Direct Communication in 3GPP

Direct Communication in 3GPPDirect Communication in 3GPP

차세대이동통신망차세대이동통신망차세대이동통신망차세대이동통신망표준기술단기강좌표준기술단기강좌표준기술단기강좌표준기술단기강좌

Hakseong KIMLG전자전자전자전자

Contents

� D2D in 3GPP workshop

� FS for Proximity Services (ProSe)Use Cases and Scenarios

Requirements

� Typical D2D communication and technologiesScenarios and basic requirements

UE Discovery

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Measurement of signal

Physical resources for D2D

Maintaining between two links

eNB controllability (tight, loose)

Interference measurement

� Related future technologies

D2D in 3GPP workshop

� D2D generally providesLTE D2D discovery provides new service opportunities

Provide new opportunities for commercial applications based on LTE platform

Increased spectral efficiency, Reduced power consumption, Cellular coverage extension, Direct communications outside the network coverage

� Use cases proposed by companiesPublic safety, Proximity based social networking, offloading, Proximity-enabled communication, Local data transfer, Data flooding, Cost efficient data exchange, home networking

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exchange, home networking

� Further study or consideration pointsDevice discovery (with/without network assistance, the first phase)

Data communication (with/without network assistance, the second phase)

Licensed or unlicensed spectrum, dedicated or shared carrier

Proper Interference management

Both FDD and TDD should be considered for global applicability

Obvious requirement for public safety system

FS for Proximity Services (ProSe)

� Feasibility Study for Proximity Services (ProSe) (Release 12)

� 3GPP TR 22.803 V1.0.0 1 (2012-08)

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� Legacy data path scenario: Default data path setup in the *EPS for communication between two UEs.

Currently, when two UEs in close **proximity communicate with each other, their data path (user plane) goes via the operator network.

The typical data path for this type of communication is shown below, where eNB(s) and/or GW(s) are involved

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UE

1eNB

1

UE

2eNB

SGW/PGW

**Proximity**Proximity: proximity is determined (“a UE is in proximity of another UE”) when given proximity criteria are fulfilled.

Proximity criteria can be different for discovery and communication

*EPC (e.g., session management, authorization, security)


� ProSe Communication scenario 1: The “direct mode” data path in the EPS for communication between two UEs

If UEs are in proximity of each other, they may be able to use a local or direct path.

For example, in 3GPP LTE spectrum, the operator can move the data path (user plane) off the access and core networks onto direct links between the UEs. This direct data path is shown below

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Note: Two eNBs are shown here for illustration

UE2

UE1

eNB

EPC

eNB


� ProSe Communication scenario 2: A “locally-routed” data path in the EPS for communication between two UEs when UEs are served by the same eNBs

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UE2

eNB EPC

UE1


� Public Safety use of ProSeIn the United States, LTE has been selected by the FCC as the technology [1][2][3] for the Public Safety Network.

In Europe, there is an ongoing discussion on spectrum to be chosen for broadband Public Safety held by CEPT ECC WG FM PT 49 [4].

Additionally, a variety of public safety over ProSe requirements have been defined [5][6][7].

The requirements raise the following points for consideration in developing the ProSe requirements for public safety use.

� A public safety UE can operate in the public safety spectrum for public safety service

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� A public safety UE can operate in the public safety spectrum for public safety service and in the MNO commercial spectrum, for general service ( e.g. voice call), however, only the public safety spectrum is used for public safety ProSe.

� Public safety UEs using ProSe communicate with each other even though they belong to different HPLMNs.

� A public safety UE can automatically use ProSe when network coverage is not available, or the user can manually set the UE to use direct discovery and communication even when network coverage is available.

� In addition, the following assumptions are made for public safety ProSe:

All public safety users utilize ProSe-enabled UEs

ProSe supports both UE discovery and data exchange

� If and when other regional and/or regulatory requirements are raised, they will be taken into account


� References for Public Safety use of ProSe[1]3GPP website announcement "FCC selects LTE for USA Public Safety" http://www.3gpp.org/FCC-selects-LTE-for-USA-Public

[2]3GPP website link to FCC announcement of selection of LTE for USA public safety "FCC TAKES ACTION TO ADVANCE NATIONWIDE BROADBAND COMMUNICATIONS FOR AMERICA’S FIRST RESPONDERS" http://www.3gpp.org/IMG/pdf/psltedoc-304244a1.pdf

[3]FCC “Third Report and Order and Fourth Further Notice of Proposed Rulemaking” pertaining to Docket Numbers: WT Docket No. 06-150, PS Docket No. 06-229 and WP Docket No. 07-100. The Report and Order was adopted on January 25, 2011 and released on January 26, 2011. http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-11-6A1.pdf

