Bluetooth Short Connection Intervals in BT6.2 – what they are and what it means
When the Bluetooth 6.2 specification update was announced, most of the attention seemed to focus on Channel Sounding as the hot new technology now available with Bluetooth devices. As a result the other new features slipped by under the radar. This article looks at the Short Connection Interval feature of the update; what it is, and why it can be useful in real world applications.
Prior to the 6.2 update, the minimum connection interval supported in Bluetooth Low Energy was 7.5ms. This corresponds to an update rate of 130Hz. For many applications, this is more than sufficient, and low power applications (looking for extended autonomy using small batteries) will typically use far longer connection intervals. Indeed many low power use cases will focus on the other end of the connection interval spectrum – the maximum being 4 seconds.
So what’s the interest in increasing speed from a connection rate 130Hz?
The answer there are some applications where the current connection rate might not be sufficient. Firstly you have to consider that not every connection event will be a success. Bluetooth maintains a good overall connection rate via its frequency hopping approach, so when one channel is occupied thus blocking a connection, on the next interval a different channel will be used. So in practice, the real connection rate could be significantly lower than the theoretical maximum in a noisy RF environment. There may also be applications where updates are required for more than one end device.
The applications where this matters are ones where latency is key. For simple data transfer, this is rarely important, as any breaks in connection can normally be recovered once connection is restored. Even for something such as music streaming (passive listening), some data buffering can be deployed to cover any gaps in the stream.
Latency becomes an issue when a true “real-time” response is required – typically when you have some direct human interaction involved. Human perception is surprisingly sensitive to even small delays, so in such cases the 130Hz (theoretical) maximum rate may not be enough.
Examples could include MMI applications where you want fine tracking of a pointer type device, live playing of audio (between an instrument and speaker) and gaming where you want ultra fast response to actions on a controller. There can also be more industrial type applications where precisely timed control of machinery is needed, or sensing applications in robotics.
So what does Bluetooth 6.2 offer? At the specification level, the minimum connection interval drops to 375uS, or the equivalent of 2.6kHz connection rate – a 20x improvement. At this connection rate, there is no humanly observable latency, and it is difficult to imagine many applications where it would not be enough. Even allowing for a real world rate somewhat lower than this, there should be no noticeable latency in an application.
It is important to note that this doesn’t change the overall maximum data throughput limit. However under certain conditions, using short connection intervals may provide a more robust connection, with more frequent opportunities for re-transmission, and a higher throughput in practice.
More information is available on the Bluetooth SIG website.
In terms of practical implementation, this feature does not require new hardware (unlike Bluetooth channel sounding), so in terms of Insight SIP modules, it is available not only on the latest generation ISP2454 series, but also on the older ISP2053 and ISP15/18/19 series, if the latest software is loaded. As is always the case with Bluetooth upgrades, it is important to note that a Bluetooth device that labelled "6.2" may not support all Bluetooth 6.2 features.
