The Role of D2D Communications in Public Safety: A Networking Perspective

Dr. Leonardo Goratti(Supported by Dr. Tinku Rasheed)

Outline•Few Basic Facts

•Current Status for Public Safety

•D2D Communications

•Proposed D2D Protocol

•Analysis

•Results

•Conclusions

Few basic Facts – 1

6.8 billion smartphone subscriptions by Q1

2014

Source: Ericsson Mobility Report, June 2014

Few Basic Facts – 2 -

Large diversity ofUse cases

& Requirements

Device-to-Device Communications

Car-to-Car Comm.

New requirements and characteristics due to

communicating machines

Avalanche of

Traffic Volume

Further expansion of mobile broadband

Additional traffic due to communicating machines

“1000x in ten years”

Massive growth in

Connected Devices

“Communicating machines”

“50 billion devices in 2020”

Source: A. Osseiran, “Toward a 5G Mobile & Wireless System Concept” FIA Athens March 2014

Few basic facts – 3

2.4 kbit/s 40 kbit/s per channel

384 kbit/s 300 Mbit/s

1G 2G 3G 4G 5G

What is the Situation for the Public Safety

Community?

Current Status for Public Safety – 1

•Public protection and Disaster Relief Organizations (PPDR) intervene in the aftermath of a crisis and include police forces, fire fighters, medical aid (e.g. 911 in the USA or 112 in Europe).

•Professional Mobile radio (PMR) networks provide communications for PPDR usersCrisis scenariosSpecial events

•TETRA, TETRAPOL, P25

Current Status for Public Safety– 2• PPDR organizations are doing a slow transition to TETRA in Europe (still rely on analogue communications in some cases)

•TETRA is similar to GSM technologyLow Data RateTDMA-basedExcellent for Group calls (one-to-many), Direct calls (one-to-one), Message dispatchingDMO of TETRA is essentially D2D

•Major drawback: PPDR organization do not exploit cutting edge technologies!

Current Status for Public Safety – 3

Current Status for Public Safety – 4

■ 　 Carriers restricted voice traffic by as much as 70 to 95 percent.*

■ 　 Packet traffic, however, was either not restricted or restricted at a lower rate (0 to 30 percent) than voice traffic.

■ 　 Carriers restricted phone traffic by as much as 80 to 90 percent.*

Max. outgoing traffic restrictions

Max. outgoing traffic restrictions

* There was 4 to 9 times the normal volume of traffic (NTT East.) * There was 50 to 60 times the normal volume of traffic (DoCoMo).

Fixed-line Communications Mobile Communications

voice packet voice packet voice packet

0%

20%

40%

60%

80%

100%

90%

30%

95%

0%

70%

0%

Current Status for Public Safety – 5

Migration

Need to Move to Mobile Broadband

D2D Communications

D2D Communications – General View •Device-to-Device (D2D) is a recent terminology adopted by 3GPP meaning direct communications between UEs in 4G technology (licensed bands)

•Emerging D2D communications are expected to share the same resources with cellular system

•D2D is supposed to be an access or link-layer technology proposed also for M2M

•D2D is not the first historical attempt to enable devices with direct communications

•Bluetooth, UWB, mmWave Communications, and WiFi Direct are some of these examples

D2D Communications – 3GPP

•3GPP studies D2D as part of the wider concept of Proximity Services (ProSe)

•D2D communication is defined as the communication between two UEs in physical proximity using LTE air interface to set up a direct link without routing via base station and possibly core network.

•In Rel. 12 3GPP considered ProSe D2D and isolation conditions for public safety

•More is expected in 3GPP Rel. 13

D2D Communications – General View

•Carriers are not completely in favor of D2D: interference problems and billing

•The use of D2D has to be distinguished for commercial and non-commercial domains

•D2D can be established with and without supervision of an evolved Node B (eNB)

•Several challenges to be solved–When to start D2D?– What resources for D2D?–Which protocol for D2D?

D2D Communications – Use Cases

Source: Lei Lei et al. “Operator Controlled Device-to-Device Communications in LTE-Advanced Networks” IEEE Wireless Communications, June 2012.

