Recently, I have been researching the Bluetooth protocol stack and came across an interesting fact.

We know that Apple’s AirPods have ushered in a new era of true wireless Bluetooth headphones (TWS), currently dominating a large share of the market. Many domestic manufacturers have followed suit, but due to Apple’s registered patents, they find themselves in a rather awkward position. Let’s analyze this through the technical principles of Bluetooth.

The Principles of Bluetooth Headphones

Why were previous Bluetooth headphones only mono? In the Bluetooth protocol, there are two schemes for connecting left and right ear headphones to a mobile phone. One scheme treats the left and right ear as two separate Bluetooth devices connected to the phone, while the other connects to the phone via a relay mode, where one earbud acts as the main device connected to the phone, and the other earbud receives data through the relay mode of the main earbud.

What are the technical challenges of these two schemes?

In the first scheme, if the left and right ears are treated as two devices connected to the phone, the most challenging issue is synchronization between the two earbuds. For the phone, the two earbuds are just separate Bluetooth devices, and if data is transmitted separately, it cannot guarantee that the data arrives at both earbuds simultaneously. This is why early Bluetooth headphones were mono. Why can’t we ensure simultaneous data arrival? Because both Bluetooth and Wi-Fi operate in the 2.4GHz frequency band, signal transmission can vary due to distance. It’s worth mentioning that since both 2.4GHz Wi-Fi and Bluetooth operate in the same frequency band, Bluetooth will experience significant interference in areas with strong Wi-Fi signals.

In the second scheme, if one earbud relays data to the other, the problem is that the relaying earbud consumes a lot of power. One earbud might still have 90% battery, while the other has only 40%. This power consumption issue can actually be addressed by periodically swapping the roles of the two earbuds, thus maintaining a similar power level for both. Currently, most manufacturers, except for Apple, adopt this scheme. However, since the secondary earbud relies on the main earbud’s relay mode to transmit data, this scheme also has a significant latency issue.

Apple’s Solution

In fact, Apple also adopted the second scheme, but how did they solve the latency issue? At the initial connection between the Bluetooth headphones and the phone, a key is generated for data decryption. This means that the data sent from the phone can only be decrypted by the Bluetooth headphones using this key. Thanks to Apple’s hardware advantages, they enable the secondary earbud to share the key with the main earbud, allowing the secondary earbud to directly listen to the communication between the main earbud and the phone, rather than relying on the relay mode. If you have a basic understanding of network security, you might have heard of man-in-the-middle (MitM) attacks.

Huawei’s Solution

Due to Apple’s patents, later manufacturers could not adopt Apple’s solution. After extensive exploration, Huawei implemented the first scheme. Leveraging their hardware experience, Huawei developed the Kirin A1 chip based on the latest Bluetooth 5.1 protocol. It’s worth noting that the latest Bluetooth 5.1 protocol stack actually includes two sets of Bluetooth protocol stacks: one is the traditional Bluetooth protocol stack, and the other is the low-energy Bluetooth (BLE) protocol stack, designed for the Internet of Things. The power consumption can be kept very low. In summary, thanks to their hardware experience, Huawei can achieve dual-channel synchronous transmission technology, allowing both earbuds to directly receive left and right channel signals from the phone and establish a direct communication mechanism with the phone.

The Importance of Software and Hardware Integration

From the analysis above, it is clear that software is often powerless in many aspects due to its inability to perfectly integrate with hardware. Many technical challenges remain insurmountable.

This reminds me of Synology, a company that produces NAS devices. In the early days, Synology only focused on software. However, as they developed, their hardware could not meet their needs in many areas. They later realized that, like Apple, they should design their own hardware to meet their software requirements. Thanks to this correct decision, Synology now occupies a significant share of the NAS market.