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11-6A1.pdf

[4]CEPT ECC WG FM PT 49 Radio Spectrum for Public Protection and Disaster Relief (PPDR), Report from FM Project Team 49 (2nd and 3rd meetings) http://www.cept.org/ecc/groups/ecc/wg-fm/fm-49

[5] National Public Safety Telecommunications Council, 700 MHz Statement of Requirements for Public Safety (SoR) http://www.npstc.org/statementOfRequirements.jsp

[6]U. S. Department of Homeland Security Technology Solutions and Standards Statement of Requirements http://www.safecomprogram.gov/library/lists/library/DispForm.aspx?ID=302

[7]TETRA Release 1: Direct Mode Operation http://www.tetramou.com/about/page/12026


� General Use Cases and ScenariosRestricted ProSe Discovery Use Case

Open ProSe Discovery Use Case

Discovery Use Case with Subscribers from Different PLMNs

Discovery Use Case with Roaming Subscribers

EPS ProSe Discovery for ProSe Use Case

Service Continuity between Infrastructure and E-UTRA ProSe Communication paths

Operator A uses ProSe to Enhance Location and Presence Services

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Operator A uses ProSe to Enhance Location and Presence Services

ProSe for Large Numbers of UEs

WLAN ProSe Communication Use Case

Service Management and Continuity for ProSe Communication via WLAN

Use Case for ProSe Application Provided by the Third-Party Application Developer


� Public Safety Use Cases and Scenarios ProSe Discovery Within Network Coverage

ProSe Discovery Out of Network Coverage

Can Discover But Not Discoverable

Basic ProSe One-to-One Direct User Traffic Initiation in Public Safety Spectrum Dedicated to ProSe

UE with Multiple One-to-One Direct User Traffic Sessions in Public Safety Spectrum Dedicated to ProSe

ProSe Group

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ProSe Group

ProSe Broadcast

ProSe Relay

ProSe Hybrid and Range Extension

ProSe Range

Public Safety Implicit Discovery


� Potential RequirementsAdditional Operational Requirements

Additional Charging Requirements

Additional Security Requirements

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Typical D2D Scenario and Advantages

� Data path of the evolved packet service (in 3GPP)

eNBeNB eNBeNB

UE1UE1 UE2UE2

eNBeNB eNBeNB

UE1UE1 UE2UE2

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� A UE directly communicates with the peer UE over-the-air.

� AdvantagesSpatial reuse of time/frequency resources

Reduction of latency

Introduction of new services such as friend discovery and proximity-based advertisement

SGW/PGWSGW/PGWSGW/PGWSGW/PGWSGW: Serving GatewaySGW: Serving Gateway

PGW:PGW: Packet data network GatewayPacket data network Gateway

Technology Requirements for UE an eNB

� Introducing D2D requires new technologies.

� For D2D, UE should to able toDiscover other UEs

� UE needs to know whether a certain UE is in its proximity or not.

(Synchronization between the peer UEs)

Measure the channel from other 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.

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� 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 (tight) or high level control (loose)

Do interference coordination

� D2D transmission of a UE should not cause serious interference to the other links.

Especially, the eNB-UE(Uu) link should be protected

UE discovery

� UE discoveryUE1 measures some known signature(e.g. sequence, signal pattern) transmitted by UE2

� Two different approaches in terms of eNB control on the discovery resources.

Approach 1: Discovery under tight eNB control

� eNB 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 (with proper

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� The measurement result at UE1 can be reported to eNB (with proper synchronization).

� Mainly useful for UEs in the connected mode.

� Fast and accurate discovery, invisible to the other UEs

Approach 2: Discovery under loose eNB control

� eNB broadcasts the set of resources that can be used for discovery signal transmission.

� Each UE generates the discovery signature to be used in the transmission (its own signature) 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

� If UE discovery is finished after eNB obtains the measurement results, e.g., the received power of the interested discovery signature.

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 link establishment/termination, resource re-allocation, link adaptation, and so on.

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so on.

� Location of the target UEIntra-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.

Intra-cell UEmeasurementIntra-cell UEmeasurement

eNB

eNB

Inter-cell UEmeasurementInter-cell UEmeasurement

D2D resource used for discovery/data

� Which resource is used for D2D signal transmission/reception?UL resource is a better choice.

� BenefitsReuse the UE ability of UL transmission.

Avoid severe interference from eNBs (DL)

Alleviate the impact on eNB-UE links (i.e. protects Uu link)

Less interference impact on UL receiver (eNB)

� The receiver in the UL resource (i.e., eNB) is usually far from the D2D UE location.

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Maintaining the two links (Uu & D2D)

� 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.Issues in TX/RX in UL resource (next)

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Issues in TX/RX in UL resource

� D2D signal transmission in UL resourcesIs it possible to transmit D2D signal together with conventional UL signal?

