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Summary of SON from LTE Release 8 & 9

In 2G/3G networks, a lot of provisioning is done manually. 3GPP is standardizing self-optimizing and self-organizing capabilities for LTE, based on network intelligence, automation and network management features in order to automate the configuration and optimization of wireless networks. This will trickle down to lesser costs and improved network performance and flexibility. But trend to adopt SON is not limited to LTE. SON has been successfully implemented in various Wimax and GSM networks also, in the industry. Key features of SON (as written in LTE specifications) are described in subsequent sections.

Base station self-configuration

Typically, when a new base-station is installed, it is manually configured by engineer(s) onsite. This includes setup of the transport links, adding the node to the corresponding concentration node (BTS or RNC), and establishing the connectivity with the core network. Apart from this the configuration of all the radio-related parameters such as the cable and feeder loss adjustments, antenna type and its orientation, transmit power, neighbor relations, etc. is also manually done. Since the process is manual, it is time-consuming, error-prone and has dependency on competence of onsite engineers. All these factors add to the cost. Self-Configuration SON functionality is aimed at reducing the amount of human intervention in the overall installation process by providing “plug and play” functionality in the base-stations. The Self-Configuration algorithm should take care of all soft-configuration aspects of the base-station once it is commissioned and powered up for the first time. It should

• detect the transport link and establish a connection with the core network elements,
• download and upgrade the corresponding software version,
• setup the initial configuration parameters including neighbor relations,
• perform a self-test and finally, set itself to operational mode.

The Self-Configuration actions will take place after the base-station is physically installed, plugged to the power line and to the transport link. When it is powered on, the eNB will boot and perform a Self Test, followed by:

• a set of self discovery functions, which include the detection of the transport type, Tower-Mounted Amplifier (TMA), antenna, antenna cable length and auto-adjustment of the receiver-path.
• After the self-detection function, the base-station will configure the physical transport link autonomously and establish a connection with the DHCP/DNS servers, which will then provide the IP addresses for the new node and those of the relevant network nodes, including Serving Gateway, MME and configuration server.
• After this, the base-station will be able to establish secure tunnels for O&M, S1 and X2 links and will be ready to communicate with the configuration server in order to acquire new configuration parameters. One of the O&M tunnels created will communicate the base-station with a dedicated management entity, which contains the software package that is required to be installed.
• The eNB will then download and install the corresponding version of the base-station software, together with the base-station configuration file. Such configuration file contains the pre-configured radio parameters that were previously planned. Note that at the time of the installation most of the radio parameters will have the default vendor values. A finer parameter optimization will take place after the base-station is in operational state (self-optimization functions).
• The configuration of neighbour relations can optionally be performed through an automated SON functionality that is covered in a later section, or else the initial setup can be done according to the output of the network planning exercise.
• After the node is properly configured, it will perform a self-test that will include hardware and software functions, and will deliver a status report to the network management node.
• Also, the unit will be automatically updated in the inventory database that will incorporate the unique hardware identifier, as well as the current configuration and status of the node.

Automatic Neighbour Relation (ANR)

In existing radio-technologies a lot of effort goes in handling of neighbour relations for handover. It is a continuous activity which becomes more intense during network expansion. ANR is aimed at minimizing the manual handling of neighbor relations when installing new base-stations and when optimizing neighbor lists. This shall increase the number of successful handovers and lead to less dropped connections due to missing neighbor relations. ANR can automatically remove unused neighbour relations based on the relation usage, handover performance or a combination thereof. When adding and removing neighbours, ANR is under control of policies set by the operator.

• The black listing allows the operator to decide neighbour relations that ANR may never add as neighbours.
• The white listing allows the operator to decide permanent neighbour relations that ANR may never remove.

These policies are controlled from an Element Management System (EMS)

Tracking Area Planning

Present day wireless operators have been forced to take an offline approach due to lack of any mechanism for effective and efficient adjustment of tracking areas. Due to the cumbersome nature of such a process, most carriers hardly change the tracking areas of their cells. In other words, TAIs for each cell are decided at the time of deployment based on rules-of-thumb, anticipated traffic patterns, etc., They are only altered in the event of extreme performance degradations.

SON TA feature has the ability to change that, both at the time of deployment using Tracking Area Planning (TAP) and during the subsequent network optimization using Tracking Area Optimization (TAO).

