GSM systems have 25 MHz of bandwidth allocated to their uplink and downlink, divided into 125 TDMA channels with 8 user timeslots per channel. A GSM frame consists of the 8 timeslots, preceded by a set of preamble bits and followed by a set of trail bits. Each timeslot consists of 3 start bits at the beginning, followed by a burst of 58 data bits, then 26 equalizer training bits, another burst of 58 data bits, 3 stop bits, and a guard time corresponding to 8.25 data bits. The transmission rate is 270.833 kbps.

(a) Sketch the structure of a GSM frame and a timeslot within the frame.

(b) Find the fraction of data bits within a timeslot as well as the information data rate for each user.

(c) Find the duration of a frame and the latency between timeslots assigned to a given user in a frame, neglecting the duration of the preamble and trail bits.

(d) What is the maximum delay spread in the channel such that the guard band and stop bits prevent overlap between timeslots?