Page 214 - From GMS to LTE

200 From GSM to LTE-Advanced Pro and 5G

to respond to RRC messages from the RNC and to send its IP packets. An additional
method was introduced with 3GPP Release 8, which foresees a special E‐DCH for
faster data transmission. Both methods limit the use of adaptive modulation and cod-
ing since the mobile cannot send frequent measurement reports to the base station to
indicate the downlink reception quality. Furthermore, it is also not possible to
acknowledge proper receipt of frames. Instead, the RNC informs the base station
when it receives measurement information in radio resource messages from the
mobile device.
Enhanced Cell/URA‐PCH states. In these two states, the mobile device is in a deep
●
sleep state and only observes the paging information channel so as to be alerted of an
incoming Paging message that is transmitted on the PCH. To transfer data, the mobile
device moves back to Cell‐FACH state. If the mobile device and the network support
Enhanced Cell/URA‐PCH states, the network can instruct the mobile device not to
use the slow PCH to receive paging information but to use a HS‐DSCH instead. The
high‐speed downlink channel is then also used for subsequent RRC commands,
which are required to move the device back into a more active state. Like the measure
above, this significantly decreases the wakeup time.
Figure 3.47 shows how this works in practice. While the message exchange to notify
the mobile device of incoming data and to move it to another activity state remains the
same, using the HS‐DSCHs for the purpose speeds up the procedure by several hun-
dred milliseconds.
Although some CPC features, such as the various DRX and DTX enhancements as
well as the Fractional DPCH functionality, have seen an uptake in practice to increase

UE Network

IP packets arrive from
URA-PCH the network but cannot be delivered
as no bearer is established

Paging
Paging response
High Speed Downlink Channels
Cell-FACH used for transmitting RRC messages
to speed up the procedure
Reestablish bearers

Cell-DCH

Data exchanged
Time

Figure 3.47 Message exchange to move a mobile device from URA‐PCH state back to Cell‐DCH state
when IP packets arrive from the network.