By Matt Rose, FCS Wireless Specialist
For the last few years, machine-to-machine and Internet-of-Things applications relied on 2G and 3G cellular systems for wide area network communications. As broad market consumers required more performance from their smartphones to stream the latest wrestling match video, these older protocols have become obsolete and high-bandwidth 4G-LTE has become the de facto standard (Figure 1). This has left M2M users without a price-sensitive network for their low power, low data rate, long-range applications. An opportunity has arisen for specialized Low Power Wide Area Networks (LPWANs) to fill this market void, and among many contenders two significant competitors have taken the lead: LoRaWAN and LTE CAT M1. What differentiates these two competing standards, and is there room enough for both of them to gain a foothold in the ring and beat out their competitors for the title of King of LPWAN?
Competitor #1: LoRaWAN
LoRaWAN is a Low Power Wide Area Network specification intended for 900MHz wireless sensor nodes in local private networks or in regional and nationwide public networks. The protocol provides interoperability among nodes without the need for complex local installations. The network architecture is laid out in a star topology where gateways relay messages between sensor nodes and the network and application servers. The LoRaWAN gateway is connected to the network server by way of Ethernet, cellular or WLAN (Wi-Fi) routers, while sensor nodes utilize chirp modulation to connect to the gateways with ranges of up to many miles (Figure 2). The LoRaWAN air protocol utilizes different frequency channels and data rates, and uses wideband linear frequency modulated pulses (chirps) whose frequency increases or decreases over a certain amount of time to encode information. The protocol’s maximum data rates range from 12.5kbps to 20kbps in North America, and in order to maximize sensor node battery life and overall network capacity, the network server uses an adaptive data rate to manage the effective data rate and the RF output for each node.
LoRaWAN has three classes of end-point devices to address the different applications. There are several layers of encryption, including network level unique network key (EUI64), application level unique application key (EUI64), and device specific key (EUI128) at the node level. Class A devices have bi-directional communications with one transmission followed by two receive slots. This is the lowest power option and would be used in a Smart City type of application. Class B devices are similar but have an option for additionally scheduled receive slots. This option gives the server the ability to be notified as to when the end node is receiving and would be used in an irrigation application. Class C nodes transmit but then are otherwise in receive mode and would be used in a smart street lighting application. LoRa sensor nodes are available from Microchip, Murata, Laird, Link Labs and Multi-tech, and gateways are available from Link Labs and Multitech (Figures 3 and 4). The first public LoRa network has been implemented by SENET in Silicon Valley, California, and Comcast has announced a public LoRa network dubbed MachineQ with first gateways planned for Q2 2017 in Philadelphia, Chicago and San Francisco. These two companies are part of the LoRa Alliance, a consortium of hundreds of small- to large-sized tech companies, which promotes and regulates the LoRaWAN standard (www.lora-alliance.org).
Competitor #2: LTE Cat M1
LTE (Long Term Evolution) is notably different from previous generations of cellular technologies with regard to carrier frequency and bandwidth (Figure 5). There are a wide number of 4G LTE bands defined by the standard and they vary depending on country as well as carrier. These licensed spectrums are split into Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD) types where the FDD spectrum requires pair bands, one for uplink and one for downlink, and the TDD uses a single band as uplink and downlink on the same frequency but separated in time. 31 pairs of LTE bands operate between 452MHz and 3.6GHz and an additional 12 TDD bands are between 703MHz and 3.8GHz. The higher frequencies allow for faster transmission in urban areas, while lower frequencies offer additional range but less bandwidth in rural areas. These bands typically offer between 10MHz and 20MHz of bandwidth for data transfer, although they can be split up into smaller 1.4MHz, 3.0MHz and 5.0MHz bands.
Specifically, LTE Category M1 (Cat M1) uses 1.4MHz bands, a maximum transmit power of 20dBm, and provides upload speeds of 200kbps on average. US wireless operators AT&T and Verizon are about to release the Cat M1 technology along with module partners such as Sierra Wireless, Link Labs, Multitech and Gemalto (Figures 6 and 7). It will be released over the 4G LTE network with an open environment and is expected to reach nationwide US coverage by the end of Q2 2017. Since AT&T and Verizon are supporting Cat M1, this allows LPWAN technologies to work with a licensed spectrum, consequently providing a secure and established public network for IoT businesses. Cat M1 works specifically with IoT applications with low to medium data usage and devices with long battery lifetimes, and is important to the carriers as it extends LTE’s market reach. By allowing LTE to cost effectively support lower data rate applications, Cat M1 is being touted as a good fit for low power sensing and monitoring devices.
The Head-to-Head Match Up!
Many parameters can be compared when deciding whether to choose a LoRaWAN or LTE Cat M1 network for your application: nationwide coverage, ability to set up a private network, certification costs, module cost and size, as well as data rate and range. The first thing to weigh is whether there is a public infrastructure avail- able in the physical area where your application will reside. If your application is in an urban or suburban area with existing LTE coverage, then it may make sense to utilize that existing network. However, Glenn Schatz, VP of Business Development at Link Labs counters, “LoRa has an advantage in areas with little to no cell coverage. Places like campuses, small downtowns, and rural areas with no LTE service can quickly implement a LoRa network.” Similarly, Brandon Dalida, Regional Sales Manager at Multitech, offers that even if there is LTE coverage available, there may not be a business case for heading down that path. “It all comes down to comparing the cost of capital expenditures versus operational expenditures. Is it more profitable for your company to own and maintain the network or is it preferable to leave network implementation and management to another entity?”
Another issue to consider is regulatory and carrier certification costs. In both cases, products with LoRaWAN and LTE Cat M1 embedded modules will require FCC (or country-appropriate) regulatory certification for intentional and unintentional emissions. However, LTE solutions will also require carrier certification from Verizon and/or AT&T, and this cost has been a barrier to entry for price-sensitive applications in the past. Regarding these costs, Jon Leitner, Senior FAE at Sierra Wireless, states, “The carriers are going to scale back testing requirements and move to a simplified model to streamline product certification.” Some carriers with legacy CDMA might have their own requirements that might not have pass-fail for all test cases. This may perhaps lessen the barrier to entry for price-sensitive products. Other considerations are the cost and size of the embedded module for your application, as well as data rate and range. In both LoRaWAN and LTE Cat M1 cases, chip suppliers and module manufacturers have brought prices and sizes in line with existing technologies such as Wifi, Zigbee and classic Bluetooth, such that module sizes on the order of 24 x 24mm (1 ̋ x 1 ̋) are available and prices are on target to eventually match those of competing air protocols. Finally, some M2M applications require very low data rates and very long ranges that LoRa is capable of, but there may be some applications that require the 100kbps to 200kbps rates that LTE CAT M1 can offer.
Who Wins The Match?
As presented above, there are a number of tradeoffs when deciding whether to choose a LoRaWAN or LTE Cat M1 network for an application. Both protocols have been well designed for low power, low data rate and long range and both fill a niche in the market, so perhaps there is enough room for two Kings of the LPWAN ring!