We are building a new shop and I need to install AP to cover the whole building. I am planing to install the new Aironet 1250 with the 2.4 Ghz 3Dbi triple omni antenna. How do you calculate the size of cell I need ? If the building is a 425 feet square how many AP do I need ?
425 sq feet does not sound like a very large building, thats just a bit bigger than a 20x20 area; 1 AP should be able to handle a 20x20 space with ease.
No seriously - you should do a site survey if possible. If the building is not built yet, perhaps try doing a survey in a similar size building. Keep in mind that there are several factors that come into play such as the structure itself, coverage areas, capacity, throughput, interference, cubicles, machinery, other frequencies, etc.
If the building has multiple floors, you will have to plan around elevator shafts, stairwells, radio overlap from one floor to the next.
Also plan for the wired infrastructure to support the AP deployment.
Do you know which freq you will be using with N-draft? N-draft is capable of channel bonding
where it "bonds" two channels together for higher bitrate, coverage,etc. This is great in the 5GHz freq, but limits your choices in the 2.4 GHz freq as there are only 3 non-overlapping channels. here is some good info on 802.11n draft:
N is on both 2.4 & 5 GHz. 5GHz will allow more flexible use of the channel bonding, but your clients would need 5GHz radios as well. There are several good survey tools available. I would definitely try to use the AP/Antenna combo and client device(s) for the survey that you plan on deploying for your permanent install - not all radios are equal. We had one company do a site survey initially and they used aironet 350 APs for the survey. We re-did the survey using 1200 series APs and the results differed significantly. Granted, our environment is unique and dynamic so wireless ever-changing