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After three years of faithful service, the wifi in my Dell 1545 Laptop
began being intermittently troublesome. Left on-line for a few hours
unattended, I would find the wifi not only dead, but whatever it finds
in knoppix-data.img would not allow me to get re-connected. I had to
re-establish persistent store to get on-line again.

I went to Dell's on-line store, gave them my product ID and found there
was a re-furbished wifi for $22 plus tax with free shipping. On this
same site I was able to download an illustrated owner's manual which
spelled-out how I might easily remove and replace the wifi. The $22
replacement arrived in a few days and I was able to do the physical part
of the replacement in mere minutes.

The wifi provided was not an exact replacement, but a slight 'upgrade'
from a/b/g to a/b/g/n. The original and the replacement have different
part numbers, but seem to be operationally interchangeable. The original
was a BCM4312, Dell part nr DW-1397; the replacement a BCM4322, DW-1510.
Both Windows 7 and Knoppix 7 easily found and correctly installed drivers.
The Windows 7 driver installation said, incorrectly, that its install
was 'unsuccessful'.

I was pleased with my diagnosis and my bargain and my successful repair.
For a while, that is. Guess what, the replacement wifi pretty much
matches the original, including my complaint of infrequent intermittence.

So, here's a more complete statement of the intermittence. Very
infrequenly, if I leave my CD-size LiveUSB on-line with no keyboard
activity I may return and find the wifi connection gone, AND the
driver unloaded from the Linux kernel. The connection does not re-
establish itself, even on reboot, without some help.

There are two simple work-arounds that solve my problem for all practical
purposes. First, if I notice a dropped connection, I can get back on-line,
without rebooting, with sudo modprobe b43. Second, I might double-down
by adding, as root, b43 to my /etc/modules file to make sure b43 gets
loaded at boot.

Both the original and the replacement wifis are among those which
the b43/linuxwireless.org folks say work both with b43 and wl drivers.
In Knoppix 6.7.1, with the original wifi I never saw this intermittence
with either driver; however, my experience was mostly with the wl driver,
I only used the b43 driver for a short time before the advent of Knoppix 7.
In Knoppix 7, there is currently only a b43 option. I've seen the
intermittence in both the original and replacement wifis.