Low-Power, Wide-Area (LPWA) networks are the new darling in the wireless community. But what exactly LPWA is and what it isn’t can be confusing. Here we examine a few of the technologies and companies that are active in this space.
The primary driver of LPWA technology is a desire to connect IOT sensors to the internet without the cost of cellular (but hold that thought), the power drain or deployment complexities of WiFi, or the range limits of Bluetooth.
Despite what some people think, LPWA technologies are not truly “low power” in the sense that they transmit more efficiently than others. In fact, LPWA transmitters take 10x or more of the power to transmit than Bluetooth does. The low power name really comes from the system architecture that allows devices to sleep 99%+ of the time. When idle (sleep) currents are just a few microamps, many years of battery life are possible.
The “Wide Area” part of the name could more accurately be described as “High Link Budget.” However, “Low Idle Current, High Link Budget” just doesn’t have the same ring to it. The great link margin of LPWA devices is generally a result of improvements in receive sensitivity at both ends of the link. This is a product of very low data rates and creative processing gain improvements.
The final innovation in LPWA technologies is multiple access. This just means that many devices can access the gateway simultaneously. Each technology has a slightly different way of doing this.
So, for each technology, we will cover
- How is high receive sensitivity achieved?
- What is the multiple access scheme?
- What are the strengths?
- What are the weaknesses?
- What is the business model?
By business model, I mean, how does the provider of each technology make money and how do they go to market. This is an important thing to understand, since some companies just provide networks, some sell technology, and some do a bit of both.
Sigfox, at the ripe old age of about 7 years is the granddaddy of the LPWA space. They were the pioneers in creating the market. They are a network provider (in the US) and a technology provider to carriers in other markets.
We’ve covered a bunch on Sigfox technology in the past, but as an overview:
- Sigfox uses a large base station with an FPGA channelizer to detect low bitrate DPSK transmissions across hundreds of potential channels.
- End nodes blindly transmit the same message 3 times, on 3 different frequencies to improve the chance that the message is received.
- Downlink is theoretically possible, but it is very limited because whenever the base station is transmitting, it is off the air, and thus increases the risk that it will miss traffic.
- This simple technology allows a host of various RF transceivers to be used, so customers have multiple sources of supply.
- The use cases must be among the simplest in IOT, since only 12 bytes of payload are available per transmission.
- Things like firmware updates or control applications are not possible with Sigfox.
- Because of FCC time-on-air limits (400 ms), Sigfox has about a 9 dB worse Link Budget in the US, which when combined with higher levels of interference in the 900 MHz band, mean that the network performance in the US is not nearly as good as in Europe for Sigfox.
- WAVIOT is a Russian company that uses technology which is almost identical Sigfox.
- One difference is that they do not offer networks, just technology.
- Unlike Sigfox anyone can buy WAVIOT equipment to build a solution.
- WAVIOT features a hopped signal that allows their link budget to exceed Sigfox’s for FCC/US based applications
- WAVIOT base station equipment is costly because of the large FPGA needed to implement all the DPSK channels.
- Like Link Labs, LoRaWAN is based on LoRa physical layer technology, however Link Labs’ Symphony Link protocol is very different, and offers many advanced features that LoRaWAN does not.
- LoRa offers much better receive sensitivity at the endnode than Sigfox, and thus the link budget is more balanced.
- Like Sigfox, LoRaWAN is an asynchronous, Aloha style access, so the same limitations around downlink apply to LoRaWAN, as with Sigfox.
- Read more about considerations for LoRaWAN here.
- The business model of LoRaWAN is complicated because LoRa is sold by Semtech, but the protocol is developed by the LoRa Alliance, and a handful of network operators are piloting carrier networks based on LoRa as well.
- Carrier networks and private deployments of LoRaWAN interfere with one another.
- This category of LTE allows for devices that are as power efficient as LoRaWAN or Sigfox, but can have the sophistication and data rate of LTE. Read more here on how LTE-M1 improves power profiles over traditional cellular.
- Obviously if you use LTE-M, you have to pay a network operator.
- Certifying devices on carrier networks can be costly.
- LTE-M1 networks won’t be deployed in the US until 2017.
- LTE-M prices will be competitive to those offered by Sigfox (I bet).
- NB-IOT (aka LTE-M2) is another 3GPP technology that was recently finalized.
- While it is not technically part of the LTE protocol (like LTE-M1), it can be deployed in masked LTE resource blocks or in guard bands.
- It was designed it fit in old GSM 200 kHz blocks of spectrum, and many operators in Europe and Asia will likely deploy it for IOT devices.
- In a way, Sigfox created NB-IOT by showing the carriers that there is a good business to be had for IOT devices.
- NB-IOT is about a year behind LTE-M1, so networks won’t likely be ready until the end of 2017 or into 2018.
- The same considerations about paying a network operator and device certification apply.
- Ingenu is a rebranded Onramp Wireless. They have their own 2.4GHz DSSS technology and deploy networks with it.
- It has great link budgets, but the DSSS modem on the endpoint is rather power hungry compared to LoRa, for instance.
- Think of them like LTE-M or NB-IOT in a way, since they are “just” an IOT network provider. The technology doesn’t matter as much as the network.
- They are deployed only in a handful of cities, as of this writing.
- It will be fun to see if they can survive in the face of huge LTE-M rollouts from ATT and Verizon.
In conclusion, there are many different LPWA options out there. If you want off-the-shelf technology for your own use, check out Symphony Link. It is the most advanced LPWA technology available, outside of LTE-M.