Direct Communication in 3GPP 차세대이동통신망 표준기술단기강좌 Hakseong KIM 전자 LG전자
2 Contents D2D in 3GPP workshop FS for Proximity Services (ProSe) Use Cases and Scenarios Requirements Typical D2D communication and technologies Scenarios and basic requirements UE Discovery Measurement of signal Physical resources for D2D Maintaining between two links eNB controllability (tight, loose) Interference measurement Related future technologies
3 D2D in 3GPP workshop D2D generally provides LTE 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 companies Public safety, Proximity based social networking, offloading, Proximity-enabled communication, Local data transfer, Data flooding, Cost efficient data exchange, home networking Further study or consideration points Device 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
4 FS for Proximity Services (ProSe) Feasibility Study for Proximity Services (ProSe) (Release 12) 3GPP TR 22.803 V1.0.0 1 (2012-08)
5 FS for Proximity Services (ProSe) 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 UE eNB 1 SGW/PGW UE eNB 2 *EPC (e.g., session management, authorization, security) **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
6 FS for Proximity Services (ProSe) 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 UE1 eNB EPC eNB Note: Two eNBs are shown here for illustration UE2
7 FS for Proximity Services (ProSe) 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 UE1 eNB EPC UE2
8 FS for Proximity Services (ProSe) Public Safety use of ProSe In the United States, LTE has been selected by the FCC as the technology  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 . Additionally, a variety of public safety over ProSe requirements have been defined . 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 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
9 FS for Proximity Services (ProSe) References for Public Safety use of ProSe 3GPP website announcement "FCC selects LTE for USA Public Safety" http://www.3gpp.org/FCC-selects-LTE-for-USA-Public 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 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 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  National Public Safety Telecommunications Council, 700 MHz Statement of Requirements for Public Safety (SoR) http://www.npstc.org/statementOfRequirements.jsp U. S. Department of Homeland Security Technology Solutions and Standards Statement of Requirements http://www.safecomprogram.gov/library/lists/library/DispForm.aspx?ID=302 TETRA Release 1: Direct Mode Operation http://www.tetramou.com/about/page/12026
10 FS for Proximity Services (ProSe) General Use Cases and Scenarios Restricted 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 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
11 FS for Proximity Services (ProSe) 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 ProSe Broadcast ProSe Relay ProSe Hybrid and Range Extension ProSe Range Public Safety Implicit Discovery
13 Typical D2D Scenario and Advantages Data path of the evolved packet service (in 3GPP) UE1 UE2 UE1 UE2 eNB eNB eNB eNB SGW: Serving Gateway SGW/PGW PGW: Packet data network Gateway SGW/PGW A UE directly communicates with the peer UE over-the-air. Advantages Spatial reuse of time/frequency resources Reduction of latency Introduction of new services such as friend discovery and proximity-based advertisement
14 Technology Requirements for UE an eNB Introducing D2D requires new technologies. For D2D, UE should to able to Discover 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. 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 to Control 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
15 UE discovery UE discovery UE1 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 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
16 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. 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. eNB Inter-cell UE measurement Intra-cell UE measurement eNB
17 D2D resource used for discovery/data Which resource is used for D2D signal transmission/reception? UL resource is a better choice. Benefits Reuse 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.
18 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)
19 Issues in TX/RX in UL resource D2D signal transmission in UL resources Is 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 resources Is it possible for a D2D UE to transmit and receive UL signals at the same time? 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
20 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. Potential to reduce the control signaling overhead and D2D communication latency Semi-static Dynamic control control signaling signaling eNB eNB D2D Comm. D2D Comm. Approach I Approach II
21 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 D2D To 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. The distance to the target reception point is different. eNB1 eNB Intra-cell interference Inter-cell interference coordination coordination
22 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 relay UE receives other UE’s data and forwards it to the target UE. Dynamic resource adaptation eNB transmits DL data in UL resource when the DL traffic is heavy.
23 UE relaying UE relaying for throughput enhancement UE 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 the eNB (UE cant be aware of the existence of this Type II relay). UE relaying can be operated within a HARQ process (by assisting ongoing HARQ process) HARQ ACK Relay UE Relay UE Relay UE Relay UE Retransmission Target UE Target UE Target UE Target UE
24 UE relay (cont’d) Information flooding UEs 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) eNB Broadcast information
25 UE relay (cont’d) Public Safety System LTE technology (destroyed) LTE infrastructure LTE carrier or others eNB eNB
26 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 sharing 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. Se Group HO rv in g ce ll
27 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 load eNB 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. Symmetric Traffic Situation Heavy DL Traffic Situation DL buffer DL buffer Buffer Status Buffer Status (Time 1) (Time 2) UL buffer UL UL traffic buffer UL traffic … … Time 1 Time 2 Resource used for DL/UL
28 Summary D2D in 3GPP workshop FS for Proximity Services (ProSe) Use cases and Scenarios Requirements Required functions and technologies for D2D UE discovery Signal reception in UL resource Maintaining UE-UE link and eNB-UE link Interference management D2D related future technologies UE relay & wireless backhaul & information flooding Dynamic resource adaptation
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