Strange random disconnection (Lost-Carrier)

["Josh Shamir" <josh.shamir@gmail.com>]

Hello,
some of my users have a strange problem; randomly, they have been disconnected after a few minutes get authenticated.
Searching in log file, i've seen that the problem is "Lost Carrier"

Wed Feb 28 09:16:24 2007 : Debug: Nothing to do.  Sleeping until we see
a request.
 
rad_recv: Accounting-Request packet from host 192.168.181.1:32919,
id=227, length=184
        Acct-Status-Type = Stop
        User-Name = "user1"
        Calling-Station-Id = "00-0A-1D-18-61-B5"
        Called-Station-Id = "00-23-F7-F2-C1-1C"
        NAS-Port-Type = Wireless-802.11
        NAS-Port = 0
        NAS-Port-Id = "00000000"
        NAS-IP-Address = 0.0.0.0
        NAS-Identifier = "20"
        Framed-IP-Address = 192.168.182.41
        Acct-Session-Id = "45e53a5100000000"
        Acct-Input-Octets = 0
        Acct-Output-Octets = 0
        Acct-Input-Gigawords = 0
        Acct-Output-Gigawords = 0
        Acct-Input-Packets = 0
        Acct-Output-Packets = 0
        Acct-Session-Time = 531
        Acct-Terminate-Cause = Lost-Carrier

Searching onf FreeRADIUS ML I have found that the Lost-Carrier is a problem between the NAS and the user, so the problem is between the Access Point and the Supplicant.
Could be a signal problem (note that the distance between the AP and the NAS is short) or there could be other things that cause this disconnection?

Thanks for help