Link Labs is a leading manufacturer and integrator of systems that rely on LoRa. We hear a lot of questions about LoRa—so we’ve compiled some of the most frequently asked questions into this article. We hope this will help you understand what LoRa is, what it is not, and how it may be able to help you.
1. What is LoRa? What makes it such a great technology?
LoRa is a unique modulation format that can be generated by Semtech LoRa parts, including the SX1272 and SX1276 transceiver chips. It’s a really inexpensive, efficient way to get processing gain in a small chip-scale transceiver. It works with a family of highly integrated base station chips (SX1301 and SX1257) with high capacity, so you can use it to build pretty sophisticated point to multipoint networks. (Learn more about LoRa in this comprehensive article.)
LoRa is a modulation format and the associated family of chips from Semtech. SIGFOX is a company that uses narrowband BPSK modulation to do wide-area IoT networking. NWave is a company that does some very similar things to SIGFOX using the Weightless standard. Other ultra-narrowband companies work with a broader family of transceiver chips, but LoRa is available only from Semtech.
3. Is LoRa a Spread Spectrum Technology?
LoRa is a spread spectrum technology, but it is not a direct sequence spread spectrum technology. Direct sequence spread spectrum is modulating the carrier with chips/symbols to spread the transmission across more spectrum, which increases coding gain and symbol depth. LoRa uses an unmodulated carrier in an FM chirp, which has similarities to M-ary FSK. So it is spread energy across a wider band, but not in the same way DSSS is.
4. What is the difference between SX1272 and SX1276?
SX1272 has three programmable LoRa bandwidth settings: 500 kHz, 250 kHz and 125 kHz. It only covers bands from 850-1GHz. SX1276 has bandwidths from 500 kHz to 7.8 kHz, and offers slightly better receive sensitivity. It covers 150 MHz bands, 433MHz, and 850-1GHZ.
5. Can I use LoRa at frequencies other than 868 MHz and 915 MHz in licensed spectrum?
You can transmit and receive the LoRa modulation at many frequencies between 150 MHz and 1 GHz—like at 169 MHz, 433 MHz, etc.—even in licensed spectrum. However, most of the LoRa chips from Semtech have pretty large holes in the sub-GHz band where they can’t transmit or receive. The Semtech basestation architecture is designed to operate only at 850 MHz to 1 GHz.
6. What is the Semtech SX1301 LoRa chip?
The SX1301 chip is the baseband signal processor for LoRa. It takes 1 bit I/Q digital baseband samples as an input. It is generally paired with two SX1257 front end digitizers, though it can be used with other forms of digital RF. This is often done with the 8xSX1301 gateway architecture Senet uses in its network deployment.
7. Why should I use a module? If there is open source code on GitHub, can’t I just use that?
There are two primary reasons you should use a module:
- It accelerates development, and you don’t have to write a whole bunch of underlying code to implement the radio system.
- It’s already fully FCC certified, so you don’t have to go through expensive testing.
The open source code available online for LoRaWAN is enough to transmit and receive the packets, but there are a lot of features of the host interface and other things that aren’t fleshed out.
8. Do I need a gateway if I’m just doing a few endpoints?
No, you do not need a gateway. You can easily implement simple protocols using LoRa, either with modules or with the chips themselves.
9. Why can’t I use LoRa in a mesh topology?
You could, actually, but you would need to convert an existing 802.15.4 or other mesh protocol to use the modulation format. Because of some of LoRa’s features, like long preambles and variable bit rates, this would be a serious engineering feat.
10. Is LoRa only for wide-area networks?
No, it’s not. LoRaWAN as a protocol is strictly for wide-area networks, but LoRa as a lower-level physical layer technology (PHY) can be used in all sorts of applications outside of wide area.
11. I have an existing RS-232/cellular/ZigBee-based system. Can I just plug in a LoRa Module and get the extra range?
Almost. There are changes required at the host interface and specifications for transmitting data in a LoRa system that require changes to the host system software. In fact, helping customers transition other types of connectivity to LoRa is a problem we work on most days at Link Labs..
12. What is LoRaWAN?
LoRaWAN is a media access control (MAC) layer protocol designed for large-scale public networks with a single operator. It is built using Semtech’s LoRa modulation scheme. This article, What Is LoRaWAN?, will walk you through how it works, why it’s ideal for public networks, chirp rate, processing gain, downlink and uplink capabilities, and much more.
13. What is the LoRa Alliance?
The LoRa Alliance is a group of companies focused on making LoRaWAN successful for wide-area networks. Link Labs is a proud member of the LoRa Alliance.
14. Can LoRa be used for geolocation?
To some extent, yes. But we invite you to read Wireless Position Location: Implementation Strategies, and Sources of Error to learn more about this. Specifically, take a look at the table on page four. It explains how the error from multipath time delay resolution at 125 kHz (which is a standard LoRaWAN channel bandwidth) is in excess of two kilometers. Thus, urban localization performance due to the bandwidth of the channel will be limited.
If you’re thinking about implementing a LoRa system and have any questions, contact us today. We’d love to help you benefit from LoRa’s great range and performance capabilities.