August 11, 2008
Pros: Wizards greatly simplify RF network design, easy prediction and visualization
Cons: Somewhat awkward site survey, no work order or AP config generation.
As enterprises roll out 802.11n, most will make hefty infrastructure investments. Skilled carpenters always “measure twice, cut once.” This conventional wisdom also applies to WLANs, where poor planning so often leads to coverage gaps, disappointing performance, and costly retrofits.
Wireless networks pose unique design challenges. APs behave differently in each location because radio waves are reflected, scattered, and attenuated by the surrounding environment. One cannot accurately visualize signal propagation or quantify a building’s impact on WLAN quality of service without modeling tools.
Rules of thumb, like positioning APs to create circular cells with 20 percent overlap, take you only so far. In reality, those cells get flattened and distorted as transmissions are absorbed and bounced off of walls, doors, and people. On the other hand, surveys that painstakingly gather in-situ RF measurements are resource-intensive. In the end, no matter how extensive the site survey, sampling can still miss problem areas.
This is the impetus behind LANPlanner, a predictive WLAN design tool based on Wireless Valley RF modeling technology acquired by Motorola in 2005.
“Model, Design, Deploy, Maintain”
LANPlanner can be used to create 2D and 3D models of each target venue, using physical characteristics to calculate a site’s RF propagation behavior and impact on WLAN performance. When used prior to deployment, LANPlanner automates design tasks such as AP placement and channel assignment, generating a Bill of Materials to guide installation. After deployment, LANPlanner can verify real-world performance and predict the consequence of potential refinements.
We used LANPlanner to design two tiny WLANs to be managed with Motorola’s RF Management Suite (one shown below). These designs barely scratched the surface of LANPlanner’s RF modeling smarts, but they let us experience Motorola’s four-step “RF-intelligent design” process: Model, Design, Deploy, Maintain.
To get started, we installed LANPlanner version 10.1.5 on a Windows XP laptop with a Cisco 802.11a/b/g adapter. Each license ($12,000) gives you the right to run this Win32 program on a single system (XP or 2000, but not yet Vista). An activated license is required, not just to create and edit designs, but also to view them. This made it harder to review our designs with others elsewhere—for that, we had to rely on printed reports.
You might be tempted to install LANPlanner on a beefy desktop with a nice big monitor, but we recommend spending your license on a laptop with a 32-bit PCMCIA slot. Why? You’ll want a mobile device with a Netgear WAG511v2 or Cisco AIR-CB21AG-A-K9 PC card to use LANPlanner’s site survey feature. LANPlanner comes with AirDefense drivers that must be applied when that card is installed, in lieu of manufacturer’s drivers. Alternatively, site survey licenses can be purchased separately ($2,500)—for example, to let remote office staff supply site readings to a central designer.
Wizard-based RF modeling
Predictive modeling tools can only do their job really well when given sound input, so invest in prep time before creating a LANPlanner project.
Gather building floor plans—preferably AutoCAD (dwg) files with embedded detail about building materials. If AutoCAD files don’t exist for a site, LANPlanner can import simple floor plan images (e.g., jpg, gif, bmp files), but then requires input to establish scale and describe walls and windows and other RF barriers on each floor.
Alternatively, LANPlanner can let you draw floor plans, but free-hand drawings won’t be as efficient or accurate. Our advice: do your homework and start a project with accurate building data; big shortcuts here diminish what you gain from using LANPlanner.
To create a new project, LANPlanner starts by presenting a list of available building materials, drawn from its extensive RF attenuation library. That list can be applied as-is or edited, but must include the major materials used by your site (or represented by layers in your AutoCAD file). Our designs used library defaults for common materials like drywall, wooden doors, glass windows, and concrete foundations.
After LANPlanner has this list, a Building Floor Manager wizard solicits input needed to generate a “3D intelligent RF map” for each floor in the building. For example, here we import a JPG floor plan and use the wizard to draw rooms and partitions on top of that background image (see figure 2-2).
Before drawing exterior walls, we selected “foundation” from the drop-down menu. When drawing interior walls, we chose “dry wall,” and so on. This task is a bit tedious, but it’s very straight-forward and fast—if you have the necessary data. Fortunately, those using AutoCAD files can skip this step—highly recommended for large sites.
After all floors have been formatted this way and scaled by drawing a line of known length, LANPlanner assembles the building by stacking floors (ordered by floor number). If floor plans are accurate and a good alignment point was selected, LANPlanner displays a 3D map that looks like your building (see figure 2-3). Eyeballing that 3D map from different angles gives you a chance to spot and correct basic mistakes before continuing to WLAN design.