But there were other unfavorable factors as well. There were shelves of products that absorbed RF signal (particular products such as grass seed), and products that bounced RF signal in unpredictable ways (such a plumbing pipe). Very often an area was scoped for a certain kind of product, and with the change of seasons these locals got restocked with a product sometimes having reverse characteristics. Where once a spot that absorbed signal (and consequently required a beefier signal) now reflected RF and was wreaking havoc with its neighbor Access Points.
The end devices that used this WLAN were mobile—ruggedized vehicle mounted touch screen PCs lashed to the grid work of a forklift or “tote tugger”, and their constant roaming in and out of RF zones with varying conditions challenged the design as well. A few of the larger warehouses (one was over one million square feet) had a considerable number of Access Points (APs)--80 or more. With three practical channels to use with 802.11g, getting enough coverage saturation without bleeding into a like channel was a test of both physics and premise.
In the beginning we hired a company to design, engineer, implement, sub-contract, and enable these large complex WLANs. We paid a hefty fee for these services, and generally things went smoothly, but after a while the end users began to notice repeated problems such as latency (delay) in specific areas. Our service vendor did “certify” the installation and coverage, but when one read the certification it said in effect that they were not responsible for malfunctioning equipment, components not working within prescribed specifications, wiring faults, end equipment faults, wireless signal saturation, operating system problems with the Access Points, antenna problems, low signal areas, interference by other systems, and on, and on. Basically they certified the paper that the certification was written on, and nothing else.
We would often sub-contract them (at one thousand dollars per day on multi-day trips, plus zone charges, and consumables) to revisit the site and perform another survey/certification report. Sometimes they were able to identify and resolve a problem, but mostly the end result was merely another report. That’s when I became involved in wireless to a higher degree. I started really knowing wireless visualization, to virtually see how waves move, propagate, bounce, diffuse, and just radiate through that theoretical pond. I accomplished this by reading, studying, and experimenting. If you can visualize how water waves move in a pool, you have a great start on visualizing radio waves. It is a bit more complex than that, but oddly enough there are many similarities to this resemblance.
The more I learned (and visualized) the more I realized that there were countless design flaws in the way these WLANs were designed. For example, the Access Points that we used had two antennas, but the engineer failed to realize that only one of the antennas was send/receive, the other wa
s receive only. He laid out an impressive array of APs and antennas on alternate aisles. It looked really good on paper too…The problem with this design is of course that a client ion in aisle B can talk to the AP but the AP isn’t set up to talk back to the client (in real life the aisles were more isolated than my quick drawing). After using tools like AirMagnet and Omni Peek I began to see in explicit detail how a WLAN should be designed and implemented. No automated system is perfect; sometimes one has to rely on skill and experience, even creativity to positively create the optimum WLAN.
As time went on, I worked with our vendors and made adjustments on paper before implementation, and in later years designed and implemented the network myself. When I certified, I certified coverage, speed, throughput, noise, and interference. I provided metrics, and graphics, confirming my findings. Most important though, was that the fact that survey was ACCURATE—not just a best guess; a hope for the best. As the quality of the installation, tweaking, tuning, and certification improved, the problems declined radically.
Some of the older WLANs had been plagued by the same problems for years; they got used to it and seldom complained. Once they got used to things being right, the expected it—demanded it, and rightfully so. This is the way it is supposed to work. Wireless LANs, although relatively easy to set up (at least on a small scale), need special handling for large installations. The experts in my example did their very best, even though in this instance fell short of what was demanded by the environment. Everyone lived for years with latency, disconnects, and frustration; not realized that they could hope for more.
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