Cell Outage Management in LTE Networks M. Amirijoo (Ericsson), L. - PDF document

FP7 ICT-SOCRATES Cell Outage Management in LTE Networks M. Amirijoo (Ericsson), L. Jorguseski (TNO ICT), T. Kürner (TU Braunschweig), R. Litjens (TNO ICT), M. Neuland (TU Braunschweig), L. C. Schmelz (Nokia Siemens Networks), U. Türke (Atesio) Abstract Cell outage management is a functionality aiming at automatically detecting and mitigating outages that occur in radio networks due to unexpected failures. The FP7 EU-funded project SOCRATES (Self- Optimisation and self-ConfiguRATion in wirelEss networkS) is heavily engaged in developing a framework and solutions for cell outage management, where appropriate measurements, control parameters, policies, assessment methodologies, and algorithms are being developed. Our vision is that radio networks autonomously detect an outage based on measurements, from e.g., user equipment and base stations, and alter the configuration of radio base stations such that coverage and service quality requirements during an outage, as specified by the operator, are satisfied. In this presentation we give an introduction in the area of cell outage management and present an overview of the results achieved so far as well as the next steps that will be pursued. 1

Outline � Introduction � Components in cell outage management � Operator policy � Measurement � Control parameters � Scenarios � Assessment criteria � Simulator � Future work WWW.FP7-SOCRATES.EU 2/20 2/20

Introduction � The first release of the 3GPP Long Term Evolution (LTE) standard has been finalized � Operators require significant reduction of manual network management for LTE � Introduction of self-organisation functionalities in LTE – Reduces manual network management – Enhances network performance � One aspect that benefits from self-organization is cell outage management (COM), which consists of: – Cell outage detection – Cell outage compensation WWW.FP7-SOCRATES.EU 3/20 3/20 The standardisation body 3rd Generation Partnership Project (3GPP) has finalised the first release (Release 8) of the UMTS successor named as Evolved UTRAN (E-UTRAN), commonly known as Long Term Evolution (LTE). Wireless network operators today spend considerable manual effort in planning, configuring, optimising, and maintaining their wireless access networks. These efforts consume a substantial part of their operational expenditure (OPEX). Consequently, an important E-UTRAN requirement from the operators’ side is a significant reduction of the manual effort in the deployment, configuration and optimisation phases for this future wireless access system. One way for achieving this requirement is the introduction of self-organisation functionalities into the E- UTRAN. Self-organisation functionalities not only reduce the manual effort involved in network management, but they also enhance the performance of the wireless network. One aspect that benefits from self-organization is the management of cell/site outages, which can be divided into two parts, namely, the detection of an outage and the compensation of the detected outage. 3

Introduction � Reasons for outages, e.g.: – hardware and software failures, – external failures such as power supply or network connectivity � Outages – may not be detected for hours or even days – may require manual analysis and unplanned site visits � Outage detection function must timely inform the operator about the occurrence and the cause of an outage � Automatic compensation actions are triggered to alleviate performance degradation WWW.FP7-SOCRATES.EU 4/20 4/20 There are multiple reasons for a cell outage, e.g., hardware and software failures (radio board failure, channel processing implementation error etc), external failures such as power supply or network connectivity failures, or even erroneous configuration. While some cell outage cases are detected by Operations Support System (OSS) functions through performance counters and/or alarms, some may not be detected for hours or even days. It is often through long term performance analysis and subscriber complaints that these outages are detected. Currently, discovery and identification of some errors involves sometimes manual analysis and may require unplanned site visits, which makes cell outage detection a costly task. It is the task of the cell outage detection function to timely inform the operator about the occurrence of an outage and the cause of the outage. In the event of a cell outage detection, appropriate compensation methods are triggered to alleviate the degraded performance due to the resulting coverage gap and loss in throughput by appropriately adjusting radio parameters in surrounding sites. In general, human involvement shall only be triggered when absolutely necessary, e.g., when manual repairs are needed. 4

Components of Cell Outage Management Control parameters Operator policy: Coverage, QoS Compensation -70 2000 -80 1500 -90 1000 -100 500 -110 0 -120 Measurements -130 Detection -500 -140 -1000 -150 -1500 Cov. map -160 -2000 -170 -2000 -1500 -1000 -500 0 500 1000 1500 2000 2500 estimation Simulation tools Scenarios Assessment criteria WWW.FP7-SOCRATES.EU 5/20 5/20 Various measurements are gathered from the user equipments (UEs) and the base stations (called eNodeBs in LTE). The measurements are then fed into the cell outage detection function, which detects whether at the current time an outage has occurred and triggers the cell outage compensation function to take appropriate actions. The goal of cell outage compensation is to minimise the network performance degradation when a cell is in outage. This is done by automatic adjustment of network parameters in order to meet the operator’s performance requirements based on coverage and other quality indicators, e.g., throughput. It is realized that performance requirements may not be achieved during an outage and, as such, the goal of the compensation function is to meet performance requirements to the largest possible extent. Cell outage compensation algorithms may for example alter the antenna tilt and azimuth, or the cell transmit power, in order to cover the area that is in outage. Altering the radio parameter of the neighbouring cells means that some of the UEs served by neighbouring cells may be affected. For example, if the coverage of a neighbouring cell increases then this implies that more UEs will be served and, consequently, the UE throughput may decrease. This should be taken into account and an appropriate balance between coverage and other quality indicators (e.g. throughput) should be achieved. This balance is indicated by means of an operator policy that governs the actions taken by the cell outage compensation function. In order to monitor and evaluate the actions taken by the cell outage compensation algorithm, there is a need to estimate the coverage around the vicinity of the outage area. This is provided by the coverage map estimation function, which continuously monitors the network coverage by means of measurements and possibly prediction data. There are also other activities being pursued along this work, namely, the development of simulation tools, scenarios that capture different outage cases, and methods and criteria for assessing the impact and performance of cell outage detection and compensation algorithms. 5

Operator Policy � In a cell outage situation an operator may still target at the ideal goal of – achieving the best coverage possible, – providing the highest accessibility, and – delivering the best possible quality in the cell outage area and all surrounding cells. � All these goals cannot be fulfilled at the same time – the targets have to be weighted and/or ranked in order to provide quantitative input to an optimisation procedure. � The optimisation goal itself may vary depending on the operator’s policy – coverage orientation – quality orientation – capacity orientation WWW.FP7-SOCRATES.EU 6/20 6/20 Every operator has its own policy for the network performance. For cell outage management the operator wants to implement its policy into the network. For this, optimisation goals and a cost function have to be defined. In a cell outage situation an operator may still target at the ideal goal of •achieving the best coverage possible, •providing the highest accessibility, and •delivering the best possible quality in the cell outage area and all surrounding cells. In most cases, all these goals cannot be fulfilled at the same time. As a consequence the targets have to be weighted and/or ranked in order to provide quantitative input to an optimisation procedure. The optimisation goal itself may vary depending on the operator’s policy. For example, one operator wants to maximize its income also during the cell outage, whereas another operator may have also the long-term user satisfaction in mind. In the first case an operator may target a high capacity sacrificing coverage in a large area yielding a low perceived coverage, which is often worse for the reputation compared to a higher blocking rate. Hence, the policy definition should be modular/flexible enough to capture different operator strategies, e.g., coverage oriented operator vs. capacity oriented operator. 6