I have been experiencing this for some time on my 615 (b2) router. Tried everything but the wireless does not work well.
One problem I was getting was that my Norton was forcing the wireless SSID to deauthenticate because it was not set to trust the SSID. Once the SSID was placed into the Norton "trusted" list, wireless connections were slightly usuable.
After additional tests, it seems that my 615 "wireless" radio might be at fault since whenever the wireless in enabled, with my three Ethernet LAN devices connected, the wireless network reboots while the wired connections continued working.