Physical Cell ID (PCI) Planning

In order for the UEs to uniquely identify the source of a receiving signal, each base-station is given a signature sequence referred to as Physical Cell ID. Based on the allocated IDs, the Base-station transmits the PCI on the downlink preamble. The UEs in its service area receive the preamble, and are able to identify the base-station, and the corresponding signal quality. It is possible, however, that a UE finds that there are two base-stations that have the same PCI. This is possible since the PCIs are reused by multiple base-stations. But it needs to be carefully planned that neighboring base-stations don't have same PCI. Typical operators use an offline planning tool or depend on manual determination to develop a PCI deployment plan. The plan uses basic information such as base-station location, potential neighbours, etc., to determine the PCI for each base-station. Such an allocation is carefully reviewed to ensure that the market does not have any PCI conflicts; hence the determined PCI values are communicated to each base-station during the installation using the configuration files or manually inputted by the staff. Needless to say, such a process does not lend itself to subsequent changes and is prone to human error. In the SON framework, as soon as the base-station is powered up during the auto-configuration phase, it is allocated to a PCI. Such a PCI is determined using a PCI Planning Tool (PPT) that not only uses the estimated coverage area information for each base-station, but also enforces significant margin and separation between two base-stations that are allocated to the same PCI. Subsequently, during the operational phase, each base-station collects the information pertaining to any PCI conflicts. Observe that PCI conflicts might happen due to errors during the initial PCI Planning phase, deployment of new base-stations, changes in the demographics of a market, power of base-stations, etc. Whenever an LTE UE receives power from two base-stations with the same PCI, it informs the serving base-station about the conflict. Such an alarm is relayed to the OSS / SON mechanism, which collects and logs the details of such conflicts. The operator can then decide on a suitable time interval for activating the PCI Optimization Tool (POT), (e.g., it might make sense to schedule such an activity during a lightly-loaded night-time period). The POT algorithm uses the collected logs, alarms and the updated coverage maps in order to identify the base-stations for which the PCI needs to be changed and the associated new PCI value.

LOAD BALANCING

The objective of Mobility Load Balancing is to intelligently spread user traffic across the system’s radio resources as necessary in order to provide quality end-user experience and performance, while simultaneously optimizing system capacity. The automating of this minimizes human intervention in the network management and optimization tasks. The scope of Mobility Load Balancing in this context is limited to base-stations only, not core entities. The actual transfer of users is accomplished by modification of either cell-neighbor-pair parameters or user-specific parameters. The implementation of MLB algorithms depends upon the architecture. A case can be made for MLB algorithms to be either distributed or centralized. In general, the selected architecture has a strong dependence upon the access technology in question. LTE may be better suited to a distributed algorithm utilizing the X2 interface, while technologies with a BSC/RAN architecture and/or macro-diversity may favor a more centralized approach.

• Distributed LB: Algorithms run locally in the base stations. Load information is exchanged between base stations so that Idle/Active HO (handover) parameters may be adjusted and/or adjustments to RRM functionality can be made.
• Centralized LB: Algorithms run in a core OSS element. Base stations report load information to a central entity which then responds with appropriate modifications to idle/active HO parameters.

In either case (distributed or centralized), it is assumed there will be centralized Operations, Administration and Management (OA&M) control for an operator to enable/disable and configure relevant algorithm settings.

MOBILITY ROBUSTNESS / HANDOVER OPTIMIZATION

The objective of MRO is to dynamically improve the network performance of HO in order to provide improved end-user experience as well as increased network capacity. This is done by automatically adapting cell parameters to adjust handover boundaries based on feedback of performance indicators. The automating of this minimizes human intervention in the network management and optimization tasks. The SON HO Optimization function is an algorithm or set of algorithms designed to improve performance of HOs from one cell to another. Performance data collected from each cell is analyzed in order to correlate HO failures that may be due to improperly configured or un-optimized parameters. Adjustments can then be made to the configuration in an attempt to improve the overall HO performance of the network. Possible cell or cell-neighbor-pair parameter modifications include:

• Trigger Thresholds
• Time-to-Trigger
• Hysteresis (ping-pong control)
• Neighbor List Relation
• Speed-Dependent Parameters
• Antenna Remote Electrical Tilt
• Idle Mode Parameters (to avoid immediate HO trigger when transitioning from idle to active states)

There is a centralized OA&M control for an operator to enable/disable and configure relevant algorithm settings.

Maintainer: Brij Bhushan Ravat

Category: Nm, LTE

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