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WLAN design validation and failure remediation



After you have designed a wireless network, the last step is validating your network. Tools for validating are site survey tools, protocol analyzers, spectrum analyzers and throughput testers.

Post-Installation site survey, or validation site survey is to be sure that the design requirements are met. This will check if the coverage is good, application validation, capacity requirements and load handling.

Coverage is not just having a green picture in a site survey tool. You need to look in to the signal strength of the second access point as well. You need or want to have a redundant network, when there is an access point not working properly. You need to set your site survey tool to listen only to the channels that you deployed in your network. Of course, it is important to know if there is interference from neighboring networks, but this is mostly done in a troubleshoot track.

When you do application validation, you need to do an active site survey. An active site survey means that you are connected to the network and when connected using the application. iPerf (throughput tester) can be used for validating the application. However, when you are using the application on different spots in the building, you also get a good idea if the application works well. When you validate a VoIP handset, walk through the building and have an active call setup with someone else. So, using the application, using the site survey tool or using a throughput tester are ways to validate the application.

Also, to validate the capacity, you should do this at a moment when the building is full. When you want to validate a stadium Wi-Fi when there is no game going on, then there are no people in the stadium. The best way to validate is during a game or concert. You can also validate it theoretically to do a site survey and look at the CCI and ACI values, but also the signal strength and data rate values. Output power, channel configuration, and too many access points can affect the capacity in a negative way.

Load handling is related to capacity. Capacity is the number of users that can connect to the network and still have good performance, so handling the load is a subset of the capacity. Throughput testing is not always helping with this. If only one user is connected, you do not have a good view. This is similar to what I mentioned in last paragraph with validating a stadium Wi-Fi with no people in the stadium. So, test how the access point handles the load while connected with one client and do a throughput test, and after that with two clients, five clients, and ten clients for example. You will see a trend and you can have an idea of how much the throughput will drop with adding clients to the access point and see how many clients the access point supports with still a good throughput value.

Failure remediation

The validation survey is to validate the network and to check if any optimization needs to be done. When capacity or load handling suffers, you should adjust channel plan and output power. When you configure the access points on other output power than designed you can have CCI or ACI. When you configure them on lower output power, the chance is that there are coverage holes. Also, selecting wrong channels or channel width (20 MHz vs 40 MHz or higher) can occur in CCI/ACI. When the answer to the validation is more access points, take into consideration how this will affect the surrounding access points. For example, which channel plan, the channel width, and output power. There is a chance that the other access points should be reconfigured because of adding new access points. When there is a lot of CCI and ACI it is possible that you need to remove an access point. But keep in mind what this will affect the surrounding access points—will removing causing a coverage hole? Can the surrounding access points increase their output power to cover this or do some access points need to be moved? This is also one of the reasons why ‘put extra access points up’ not a solution for Wi-Fi problems. A solution can also be to swap out the antennas for better antennas.

Fine-tuning can also be needed after a validation survey. For example, enable, disable or modify RRM settings, and enable or disable features like band steering, load balancing, fragmentation, aggregation or short guard interval.