25 148 8.25 bits, or 4.125 bits on either side of the burst, and is an empty
space. These are inserted to avoid overlapping between adjacent time slots due to the MSs geographically
located in different parts of the cell. A scenario will occur when two mobiles are using
adjacent time slots and one is located near the BTS and the other is located far away. Due to the propagation
time differences, the time slots would overlap in the absence of guard bits. The total guard
time is 30.46 sec in duration. The tail bits are always transmitted with values of 0. Lastly, there are
two stealing flags (SF) associated with each on the interleaved data bits.
Synchronization Time Slot. This burst is used to aid time synchronization at the mobile, a 64-bit
sequence is used. Ablock diagram of this time slot is shown in Fig. 1.11. The TDMA frame number
and BTS Identification Code (BSIC) are transmitted. The tail bits and guard bits are the same. The
training sequence is extended to 64 bits in duration.
8 CHAPTER ONE
1 2 3 4 5 6 7 8
Frame = 4.615 msec
Data
39
Tail
Bits 3
Extend Training
64
Data
39
Tail
Bits 3
Time Slot = 0.577 msec = 156.25 Bits
FIGURE 1.11 Synchronization time-slot structure.
EDGE Evolution.
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