Technologies based on Device-to-device CommunicationsThe 5th International Workshop LTE-Advanced and BeyondHanbyul Seo, LG Electronics
D2D communications Data path of the evolved packet service* A UE directly communicates with the peer UE over-the-air. AdvantagesSpatial reuse of time/frequency resourcesReduction of latencyIntroduction of new services such as friend discovery and proximity-basedadvertisement* S1-120349, 3rd Generation Partnership Project; Technical Specification Group SA; Feasibility Study for Proximity Services(ProSe)SGW: Serving gateway, PGS: Packet data network gatewayUE1UE2eNBeNBSGW/PGWUE1UE2eNBeNBSGW/PGWConventional data path setup An exemplary data path setup in D2D
D2D communications (cont’d) Introduction of D2D requires new features. For D2D, UE should to able toDiscover other UEs UE needs to know whether a certain UE is in its proximity or not.Measure the channel from other UEs Synchronization between the peer UEs The measurement result needs be reported to other UEs or to eNB.Receive signal via UL resource It is expected that D2D communication will take place in UL resource.Maintain two different links One link with BS, another one with other UE(s) Coexistence should be guaranteed in terms of control signaling, HARQ operation,handover, and so on. For D2D, eNB should be able toControl D2D links Scheduling individual D2D transmission or high level controlDo interference coordination D2D transmission of a UE should not cause serious interference to the otherlinks.Especially, the eNB-UE link should be protected.
UE discovery UE discovery?UE1 measures some known signature transmitted by UE2. Two different approaches in terms of eNB control on the discoveryresources. Approach 1: Discovery under tight eNB controleNB orders UE1 to receive a certain discovery signature transmitted by UE2.eNB orders UE2 to transmit the signature in a given resource.The measurement result at UE1 can be reported to eNB.Mainly useful for UEs in the connected mode.Fast and accurate discovery, invisible to the other UEs Approach 2: Discovery under loose eNB controleNB broadcasts the set of resources that can be used for discovery signaltransmission.Each UE generates the discovery signature to be used in the transmission (its ownsignature) or reception (peer UE’s signature) Some hashing function from UE ID can be used.Can be used for UEs in the idle mode.Low control signaling overhead
Measurement of UE signal UE discovery is finished when eNB obtains the measurementresults, e.g., the received power of the interested discoverysignature.eNB can initiate D2D data communications based on the measurement result.This UE signal measurement can be treated as a new RRM measurement. This measurement is also needed to maintain the D2D link.Needs to be reported to eNB or the peer UE to make a suitable decision on the linkestablishment/termination, resource re-allocation, link adaptation, and so on. Location of the target UE?Intra-cell UE measurement Relatively easy to get synchronized with the peer UE.Inter-cell UE measurement More challenging especially when the two cells are not synchronized.eNBIntra-cell UEmeasurementeNBeNBInter-cell UEmeasurement
UE signal reception in UL resource Which resource is used for D2D signal transmission/reception?UL resource is a better choice. Reuse the UE ability of UL transmission. Avoid severe interference from eNBs. Alleviate the impact on eNB-UE links.The receiver in the UL resource (i.e., eNB) is usually far from the D2D UE location.SINR comparison in DL resource and UL resource0.000.100.200.300.400.500.600.700.800.901.00-150.00 -100.00 -50.00 0.00 50.00 100.00CDFD2D geometry [dB]D2D in DL resourceD2D in UL resource
Maintaining the two links D2D UE still needs to communicate with eNB.UE needs to maintain both UE-UE link and eNB-UE link simultaneously. D2D communication may have impact on eNB-UE communication.For control signaling and data communication with the other devices An example of such impactIs it possible for a D2D UE to transmit and receive UL signals at the same time? Expected to be difficult due to the self-interference => Half-duplex operation needs to beconsidered in UL resources. Potential impact on the conventional UL communicationDLULPDSCHD2D signal RxHARQ-ACK?SF #n SF #n+1 SF #n+2 SF #n+3
eNB control for D2D links eNB should be able to control D2D links.At least for the interference coordination purpose The range of the eNB controllability?Approach 1: eNB fully controls D2D transmission/reception. Including resource allocation, HARQ, link adaptation, power control, … Potential to have better interference coordination and coexistence with eNB-UE linksApproach 2: Some transmission attributes are determined by the UEs. For example, the transmit UE autonomously determines HARQ and link adaptation parts whileusing time/frequency resources and transmit power the eNB indicated in a semi-static manner. Potential to reduce the control signaling overhead and D2D communication latencyeNBD2D Comm.Dynamic controlsignalingTime 0eNBD2D Comm.Dynamic controlsignalingTime 1eNBD2D Comm.Semi-staticcontrol signalingTime 0eNBD2D Comm.Time 1Approach 1Approach 2
Interference management D2D signal is new source of interference.New type of interference can be generated: UE-to-UE interference if UL resource isused for D2D.Transmit power control is needed for D2D To protect UEs receiving DL signal. To enable the spatial resource reuse as much as possible.D2D transmit power control needs to be separated from that of eNB-UE link. The distance to the target reception point is different.eNBIntra-cell interferencecoordinationControl eNBInter-cell interferencecoordinationD2D
Advanced communication schemes basedon D2D D2D is a communication technology which requires a lot of newfunctionalities. More advanced communication schemes can be built by using theD2D functionalities. UE relayUE receives other UE’s data and forwards it to the target UE. Dynamic resource adaptationeNB transmits DL data in UL resource when the DL traffic is heavy.
