This white paper is for the enterprise IT administrator tasked with deploying a wireless LAN (WLAN) of any scale, the significant investment in equipment, time and resources to properly plan and install the deployment is daunting.
Revolutionizing Wireless LAN Deployment
Economics with the Meru Networks Radio Switch
Deployment Challenges for Today's Wireless LAN Architectures For the enterprise IT administrator tasked with deploying a wireless LAN (WLAN) of any scale, the significant investment in equipment, time and resources to properly plan and install the deployment is daunting. Regardless of whether the wireless LAN solution is 1'heavy' or 'light' , the current generation of WLAN solutions rely on careful channel planning and time-consuming site surveys to utilize the limited spectrum in the most efficient method. Channel planning in particular plays a crucial role in the performance of the network, and is directly correlated to the complexity and time involved for deploying in a high density environment. However, as we will see, due to fundamental restrictions in the 802.11b and 802.11g bands, even the most carefully designed channel plans do not eliminate issues that severely impact a dense WLAN network requiring a completely new approach.
Understanding the Reasoning Behind Channel Planning The 802.11 standards utilize the 2.4 GHz (802.11b and 802.11g) and the 5 GHz (802.11a) bands. Currently, the deployment choice for the majority of enterprises is 802.11b and 802.11g due to their compatibility and the near ubiquity of those standards in today's various client devices. 2In the 2.4 GHz band, there are up to 11 channels available. Each channel offers 11 Mbps (802.11b) or 54 Mbps (802.11g) over-the-air data rates. All clients that are associated with the access point will share either 11 Mbps or 54 Mbps available in that channel. If there are numerous clients in a limited physical area, or the supported applications require significant bandwidth, adding capacity to the network is accomplished by using more access points. As wireless is a shared medium like Ethernet hubs, adding capacity to a WLAN network means that non-overlapping channels must be used. Otherwise, if the same channel is used by a second (or third or fourth) access point in the same physical area, then no additional capacity will be added. In the 2.4 GHz band, ensuring only non-overlapping channels are used when deploying a WLAN restricts the network designer to three (3) channels.
1 The term 'light' has caught on to describe wireless LAN architectures that centralize some intelligence in a wireless LAN switch or appliance. 'Heavy' refers to traditional AP architectures where there is no requirement for a wireless LAN switch or appliance. 2 Fourteen channels are available in Japan. Revolutionizing Wireless LAN Deployment
Factors Impacting Wireless LAN Deployment With this limitation, designing a WLAN network for higher density usage becomes much more challenging. Several factors play into this. The first is spatial. Standard Access Points propagate their signals in all directions, as they are equipped with an omni-directional antenna. Omni directional antennas direct the AP signals equally in all directions, both in the horizontal as well as the vertical plane. For multi-story buildings, this adds a third dimension to the challenge of preventing overlapping channels as the diagram below demonstrates. In fact, it is impossible to have non-overlapping access point 3coverage areas with only three channels. The second factor that complicates designing a high density wireless LAN network is the fact that over-the-air speed decreases as distance from the access point increases. That is, the highest data rates (11 Mbps or 54 Mbps) are only available at short ranges from the access point. Farther from the access point, data rates decrease as shown in the figure below.
3 This effect is related to a classic problem in mathematics known as the Four Color Theorem. The Four Color Theorem dates back to 1852 when Francis Guthrie, while trying to color the map of counties of England noticed that four colors was sufficient for his task. He asked his brother Frederick if it was true that any map can be colored using four colors in such a way that adjacent regions (i.e. those sharing a common boundary segment, not just a point) receive different colors. This theorem was finally confirmed by Appel and Haken in 1976, when they published their proof of the Four Color Theorem. What this t... [download for more]