D2D Communications – FP7 ABSOLUTE (www.absolute-project.eu)

D2D scenarios 2

D2D scenarios 1

D2D scenarios 3

D2D Communications – Public Safety

•D2D communications for PPDR organizationsRange extensionRelieve lack of resources or network failures

•Guarantee voice servicesGroup calls (one-to-many)Direct calls (one-to-one)Fast call setup time: few milliseconds with LTE-AMessage dispatching

•Many new onesHigh-definition video, Social networking, location augmentation, MTC, location-based services, and fast file transfer

D2D communications exploit the physical proximity of

professional user equipments

D2D Communications – Functions

•Discovery of peers•Devices synchronization•Protocols for establishing direct links•Resources allocation•Different levels of network involvementNetwork controlledLoosely network controlledNo network controlled: ad-hoc fashion

D2D Communications – Peers Discovery

Source: G. Fodor, et al. “Design Aspects of Network Assisted Device-to-Device Communications,” IEEE Communications Magazine, March 2012.

Proposed D2D protocol

Proposed D2D Protocol•First pillar

Cellular uplink resources for D2D UEs can Tx/Rx in uplinkReduce harmful interference in downlink

•Second pillarReuse existing PUCCH regions of PRACH allocationsNew one could be defined (reserved PRACH, R-PRACH)Uplink structure known to the UEs

•Third pillarAllow some modifications to have new PRACHs for data reservationPUSCH for data exchange in D2D fashion

Proposed D2D Protocol – UEs in Isolation

•Time of Interruption (ToI): time the A-eNB is unavailable

•One UE broadcasts direct beacons (D-Beacons)•Beaconing device (b-UE): the UE of the team leader•D-Beacons for peer discovery and local synch•PUCCH: D-Beacons and association responses•PRACH: association requests to the b-UE•Reserved PRACH: D2D links reservations (Req. + Resp.)

•PUSCH: used for D2D data exchange

Proposed D2D Protocol – UEs in Isolation

•D-Beacon interval: multiples of LTE radio frame (10 ms)•The D2D network is vanished as soon as connectivity with the eNB is recoveredIf UEs can rely on “two different receivers” they can keep monitoring the downlink frequency of the eNBIf only one receiving chain: every N D-beacon intervals UEs should skip D2D to listen to the downlink

•Role of the b-UE can be rotated among UEs to save energy•D2D links established in P2P with no supervision of the b-UEAutonomous Network formation!

Proposed D2D Protocol – UEs in Isolation

Structure of the proposed D2D framework

t

f

PUCCH (used by the b-UE)

PUCCH

PRACHPRACH

(reserved)

PUSCH

PRACH(reserved)

PRACH

12 subcarriersD-beacon interval

NRB0(UL)

NRB-1(UL)

Proposed D2D Protocol – UEs in Isolation

•D2D network associationFour-way handshake as in standard LTEUEs select a preamble in contention mode collisionsThe b-UE replies over the PUCCH (no collisions)UEs which have assigned a network identifier could reuse thatTo facilitate subsequent network operations single UEs could reuse the selected preamble or Use a unique preamble sequence for the whole D2D network

Used in the analysis

Proposed D2D Protocol – UEs in Network Coverage

D2D protocol as before but prior to eNB authorization and reasoning

4G

Connectivity

Cognitive Process

eNB Supervision

Tx. Parameter

Setting

Location Awareness

Analysis

Analysis – 1 •In D2D communications relying on “Reuse 1” 4G cellular technology Interference is a major problem

•We rely on the theory of Spatial Point Processes•Point Processes are useful to model location of transmitters that follow specific spatial patterns(locations), adding fading and shadowing

•Early attempts to use Point Processes in wireless[1] E. Sousa and J. Silvester, “Optimum Transmission Ranges in a Direct-Sequence Spread-Spectrum Multihop Packet

Radio Network,” IEEE J. on Selected Areas in Communications, vol.. 8. no. 5. June 1900[2] R. Nelson and L. Kleinrock, “The Spatial Capacity of a Slo’tted ALOHA Multihop Packet Radio Network with

Capture,” IEEE Trans. on Commun., vol. COM-32, no. 6, June 1984[3] J. Ilok and D. Hatzinakos, “Analytic Alpha-Stable Noise Modeling in a Poisson Field of Interferers or Scatterers,”

IEEE trans. on Signal Processing, vol. 46, no. 6, June 1998.

