What Affects Wireless Signals?

Because wireless signals travel through the atmosphere, they are susceptible to different types of interference than are standard wired networks. Interference weakens wireless signals and therefore is an important consideration when working with wireless networking.

Interference

Wireless interference is an important consideration when you plan a wireless network. Interference is, unfortunately, inevitable, but the trick is to minimize the levels of interference. Wireless LAN communications typically are based on radio frequency signals that require a clear and unobstructed transmission path. The following are some factors that cause interference:

Physical objects: Trees, masonry, buildings, and other physical structures are some of the most common sources of interference. The density of the materials used in a building’s construction determines the number of walls the RF signal can pass through and still maintain adequate coverage.

Concrete and steel walls are particularly difficult for a signal to pass through. These structures weaken or at times completely prevent wireless signals.

Radio frequency interference: Wireless technologies such as 802.11n can use an RF range of 2.4 GHz, and so do many other devices, such as cordless phones, microwaves, Bluetooth devices, and so on. Devices that share the channel can cause noise and weaken the signals.

Electrical interference: Electrical interference comes from devices such as computers, refrigerators, fans, lighting fixtures, or any other motorized devices. The impact that electrical interference has on the signal depends on the proximity of the electrical device to the wireless AP. Advances in wireless technologies and in electrical devices have reduced the impact that these types of devices have on wireless transmissions.

Environmental factors: Weather conditions can have a huge impact on wireless signal integrity. Lightning, for example, can cause electrical interference, and fog can weaken signals as they pass through.

Reflection, Refraction, and Absorption

It can be a blurry line differentiating between interference and reflection when it comes to wireless networking. The key difference between them is that interference is a conflict with something else (usually another signal), whereas reflection is a problem caused by a bouncing of the same signal off of an object. A subset of this is refraction, which involves a change in direction of the wave as a result of its traveling at different speeds at different points. Put in simple terms, reflection happens when the signal hits a piece of metal and cannot pass through, and refraction happens when the signal goes through a body of water.

If the wave is completely swallowed by the object it hits (not reflected, or refracted), then it is said to be absorbed. Where security is concerned, items known to absorb wireless signals can be used to prevent the signal from traveling beyond an established perimeter. Shielding paint (sometimes called RF paint) can be used for this purpose, as can copper plates and aluminum sheets. Many wireless implementations are found in the office or at home. Even when outside interference such as weather is not a problem, every office has plenty of wireless obstacles. Table below highlights a few examples to be aware of when implementing a wireless network indoors.

Like any other network medium, APs have a limited transmission distance. This limitation is an important consideration when you decide where an AP should be placed on the network. When troubleshooting a wireless network, pay close attention to how far the client systems are from the AP.

When faced with a problem in which client systems cannot consistently access the AP, you could try moving the AP to better cover the area, but then you may disrupt access for users in other areas. So what can be done to troubleshoot AP coverage?

Depending on the network environment, the quick solution may be to throw money at the problem and purchase another access point, cabling, and other hardware to expand the transmission area. However, you can try a few things before installing another wireless AP.

The following list starts with the least expensive solution and progresses to the most expensive:

Increase transmission power: Some APs have a setting to adjust the transmission power output (power levels). By default, most of these settings are set to the maximum output; however, this is worth verifying just in case. You can decrease the transmission power if you are trying to reduce the dispersion of radio waves beyond the immediate network. Increasing the power gives clients stronger data signals and greater transmission distances.

Relocate the AP: When wireless client systems suffer from connectivity problems, the solution may be as simple as relocating the AP. You could relocate it across the room, a few feet away, or across the hall. Finding the right location will likely take a little trial and error.

Adjust or replace antennas: If the AP distance is insufficient for some network clients, it might be necessary to replace the default antenna used with both the AP and the client with higher-end antennas. Upgrading an antenna can make a big difference in terms of transmission range. Unfortunately, not all APs have replaceable antennas.

Signal amplification: Radio frequency (RF) amplifiers add significant distance to wireless signals. An RF amplifier increases the strength and readability of the data transmission. The amplifier improves both the received and transmitted signals, resulting in an increase in wireless network performance.

Use a repeater: Before installing a new AP, you might want to think about a wireless repeater. When set to the same channel as the AP, the repeater takes the transmission and repeats it. So, the AP transmission gets to the repeater, and then the repeater duplicates the signal and passes it on. This is an effective strategy to increase wireless transmission distances