Joe Schmelzer 2017-08-02 04:15:12
Good indoor wireless communications coverage plays an important role in supporting cellular internet-of-things (IoT) operations. IoT services have many communications standards to choose from. They also have three ways to deliver coverage indoors. A variety of approaches have been promoted and trialed for wide-area wireless for the internet of things (IoT) — the term that has emerged to refer to the network of devices that keeps a smart home running, a business campus interconnected or a disabled vehicle in communication with its road service provider. Among the contenders for hegemony in this fast-growing domain are the Dash7 Alliance protocol, Sigfox network technology, Weightless connectivity technology, LoRa (long-range) spread-spectrum technology, RPMA (random-phase multiple-access) spreadspectrum technology and even 2G digital cellular technology, to name only some. Each comes with self-proclaimed strengths and weaknesses. The 3rd Generation Partnership Project (3GPP), the standards body that delivered Long Term Evolution (LTE) high-speed wireless communications , has included two variants of LTE in its Release 13 for use in the IoT context: Cat M1 (Category M1 — the “M” originally stood for “metering” and referred to smart metering using IoT) and NB-IoT (narrowband IoT). It is likely that multiple standards will be used because there is a wide variety of use cases (ways to use a system to accomplish a particular goal). Devices that support the LTE Cat-M1 standards for IoT have just started shipping over the last several months, and they benefit from having the broad support of the existing cellular network providers that have deployed LTE, or plan to. The ecosystem for LTE Cat-M1, specifically, is a little ahead of NB-IoT, which means modules, devices and network support are already available. The NB-IoT devices are “coming soon.” In October 2016, Verizon claimed to have made the first LTE Cat-M1 call. Meanwhile, in San Francisco, AT&T claimed to have placed a fully commercial LTE Cat-M1 site in operation. AT&T’s Glenn Lurie in 2015 announced that the carrier was chasing the IoT via cellular-only solutions based on LTE. Winning General Motors’ connected car business through the OnStar program gave AT&T instant scale, and AT&T has been charging forward ever since. Other carriers have been working on it, but they have not been as vocal about their efforts for as long as AT&T has. LTE-based IoT solutions are also seeing traction in Europe, with Tier 1 operators such as Vodafone giving their endorsement. To put IoT over cellular in context, there are a number of competing methodologies for connecting IoT devices, from fixed line to wireless. It is when we consider the competing low-power, wide-area network (LPWAN) solutions — Sigfox, Weightless, RPMA, Dash7 and LoRa — none of which is LTE-based, that we can see why LTE-based IoT is gaining such traction: It can be applied to existing LTE networks as a software upgrade and therefore is much easier (and less costly) for operators to deploy. So what are the markets going to look like, and where will the lion’s share go? Some say that cellular IoT solutions could reach as high as a 90 percent market share, which makes sense only given the robustness and prevalence of today’s LTE networks. According to a new research report from IoT analysis firm Berg Insight, global shipments of cellular IoT devices will grow at a compound annual growth rate (CAGR) of 22.7 percent from 155.6 million units in 2016 to reach 530.1 million units in 2022. Other researchers report the number even higher. LTE-based IoT and Coverage LTE-based IoT (LTE Cat-M and NB-IoT) devices offer a number of advantages over standard 3G and 4G technologies. The big three are extended battery life, lower cost and better coverage. Coverage is our focus in this article. LTE-based IoT delivers better coverage primarily because of a substantially better link budget. The link budget is an important measure for power calculation. It calculates the power received at the receiver (device) and accounts for gains and losses along the way. A link budget essentially indicates how bad the signal can be from the tower to the device (and vice versa) and still allow the system to communicate. A cellular IoT link budget (about −164 dB) is about 20 dB better than standard 3G and 4G technologies (about −144 dB). This provides coverage to an area approximately seven times larger (in an open environment). A 20 dB improvement will also result in better in-building penetration. Standards bodies worked to ensure a better link budget for cellular IoT for good reason. With 3G and 4G, operators continue to struggle to provide good in-building coverage from external macro networks. A recent Zinwave study showed that 66 to 83 percent of workers have “frequent” or “sometimes” bad cellular coverage. More than 45 percent of warehouse workers reported frequent problems connecting. Everyone agrees these numbers are unacceptable, yet the problem is becoming more pronounced as mobile adoption continues to grow. We do everything over mobile now. All tools are mobile, and being disconnected is not an option. One can easily imagine how ineffective any mission-critical business operation would be if it had to rely on such poor connectivity metrics. Even non-mission-critical operations are nonstarters at that level of connectivity. LTE-based cellular IoT solutions are new on the market, with the first commercial deployments having begun in the last six months. In spite of the improved link budgets and wider coverage areas, these technologies are subject to the same in-building penetration challenges and resulting coverage problems as cellular. Sigfox, for example, has a link budget of 159 dB. This provides a phenomenal coverage area — about 12.5 miles. As you can see in the illustration in Figure 1, just three towers can cover all of metropolitan Melbourne, Australia. When you read the fine print of the coverage map however, it tells a slightly different story: “This map is only a guide and not a guarantee of service level. Coverage estimation based on computer prediction in outdoor locations [emphasis added] for device class U0 (maximum output power level is defined in SIGFOX Ready certification requirements).” This is not a slight on Sigfox. All of these technologies are outside-in, and they are all subject to the same laws of physics, attenuation and propagation. The operator of one of the best cellular networks in the world, Verizon Wireless, makes a similar statement about coverage: “Customer equipment, weather, topography and