Bluetooth SCI Reduces LE Connection Intervals to 375 μs

In an article by Niclas Granqvist, senior technical leader at Logitech, and Alfredo Perez, senior technical marketing manager at Bluetooth SIG, Bluetooth SCI is presented as a specification feature that reduces Bluetooth LE connection intervals from 7.5 ms to 375 μs. The update matters for HID devices, AR/VR, industrial sensors, and RTLS.

Specification Update in Bluetooth Core 6.2

Bluetooth Shorter Connection Intervals, or SCI, is part of Bluetooth Core 6.2. The feature reduces the minimum connection interval for Bluetooth LE links below the previous 7.5 ms limit. According to the Bluetooth SIG, SCI lowers the interval by a factor of 20, down to 375 μs.

SCI applies to Bluetooth LE connections using LE ACL transport. Its purpose is not to increase the raw radio speed, but to allow connected devices to exchange packets more frequently within a given time window.

This distinction is important for developers and system architects. SCI changes the timing framework for communication between connected Bluetooth LE devices, while continuing to work with existing Bluetooth LE GFSK PHYs.

How Bluetooth SCI Works

Bluetooth SCI adds procedures that allow Central and Peripheral devices to negotiate and update connection timing parameters on an existing ACL link. Devices first connect through standard Bluetooth LE procedures and exchange information about supported features.

If both devices support SCI, the Central device can select the parameters for a connection rate change and initiate the update procedure. A Peripheral device can also request that the Central initiate such a procedure.

The updated parameters include the connection interval, subrate factor, peripheral latency, continuation number, and LE ACL flush timeout. Together, these mechanisms allow Bluetooth LE links to be adapted more precisely to the timing needs of an application.

SCI required changes in several parts of the specification, including Link Layer control PDUs, HCI commands and events, and feature exchange mechanisms. According to the source text, the radio itself was not changed, which means the feature is based on protocol-level updates rather than a new physical layer.

Relevance for HID and Low-Latency Applications

Before SCI, the 7.5 ms minimum connection interval supported update rates of around 133 Hz. This is sufficient for many Bluetooth LE applications, including fitness trackers, smart home sensors, and medical devices.

For gaming peripherals and other high-performance human interface devices, this can be limiting. Nordic Semiconductor states in the Bluetooth SIG interview that gaming HID devices such as mice and gamepads often target report rates of 1 kHz or higher. With SCI, Bluetooth LE can support report rates of up to 2666 Hz for wireless HID use cases.

This makes SCI relevant for manufacturers of gaming controllers, mice, keyboards, professional input devices, AR/VR controllers, and other latency-sensitive peripherals. The Bluetooth SIG source also points to future standardization work around ultra-low-latency HID applications.

Industrial and IoT Use Cases

The relevance of SCI is not limited to consumer peripherals. Nordic Semiconductor also identifies real-time industrial sensors, real-time location systems, motion trackers, sports performance monitoring, and AR/VR devices as potential application areas.

For system integrators and solution providers, the technical value lies in more frequent communication opportunities, lower communication latency, and faster retransmission possibilities. This can be relevant where timing affects usability, measurement quality, or control behavior.

The optional flush functionality is also significant for time-sensitive data. It allows outdated data to be discarded so that stale traffic does not block newer information. This is particularly relevant for sensor data, input events, or other information that loses value quickly.

Performance Requires System-Level Design

SCI does not automatically make every Bluetooth LE product faster or more efficient. Developers still need to consider power consumption, application timing, and connection behavior.

Nordic Semiconductor notes that Bluetooth Frame Space Update, introduced in Bluetooth Core 6.0, is recommended to fully use SCI’s potential. Connection Subrating is also important, since it allows devices to skip connection events when no data needs to be sent.

For battery-powered devices, the practical design task is to balance high update rates with energy efficiency. The source text notes that 1 kHz can be a useful balance point for ultra-low-latency HID devices, depending on the use case.

Company Involvement

The source material identifies Logitech and Nordic Semiconductor as companies involved in the development and adoption of Bluetooth SCI. Logitech participated in Bluetooth SIG working groups, while Nordic Semiconductor describes SCI as a feature that affects its Bluetooth product portfolio and customer base.

Both examples indicate that SCI is moving from specification work into practical product planning. For OEMs, silicon vendors, and integrators, this makes SCI a relevant feature to track when evaluating future Bluetooth LE designs for latency-sensitive applications.

Read More

Read more in the Bluetooth SIG articles “Bluetooth Shorter Connection Intervals: Paving the way for Bluetooth innovation” and “How Bluetooth Shorter Connection Intervals will impact the next generation of wireless innovations.”