Bluetooth Low Energy (BLE) offers three PHY modes—1M for legacy support, 2M for high throughput, and Coded PHY for long-range communication. Each mode is optimized for specific use cases, balancing speed, range, and energy efficiency. This post shows how we choose the right PHY mode for our BLE applications.

With the release of Bluetooth 5.0 a few years back, Bluetooth Low Energy (BLE) introduced multiple PHY (Physical Layer) modes, expanding its versatility and opening up new application possibilities. Beyond the default 1M PHY, engineers can use the 2M PHY for higher throughput and Coded PHY for long-range communication. These options have significantly broadened the range of Bluetooth applications.

While experienced Bluetooth engineers may already be familiar with these advancements, many newcomers still struggle to choose the best PHY mode for their specific use cases. Here is our experience with the different PHY modes and our thoughts on choosing the right one for our applications.

Available BLE PHY Modes

As of 2025, the Bluetooth specification defines the following PHY modes:

1M PHY

The 1M PHY is the original BLE mode and the only option for devices before Bluetooth 5.0. This mode has no error correction and uses a physical modulation of 1 Msym/s, meaning sending 1 bit takes 1 us on the air.

2M PHY

This PHY supports BLE applications that require higher throughput. The 2M PHY has no error correction and uses a physical modulation of 2Msym/s. Sending 1 bit over the 2M PHY takes 0.5us on the air, making it twice as fast as the 1M PHY.

Coded PHY

The Coded PHY supports much longer communication distances. It uses forward error correction and symbol coding of either 2 (Coded S2) or 8 (Coded S8). These two mechanisms increase signal robustness over long distances, leading to a significantly longer communication range.

Sending 1 bit over the Coded S2 takes approximately 2us. Sending 1 bit over the Coded S8 takes 8us.

Our Rules of Thumb for Choosing a BLE PHY Mode

From our years of working with BLE, here are the guidelines we follow when selecting a PHY mode:

1. Default to 2M PHY:
   • This mode is our go-to for most applications due to its combination of higher throughput, energy efficiency, and resilience to interference.
   • Faster transmissions reduce the risk of packet loss from interference, ensuring reliable communication.
2. Use Coded PHY for Long Ranges:
   • In outdoor environments or low-interference scenarios, the Coded PHY is ideal for extending communication distances.
   • However, in indoor environments with significant interference, we recommend avoiding Coded PHY in favor of 2M PHY.
3. Choose 1M PHY for Legacy Support:
   • When compatibility with older BLE devices is essential, the 1M PHY is the only viable option.
   • While it lacks advanced features, its broad compatibility makes it a necessity for certain applications.

Summary

The PHY mode you are using for your BLE devices heavily impacts the performance of your BLE application. Our thoughts:

• 2M PHY: Ideal for most use cases, offering speed, energy efficiency, and reliability.
• Coded PHY: Best for long-range applications, particularly in outdoor or low-interference environments.
• 1M PHY: The fallback for legacy device support.

By carefully selecting the right PHY mode for your needs, you can ensure your BLE application achieves optimal performance, whether prioritizing speed, range, or compatibility.