UE relay UE relaying for throughput enhancementUE receives other UE’s data and forwards it to the target UE.Throughput improvement by reinforcing the weak channel between eNB and the target UE Type 2 relayA terminology introduced during the study on relaying in 3GPP*A relay node does not create any new cell. It appears as a group of antennas to the destination UE. The destination UE thinks that it is connected to the eNB and controlled by the eNB. More suitable for the UE relayUE relaying can be operated within a HARQ process.Control* TR 36.814, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Further Advancementsfor E-UTRA Physical Layer Aspects.Target UERelay UEDataOverhearTime 1HARQ ACKTarget UERelay UETime 2HARQ NACKTarget UERelay UETime 4HARQ ACKControlTarget UERelay UEData asretransmissionTime 3
UE relay (cont’d) Information floodingUEs are involved in broadcasting the information relevant to all the other UEs. E.g., public warning systemThe broadcast coverage can be improved.eNBBroadcastinformationBroadcastinformationBroadcastinformationBroadcastinformation
UE relay (cont’d) Commonality among UEs can be found based on UE discovery procedureeNB-UE communication can be enhanced if eNB knows which UEs are close to each other. Information sharingUEs in the close proximity can share the common information.An example is the group handover. A UE is selected and performs the handover procedure for a group of UEs. The handover result (e.g., the new cell identification, system information, timing information,and so on) is forwarded to the UEs. Signaling overhead and handover latency can be reduced.Group HO
UE relay (cont’d) Collaborative transmission/receptionUEs in close proximity exchange the signal to transmit and a UE transmits another UE’s data signal.A UE receives another UE’s data signal and exchange it.This effectively increases the number of transmit/receive antennas. For higher data rank or more diversity orderTime 1Transmit signalexchangeTime 2Data transmissionVirtual MIMOoperationTime 0Transmit signalS1Transmit signalS2 S1+S2S1+S2
Dynamic resource adaptation The current cellular system statically divides the whole resource for the useof DL and UL transmission.DL and UL band in FDD, DL and UL subframe in TDD Dynamic resource adaptation in consideration of the traffic loadeNB transmits DL data in UL resource when the DL traffic is heavy. UE transmission in DL resource seems difficult due to the implementation cost and heavierinter-cell interference.A D2D UE is already equipped with the ability to receive data in UL resource.Symmetric Traffic Situation…Time 1 Time 2Resource used for DL/ULBuffer Status(Time 1)UL trafficDL bufferUL bufferHeavy DL Traffic SituationUL trafficDL bufferUL bufferBuffer Status(Time 2)
Dynamic resource adaptation (cont’d) eNB transmission in UL resource?Can be seen as D2D between a normal UE and a special UE which is possessed byeNB?Interference issues eNB-eNB interference management by eNB transmit power control, resourcecoordination, … UE-UE interference is similar to the conventional D2D operationTransmissionin UL resourceWireline connectioneNB transmissionin UL resourceA cell operating eNB-to-UE transmissionA cell operating UE-to-eNB transmissionUE transmissionin UL resourceeNB-to-eNBinterferenceUE-to-UEinterference
Dynamic resource adaptation (cont’d) A study item has been completed for TDD in 3GPP LTE*Significant performance gain was observed in the dynamic resource adaptation.A couple of issues were identified in control signaling, HARQ, interferencemanagement, …* RP-101427, Further Enhancements to LTE TDD for DL-UL Interference Management and Traffic Adaptation02468101214161820222426280 0.5 1 1.5 2UEAvg.DLPktThpt[Mbps]DLArrival RateInfinity Resource Reconfiguration Period10ms Resource Reconfiguration Period640ms Resource Reconfiguration Period024681012141618200 0.25 0.5 0.75 1UEAvg.ULPktThpt[Mbps]ULArrival RateInfinity Resource Reconfiguration Period10ms Resource Reconfiguration Period640ms Resource Reconfiguration Period
Summary Required functions for D2DUE discoverySignal reception in UL resourceMaintaining UE-UE link and eNB-UE linkInterference management The functions introduced for D2D can beimportant enablers of advanced communicationschemes includingUE relayDynamic resource adaptation
A particular slide catching your eye?
Clipping is a handy way to collect important slides you want to go back to later.