Apple iPod Touch dropping connection in Cisco WIFI network

Folks,

We have deployed Apple iPod Touch devices in a Distribution Center environment, users are constantly scanning barcodes and inputting data that get reported to the WMS that runs on an IBM iSeries server connected through a CISCO Wifi network. They all walk around performing picking and other functions that they report constantly to the WMS in an area of about 100,000 sqft. We have access points that cover the area pretty well, so they are connected and able to do their job for the most part, but have WIFI drops about 6 to 8 times a day. Because of this they lose continuity of their work and have to restart and redo the work which results in lost productivity,

For some reason the iPod Touch devices are losing connectivity about 8 times a day. Here is a pattern we are seeing

1 - It seems to be happening in certain areas

2 - It seems to be happening after 4 PM every day

3 - WIFI drops are also happening when users take lunch breaks for an hour

4 - Also we are hearing that the iPod Touches are creating lot more traffic due to them pinging the NTP server and other servers accessing internet and so forth

Any idea what is causing this? Typically our experience has been we will deploy these devices and don't have to do anything, they will all work smoothly, without a single drop.

Any thoughts on why we are running into these issues in this particular instant?

Many thanks for the help with any guidance to resolve this issue.