•[3] established that a homogeneous Poisson Point Process is equivalent to a Poisson process on the line with intensity πλ

Analysis – 2

•Definition1: A point Process (PP) is a random variable taking values in the space N

•A PP is denoted by Φ, whereas an instantiation of the process is denoted by

, where 1A is the indicator function•In a region AϵRd the number of points of a PP is N(A), or intensity measure

•A PP can be finite (N(A) for any bounded region) and simple (xi≠xj for all i≠j)

D.J. Daley, D. Vere-Jones , An introduction to the theory of point processes, Vol 1 and 2, Springer

x

A xA )(1)(

Analysis – 3

•A Poisson PP (PPP) is a special case of great importancePPP is simple,PPP is stationary and isotropicPoints in space are independently distributedNumber of points in independent sets are also independent

A

k

s sek

AkP

!}in nodes {

Analysis – 4

•Palm distribution theory formalize the concept of a typical point for PPs

•Slivnyak’s Theorem: For a stationary PPP holds that

•Campbell Theorem: For a stationary PPP of intensity λ and a non-negative measurable function f(x)

•Laplace functional: For a stationary PPP of intensity λ and a function f(x) with values in [0,1]

•For Cluster PPs Lλ is similar but more complex•Cluster Processes are important for D2D

}Yproperty has}{Pr{}|property has Pr{ ooY

2

)())((Rx

dxxfxfE

2

))(1(exp)()(Rx

dxxfxfEfL

Analysis – 5

•By Slivnyak’s theorem we can select the reference (typical) receiver placed in any point

•By the stationary and isotropy of PPPs it’s enough to consider the distance y-x rather than specific points

r0 r2

r1

r3

ReferenceUE

x

xtx xylgPyI )(

i

iiti rgsPEsL )exp()( rxy

Results – Connectivity Analysis

•b-UEs and r-UEs scattered according to two homogeneous PPPs with intensity λs=λsu+λsb over a surface of area |A|, for a set |S| of all terminals

•We assume a b-UE transmits beacons with prob. P•We consider Rayleigh fading

iitii

ts

rPg

rPgSINRrP 000

0 PrPr)(

termInterf

iitii

t

termNoise

ts rPg

P

r

P

rP

.

0

0

0

0 expexp

WN0

Results – Connectivity Analysis•Results obtained so far for the proposed D2D protocol addressed the problem of connectivity

•Aggregate interference at a reference D2D receiver and after a few tedious computations

•The success probability can be found writing the Laplace functional with f(x)=exp(-sPtgr-α) in correspondence of s=θr0

α/Pt0

•Aggregate interference is modeled with the family of heavy tailed Stable distributions Source: M. Z. Win, et al. “A Mathematical Theory of Network Interference and Its Applications,” Proc. IEEE,

vol. 97, no. 2, February, 2009.

/2

0/2

/21

00 /cos

/21expexp)(

t

Iisb

ts P

PrEC

P

rrp

Results – Connectivity Analysis

•The connectivity probability in D2D mode Pc is computed by removing the conditioning on the number of nodes

Mppc

seMp 11exp1

sbsu

su

KNM

MAN

MAK

sb

su

)1(

- α=2.1 --α=4 -

Results – Secure ConnectivityD-beacons broadcasting

b-UE

r-UE 1

D-beacon

1011

r-UE 2

D-b

eaco

n

1011

August 27, 2014 37

r-UE 3

r-UE n

D-beacon1011

D-beacon

1011

keyring

1001

keyring

0100

keyring

1100

keyring

0001

XAssociation request

Association request

Conclusions•D2D is an emerging wireless technology for direct communications among

devices •D2D is expected to be a key technology to improve system capacity and

user experience in various scenarios in Beyond 4G/5G technologies•Public safety is a key driving force for LTE D2D in 3GPP Rel-13

There are several technical issues to be addressed including how to coexist with cellular users and how to deal with interferenceD2D ProSe discovery and communications require fundamental adaptation to the LTE physical layer (PHY) and radio. It will take a few years to complete the major changes and another additional time frame before products are available in the market.

•To leverage all the benefits arising from the adoption of D2D communications a cognitive mechanism has to be established to efficiently share the spectrum with cellular communications

QUESTIONS?