WiFi stops working after a while in Lenovo ThinkPad W520 (Ubuntu 12.04)

After several minutes(I do not know how many) there is no internet connection on my laptop via Wi-Fi.Ubuntu doesn't show any kind of message that my WiFi was disconnected neither there is a signal drop,but suddenly Firefox stops connecting to web pages.I checked my modem/router and it seems that it is working fine.I tried also to reboot the WiFi device and nothing happens.The only thing that it makes it work again is a reboot of the system and if I do not want to do a reboot then I am enforced to connect to the Internet using Ethernet cable.Does anybody know what is happening?

 ## Some Hardware info that might be helpful ##


el10780@ThinkPad-W520:~$ sudo lshw -class network
  *-network               
       description: Ethernet interface
       product: 82579LM Gigabit Network Connection
       vendor: Intel Corporation
       physical id: 19
       bus info: pci@0000:00:19.0
       logical name: eth0
       version: 04
       serial: f0:de:f1:f1:be:10
       size: 100Mbit/s
       capacity: 1Gbit/s
       width: 32 bits
       clock: 33MHz
       capabilities: pm msi bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=1.5.1-k duplex=full firmware=0.13-3 ip=192.168.0.10 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s
       resources: irq:50 memory:f3a00000-f3a1ffff memory:f3a2b000-f3a2bfff ioport:6080(size=32)
  *-network
       description: Wireless interface
       product: Centrino Advanced-N + WiMAX 6250
       vendor: Intel Corporation
       physical id: 0
       bus info: pci@0000:03:00.0
       logical name: wlan0
       version: 5e
       serial: 64:80:99:63:14:74
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless
       configuration: broadcast=yes driver=iwlwifi driverversion=3.2.0-26-generic firmware=41.28.5.1 build 33926 ip=192.168.0.6 latency=0 link=yes multicast=yes wireless=IEEE 802.11abgn
       resources: irq:52 memory:f3900000-f3901fff
  *-network
       description: Ethernet interface
       physical id: 1
       bus info: usb@2:1.3
       logical name: wmx0
       serial: 00:1d:e1:53:b2:e8
       capabilities: ethernet physical
       configuration: driver=i2400m firmware=i6050-fw-usb-1.5.sbcf link=no

el10780@ThinkPad-W520:~$ lspci
00:00.0 Host bridge: Intel Corporation 2nd Generation Core Processor Family DRAM Controller (rev 09)
00:01.0 PCI bridge: Intel Corporation Xeon E3-1200/2nd Generation Core Processor Family PCI Express Root Port (rev 09)
00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
00:16.0 Communication controller: Intel Corporation 6 Series/C200 Series Chipset Family MEI Controller #1 (rev 04)
00:16.3 Serial controller: Intel Corporation 6 Series/C200 Series Chipset Family KT Controller (rev 04)
00:19.0 Ethernet controller: Intel Corporation 82579LM Gigabit Network Connection (rev 04)
00:1a.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #2 (rev 04)
00:1b.0 Audio device: Intel Corporation 6 Series/C200 Series Chipset Family High Definition Audio Controller (rev 04)
00:1c.0 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 1 (rev b4)
00:1c.1 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 2 (rev b4)
00:1c.3 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 4 (rev b4)
00:1c.4 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 5 (rev b4)
00:1c.6 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 7 (rev b4)
00:1d.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #1 (rev 04)
00:1f.0 ISA bridge: Intel Corporation QM67 Express Chipset Family LPC Controller (rev 04)
00:1f.2 SATA controller: Intel Corporation 6 Series/C200 Series Chipset Family 6 port SATA AHCI Controller (rev 04)
00:1f.3 SMBus: Intel Corporation 6 Series/C200 Series Chipset Family SMBus Controller (rev 04)
01:00.0 VGA compatible controller: NVIDIA Corporation GF108 [Quadro 1000M] (rev a1)
03:00.0 Network controller: Intel Corporation Centrino Advanced-N + WiMAX 6250 (rev 5e)
0d:00.0 System peripheral: Ricoh Co Ltd Device e823 (rev 08)
0d:00.3 FireWire (IEEE 1394): Ricoh Co Ltd R5C832 PCIe IEEE 1394 Controller (rev 04)
0e:00.0 USB controller: NEC Corporation uPD720200 USB 3.0 Host Controller (rev 04)

el10780@ThinkPad-W520:~$ rfkill list all
0: hci0: Bluetooth
    Soft blocked: no
    Hard blocked: no
1: tpacpi_bluetooth_sw: Bluetooth
    Soft blocked: no
    Hard blocked: no
2: phy0: Wireless LAN
    Soft blocked: no
    Hard blocked: no
3: i2400m-usb:2-1.3:1.0: WiMAX
    Soft blocked: yes
    Hard blocked: no

The weirdest thing is this screenshot which I took after running the **Additional Drivers** program.I mean I have a NVidia Quadro 1000M and my Intel Centrino WiFi Card and this shows that there are not proprietay drivers for my system.

http://imageshack.us/photo/my-images/268/screenshotfrom201207062.png/