ZigBee heads for Thread convergence and Wi-SUN battle with dual-radio spec

The Zigbee Alliance has unveiled its Zigbee Pro 2017 specification, which now supports dual-mode devices that use the 2.4GHz band and a sub-1 GHz band.

Zigbee has supported both bands for some time, but the dual-mode spec opens the door for a new breed of devices, as the Alliance looks to expand into new markets like smart cities.

Notably, the spec unites the two separate approaches to Zigbee deployment. The 2.4GHz band is used by the overwhelming majority of devices supporting the low power personal area network (LPPAN) standard, which in turn are mostly used inside households. The sub-1 GHz support has been used by fewer devices, most commonly in smart meters, acting as the link to the in-home display.

The new capabilities emerge as the Zigbee Alliance continues its attempt to bring better interoperability to the IoT, via its dotdot program. dotdot is also known as the Zigbee Cluster Library, or the Zigbee Universal Language, which is sometimes written as :||. It will now come to additional physical layers, so that a developer could use dotdot across multiple PHY layers, such as Zigbee, Bluetooth or Thread. In theory, once dotdot supports a given PHY layer, developers will only need to use a single stack for the upper layers of the OSI network model.

This could bring closer merger between ZigBee Alliance and Thread Group. The latter was set up to support an implementation of the 6LoWPAN specifications, devised by Google subsdiary Nest, and is supported by ARM, Samsung and others. Both ZigBee and Thread are based on the 802.15.4 protocol and Google has been clear that it would welcome ZigBee into the Thread fold to create a single platform to compete with the other significant LPPAN standard, Bluetooth.

There are overlapping objectives, memberships and efforts between ZigBee and Thread. Essentially, Thread needs an application layer, and has been using ZigBee to this end. With both groups looking to expand more fully into business applications – for instance, both have signed deals with the Fairhair Alliance – it seems likely that we’ll see another IoT wrap-up akin to the convergence of AllSeen Alliance and Open Connectivity Foundation.

“PRO 2017 is the ideal wireless solution to cast large IoT networks across buildings, business parks, large facilities, and venues challenged by connectivity issues, such as reinforced concrete and steel studs,” said the Alliance’s VP of technology, Victor Berrios. “The deployment potential is tremendous for smart homes, smart buildings, and smart cities.”

Because of the wide gap between the two spectrum bands, developers will need to use two individual radios – one for each band. While some suppliers ship the two radios in a single package, which would look like a single device to the developer, it seems that due to the current state of RF technology, the dual-radio constraint is going to persist for quite some time – blame physics.

But the dual-radio approach won’t be a significant constraint on growth, given that not all Zigbee devices are going to require both. Gateway devices and repeater units are the most likely candidates to embrace these dual-mode designs, to boost the coverage of networks that do not have equidistant nodes – think stairway lights linking via sub-1 GHz but supporting switches and sockets via the 2.4 GHz band, to help mesh an entire building where relying solely on 2.4 GHz isn’t an option.

The Zigbee Alliance cites outdoor lighting and facilities management, in retail or data center environments, as good example use cases for the dual-band approach, but the new implementation could be used in all manner of buildings or campuses – with things like warehouses and supply chain facilities standing out as prime candidates for meshing applications together to boost automation and efficiency.

Leslie Mulder, chair of the Zigbee PRO technical steering committee and founder of Exegin Technologies, explained that the there are already some sub-1 GHz Zigbee devices in the market today, although many use other flavors of Zigbee to communicate – including Zigbee IP or JupiterMesh, and some proprietary implementations.

Mulder added that the primary adopter of sub-GHz Zigbee PRO has been the UK’s Smart Energy Program, the national smart metering initiative. Mulder said that the Alliance had specifically added FSK (frequency shift keying) modulation to the sub-1 GHz network stack in order to meet the program’s requirements.

The key feature of the dual-band network stack in the Smart Energy Program was the ability to let a single instance of the stack act as an intermediary between 2.4 GHz and sub-1 GHz devices – acting as the Zigbee Coordinator, forming the personal area network on both radios, and then bridging devices from both radios in a seamless fashion so that the single-band end devices can speak to each other.

Zigbee is increasingly looking to grow into the utility market, and has a dedicated specification to that end – Zigbee Smart Energy. The UK project will involve some 30m meters by 2020, and the Alliance adds that the USA is collectively in the process of installing some 70m Zigbee-enabled meters, with another 40m in RFPs and business case development programs. Typically, ZigBee is used to link the meter to an in-home display that shows electricity usage.

Moving forward, the meter’s Zigbee link would be primarily used for communicating with devices inside the home or building – linking the utility-controlled meter to those smart devices, in order to carry out demand-response (DR) functions. This connection would allow the utility to use DR to better manage its grid-load, in exchange for discounts or rebates for customers that allow the utility to remotely adjust their usage.

An example of this would be in the case of a sudden drop in distributed solar generation, where the utility faces blackouts if it doesn’t fire up its reserve coal generation capacity – an expensive process, and one that can get it in trouble with emissions regulators. DR would allow the utility to adjust its customers’ usage, turning down the AC or delaying a washing machine for example, which when conducted at scale can remove the need for that coal plant entirely.

Wi-SUN is another protocol that uses the same IEEE 802.15.4 standard as ZigBee and Thread for its foundation, with both a Home Area Network (HAN) and a newer Field Area Network (FAN) protocol. With the developing focus on utility deployments, it does look as though Zigbee is moving to compete against the Wi-SUN protocol – already popular among utilities, and used by the likes of Silver Spring Networks.

The Zigbee Alliance is working on a Neighborhood Area Network (NAN), aimed at providing the last mile connections between the utility and its end customers, linking substations and smart meters. Although the current web page for the NAN doesn’t mention JupiterMesh, Riot covered the launch of JupiterMesh 12-months ago, in which the NAN term was used.