How cellular and RF mesh systems work
Let’s look at two of the most popular and effective communications architectures for connected street lighting: cellular and RF mesh.
In a cellular system, each streetlight connects directly to a mobile network operator’s public cellular network for two-way data communications with the CMS in the cloud.
In an RF mesh system, on the other hand, a certain number of adjacent streetlights—typically 15, but as many as 32—create their own device-to-device network, allowing them to share data with one another. The streetlight with the strongest signal in the group sends all information to a gateway, which is usually a device installed inside a NEMA-rated enclosed cabinet somewhere on the street. Communications between the gateway and the CMS can either be a wireless cellular connection, or a wired connection via Ethernet LAN or fiber.
Both cellular and RF mesh offer the set of capabilities necessary for good street lighting operations—including range, throughput, and reliability—but they have different pros and cons which deserve careful consideration. Here are a few.
Licensed vs. unlicensed frequencies
One important consideration is type of network: licensed or unlicensed.
Cellular networks use licensed frequencies employed by mobile network operators (MNOs), such as Verizon and AT&T. The good news here is that the MNOs pay for the licensed spectrum, the technology is standardized and proven, and the networks are managed and maintained by the MNOs themselves.
Unlike cellular, RF mesh uses unlicensed communications frequencies (at 868 or 915 MHz). This means that you can create your own private network wherever you like, as long as the network complies with existing standards and the communications frequencies are approved in the country of use.
One potential disadvantage for cellular networks are periodic changes in standards. If your system uses the 2G network, for example, you would need to modify or upgrade your hardware if the MNO decides to phase out the 2G network in your city. Similarly, you would need a hardware change if you wanted to take advantage of new 5G capabilities when they come online. But major network changes like these occur very infrequently, and they happen very slowly when they do, so there’s little benefit in delaying a needed implementation to align with a future shift in cellular standards.
Some providers claim that, as 20-year networks, mesh networks are less subject to changes in standards or technology than cellular networks. In practice, however, the lifetimes of cellular standards are comparable: 2G was introduced almost 30 years ago, 3G almost 20 years ago, and 4G over 10 years ago, and they are all still available as of today.