Sensor Timestamp Difference Resend for LLN Accuracy
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Solution Overview
Problem
Constrained sensors in Low-Power and Lossy Networks (LLNs) face challenges in providing accurate timestamps for buffered measurements without additional hardware or frequent network synchronization, as they lack mechanisms for tracking absolute time and are resource-constrained.
Innovation Solution
A device transmits sensor measurements with associated timestamps based on its internal clock, determines timestamp differences for missed measurements, and resends them with these differences to ensure accurate temporal context without requiring GPS, real-time clocks, or periodic network syncing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensor is equipped with network time synchronization protocol capability to provide accurate timestamps, then timestamp accuracy is improved, but resource consumption (power, computational burden, bandwidth) increases
Solution Approach 1:
The patent introduces an intermediary timestamp difference value that bridges the gap between unsynchronized sensor timestamps and application-level time reference. Instead of synchronizing the sensor clock itself, the system calculates and transmits the difference between the sensor's local time and the network time, allowing the application to reconstruct accurate timestamps without requiring the sensor to run synchronization protocols
Solution Approach 2:
The patent extracts the timestamp synchronization problem from the sensor device and relocates it to the application layer. The sensor only needs to provide its local timestamp and the time difference value, while the actual time synchronization computation is performed externally by the application, removing the burden of time synchronization hardware and protocols from the constrained sensor
2Device complexity
If a sensor periodically offloads measurements to another device for processing, then computational burden on sensor is reduced, but loss of contemporaneous data transmission occurs
Solution Approach 1:
The patent applies preliminary action by having the sensor calculate and attach the timestamp difference value to each measurement data packet before transmission. This pre-computation ensures that even though data transmission is delayed and batched, the temporal context information is already prepared and preserved, eliminating the need for real-time synchronization during periodic offloading
Data Source
AI summary
In one embodiment, a device may transmit, via a network to an application, a series of sensor measurements captured by the device, each sensor measurement having an associated timestamp based on a clock of the device. The device may receive, from the application, an indication that at least a portion of the series of sensor measurement were not received by the application. The device may determine, for those sensor measurements not received by the application, timestamp differences between their timestamps and a current time of the clock of the apparatus, after receiving the indication. The device may resend the portion of the series of sensor measurements to the application and their timestamp differences.