[Ble--link Layer] Physical channel (to be continued)

Briefly

Wired communication, is directly connected with the cable, and then the length of the distance, some will need to load the wave, the signal may be modulated by different modulation mode. Wireless communication is the same, but the transmission of the signal is through the radio frequency, through a certain frequency band, the wireless channel modulation, the data sent out.

BLE physical channel

In the physical layer section mentioned the BLE physical channel, a total of 40, in the 2.4GHz ISM band. In fact, the BLE 40 physical channels are divided into two groups, a group is the advertising channel (3), a group is the data channel (37), as follows:

Before the connection was successfully established, the device interacted with the data through the advertising channel, and after the connection was successfully established, the data channel was used to interact.
Two wireless devices to communicate between, in addition to follow the same protocol, the two must be transferred to the same channel, the normal data can be exchanged, or one in 2404MHz, the other at 2430MHz, the two can not receive the other side of the data (is often said not the same channel ...) ）。
So before the connection is established, only three advertising channel is justified, so that the other side to scan, the likelihood of hitting the same channel greatly increased, or scan sweeping half a day, are not on the same channel, that also how to communicate. BLE also uses frequency hopping, which is due to wireless interference and security considerations.

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[Ble--link Layer] Physical channel (to be continued)