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1、精品论文A Cell Outage Healing Algorithm Based on Power Control for SON SystemZhang Xing, Zhang Yangan5(Institute of Information Photonics and Optical Communications,Beijing University of Posts andTelecommunications, Beijing 100876)Abstract: In this paper a cell outage healing algorithm is proposed for S
2、elf-Organizing Networks.Cell outage detection (COD) is a Self-Healing function in Self-Organizing Networks concept. COD is a function of realization that a cell outage is occurring or about to occur.The main contribution of this10paper is a cell outage healing scheme based on definite solution inter
3、val. When the existence of quality redundancy in surrounding cell of outage cell is detected from measurement through O&M, we trade off between quality redundancy and coverage of the compensation cell by adjust the control parameters, and then compensate the outage cell by the coverage extension of
4、compensation cells.Keywords: Self-Healing; Self-Organizing Networks; power control; cell outage150IntroductionThe reasons of cell outage in cellular networks can be different. It may be caused by software or hardware faulty. Cell Outage Management (COM) is divided into cell outage detection (COD) an
5、d cell outage healing (COH). COD is a kind of function identifying that a problem is about to20occur or occurring, while COH is identification and application of the appropriate corrective action to restore the service. We can find that the some parameters are selected as most effective COH paramete
6、rs. COD flow of Self-Healing concept is described in 3GPP TS 1. The part of “Monitor the TCoSH (Trigger Condition of Self-Healing)” is gathering the network conditions including some measurements from eNodeBs (eNBs), User Equipment (UEs) and other Network25Elements in real time. The COD function wil
7、l test whether the system could reach a TCoSH every once in a while. If it isnt reached, we will do nothing with it and keep on monitoring and detecting the network. If a TCoSH is reached, we will trigger an appropriate Self-Healing Process.The SON target is to maintain network quality and coverage
8、performance with minimum manual intervention from the operator. Introducing SON functions into the Universal Terrestrial30Radio Access Network (UTRAN) is very important for operators to minimize OPEX 。Self-organizing functionalities have been brought into the Evolved-UTRAN in 3GPP R8.It consists of
9、3 sub-function modules such as self-configuration, Self- optimization and Self-healing. The Self-healing concepts and requirements have been presented in 3GPP Technical Specification 2.The other two sub-function modules is studied in 3.35Cell outage can be alleviated even eliminated effectively by a
10、 series of self-healing mechanism in self-healing function modules. Some kind of outage fault can be solved by cell outage detect and single-cell outage recovery while others need to be made up by multi-cell joint healing. A cell outage detection algorithm based on the neighbor cell list reporting o
11、f mobileterminals is presented and evaluated in 4.Fig.1 depicts the integration process of cell outage40healing. The purpose of Self-healing is to elimination and mitigation cell outage automatically by triggering the appropriate recovery action when Trigger Condition of Self-Healing (TCoSH) is met.
12、 It means that when the alarm which can be automatically resolved is detect, more necessary information is collected for the deep analysis to determine if it is necessary to start SH process.Cell outage healing process needs to be started when the problem cannot be solved by single cellBrief author
13、introduction:ZhangXing, (1986-), Male, Master, Communication and Information System. Correspondance author: Zhang YangAn, (1972-), male, Associate Professor, Access Network and Communication Network. E-mail: - 9 -45recovery. By adjusting control parameters in the neighbor of outage cell, users in th
14、e outage cell is taken over by healing cell so that the basic radio traffic in the coverage hole is maintained. The COH concept and workflow is introduced in 5.The rest of this paper is organized as follows: Section 2 introduces cell outage healing including parameter measurement, healing strategy a
15、nd control parameters. In Section 3, we50represent the details of the proposed healing scheme. The evaluation methodology, system model and simulation results are explained in Section 4. Finally, Section 5 will summarize the paper and give key point for future research.1Self-Healing Mechanism Descri
16、ption1.1Cell outage healing network55The study on detail of cell outage healing will be present in this part. Fig.1 shows overview of the cell outage healing network.odulemCOCodmbased KPIsCOD uleO&MFig. 1 Architecture of Cell outage healing network60The above figure indicates that the parameters nee
17、ded in COH can be measured from several ways. We can obtain cell load, radio link/handover failure statistics and interference levels form eNBs. Reference Signal Received Power (RSRP) which indicates the strength of received signal can be got from measurement of UE. In O&M some quality-based KPIs ca
18、n be measured, which isused for the set of quality threshold according to 6.651.2Workflow of cell outage healingOur COH scheme can be divided into two stages, firstly the triggering of healing module when periodic outage detection by some alarms happens and then the implement of COH scheme. When a p
19、eriodic outage detection or triggered by some alarms happens. The details of the COH flow chart are presented in fig.2.70Fig. 2 Flow Chart of COHHealing strategy is the key differentiation factor of the COH scheme. It defines the balance between network performance and operational costs considering
20、influence factor such as location,75time as well as the operational state of a cell (1.normal state 2.outage state pensating state).Our healing strategy is get better coverage at the cost of reasonable throughput decline in healing cell. If quality of service in neighbor of outage cell exceed the le
21、vel needed to satisfy the user, the quality redundancy can be utilize to extend its coverage to compensate users in the outage cell.80Based on our study, we can extend the coverage of neighbor cells by adjust channel parameters (e.g. Public pilot channel transmitting power, uplink target received po
22、wer etc.) and antenna parameter (e.g. antenna direction angle, antenna tilt, beam choice and antenna power) to achieve healing to the coverage hole. In 7, uplink target received power is considered as a key parameter in power control mechanism. Physical layer standard about E-UTRA is discribed in 8.
