Mobilné komunikácieLecture 3: D2D communication for 5G

Ján PapajKEMT – FEI – TUKE

jan.papaj@tuke.sk

OutlineIntroductionEvolution towards 5G

Introduction – Why D2D CommunicationD2D CommunicationD2D Offloading

D2D Research at TCSStandardization of D2D CommunicationConclusion

Can we Match to the Growth? Both backhaul as well as the access capacity should be increased Increasing Access Capacity…

Add more BTSs At present we have 7,36,654 BTS in India Tata Teleservices alone has 3000+ BTS in Bangalore New BTS will add CAPEX and OPEX

Release new spectrum Huge cost for the operators Seems to be a challenge

• Only 200+ MHz available in India Improve the spectral efficiency

Not possible always• Theoretical Limits are being reached

Usability is the key • Yet to deploy LTE Rel 8

» Spectral efficiency = 4-5Increasing Backhaul Capacity

Nationwide optical fibre backboneOnly a few operators can do this

CAPEX and OPEX issue again

Source – Huawei - The_full_spectrum_of_possibilities

Source – ITU -Link: http://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-M.2243-2011-PDF-E.pdf

Preliminaries - What is device cooperation?

Device cooperation is a technique to exploit D2D(Device-to-Device) link in addition to the existing WWAN link for the following benefits. • Capacity enhancement• Reduction of power consumption

Related terminologies• Source device: The end device whom the data traffic to the BS is generated from or the data

traffic generated from the BS is targeting for• Cooperative device: The device who helps the source device(s) in UL or the BS in DL by

relaying or co-transmitting data and control information• Network lifetime: Duration of time until the first node (device) failure due to battery depletion

WWAN BSWWAN link

WWAN link (e.g. 802.16m)

D2D link

Preliminaries - Device cooperation modes

Mobile relaying• A cooperative device performs the functionality of a RS(Relay Station). A cooperative device forwards the data of a source

device to the BS. For example, the source device send data traffic to the cooperative device through D2D link at T1, and the cooperative device send it to the BS at T2 as shown in Fig. 1. Additionally, a concept of group anchor where an anchor devicecollects data traffic from multiple source devices and forwards it to the BS, can be another example of mobile relaying.

Cooperative transmission• Both of a cooperative device and a source device transmit data traffic of a source device to the BS. In this mode, the data traffic

of the source device is shared with the cooperative device through the D2D link transmission in advance, and then the shared data traffic is transmitted to the BS from the source and cooperative device jointly. For example, the source device send data to the cooperative device at T1, and both of the source and cooperative devices transmit the data to the BS simultaneously at T2as shown in Fig. 2.

BS

Cooperative device

Source device

T1

T2

Fig. 1. Mobile relaying

(a) Mobile relaying (b) Group anchor

BS

Source device

Cooperative device

T1

T2

T2

Fig. 2. Cooperative transmission

PurposeTo propose/design optimal scheduling algorithms for D2D uplink/downlink in data networks

such as HSPA, LTE, LTE-A, etc., networks. D2D communication model for LTE/LTE-A systems that can be used for mobile data offloading

Why D2D?Possible to have direct communication between close proximity UEs

Reuse of cellular resources –use cellular spectrum D2D users can use same resource blocks of the cellular users Higher and better network performance than WiFi, Bluetooth, etc. Viz: in social networking, online gaming, multimedia sharing, etc.

Gain and gain Reuse gain, proximity gain, hop gain Higher data rate, low end-to-end delay

Emergency services

D2D Communication

● Securityo The security features of WiFi and Bluetooth are much less robust than

those used in public cellular systems. They would not be adequate for major public services and they would be unsuitable for public safety applications.

● Independence from cellular networkso WiFi and Bluetooth operate independently from cellular radio

technology such as LTE. Any form of device-to-device discovery based on them would have to run in parallel with cellular radio operation, which would be inefficient and would become a significant drain on device batteries.

