What's with wireless?
December 2012, Fieldbus & Industrial Networking
The changes that are taking place in wireless technology have several drivers, including: the requirement for intercommunication; the need for speed; the demands of co-existence; and the need to extend battery life of wireless devices.
These drivers are similar whether we are talking about personal, commercial or industrial use of wireless. At a personal level we want our smartphones, laptops, printers, TVs and home automation systems to talk to each other, wirelessly, instantaneously, without interference and without needing to make a dash for the nearest charger socket every time we come to a standstill. Similarly, from an industrial perspective we would like our sensors, instrument transmitters, actuators, programming devices and control systems to communicate wirelessly, in real-time, without interference and with a battery life of up to 10 years in the case of wireless instruments.
In response to these demands, higher level protocols are being adopted as standards for intercommunication, new low level protocols and frequency bands are being employed to accommodate higher bandwidth transmission and to reduce the problems of overcrowding, and more efficient protocols along with improved silicone are being introduced to reduce energy consumption and extend battery life.
In monitoring and control the wireless landscape is well-defined by various standards that fall under the IEEE 802 umbrella. As instrumentation and control practitioners our interests are broadly covered by IEEE 802.11 (Wireless Local Area Networks – WLAN), IEEE 802.15 (Wireless Personal Area Networks – WPAN) and Bluetooth, which has a foot in each of these standards. IEEE 802.11 and 802.15 cover the physical media layer (PHY) and media access control layer (MAC) of the communications stack – they do not fully define higher levels of the OSI model. A practical consequence of this is that even though two wireless systems may comply with one of the above-mentioned 802 standards or their derivatives, there is no guarantee (or even likelihood) that they will readily intercommunicate in a plug-and-play way.
IEEE 802.11 WLAN
IEEE 802.11 underlies the Wi-Fi technology with which most readers are already familiar. A Wi-Fi access point is typically used as the gateway between a wired or fibre intranet and Wi-Fi enabled mobile wireless devices such as smartphones, laptops and tablets. 802.11 supports mesh (aka Wi-Fi Mesh) as well non-mesh networking. In its current 802.11n iteration the specification covers data rates of up to 150 Mb/s per spatial stream with up to four simultaneous MIMO (multiple-input multiple-output) streams providing a maximum throughput of 600 Mb/s. 802.11n specifies usage in the 2,4 GHz and 5 GHz bands.
The 802.11ac specification, which is in draft format, supports data rates of up to 867 Mb/s per stream on the 5 GHz band and up to eight MIMO streams. This brings the prospect of Gigabit plus data transfer rates over wireless and the good news is that power consumption is less than 802.11n for the equivalent data rate as a result of more efficient data encoding. 802.11ac commercial product is already available and is expected to be commonplace in 2013.
But it does not stop there – the Wireless Gigabit Alliance (WiGig) is already promoting 802.11ad. This will introduce 60 GHz connectivity with data rates of around 7 Gb/s on a single stream and at even lower equivalent power consumption. Product incorporating this technology is expected to be commercially available during 2014 with broad-scale commercial introduction from 2015 onwards.
IEEE 802.15 WPAN
There are multiple task groups that operate under the IEEE 802.15 umbrella. The main ones of interest are IEEE 802.15.1 (Bluetooth) and 802.15.4 (Low Rate WPAN), which underpins WirelessHART, ISA100.11a, WIA-PA (IEC 62601), ZigBee, 6LoWPAN and other high level wireless protocols. 802.15.4 covers both mesh and non-mesh wireless networking.
Well-known industrial control vendors supporting WirelessHART include ABB, Emerson and Siemens. The technology has achieved significant penetration – in July 2012 the HART Communication Foundation announced that there are more than eight thousand wireless networks employing WirelessHART. In October 2012 Emerson predicted that it will have 100 000 Emerson wireless devices installed by the end of 2012 and told Emerson Global User Exchange delegates of projects that are under way or in the planning stage with up to 15 000 wireless nodes.
At the end of October 2012, in a claimed ‘world first’, Emerson announced the release of the Fisher 4320 Wireless Position Monitor with On/Off Control Output Option for linkage-less position feedback and discrete valve control over Smart Wireless self-organising mesh networks. Offering closed loop control over wireless represents a major step promoting industrial wireless as not only a monitoring solution but also as a control solution.
Fisher 4320 Wireless Position Monitor with the on/off control output option facilitates closed loop control over WirelessHART.
ISA100.11a is the foundation for Honeywell’s OneWireless, Yokogawa’s Field Wireless products and GE’s Essential Insight.mesh among others. The standard has the advantage of coming into being somewhat later than the evolutionary development of WirelessHART and hence embraces IPv6 addressing. It also considers wireless technology for backhaul applications – getting the data from the wireless mesh back to the control system.
With the ever-rising threat of malware for industrial espionage and infrastructure disruption, one of the most recent and significant events in the ISA100.11a world is the announcement by 3eTI, a wireless supplier to the US Navy, of the launch of its AirGuard iMesh suite of products – a military-grade secure ISA100 wireless mesh network solution.
WIA-PA (Wireless Networks for Industrial Automation – Process Automation) is the Chinese standard for industrial wireless. Given the huge Chinese market and the acceptance of WIA-PA as international standard IEC 62601 some industry commentators see this protocol having the possibility of overwhelming both WirelessHART and ISA100.11a.
While the wireless wars of the past decade were being waged between WirelessHART and ISA100a, ZigBee continued to go from strength to strength. And it is still experiencing rapid growth. The protocol is widely used in M2M (Machine to Machine) communication and is slated to be a key technology in IoT (the Internet of Things).
