lte direct overview -...

MAY CONTAIN U.S. AND INTERNATIONAL EXPORT CONTROLLED INFORMATION This technical data may be subject to U.S. and international export, re-export, or transfer (“export”) laws. Diversion contrary to U.S. and international law is strictly prohibited. Copyright © 2012 QUALCOMM Incorporated. All rights reserved.

LTE Direct Overview

Sajith Balraj Qualcomm Research

Copyright © 2012 QUALCOMM Incorporated. All rights reserved.

Exploding Adoption of Mobile App Universe

Source: Internet Trends Kleiner Perkins Caufield & Byers


The Rising Need For Ambient Awareness Intersecting market forces creating urgent industry appetite

am·bi·ent a·ware·ness [am-bee-uhnt uh-wair-nis] noun

the state or condition of one’s mobile app continuously and passively monitoring for relevant value in one’s proximity.


Obstacles To Scale

Despite opportunity, still no mainstream consumer deployment

• GPS and network calls place onerous burden on ambient awareness

• Power drain #1 reason consumers unsubscribe from PBS

Battery

• Continuous location tracking entails high consumer privacy cost

• Stubborn majority cite privacy costs as higher than perceived benefits

Privacy

• Signal load and server processing hard to handle at high density

• May present ceiling to scale for most applications

High Density


LTE Direct – A New Wireless Sense Efficient, Proximate, Device-to-Device Communication Technology

Continuous Awareness of Device Services

LTE Direct

Low-overhead discovery through synchronous operation Autonomous, “Always

ON” discovery of what’s around

Power efficient, broadcast based design

Relevant Discovery Across 1000s of services

No location tracking Potential app controls

over ‘cloud sharing

Privacy Sensitive

High spectral efficiency and reuse

High Density of Direct Data Connections

Distributed Interference management

Range of several 100s of meters*

* For typical outdoor scenario with maximum path loss of 135dB


Devices Advertise their Services

I have tickets to sell for today’s game

Abe’s Books: Book Signing in the next HOUR!

Bob @ StarBucks on 4th Ave

Sushi Palace- Today’s Specials

Joe: Looking for new Extinct Warriors game

…

…

… …

… … … …

…

…

…

… … …

… … …

… …

Friend Finder

Ticket Finder


All Services Identified; Relevance Determined






…

…

… …

… … … …

…

…

…

… … …

… … …

… …

Friend Finder

Ticket Finder

Seller: 4:00 pm game seat 45B

Sally @ Sea Cafe


Communicating with the Desired Service






…

…

… …

… … … …

…

…

…

… … …

… … …

… …

Ticket Finder

Seller: 4:00 pm game seat 45B


What is LTE-Direct?

• Licensed spectrum framework • Synchronous system • Device transmits at nominal mobile power

levels • Proposed as a Rel 12 3GPP feature

• Study Item approved in 3GPP SA1 in Sept 11 • Proposing RAN Study Item for Rel 12

• LTE-Direct proposal includes two sub-features • Device to Device Peer Discovery (PD) • Device to Device Data Communications (Comms)

LTE-D as an integrated feature of the LTE Ecosystem


Expressions enable efficient discovery

• An Expression(s) is used by peers in discovery of proximate services, apps and context.

• Expression(s) are also used by proximate peers to establish direct communications.


Expression Basics

• Expressions at the application/service layer are referred to as “Expression Names”

• Names are mapped to 128 bits at the physical layer and referred to as “Expression Code”

• Expressions are classified as Public or Private Expressions based on the type of mapping


Highly Efficient Discovery Design

• LTE Direct discovery resources configured by the RAN • Resources time-synced within the

geography • UEs transmit and receive Expressions

within the discovery resources

• Resource Assignment

• FDD Uplink or TDD resources are assigned for Discovery.

• Resource semi-statically allocated (typically <1% )

• eNB(s) assign part of discovery resources via SIB to authorized LTE D devices

UE 2

UE 1

WAN LTE D

Discovery LTE D

Discovery

qualitative illustration; all UEs on the same carrier frequency

Band displayed is Uplink of FDD or TDD

UE 3

2. Resource (SIB)

3.Discovery


• 10 MHz FDD system: 44 PUSCH RBs used for discovery

• Sub-frame allocation are variable and controlled by eNB – Example: 64 sub-frames every discovery period of 20sec – Number of direct discovery resources (DRIDs): 44*64 = 2816

Discovery Design: An Example

20 sec

Uplink

D2D Peer Discovery

D2D Peer Discovery WAN


Comparison Study

• Schemes are compared based on – Power consumption of UEs – OTA system resources used for comparable discovery – Schemes are normalized with respect to discovery radius and latency

