Hands-on Exercise:

Hands-on Exercise: Understand Basic Performance Impacts of Radio Signal Interference

This exercise helps you understand the impact that radio signal interference, such as interference from microwave ovens and cordless phones, has on the performance of a WLAN from a user perspective.

Perform the following steps:

• Step 1. Identify sources of radio signal interference to test. For example, you might choose to test a microwave oven, cordless phone, Bluetooth headset, or any other devices that operate in the 2.4-GHz or 5-GHz bands.
• Step 2. Configure a 2.4-GHz 802.11n wireless client device to test performance against a point located on the wired network. For example, you can run a throughput test from the client device against an online performance tester, such as the one at http://performance.toast.net. The main idea is to measure performance for comparison purposes as you test different sources of interference.
• Step 3. Run a performance test with a client device configured with a 2.4-GHz radio (and associated with a 2.4-GHz 802.11n access point) within close proximity to the source of interference. This will give you an idea of the maximum impacts on performance because the interfering signals will be strongest. Perform the test with the interference active and inactive. For example, place the client device 1 or 2 feet away from a microwave oven and run the performance test while the microwave oven is on (maybe while heating a cup of water). Note the performance. With the microwave oven off, rerun the performance test and note the corresponding performance. Compare the two performance levels. How much did the interference degrade the performance?
• Step 4. Repeat the performance tests with the applicable access point set to different RF channels. How does a different access point channel setting impact the performance when the interference is active and inactive? What changes do you see in baseline performance (when the interference is not present) among the different channels?
• Step 5. Repeat the performance tests with the client device configured with a 5-GHz client radio and associated with a 5-GHz 802.11n access point. How does moving to the 5-GHz band impact the performance when the interference is active and inactive? What changes do you see in baseline performance when moving from the 2.4-GHz band to the 5-GHz band?
• Step 6. Repeat the performance tests with the client device located farther away from the interference source. This will provide insight on more practical impacts on performance, based on areas where users would likely use the WLAN.

You might or might not notice any degradation in performance, depending on the part of the spectrum that the interference is present in relation to your access point channel. Probably the largest drop in performance will occur when testing a microwave oven within close range of a 2.4-GHz client device with the associated access point set to a channel that falls within the frequency range of the microwave oven. You will probably notice an increase in baseline performance when moving from the 2.4-GHz band to the 5-GHz band.