1. The Role of D2D Communications in Public Safety: A Networking Perspective Dr. Leonardo Goratti (Supported by Dr. Tinku Rasheed)

2. Outline Few Basic Facts Current Status for Public Safety
D2D Communications
Proposed D2D Protocol
Analysis
Results
Conclusions

3. 6.8 billion smartphone subscriptions by Q1 2014
Few basic Facts – 1
6.8 billion smartphone subscriptions by Q1 2014
Source: Ericsson Mobility Report, June 2014

4. Few Basic Facts – 2 - Traffic Volume Use cases Connected Devices &
Avalanche of
Traffic Volume
Large diversity of
Use cases
&
Requirements
Massive growth in
Connected Devices
Further expansion of mobile broadband
Additional traffic due to communicating machines
“Communicating machines”
Device-to-Device Communications
Car-to-Car Comm.
New requirements and characteristics due to communicating machines
“1000x in ten years”
“50 billion devices in 2020”
Source: A. Osseiran, “Toward a 5G Mobile & Wireless System Concept” FIA Athens March 2014

5. Few basic facts – 3 1G 2G 3G 4G 5G 40 kbit/s per channel 2.4 kbit/s
300 Mbit/s

6. What is the Situation for the Public Safety Community?

7. 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 users
Crisis scenarios
Special events
TETRA, TETRAPOL, P25

8. 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 technology
Low Data Rate
TDMA-based
Excellent for Group calls (one-to-many), Direct calls (one-to-one), Message dispatching
DMO of TETRA is essentially D2D
Major drawback: PPDR organization do not exploit cutting edge technologies!

9. Current Status for Public Safety – 3

10. 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
* 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

11. Current Status for Public Safety – 5
Need to Move to Mobile Broadband
Migration

12. D2D Communications

13. 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

14. 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

15. 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?

16. D2D Communications – Use Cases
Source: Lei Lei et al. “Operator Controlled Device-to-Device Communications in LTE-Advanced Networks” IEEE Wireless Communications, June 2012.

17. D2D Communications – FP7 ABSOLUTE (www.absolute-project.eu)
D2D scenarios 1
D2D scenarios 3
D2D scenarios 2

18. D2D Communications – Public Safety
D2D communications for PPDR organizations
Range extension
Relieve lack of resources or network failures
Guarantee voice services
Group calls (one-to-many)
Direct calls (one-to-one)
Fast call setup time: few milliseconds with LTE-A
Message dispatching
Many new ones
High-definition video,
Social networking, location augmentation, MTC, location-based services, and fast file transfer
D2D communications exploit the physical proximity of professional user equipments

19. D2D Communications – Functions
Discovery of peers
Devices synchronization
Protocols for establishing direct links
Resources allocation
Different levels of network involvement
Network controlled
Loosely network controlled
No network controlled: ad-hoc fashion

20. D2D Communications – Peers Discovery
Source: G. Fodor, et al. “Design Aspects of Network Assisted Device-to-Device Communications,” IEEE Communications Magazine, March 2012.

21. Proposed D2D protocol

22. Proposed D2D Protocol First pillar Second pillar Third pillar
Cellular uplink resources for D2D
UEs can Tx/Rx in uplink
Reduce harmful interference in downlink
Second pillar
Reuse existing PUCCH regions of PRACH allocations
New one could be defined (reserved PRACH, R-PRACH)
Uplink structure known to the UEs
Third pillar
Allow some modifications to have new PRACHs for data reservation
PUSCH for data exchange in D2D fashion

23. 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

24. 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 recovered
If UEs can rely on “two different receivers” they can keep monitoring the downlink frequency of the eNB
If 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- UE
Autonomous Network formation!

25. Proposed D2D Protocol – UEs in Isolation
Structure of the proposed D2D framework

26. Proposed D2D Protocol – UEs in Isolation
D2D network association
Four-way handshake as in standard LTE
UEs select a preamble in contention mode collisions
The b-UE replies over the PUCCH (no collisions)
UEs which have assigned a network identifier could reuse that
To 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

27. 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

28. Analysis

29. 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

30. 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

31. Analysis – 3 A Poisson PP (PPP) is a special case of great importance
PPP is simple,
PPP is stationary and isotropic
Points in space are independently distributed
Number of points in independent sets are also independent

32. 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

33. 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

34. 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

35. 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=θr0α/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.

36. Results – Connectivity Analysis
The connectivity probability in D2D mode Pc is computed by removing the conditioning on the number of nodes
- α=2.1 -
-α=4 -

37. Results – Secure Connectivity
D-beacons broadcasting
b-UE
D-beacon
1011
r-UE n
D-beacon
1011
Association request
D-beacon
1011
keyring
0001
Association request
r-UE 1
D-beacon
1011 X
keyring
1001
r-UE 3
r-UE 2
keyring
1100
keyring
0100
August 27, 2014 37

38. 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 interference
D2D 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

39. QUESTIONS?