I too have sporadic dropouts of my WiFi. The yellow "!" appears over the signal strength indicator in the system tray and the connection indicates it is "Limited". It happens 1-3 times per day (often when I am at work). Sometimes right clicking and running the auto diagnose and repair fixes the issue (it appears it is reseting the wireless card). When that does not work, I usually either try disabling/enabling the device in device manager, or as a last resort, rebooting - which usually works. System details are below.
I do suspect the problem comes from an interaction between my wireless router and the 6235 wireless card. My router may be one of those "Pre-N" routers (its ~3 years old, probably the model itself is ~4 yrs old). I have detailed all the routers settings below as well. I do suspect that if I upgraded the router the problem may go away.
I have tried a few othe the fixes mentioned here. I dont consider disabling -N an option, as that puts the connection slower than my ISP, plus I do move around files on the network and having b/g only seems to result in an even slower actual speed than then connection speed of 54 Mbps in my case.
I'd also prefer not to use wireless drivers from Microsoft, and although some posters have reported positive results, there were also hints of other issues that came up in some posts, plus some features may not be supported.
The settings below are going to be my baseline test for the next few days. If my wife/daughter/mother-in-law report a problem in the next few days, I can say for sure this "baseline" configuration is a problem, then tweak (one thing at a time) from there.
System
Intel® NUC Kit D54250WYK (core I5-4250U)
8 GB Memory
240 GB Intel SSD
Intel(R) Centrino(R) Advanced-N 6235
Windows 8.1 PRO 64bit (kept up to date)
Intel(R) Centrino(R) Advanced-N 6235 - Driver (Driver only; elected not to install full PROset)
Driver Provider: Intel
Driver Date: 9/23/2013
Driver Version: 15.10.4.2
Intel(R) Centrino(R) Advanced-N 6235 - Power Management
Allow the computer to turn off this device to save power: checked
Allow this device tp wake the computer: unchecked
Intel(R) Centrino(R) Advanced-N 6235 - Properties (should be the defaults)
802 11n Channel Width for band 2.4: 20 MHz Only
802 11n Channel Width for band 5.2: Auto
802.11n Mode: Enabled
Ad Hoc Channel 802 11b/g: 11
Ad Hoc QoS Mode: WMM Disabled
ARP offload for WoWLAN: Enabled
Bluetooth(R) AMP: Enabled
Fat Channel Intolerant: Disabled
GTK rekeying for WoWLAN: Enabled
Mixed mode Protection: CTS-to-self Enabled
NS offload for WoWLAN: Enabled
Preferred Band: 1. No Preference
Roaming Aggressiveness: 3. Medium
Sleep on WoWLAN Disconnect: Disabled
Transmit Power: 5. Highest
Wake on Magic Packet: Enabled
Wake on Pattern Match: Enabled
Wireless Mode: 6. 802.11 a/b/g
Primary Wireless Router (connects/looses connection to this)
Model: Netgear WNDR3700v3
Firmware Version: V1.0.0.36_1.0.30 (latest)
Wireless settings are after resetting router to factory defaults, then setting up from scratch. Only changes from default were setting up the SSID's for the primary 2.4/5.2 and guest 2.4/5.2 networks, setting up security and changing the router password.
Wireless Setup: Wireless Network (2.4GHz b/g/n)
Channel: Auto
Mode: Up to 145 Mbps
Security Options: WPA2-PSK [AES]
Wireless Setup: Wireless Network (5GHz a/n)
Channel: 153
Mode: Up to 300 Mbps
Security Options: WPA2-PSK [AES]
Wireless Advanced Settings (2.4GHz b/g/n)
Enable Wireless Router Radio: Checked
Enable 20/40Hz Coexistence: Checked
Fragmentation Length (256-2346): 2346
CTS/RTS Threshold (1-2347): 2347
Preamble Mode: Long Preamble
Wireless Advanced Settings (5GHz a/n)
Enable Wireless Router Radio: Checked
Fragmentation Length (256-2346): 2346
CTS/RTS Threshold (1-2347): 2347
Preamble Mode: Long Preamble
Secondary AP (router with DHCP set to off, acts as AP only)
Model Netgear WNR3500
Wireless Router Settings
Name (SSID) : Same as primary router
Channel: Auto
Mode: Up to 300 Mbps
Fragmentation Length (256-2346): 2346
CTS/RTS Threshold (1-2347): 2347
Preamble Mode: Long Preamble (default is Auto)
Network Misc: We have many wireless devices connecting to the primary router and the secondary router that is configured as a AP. This includes 3 thermostats, 3 phones, 2 tablets, 2 kindles, 1 ipod, 1 Logitech WiFi Radio, 2 laptops and the NUC.