PHY Packet Fields:

Preamble (32 bits): Synchronization

Start-of-Packet Delimiter (8 bits): Signify end of preamble

PHY Header (8 bits): Specify length of PSDU

PSDU ($\leq$127 bytes): PHY Payload

• The data rate in this is of 250 kbps for 2.4 Ghz ISM band.
• The preamble sequence (32 binary 0) used for receiver timing necessary start of frame delimiter (SFD) indicates the end of synchronization field.
• The frame length indicates the size of PSDU.
• The average size of PPDU is 22 bytes which is 176 bits.
• The frame length field is also known as PHY header.
• First 40 bits are known as synchronization headers which are used for synchronization purpose.

IEEE 802.15.4 PHY layer Specifications are

1. 3 Bands,27 channels

   4 Ghz (ISM): 16 Channels,250 Kbps

   868.3 Mhz (ISM): 1 Channel,20 Kbps

   915 Mhz (America):10 Channels,40 Kbps

2. Channel spacing:5 Mhz

3. Coding:DSSS 4 .Modulation:Offset_QPSK