October 19, 2017
|By: Jim Harrison
Guest Blogger, Lincoln Technology Communications
OK, we know the IoT is important, and for the past three of four years you could not go to a conference or read an EE-focused article without being bombarded with information about the IoT. But, as I see it, progress in IoT setup and deployment has been really slow. For one thing, we are still trying to figure out what form of LPWAN to use to connect millions of sensors and actuators that are part of a myriad of different applications.
As most everyone knows, the IoT is planning on connecting almost everything to the internet so we can measure, monitor, and track them all. To accomplish this we need some long-range wireless communication method—much longer range than you can get from WiFi®, ZigBee®, or Bluetooth®. There are three viable types of wireless connections for this: satellite, cellular, and low-power wide area (LPWAN) networks.
Satellite systems take a lot of equipment and a great deal of power, so they do not fit many IoT applications. But for some it’s perfect. Here are a few available satellite connections. ViaSat-1 has been providing internet service to aircraft and ground-based users for a while and claims it has 700,000 customers. ViaSat-2 was launched in June and will provide 100Mbps speeds for residential customers. Hughes launched its second high-capacity Jupiter-2 satellite in December 2016, and SpaceX has requested permission to launch a staggering 4,425 satellites. Exede currently offers satellite-based internet at up to 25Mbps download speed for $50/month.
NB-IoT and LTE-M offer connection via the telephone network. Cellular connectivity is clearly an option, although the equipment and service are more expensive than LPWAN systems. The main benefit of cellular is that it gives the subscriber a global network. But, of course, there are dead spots to deal with–and then there’s the phone companies to deal with. The thing is, it has a big network, while others are building out.
The 3rd Generation Partnership Project (3GPP) unites seven telecommunications standard development organizations and provides specifications that define 3GPP cellular network technologies – including Narrowband IoT (NB-IOT) WAN and LTE-M implementations. Like what I’m calling LPWANs below, these networks allow node battery lifetime as long as 10 years for a wide range of use cases. And they are rolling out lower cost modems in 2017/2018.
The various versions of LPWAN may be the lowest cost and easiest way to go. They tend to be very reliable, have very low-power nodes (10 years on one battery), and be easy to set up. But, there are many versions vying for your attention, each with their advantages, and some may not stay around very long. Actually, some will not stay around very long.
The Wi-Fi Alliance has developed HaLow LPWAN technology. The technology operates in the 902MHz to 928MHz portion of the spectrum, transmits data at 150kbps to 18Mbps, and has transmission range of up to 1 kilometer. It uses IEEE® 802.11ah, which is a lot like a scaled down WiFi connection.
(Random Phase Multiple Access) LPWAN technology is offered by Ingenu, and uses the 2.4GHz spectrum with direct-sequence spread spectrum (DSSS) and differential BPSK modulation. It offers a peak data rate of 634kbps–the highest of all the LPWAN versions. Like SigFox, it is a proprietary network operated by the company and its partners, and you must subscribe to this network. RPMA is pursuing an ambitious goal of becoming a global network and is building its towers with a potential to maintain up to two million devices each with bi-directional transmission. At present, there are around 30 "connected cities" in the US, with many more coming.
LoRa offers open standards for bidirectional devices championed by the LoRa Alliance, with members including IBM, Renesas, Cisco, Semtech, and STMicro. The technology uses chirp spread spectrum modulation with data rates from 300bps to 50kbps. To implement LoRa you must use a Semtech transceiver chip. Semtech's SX1276 transceiver chip is available for around $4 each/3,000 and many modules are available. The company produces transceiver chips for both nodes and gateways. A single gateway can communicate with several hundred thousand nodes up to 20 miles away in unobstructed environments with a transmit power of +20dBm and a receive sensitivity of up to -148dbm. From what data I can find, I would say around 2kbps would be the data rate to count on for any long-range application.
Companies such as Senet provide a public network of LoRa base stations and cloud data management. But, you can also use your own gateway. In a city, the signal can penetrate buildings to achieve a range of a mile or two. End nodes can remain operational for up to 10 years running on two AAA batteries providing 10mA for the receiver and under 200nA draw in sleep mode. The LoRaWAN specification does not have any means to enforce quality of service and, therefore, it probably should not be used for critical applications.
