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204 From GSM to LTE-Advanced Pro and 5G

state or the Cell‐PCH or URA‐PCH state. Some networks even skip the Cell‐FACH
state entirely and move the connection from Cell‐DCH directly to Cell‐PCH or URA‐
PCH state. In practice, it can be observed today that most mobile devices do not wait
for the network to act but request the release of the physical connection themselves if
they come to the conclusion that it is unlikely that further data will be sent. This mecha-
nism is described in the next section.

3.13.3 Power Consumption
Figure 3.49 shows the power consumption in the different states. On the left, the mobile
device is in Cell‐DCH state on high‐speed channels. Power consumption is very high
and ranges between 1.5 and 2 W. Typical mobile device batteries have a capacity of
around 10 watt hours. Therefore, being in Cell‐DCH state continuously would drain the
battery in a few hours.
In the middle of Figure 3.49, the mobile device is in Cell‐FACH state and power con-
sumption is reduced to about 0.8 W. In the example, the idle timer in the network is set to
45 seconds and after expiry the mobile is set into idle state. Here, the power requirements
go down to 0.3 W. Most of the power, however, is used for the background light of the
display. Once the light is turned off, power requirements are reduced to less than 0.1 W.
The autonomy time of a mobile device is mainly influenced by the type of application
running on a device and the timer settings in the network. If, for example, an e‐mail
client is used on a device that checks the inbox in the network once every 10 minutes or
requires a keep‐alive message to be sent in this interval to keep the logical connection
to the server open, a radio connection has to be established six times an hour. If the
Cell‐DCH timer is set to 15 seconds, the mobile device remains in this highly

Figure 3.49 FACH and DCH power consumption.
Source: Reproduced from Nokia © 2010.