On Wed, 20 Feb 2013 10:18:00 +0000 (UTC)
Nick Leverton wrote:
In article ,
wrote:
On Tue, 19 Feb 2013 20:09:07 +0000
"Clive D. W. Feather" wrote:

Bluetooth and WiFi in the 2.4 GHz band is limited to 10 mW and has other
restrictions on duty cycle and power density. Railway equipment in 2.446
to 2.454 is allowed 500 mW in a narrow channel ( 1.5 MHz). Given that
the application is a train passing straight over the transponder in the
four foot, I suspect that the WiFi signal won't even be noticed.

Thats all very well, but whats stopping someone shoving a bluetooth signal
through a linear amp to disrupt the comms? If you think thats a stupid thing
to do , well hackers tend to do stupid things.

There was the case in China recently where repeated disruption to a
2.4GHz metro train control system was blamed on a high number of personal
wireless hubs built into passengers' equipment. This article is a bit
lacking in technical details but gives the outline:
http://english.caijing.com.cn/2012-11-20/112296950.html

Oh dear. Looks like LU may have saved a few pennies but potentially left
themselves with a serious problem especially if the new system on the Met
also uses 2.4 Ghz because thats mostly above ground. One hacker with a grudge
could probably bring the entire line to a halt. Or even worse, if they can
duplicate the comms protocol and override the real signal then they could
potentially cause a crash.

Spud