Detailed description of causes of Wi-Fi signal weakening

Wireless Interference may take multiple approaches. From apparently cordless phones and conference calls to fluorescent lights, mobile monitors, and wireless cameras, a large number of devices may impede Wi-Fi connections or even weaken their spectrum.

At the Burton Group Catalyst Conference meeting held in San Francisco last month, one of the founders and CTO of Cognio, a wireless spectrum analysis tool manufacturer, neil Diener gave a speech entitled "Understanding the Impact of RF Interference on the Performance of 802.11 Wireless LAN (Understanding the Impact of RF Interference on 802.11 Wireless LAN Performance, to help enterprises better understand and avoid interference that may restrict connections in the WLAN environment.

As Wi-Fi runs in an unlicensed band, the company's wireless spectrum may be shared by other seemingly harmless devices, such as Bluetooth and wireless game controllers. However, interference from these devices, or interference caused by too many devices in the wireless network, will seriously affect other devices.

Diener says there are two common types of Wi-Fi interference: co-channel interference and adjacent channel interference. The same channel interferes with access points that use the same channel from the next room or from the same room. Adjacent channel interference may come from Access Points on different channels-for example, one access point works on channel 1 while the other access point works on Channel 2. Diener said that adjacent channel interference is generally more destructive than same channel interference.

No matter which type of interference, the same result will occur. It affects the Protocol by causing conflicts, retransmission, and rate rollback. It damages the network by reducing throughput and capacity and introducing latency and jitter. It also has an impact on users-users may wonder why they cannot connect, why connections are so slow, or why sounds and images are mixed up. All these factors will affect IT, and a large number of faulty calls will have a heavy impact on IT and lead to high support costs.

However, Diener says there are two ways to avoid interference, at least to take the initiative to avoid interference.

He said the company should conduct an original survey on all RF servers. This should be performed once before or as part of the post-deployment coverage scan. The purpose of the investigation is to discover all previous problems so that a plan can be made for known sources of interference and an RF baseline can be established. The company can also conduct periodic update RF surveys (once a year or based on budget) to identify all new devices added to the spectrum and compare deviations from the RF baseline.

Finally, Diener said that the company should establish, publish, and implement spectrum policies, and define which devices are allowed to be used and which devices are not allowed to be used in these policies. This will provide employees with information about devices that are allowed to be used. This strategy, combined with the company policy and policy implementation, will be able to maintain the purity of the RF spectrum (without interference ).

Chip Greene, a senior network expert responsible for wireless and wired networks at the University of Richmond, said over 600 access points were deployed on the Richmond campus and are currently upgrading these access points to lightweight access points. Deployed access points cover every corner of the campus to provide services for students, teachers, staff, and authorized visitors.

"It is not difficult to control the radio waves," he said.

For Greene, the main interference problem comes from cordless phones and wireless conference phones at GHz. Sometimes, audio and video devices that control the projector may also interfere.

For example, whenever a wireless conference call is used in a room under the instructor's office, the signal-to-noise ratio of the wireless channel is changed, causing intermittent interference and connection problems, although the Office is actually located exactly between two access points.

"Troubleshooting is 'funny, because interference is always intermittent," Greene said.

Greene uses a spectrum analyzer to observe the RF spectrum and uses a portable analyzer to trace the devices that produce interference. Since conference calls cost a lot of money in the telecommunications sector, Greene had to add more access points to the network to compensate for noise, though he was reluctant to do so.

However, all interference is both "interesting" and frustrating. Greene says it is interesting to go out to repair and investigate the causes of interference, but when the connection is damaged and the spectrum is affected, it is often very frustrating.

Greene said he suggested companies "Have patience when dealing with interference, because RF is a very dynamic environment and is very easy to change. You need to check a lot and ask more why ."

Diener says reducing interference can be as simple as removing a microwave oven or disabling Bluetooth in the company. Companies can use similar devices without interference to replace cordless phones. Other methods include changing the Access Point channel, increasing the transmission power of the Access Point, and controlling the data transmission rate.

There are also some extreme practices, including shielding interference, ground shielding, RF absorption, and window shielding using a faradha cage-but these practices are often too costly.

"The company must be aware that (interference) is an important issue," Diener said. "You may not be able to make a plan in advance for interference, however, you can perform a scan to ensure that the actual situation matches your simulated situation."

The medical system in a hospital that works with Diener uses a bar code scanner to identify the drug. These scanners use Bluetooth connections to interfere with Wi-Fi signals. In collaboration with Scanner manufacturers, the company adjusted the Bluetooth frequency to eliminate interference with WLAN.

"No matter whether they know the presence of interference," Diener said. "interference may happen anywhere. Maybe there are not as many as 1,000 devices in that place, but it does exist. This is a potential problem. It's like heart disease. It can happen no matter whether you know it or not. What you need to do is try to avoid it ."

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