WiFi roaming is seriously lagging. How to effectively improve it and achieve seamless roaming?

User satisfaction with Wi-Fi depends in part on whether the network supports smooth handoffs between access points as users and their devices roam. If the AP doesn't do its job well, users will complain.

The initial tendency may be to install more APs in the hope of finding a simple solution, but doing so without careful analysis can make the situation worse. Proper roaming requires more than just good signal strength across the coverage area; it also requires a careful balance of coverage from each AP on both the 2.4 and 5 GHz bands for roaming to work properly.

Understanding Access Point Overlap

Once connected to a specific Wi-Fi network specified by its Service Set Identifier (SSID), a Wi-Fi client continuously scans for other APs with the same SSID in the background. If it finds an AP with a better signal, it should seamlessly connect to it, abandoning the previous connection, and should do so without causing a poor end-user experience.

Getting the coverage overlap between all the APs in the network just right is one of the most important things you can do to help improve roaming. At the same time, it's also the hardest thing to do. You have to check coverage across the entire coverage area and analyze the overlap. If you find problems, you need to figure out how to fix them and then double-check that they're actually fixed.

You want to use -67dBm as the signal boundary for each signal range, resulting in about 15% to 20% coverage overlap between AP signal ranges. You also want to look at both bands, remembering that 2.4GHz naturally offers longer range than 5GHz, and less overlap can lead to areas with poor signal. If you have too much overlap between AP signal ranges in any one band, you'll create co-channel interference and "sticky" clients that don't roam, causing the APs to be overloaded with clients. You want the AP signal ranges to be spaced just right so that clients will always roam to the best AP for that particular location.

Evaluating Overlap and Roaming

It is important to build AP-cell overlap maps and test the effects of roaming before and after making changes. There are different ways to do this, but they all involve walking around the entire network coverage area. A very effective method is to conduct a walkthrough with professional survey software such as AirMagnet or Ekahau and analyze the data. These tools provide heat maps that show the coverage area of ​​each AP and how clients roam between APs. It is also possible to use free applications to spot check the signal levels of APs and which AP the clients are connecting to.

Before testing, make sure you have an accurate, up-to-date floor plan of all coverage areas with AP locations and their wireless MAC addresses labeled. This way, as you move around or analyze the results later, you can see which APs clients are connecting to throughout the coverage area.

While conducting the inspection, use a survey tool on a laptop or other mobile device to display the MAC address of the AP it is connected to, as well as the signal levels of other APs.

If using professional survey software, engage in both active and passive survey modes. Active mode means that the client will connect to the SSID and roam between APs like a normal client. Passive mode means that the software will also capture signal data for all APs so that you can compare the signal levels of other APs to the AP that the active client is connected to.

Remember, you want clients to roam between APs correctly. You don't want them to keep connecting to an AP with a poor signal if another AP with a much better signal comes into range.

Fine-tune AP-cell to achieve zero overlap

If you find that the AP signal ranges overlap too much, you can consider reducing their transmit power. If you find that the 2.4GHz channel has a much larger range than the 5GHz, and you think you still have enough 2.4GHz APs to solve the capacity problem, you can even disable the 2.4GHz radio/SSID on some APs. You can also move or remove APs if you think there are too many signals.

If the AP signal ranges do not overlap enough or do not overlap at all, consider increasing the transmit power of the APs if they are set too low. Remember, you are not asking the APs to transmit at their maximum power, but rather at a level close to the lower power of the Wi-Fi clients. As a last resort, move or add APs to ensure adequate coverage.

After making any changes, re-evaluate AP signal range sizes and overlap to ensure they are normal.

Fine-tuning and roaming

Once you have adjusted the signal range, there are several ways to improve roaming.

• Broadcasting the same SSID for both the 2.4GHz and 5GHz bands makes it easy for clients to choose which band is best, or any band steering features supported by the APs can be used.
• Enable fast roaming (802.11r) on the AP so that some background connection processes can occur before reassociating or roaming to another AP.
• Enable fast reconnect on any Wi-Fi client using 802.1x authentication, again to allow for some background connection processing to be performed ahead of time.
• Change the roaming sensitivity on the AP (if supported) to encourage clients to roam faster or slower.
• Disable lower data rates supported by the AP to force faster roaming. Keep in mind that this may cut off support for legacy clients.
• If feasible, change the roaming sensitivity of Wi-Fi clients to encourage them to roam faster or slower.

After making adjustments, reevaluate roaming and see if it's better. If you don't want to do a full survey again, at least do a spot check. If you're still seeing roaming issues and have older APs, consider upgrading them with a controller-based system.

Remember to always perform a complete wireless survey to find the best AP locations and ensure that AP unit overlap is acceptable. Also check for interference from neighboring networks or other non-Wi-Fi devices.