Tech Journal

Making the Most of the Unlicensed Spectrum

Posted by Frank Gielissen and Maarten Weyn (Aloxy) on Jun 22, 2020 12:00:00 AM

Low Power, Wide Area Networks (LPWANs) are key to the success of Internet of Things (IoT) deployments that need to cover a broad geographical area. LoRaWAN® is an open protocol for one type of LPWAN, while DASH7 is another. Both use the unlicensed spectrum and together they offer complementary benefits.

The “unlicensed spectrum” refers to the portion of the RF spectrum that people and companies can broadcast over without a license from a government agency. Generally, the portion of the unlicensed spectrum used for the IoT falls in what is known as the “ISM band” — the share of the RF spectrum that is reserved for industrial, scientific and medical purposes. In the EU, both LoRaWAN and DASH7 use the 868 MHz band (915 MHz in the U.S. and Australia; 923 MHz in Asia). Additionally, both are deployed in a star-of-stars topology, where transmissions from multiple devices can be received by multiple gateways.

LoRa® and LoRaWAN

Operating on the physical (PHY) layer, LoRa® is a proprietary RF modulation technology for LPWANs. It is derived from existing chirp spread spectrum technology and uses six orthogonal data rates, or spreading factors (SF7 – SF12) for long range data transmissions: up to three miles (five kilometers) in urban areas, and up to 10 miles (15 kilometers) or more in rural areas (with a clear line of sight), although distances are much shorter in highly industrial areas that include many metal structures. The larger the spreading factor used, the farther the signal will be able to travel and still be received without errors by the RF receiver.

When it comes to capacity, the number of messages supported in any given LoRaWAN deployment depends upon the number of gateways that are installed. While there is no one-to-one relationship between LoRa-based devices and gateways in a LoRaWAN network, a single eight-channel gateway can support a few thousands of messages over the course of a 24-hour period. If each end device sends 10 messages a day, such a gateway can support about 10,000 devices. You will notice, though, that 10 messages a day per device really is not that many. This is where DASH7 comes in.

DASH7

Also operating on the PHY layer, DASH7 uses Gaussian Frequency-Shift Keying (GFSK) modulation. It also uses a higher data rate than LoRaWAN, which leads to shorter transmission ranges and the need for a denser network of gateways. That higher data rate is great for maximizing battery life, thanks to the fact that DASH7 transmissions require a shorter time on air. This allows a greater number of transmissions over the same time period and thus improving scalability, without battery drain.

The higher data rate and the listen-before-talk methodology increases the number of confirmed messages and limits the number of collisions, creating a more reliable network.

Better Together: Dual Modality

Aloxy has developed a DASH7 communication module that can be added to a MultiTech LoRaWAN-based gateway and which allows communication over both protocols, thus enabling the best approach for an application based on network conditions and application requirements. Where LoRaWAN is great for meter reading, for example, DASH7 may better suited for valve monitoring. Similarly, you might choose LoRaWAN functionality when monitoring temperature trends, and DASH7 features when more symmetric uplinks and downlinks are required.

Aloxy has already entered the market with such dual deployment scenarios. In one instance, it developed an affordable, plug-and-play wireless solution to increase the safety of error-prone manual valve operations in the chemical industry. This dual deployment realized the following benefits:

  • Longer-range communications than those available with Wi-Fi
  • LPWAN approach is very well-suited for industrial environments
  • Good balance of trade-offs between transmission data rates and battery power consumption
  • On-premise deployments can implement multiple protocols, allowing the most suitable protocol to be used for a given application
  • Ability to switch between LPWAN technologies in case it better fits the new conditions

For this solution, Aloxy opted to use the ruggedized and highly-scalable MultiTech Conduit IP67 base station for the gateway. The Conduit IP67 uses a multi-modal module that supports the use of multiple, simultaneous radio technologies, including both LoRaWAN and DASH7 protocols. And, thanks to this dual deployment, the industrial workers in this case now have a safer environment in which to operate.

Conclusion

While LoRaWAN and DASH7 each have their own place in the IoT ecosystem, when deployed together these complementary technologies can provide great benefits for industrial customers.

 

 

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Topics: LoRa Developers, LPWAN