Do not trust the bars... 5 full bars might be lots of noise and just 2 bars might be without noise. More about this here (is about Windows but same physics apply for Ubuntu). There is a better method:
more /proc/net/wireless shows quality of the link, signal strength and noise level.
rinzwind@discworld:~$ more /proc/net/wireless
Inter-| sta-| Quality | Discarded packets | Missed | WE
face | tus | link level noise | nwid crypt frag retry misc | beacon | 22
wlan0: 0000 57. -53. -256 0 0 0 34 1185 0
For each device, the following information is given:
- Status : Its current state. This is a device dependent information.
- Quality - link : general quality of the reception.
- Quality - level : signal strength at the receiver.
- Quality - noise : silence level (no packet) at the receiver.
- Discarded - nwid : number of discarded packets due to invalid network id.
- Discarded - crypt : number of packet unable to decrypt.
- Discarded - misc : unused (for now).
A high value of Discarded - nwid packet might indicate a nwid configuration problem or an adjacent network. The Quality - level might help him to track shadow areas.
The basic difference between Quality - link and Quality - level is that the first indicate how good the reception is (for example the percentage of correctly received packets) and the second how strong the signal is. The Quality - level is some directly measurable data that is likely to have the same signification across devices.
sudo iwspy wlan0) can show command line results on your wireless but only if it supports promiscuous mode otherwise it will show "Interface doesn't support wireless statistic collection"
Now more related to the problem at hand ...
This http://superuser.com/questions/431523/improving-wifi-connections-in-linux states:
- Use a program or iwlist to scan for other wireless networks and, if possible, set the frequency/channel of your router to be at least two channel numbers away from any neighboring networks
- sens - sensitivity is very subjective and requires you to fiddle with it a lot
- rts - setting this to auto helps
- txpower - check your NIC to see what it's capable of, I've had good luck setting linksys/cisco NICs to 84mW
Also interesting: Wireless Internet Connection so slow after upgrade to 11.10