IoT products will have radio frequency transmission; such as 1 cm of RFID, 10 meters of Bluetooth, 100 meters of Wi-Fi, long-distance of 2G, 4G and NB-IOT, all of them are communicated through radio frequency transmission of data. Different transmission methods are equivalent to different languages. Some people speak Chinese, some speak English, and some speak French…
It is "the energy of electromagnetic wave", the unit is W, dBm. The RF transmission with low transmit power has a short distance, for example, the transmission distance of Bluetooth 0dBm (1mW) is only ten meters. The transmission power of 2G is 30dBm (2W), and the transmission distance can reach more than 30km. In the same way, when we speak, the loud voice will spread far away, and the low voice will spread close.
It is the lowest electromagnetic wave energy that the receiver can recognize. The unit is also dBm. For example, the receiving sensitivity of Bluetooth is around -90dBm, the receiving sensitivity of 2G is around -108dBm, the receiving sensitivity of NB-IOT is around -130dBm, and the receiving sensitivity of GPS is around -150dBm.
The larger the number after the minus sign, the lower the signal strength, the higher the sensitivity, and the longer the transmission distance. The reason why the receiving sensitivity does not use the concept of "Watt" is because it is too small. For example, Bluetooth's -90dBm, which is about 0.000000001 mW, and GPS's -150dBm, is only 0.000000000000001mW.
Similarly, the receiving sensitivity is equivalent to the smallest sound that human ears can hear. Some people have sensitive ears, and some people have deaf ears. Ears with higher sensitivity can hear sounds from longer distance.
Interference signal (noise):
It is mainly refer to Electromagnetic Interference / RF Interference. It's like talking on the street with a loud voice; but you can whisper in the mid-night. The external sound will affect the conversation between the two people, and the external radio frequency signal will also affect the radio frequency reception.
So how to deal with these EMI/RF interference signals? We think usually there are follow methods:
1. Increase the transmit power;
2. Improve receiving sensitivity;
3. Increase shielding measures. For example, radio frequency shielding frame, coaxial cable, etc.
4. Reduce the transmission rate (this is one reason why NB-IOT has higher sensitivity)
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