Re: GSM Layer 1 book
The book by Gunnar
Gsm Networks: Protocols, Terminology, and Implementation (Artech House Mobile Communications Library.)
is considered as a good book for GSM understanding at all layers including signalling.
The other book is
GSM Switching, Services, and Protocols
by Joerg Eberspaecher, Hans-Joerg Voegel, Christian Bettstetter
which also included two to three chapters over layer 1 and air interface,
Please use amazon.com to look for the contents of these books to see if this is realy what u are looking for ? .