Update to Cloud Connector Cellular Signal Strength Indicator - A Better Measure Of Signal Quality

Today, we are improving the way all 4G Cloud Connectors report cellular signal strength to give customers a more accurate indication of the robustness of the installation.

The quality of the cellular connection between a Cloud Connector and DT’s cloud service depends on a number of factors:

• the distance to the nearest base station
• how much radio noise there is in the area
• network congestion
• placement and orientation of the Cloud Connector. 

Much like a smartphone, the 4G Cloud Connector contains an LTE cellular modem that can report a number of different metrics related to the quality and signal strength of the cellular connection. Until now, 4G Cloud Connectors have only used the Received Signal Strength Indicator (RSSI) to indicate the signal quality, represented by 4 dots on the display and as a percentage in DT Studio.

RSSI describes how much power there is in the signal received from the base station. Traditionally, RSSI is used to determine the signal quality because it is always available, regardless of whether the cellular modem is connected to 2G, 3G, 4G, or 5G. However, it does not represent the quality of the received signal. 

This is analogous to how a rock concert can be loud and at the same time sound distorted or too bass-heavy. As some of our customers have experienced, despite seemingly good cellular connection reported by the Cloud Connector, the cellular connection can still be fragile and sensor events may not show up in Studio.

Update to CCON Cellular Signal Strength Indicator

We strongly believe that a robust connection and good observability are critical for a successful IoT sensor deployment. This is why we have collected tens of thousands of data points from our fleet of 4G Cloud Connectors to assess how we can use the various metrics reported by the cellular modem to improve the signal quality indicator for our customers. 

Today, we are launching a new signal quality estimation scheme that not only better reflects the real-world performance, but is tailor-made for our 4G Cloud Connectors. We have developed it with inspiration from the Android Open Source Project. 

How Does The Cloud Connector Update Work

The cellular modems used in our 4G Cloud Connectors report several other metrics related to the cellular connection in addition to RSSI. The three metrics of interest are RSRP, RSRQ, and SINR.

• Reference Signal Received Power (RSRP) is a 4G-specific measurement that represents the average power of cell-specific reference signals. In our 4G Cloud Connectors, RSRP is nearly directly proportional to RSSI.
• Reference Signal Received Quality (RSRQ) aims to describe the quality of the received signal, and takes into account the RSSI, RSRP, and how much of the available bandwidth is used.
• Signal to Interference plus Noise (SINR) is yet another measure of the quality of the cellular connection. In contrast to RSRP and RSRQ, which are defined by the standards organization that writes the technical specifications for cellular networks, SINR is defined by the modem vendors themselves. 

For in-depth information about these parameters, you can see ETSI TS 36.214.

A common method of finding the overall signal quality based on these parameters is to compare them with pre-defined limits for “good”, “moderate” and “poor” quality. The parameter with the worst performance determines the final signal quality. This method works well, but the obvious question is: what limits are appropriate for these parameters?

We have taken an empirical approach and looked at the historical performance of our 4G Cloud Connectors. This enabled us to determine the range in which each parameter varies and how the parameters correlate with one another. Interestingly, the EU 4G and US 4G Cloud Connector models behave very differently, thus we have followed a tailored approach.

What The Cloud Connector Update Means For You

One important thing to note about this new signal quality indicator is that it is stricter than the previous RSSI-based implementation. This means that your Cloud Connectors will now report lower signal quality than previously. 

On average, the EU 4G models will report ~22 % lower signal quality than before, and the US 4G models will report ~33 % lower signal quality. This change is purely visual. There is no change in the quality of the Cloud Connector cellular performance. It is only intended as a more accurate representation of the actual performance of the cellular connection.