Dynamic Frequency Selection (DFS) is a mechanism used in Wi-Fi networks operating in the 5 GHz band. It allows Wi-Fi devices to share frequency channels with radar systems without causing interference by automatically switching to a different channel if radar signals are detected.

DFS enables organizations to access additional Wi-Fi channels in the 5 GHz band, significantly increasing network capacity and reducing interference in crowded wireless environments. However, it also has downsides, so organizations should carefully consider the pros and cons before settling on this network strategy.

This article delves into the intricacies of DFS, explaining how it works, its benefits and challenges, and why it matters for your organization’s Wi-Fi network. We’ll explore the evolution of Wi-Fi channels, the mechanics of DFS, considerations for implementation, and best practices for optimizing your wireless network performance.

Dynamic Frequency Selection (DFS): An Overview

To fully appreciate the significance of DFS in modern Wi-Fi networks, you need to understand the evolution of Wi-Fi channels and the challenges that led to its development. This journey through Wi-Fi’s spectrum usage illustrates why DFS has become a critical feature for organizations seeking to optimize their wireless networks.

The Evolution of Wi-Fi Channels

1. 2.4 GHz Band: The Early Days — The earliest Wi-Fi standards operated exclusively in the 2.4 GHz band. While groundbreaking at the time, this band offered only three non-overlapping channels (1, 6, and 11). As Wi-Fi adoption grew, this limited number of channels led to significant co-channel interference, especially in dense environments like office buildings or apartment complexes.
2. 5 GHz Band: Expanding Horizons — To address the limitations of the 2.4 GHz band, Wi-Fi standards expanded into the 5 GHz band. This move initially provided eight non-overlapping channels in the UNII-1 and UNII-3 bands. The increased number of channels significantly reduced co-channel interference, offering better performance and reliability for users.
3. Extended 5 GHz Channels: The DFS Solution — As demand for wireless bandwidth continued to grow, regulators opened up additional channels in the 5 GHz band to further improve capacity. However, these new channels overlapped with frequencies already in use by radar systems, including those used for weather and military applications. This overlap created a potential for interference between Wi-Fi networks and critical radar operations.

How DFS Works

DFS is a regulatory requirement in many countries for devices operating in certain parts of the 5 GHz band. Here’s how it functions:

1. Channel Availability Check: When an access point (AP) is set to use a DFS channel, it must first perform a channel availability check. This involves monitoring the channel for 60 seconds (or up to 10 minutes in some regions) to ensure no radar signals are present.
2. Continuous Monitoring: Once the AP starts using the channel, it continues to monitor for radar signals.
3. Radar Detection: If a radar signal is detected, the AP must: a) stop transmitting within 200 milliseconds, b) select a new channel, and c) wait for at least 30 minutes before using the original channel again.
4. Client Notification: The AP should notify connected clients about the channel change, although implementation can vary between manufacturers. Regardless, this change will be disruptive to clients, particularly those using real-time applications.

By actively monitoring for radar signals and quickly switching channels when necessary, DFS enables Wi-Fi networks to safely coexist with radar operations.

This innovative approach has opened up a significant amount of additional spectrum for Wi-Fi use, providing organizations with more flexibility in network design and improved performance capabilities.

This works well when radar is not in use – but when it is, it can create headaches for the organizations that use this strategy, says Tom Borkowski, founder of TPK Advanced Wireless.

“The Wi-Fi infrastructure has to give way to any radar events that it hears,” he says. “Radar takes priority because some of these are used for emergency services.”

This happens instantly, and no alert is sent to an affected organization.

“If an access point hears a radar event, it has to immediately change channels and go somewhere else,” Tom says. “And it doesn’t give any warning to any clients that might be using that access point. It just switches, and anybody that’s connected to it disconnects.'”

