No, it's not a known issue. Check for a firmware update for your WiFi router on the manufacturer's support web page.
If you need more help please give the make, model and version of your WiFi router.
This is what I have the router set to now.
Security Options None WEP WPA-PSK [TKIP] WPA2-PSK [AES] WPA-PSK [TKIP] + WPA2-PSK [AES]
If I change it to WPA2-PSK [AES]
The wifi performance on the iPhone 4 w iOS6 works slower