Page 52 - From GMS to LTE

38 From GSM to LTE-Advanced Pro and 5G

Table 1.6 GSM power levels and corresponding power output.

GSM 900 Power level GSM 900 Power output GSM 1800 Power level GSM 1800 Power output
(0–2) (8 W) – –
5 2 W 0 1 W
6 1.26 W 1 631 mW
7 794 mW 2 398 mW
8 501 mW 3 251 mW
9 316 mW 4 158 mW
10 200 mW 5 100 mW
11 126 mW 6 63 mW
12 79 mW 7 40 mW
13 50 mW 8 25 mW
14 32 mW 9 16 mW
15 20 mW 10 10 mW
16 13 mW 11 6.3 mW
17 8 mW 12 4 mW
18 5 mW 13 2.5 mW
19 3.2 mW 14 1.6 mW
– – 15 1.0 mW

broadcast the common channels like frame control header (FCH), SCH and BCCH of a
cell. On such carriers, the power output has to be constant to allow mobile devices
which are currently located in other cells of the network to perform their neighboring
cell measurements. This would not be possible if the signal amplitude varies over time
as the mobile devices can only listen to the carrier signal of neighboring cells for a
short time.
Owing to the limited speed of radio waves, a time shift of the arrival of the signal can
be observed when a subscriber moves away from a base station during an ongoing call.
If no countermeasures are taken, this would mean that at some point the signal of a
subscriber would overlap with the next timeslot despite the guard time of each burst,
which is shown in Figure 1.26. Thus, the signal of each subscriber has to be carefully
monitored and the timing of the transmission of the subscriber has to be adapted. This
procedure is called timing advance control (Figure 1.29).
The timing advance can be controlled in 64 steps (0–63) of 550 m. The maximum
distance between a base station and a mobile subscriber is in theory 64 × 550 m = 35.2 km.
In practice, such a distance is not reached very often as base stations usually cover a
much smaller area for capacity reasons. Furthermore, the transmission power of the
mobile device is also not sufficient to bridge such a distance under non‐line‐of‐sight
conditions to the base station. Therefore, one of the few scenarios where such a distance
has to be overcome is in coastal areas, from ships at sea.
The control of the timing advance already starts with the first network access on the
RACH with a Channel Request message. This message is encoded into a very short