LTE RAN – Long Term Evolution Radio Access Network

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The LTE RAN consists of these parts:
§  RBS
§  OSS-RC RAN components
§  Interconnecting IP transport network
The following figure shows the logical structure of a single RBS in LTE RAN and how it interconnects with other components of LTE RAN:



Logically, each RBS is comprised of sectors, a digital unit, and a support system. Each sector is connected to one or a number of antenna unit groups. Connection to other RAN and core network elements is provided by the IP transport infrastructure. In some implementations, common elements of the RBS can be shared with other technologies such as WCDMA or GSM. Refer to RBS Configurations for further details.
The following list defines terms used to describe parts of the LTE RBS:
Antenna Unit Group
An Antenna Unit Group (AUG) is the logical structure that includes all details of an antenna and associated equipment. This includes the antenna, and any associated Tower Mounted Amplifiers (TMA) and Remote Electrical Tilt (RET) equipment. An AUG may contain a single branch as in the case of a vertically polarized antenna, or it may contain two branches in the case of a cross polar antenna. Each AUG is connected to one sector. Multi-band antennas may be logically connected to more than one AUG with the different frequency band elements of the antenna connect to different AUGs.
Cell
A part of a sector with its own carrier frequency and channels within the sector frequency band. There may be up to three cells per RBS. It is possible to configure only one cell per sector.
CPRI Connection
The Common Public Radio Interface (CPRI) connection provides the communications link between the digital unit and the radio unit. The CPRI standard allows the use of either electrical or optical interface cables. Electrical cables are used for radio units installed in the RBS cabinet and optical cables are used for remote radio units.
Digital Unit LTE
The Digital Unit LTE (DUL) includes the baseband, control, and switching functions of the LTE component of the RBS. It also contains the interfaces to the RUs, IP transport and RBS synchronization. The baseband capacity is pooled to support multiple sectors. Multiple digital units can be installed in an RBS. Refer to Digital Unit Description for further details.
eNode B
The terminology used in the 3GPP standards for an RBS.
IP Transport
The IP Transport provides connectivity from the RBS to the core network, to other RBSs, and to OSS-RC. System synchronization can also be provided via the IP transport interface using the Clock Source over NTP feature. The physical IP Transport infrastructure provides a number of logical channels. Refer to Transport Network Configuration for further details.
MME
The Mobility Management Entity (MME) manages the core network control functions. The MME nodes are designed to operate in a pooled architecture. The MME handles the mobility and session management functions including:
  • UE registration and detachment handling
  • Security and Authentication, Authorization and Accounting (AAA)
  • Evolved Packet System (EPS) bearer handling
  • Mobility Anchor for active-mode UE
  • Mobility Management for idle-mode UE
OSS-RC
OSS-RC facilitates remote network management of LTE RAN.
Radio Unit
A Radio Unit (RU) refers to the physical hardware that serves a sector. Each radio unit is connected to antenna equipment that is part of an AUG. A radio unit can be physically located in the RBS cabinet, or it can be located externally to the RBS where it is referred to as a Remote Radio Unit (RRU). Refer to Radio Unit Description for further details.
Synchronization
The LTE Digital Unit uses an external synchronization source for generating the required system clock signals. The default method for synchronization is via external Global Positioning System (GPS) equipment. It is also possible to use a Network Time Protocol (NTP) time server to provide synchronization via the IP transport interface. For further details refer to Clock Source over NTP.
RET
Remote Electrical Tilt control signalling allows the antenna electrical tilt to be read or adjusted from a remote location such as from OSS-RC.
Sector
A geographical area spanned by the transmission angle from one or a group of antennas. The sector is configured to handle one specific frequency band.
SGW
The Serving Gateway (SGW) provides an interface to external networks for User Plane (UP) data. It is also anchor point for the user plane for UE mobility between RBS. The SGW also performs some Quality of Service (QoS) related signalling. The SGW nodes are designed to operate in a pooled architecture.
Support System
The Support System provides basic functions to the RBS. This can includes functions such as power supplies, battery backup, external alarms, and climate control systems. In some instances the Support System can be shared with other technologies. Refer to Support System for further details.
TMA
The Tower Mounted Amplifier (TMA) improves uplink system sensitivity and uplink coverage. TMAs are mounted close to the antenna and amplify the uplink Radio Frequency (RF) signals.

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