As per your query,You are having signal drop or week signals from client stations.
One of the biggest causes of dropped or weak wireless signals is interference from other objects (including walls, metal objects like filing cabinets, etc.). Being very far from the wireless signal source also negatively impacts signal strength.
Here are few things which you might want to try to mitigate this:
1.It is highly recommended to have site surveying done prior to Access points deployment.
2.Ensure that your Client station OS and wireless card updated with latest driver.
3.Assign static channel such as 1,6 or 11.You may be able to get a clearer signal on your network by changing the channel that the wireless AP is using. You can use a utility like" InSSIder" to see what channels nearby wireless networks are using and choose a different one for your wireless network.
As per your requirement you could go with ZF7372 and ZF7982 APs ,capable of supporting 500 clients ,for more details you could refer to "www.ruckuswireless.com
hope that helps!!
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