Created: 18 Mar 2005
I’ve been doing a little research into GSM in my lunchtime, as I’m interested in using GSM speech compression for a project or two. I’ve found this excellent summary of the GSM standard. I find it completely astounding that such a commodity consumer device is so sophisticated.
GSM mobiles use discontinuous transmission to reduce power consumption. They turn off the transmitter when the caller is not speaking. The interesting problem to solve being how to differentiate between speech and background noise. When not transmitting, ordinarily there would be complete silence at the other caller’s end, which would probably lead them to believe wrongly that the connection had died. _ “To assure the receiver that the connection is not dead, comfort noise is created at the receiving end by trying to match the characteristics of the transmitting end’s background noise.” _ All this to make the phone more intuitive to use.