@Sufiii 

Hey

Without knowing more info on your setup or what you mean by "connection not stable"...  thinking out loud the EAP115 is an older device now and only supports 300mbps on 2.4ghz.   100 devices is going to flood the airspace

Even with 4x APs, that is 25 devices per AP which is not going to fair well on a 2.4ghz frequency.  In my honest opinion you shouldnt have that many devices without some on the 5ghz.  

1. Have you got your channels set manually?   1  6   11     1   in that order is how I would approach it.  Set this manually and dont let the controller do it, keep the two  channel 1 APs as far away from eachother as possible
2. Also stick to 20mhz channels to avoid interference, you wont have the airspace for 40mhz channels.  
3. On the controller enable airtime fairness, this would likely help given the volume of devices by giving everyone a fair and even timeslot.
4. Are you running a controller?   You should be as it would help load balance by roaming the devices as required.

If you want my opinion... you should consider upgrading the APs to EAP225 or 245 and setup a controller (if you dont have one alrady).  This will give you access to the 5ghz frequency which has capacity for the volume of devices you are running, the band steering and load balancing from the controller will help massively.

@Philbert 

Thank you for your reply, 

I have 4 EAP 115 and controlling through OC200 tp link controller. and the channels are set manually as you said, also radius using 20Ghz. still the network is not stable. disconnecting and connecting frequently. 

@Sufiii 

Without checking the logs for this, its hard to say what is causing it.

However, in my honest opinion... I would be very surprised if 4x EAP115s could handle 100 clients.  Its not the capacity of the device par say, rather the fact all these clients are going to be on 2.4ghz frequency, this is incredibly saturated airspace and personally I wouldn't be using more than 30 devices on it .  Especially over the distances, you mentioned

In reality, the maximum number of clients per AP if using 2.4ghz is around 15 at best, you could double that to 30 per AP on the 5ghz for a combined of around 45 per AP on a dual frequency setup (enable band steering).

If you were one of my customers, I would be recommending that you consider moving to a dual-frequency setup with EAP225 or even better 245s

Honestly mate.. This has all the symptoms of airspace saturation.

@Philbert 

I really appreciate for your reply on this. Thank you so much for helping me to understanding. 
 

i have decided to change the EAPs to EA 245, unfortunately the model not available in my region. So im going to change a single ubiquity HD.  
 

Thanks & regards,

@Sufiii 

Following the suggestion of Philbert, I think you can actually select another models.

Not only the EAP245 supports 2.4GHz/5GHz signal and all those features, they have other models like EAP225(V3)/EAP265 HD.

Just because you already have controller running, might as well finding more options. Then you don't have to setup a whole new network all over again.

@Yannie 

Yannie is correct, really any of the 2xx or 6xx range will support 5ghz and therefore should help

Good luck if you do go for Ubiquiti, but even with the HD model 100 is a big ask.  Personally, I would want more than one AP, its not the capacity of the AP, rather the airspace congestion.