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By Ron White, 3D-P Vice President of Technology
The Evolution of a Network
In real-world outdoor deployments of wireless networks, most infrastructure deployments begin with a network design covering primary areas of coverage, and allowing overlap to secondary areas. As the client’s coverage and throughput requirements mature beyond the initial scope of the network, network black spots and areas of weak throughput are typically found. New infrastructure is often deployed to cover these holes. These new infrastructure devices effectively increase the noise floor in the network coverage area. This increased noise floor reduces the fade margin to the point that the performance of individual client radios is reduced rather than increased, particularly in areas where distance to AP’s is great, or multiple AP’s are visible. This shows up as new coverage issues (fade margin has eroded to the point that signal strength is less than noise floor) and performance issues (fade margin is low enough that high data rates are no longer available).
Adding higher gain antenna’s and amplifiers on the clients, and the addition of even more infrastructure is typically the attempted solution for these problems. These solutions again increase the noise floor and actually cause additional coverage and performance issues, typically showing up in slightly different areas of the network. A vicious cycle has begun.
Solving the Coverage and Throughput Problem
The solution to this problem involves reducing the coverage areas of individual access points, and reducing the power on individual clients. These solutions are both quite the opposite of the typical solution. Individual coverage zones for each AP must be designed. Terrain, antenna selection, and output power should be utilized in the building of these coverage zones. Individual coverage zones should have an overlap at the edges of each zone, but should not completely overlap each other. This way a client traveling between the two zones will have a single AP which is the obvious choice for communication. When the unit leaves this coverage zone, there will be an overlapping zone where the device will be able to see both AP’s, and as it continues on it will switch to the new coverage zone. While working in one coverage zone, the noise from the others is reduced by the terrain, antenna, and power masking that is utilized to define the coverage zone. Utilizing this design, the units within the zone obtain good performance. Coverage is ensured through multiple coverage zones. It’s just important to ensure the size of the zone is designed and maintained, through the use of power, terrain, and antenna selection. If those zones are allowed to creep and overlap each other beyond the design, the network will soon be right back where it started, and that vicious cycle begins again.