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?