PHY physical layer, frame structure, parameters, data, energy, modulation, frame, format
1. What are the main functions of the PHY layer?
Activation and shutdown of radio transceiver
Energy detection (ED) in the current channel
Link quality indication (LQI) of received data packets
Idle channel evaluation (CCA) for carrier listening multiple access/conflict avoidance (CSMA-CA)
Channel frequency selection
Data transmission and reception
2. Physical parameters
868/915 MHz DSSS (direct sequence spread spectrum) adopts BPSK (binary phase shift keying) modulation
868/915 MHz DSSS (direct sequence spread spectrum) adopts O-QPSK modulation
868/915 MHz PSSS (parallel sequence spread spectrum) adopts BPSK and ASK (amplitude shift keying) modulation
2450 MHz DSSS (direct sequence spread spectrum) adopts O-QPSK modulation
3. PHY frame format
SHR: Synchronization header (including Preamble and SFD), allowing a receiving device to synchronize and lock to each stream at the same time.
PHR: PHY frame header (including Frame length and Reserved), the length information of the frame.
PHY Payload: A variable-length payload that carries the data frame of the MAC sublayer.
Among them, the SHR field: Preamble, which is used by the radio transceiver to obtain the chip and synchronization identification from the received data information. The length of the Preamble field is determined by the physical parameters as shown in the figure below.：
SFD, indicating the end of the SHR and the beginning of the packet, different physical parameters have different lengths as shown in the figure below：