Parameters Default Values

Range

Number of People* 2000 0-2000/cell

Latency 20 sec

Cell radius 1000m

Discovery radius 500m

Mobility 10 km/hr

Number of RBs available for discovery per sub-frame

44

Fraction of mobile People* 20% 1%-100%

Probability of interest* * 0.15 0.01-1

* we study sensitivity with respect to these parameters ** probability that UEs are interested in other UEs


LTE Direct Discovery Significantly Outperforms OTT Discovery

Direct discovery performs better less than 7% reduction in stand-by time due to

direct discovery, compared to up to 150% reduction in stand-by time due to over the top discovery

Direct discovery uses less resources Broadcast vs. Multiple Unicast messages 12x more resources used at 2000 UEs

0 200 400 600 800 1000 1200 1400 1600 1800 20000

50

100

150

Number of UEs per cell

Perc

enta

ge in

crea

se

Power consumption increase wrt legacy

Over the top discoveryDirect discovery

0 200 400 600 800 1000 1200 1400 1600 1800 200010

0

101

102

103

Number of UEs per cellRB

s pe

r sec

ond

Resource usage comparison

Over the top discoveryDirect discovery


WFD Message Based Discovery vs LTE Direct Broadcast Discovery

Wi-Fi Direct Discovery • Two step asynchronous message

based discovery – WFD Device exchanges device discovery

request response messages followed by service discovery with every WFD in range

LTE Direct Discovery • Devices broadcast their services at physical

layer using 128 bits • Devices wakeup periodically synchronously to

discover all devices within range


LTE Direct Enables Discovery of ~ 16X More Devices

LTE Direct WiFi Direct Profile 1

WiFi Direct Profile 2

Number of devices discovered 7200 369 369

Total Active Duration (s) 0.64 119 82

• Message-based discovery limits Wi-Fi Direct discovery capacity • Low duty cycle discovery in LTE Direct leads to significant power improvement

vs Wi-Fi Direct

– Assumptions • Times Square (outdoor dense deployment scenario) • Ped A channel model • ITU-1411 NLOS model; Wi-Fi Direct – 10dB shadowing and 20dB wall penetration loss • BW Assumptions: LTE Direct 10 MHz, Wi-Fi Direct – 20 MHz @ 5 GHz • 23dBm tx power, -5dB antenna gain, 7dB noise figure • WiFi Direct Profile 1 – 100 % Service Discovery • WiFi Direct Profile 2 – 10 % Service Discovery


LTE Direct Communication

LTE Direct Communication follows from discovery as a LTE system feature

Network authorizes devices to

communicate directly – For system capacity optimization

Needed for Public Safety use case

eNBs


LTE Direct Communication: Network Assisted Connection Setup

Direct connection setup via network

– Allow an operator to authorize and control the direct connection setup between UEs.

– Allow an operator to determine the user traffic routing between Direct and NW paths.

Operator Network

1. Direct discovery

2. Direct connection context setup via

Network

MME MME

3. Direct Alert & Direct radio bearer configuration

4. Direct communication

eNB eNB


Spectrally Efficient D2D Communications • Distributed link scheduling maximizes resource utilization • Distributed link scheduling protocol enables maximal spatial

reuse depending on the interference environment – Orthogonalize in time if interference is too high – Otherwise reuse traffic resources for maximum spectral efficiency

Resources Reused

Resources Orthogonalized

http://www.istockphoto.com/stock-illustration-11638078-mobil-phone.php







Low Priority Connections Yield To High Priority Connections in Proximity

• Transmitter yielding

– A transmitter will not transmit if this action will result in deteriorating (SIR) higher priority scheduled links

• Receiver yielding – The receiver to which a transmitter is trying to communicate with will

only accept the transmission over the link if its link has minimum quality (minimum SIR)

High Priority Traffic Channel

Low Priority Traffic Channel

A

C

B

D

Transmitter may yield to A-B

Receiver may yield due to A-B






Peer to Peer Traffic Optimization

1

10

100

1000

10000

< 50m < 100m < 200m

Mbp

s

Capacity* per Km2

(10 MHz)

Link distance uniform up to x meters

1,260

374

94

*Preliminary results 900MHz, ITU-R 1411 LOS model. Assumes fully loaded system.

Lots of Spatial Re-use with Distributed Scheduling

















MAY CONTAIN U.S. AND INTERNATIONAL EXPORT CONTROLLED INFORMATION This technical data may be subject to U.S. and international export, re-export, or transfer (“export”) laws. Diversion contrary to U.S. and international law is strictly prohibited. Copyright © 2012 QUALCOMM Incorporated. All rights reserved.

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lte direct overview -...

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