Sensor Time Stamp Correction via Statistical Averaging

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Solution Overview

Problem

Existing time stamp correction methods for sensor data in IoT networks face errors due to time shifts between master and slave devices, and low-accuracy oscillators in sensors, leading to inaccuracies in time synchronization, especially in wearable devices.

Innovation Solution

A sensing system with a sensor terminal using a real-time clock circuit and a data collection terminal with a reference clock generation circuit, where the sensor terminal counts a sensor clock and adds the count value to packets, and the data collection terminal recalculates time stamps based on packet transmission intervals and reference arrival times using statistical processing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a simple time stamp mechanism using an incremental counter is provided in the sensor, then monotony is guaranteed and packet loss can be recognized, but the accuracy is low and an error of several seconds occurs in one day

Engineering Contradiction:

Improvemonotony guaranteeVSAvoidtime stamp accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent introduces a data collection terminal as an intermediary that performs the time stamping function. Instead of relying on the sensor terminal's low-accuracy oscillator, the data collection terminal uses a more accurate time source to generate time stamps for received packets, thereby improving time stamp accuracy while the sensor terminal maintains its simple incremental counter for monotony guarantee

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the sensor terminal's hardware oscillator-based time keeping mechanism with a software-based time stamping mechanism at the data collection terminal. This substitution allows the use of more accurate time sources and statistical processing to achieve better time accuracy without requiring high-performance hardware clocks in the sensor terminal

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If the accuracy of the time stamp of the data collection terminal is very high, then synchronization can be applied to the upper network at a level to 1 ms or less, but if a transmission delay occurs, the delay causes an error in the time stamp

Engineering Contradiction:

Improvetime stamp accuracyVSAvoidtime stamp error under transmission delay

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where the data collection terminal performs statistical processing on multiple time stamps and their corresponding incremental counter values. By analyzing the relationship between these paired values and calculating transmission intervals, the system can identify and compensate for transmission delays, thereby maintaining time stamp accuracy even when delays occur

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent performs preliminary statistical processing and analysis of multiple packets to establish the relationship between incremental counter values and time stamps before final time stamp assignment. By pre-calculating transmission intervals and detecting delays through statistical patterns, the system can correct time stamps in advance or in real-time, preventing delay-induced errors

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If a time stamp is added by a data collection terminal, then a reference time concerning sensing can be obtained, but a delay time concerning communication between a sensor and the data collection terminal cannot be canceled and an error is always generated in the time stamp

Engineering Contradiction:

Improvereference time accuracyVSAvoidcommunication delay error

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent uses feedback through statistical processing of multiple packets to detect and compensate for communication delays. By analyzing the correlation between incremental counter values (which are delay-free) and time stamps, the system can calculate and subtract the average transmission delay from subsequent time stamps, thereby eliminating the systematic error introduced by communication delays

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the approach from using raw time stamp values to using statistically processed time stamp values that have been adjusted based on observed transmission patterns. By dynamically adjusting the time stamp parameter through statistical analysis of multiple packets, the system compensates for communication delays and provides more accurate reference times

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11284229B2Sensing system and time stamp correction method

Publication Date: 2022.03.22 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

A sensor control circuit periodically transmits packets in synchronism with a one-by-one monotonous change in count values from a real-time clock circuit. The count values repeat the change within a predetermined numerical value range. The sensor control circuit transmits the count values by adding them to the packets. A collection control circuit acquires values of a reference clock synchronized with a reference time of an upper network from a reference clock generation circuit in accordance with reception of the packets, stores the values in a storage circuit as time stamps representing arrival times of the packets, performs statistical processing of the time stamps and the count values concerning the packets received, and corrects the time stamps based on an packet transmission interval and a reference arrival time representing the arrival time of a head packet, which are obtained from the statistical processing.