February 19, 2010 1 Comment
You want Wi-Fi, and you want it to work. And let’s say you want to design the network so that it works not only for data, but also for voice and RTLS (location tracking).
Once you have your requirements figured out, it’s time to start planning the network. The network plan (or predictive design) is all about answering a few key questions:
- How many APs am I going to need?
- Where should I place the access points?
- How should I configure the APs?
- What kind of antennas should I use, and how should I align them?
- How is my coverage and performance going to look like?
These questions can be answered quite accurately prior to going on-site by making a predictive design using a Wi-Fi planning tool. We at Ekahau offer one with Ekahau Site Survey Pro, for example. Of course, you can just put the APs “where it feels about right”, but very few of us are such hardcore experts that this actually will work optimally. There’s things like different kinds of wall materials, directional antennas, and floor-to-floor signal bleed-through that make things a bit complicated.
The Wi-Fi network planning tools work generally as follows: you put in a floor plan, set the scale of the plan, and perhaps define wall materials on the floor plan. This way, the tool knows how far the Wi-Fi signals will travel in each direction. When designing the network, you will see heatmaps of the predicted network coverage and performance.
There’s a few best practices you might want to follow when making a predictive design:
- Use one map image per floor. Breaking floors into parts may not work very well. Neither may using several floor plans on one map image
- Don’t make it too exact a science: There’s probably no need to define every piece of furniture in the design. Simply drawing the main interior and exterior walls should be enough.
- If you’re working with multi-floor buildings, ensure you account for floor-to-floor bleed-through. It’s important to see the impact of APs on the floors above and below; They can both give you beneficial coverage and cause interference. Some tools can do this, but most can’t.
- When designing for coverage in dual-band networks, you may want to design for 5Ghz. If 5Ghz works, 2.4GHz will work also.
- If you’re going to use location tracking (RTLS) indoors, place the APs in the corners and rooms instead of hallways. Don’t place APs in the same locations on neighboring floors, but rather make a zig-zag pattern.
- The radiation patterns of the APs vary between vendors and models. Use the exact AP and antenna models in the predictive design to make it more accurate.
- Use the heatmaps to find out whether your requirements are met or not. Avoid using too many APs, but on the other hand don’t be too cheap as you’ll run into connectivity issues.
- If you want to focus the signals to stay inside the building, or cover a specific area, you can simulate directional antennas in the design phase already.
- In high-ceiling environments, you may need to design for antenna downtilt / uptilt.
- Typically you have different kinds of criteria for the network. For example with VoIP, you will need certain minimum signal strength, SNR, data rate, AP overlap, etc. You can check these as separate heatmaps on the planning tool, but using a combined view is very powerful: a single view answers the question “are all my requirements met – is my network truly ready for VoIP?” (see the image below)
After the off-site design has been finished, it’s time to go on-site to perform pre-deployment and post-deployment surveys to ensure your plan is accurate. But more about those later.
Sr. Product Manager / Ekahau