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5 +1 things driving IIoT and 4.0: wireless connectivity (II)

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WiFi in the clouds image

Part 1 of this series looked at the specific challenges for wireless communication in an industrial environment, whereas this article will give a summary of several specific wireless standards. But you will realise that they all have introduced new versions which overcome their weak properties. The intense competition tends to improve each technology so that it becomes difficult to select a single fitting one.

You can sort wireless technologies into categories by using their derivation:

  • IEEE 802 technologies

    • 802.11 technologies (WLAN)

    • 802.15 technologies (WPAN)

      • 802.15.1 technologies (Bluetooth)

      • 802.15.4 technologies

  • LPWAN technologies

  • Cell phone technologies

This second part will cover all IEEE 802 technologies. Part three will cover LPWAN and cell phone technologies.

IEEE 802.11 WiFi (LAN)

WiFi Symbol

typical data rate frequencies typ. range indoor max. range

145Mbps (WI-Fi 4 @2.4GHz)
650Mbps (Wi-Fi 5 @ 5GHz)
>1Gbps (Wi-Fi 6)
decreasing with distance

2.4GHz, 5GHz 20m (Expandable with Wi-Fi Mesh)

400m @2.4GHz 50m @5GHz

typical latency security low power mobility (roaming)
1-3 ms but not deterministic (can be up to >1 s for a packet)
robustness coexistence numb. nodes  
 
availability ease of install. cost  
 

 

You all know Wi-Fi. One of its benefits is the excellent availability of infrastructure devices and service companies. For own device designs, there are many chips and modules on the market for reasonable prices. Wi-Fi also has an excellent data rate and is perfect for huge data packets. But classical Wi-Fi does have two significant problems in industrial environments: The range is not the best, and obstacles or interference can lower it even more. Longer distances will decrease data. The other problem is caused by sharing the 2.4 GHz with other applications and technologies. 5 GHz is less likely to have coexistence problems but does not penetrate solid objects as well as 2.4 GHz. Wi-Fi always needs careful planning and frequency use strategy to achieve maximum robustness and data rate.

The security of Wi-Fi used to be weak, but it has been enhanced a lot. There are products now available which support WPA, and it is part of the newest version, 802.11ax (Wi-Fi 6)

Wi-Fi 6 (802.11ax)

Using more efficient data encoding, Wi-Fi 6 can increase data rates up to 40% compared to Wi-Fi 5.

Wi-Fi 6 also addresses the power consumption issue with Wi-Fi. It now has a “target wake time” (TWT) feature to allow low power operation: The access point can tell the connected device when to put its Wi-Fi radio on and off to receive the next transmission.

Wi-FI does have a problem when you are in a place with many WI-Fi devices. You may have experienced this in airports or shopping malls: The data rate decreases drastically. Wi-Fi 6 offers new technologies to solve this problem. one is called "Orthogonal Frequency Division Multiple Access" (OFDMA).

Wi-Fi HaLow (802.11ah)

This version addresses the range and power consumption problems of Wi-Fi. It defines the use of licence-free sub-GHz bands to reach higher distances and aims at the power consumption of LPWAN technologies. But the data rate naturally decreases to values up to 347 Mbps. The protocol was approved in 2016 but could not gain a significant impact on the market.

IEEE 802.15 WPAN (personal Area Network)

Originally this part of IEEE 802 was established for "Short Range Communication" or "Short Range Devices" (SRD) like headphones, mouse, keyboard or printer connections. But time by time, the technology entered other application fields and was adopted to higher ranges. Today, e.g. Bluetooth has similar ranges to WLAN and the title WPAN is more a legacy than a propper description.