A great current use case was developed by PNI Sensor Corporation. PNI's PlacePod Smart Parking Sensor has been installed in a Montreal parking control demonstration project. Looking for a parking space in a crowded city is not only annoying, it wastes fuel, pollutes the air, and adds greatly to traffic density. With sensors in each parking spot, the city can provide a map to car apps that show all available spaces. The city uses sensor data to promote turnover in its busy business district. They can also monitor usage and see, for example, when disabled parking spaces are full or not being used. The LoRa gateways are needed only every few blocks, even in the complicated concrete jungle, to collect the data from hundreds of sensors. The buried-in-the-street sensors must work over very large temperature extremes and with a varying RF environment. I spoke with Becky Oh, the president and CEO of PNI Sensor, who said "the 65 sensors in Montreal are working splendidly. We partner with X-Telia, and the PlacePod sensors are deployed on their public LoRa network. All of the WAN connections have been solid."
PNI's in-ground PlacePod Smart Parking Sensor uses LoWa connection. (Photo courtesy of PNI Corporation)
Sigfox wireless technology originated with the French company of the same name. It operates in the 868MHz and 915MHz ISM bands and takes very little bandwidth or power. Data rate is a very slow, at 100bps to 600bps, but, because of its narrow bandwidth, short messages, and 162 dB link budget, a range up to 50km (31 miles) is possible. It has bi-directional functionality, but downstream is really very slow.
You must connect to a Sigfox network base station. They have coverage in almost all of Europe and are in 10 large US cities and growing. Sigfox, in principle, works with one partner, a so-called Sigfox network operator, per country, and has a focus on deploying as much coverage as possible across the globe. Subscription fees are rumored to be as low as $5/year.
A SigFox uplink message has up to 12-byte payload and takes an average 2s over the air to reach the base stations which monitor the spectrum. SigFox radios use ultra-narrowband (UNB) modulation with binary phase-shift keying (BPSK). It is a software-based solution, where all the network and computing complexity is managed in the cloud, rather than on the devices. SigFox offers only a basic level of security (16-bit encryption). The technology's intellectual property is available free to silicon and module vendors and there are currently multiple companies selling SIGFOX chipsets, antennas, expansion, and evaluation boards, including ON Semiconductor, Texas Instruments, ST Microelectronics, and Atmel/Microchip.
There are three published Weightless WAN connectivity standards: Weightless-P, Weightless-N, and Weightless-W, all administered by the Weightless SIG. Weightless-P is a narrowband (12.5KHz) LPWAN full-duplex synchronous network technology supporting a very large number of end devices per base station with long range, years of battery life, and firmware-over-the-air (FOTA) capability. Weightless-P has adaptive data rates from 625bps to 100kbp, depending on device link quality and adaptive power control. It uses frequency hopping with channel black-listing.
The Weightless SIG is comprised of just three companies: Ubiik, Arm, and Accenture. That may be good or bad. I did see that Arm has nothing about Weightless on their web site. Arm told me this: Arm was involved in the founding of Weightless SIG and have had active members on the Weightless SIG Board since its inception. Arm supports the wider LPWAN ecosystem play, including LoRa, Sigfox and Weightless. Arm's focus today is on broadening IoT adoption, and they recently announced the Arm Cordio-N NB-IoT solution. The company sees NB-IoT as a principle technology that can achieve scale.
Weightless is a synchronous network, and LoRaWAN and Sigfox are not. Synchronous has some advantages in error correction and detection. In simulations I have found, Weightless gets about 10x the data rate of SigFox and 2 to 5x that of LoRa. Oddly, I can find no field comparison test results for these networks.
Weightless does offer good security, with AES-128/256 encryption and authentication of both the terminal and the network. Temporary device identifiers offer anonymity for security and privacy. It has forward-error correction, automatic retransmission request, and adaptive channel coding. Weightless also supports acknowledged and unacknowledged unicast and multicast traffic.
If you know of any results from comparison tests of these WAN types demonstrating real-world speed, reach, and power, please let me know at LincolnTech@lincolneng.com.