Challenges and Considerations with DFS

Because of this reality, although DFS allows for more available channels, it comes with several challenges:

1. Interruptions: Radar detection can cause brief network interruptions as the AP      changes channels.
2. Client Support: Not all client devices support DFS channels, which can lead to connectivity issues.
3. Reduced Performance: In some cases, using DFS channels may result in reduced network performance due to the need for continuous monitoring and potential channel changes.
4. False Positives: Some APs may trigger false positive DFS events, causing unnecessary channel changes. “Access points are notorious for giving false positive DFS events, and so they may hear something that isn’t actually happening,” Tom says. “So they err on the side of caution, and then they will switch to another channel, even though they really don’t have to. This happens a lot.'”

Should Your Organization Use DFS Channels?

The decision to use DFS channels depends on several factors:

1. Network Density: In high-density environments with many APs, DFS channels may be necessary to avoid co-channel interference.
2. Location: If your organization is near airports, weather stations, or military bases, you may experience frequent radar events on DFS channels.
3. Client Devices: Ensure that your organization’s devices support DFS channels before implementing them.
4. Application Requirements: Consider whether your critical applications can tolerate occasional brief interruptions.

“You need to do an assessment to see if you even need to be leveraging DFS channels,” Tom says. “It may depend on how many access points you have in the environment and what client devices you have because some client devices also don’t support DFS channels.'”

Best Practices for Implementing DFS

If you decide to use DFS channels in your organization, consider these best practices:

1. Conduct a thorough site survey: Assess your environment for potential sources of radar interference.
2. Use enterprise-grade equipment: Higher-quality APs often have better DFS detection mechanisms and can reduce false positives.
3. Monitor and analyze: Keep track of DFS events in your network and analyze patterns to optimize channel selection.
4. Have a fallback plan: Configure your network to have non-DFS channels available as a backup.
5. Educate your IT team: Ensure your IT staff understands DFS and can troubleshoot related issues.

“There’s a cost-benefit analysis that goes into whether or not you want to take advantage of those specific frequencies,” Tom says. “And it really requires a deep assessment of the customer’s environment. There’s not a hard and fast rule that, ‘yes, you should use DFS’ or ‘no, you shouldn’t.’ It all depends, really.”

The Future of Wi-Fi and DFS

As Wi-Fi technology continues to evolve, we’re seeing new developments that may impact the use of DFS:

1. 6 GHz Band: The introduction of Wi-Fi 6E and the 6 GHz band offers numerous channels without DFS requirements, potentially reducing reliance on DFS channels in the future.
2. AI-driven Network Optimization: Advanced AI algorithms may help in predicting radar events and optimizing channel selection, reducing the impact of DFS on network performance.

Ready to Optimize Your Network with DFS? Let TPK Advanced Wireless Guide You

DFS offers powerful potential to enhance your organization’s wireless network capacity and performance. However, implementing DFS effectively requires careful planning and expert knowledge. That’s where TPK Advanced Wireless comes in.

Why Choose TPK Advanced Wireless for Your DFS Assessment?

1. Comprehensive Site Surveys: Our team conducts thorough wireless site surveys, including passive and active surveys, to assess your current network environment and identify potential challenges for DFS implementation.
2. Advanced “AP on a Stick” Method: We use cutting-edge techniques like the “AP on a stick” survey to accurately predict signal strength and data rates, ensuring optimal placement of access points for DFS channels.
3. Spectrum Analysis: Our spectrum surveys identify potential sources of interference that could impact DFS performance, helping you make informed decisions about channel usage.
4. Tailored Solutions: As a vendor-agnostic provider, we recommend solutions based on your specific needs, not on pushing particular hardware.
5. Expertise Across Industries: With experience in diverse environments, from offices to warehouses, we understand the unique challenges each setting presents for DFS implementation.

Don’t leave your DFS implementation to chance. Contact TPK Advanced Wireless today for a free consultation. Our experts will conduct a thorough site survey, providing you with all the information you need to make the best decision for your organization’s wireless infrastructure.

Take the first step towards a more robust, efficient Wi-Fi network. Reach out to Advanced Wireless now and discover how DFS can transform your wireless capabilities.