The transmit power difference needs to be considered.

If not, some solution may be needed to keep the conventional UL communication.

� D2D signal reception in UL resourcesIs it possible for a D2D UE to transmit and receive UL signals at the same time?

Difficult due to the self-interference

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Difficult due to the self-interference

� Half-duplex operation needs to be considered in UL resources.

� If TX and RX are different directions (e.g. relay), it’s possible

Another impact on the conventional UL communication

� Handling of HARQ-ACK to eNB when D2D transmit or receives its signal

May not be legacy HARQ process with 8ms periodicity

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 links

Approach 2: Some transmission attributes are determined by the UEs.

� For example, the transmit UE autonomously determines HARQ and link adaptation parts while using time/frequency resources and transmit power the eNB indicated in a semi-static manner.

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a semi-static manner.

� Potential to reduce the control signaling overhead and D2D communication latency

eNB

D2D Comm.

Dynamic control signaling

Approach I

eNB

D2D Comm.

Semi-static control signaling

Approach II

Interference management

� D2D signal is new source of interference.New type of interference can be generated

� UE-to-UE interference if UL resource is used for D2D.

� Cases: transmit power control is needed for D2DTo protect UEs/eNB receiving UL signal in the same carrier (FDD/TDD)

To protect UEs receiving DL signal in the same carrier (TDD only)

To enable the spatial resource reuse as much as possible.

� D2D transmit power control needs to be separated from that of eNB-UE link.

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eNB-UE link.The distance to the target reception point is different.

eNB1

Intra-cell interference coordination

Intra-cell interference coordination

eNB

Inter-cell interference coordination

Inter-cell interference coordination

Future technologies related to D2D

� D2D is a communication technology which requires a lot of new functionalities.

� More advanced communication schemes can be built by using the D2D functionalities.

� UE relayUE receives other UE’s data and forwards it to the target UE.

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UE 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 relaying

� UE relaying for throughput enhancementUE receives other UE’s data and forwards it to the target UE.

Throughput improvement by strengthening the weak channel between eNB and the target UE

� Type 2 relay as “UE relaying”A terminology introduced during the study on relaying in 3GPP (TR36.814)

A relay node does not create any new cell (no PCID).

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

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The destination UE thinks that it is connected to the eNB and controlled by the eNB (UE can't be aware of the existence of this Type II relay).

UE relaying can be operated within a HARQ process (by assisting ongoing HARQ process)

Target UETarget UE

Relay UERelay UE

HARQACK

HARQACK

Target UETarget UE

Relay UERelay UE

Target UETarget UE

Relay UERelay UE

Target UETarget UE

Relay UERelay UE

RetransmissionRetransmission

UE relay (cont’d)

� Information floodingUEs are involved in broadcasting the information relevant to all the other UEs.

� The broadcast coverage can be improved.

� Public Warning System (PWS)US: CMAS (Commercial Mobile Alert System)

Korea: KPAS (Korean Public Alert System)

Japan: ETWS (Earthquake Tsunami Warning System)

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eNBBroadcast

informationBroadcast

information

UE relay (cont’d)

� Public Safety SystemLTE technology

LTE infrastructure

LTE carrier or others

eNB

(destroyed)

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eNB

UE relay (cont’d)

� eNB-UE communication can be enhanced if eNB knows which UEs are close to each other.

Commonality among UEs can be found based on UE discovery procedure

D2D handover, Group UEs handover

� e.g. Group handover over HO information sharingA 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.

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Signaling overhead and handover latency can be reduced.

Serving cell

Group HOGroup HO

Dynamic resource adaptation

� The current cellular system statically divides the whole resource for the use of 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 heavier inter-cell interference.

A D2D UE is already equipped with the ability to receive data in UL resource.

Heavy DL Traffic SituationHeavy DL Traffic Situation

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Symmetric Traffic SituationSymmetric Traffic Situation

……

Time 1Time 1 Time 2Time 2

Resource used for DL/UL Resource used for DL/UL

Buffer Status

(Time 1)

Buffer Status

(Time 1)�UL traffic�UL traffic

DL bufferDL buffer

UL bufferUL buffer

Heavy DL Traffic SituationHeavy DL Traffic Situation

�UL traffic�UL traffic

DL bufferDL buffer

UL bufferUL buffer

Buffer Status

(Time 2)

Buffer Status

(Time 2)

……

Summary

� D2D in 3GPP workshop

� FS for Proximity Services (ProSe)Use cases and Scenarios

Requirements

� Required functions and technologies for D2DUE discovery

Signal reception in UL resource

Maintaining UE-UE link and eNB-UE link

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Interference management

� D2D related future technologiesUE relay & wireless backhaul & information flooding

Dynamic resource adaptation