Handover Parameters In Lte e569

HANDOVER PARAMETERS IN LTE Asad BasitElectrical DepartmentComsats institute of Information [email protected] Abstract-Handover is the decisive part inmobile communication because ittransfers ongoing data and calls from onepoint to another point when the UE (equipment) moves. In order to reduce HOfailures self-optimization algorithms aredeployedAutomatic configuration andoptimization is a key concept in LTE.Thus self-organized solution for the LTEhandover parameters is proposed, basedon the mobility performance indicators.This paper explained the major eventsand process that are involved inHandover process .I.INTRODUCTIONHandover is a procedure for assuring thats can move freely within a network.Since its success rate is a key indicator of satisfaction. It is vital that this procedure happens as fast and as frequentlyas possible. In currently deployed setup,handover optimization is performedmanually. This approach is time consumingand cannot be carried out as often as needed.Thus by developing self-optimizingalgorithm that can tune parameters of thehandover process, this enables a betteroverall network performance and quality ofservice (QOS).The main targets are reducingthe number of HOs that are begin but notcarried out to execution which results in HOfailures, repeated back and forth HOs between two base stations often called „pingpong‟ HOs and c alls being dropped.Handover can be defined by a very preciseflow of events. The main challenges facingis finding the perfect balance between thecontrol parameters of the HO process andensure that the network is in stable point fora long time. This paper describes themeasurement parameters involved in HO process and Handover process carried out inLTE.II.METRICSThe metrics used in handover parameteroptimization are further sub divided intosystem metrics, control parameters andassessment metrics. The received power(RSRP) and signal-to interference and noise(SINR) and received signal quality (RSRQ)are system metrics. They are used to selectthe connected cell and possible handovercandidates. The control parameters are tuned by the optimization algorithm to increase the HO performance of the network. Themetrics are used as measurements during theoptimization process and as performanceindicators for the optimization algorithmevaluation.III. SYSTEM METRICSIn LTE or other cellular networks, UE reportsome kind of signal to base station forvarious decision making. This could be usedfor better uplink scheduling, cell selection,downlink scheduling, multipath propagationand other location based services. Theseincludes the following i-e RSRP, RSRQ,SNR, RSSI etc.A. RSRQ (Reference Signal ReceivedPower)RSRP (Reference Signal Receive Power) isthe average power of Resource Elements(RE) that carry cell specific ReferenceSignals over the entire bandwidth. Itstypically range is about -44 to -130dbm.Thismeasurement is used in RRC idle/connected,HO scenarios, Cell Selection/Reselection.RSRP measures only the Reference signal(RS) power and excludes all noise andinterference power. The RSRP is calculatedfrom the cell transmit power (Pc), the pathloss values from the s to different cells(Lue) and additional shadow fading withlog-normal distribution and a standarddeviation of 3db (Lfad).The resulting RSRPvalues are calculated per cell c and UE by :RSRP c, ue = Pc – Lue – LfadSince this measures only the reference power, we can say that this is the strength ofthe wanted signal. But it does not gives anyinformation about signal quality. RSRP tellsus the signal strength of the desired signal,not the quality of signal. For quality of thesignal information we use another parametercalled RSSQ.B. RSRQ (REFERENCE SIGNALRECIEVED QUALITY)Although RSRP is an important measure, but it gives no indication of signal quality.RSRQ is defined as (N x RSRP)/RSSI,where N is the number of RBs over themeasurement bandwidth. Thus this is not thedirect measurement, it is a derived valuefrom RSRP and RSSI. By dividing RSRP byRSSI, it could give some information aboutinterference also tells about the strength ofthe wanted signal. Measuring RSRQ becomes important near the cell edge whendecisions need to be made, regardless ofabsolute RSRP, to perform a handover to thenext cell. Reference signal receive quality isused only during connected states. Inter andintra frequency absolute RSRQ accuracyvaries from ±2.5 to ±4 db.C. RSSI (RECEIVED SIGNALSTRENGTH INDICATOR)RSSI is a measurement of all the powercontained in the applicable spectrum (1.4, 3,5, 10, 20 MHz). This could be data channels,control channels, adjacent cell power, and background noise. Thus RSSI is a parameterwhich provides information about the totalreceived wide-band power including allinterference. The RSSI is the total powerthat UE observes across the whole band, thisincludes power from the serving cell, adjacent channel interference and co-channel non-serving cell signal, thermalnoise within the specified band.IV. CONTROL PARAMETERSThe control parameters are tuned by theoptimization algorithm to increase the HO performance of the network. The metrics areused as measurements during theoptimization process and as performanceindicators for the optimization algorithmevaluation. After UE reports the signalstrength of the serving and neighbor cell.Then control parameters are deployed tomake the handover successful. These parameters includes