D2D vs Ad-hoc

● Unlicensed spectrumo WiFi and Bluetooth operate in unlicensed spectrum, without any

centralised control of usage or interference. This is not generally a problem when usage densities are low, but it would become a major limitation as proximity-based services proliferate. Throughput, range and reliability would all suffer.

● Manual pairingo WiFi and Bluetooth rely on manual pairing of devices to enable

communication between them, which would be a serious stumbling block for autonomous, dynamic proximity-based services.

● Transmission distance and data transfer rate (see next slide)

D2D vs Ad-hoc

Machine to Machine (M2M) Communication Machine Type Communication – 3GPP TR 22.368

D2D vs. M2M

D2D vs. Ad-hoc NetworksD2D Ad-hoc Networks

Licensed and Free Spectrum Free Spectrum

QoS can be ensured No QoS guarantee

Seamless Connectivity Manual Connectivity

Security is guaranteed Security is a challenge

D2D M2MDescribes connectivity Services Application Oriented

Direct device to device communication Remote devices communicates through a centralized node

Access specific Access agnostic

Local comm. improves spectral efficiency Not applicable

D2D vs. M2M and Ad-hoc Networks

Big Question Is it possible for UEs in proximity to communicate among themselves ?

Regular Communication Model In coverage D2D Communication Model

eNB

Data PathControl Path (C-Plane)

D2D (U-Plane)

eNB

Control Path (C-Plane)Data Path

Device to Device (D2D) Communications

D2D Discovery: Posteriori discovery

D2D Discovery●●●

●

Devices can discover the presence of other devices in their vicinity Proximity discovery is a natural trigger for direct communicationProximity discovery can be used as a standalone service and not trigger communication (social networking)General requirements:o

o

o

Fast discoveryLow energy consumptionMinimize additional interference to the WAN and resource degradation

D2D Discovery: Methods● D2D provides 2 methods of discovery:

● Network discovery (Radio)o A device is able to discover and be discovered by other devices in

radio proximity● User assisted discovery (Application Layer)

o A user of a service or social networking application is able to discover and be discovered by other users of the same service or social networking application

D2D Discovery: Node/Peer discovery

●●

●

● Before two devices can directly communicate with one another, they must first discover that they are near each otherTwo peer devices need to meet in space, time and frequencyNo coordinated discovery: Peer discovery is a randomized procedure, in which a device sends signals without any knowledge about the location of the intended peer (energy consuming)Coordinated discovery: The network uses its knowledge of approximate device locations to recognize devices which could benefit from D2D communications. When a D2D pair has been found, the network coordinates the time and frequency allocation for sending/scanning for beacons

Overlay and Underlay D2D

Higher spectrum efficiency by spatial reuseNeed to cope with interference

15

Dedicated resources for D2DReduce the concern about interferenceNeed explicit resource allocation

D2D

Cellular

Underlay

D2D

Cellular

Overlay

Cellular

● Communication occurs under licensed spectrum: Cellular spectrum is used for both cellular link and D2D

● High control over cellular (licensed) spectrum● Underlay:

o Cellular and D2D communication share the same radio resources● Overlay:

o Cellular and D2D are given dedicated cellular resources (a cellular resource is subtracted from cellular users)

● Underlay is more popular than overlay: probably due to its hight spectral efficiency

D2D communication Inband: Overview

● Pros:- Underlay D2D increase the spectral efficiency of cellular spectrum Any cellular device is capable of using inband

- QoS is easy because the cellular spectrum can be fully managed by theeNB,

- Transmission distance ~ 1km. - Data rate ~ 1Gbps

D2D communication Inband: Pros and cons

● Conso

oCellular resources might be wasted in overlayInterference mgmt among D2D and cellular transmission is very challenging/complex

●●●●

Communication occurs under unlicensed spectrumAims to eliminate the interference issue between D2D and cellular linksRequires an extra interface, usually Wi-Fi direct, ZigBee or Bluetooth Classified in:o Controlled

