© 2019 Perspecta Labs

Device-to-Device System for Public 

Safety (DDPS) 

NATIONAL INSTITUTE OF STANDARDS AND 

TECHNOLOGY PUBLIC SAFETY INNOVATION 

ACCELERATOR PROGRAM (PSIAP)

Contact: Dr. Richard C. Lau

Chief Scientist & Perspecta Labs Fellow

Tel: (732) 898-8476

Email: clau@perspectalabs.com
2

DISCLAIMER

This presentation was produced by guest speaker(s) 

and presented at the National Institute of Standards 

and Technology’s 2019 Public Safety Broadband 

Stakeholder Meeting. The contents of this 

presentation do not necessarily reflect the views or 

policies of the National Institute of Standards and 

Technology or the U.S. Government.

Posted with permission
Agenda

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DDPS overview

Team

Goals and targeted applications

Achievements

Service continuity scenario

DDPS software development

DDPS software components

Off-network support

UE-to-network relay operation support

DDPS demonstration

Indoor testbed setup

Outdoor testbed setup

Field demo

Conclusion
DDPS overview

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• Perspecta Labs

−Richard Lau (Lead)

−Members: Stephanie Demers, Eric Becks, Heechang Kim

• EURECOM

−Raymond Knopp (Lead)

−Panagiotis Matzakos

−Mohit Vyas

DDPS team
Internet

DDPS scenarios for first responder application

First 

Responder 1 

DDPS goals are to build open source platform for ProSe: 

- Supports on-net, off-net, and partial coverage

- Demo D2D 1:N (group) and 1:1 (direct) private communications 

- Applications: push-to-talk, image transfer, and text message

Legacy LTE

ProSe

Group communication

eNodeB

Off-network

out-of-coverage

area Legacy LTE

eNodeB

On-network 

coverage area

Extended 

coverage

area

Sidelink

ProSe: Discovery à Sidelink data à Relay à group à multiple groups
• Build a complete ProSe protocol stack in software 

− Extend OpenAirInterfaceTM (OAI) implementation to support D2D services on- and off-network based 

on 3GPP Rel-14 specifications

− Help create an ecosystem that can ultimately lead to a small form factor platform

• Create test bed and demonstrate a full ProSe network prototype on SDR platform

• Extend OAI code to solve complex service continuity challenges

Relay UE

Internet

Remote UE

Legacy LTE

Sidelink

eNodeB

MME

HSS

SPGW/

PGW

NAT

EPC

Off-net UEs

Sidelink

• Solve open issues related to resource 

allocation and time synchronization:

− New scheduling algorithms for autonomous 

resource allocation to minimize collision 

probability. 

− Novel multi-antenna-based synchronization 

techniques to achieve significant improvement in 

UE autonomous synchronization

DDPS achievements (1/2)
DDPS achievements (2/2)

• D2D software stack implementation in OAI including sidelink channel implementation with: 

− RRC: SIBs 18 and 19, and SidelinkUEInformation handling

− PDCP: PC5-S and PC5-U traffic for Sidelink

− MAC: SL-DCH, SL-SCH

− PHY: PSDCH, PSSCH, PSCCH, SLSS

• Create a Technology Transfer Package

− Merge DDPS code into the OAI main branch

− OAI user guide for D2D implementation

− Explore synergy with other organization of interest

• Building the code and supporting Off-net sidelink scenarios : 

https://gitlab.eurecom.fr/oai/openairinterface5g/blob/LTE-sidelink/d2d_emulator_setup.txt

• Additional instructions to support On-net sidelink scenarios: 

https://gitlab.eurecom.fr/oai/openairinterface5g/blob/LTE-sidelink/targets/DOCS/D2D-on-net-and-relaysetup-instructions.pdf
Internet

eNodeB

MME

HSS

SPGW/

PGW

NAT

EPC

Service continuity scenario

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Relay UE

Remote UE

Legacy LTE

Sidelink

Step 1: On-net UE attaches 

to the LTE network

Step 2: Remote UE 

synchronize with the 

synchRef Relay UE

Step 3: Relay UE announces 

itself as a Relay and Remote 

UE discovers it

Step 4: Remote UE selects 

Relay UE and establishes a 

secure direct link with it

Step 5: Remote off-network 

UE now has access to the 

internet via the Relay UE 

that forwards its traffic

Step 6: Relay UE moves outside 

of LTE coverage and becomes 

off-network. The two UEs are 

within close proximity and 

remain synchronized

Step 7: The two UEs announce 

their group memberships and 

discover each other groups

Sidelink

Step 8: The two UEs can 

communicate over a common 

group or establish a direct link 

with a group member while offnetwork
DDPS software development

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DDPS software components

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• Service authorization is done via toggle switch on the UE’s GUI for ease of testing/demoing

• Synchronization 

• A SyncRef UE is manually configured as an input command argument for ease of testing/demoing

• The SyncRef UE transmits Sidelink Synchronization Signal (SLSS) and the MasterInformationBlock-SL 

(MIB-SL) message on the frequency used for sidelink discovery

• SLSS and MIB-SL for synchronization in time and frequency have been implemented, as well as the 

SL-BCH (Sidelink Broadcast Channel) and the Physical Sidelink Broadcast Channel (PSBCH)

• Group member discovery announcement and monitoring implemented

• Model A Group Member Direct Discovery for Public Safety Use was implemented

• List of discovered groups and group members are displayed on each UE’s DDPS GUI

Off-network support (1/2)

