LPWAN Measuring Device Clock Synchronization via Cellular Time Comparison
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Solution Overview
Problem
Utility providers face challenges in obtaining accurate and reliable clock time information for consumption meters using public cellular communications networks, which introduce high and unpredictable communication latencies, affecting the accuracy of Network Time Protocol (NTP) responses.
Innovation Solution
A stationary measuring device with a Low Power Wide Area Network (LPWAN) communication module that sends a request for clock time to a time server, receives and compares it with cellular network time from a base station, determining the current clock time based on pre-determined ranges and round-trip times to mitigate latency issues, using NTP time as the primary source when cellular network time is unreliable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a public cellular communications network (LPWAN) is used to collect consumption data, then the infrastructure cost is reduced, but the communication latency becomes high and unpredictable, affecting the accuracy of NTP time responses
Solution Approach 1:
The device performs a preliminary action by receiving the cellular network time from the base station before requesting NTP time from the time server. This preliminary time reference is stored and used to select an appropriate time server and to evaluate the reliability of the NTP response, thereby compensating for the high and unpredictable latency inherent in LPWAN networks.
Solution Approach 2:
The cellular network time from the base station acts as an intermediary reference. Instead of directly relying on the NTP response which suffers from high latency, the device uses the cellular network time as a mediator to verify and adjust the NTP time, ensuring accurate clock synchronization despite the unreliable communication channel.
2Ease of operation
If NTP is used to obtain current clock time, then time information can be retrieved, but the high communication latency in LPWAN networks makes the NTP response inaccurate
Solution Approach 1:
The device implements feedback by continuously monitoring the cellular network time from the base station and comparing it with the NTP time received from the time server. Based on this feedback, the device determines whether to use the NTP time or adjust it using the cellular network time reference, thereby ensuring reliable timekeeping despite latency issues.
Solution Approach 2:
The device performs a preliminary action by receiving the cellular network time from the base station before requesting NTP time from the time server. This preliminary time reference is stored and used to select an appropriate time server and to evaluate the reliability of the NTP response, thereby compensating for the high and unpredictable latency inherent in LPWAN networks.
3Loss of time
If cellular network time from base station is used, then communication latency is reduced, but trust issues arise because the LPWAN infrastructure is controlled by external parties
Solution Approach 1:
The device merges two time sources: the cellular network time from the base station and the NTP time from the time server. By combining these sources and comparing them, the device leverages the low-latency advantage of cellular network time while using the NTP time as a trusted reference to verify accuracy, thus resolving the trust issue.
Solution Approach 2:
The cellular network time from the base station acts as an intermediary reference. Instead of directly relying on the NTP response which suffers from high latency, the device uses the cellular network time as a mediator to verify and adjust the NTP time, ensuring accurate clock synchronization despite the unreliable communication channel.
Data Source
AI summary
A stationary measuring device (7) measures or detects a value at a utility installation. The measuring device includes a low power wide area network (LPWAN) communication module configured to establish a wireless communication connection to a LPWAN for communicating data to a head-end-system (HES) (3) via the LPWAN. The LPWAN communication module is configured to: send a request for a first clock time from the measuring device to a time server; receive the first clock time from the time server in response to the request; receive a second clock time from a base station of the LPWAN; compare the first clock time and the second clock time with each other; and determine a current clock time based on the second clock time if the second clock time lies within a pre-determined range about the first clock time.