Standardising IoT connectivity by the kilometre: SIGFOX, LoRa or LTE?

As everyone is probably tired of hearing, the Internet of Things is supposed to connect everyone with everything connectable, everywhere.

There are basically two ways to provide connectivity between IoT devices and their host systems at distances beyond those of ZigBee, Wi-Fi and Bluetooth: cellular networks and low-power wide area networks (LPWANs) developed by other companies. The goal of the LPWAN developers is to deploy networks in as many urban areas as possible before wireless carriers deploy theirs in the form of three solutions:

• EC-GSM (extended coverage), which allows existing GSM cellular networks to be used for IoT applications through the addition of software.
• Variants of LTE called, for the purposes of this article, LTE-M, as it is an umbrella term that covers a variety of LTE specifications destined for IoT connectivity use.
• The fifth generation of wireless, 5G, coming sometime after 2020.

So the race is on. The wireless carriers have an enormous advantage in that they already have coverage virtually everywhere, but if the LPWAN providers rapidly get their solutions in place, it’s reasonable to assume that the potentially enormous revenue to be gleaned from IoT connectivity will wind up being shared between the wireless carriers and LPWAN providers.

LPWAN variants

LPWANs can be differentiated by the modulation schemes they employ, which are ultra-narrowband, narrowband and wideband. Ultra-narrowband networks trade on the fact that as transmit bandwidth shrinks the noise floor rises, which positively impacts receiver sensitivity, range and the need for lower transmitted power. Ultra-narrowband systems can achieve only low data rates and small data packet sizes, along with unidirectional or bidirectional communications. Narrowband networks can provide a satisfactory compromise between their narrower and wider counterparts, providing considerable range and capacity. Finally, wideband networks, with channels sizes of 500 kHz to greater than 1 MHz, have the highest data rates. The performance of ultra-narrowband, narrowband and wideband networks varies greatly with each vendor.

The contenders

In addition to IoT connectivity provided by wireless carriers (LTE/4G/5G), there are a variety of competitors, the largest six of which are covered below: LoRa, Symphony Link (and Ensemble), SIGFOX, Weightless, Nwave and Ingenu. All have developed solutions that make them different from each other in many ways based on the use of proprietary software, networking techniques and other factors.

LoRa

LoRa (an acronym of Long Range) is the physical layer of a set of open standards for bidirectional devices championed by the LoRa Alliance. Its network implementation is called LoRaWAN and was developed by Semtech, along with IBM Research and Actility. LoRa uses chirp spread spectrum modulation and a base station can typically cover hundreds of square kilometres.

The technology allows communication to be conducted over multiple channels at varying data rates, depending on range and required message duration. Data rates range from 300 bps to 50 kbps, managed by the network server along with the RF output power of each user IoT device. The approach provides security at the network, application and device levels and can accommodate all classes of bidirectional IoT devices.

Symphony Link and Ensemble

This technology, developed by Link Labs, is a proprietary variant of LoRaWAN that uses its physical layer but a different MAC architecture to provide additional functionality. The company’s premier product, called Symphony Link system, uses an eight-channel base station operating in the 433 MHz or 915 MHz ISM bands as well as the 868 MHz band used in Europe. It can transmit over a range of at least 16 km and backhauls data using either Wi-Fi, a cellular network or Ethernet using a cloud server to handle message routing, provisioning and network management.

SIGFOX

SIGFOX is the product of a company by the same name that has deployed networks in 19 countries, making it the current leader of the pack. SIGFOX operates at 868 or 915 MHz and transmits very small amounts of data very slowly (300 bps) using Binary Phase Shift Keying (BPSK). SIGFOX can achieve long-range coverage and has general characteristics that make it suited to any IoT application requiring only small amounts of data.

A SIGFOX network uses ultra-narrowband modulation that allows messages to travel up to 1000 km with a single base station, with capacity of up to 1 million IoT devices per base station. Data payload is 12 bytes per message and up to 140 messages per day per device, which is adequate for a substantial number of applications. Initial networks were unidirectional but bidirectional capability may soon be available.

Weightless

This open standard has three versions: Weightless-N, Weightless-P and Weightless-W. Weightless-N is unidirectional, provides range of more than 5 km and is the most basic variant. Weightless-N-enabled IoT devices can operate for 10 years before battery replacement. Weightless-P is a bidirectional version with a more complete feature set and a range of 2 km or more, whose enabled devices can last between three and eight years. Weightless-W is the most extensive bidirectional implementation and offers a range of more than 5 km, and enabled devices can operate between three and five years.

The Weightless network uses GMSK and offset-QPSK spread spectrum modulation schemes and 12.5 kHz-wide channels, and has a transmitted RF power of only 17 dBm. When enabled in an IoT device, quiescent current consumption is only 100 µW, making it compatible with the many IoT sensors that get their power from a lithium-ion watch battery. Weightless can be used in any licence-free band. 128/256 AES encryption and authentication are available for both the terminals in the network.

Nwave

Nwave uses ultra-narrowband technology and software-defined radio (SDR) techniques and can operate in any unlicensed frequency band. The base station can accommodate up to 1 million IoT devices over a range of 10 km with RF output power of 100 mW or less and a data rate of 100 bps. Battery-operated devices can operate for up to 10 years.

Ingenu (formerly On-Ramp Wireless)

Ingenu’s Machine Network operates in the 2.4 GHz band and bases its capabilities on a modulation scheme called Random Phase Multiple Access (RPMA) that uses direct-sequence spread spectrum and tight control over transmit power along with high receiver sensitivity to provide a high link budget. RPMA ‘self modulates’ to find an interference-free transmission path between the network and device. The company claims it can cover over 480 km per base station under typical conditions.

Last but not least

The elephant in the room is LTE delivered by wireless carriers. As IoT has been in the works for years, the Third Generation Partnership Project (3GPP) has been working to accommodate it in the wireless standards development process. LTE-M was rolled out in 3GPP Release 12 and Release 13 adds many specifications focused exclusively on serving IoT. It includes narrow 200 kHz bandwidth capability and also ‘wider’ bandwidth capability of 1.4 MHz bandwidth, the latter still being much narrower than standard LTE. All duplex modes are designed to minimise latency, transmit power for enabled devices is a modest 20 dBm, and other provisions should allow them to operate for up to five years on two AA batteries. It also presumes that the cost of LTE modems will need to decline by up to 50%.

There is speculation about whether wireless carriers will ultimately reign over all of IoT connectivity. Those who believe that it will note that the physical infrastructure is already in place, so only relatively minor modifications will be required, and that the wireless industry has huge resources that it will surely devote to ensure it gains most of the market. As this story goes, it’s possible that the wireless industry could wipe out all its competitors in one fell swoop. That said, while AT&T recently announced that it will use an ‘all-LTE’ approach to providing IoT connectivity, it will not rule out using one or more of the LPWANs if it makes sense in a specific situation.

At the other end of the spectrum are those who believe that wireless carriers will take advantage of the potentially higher performance they can provide to serve the most demanding, high data rate cloud-based applications that require connection of IoT devices over huge geographical areas, thus justifying higher service costs. A typical application might be a manufacturer of industrial machines enabled with IoT sensors that are installed throughout the world. The remainder of the market would be served by LPWAN providers. Regardless of how this marketplace eventually matures, there is now no doubt that IoT will be far more visible to greater numbers of people in the next few years.

*Barry Manz is President of Manz Communications, Inc. He has worked with over 100 companies in RF, microwave, defence, test and measurement, semiconductor, embedded systems, lightwave and other markets. He edits for the Journal of Electronic Defense and Military Microwave Digest, and was chief editor of Microwaves & RF magazine.

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