other environmental considerations associated with radio technology also affect service and service may vary significantly within buildings.” In-building IoT Options According to the most recent Ericsson Mobility Report, there will be about 18 billion wireless IoT devices in 2022. Of those, one in eight (or 2 billion units) will be wide-area reliable, and pervasive in-building coverage is needed to support the 30 percent compound annual growth rate (CAGR) that Ericsson is projecting, along with most experts covering IoT, as seen in Table 1. Fortunately, solutions exist. There are three ways coverage can be delivered indoors in the IoT context: wired-to-router, wireless mesh and wireless boosters. Wired-to-Router Network For many applications, the simple solution of a wired-to-router network will suffice. If the on-premise IoT solution is simply making use of a wide-area wireless- enabled router or gateway in which the on-site sensors and nodes are connected via wire, then an antenna could be run to the exterior of the building. To provide coverage to a single fixed point, this is a fine option (see Figure 2). However, for the antenna to pick up signal, there must be some service available to the exterior of the building. There are also some limitations around equipment placement — the antenna run cannot be too long because of the attenuation of the signal over the length of the coaxial cable. Wireless Mesh Network Some IoT networking technologies implement a form of mesh capability, allowing for a string of pearls style approach to coverage. In this model, each network node becomes both a sensor and a gateway for other devices. Some applications can leverage this capability quite well. 802.15.4 (Zigbee) is one such networking technology that makes use of mesh capability (see Figure 3). There are two main weaknesses with this approach to extending the IoT network and coverage. First, because each node becomes a full-time participant in the communications path, the nodes must be on all the time. This makes a battery-powered mesh network difficult to maintain. Battery life for a node can decrease from 10 years to only a few months, depending on where it sits in the network and how often it is used. Keep in mind, if a single node goes down in the network chain, all of the nodes after it are incommunicado. This is mostly a non-issue where nodes are powered, as with most smart home applications, for example. Zigbee, having mesh capability, is a great technology for the connected home, where battery-powered devices are less common and thus are not limited to the lifespan of a battery. A Zigbee-enabled smart home battery- powered device might last only 12 to 18 months. The second issue is latency. Each node introduces latency into the network architecture. Depending on the type of application and messaging layered on top of the network infrastructure, this could be a problem. Messages time out and real-time applications suffer. Even the smallest, localized smart home network based on Zigbee, with powered nodes, struggles to maintain and support lowlatency applications. Higher latencies limit the types of applications that can be deployed over the network. Wireless Boosted Network Smart signal boosters can offer a highly attractive alternative for bringing cellular IoT coverage indoors. A good smart signal booster is transparent to the cellular network: It simply relays the external coverage internally, with so little delay that it is invisible to the cellular network. The cellular devices inside the building just receive a good signal, improving both voice and data signals. A smart signal booster is inherently different from older repeater technology because it is approved by the FCC to boost gain to 100 dB, which is 1,000 times greater than levels allowed with analog bidirectional amplifier (BDA) repeaters. Smart signal boosters have been approved by more than 200 global carriers for use on their networks because they are guaranteed to be network-safe, and they won’t interfere with the macro network or other wireless devices on the network. In an LTE-based IoT infrastructure, smart signal booster technology offers significant advantages. For one, it is transparent to the network. There is no additional latency or setup required. A device could be installed in a concrete bunker, and with the right smart signal booster, the device would appear on the network as if it were sitting in a wide- open coverage area with no structural obstacles. For mission-critical business solutions that rely on real-time communications, this is an important option. Also, unlike mesh networks, IoT nodes that are inside the coverage bubble of a smart signal booster don’t have to do any additional work, so they can be much lighter weight in terms of capability. They can operate as intended, waking only when prompted, or on a timer. This delivers the 10-year battery life desired by the IoT industry. Buildings with IoT solutions being serviced by a smart signal booster have a lot of flexibility because nodes can be added or subtracted without any special setup or configuration, which is another advantage. They can be fully mobile and not rely on tethering from a cable or network connection (see Figure 4). Yet another advantage is that, unlike other options (e.g., simply adding an antenna to the IoT router), data and voice applications will benefit with the right smart signal booster. Not only will the IoT node be connected in a high-speed low latency connection, voice calls over LTE will be improved. Summary Because LTE-based IoT offers a number of advantages from an architectural, financial and efficiency perspective, it is not surprising to see the momentum in adoption and device shipments. But one cannot underestimate the critical importance of good indoor coverage to support cellular IoT operations. In a simplified way, Figure 5 illustrates the effect of poor indoor coverage on industries with mission-critical operations. As LTE-based IoT emerges as a favored option, organizations should consider themselves on notice to resolve these issues in their systems. The good news is affordable and flexible options are available that can address virtually any indoor coverage challenge, large or small. Joe Schmelzer is senior director of products at Nextivity. He has developed a variety of products and industrial devices for chipset vendors, original equipment manufacturers and service providers, including products for Sony, Qualcomm, Google, Verizon Wireless, AT&T, Dell and HP. For more information, visit www.cel-fi.com.
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