IEEE 802.15.4 Protocol
Introduction
IEEE 802.15.4 is a standard for low-rate wireless personal area networks (LR-WPAN). It is designed for low power, low data rate, and short-range communication.
Step-by-Step Working
1. Device Types
- FFD (Full Function Device): Can act as coordinator and communicate with all devices.
- RFD (Reduced Function Device): Simple devices like sensors, communicate only with coordinator.
2. Network Formation
- One device becomes PAN Coordinator.
- Creates a Personal Area Network (PAN).
- Assigns a PAN ID.
3. Channel Selection
- Operates at 2.4 GHz, 915 MHz, and 868 MHz bands.
- Coordinator selects a free channel.
4. Device Association
- Devices send association request.
- Coordinator assigns a 16-bit address.
5. Data Transmission
- Beacon-enabled mode: Coordinator sends periodic beacons.
- Non-beacon mode: Uses CSMA/CA for communication.
6. Channel Access (CSMA/CA)
- Check if channel is free.
- Wait for random backoff time.
- Transmit data.
- Retry if channel is busy.
7. Frame Structure
- Beacon Frame
- Data Frame
- ACK Frame
- MAC Command Frame
8. Acknowledgement
- Receiver sends ACK.
- If no ACK, retransmission occurs.
9. Power Saving
- Devices enter sleep mode to save energy.
10. Security
- Uses AES-128 encryption.
- Provides authentication and data integrity.
Key Features
- Data rate: 20 kbps – 250 kbps
- Range: 10–100 meters
- Low power consumption
- Supports star and peer-to-peer topology
Example
In a smart home system:
- Coordinator acts as smart hub.
- Sensor joins network.
- Sensor sends data.
- Coordinator receives and acknowledges.