2.4.1 Channel Types
To be able to transport data across the LTE radio interface, different channels are used. By dividing into different channels, data can be segregated and efficiently
2.4. CHANNEL HIERARCHY 15 carried in an orderly fashion. LTE has defined three different channel types, used to group different types of data: physical channels, transport channels, and logical channels. Figure 2.5 illustrates the LTE channel hierarchy, whereas the most relevant channel types for this thesis, are marked in red.
Figure 2.5: Mapping between logical, transport, and physical channels in LTE.
Source: [Cho10].
2.4.2 Logical Channels
Logical channels have the overall responsibility to define the type of data transmitted over the air [3GP10]. The logical channels are mainly divided into two categories:
traffic channels carrying user plane data, and control channels carrying signaling messages. The following logical channels are considered relevant for this thesis:
– Paging Control Channel (PCCH): A channel used to transfer paging messages and system information change notifications [3GP10]. The Paging Control Channel (PCCH) is used to carry paging messages when the network doesn’t know which cell a UE might camp.
– Broadcast Control Channel (BCCH):A downlink channel used to broad-cast system information. The Broadbroad-cast Control Channel (BCCH) is either mapped to the Broadcast Channel (BCH) or the Downlink Shared Channel (DL-SCH) dependent on the data it is transferring.
2.4.3 Transport Channels
Transport channels define how and with what characteristics data are transmitted over the air [3GP10]. Figure 2.5 depicts the mapping between the logical channels and the transport channels. The following transport channels are considered relevant for this thesis:
– Paging Channel (PCH): The Paging Channel (PCH) is responsible for broadcasting paging messages in the entire coverage area of the cell. The PCH channel maps to the physical channel Physical Downlink Shared Channel (PDSCH), which is dynamically allocated [3GP10].
– Broadcast Channel (BCH): Similarly to the PCH channel is the BCH channel responsible for broadcasting data to the entire coverage area of the cell [3GP10]. Unlike PCH, the BCH transport format is fixed and carries Master Information Blocks (MIBs) containing system information.
– Downlink Shared Channel (DL-SCH):DL-SCH is the primary transport channel for data transfer, and multiple logical channels map to it. In addition to transmitting application data, DL-SCH is used to broadcast SIBs and signaling messages.
2.4.4 Physical Channels
Physical channels define where data is transmitted over the air. Physical channels are used to carry data and signaling messages among the different levels of the physical layer [Tut17]. Below is a list of the most relevant physical channels for this thesis:
– Physical Broadcast Channel (PBCH):The Physical Broadcast Channel (PBCH) is used to transmit system information to UEs accessing a new net-work. The system information is carried in a MIB message and broadcasted independent of any subscribers presence [Poo12].
– Physical Downlink Shared Channel (PDSCH):The PDSCH is the pri-mary channel used to transmit data over the air and is dynamically allocated to subscribers. Also, PDSCH carries broadcast messages not sent by the PBCH, which includes SIBs and paging messages [3GP08c].
2.5 LTE PLMNs in Norway
Currently, there are three PLMNs providing LTE services in Norway: Telenor, Telia, and ice.net. A PLMN is uniquely identified by a PLMN ID, which is composed of the MCC and the MNC.
2.5.1 PLMN ID Allocation in Norway
The MCC consists of a three-digit number used to identify the homeland of the mobile network operator. The MCC of Norway is 242. The MNC consists of a two or three digit number used to identify the mobile network operator uniquely. Table 2.1 shows the allocated MNCs for the leading commercial mobile operators in Norway.
2.5. LTE PLMNS IN NORWAY 17 Table 2.1: MCC and MNC distribution for three PLMNs in Norway [Int16].
PLMN MNC MCC
ice.net 14 242
Telia 02 242
Telenor 01 242
2.5.2 LTE Frequency Allocation in Norway
Norwegian PLMNs have been allocated Downlink (DL) and Uplink (UL) frequencies in four E-UTRA bands: band 3 (1800 MHz), band 7 (2600 MHz), band 20 (800 MHz), and band 31(450 MHz). Telia and Telenor have frequencies in band 3, 7, and 20 while ice.net has frequencies in band 3, 20, and 31 [Nas]. Band 3 and band 7 are common for the three PLMNs in Norway, and Table 2.2 provides a complete overview of all the allocated LTE frequencies in these bands.
Table 2.2: LTE frequency distribution in E-UTRA band 20 and band 3, as of 04.04.2017 [Nas].
Band 20 (800MHz) Band 3 (1800MHz) PLMN DL (MHz) UL (MHz) DL (MHz) UL (MHz)
The LTE network architecture can be divided into three areas: MME pool area, S-GW service area, and TA [Cox12]. The intention with the MME pool area is to distribute the signaling load among several MMEs and hence reduce the processing load for each MME. An MME pool area is typically covering a large geographical area such as densely populated cities [Cox12]. The S-GW service area has a similar structure as the MME pool area; however, an S-GW service area does not necessarily have to cover the same area as the MME pool area [Cox12].
MME pool areas and S-GW service areas consist of one or more TAs. A TA contains multiple BSs and is used to track the movement of UEs that are in standby mode [Cox12]. The Tracking Area Identity (TAI) uniquely identifies TAs; moreover, the TA can be identified within a particular network using the Tracking Area Code (TAC) [Cox12]. Figure 2.6 illustrates the relation between the MME pool area, the
S-GW service area, and the TA.
Figure 2.6: The relation between MME pool area, SGW service area, and TA.
Source: [Cox12].