HMS Industrial Networks
Wireless communication in tough, demanding applications is nothing new. Wireless has been used for more than 30 years through the use of proprietary radios. However, with the modernization of industrial networks and the emergence of different Ethernet protocols and the Industrial Internet of Things, there has been an increasing demand for standardized wireless technologies.
But one wireless technology cannot offer all the features and strengths that fit the various application requirements. Standardized wireless technologies including WLAN (also commonly referred to as WiFi), Classic Bluetooth and Bluetooth Low Energy, 802.15.4 as well as number of proprietary technologies all cater for different requirements. These could either be high data throughput, robustness or low power.
This article compares the wireless technologies available so you can find the solution that fits your application the best.
Overview: Which Wireless Technology is the Best Choice?
Classic Bluetooth Technology
Bluetooth technology (IEEE 802.15.1) is well-suited for wireless integration of automation devices in serial, fieldbus and Ethernet networks. Bluetooth technology is especially suitable for devices with high demands on small footprint, low power consumption and cost-efficiency.
Bluetooth Technology Facts:
- Range of 10 meters up to over 300 meters with a long-range module.
- Cyclic and fast transmission of smaller data packages.
- Data throughput of maximum 780 kbit/s gross (up to ~700 kbit/s net). With Bluetooth v4.0+EDR (Enhanced Data Rate), the data through-put is 2.1 Mbit/s gross (~1.5 Mbit/s net).
- Latency of 5 –10 ms.
- Security features with 128-bit encryption that offers protection against data eavesdropping.
- High system density where several wireless devices can be connected in the same radio environment and operate flawlessly
- Robust features like Adaptive Frequency Hopping (AFH), Forward Error Correction (FEC), narrow frequency channels, and low sensitivity to reflections /multi-pathing.
- High availability in consumer products (phones, tablets, laptops etc).
Bluetooth Low Energy
Bluetooth Low Energy (previously marketed as Bluetooth Smart) was introduced in 2011 and has been a hot topic ever since. The technology has some important limitations as well as benefits and is quite different from Classic Bluetooth technology:
- Bluetooth low energy technology is ideal for episodic or periodic transfer of small amounts of data.
- In a Bluetooth application where streaming data is used, Classic Bluetooth technology is the preferred choice as it achieves substantially greater throughput than Bluetooth low energy technology.
- High availability in consumer products.
Comparison: Classic Bluetooth vs. Bluetooth Low Energy
Since a Bluetooth Low Energy device is in sleep mode most of the time – the maximum/peak power consumption is only 15 mA and the average power consumption is of only about 1 uA.
Connection Set-up Times
In Bluetooth Low Energy, the actual connection times are of only a few mS and thereby the connection is quickly initiated as the device wakes up.
Many features of Classic Bluetooth technology are inherited in Bluetooth low energy technology including Adaptive Frequency Hopping (AFH) as well as part of the Logical Link Control and Adaptation Protocol (L2CAP) interface.
Data transfer rates with Classic Bluetooth technology using Enhanced Data Rate (Bluetooth v2.1 + EDR) can exceed 2 Mbps (actual payload), but practical transfer rates for Bluetooth Low Energy technology are below 100 kbps (actual payload of roughly 1/20).
Bluetooth Low Energy technology provides no support for the Serial Port Profile (SPP) in the standard Specification v4.0. Many other profiles are not offered for Bluetooth low energy technology because of the differences in the connection models. The Classic Bluetooth scenarios that are not part of Bluetooth Low Energy technology include headset (HSP), audio distribution (A2DP), video distribution (VDP) and file transfer (FTP).
Number of Nodes
Just as with Classic Bluetooth technology, Bluetooth Low Energy technology is based on a master connected to a number of slaves. However, in Bluetooth Low Energy, the number of slaves can be a lot more. How many depends on the implementation and available memory.
The “Advertising“ functionality of Bluetooth Low Energy technology makes it possible for a slave to announce that it has something to transmit to other devices that are “scanning.“ “Advertising“ messages can also include an event or a measurement value.
In Bluetooth Low Energy technology, all parameters have a state that is accessed using the Attribute Protocol. Attributes are represented as characteristics that describe signal value, presentation format, client configuration, etc.
Wireless LAN (WLAN)
Wireless LAN (IEEE 802.11) is well-suited for monitoring, configuring and data acquisition, but can also be used for time-critical control in the same applications. Furthermore, the built-in roaming functionality is useful in factory automation applications with moving devices.
Wireless LAN Facts
- Range 200 meters (up to 400-500 meters in free line-of-sight) in the 2.4 GHz band and some 50 meters in the 5 GHz band (802.11a) (free line of sight up to 150 meters); however, obstacles and interference could lower the range substantially.
- Data throughput of 11 to 54 Mbit/s gross (~5 to 25 Mbit/s net) for IEEE 802.11b/g and 300 Mbit/s gross (~70 Mbit/s net for IEEE 802.11n).
- Security models like WEP, WPA, WPA2, TPIK and PSK EAP.
- IEEE 802.11a operates on the 5 GHz band and provides the possibility for 19 additional non-overlapping channels in addition to the three non-overlapping channels in the 2.4 GHz band.
- High availability in consumer products.
The Difference Between 2.4 GHz and 5 GHz Wireless LAN
As the use of wireless technologies is increasing in the 2.4GHz band, interference problems can occur. To make sure that the wireless solution is robust, companies are starting to use the 2.4GHz band for office and IT communication and then use the 5GHz band for the manufacturing and M2M communication.
