BLE Clock Synchronization via Scan Command and Broadcast

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Solution Overview

Problem

Bluetooth Low Energy (BLE) networks face challenges in clock synchronization due to the long connection interval, leading to random and non-deterministic delays in data exchange, which limits synchronization accuracy to below 1 ms necessary for applications like sensor networks measuring brain activity.

Innovation Solution

A method involving a master device sending a scan command and broadcasting data with a time stamp, allowing slave devices to reset their clocks accurately, with optional configurations for specifying scanning and broadcasting periods, and verifying synchronization through subsequent time stamp exchanges.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the connection interval is extended to save power, then energy consumption is reduced, but synchronization accuracy deteriorates due to random delays up to 7.5 ms

Engineering Contradiction:

Improvepower consumptionVSAvoidsynchronization accuracy

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

The master device sends a scan command to the slave device before the actual data exchange, causing the slave device to enter scanning mode and prepare its receiver in advance. This preliminary action ensures that when the broadcast data arrives, the slave device is already ready to receive and process it immediately, eliminating the random delay that would otherwise occur while waiting for connection events.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses periodic broadcasting at predetermined intervals instead of relying on connection-based periodic communication. The master device broadcasts data containing timestamps at regular intervals, and slave devices scan for these broadcasts periodically, creating a deterministic timing pattern that enables accurate synchronization while maintaining power savings.

Inventive Principle:

Principle #19Periodic action

2Duration of action of stationary object

If connection events occur infrequently to maintain low power mode, then battery life is extended, but data exchange timing becomes non-deterministic with delays up to 7.5 ms

Engineering Contradiction:

Improvebattery lifeVSAvoiddata exchange delay

Core Design Contradiction:

Duration of action of stationary objectVSLoss of time

Solution Approach 1:

The slave device enters scanning mode continuously or periodically to continuously monitor for broadcast data from the master device. This continuous scanning action ensures that data exchange can occur immediately when broadcast, eliminating gaps and random delays while maintaining the slave device in a low-power state between scanning intervals.

Inventive Principle:

Principle #20Continuity of useful action

Solution Approach 2:

The broadcast data acts as an intermediary carrier that conveys timestamps and synchronization information from the master device to slave devices. This intermediary mechanism enables deterministic timing without requiring continuous connection events, as the broadcast data encapsulates all necessary timing information that slave devices can process immediately upon reception.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If standard BLE connection protocol is used for time stamp exchange, then compatibility is maintained, but synchronization accuracy is limited to within 1 ms due to connection interval constraints

Engineering Contradiction:

Improveprotocol compatibilityVSAvoidtime stamp accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The synchronization process is segmented into distinct phases: scan command transmission, scanning mode activation, broadcast data transmission with timestamps, and clock resetting. This segmentation allows each phase to be optimized independently, with the scan command initiating a dedicated synchronization sequence that is separate from regular data exchange, enabling microsecond-level accuracy while maintaining BLE protocol compatibility.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system changes the operational parameters of the slave device by setting it to scanning mode with specific scanning intervals, and the master device broadcasts at predetermined intervals with precise timestamps. These parameter changes create a deterministic timing pattern that overrides the random delays inherent in standard connection-based communication, achieving sub-millisecond synchronization accuracy.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS10462759B2System and method for clock synchronization on a wireless network

Publication Date: 2019.10.29 DIALOG SEMICONDUCTOR BV

AI summary

A method of synchronizing the clocks of a master device and at least a first slave device which are connected on a wireless network. The method includes sending a scan command from the master device to at least the first slave device, setting the master device to a broadcast mode and broadcasting data, the broadcast data comprising a first time stamp; scanning the broadcasting data at at least the first slave device and resetting the clock of the first slave device using the first time stamp. In particular, but not exclusively, the present disclosure relates to synchronizing the clocks of two devices which are connected on a Bluetooth Low Energy (BLE) wireless network.