[iwlwifi] Wifi roams frequently and ends up disconnected

Since moving from 10.04 to 12.04 (via a clean install), my WiFi connection at work frequently roams from one AP to another (even though the laptop has not been moved), and ultimately fails to connect at all.

If I move to a different location in the facility, the problem goes away. Thus, I suspect it's a function of the relative signal quality of the various APs.

When the laptop is booted into Windows 7, in the location (my office) that is most problematic, the WiFi connection is stable. When I'm running Ubuntu at home or another place where there's a single AP, the connection is stable.

My adapter is an Intel 5300 with the iwlwifi driver. Security settings on the work network are WPA2 Enterprise, PEAP, MSCHAPv2. The APs are Cisco, but I don't have access to their configuration or model info.

When I ran apport for this bug report, I also had a wired connection plugged in, so I could be sure I'd complete the process. The problem I'm reporting happens without that wired connection.

I'll attach two syslogs. One shows the typical sequence when the connection roams spontaneously. The other shows the sequence when wifi ultimately fails to connect at all.

I'm available to try alternative configurations and packages.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: network-manager 0.9.4.0-0ubuntu4.1
ProcVersionSignature: Ubuntu 3.2.0-31.50-generic 3.2.28
Uname: Linux 3.2.0-31-generic x86_64
ApportVersion: 2.0.1-0ubuntu13
Architecture: amd64
Date: Thu Sep 27 09:58:17 2012
IfupdownConfig:
 auto lo
 iface lo inet loopback
InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120823.1)
IpRoute:
 default via 172.31.16.1 dev eth0 proto static
 169.254.0.0/16 dev eth0 scope link metric 1000
 172.31.16.0/20 dev eth0 proto kernel scope link src 172.31.20.32 metric 1
 172.31.16.0/20 dev wlan0 proto kernel scope link src 172.31.21.152 metric 2
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=true
 WWANEnabled=true
 WimaxEnabled=true
ProcEnviron:
 TERM=xterm
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: network-manager
UpgradeStatus: No upgrade log present (probably fresh install)
nmcli-dev:
 DEVICE TYPE STATE DBUS-PATH
 wlan0 802-11-wireless connected /org/freedesktop/NetworkManager/Devices/1
 eth0 802-3-ethernet connected /org/freedesktop/NetworkManager/Devices/0
nmcli-nm:
 RUNNING VERSION STATE NET-ENABLED WIFI-HARDWARE WIFI WWAN-HARDWARE WWAN
 running 0.9.4.0 connected enabled enabled enabled enabled enabled