1. LE PHY classes：
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2. Collision has highly probability to incur during multiple Bluetooth devices tune frequency. Hence, access address is used to improve it.
3. The packet format of LE uncover PHY is as following figure. The theory transmission time of the packet is from 44 to 2120us.
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4.1 Preamble:
A fixed sequence of Alternating 0 and 1. The first bit of preamble should be same as LSB of access address.
