Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 31 of 182
1.5.3.3 2G and 3G cyclic idle/active mode (power saving enabled)
The power saving configuration is disabled by default, but it can be enabled using the appropriate AT
command (see the u-blox AT Commands Manual [2], AT+UPSV command). When power saving is
enabled, the module automatically enters idle mode whenever possible.
When power saving is enabled, the module is registered or attached to a network and a voice or data
call is not enabled, the module automatically enters idle mode whenever possible, but it must
periodically monitor the paging channel of the current base station (paging block reception), in
accordance with GSM system requirements. When the module monitors the paging channel, it wakes
up to active mode, to enable the reception of paging block. In between, the module switches to idle
mode. This is known as GSM discontinuous reception (DRX).
The module processor core is activated during the paging block reception, and automatically switches
its reference clock frequency from 32 kHz to the 26 MHz used in active mode.
The time period between two paging block receptions is defined by the network (2G or 3G). This is the
paging period parameter, fixed by the base station through broadcast channel sent to all users on the
same serving cell.
For a 2G network, the time interval between two paging block receptions can be from 470.76 ms (DRX
= 2, i.e. width of 2 GSM multiframes = 2 x 51 GSM frames = 2 x 51 x 4.615 ms) up to 2118.42 ms (DRX =
9, i.e. width of 9 GSM multiframes = 9 x 51 frames = 9 x 51 x 4.615 ms).
For a 3G network, the principle is similar but time interval changes from 640 ms (DRX = 6, i.e. the width
of 2
6
x 3G frames = 64 x 10 ms = 640 ms) up to 5120 ms (DRX = 9, i.e. width of 2
9
x 3G frames = 512 x 10
ms = 5120 ms).
An example of a module’s current consumption profile is shown in Figure 14: the module is registered
with the network (2G or 3G), automatically enters idle mode and periodically wakes up to active mode
to monitor the paging channel for paging block reception.
20-30 ms
IDLE MODE ACTIVE MODE IDLE MODE
Active Mode
Enabled
Idle Mode
Enabled
2G case: 0.44-2.09 s
3G case: 0.61-5.09 s
IDLE MODE
20-30 ms
ACTIVE MODE
Time
[s]
Current [mA]
100
50
0
Time
[ms]
Current [mA]
100
50
0
RX
Enabled
DSP
Enabled
Figure 14: Description of VCC current consumption profile versus time when the module is registered with 2G or 3G networks:
the module is in idle mode and periodically wakes up to active mode to monitor the paging channel for paging block reception