IEEE 802.15.1 Bluetooth

Bluetooth Symbol

typical data rate Frequencies typ. range indoor max. range

50Mbps (BT 5.0)
780 Kbps(BT 4)

2.4GHz 20m @class 1 (Expandable with BT Mesh)

400m

typical latency security low power mobility (roaming)
10-15 ms
BT Mesh: can be much higher
(BT5)
robustness coexistence numb. nodes  
 
availability ease of install. cost  

 

 

Although Bluetooth (BT) has an ambiguous reputation because of the user-unfriendly pairing procedure of BT3 consumer products, it is well suited for industrial purposes. The reason is its robustness resulting from "Forward Error Correction" (FEC), low sensitivity to reflections, and the frequency hopping technology: It uses 79 channels of 1 MHz and can perform up to 1600 changes per second to escape from interferences. The latest version even uses AFH ("adaptive frequency hopping"), which can exclude disturbed channels. Since BT5, you can use "quick connection" without pairing or pairing by NFC.

The former data rate of up to 706.25 kbit/s (receiving) and up to 57.6 kbit/s (sending) is history. Since BT5.0, the "EDR" (enhanced data rate) is up to 50 Mbit/s. This is far enough for most industrial use cases.

All these benefits have persuaded major manufacturers of industrial automation products, like Phoenix Contact, WAGO or Schildknecht) to use BT for their products.

Formerly, a device could have only up to 6 active connections. This is history too.

The distance depends on the power class (indoor values):

  • class 1 up to 100 mW (20 dBm) 100m
  • class 2 2,5 mW (4 dBm) up to 50 m
  • class 3 up to 1 mW (0 dBm) up to 10 m

Security is one of the powerful features of BT. Since BT 4.2, you can use the ECC-/AES-CMAC-Standard. If the device uses all 16 characters (128 bit) for its PIN, you have substantial security for a wireless network. Even the PROFIBUS Nutzerorganisation e. V. (PNO) has defined BT (as well as WI-FI) to be the wireless technology for PROFINET data packages. Lately also CAN in Automation (CiA) has decided to use BT for wireless transmission of CAN telegrams.

BTLE (since BT4)

has features to lower the power consumption drastically (average is 1 µA). The arousal from sleep does, of course, increase the latency by several ms. Its data transfer rate is practically limited to values of less than 100 kbps. BTLE has also introduced a technique called "Connect-Communicate-Disconnect", which allows a device to connect to several hundred other devices. Due to these features, BTL is ideal for episodic or periodic transfer of small amounts of data, like from homogenous moulded battery-powered sensors. When the battery is flat after some years of operation, you exchange the whole sensor.

Bluetooth Mesh (BT5)

uses the flood network principle to build a mesh network. Network nodes that receive a valid message (i.e., the encryption key is right) resend this message. To avoid retransmission, the nodes have a list of previously sent messages, and messages get a limited lifetime (limited number of hops from node to node. There is strong encryption for every message using two keys: One for the network and one for the application. BT5 theoretically can handle up to 32767 nodes in a network. Installing a new device into the network (called "provisioning", a security-critical process) is done with high security using ECC Key Exchange algorithms.

IEEE 802.15.1 (IO-Link Wireless)

The purpose of the wired version of IO-Link is to transmit sensor or actuator data on the lowest level. It is mainly used in industrial factory automation. IO-Link Wireless is an extension of wired IO-Link on the physical level only. It uses the same IEEE 802.15.1 radio technology as used by Bluetooth Low Energy but a different stack. Therefore the features are comparable to BTLE, plus the benefit to be easily integrated into an existing IO-Link infrastructure.

IEEE 802.15.1 (WISA, Wireless Interface to Sensors and Actuators)

There are two standards which are commonly known as "WSAN" (Wireless
Sensor Actuator Network) and which were defined specifically for industrial applications. One of them is IEEE 802.15.4 based and called Wireless HART (see below). The other is called WISA and is IEEE 802.15.1 based. WISA was initially defined by ABB and accepted by the PNO as the wireless standard (called "WSAN-AIS") for PROFINET.

It slightly differs from Bluetooth radio (e.g., 82 channels of 1 MHz, 1 Mbps data rate and a different frequency hopping scheme, 120 nodes )

The pros and cons are similar to BT4, but coexistence, number of nodes and latency are inferior to BT5. If you need to integrate wireless connections into an existing PROFINET installation, WISA is worth to be considered.