In October 2012 the ZigBee Alliance celebrated its first decade with 600 certified products and a claim of billions of ZigBee chips sold. With nine standards that cover the gamut from Home Automation through Building Automation and Smart Energy, ZigBee is projected to hold 50% of the IEEE 802.11.15 market by 20151.
ZigBee is the basis for many of the Smart City projects that have already been implemented. Sweden’s Göteborg Energi installed 265 000 smart electricity meters which communicate to 8000 concentrators via ZigBee. On the other side of the Atlantic, Kansas City, Kansas kicked off a project earlier this year that will see approximately 70 000 smart electricity meters and 51 000 smart water meters linked via ZigBee for remote demand side management and billing.
6LoWPAN refers to IPv6 over Low-Power Wireless Personal Area Networks and is a protocol for supporting IPv6 on low power, low cost wireless devices over wireless networks based on IEEE 802.15.4. With its support for IPv6, 6LoWPAN is a challenger for ZigBee in the IoT.
In October 2012 Linear Technology’s Dust Network product group announced the SmartMesh LTC5800 (system-on-chip) and LTP5900 (module) families – low power IEEE 802.15.4e compliant wireless sensor networking products. These SmartMesh ICs and modules enable tiny sensors (motes) to be designed with a battery life of over 10 years. Two communication standards are supported: the SmartMesh IP version for 6LoWPAN compliance and SmartMesh WirelessHART for IEC62591 compliance.
In February 2012 the IEEE approved the IEEE 802.15.4e MAC Enhancement Standard document for publication. This amendment to 802.15.4 addresses improvements for industrial automation application aligns 802.15.4 with modifications proposed in WIA-PA. Key changes include support for low latency deterministic operation, improved link reliability, synchronised time slotted channel hopping, greater numbers of network devices and lower energy consumption for longer battery life.
Bluetooth, which started out in v1 being based on 802.15.1, has spawned siblings (v3 and now v4) that have morphed to be able to link directly to 802.11 based infrastructure via the inclusion of an embedded 802.11 Protocol Adaption Layer (PAL). This is how data transfer rates jumped by a factor of 10 from Bluetooth 2.0 to Bluetooth 3.0.
Bluetooth 4.0 defines two modes of operation: Classic mode and Low Energy mode. Devices may be single mode devices (supporting only one mode) or dual-mode devices. Classic mode is good for around 2 Mb/s whereas Low Energy Mode offers only around 100 Kb/s throughput, but at significantly lower energy consumption.
With v4 released in 2011, it was forecast that all Bluetooth devices would be v4 compliant before the end of 2012. Adoption has been slower than predicted and major mobile platform vendors are now expected to ramp up delivery of Bluetooth 4.0 devices during 2013.
The implementation of new wireless technology in industrial applications almost always lags its release in consumer products, but it is inevitable that many of the developments covered in this article will find their way on to the factory floor and into process plants.
When planning investments in wireless technology we suggest that readers:
* Select your application. Not all applications are good candidates for wireless. There are very few wireless systems approved for functional safety applications. Wireless could be a good fit for condensate and steam trap monitoring, but less suited for high speed sequencing.
* Select devices that support both the 2,4 GHz and 5 GHz bands – the airwaves are getting crowded and channel spacing is wider at 5 GHz and less sensitive to interference.
* Be aware that as band frequencies rise, aerial design and placement becomes more important and range diminishes.
* List all your wireless devices and actively manage channel usage where this is within your control.
* Persuade selected vendors to demonstrate products in situ or provide loan equipment before you buy.
* Consider a wireless survey as part of your planning process. Document your channel usage. And even if channels are not crowded yet, they will become so as the Internet of Things becomes a reality.
* Delay, where possible, buying devices with Bluetooth 3.0 interfaces (laptops, smartphones, tablets,) until they are available with Bluetooth 4.0.
* Think about how you are going to manage battery replacement – would you want to change 15 000 batteries? What would be the effect of that on Total Cost of Ownership?
* Keep an eye on what new technologies are looming on the horizon and read market reports. For instance, if you knew that within the next five years, shipments of RFICs for Wireless Sensor Network (WSN) markets could exceed one billion units per year and that ZigBee and 802.15.4 would have the largest market share but low power variants of Bluetooth and Wi-Fi were predicted to grow even faster², how might that affect your planning?
If you are going to use wireless in control, as opposed to pure monitoring we suggest that readers:
* Establish what kind of latency and jitter you can expect – both now and as your network grows – and whether that is acceptable for the candidate loop.
* Build in solid feedback and watchdog circuits into your loop design – especially if your control involves sequential operation of actuators.
1 ABI Research, Study: Wireless sensor networks; http://tinyurl.com/ckfdnz8
2 ON World, Report: 802.15.4 & ZigBee: Expanding markets, growing threats; http://tinyurl.com/br9d5hr
Sources & Resources
6LoWPAN Working Group, http://6lowpan.net
Bluetooth Special Interest Group, http://www.bluetooth.org
HART Communication Foundation,
Prentice Hall, Bluetooth Low Energy; The Developer’s Handbook Robin Heydon: ISBN-13: 978-0-13-288836-3
Wi-Fi Alliance, http://www.wi-fi.org
Wireless Gigabit Alliance, http://wirelessgigabitalliance.org
ZigBee Alliance, http://www.zigbee.org
About the author
Andrew Ashton has electrical, mechanical and business qualifications and has been active in automation and process control since the early 1980s. Since 1991 he has headed up a company that has developed formulation management systems for the food, pharmaceutical and chemical manufacturing industries and manufacturing solutions involving the integration of various communication technologies and databases. Developed systems address issues around traceability, systems integration, manufacturing efficiency and effectiveness. Andrew is a contributing editor for S A Instrumentation and Control.