♣ The control of the second interface is under the cellular network● Similar to Android NFC / Androidbeam

o Autonomous♣ D2D controlled by the users: second interface is not under cellular control

● Transmission distance and data transfer rate is extremely lower than Inband

D2D communication Outband: Overview

● Pros:o

oNo interference with cellular communication (unlicensed spectrum) Users can have simultaneous cellular and D2D transmission

● Conso

o

o

o

Cellular devices requires two wireless interfaces (e.g. LTE and WiFi) Power consumption of the extra interface (WiFi)Lower transmission distance Lower transmission data rate

D2D communication Outband: Pros and cons

D2D Interference ManagementPossible solutions

Resource allocation (OFDMA)Throughput maximizationRevenue maximization Energy consumptionIncentive

MIMO techniques, such as interference alignment

Classification based on Frequency of use In-band - Network assistedOut-band - Independent

Classification based on ServicesEmergency services (both in/out band)Commercial services (in-band only)

Emergency Services Commercial ServicesD2D

eNB

Control PathData Path

D2D

eNB

Control PathData Path

D2D Communication - Classification

TDD Frame structure

Technology behind D2D CommunicationDiscovery and classifications

Discovery typesProactive – Discovery signal is per group of UEs or all UEsReactive – Discovery signal is per UE

eNB Classifies D2D and Cellular pairsBased on - location, distance, power control, interference, etc.

Restructuring of the Scheduling procedures Scheduling of cellular and D2D transmissions

Overlapping - non-interfering same RB schedulingNon-overlapping – unused cellular RBs used for D2D

D2D frame usageIn TDD – UL sub-frame (U) will be usedIn FDD – UL spectrum will be used

RBs can be re-used through scheduling

Challenges in D2D CommunicationsCommunication Challenges

Location of the devices Ensure accuracy

Signaling techniques need to be amendedSignaling overhead to be evaluated

New Modulation Schemes can be proposedCellular: SC-FDMA Tx (UE-eNB) and OFDMA Rx (eNB-UE) D2D: SC-FDMA receiver in UE (UE-UE)

Interference ManagementTo ensure interference below threshold in case of overlapping D2D

Power control modelSelect the transmit power depending on distance/channel characteristics

Channel modelShort distance (indoor/outdoor) channel model can be explored

D2D traffic characterizationWhat percentage of the users are D2D?

Why LTE D2D Communication ?LTE-D2D

Strong Resource Management

Tighter spectrum reuse

Offloading can be achieved

Better Performance

Higher data rate, low end-to-end

delay

Energy Efficient

Reliability and Scalability

Operator initiated Services

Security can be guaranteed

Regulatory and Standardization

Under 3GPP and TSD

Standardization attempts under 3GPP Rel 12/13 (ProSe) - 3GPP TR 21.905 / TR 22.803 / TR 36.814/ TR 36.843 Discovery for ProSe

UEs at proximity should identify each other using E-UTRA/EPC

ProSe D2D communication Communication between two UEs in proximity Path can be established directly or through eNB

UsageCommercial /SocialPublic Safety (with and without coverage)Network Offloading

UE -1

ProSeAPP LTE - Uu

E - UTRAN

UE-2

ProSeAPP

EPC (MME,

S/PGW)

S 1

ProSeAPP Server

SGi

ProSe Function

PC 4 PC 2

PC 5 LTE - Uu

PC 3

PC 1

PC 6

HSS/SLP

Source - 3GPP-23.703-V12.0.0

ProSe System Architecture

D2D Communication @ 3GPP

HSS/SLP

4

PC

EPC

(MME, S/PGW)

6

PC

1

PC

3

PC

Uu

-

LTE

5

PC

2

PC

ProSe Function

SGi

Server

ProSeAPP

1

S

ProSeAPP

UE-2

UTRAN

-

E

Uu

-

LTE

ProSeAPP

UE -1

D2D Use CasesUsecase – 1

M2M communication using D2D underlaying LTEeNB classifies, schedules the communication

Usecase – 2 M2M communication using D2D offloading

Offloader can relay data

● Two categories:o

oSimple D2D: sender and receiver exchange data with each other Relay: D2D user forward data from and to other users

●●

Use cases examples: Local Data Service

♣

♣

♣

♣

♣

♣

Information sharing (bittorrent) Mobile multiplayer gaming

Mobile advertising (proximity services)Streaming services (IPTV, google chromecast, apple airplay) Social (Tinder, Waze, Facebook)

Community services

D2D use cases

● V2V - Vehicle to Vehicle communication:o Collision avoidance system requires a very low latency for example to

coordinate braking between vehicleso V2V can provide not only information about the nearest car in front,

but also from other cars within the communication range, including traffic (waze ?)

● Group handover of multiple users (for example in a Bus)o By using D2D the devices in a group inform each other about the

handover and its parameters with minimal signaling from the network

D2D use cases

● Multiuser cooperative communication (MUCC)o

oBenefited user (BU) is in an area with poor cellular signalAnother user is in an area with good cellular signal. This user may help BU to improve its signal and act as a supporting user (SU)

D2D use cases

● D2D communications with network coding

- Users requesting the same content can form cooperative clusters to achieve higher energy efficiency

- eNB transmits the content to the cluster heads- Cluster heads multicasts the contents to the other devices within the cluster

through D2D links Eg: world cup games - IPTV:

o Multicast of linear channels, Pay-Per-View, VideoRecording

D2D use cases

● Public safety (police, fire and ambulance services)o Many of these organisations uses relatively old technology such as

TETRA system developed in the 90’s with limited capabilityo US government has expressed desire to move to LTE for public safetyo Crucial requirement for these users is the ability to communicate with

each other outside of a mobile network (walkie talkie), which is not supported by LTE, but is one of LTE D2D objectives

D2D use cases

Direct M2M under LTEDirect M2M for close proximity devices

Communicate directly whenever close to receiver (UE/eNB/AP)eNB takes care of Interference and control managementClassification, scheduling, etc. through APPs

M2M offloading for bad-channel devicesRemote sensors, non-LOS connectionsForeign and unpredictable channel conditionsOffload message packet to a nearby offloaderImproved spectral efficiency and system utilization

ExamplesOffloading of images from cam to mobileDirect songs/images transfer from smartphone to

car/home AP

Evaluation of D2D Communications (1/3)Network assisted D2D is considered

Carrier frequency – 2 GHzeNB needs to identify the D2D and cellular pairs

3GPP’s D2DSS signaling for discoveryTwo types of communications will exist

Existing cellular communications and D2DShould not interfere in case of overlapping communication

Broad AssumptionsD2D does not use the full duplex on a given carrierMobility – 3km/hrFull synchronization between UEs and UE to eNB is possibleUnicast communication only

Evaluation of D2D Communications (2/3)Simulations

30% average D2D users consideredStatic users only

Discovery and classificationAssumed 3GPP specifications for discoveryProximity based classification by eNB - proactive

Optimal D2D scheduling under LTE Two phase schedulingModelled as a Binary Integer ProgramSolved using Matlab

Power control Simultaneous transmission : non-interfering

QoS ImprovementReduced delayEnergy efficientImproved spectral efficiency

Network and per-user spectral efficient improved15% at-least

Simulation topology: Cellular vs. D2D

UE1

UE2

UE3eNB

UE1

UE2

UE3eNB

Evaluation of D2D Communications (3/3)Emulations

Through test-bed level implementationWiFi AP as LTE eNB, smartphones as UEs

Discovery based on signal strength and locationService classification – D2D/Cellular

Depending on location, distance, interference, etc.Power control mechanism for smartphones

eNB computes required Tx power for small D2D distanceeNB notifies UE the reduced Tx power, modulation, timing, etc.

TDD scheduling scheme implementedD2D & cellular transmissions on same channelTime synchronization is assumed

APP based deploymentJAVA API for eNB

Desktop with Ubuntu – 14.04 as eNBLivetek WiFi adapter

Android APP for Tx, Rx (UEs)Lenovo Nexus 5, Android KitKat 4.4.2

Control Flow Diagram for D2D

Test-bed Topology

D2D

eNB

Control PathData PathOffloading Path

D2DD2D

D2D Offloading If the load at eNB is high or if the channel between the UE - eNB is poor

Offloading via another UE can be plannedMultiple UEs may be involved Effective data rate/spectral efficiency can be improvedEnergy saving can be achievedBoth licensed and un-licensed spectrums can be used

Challenges in D2D OffloadingTraffic characterization

Distorted user discoverySynchronization between UEs

Network assisted vs. independentInterference management and SchedulingEnergy consumption due to sensing and location updates

D2D Offloading EvaluationsSimulations

Matlab based offloading scheduling under LTE Static users, 30% are distorted (poor signal)Cell radius: 300 mt,D2D range: 5-30 mtsFixed/adaptive modulation scheme

Channel modellingChannel between UE-eNB and UE-UEShort term, long term fading is considered

SchedulingRound robin scheduling D2D transmission scheduled prior to relay

QoS ImprovementGuaranteed delivery for distorted users

Low delay due to reduced failure rateImproved spectral efficiency

User and system throughput improved : 30-40% Better system utilization

D2D Offloading - DiscussionsPractical Deployment Scenario

Single operator caseBilling is the key issueTraffic characteristics

Data usage pattern of UEs Signaling for distorted users – eNB assited/Distributed

Multiple operators caseFurther research required

StandardizationMobility modeling & dynamic classification

Location of UEs – discovery and classificationModeling the mobile channel

Secure D2D communicationControl signaling, authentication, connection timing, etc.

Power-control at UEEquipment manufacturers should be involved

● Although basic requirements are set, details are being still studied/developed

● Big impact of the new technologies proposed:o D2D discovery

♣

♣

Good: Might be a key tool for social networking and other internet appsBad: Privacy concerns, device battery consumption

o D2D communication:♣

♣

Good: Offloading traffic, High data rate speeds Bad: Interference / deterioration of existing services

Conclusion

Conclusion D2D provides one more mechanism for network offloading Is now on the way towards standardization through 3GPP

Rel 12 ProSe Discovery, ProSe Communication One-to-Many ProSe UE-to-NW relay (with no RAN impact), ECP support for WLAN

Rel 13 Communication: One-to-One communication; direct and via eNB, Service continuity Discovery: Interaction with 3rd party apps & UE terminal apps

LTE-D2D is being positioned for emergency services in the US Is a new tool for social networking Many issues are still being unresolved and thus a fertile ground for research

Mobilné komunikácie�Lecture 3: D2D communication for 5GOutlineCan we Match to the Growth? Preliminaries - What is device cooperation?Preliminaries - Device cooperation modesD2D CommunicationD2D vs Ad-hocD2D vs Ad-hocD2D vs. M2M and Ad-hoc NetworksDevice to Device (D2D) CommunicationsD2D Discovery: Posteriori discoveryD2D DiscoveryD2D Discovery: MethodsD2D Discovery: Node/Peer discoveryOverlay and Underlay D2DD2D communication Inband: OverviewD2D communication Inband: Pros and consD2D communication Outband: OverviewD2D communication Outband: Pros and consD2D Interference ManagementD2D Communication - Classification�Technology behind D2D CommunicationChallenges in D2D CommunicationsWhy LTE D2D Communication ?D2D Communication @ 3GPPD2D Use CasesD2D use casesD2D use casesD2D use casesD2D use casesD2D use casesDirect M2M under LTEEvaluation of D2D Communications (1/3)Evaluation of D2D Communications (2/3)Evaluation of D2D Communications (3/3)D2D Offloading D2D Offloading EvaluationsD2D Offloading - DiscussionsConclusionConclusionSlide Number 41