When I looked about 4 or 5 months ago, I could find little technical information on the web for any of the CBTC systems. The manufacturers all had brochures, but they mostly focused on explaining the benefits of CBTC systems and high level glossy pictures, with little real technical detail. They certainly didn't give you a good idea about how the systems actually worked.
I found the best source of information were recent books; particularly Volumes 2 & 3 of 'Railway signalling and automation' by Walter Schon, Guy Larraufi, Gilbert Moens, and Jacques Pore. (I was lucky enough to find relatively cheap secondhand copies in a bookshop in the wilds of the eastern UK fens
Be aware that SelTrac is more a marketing name than a technology name. The underlying technology has evolved considerably from the original system in the 1980s, and the various generations are not compatible.
I would still be interested more information if anyone knows of other sources...