Device-to-Device (D2D) Communication

Networks Lab, TCS Research

TSDSI SG1 F2F meeting, IEEE Bangalore, July 2015

Outline

Introduction

Evolution towards 5G

Introduction – Why D2D Communication

D2D Communication

D2D Offloading

D2D Research at TCS

Standardization of D2D Communication

Conclusion

Growth of Networks

Challenges for future wireless communication -

Massive growth in connected devices Smart phones, laptops, sensor devices, etc

Massive growth on network traffic Almost 1000+ times or more

61% CAGR expected

Wide range of applications and their requirements Social media, video on demand, live TVs, gaming, IoT, etc

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 = 4-5

Increasing Backhaul Capacity

Nationwide optical fibre backbone

Only 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

D2D Communication

Purpose

To 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

Big Question

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

Regular Communication Model In coverage D2D Communication Model

eNB

Data Path

Control Path (C-Plane)

D2D (U-Plane)

eNB

Control Path (C-Plane)

Data Path

Device to Device (D2D) Communications

D2D vs. M2M and Ad-hoc Networks

Machine to Machine (M2M) Communication

Machine Type Communication – 3GPP TR 22.368

D2D vs. M2M

D2D vs. Ad-hoc Networks

D2D 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 M2M

Describes 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

Classification based on Frequency of use

In-band - Network assisted

Out-band - Independent

Classification based on Services

Emergency services (both in/out band)

Commercial services (in-band only)

Emergency Services Commercial Services

D2D

eNB

Control Path

Data Path

D2D

eNB

Control Path

Data Path

D2D Communication - Classification

TDD Frame structure

Technology behind D2D Communication

Discovery and classifications

Discovery types Proactive – Discovery signal is per group of UEs or all UEs

Reactive – Discovery signal is per UE

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

Restructuring of the Scheduling procedures

Scheduling of cellular and D2D transmissions Overlapping - non-interfering same RB scheduling

Non-overlapping – unused cellular RBs used for D2D

D2D frame usage In TDD – UL sub-frame (U) will be used

In FDD – UL spectrum will be used

RBs can be re-used through scheduling

Challenges in D2D Communications

Communication Challenges

Location of the devices Ensure accuracy

Signaling techniques need to be amended Signaling overhead to be evaluated

New Modulation Schemes can be proposed Cellular: SC-FDMA Tx (UE-eNB) and OFDMA Rx (eNB-UE)

D2D: SC-FDMA receiver in UE (UE-UE)

Interference Management To ensure interference below threshold in case of overlapping D2D

Power control model Select the transmit power depending on distance/channel characteristics

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

D2D traffic characterization

What 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

D2D Communication @ 3GPP

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

Usage

Commercial /Social

Public 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 Use Cases

Usecase – 1

D2D communication underlaying LTE eNB classifies, schedules the communication

Usecase – 2

D2D offloading Offloader can relay data

Evaluation of D2D Communications (1/3)

Network assisted D2D is considered

Carrier frequency – 2 GHz

eNB needs to identify the D2D and cellular pairs 3GPP’s D2DSS signaling for discovery

Two types of communications will exist Existing cellular communications and D2D

Should not interfere in case of overlapping communication

Broad Assumptions

D2D does not use the full duplex on a given carrier

Mobility – 3km/hr

Full synchronization between UEs and UE to eNB is possible

Unicast communication only

Evaluation of D2D Communications (2/3)

Simulations 30% average D2D users considered

Static users only

Discovery and classification Assumed 3GPP specifications for discovery

Proximity based classification by eNB - proactive

Optimal D2D scheduling under LTE Two phase scheduling

Modelled as a Binary Integer Program

Solved using Matlab

Power control Simultaneous transmission : non-interfering

QoS Improvement Reduced delay

Energy efficient

Improved spectral efficiency Network and per-user spectral efficient improved

• 15% at-least

Simulation topology: Cellular vs. D2D

UE1

UE2

UE3 eNB

UE1

UE2

UE3

eNB

Evaluation of D2D Communications (3/3)

Emulations Through test-bed level implementation

WiFi AP as LTE eNB, smartphones as UEs

Discovery based on signal strength and location Service classification – D2D/Cellular

• Depending on location, distance, interference, etc.

Power control mechanism for smartphones eNB computes required Tx power for small D2D distance

eNB notifies UE the reduced Tx power, modulation, timing, etc.

TDD scheduling scheme implemented D2D & cellular transmissions on same channel

Time synchronization is assumed

APP based deployment JAVA API for eNB

Desktop with Ubuntu – 14.04 as eNB

Livetek 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 Path

Data Path

Offloading Path

D2D D2D

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 planned Multiple UEs may be involved

Effective data rate/spectral efficiency can be improved

Energy saving can be achieved

Both licensed and un-licensed spectrums can be used

Challenges in D2D Offloading

Traffic characterization Distorted user discovery

Synchronization between UEs Network assisted vs. independent

Interference management and Scheduling

Energy consumption due to sensing and location updates

D2D Offloading Evaluations

Simulations Matlab based offloading scheduling under LTE

Static users, 30% are distorted (poor signal)

Cell radius: 300 mt,

D2D range: 5-30 mts

Fixed/adaptive modulation scheme

Channel modelling Channel between UE-eNB and UE-UE

Short term, long term fading is considered

Scheduling Round robin scheduling

D2D transmission scheduled prior to relay

QoS Improvement Guaranteed delivery for distorted users

Low delay due to reduced failure rate

Improved spectral efficiency User and system throughput improved : 30-40%

Better system utilization

D2D Offloading - Discussions

Practical Deployment Scenario

Single operator case Billing is the key issue

Traffic characteristics

• Data usage pattern of UEs

• Signaling for distorted users – eNB assited/Distributed

Multiple operators case Further research required

Standardization

Mobility modeling & dynamic classification Location of UEs – discovery and classification

Modeling the mobile channel

Secure D2D communication Control signaling, authentication, connection timing, etc.

Power-control at UE Equipment manufacturers should be involved

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 and standardization

Conclusion

References

Alastair Brydon ,"Opportunities and threats from LTE Device-to-Device (D2D) communication",, Unwired insight - The wireless blog, Feb. 2014

X. Lin, J. G. Andrews, A. Ghosh, and R. Ratasuk, “An overview of 3GPP device-to-device proximity services,” IEEE Communications Magazine, December 2013

X. Wu, S. Tavildar, S. Shakkottai, T. Richardson, J. Li, R. Laroia, and A. Jovicic, “FlashLinQ: A synchronous distributed scheduler for peer-to-peer ad hoc networks,” in IEEE Allerton Conference on Communication, Control, and Computing, 2010, pp. 514–521

K. Doppler, M. Rinne, C. Wijting, C. Ribeiro, and K. Hugl, “Deviceto-device communication as an underlay to LTE-advanced networks,” IEEE Communications Magazine, vol. 47, no. 12, pp. 42–49, 2009

3GPP TR 23.703, “Study on architecture enhancements to support proximity services (ProSe) (Release 12),” v. 12.0.0, February, 2014

3GPP TR 22.803, “Feasibility study for Proximity Services (ProSe) (Release 12),” v. 12.2.0, June, 2013.

References

Thank You