LE Coded PHY
BLE physical layer using FEC encoding (S=2 or S=8) for extended range up to 4x at the cost of lower data rate.
LE Coded PHY
The LE Coded PHY is an optional physical layer introduced in Bluetooth 5.0 that trades data rate for significantly extended range. By applying Forward Error Correction (FEC) encoding, it can achieve up to 4x the range of LE 1M PHY at the cost of reduced throughput, making it the preferred PHY for long-range IoT deployments.
Encoding Modes
LE Coded PHY operates at the same 1 megasymbol/second rate as LE 1M PHY but encodes the data bits with redundancy using a convolutional FEC code:
- S=2 coding: Each data bit is encoded as 2 symbols, yielding a 500 kbps effective data rate. This approximately doubles the range compared to LE 1M PHY.
- S=8 coding: Each data bit is encoded as 8 symbols, yielding a 125 kbps effective data rate. This provides approximately 4x the range of LE 1M PHY.
The FEC encoding allows the receiver to recover data even when the signal-to-noise ratio is significantly lower than what uncoded GFSK requires. The specification mandates RX sensitivity of -75 dBm for S=2 and -82 dBm for S=8, though practical implementations achieve much better numbers.
Use Cases
LE Coded PHY is designed for applications requiring communication over hundreds of meters or through walls and obstacles that attenuate the 2.4 GHz signal. Common use cases include agricultural sensor networks, industrial asset tracking across large warehouses, outdoor environmental monitoring, and smart building deployments where sensors are installed deep inside walls or HVAC ducts.
Trade-offs
The extended range comes at the cost of significantly higher radio-on time per byte of data. An S=8 coded packet takes 8x longer to transmit than the same data at LE 1M PHY, consuming proportionally more energy. For applications that transmit small amounts of data infrequently, the energy cost is acceptable. For bulk data transfer, LE 2M PHY is the better choice.
Advertising Support
LE Coded PHY can be used for extended advertising packets on secondary advertising channels, enabling long-range beacons and broadcast applications. An indoor positioning system can deploy coded PHY beacons to cover a larger area with fewer infrastructure nodes.
Related Terms
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