BLE for long range communication

LE Coded PHY is the long-range mode of Bluetooth that was introduced in Bluetooth 5.0 . It basically extends the range of regular BLE devices from 30-100 ft to upto a kilometre.

Since the signal is coded, the Tx power ( per time interval ) remains the same. However, the throughput will drop since the signal is now coded.

The LE Coded PHY can be operated with two data rates:

• S2 : In LE Coded S=2 mode, each bit is represented by two symbols. Thus, the data rate is half of 1 M - ie. 500kbps. In this mode the range is roughly doubled compared to the LE 1M PHY.
• S8: In LE Coded S=8, each bit is represented by eight symbols. This gives a data rate of 125kbps ( 1 M divided by 8 ). In this mode the range is roughly quadrupled compared to the LE 1M PHY.

Every packet sent on LE Coded PHY contains a coding indicator (CI), which indicates the coding of the packet.

By using coded PHY, one could achieve a range of upto 1 km in normal / hilly terrain, and upto few hundred metres in apartment buildings.

In LE Coded PHY, the raw data is still transmitted at the rate of 1 Mbps, but there are multiple symbols transmitted for each of the bits of data, the link layer, header, and packet. Effectively, this means that Coded PHY uses multiple symbols to represent each transmitted bit, which impacts the data throughput.

LE Coded PHY can be used in three different modes,

• Advertising-only State: Use Coded PHY for advertising and this data is picked by a device that supports Coded PHY. It is a good way for one-to-many communication.
• Connection State: Switching to Coded PHY mode during an existing (1M or 2M) connection, using the PHY update procedure.
• A Combination of the Two States: If you’re looking to utilize communication that utilizes long distances during the advertising and connection states

The full packet format of packets sent on LE Coded PHY is found in the Bluetooth Core Specification Version 5.0, Vol 6, Part B, 2.2 PACKET FORMAT FOR THE LE CODED PHY.