1. Introduction to the Main Functions of the PHY Layer
Radio Transmission and Reception Activation and Deactivation
Energy Detection (ED) within the Current Channel
Link Quality Indication (LQI) for Received Packets
Free Channel Assessment (CCA) for Carrier Sense Multiple Access/Collision Avoidance (CSMA-CA)
Channel Frequency Selection
Data Transmission and Reception
2. Introduction to Physical Parameters
868/915 MHz DSSS (Direct Sequence Spread Spectrum) uses BPSK (Binary Phase Shift Keying) modulation
868/915 MHz DSSS (Direct Sequence Spread Spectrum) uses O-QPSK modulation
868/915 MHz PSSS (Parallel Sequence Spread Spectrum) uses BPSK and ASK (Amplitude Shift Keying) modulation
2450 MHz DSSS (Direct Sequence Spread Spectrum) uses O-QPSK modulation
3. Introduction to PHY Frame Format
SHR: Synchronization Header (including Preamble and SFD), allows a receiving device to synchronize and lock onto each bit of the stream simultaneously.
PHR: PHY Frame Header (including Frame Length and Reserved), containing frame length information.
PHY Payload: Variable-length payload carrying data frames from the MAC sublayer.
The SHR field, Preamble, is used by the radio transceiver to extract chip and synchronization identifiers from the received data. The length of the Preamble field is determined by physical parameters, as shown in the following figure:
SFD indicates the end of SHR and the beginning of a data packet. Different physical parameters have different lengths, as shown in the figure below:
