hello,
there might be many usages for dummy bursts.. i don’t know all of them, so i’ll just give you what i can remember of :
in GSM : during DTX, dummy bursts are sent in order to be able to measure the radio link and generate comfort noise.
in GPRS : for R4 onwards mobiles, during the delayed UL TBF release extended phase, the MS will send dummy UL packets.
in Location Services : in some positionning methods, the MS might have to send dummy bursts.