Don’t Be Afraid to Use Wireless in Your OT Network
Key Highlights
- Traditional wired systems have their own limitations in industrial settings. For example, conductor bars are restricted to analog signals, festoons and cable reels are limited to 330 feet for Ethernet, and fiber optic cables are prone to degradation that causes unexpected outages and expensive replacements.
- Learn how systems like slotted waveguides and Cisco URWB deliver interference resistance, long-range reliability and simplified maintenance.
- Optical modems provide invisible wireless connectivity for linearly moving components by converting Ethernet signals to infrared light, operating independently of Wi-Fi and radio frequencies to eliminate interference while replacing traditional energy chains and physical cabling.
While the general rule still applies — if you can hardwire it, do so — modern wireless technology has advanced significantly from the days when a microwave could disrupt your entire network. Industrial-grade wireless and optical options now deliver the speed, reliability and security needed for operational technology (OT) environments that demand constant uptime.
Of course, basic industrial communications can be achieved using conductor bars, festoons and cable reels, but these methods come with notable drawbacks. Conductor bars typically only support analog signals, meaning you would need to install an additional conductor bar for each communication channel. These bars can handle basic communication but lack the high bandwidth required by modern HMI systems. Festoons and cable reels are suitable for short distances but cannot support copper Ethernet beyond 330 feet, and fiber optic cables tend to degrade over time, leading to unexpected outages and costly replacements.
This is where wireless technologies can save time and money. While there are numerous wireless technologies and configurations available, I’ll focus on two: the Waveguide Wireless Rail System and Cisco Ultra Reliable Wireless Backhaul.
Waveguide wireless rail system
A waveguide is a hollow body with conducting walls in which electromagnetic waves can propagate. Rectangular and circular cross-sections are primarily used for this purpose. The propagation of electromagnetic waves in the waveguide depends on its geometry and the excitation of the wave. The geometry determines a lower frequency threshold above which a wave can propagate.
URWB’s use of multi path operation (MPO) addresses wireless interference by using both radios on the access point, each operating on a different frequency. If one frequency experiences issues, packets are still transmitted over the other radio frequency. This ensures that if interference occurs on a single frequency, the system can still transmit data over an alternative frequency.
The principle behind a slotted waveguide is based on a rectangular waveguide. A radio wave is fed into the slotted waveguide (SWG) and travels orthogonally to the antenna through the profile. The slotted waveguide has a longitudinal slot on one side, allowing a coupling element (antenna) to be inserted through the opening. This coupling element can be moved along the slot.
The greatest advantage of this system is that the radio wave within the SWG is electromagnetically decoupled from the external environment, making interference nearly impossible. This allows for more efficient use of the available frequency spectrum.
Additionally, signal attenuation over distance is significantly less than with omnidirectional antennas, enabling broader signal transmission ranges and longer segment lengths.
While this system offers the best wireless containment and interference resistance, it requires routine maintenance similar to that of a power conductor bar. Two main players in this space are Vahle and Conductix, each offering their own proprietary benefits.
Cisco Ultra Reliable Wireless Backhaul
Cisco Ultra-Reliable Wireless Backhaul (URWB) is a wireless technology designed to provide reliable connectivity for both fixed and mobile assets, particularly in industrial settings where fiber optic cabling is impractical or too costly. URWB supports high-throughput performance, low latency and low packet loss, making it suitable for applications such as autonomous vehicles, robots and manufacturing operations.
Cisco URWB uses a proprietary version of multiprotocol label switching, allowing client devices to connect to multiple wireless access points simultaneously. This means that data sent from carriers and bridges is duplicated and received on multiple infrastructure radios before being delivered to the primary controller.
A waveguide is a hollow body with conducting walls in which electromagnetic waves can propagate. Rectangular and circular cross-sections are primarily used for this purpose. The propagation of electromagnetic waves in the waveguide depends on its geometry and the excitation of the wave.
The primary controller then determines which packets to keep and which to discard as duplicates. Since clients are always connected to multiple infrastructure radios, roaming between them does not result in packet loss when switching to a stronger signal.
URWB’s use of multi path operation (MPO) addresses wireless interference by using both radios on the access point, each operating on a different frequency. If one frequency experiences issues, packets are still transmitted over the other radio frequency. This ensures that if interference occurs on a single frequency, the system can still transmit data over an alternative frequency.
In a Cisco test using URWB with and without MPO enabled, they reduced an already low packet loss of 0.26% (287 packets) to 0.00005% (5 packets) over a 1.5-hour period.
Optical modems
While optical modems wouldn't be used as a primary communication method, they are worth mentioning. An optical modem is a device that converts electrical signals into infrared light signals and vice versa. This is similar to a media converter that converts signals between copper and fiber media.
Two optical modems are needed to enable data transmission. Since the communication between optical modems is wireless and optical (infrared), the devices must be mounted in line with each other and have a clear line of sight between them. These are often used in applications where components move linearly relative to each other in a fixed area, replacing energy chains or physical cables (either copper or fiber).
Optical modems are typically invisible on the network, simulating the functionality of a copper connection between Ethernet components such as PLCs. In a typical installation of a pair of optical modems, an Ethernet signal destined for a target device is passed to the optical modem via a copper connection, where it is then converted into an optical signal. The optical signal is received by the opposing optical modem, where it is converted back to a copper connection to continue to the target device.
Due to the wireless communication between optical modem devices being solely optical (infrared), the data transmission does not interfere with or get affected by Wi-Fi or radio signals/noise from nearby components.
Danniel Butler is a network engineer at Concept Systems, certified members of the Control System Integrators Association (CSIA). For more information about Concept Systems, visit its profile on the Industrial Automation Exchange.