23、85In this paper we focus on the channel parameters. While enhancing the public pilot channel transmitting power not only extend the coverage of neighbor cells but also increase the Inter-cell interference(ICI) which cause the decrease of cell capacity, so it is not suitable as optional parameter. Ra
24、ther, the reduction of uplink target received power can alleviate the Co-Channel inter-cell Interference so that improve network capacity, meanwhile, extend the coverage of90neighbor cells. Thus, uplink target received power is selected as control parameter in the proposed healing algorithm, which m
25、inimizes the uplink target received power in the premise of guaranteeing necessary communication quality. Paper 9,10 provides other candidate control parameters of COH in different scenarios. Research on COH by adjust antenna parameter will be carried in further research.952Cell Outage Healing Algor
26、ithm1002.1Parameter definitionThe coverage and quality are important parameters that characterize the system performance in LTE system, which stand for the systems ability of providing wireless services from different angles. They are also a set of contradictory parameters that can be transformed fr
27、om one to another by adjusting control parameters such as uplink target received power. In older to provide user with the optimal service experience, coverage and quality must be keep in a state of balance considering the operator policy.Radio parameters that, to some extent, influence coverage and
28、spatial properties of service105quality are candidate control parameters for COH. This scheme uses the throughput as a measure indicator of quality of service. Through theoretical analysis shown in section 2, when the user experience exceeded the level they actually needed, which means that there is
29、 quality redundancy in the network, we can get coverage enhancement at the expense of throughput decline by lowingthe uplink target received power.1102.1.1Quality evaluation parametersDefinition of quality evaluation parameters:QUL denote the uplink quality evaluationparameters whileQDLis defined fo
30、r down link. In the simulation model we look upon the 5ththroughput percentileT5% as cell edge throughput which can be regarded as a key indicator tomeasure the quality of service.1152.1.2Target threshold quality parametersDefinition of target threshold quality parameters:QUT ,UL denote the upper th
31、reshold qualityparameters for uplink. Similarly,QUT , DLis upper threshold for downlink. When the throughputin actual network exceeds the threshold, it means that there is quality redundancy which can be used as healing resource for outage cell. We also need a lower limit to ensure the normal operat
32、ionof the healing cell, so QDT ,ULis the lower limit threshold quality parameters in uplink while120QDT ,ULis homologous in downlink. If the quality of a cell is below the lower limit threshold, itindicates that the user service quality cannot be guaranteed so that the cell is not suitable as a heal
33、ing one. In real network the edge throughput of 21 BTS is collect and sorted in ascending order. Value at 30 percentile of the series can be seen as the lower threshold while value at 70 percentile is upper threshold accordingly.1252.1.3Control parametersUplink target received power Pris set to be t
34、he control parameters, lower Prallow thatUE reduce uplink shared channel transmit power level, thus further alleviate the ICI and its average value on each of the PRB. Finally, the coverage of healing cell is extended in level of the whole network. This scheme adopts discrete way to adjust the contr
35、ol parameters. So we define130 P 0as the quantitative power size in order to adjust a quantitative level each time. Then we cancarry on the semi-static simulation.2.2Algorithm descriptionAccording to the basic idea of the scheme as well as assessment and control parameters defined above, the healing
36、 algorithm is described as follow.135After cell outage crop up in the network,T5%in its neighbor cells is measured within acertain time window. If the measurement is greater than the upper threshold QUT , this means thatthere is quality redundancy in the neighbor cell. We treat it as healing cell an
37、d the Prwill be turndownPrin this condition.P = Pr PrPr Pr ,minrPr ,minelse140On the contrary, If measuredT5%is less than the lower threshold QDT , it indicates that thePr need to be triggered by a Princrease so that the normal operation of the healing cell can beguaranteed.P = Pr + PrPr Pr ,maxrPr
38、,maxelse145Pr ,max : Maximum received power allowed by BS.Pr ,min : Minimum received power, in older to support the lowest MCS level, SINR mustbe greater than a lower threshold SINRminSignal should meet the conditions:If SINRmin = 7.5dB , then the Power of ReceivedSr SINRmin ( N0 + Imax ) , Imaxdeno
39、tes the maximum uplink ICI can be observed in thesystem, N0is white noise.150155160If the measurement is between the upper and lower threshold, the control parameter will not be modified, because this means that the quality parameter is just within the target range.After the adjustment of control pa
40、rameters, the quality parameter is measured again, then deep analysis will be carried on it, and the feedback shows that whether there is over healing or under healing in the last. Based on the feedback, the algorithm will be executed more accurately.3Evaluation Methodology and Performance AnalysisI
41、n this section, the performance of the proposed algorithm will be verified based on our simulation platform. We consider a hexagonal layout of 73 cells.3.1Simulation ScenarioKey system parameters are listed in Table.1:Table. 1 System ParametersParametersValueScenarioUmaBS number7BTS per BS3Antenna d
42、own-tilt15System bandwidth10MHzMaximum BS output power46dBmMaximum UE output Power23dBmNoise spectral power density-174dBm/HzBS Antenna Height30mInter-site distance500mBS Antenna polarized modeCross-polarize3dBBeamWidthHDeg703dBBeamWidthVDeg10BS Antenna gain15dBBS Noise figure5dBPenetration lost-20d
43、BMS Noise figure9dbThe structure topology of the cell in the scenario is shown in the fig.3.165Fig. 3 LTE Cell Network Topology3.2Analysis of simulation results1701753.2.1Performance analysis of MSBefore we start the proposed scheme, user in outage cell is taken over by the neighboring cell in accordance with the principles of minimum linkloss without considering the quality and resource of the neighboring cell. So if the outage user is handover to a cell that has no sufficient radio resource, the user will not ge