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Measure Cellular Signal Strength to Keep IoT Devices Connected

When most people think about the cellular system, they think about smartphones and how they help us keep in touch and retrieve information. As engineers looking to deploy an Internet of Things (IoT) network of devices, we see a whole other side. We see dropped signals, delays in mission-critical information, and many possible sources of interference. This isn’t good given that IoT networks connect not just light switches and smart home devices, but also critical systems controlled by governments, municipalities, and industry. However, a little analyzer used during deployment can go a long way toward avoiding incidents due to lost signals.

Figure 1: The SNYPER-LTEM Graphyte can measure the signal strength from classic 2G/3G and LTE network base stations, as well as signals in Cat M and LTE Cat NB IoT bands. (Image source: Siretta)

For sure, there are many technologies, including Wi-Fi and Bluetooth, that can be used to connect IoT devices to the internet, but there are four compelling reasons to use the cellular network, including:

  1. Cost: Cellular carriers have made massive investments in their networks and the competition among carriers has made cellular service very cost-effective.
  2. Availability: Cellular now covers more than 90 percent of the world’s population, and U.S. carriers claim 99%+ LTE coverage.
  3. Range: Cellular networks provide greater range than many other IoT technologies, such as Wi-Fi and Bluetooth.
  4. Licensed bands: Operating in licensed bands of the spectrum helps minimize interference.

To ensure the cellular network is robust and signals are strong where you plan to install an IoT system, you need to measure cellular signal strength levels. The Siretta SNYPER line of signal analyzers takes the mystery out of making these measurements. These handheld instruments allow you to quickly find and measure signal strengths from 2G/GSM, 3G/UMTS and 4G/LTE, and now Cat M and Narrowband IoT (NB IoT) network base stations. With this information you can decide which network operators will best meet your needs and where to put antennas for maximum performance.

For IoT connections over classic cellular networks, the SNYPER-LTE Graphyte covers 4G/LTE and 3G/UMTS bands. However, for IoT-specific bands, the SNYPER-LTEM Graphyte covers 4G/LTE Cat M, LTE Cat NB IoT, and 2G/GSM (Figure 1).

IoT keeps traffic moving

One example of how you might use the cellular network to control a real-world device is the traffic control system shown below. A cellular modem connected to the traffic light’s control box to communicate with a server that is programmed for traffic control management. Via this connection, the server can set the timing of the traffic light depending on the time of day, thereby improving traffic flow.

The traffic light can also communicate with the server. For example, if the traffic light had traffic monitoring capabilities, it could stream traffic information over the network back to the server in real time. This would allow the system to make timing adjustments to this light and adjacent lights to allow traffic to flow more smoothly. It would also allow the traffic light to report any problems detected by the system, enabling repair crews to get to the site more quickly to resolve the problem and keep traffic flowing (Figure 2).

Figure 2: To reliably connect devices and systems to the internet via a cellular network you must ensure that signals are strong. (Image source: Siretta)

Signal strength is key

While the cellular network is nearly ubiquitous, it’s not without problems: dropped calls tell us that every day. Still, walk a few feet and you get a decent signal again. Unfortunately, our traffic light can’t do that. So, when you install a system like this, you need to ensure that there’s ample signal strength for it to reliably communicate. Intermittent signals and low signal levels result in poor system performance, slow response times, and reliability issues. Some cellular modems can indicate signal strength, but only report on the connection available to them. That’s really not enough information for deciding on what service provider to use or where to place an antenna.

The Siretta SNYPER cellular signal strength analyzer can do this for you. These handheld instruments are network independent, meaning that you can measure and analyze the signal strength of all available networks at a particular location, and the SNYPER can do this without the need to buy a SIM for each network. Figure 3 shows how you might use a SNYPER to perform a cellular site survey.

Figure 3: The Siretta Snyper can measure signal strengths from a number of different base stations and help you quickly decide which network is best for your application. (Image source: Digi-Key Electronics)

The SNYPER can measure the signal strength of all the base stations in the area and provide a summary, including their relative signal strengths and number of cells available. This information allows you to very quickly make a decision about the best network to use for your application in the area, and to determine what options you have with regards to secondary backup networks.

Some models offer USB mass storage, allowing you to save up to 50 full network surveys directly on to the unit. This feature is an invaluable tool for maintenance engineers and system installers that greatly improves productivity by allowing them to remain out in the field all day long, going from site to site and performing multiple surveys.

The Siretta SNYPER can also help you position antennas for maximum signal strength. This may mean moving the antenna further away from the cellular modem or positioning it higher up by mounting to a wall or pole.

In some cases, you may want to use a directional antenna, such as a Yagi, to improve signal strength. To use a Yagi, you will of course need to know where to point it. By using a SNYPER with a directional antenna, you can not only measure signal strength, but also locate the position of the network basestations in the area. Using this information you can point the Yagi in the right direction.

Conclusion

For many engineers who may not be RF experts, measuring signal strength is somewhat of a black art. The Siretta SNYPER de-mystifies the process, allowing you to quickly and accurately measure 2G, 3G and 4G signal strength, choose the right cellular network for your application, and position antennas properly. The end result is a reliable IoT installation for which motorists will be most grateful.

About this author

Image of Dan Romanchik

Dan Romanchik is an electronics engineer, freelance writer, and well-known amateur radio operator. He has written for many high-tech companies, and his articles have appeared in IEEE Spectrum, Electronic Design, Electronic Components, and Machine Design. Before becoming a freelance writer, he was Senior Technical Editor for Test&Measurement World, where he covered nearly every aspect of electronics test and measurement. Prior to that he was test engineering manager for a division of a large telecom company.

He is the author of five amateur radio books, including three that make up the “No Nonsense” series of amateur radio license study guides, the CW Geek’s Guide to Having Fun with Morse Code, and 21 Things to Do After You Get Your Amateur Radio License. He teaches amateur radio classes, both in person and online, and regularly gives presentations to amateur radio clubs on a variety of topics. He blogs about amateur radio on his website, KB6NU.Com.

Dan has a BEEE from the University of Detroit and an Amateur Extra Class amateur radio license (callsign KB6NU). He is a member of the Institute for Electrical and Electronics Engineers (IEEE) and the Association for Computing Machinery (ACM).

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