Transferring data over the airwaves has been commonplace since at least 1997, when the 802.11 standard entered the scene. In some specific applications, it’s been around even longer than that. The 802.11 standard has evolved since its debut at 2Mbit/s, today reaching speeds nearing 10 Gbit/s via 802.11ax (a staggering 5000-time increase).
While the advances in speed are shocking, we haven’t seen the same progress on the distance this data can travel. Distance has remained comparatively static, reaching out to somewhere around 150 feet indoors or 300 feet unobstructed. While you can, for example, connect to your wireless router throughout a medium-sized house, you won’t be able to connect to much beyond the four walls of your home.
For long-range data transfer, there’s always the option of using the cellular network. But what if you need an array of sensor nodes for IoT monitoring outside of Wi-Fi range? Providing cell modems and data service for many sensors spread over a large farm, for instance, would soon become cost prohibitive. Wi-Fi and cellular data speeds are overkill in situations where you’re only transferring small bits of data a few times per hour or even per day. In this space, Long Range Wide Area Network (LoRaWAN) systems, which can transfer small amounts of data several kilometers or more, may be a perfect fit.
How LoRaWAN Works
LoRaWAN operates on the license-free industrial, scientific, and medical radio band (centered on 915 MHz in North America). This means there is no monthly data charge to use it and you can set it up anywhere, though the required radio band may be different depending on your location. In its simplest implementation, two or more LoRaWAN transceivers, like those implemented in Arduino’s MKR WAN 1300, can talk directly to each other.
Taking this concept further, you can also use a LoRaWAN Internet gateway. The gateway transfers data collected from an array of sensors to the cloud using a wired connection (or via Wi-Fi or a cellular connection). From there, you can display and use the data in a wide variety of scenarios.
We can use this data in many different applications from farm work to urban monitoring, such as to:
- Indicate whether garden beds or lawns need watering
- Check the status of or activate an automatic gate
- Monitor cow or another animal movement
- Deployed to track taxis
- Monitor the status of parking spaces
- Read utility meters
While LoRaWAN isn’t appropriate for data-intensive tasks like Wi-Fi, a LoRaWAN system’s range is very useful in low bandwidth, long-range scenarios.
LoRaWAN Range Details
While you’ll often see LoRaWAN ranges described in “kilometers,” figuring out exactly how many kilometers of range it has can be a little trickier. It may be five kilometers, ten kilometers, or more. Transmission range varies dramatically depending on where you’re taking the measurement and how the signal is optimized.
LoRaWAN works on the 125, 250, or 500kHz bandwidth, and in the US these bands are centered on 915MHz, ranging from 902 to 928Mhz. This frequency range is divided up into 64 125kHz channels, along with 500kHz uplink channel and 500kHz downlink channels. Wi-Fi also operates at several different channels at either 2.4 or 5GHz, but the lower frequencies used by LoRaWan allow for a much longer transmission range.
LoRaWAN communication takes place as a series of “chirps.” Specific frequency range emitted within a channel’s bandwidth designates a numeric symbol and thus a binary sequence, known as “upchirps” and “downchirps.”
- Upchirps. These are created when the US LoRaWAN channel operates at the 914.9 MHz specification and 125kHz bandwidth. The channel produces chirps that range from a minimum of 914,837.5kHz to 914,962.5kHz.
- Downchirps. These are the opposite of upchirps, and they transmit from a high frequency to a low frequency for signaling.
We can define each chirp by a spreading factor (SF) from 7-12, which defines both the number of bits in a chirp and how long each chirp takes. For each shift in level, we know that the length of time a chirp takes will double. Here are three examples:
1. Defining 7 as the base spread factor of 1 time period (TP), you’d transmit 7 bits of data in 2^0 or 1 TP.
2. Spread factor 8 would transmit 8 bits in 2^1 or 2 TP.
3. At a spread factor of 12, time would be 2^5, or 32 TP, while transmitting 12 bits, giving .375 bits/TP. Conversely, a spread factor of 7 would give 7 bits/TP or 18.67 times the bandwidth of a spread factor of 12.
Bandwidth factors into this linearly as well, giving a bit rate in bits per second equal to SF times (1/[2SF/BW]) bits/second, though these equations and calculations ignore error correction features. We can optimize this using an adaptive data rate (ADR). The ADR will optimize the proper settings for range, data rate, and power usage.
A range of a few kilometers is impressive, but consider that Swiss electronics YouTuber Andreas Spiess set the world record for a LoRaWAN connection in February 2017, communicating between base stations spaced an astounding 212 km, or over 131 miles away from each other. Later that year, however, a balloon launched in the Netherlands was able to communicate from over 702km away.
Long-range Wi-Fi is possible, but unlike LoRaWAN, achieving it requires properly focusing directional antennas. We may be able to attain data rates in the hundreds of Mb/s over hundreds of kilometers, though we will run into several complicating factors:
1. Portability is virtually nonexistent.
2. Setup is much more involved.
3. Power efficiency is very much a secondary concern when compared to LoRaWAN modules that may need to run on remote power.
So how does LoRaWAN compare to Wi-Fi? As we’ve explored here, it’s both much better and much worse. Put simply, LoRaWAN boasts tremendous abilities when you need long range, but it can’t compare with Wi-Fi when it comes to data rates. One potential competitor may eventually be cellular data, which boasts both excellent range and good data speeds.