Wireless technologies are no longer a luxury or bonus; they’re mandatory for modern industrial networking. As the Industrial Internet of Things (IIoT) becomes the standard for how communications networks are run and structured, wireless infrastructure will serve as the glue that holds these application scenarios together.
Wireless local area networks (WLANs) require a carefully balanced set of network characteristics. Some elements, like low latency and reliable throughput, play more important roles than others. To evaluate the quality of a wireless network, consider these performance indicators:
- Packet loss rate: The percentage of sent messages (or packets/frames) not received successfully by the intended recipient. In ideal situations, this rate would be no greater than 0.1 percent. However, in noisier environments, error rates may reach 2-3 percent.
- Latency: The delay in transmission for the delivery of a message via a wireless connection. The strongest networks have low latency, which in most cases is far less than 50-100ms.
- Data throughput: The ability to reliably transmit a certain amount of data over a specified time. The higher and stronger the throughput (e.g., more than 50-100 Mbits/s), the better the network.
- Interruption: A break in the transmission that takes place when a client roams from one access point to another. Ideally, networks will have few, low impact interruptions (e.g., less than 50ms).
- Range: The area included by an access point or the seamlessness in the coverage of a facility that determines whether the WLAN connections are strong enough to reach all necessary locations. Ranges can be large or small, depending on the design and objectives of the specific network, but stronger networks typically have longer ranges.
Six New WLAN Technologies to Improve Network Performance
The IEEE 802.11 standards for media access control and physical layer specifications identify special technologies for WLANs. These can be used in a variety of industrial applications to meet the criteria list above and bolster overall network reliability and performance.
Characterized by long range and high transmission speeds, WLANs require a strong design that is optimized to meet the unique requirements of industrial applications. Optimization technologies, along with the latest technical options and modern equipment, will put teams on the path to ensure the quality and throughput of wireless networks, no matter the application scenario.
Here are six new WLAN technologies to know more about:
1. Adaptive noise immunity (ANI): Enabling the ANI mechanism in an access point will help prevent the interference of other signals and improve the data throughput. With a heightened sensitivity to detect the correct WLAN signals, it's far less likely for the receiver to improperly process an interfering signal instead. This reduces both missed and delayed transmissions, ultimately optimizing the throughput.
2. Adaptive radio frequency (RF) optimization: Since it's possible for external interferences to change dynamically, some WLAN systems may benefit from a mechanism that automatically switches to a different radio channel. Modern access points with this feature can minimize external interference by adapting the radio channel to its environment, without manual intervention.
3. Band and client steering: In networks with multiple access points and clients, it can be helpful to shift clients to another frequency band or access point with a lighter load. For example, if a client normally connects to a 2.4 GHz band, but can communicate in the 5 GHz frequency range too - it enables an automatic shift away from the often overloaded 2.4 GHz. Alternatively, client steering moves traffic from overloaded access points to less loaded ones. Either tactic accomplishes a more even load distribution across the wireless network and less disruption from interfering transmissions.
4. Airtime fairness: Clients within a network often compete for available bandwidth. To avoid this, the airtime fairness method ensures an efficient use of the available bandwidth for communication from the access point to the client. It controls the queue of packets to be transmitted at the access point. Slow clients are served with fewer packets so that other clients can move more data downstream and use the channel for a longer period of time.
5. Parallel WLAN connections: Packet loss is a major issue when using radio technology, as packets can arrive with insufficient quality or be disrupted by simultaneous transmissions from other users. Parallel Redundancy Protocol (PRP) can help alleviate this issue, as it allows packets to be transmitted simultaneously over two independent radio links. In the event of interference, PRP ensures packet delivery via a second link. PRP not only improves WLAN connection reliability, but also limits latency issues and jitter, since the faster of the two duplicate packets will be forwarded in each instance.
6. Fast roaming: In application scenarios, such as trains or autonomous vehicles, the mobile clients must connect to different access points as they move along. While fast roaming between WLAN access points has been possible for a long time, it's still critical to find ways to switch mobile clients as quickly as possible from access point to access point and reduce interruption times. This has also become more challenging as new security measures may slow down the switching time.
Fast Roaming: A Deeper Look at How to Facilitate Fast and Secure Connections
When it comes to reliably tapping wireless communication in mobile vehicles, the ultimate goal is to enable mobile clients to automatically connect to the access point with the best signal and ensure uninterrupted network coverage. Fast roaming mechanisms are therefor especially important in trains, automated guided vehicles and other autonomous vehicles.
In order to ensure both a fast and secure exchange, these two questions must be answered:
How can mobile clients switch quickly from one access point to another?
When roaming between two access points, consider achieving fast roaming through reduced scan times. A client must first identify the target access point before making the switch, which can be a complex process. To avoid interference, the target access point is typically operated on a different channel or frequency. Since a client can only receive the access points on the current channel, an off-channel background scanning mechanism is required. It is important that this background scanning mechanism detects the best suited target AP without a significant increase of packet loss.
How can the time for the negotiation of security parameters be minimized?
The security of a WLAN connection can only be guaranteed if a client properly authenticates at the access point when connecting, and if a valid key is provided for data packet encryption. These steps take time and must be repeated with every roaming process. Fast roaming is therefore only possible when using a fast authentication mechanism. In secure fast roaming, a coordination unit distributes all necessary information for rapid authentication of the client among all WLAN access points in the network. Each access point can identify every client on the network quickly, securely and uniquely, providing more robust network security.
Disruption-free network coverage can be achieved with the right wireless technologies, best practices and protocols. To truly be successful, teams need to understand the common issues with wireless networks, know which solutions are available and decipher how they fit with each unique application scenario.
Techniques, such as adaptive noise immunity, client or band steering, and PRP, can significantly improve the performance, reliability and transmission latency of wireless networks in industrial settings. By making sure WLAN quality is at its highest through these new technologies, teams maximize uptime and avoid costly disruptions to the network.
To learn more about what makes a solid wireless network and best practices for WLANs, read this white paper: IEEE 802.11 Radio Optimization.
About the Authors
Tobias Heer has been with Belden since 2012 and specializes in topics that revolve around security and wireless in industrial control systems. He is a professor for IT Security at the University of Applied Science in Albstadt-Sigmaringen, Germany. Tobias received his doctoral degree in 2011 and worked as a postdoctoral researcher at the Chair of Communication and Distributed Systems at RWTH Aachen University. His focus areas are network protocol design, network security and wireless communication. Tobias was involved in the development and standardization of secure internet protocols in the Internet Engineering Task Force (IETF).
Bernhard Wiegel has been with Belden since 2012 and specializes in wireless communication and networks. For the last three years, his role at Belden/Hirschmann has been the lead engineer for the development of the HiLCOS software, which is run on most Hirschmann wireless products. Bernhard received his diploma in electrical engineering in 2006 and his doctoral in 2013 from Ulm University in Germany.