The Wireless LAN IEEE 802.11b/g radios utilize the 2.4GHz frequency band (2.412 – 2.472GHz) and the IEEE 802.11a radio utilizes the 5GHz frequency band (5.180 – 5.825GHz). IEEE 802.11n radios can operate in either frequency band. There are the following worldwide implementation attributes:
- The 2.4GHz ISM band provides 13 overlapping channels spread equally over the frequencies plus a 14th channel used in Japan with the center frequency 2.484GHz. This leaves available only three non-overlapping channels in the 2.4GHz band.
- The 5GHz ISM band is divided up into sub-bands called U-NII bands (Unlicensed National Information Infrastructure) and are usually named U-NII-1, U-NII-2, U-NII-2e, and U-NII-3 where U-NII-3 is not freely available worldwide. In total, this gives 23 non-overlapping channels where four of these have limitations based on location.
IEEE 802.15.4 Bluetooth (ZigBee, WirelessHART, ISA SP-100)
IEEE 802.15.4 is available in a number of standards as well as part of proprietary wireless protocols. ZigBee, WirelessHART and ISA SP-100 are all used in industrial applications and all are based on IEEE 802.15.4. The 802.15.4 technologies are mostly used for process and building automation application and the low power features makes it well suited for battery operated devices. The technology also offers mesh network functionality that makes it capable to cover wide areas when there are now requirements on low latency.
As more than one wireless technology is often used in parallel, there could potentially be disturbances resulting in higher latency or even data losses. These potential side effects cannot be accepted in mission-critical industrial and medical applications. Therefore, it is important to optimize coexistence of various wireless technologies in order to get a disturbance-free operation.
All of today’s most used wireless technologies operate in the 2.4 GHz band and they address potential disturbances in different ways:
Wireless LAN / WLAN, also commonly referred to as Wi-Fi, has three non-overlapping channels with a bandwidth of 22 MHz and is using Direct-Sequence Spread Spectrum (DSSS). DSSS makes sure that the transmitted signal takes up more bandwidth than the information signal that is being modulated and thereby the wireless communication link becomes less vulnerable to disturbances.
Classic Bluetooth technology has 79 channels with a bandwidth of 1 MHz and combines this with Adaptive Frequency Hopping (AFH) in order to avoid interferences. AFH monitors the bit-rate and when disturbances (such as when another wireless technology occupies the link) are found, Bluetooth technology stops to use the channels that are occupied. The channel is monitored in the background and as soon as the occupied channel is free, it can be used again.
Bluetooth low energy technology also uses AFH; but Bluetooth low energy technology only uses 40 2 MHz wide channels.
Different Ways to Avoid Disturbance:
Implement 5GHz WLAN
The WLAN IEEE 802.11 b, g radios utilize the 2.4GHz frequency band and the IEEE 802.11a radio utilizes the 5GHz frequency band. IEEE 802.11n radios can operate in either frequency band. In order to get disturbance-free WLAN communication links, it is thus possible to use the 5 GHz band instead of the 2.4 GHz band. However, even though the 5 GHz band is increasing in popularity in industrial and medical applications, there is a large installed base of IEEE 802.11 b, g networks that requires a good coexistence solution.
In order to secure disturbance-free communication for WLAN in the 2.4GHs band, it is possible to use special antenna solutions (like leakage cables); however, these solutions are typical expensive installations.
It is also possible to beforehand choose channels that are not to be used (frequency planning) in order to avoid interference with other wireless systems used in the same environment.
For instance, in cases where WLAN and IEEE 802.15.4 are used in parallel, coexistence can be implemented by making room for some IEEE 802.15.4 channels in-between the three WLAN channels. By doing so, it is possible for WLAN and IEEE 802.15.4 to work reliably in parallel. When using Bluetooth, the same feature is possible by using channel blacklisting.
Adaptive Frequency Hopping (AFH)
Both Classic Bluetooth and Bluetooth low energy apply the Adaptive Frequency Hopping (AFH) feature which detects potential channel interference; for instance, a WLAN 802.11 b, g, n device transmitting in close proximity. If such interference is found the channel is automatically blacklisted. In order to handle temporary interference, an implemented scheme re-tries the blacklisted channels and if the interference has ceased the channel can be used. AFH prevents Bluetooth from interfering with other nearby wireless technologies.
Low Emission Mode
Classic Bluetooth is built to be robust mainly thanks to AFH. But when performing device discovery or establishing a device connection, the Bluetooth activities can disturb a WLAN network.
In order to make sure that Classic Bluetooth operates smoothly in parallel with other wireless technologies, there is an extended Bluetooth coexistence feature which is named “Low Emission Mode®.” This is developed by u-Blox and is available in the Anybus Wireless Bridge from HMS.
With the Low Emission Mode, coexistence is solved during device discovery and connection set-up without jeopardizing the Bluetooth Specification or interoperability between various Bluetooth enabled products.
Conclusion: Which Technology Should you Choose?
As we have seen, there is no one-for-all technology for industrial wireless communication. On a general note, we can say that if if high data throughput is most important – choose WLAN. If connection robustness/stability or cost efficiency is most important – choose Bluetooth. However, there are a lot of gray zones here and sometimes, you want a bit of both.
Choose a Solution That Supports Many Wireless Technologies
Since your requirements may change as your networking infrastructure changes, it is wise to choose a wireless solution which can support the different technologies on the market. This way you can easily update your wireless infrastructure as your prerequisites change. The Anybus Wireless Bridge, Anybus Wireless Bolt and IXXAT CANBlueII from HMS Industrial Networks are examples of solutions supporting the different wireless technologies on the market.
Learn more at www.anybus.com/wireless