Page 251 - From GMS to LTE

Long Term Evolution (LTE) and LTE-Advanced Pro 237

milliseconds. All other SIBs are grouped into System Information messages whose
periodicities are variable. Which SIBs are contained in which System Information
message, and their periodicities, are announced in SIB 1.
Not all of the SIBs shown in Table 4.4 are usually broadcast as some of them are
functionality dependent. In practice, the MIB and, in addition, SIB 1 and SIB 2 are
always broadcast because they are mandatory. They are followed by SIB 3 and option-
ally SIB 4. SIB 5 is required if the LTE network uses more than one carrier frequency.
The broadcast of SIB 5 to SIB 7 then depends on the other radio technologies used by
the network operator.

4.3.8 The LTE Channel Model in the Uplink Direction
In the uplink direction, a similar channel model is used as in the downlink direction.
There are again logical, transport and physical channels to separate logical data streams
from the physical transmission over the air interface and to multiplex different data
streams onto a single channel. As shown in Figure 4.11, the most important channel is
the Physical Uplink Shared Channel (PUSCH). Its main task is to carry user data in
addition to signaling information and signal quality feedback.
Data from the PUSCH are split into three different logical channels. The channel that
transports the user data is referred to as the DTCH. In addition, the DCCH is used for
higher‐layer signaling information. During connection establishment, signaling mes-
sages are transported over the Common Control Channel (CCCH).
Before a mobile device can send data in the uplink direction, it needs to synchronize
with the network and has to request the assignment of resources on the PUSCH. This is
required in the following scenarios:
The mobile has been dormant for some time and wants to reestablish the connection.
●
A radio link failure has occurred and the mobile has found a suitable cell again.
●
During a handover process, the mobile needs to synchronize with a new cell before
●
user data traffic can be resumed.
Optionally for requesting uplink resources.
●
Figure 4.11 LTE channel uplink Uplink channels
structure.
Logical
channels CCCH DCCH DTCH
(what)

Transport
channels UL-SCH RACH
(how)

Physical
channels PUSCH PRACH PUCCH