05 Feb 2018

Long-range wireless networks can get a bandwidth boost from picocells

Martin Keenan, Technical Director, Avnet Abacus looks at the operation of long range wireless networks

As the IoT expands to touch every aspect of our lives, it is clear that wireless connectivity is the invisible force that binds it all together. That shouldn’t be difficult to accept, as wireless communications has shaped the world for well over a century and will continue to do so far into the future.

In terms of connecting things, the choice of wireless technologies in use is bewildering and only getting bigger. Most people will be familiar with pairing Bluetooth devices to create a connection but in the IoT this process will need to be managed by the devices themselves, automatically, within networks of perhaps hundreds of endpoints.

To address this, the network topology emerging in the IoT has hierarchy. Figure 1 shows that, while some endpoints may be enabled to connect directly to cloud services, the majority are likely to be connected to a local gateway.

A typical IoT network topology

Figure 1: A typical IoT network topology

This approach has many advantages, not least because it can make network management, device provisioning and firmware updates potentially simpler. It also means that not all endpoints need to support an IP based protocol; instead they could use a much leaner wireless technology to communicate to the gateway and reduce their own processing overhead. Gateways can also be used to extend the coverage of a network, by providing ‘waypoints’ for communications.

Network robustness

Network robustness is a major concern for anyone using the IoT and so the way that endpoints connect to gateways could be crucial. Many popular protocols have now adopted mesh networking, which allows endpoints to talk to each other, as well as a gateway. This can be an effective way to propagate connections throughout the network and potentially extend the range between a gateway and an endpoint, particularly for low power endpoints such as those operating from a primary cell.

However, some protocols are taking a significantly different approach to range extension, by implementing an inherently long-range wireless technology without breaking the power budget. These so-called low power wide area networks, or LPWANs, fit between local area networking technologies like Bluetooth and ZigBee, and the wide area coverage of cellular networks.

Like cellular networks, some LPWANs can deliver a service without the customer needing to build and maintain an entire network. And because they operate in the license-free part of the spectrum, networks can be deployed by practically anyone. One of the fastest growing LPWAN technologies today is LoRaWAN, which is being used to build public networks around the globe.

A typical LoRaWAN network would take the form shown in Figure 2.

LoRaWAN uses a star-of-star network topology

Figure 2: LoRaWAN uses a star-of-star network topology
(Source: The LoRa Alliance [www.lora-alliance.org]

Unlike many of the personal area network technologies, LoRaWAN uses a star topology, in which the messages sent by endpoints are typically received by several gateways. All of the messages are then aggregated to the server, where the network management part of the protocol removes duplicate messages and carries out further processing. Because endpoints are not associated with a specific gateway there is no hand-off required, which means the protocol is well suited to endpoints that are attached to mobile assets, such as vehicles or freight. As an example, LoRaWAN-enabled palettes are already available and can be used to track goods in transit. It also makes it simpler to add gateways to the network, which has far reaching advantages.

Range and bandwidth

A major feature of an LPWAN is its range and with LoRaWAN this can be tens of kilometres. The availability and coverage of public LoRaWAN networks is increasing and it is also possible to use the underlying technology, the LoRa PHY, to create private networks with similar range (although it should be noted that the features used to manage the network to deliver the best performance are part of the LoRaWAN protocol and not the PHY).

With the ability to support hundreds of endpoints across large distances, LoRaWAN networks need fewer gateways (sometimes called base stations) than a mesh network needs nodes. Public networks will deploy these gateways in order to provide the best service for paying users. Nevertheless, it may sometimes be necessary to increase or improve coverage, particularly in areas where there is a large aggregation of endpoints or where the RF signal is attenuated, such as inside buildings.

The LoRaWAN protocol uses an adaptive data rate scheme to optimise the available bandwidth, by telling each endpoint which data rate to use. Those endpoints with a stronger connection to a gateway will likely get a higher data rate, because it allows them to spend less time on air and therefore consume less bandwidth overall. For this reason the LoRaWAN protocol supports the use of multiple gateways; essentially gateways are transparent conduits between the endpoints and the network server. Typically, a gateway would feature an IP-based backhaul connection, such as Ethernet or WiFi.

Because gateways are intended to be relatively simple they can be implemented in a number of ways. For example, Semtech, the patent owner of LoRa and the provider of all LoRa transceivers, has developed a number of digital baseband devices and used one, the SX1308, to create a reference design for a LoRa picocell gateway. A growing number of suppliers are bringing gateways of all sizes – macro, micro and pico – to market for deployment by virtually anyone looking to improve the network locally.

Think globally, act locally

Although a single gateway could potentially provide coverage for an entire city, the option to implement a LoRaWAN gateway locally is compelling. Because of the way the LoRaWAN protocol operates, a picocell can instantly increase the overall bandwidth of a network while favouring those devices physically closest to it. For this reason, LoRaWAN adopters in the commercial or industrial sectors may well choose to augment a private network’s coverage by implementing their own picocell gateway.

Manufacturers looking to take advantage of the benefits of LoRaWAN are also well supported. There are a growing number of pre-certified wireless modules that support LoRaWAN, such as the CMWX1ZZABZ-078 from Murata. As Figure 3 shows, the module integrates the SX1276 RF transceiver from Semtech and an STM32L ARM Cortex-M0+ MCU from STMicroelectronics.

Figure 3: The CMWX1ZZABZ-078 LPWAN wireless module from Murata supports LoRaWAN and Sigfox
(Source: Avnet Abacus)

The transceiver supports both LoRa and Sigfox physical layers, while the MCU is able to run either protocol, or a proprietary protocol if the application requires. This level of flexibility means this module could be used in an endpoint targeting a wide number of LPWAN technologies, delivering a range of up to 15km in non-urban areas.

Conclusion

The introduction of LPWANs adds a new dimension to the IoT. With a fully managed network with inherent cloud connectivity, getting things connected becomes potentially much simpler. Even endpoints located remotely can take advantage of the wide area coverage that technologies such as LoRaWAN now offer. Connecting to a private network is made simpler through over-the-air provisioning with LoRaWAN, not something all LPWANs offer. Its ability to deliver geolocation data, combined with long range, low power and no gateway hand-off means LoRaWAN could become the wireless technology of choice for asset tracking, as well as smart metering (gateways can be mobile, too), smart homes and smart cities.

With the potential to improve bandwidth through the addition of picocells, LoRaWAN is possibly the LPWAN that scales most readily. The availability of low cost, low power and compact wireless modules means adding long-range wireless connectivity to assets is almost a plug-and-play process.

Avnet Abacus works closely with Murata to provide high levels of engineering support for LoRa application development. Find out more about Murata’s LoRa module and request samples here.

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About the author

Martin Keenan is Technical Director responsible for marketing strategy across IP&E, power and battery products into key market segments. Martin has over 15 years' experience in the electronics industry having begun his career at Nortel Networks, and since occupied roles at RS Components, Avnet and Altera.

Avnet Abacus is a pan-European demand creation distributor specialising in interconnect, passive, electromechanical, power supply and battery products. Avnet Abacus’ extensive product range and exceptional line card is supported by a team of over 50 product specialists based across Europe, delivering technical expertise and technology focused initiatives. Avnet Abacus is a regional business unit of Avnet, (NYSE:AVT).

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