 

IEEE 802.15.4

This standard defines several basic procedures and features, but the following derivates have added their specific add-ons.

ZigBee

ZigBee logo

typical data rate Frequencies typ. range indoor max. range

250 kbps @2.4 GHz

2.4GHz (IEEE 811.15.4)
900-928 MHz, 868 MHz

10 - 100 m (expandable with mesh)

200m

typical latency security low power mobility (roaming)
25 up to several 100 ms
depending on payload size, number of devices and topology
robustness coexistence numb. nodes  
 
availability ease of install. cost  

 

 

ZigBee IP definitions put a significant emphasis on seamless connectivity to the internet. It, e.g. uses 6LoWPAN for IPv6 connectivity and has added routing and security features to the 802.15.4 standard. It has been the first open standard for IPv6 based wireless mesh networks (although you can choose different network topologies). As an "internet friendly" standard, it can communicate using the TCP, RPL and UDP protocols. Each node has its IP.

ZigBee has become very popular for home and building automation and M2M communication. It works as well as in the sub-GHz bands as in the 2.4 GHz band. It uses AES-128-CCM security algorithms. It used to be the most cost-efficient wireless network technology in automation. As low prices BT and Wi-Fi modules are now available, there is no longer a substantial benefit from using ZigBee for typical I4.0 projects.

The newest version (called ZigBee PRO) is aiming at IoT applications. It offers low power operation (including energy harvesting functionality) and can connect up to 64,000 devices in a network.

 

WirelessHART®

typical data rate Frequencies typ. range indoor max. range

250 kbps @2.4 GHz

2.4GHz

10 - 100 m (expandable with mesh)

250m

typical latency security low power mobility (roaming)
2 seconds
robustness coexistence numb. nodes  
 
availability ease of install. cost  

 

 

Wired HART® (Highway Addressable Remote Transducer Protocol) has been used for over 30 years. It enables sensors and actors to communicate over a current loop with controllers digitally. The wireless extension was defined in 2010 in IEC 62591. It is mainly used in process automation and monitoring applications because it is too slow (data rate of 250 kbps and latency of 2 seconds) for factory automation. The physical transmission is based on IEEE 802.15.4 but is uses only 15 channels of the 2.4 GHz band.

Frequency hopping and mesh topology account for acceptable robustness. AES-128 encryption is used for security.

The PNO chose WirelessHART for the WSAN-PA standard. Therefore it is frequently used for process monitoring and cycle times of several seconds. The extremely high latency of 2 seconds is caused by the fact that the concept uses superframes, allowing only one communication every 1500 ms for each device. This latency makes it unlikely that this standard will become a relevant player in IIoT. It intended to replace wired HART connections, and it works great for this purpose.

ISA 100

ISA 100 Logo

The ISA100 standard has been developed for industrial applications. It is a complex stack That reaches up to the application layer. The MAC and physical layer are based on IEEE 802.15.4. ISA100 uses frequency hopping at 2.4 GHz and mesh topology. The Network and transport layers are based on TCP or UDP and IPv6.

Possibly because of its complexity and openness, this standard has not yet penetrated the European market. It offers similar features as Wireless HART, and thus I have omitted the feature table.

 

Please note that this summary is not a complete list of existing technologies. Others are trying to get their stake from the industrial automation market, like ANT from Garmin or KNX RF, Wi-SUN or Thread, to name just some of them. You are kindly invited to add a comment if you have the feeling that we all should learn about another technology.

 

Volker de Haas started electronics and computing with a KIM1 and machine language in the 70s. Then FORTRAN, PASCAL, BASIC, C, MUMPS. Developed complex digital circuits and analogue electronics for neuroscience labs (and his MD grade). Later: database engineering, C++, C#, industrial hard- and software developer (transport, automotive, automation). Designed and constructed the open-source PLC / IPC "Revolution Pi". Now offering advanced development and exceptional exhibits.

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