event A1 to A5 and B1,B2, MRO, offset, Time to trigger, thus toincrease the success rate of handover.V. MEASUREMENT REPORTTRIGGERINGAfter UE measure the signal strength of itsserving cell and the neighbor ones. Then itreports the result to eNB, periodically orwhen a measurement event is triggered asone of the reporting criteria set bymeasurement configuration is satisfied.For LTE, the following criteria specifiedreporting and events:  Event A1: Serving cell becomes better than threshold.  Event A2: Serving cell becomes lessthan the threshold.  Event A3: Neighbour cell becomesan offset better than the serving cell.  Event A4: Neighbour becomes offset better than threshold.  Event A5: Serving cell becomesworse than a threshold.For inter-RAT mobility, the followingcriteria for reporting and events.  Event B1:Neighbor cell becomes better than threshold.  Event B2: Serving cell becomesworse than threshold.A. EVENT A3 IN LTE:A3 event in LTE is used for intra-LTEhandover in LTE. When neighbor LTE cell become stronger than source LTE cell thanUE will trigger event A3 and sendmeasurement report containing RSRP andRSRQ along with target cell PCI to eNodeB.Then eNodeB send RRC reconfigurationmessage to UE which contains otherhandover parameters.The equipment uses parameters sent bythe RBS to determine when to performhandover measurements. Measurementscommences on the serving and neighboringcells when the RSRP of the serving cell falls below the value defined in the s-Measure parameter. Figure 1UE uses either RSRP or RSRQmeasurements to determine whether to enterthe EventA3 condition. The trigger QuantityA3 parameter is used to configure whetherRSRP or RSRQ values are used to triggerEventA3. Measurements of RSRP andRSRQ are performed on the serving anddetected neighboring cells. The measuredvalues of RSRP and RSRQ then filtered based upon the settings of the parameter filter Coefficient EUtran RSRPand filter Coefficient E-Utran RSRQ parameters.The filter averages a number ofmeasurements in order to filter out theimpact of large scale fast fading. The equipment then uses an offset value, a3offset, and a hysteresis value, hysteresis A3,to determine whether to trigger the Event A3 Entering A3 Event conditions are defined bythe followingMn − HysteresisA3>Ms+a3offsetMn = measured value of the neighboringcell (either RSRP or RSRQ)Ms = measured value of the serving cell(either RSRP or RSRQ)Once Event A3 is triggered, the equipment will wait a predetermined time(timeToTriggerA3) before it commencessending measurement reports to the servingRBS. These measurement reports containmeasurements for the serving cells and up tothree detected intra frequency neighborcells. The report Quantity A3 parameterindicates whether RSRP or RSRQmeasurements, or both, are to be included inthe measurement reports.The parameter report Interval A3 determinesthe time interval between measurementreports. The parameter report AmountA3 indicates how many reports to send; avalue of 0 indicates that the reports should be sent indefinitely whilst the EventA3condition is active. The equipment usesthe same offset and hysteresis values todetermine when to leave EventA3 when theserving cell improves in RSRP or RSRQrelative to the neighboring cells. Theformula used by the UE is given by:Mn + HysteresisA3 < Ms + a3offset B. A3 OFFSET This parameter can be found in 3GPP36.331.The value sent over the RRCinterface is twice the value configured, thatis, the UE has to divide the received value by 2.The role of the offset in Event A3 is tomake the serving cell look better than itscurrent measurement in comparison to theneighbor.C.

HYSTERESIS A3The role of the hysteresis in Event A3 is tomake the measured neighbor look worsethan the serving one, to ensure it is reallystronger before the UE decides to send ameasurement report to initiate a handover.D. TIME TO TIGGER A3In Event A3 the role of ttt is to avoid ping- pong effect. Time to trigger A3 typicalvalues are [0, 40, 64, 80, 100, 128, 160, 256,320, 480, 512, 640, 1024, 1280, 2560, 5120]milliseconds.Cell Individual offset EUTRAN:This parameter is applied individually toeach neighbor cell with load management purposes. The higher the value given to a neighbor cell, the “more attractive” it will be. This parameter can only be used in anRRC connection reconfiguration.CONCLUSIONThere are always increasing demands ofhigh speed data applications in wirelesssystems with seamless and fast access ofcommunication services and better QOS.LTE required such algorithm whichautomatically optimize and configure theSo Automatic configuration andoptimization of networks is a key concept inLTE. There are some important parametersdescribed in the paper which are involved inthe HO. Event A3 is the most important parameter widely used in LTE handover process.REFERENCES [1] NTT DoCoMo, “Evaluation of Rel -8 LTE mobility performance”, 3GPP R2-093273, May 2009.[2] Capdevielle, V., Feki, A., &Fakhreddine, A. (2013, May). Self-optimization of handover parameters in LTEnetworks. In Modeling & Optimization inMobile, Ad Hoc & Wireless Networks(WiOpt), 2013 11th InternationalSymposium on (pp. 133-139). IEEE.[3] Legg, P., Hui, G., & Johansson, J. (2010,September). A simulation study of LTEintra-frequency handover performance.In Vehicular Technology Conference Fall(VTC 2010-Fall), 2010 IEEE 72nd (pp. 1-5).IEEE.[4] Ismail, M., Yusof, A. L., Ya'acob, N.,Ali, S. N., Rosdi, M., & Zainali, M. A.(2013, August). The performance of intraand inter handover with overlapping cell inLTE based network. In System Engineeringand Technology (ICSET), 2013 IEEE 3rdInternational Conference on (pp. 148-151). IEEE