The site is quite large but typically each area is isolated from the next.
What do you mean by "isolated"? Describe the walls? The heights of the ceiling? The height where you plan to install the AP? How do you plan to install the AP? Too much info is WAY BETTER than no info.
Is it possible to avoid overlapping signals as well without a controller?
The best way is with a controller because not only does the radio interferrence get monitored and change automatically but you configure all your APs ONCE, on the controller. Your APs will become a true plug-and-play.
You have but three choices:
1. You can stick with SMB. You need to configure each and one of them. It's cheap.
2. Cisco recently bought out Meraki. It's cheaper than the Cisco enterprise grade and Meraki's got PoE switches, wireless controllers and AP.
3. Cisco Aironet products. Big-daddy of them all. Cisco CleanAir and operating in a bar with lots of potential wireless interferrance ... it's the best thing that you can have right now.
You can get the refurbished Cisco Aironet and PoE switches from Cisco Refurbished Equipment for less but you also get the warranty and/or Service Contract.
Cisco's APs now have Cisco Limited Lifetime Warranty so you don't need to purchase maintenance. If you want to purchase a Wireless LAN Controller, purchase the maintenance and service contract for the WLC so you can download the firmware. For switches, some Cisco Catalyst (enterprise) switches now come with Enhanced Limited Lifetime Warranty (next day replacement vs 10 business days replacement).
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