Page 212 - From GMS to LTE

198 From GSM to LTE-Advanced Pro and 5G

Sporadically sent data packets

Default HSPA Control channel

HSPA + CPC

Control channel is switched off
t

Figure 3.46 Control channel switch‐off during times with little activity.
listen to it at different times. This means that fewer spreading codes are used by the
system for this purpose, which in turn leaves more resources for the high‐speed
downlink channels or allows a significantly higher number of users to be kept in HSPA
Cell‐DCH state simultaneously.

3.12.3 HS‐SCCH Discontinuous Reception
While a mobile is in HSPA mode, it has to monitor one or more HS‐SCCHs to see when
packets are delivered to it on the high‐speed shared channels. This monitoring is con-
tinuous, that is, the receiver can never be switched off. For situations when no data is
transmitted or the average data‐transfer rate is much lower than that which could be
delivered over the high‐speed shared channels, the Node‐B can instruct the mobile
device to listen only to selected slots of the shared control channel. The slots that the
mobile does not have to observe are aligned as much as possible with the uplink control
channel gating (switch‐off) times. Therefore, there are times when the mobile device
can power down its receiver to conserve energy. Should more data arrive from the
network than can be delivered with the selected DRX cycle at some point, the DRX
mode is switched off and the network can once again schedule data in the downlink
continuously.

3.12.4 HS‐SCCH‐less Operation
This feature is not intended to improve battery performance but to increase the number
of simultaneous real‐time IMS VoIP users in the network. VoIP requires relatively little
bandwidth per user and hence the number of simultaneous users can be high. On the
radio link, however, each connection has a certain signaling overhead. Therefore, more
users mean more signaling overhead, which decreases the overall available bandwidth
for user data. In the case of HSPA, the main signaling resources are the HS‐SCCHs. The
more the number of active users, the more will be their proportional requirement of the
available bandwidth.
HS‐SCCH‐less operation aims at reducing this overhead. For real‐time users who
require only limited bandwidth, the network can schedule data on high‐speed downlink
channels without prior announcements on a shared control channel. This is done as