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Legacy LTE

eNodeB

Off-net UEs

Sidelink
• One

-to-many group communication 

• A discovered group can be selected on the UE’s 

DDPS GUI to start a 1:N communication with the 

members of that group over Sidelink Traffic 

Channel (STCH) 

• One-to-one direct communication

• A discovered group member can be selected on 

the UE’s DDPS GUI and a direct secure link can 

be established with that group member over the 

PC5 control plane

• Once is a secure direct link is established, 

exchange of traffic over STCH is possible

• The direct link can be released when not needed 

anymore

Off-network support (2/2)

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• System information broadcast (SIB)

• eNodeB was extended to broadcast SIB18 (sidelink comm

related resource config info) and SIB19 (sidelink discovery 

related resource configuration info)

• Relay UE discovery announcement and remote UE 

monitoring

• Model A UE-to-Network Relay Discovery procedure was 

implemented

• List of discovered relay UEs are displayed on each remote 

UE’s DDPS GUI

• Simultaneous support of LTE and sidelink in Relay UE

• Two separate USRB B210s are connected to the PC where 

the relay UE resides. First USRP is used for LTE UL/DL and 

sidelink tx. Second USRP is used for the sidelink rx

UE-to-network relay operation support (1/2)

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Relay UE

Internet

Remote UE

Legacy LTE

Sidelink

eNodeB

MME

HSS

SPGW/

PGW

NAT

EPC
• Link setup/release between relay and remote UE

• A discovered relay UE can be selected on the remote UE’s 

DDPS GUI and a direct secure link can be established with 

that relay

• Routing extension to support traffic relaying

• At the relay UE, UL traffic is forwarded from sidelink (oip0) 

to LTE (oip1) interface based on ip table rules and ue_ip.ko

driver extensions. UL traffic is also masked with the oip1 IP 

address of the relay UE as source IP and transferred to the 

core network using the relay existing PDN connection. 

• At the relay UE, DL traffic is received at the oip1 interface of 

the relay UE and recognized as remote UE traffic based on 

the applied NAT routing rule. Then, it is forwarded to the 

sidelink interface (oip0) with the original IP address of the 

remote UE and eventually received at the remote UE.

UE-to-network relay operation support (2/2)

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DDPS demonstration

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• Indoor RF testbed includes 

• eNodeB connected to a USRP and two antennas 

• UE-to-network relay UE 

• Off-network UE that acts as a remote UE 

connected to one USRP and two antennas to 

transmit and receive over the sidelink channel

• On-network UE that acts as relay UE and attaches 

to the eNodeB and serves as the source synchRef

for the remote UE. It has two USRPs and three 

antennas to communicate over LTE UL/DL and 

transmit and receive over sidelink

• One laptop is used for the EPC (HSS, MME, and 

S/PGW), which is wired to the eNodeB. The EPC 

is also connected to a NAT machine

Indoor RF service continuity testbed

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EPC

NAT

Relay 

UE Remote 

UE

eNodeB

• Used to test and demo successfully the service continuity scenario
• Three carts are used for the eNodeB, relay UE, 

and remote UE respectively

• Each cart consists of the following components: • A tub cart, 36” high x 35” wide x 18” deep on 5” 

locking wheels.

• SDR electronics, consisting of a laptop computer, one 

or two B210 SDR transceivers, with optional National 

Instruments Octoclock and/or analog front end 

electronics.

• An (steel) plate for magnetic mount antennas, 

accommodating two antennas (Wilson 311125 

magnetic mount antennas) and a GPS antenna.

• One or more rechargeable Lithium batteries for 

“portable” operation

• Used to field demo off-network D2D operation

Outdoor RF testbed

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Remote UE and eNodeB Schematic

Schematics

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Relay UE Schematic
Outdoor field demo

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• 50 PRBs, 0dBm transmit power, sidelink Band 14 used

• Distance between off-net UEs: 5, 10, 15, and 20 meters

UE1 UE2

Most images sent were received perfectly

At 20 meters distance, one 

image was received distorted
Outdoor field demo

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Measured 915 MHz ISM band occupancy

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Estimated operational distance – ISM interference 

environment

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Conclusion

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• Despite standardization, there is no mature LTE D2D when cellular communication fails

• DDPS is an effort to facilitate the development of an LTE D2D ecosystem based on ProSe

• The key DDPS technologies include building a complete ProSe stack for Mission Critical 

Voice by extending the OAI implementation and solving key related problems

• DDPS testbed demonstrates feasibility of ProSe for first responder applications

• Challenges

• Synchronization, resource allocation, service continuity

• Testbed implementation, frequency agility including Band 14 and ISM band

• Current SDR platform sufficient for demo of ProSe, but more computationally powerful platform and 

smaller form factor hardware are needed for deployment

Conclusion

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Thank you
Come back for the 

Next 

Session

4:20 PM

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#PSCR2019
Backup material

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• D2D software stack implementation in OAI including sidelink channel implementation with: 

• RRC: SIBs 18 and 19, and SidelinkUEInformation handling

• PDCP: PC5-S and PC5-U traffic for Sidelink

• MAC: SL-DCH, SL-SCH

• PHY: PSDCH, PSSCH, PSCCH, SLSS

• Sidelink synchronization between off-network UEs and between Relay and Remote UEs

• Relay UE support with 2 USRPs (USRP1: LTE UL/DL + sidelink Tx; USRP 2: sidelink Rx)

• Group members and UE-to-Network relay discovery announcement and monitoring

• Group members registration and authentication

• Creation/Rrelease of direct link between off-net UEs and between Relay and Remote UEs

• D2D 1:N (group) comm and 1:1 (direct) private comm and traffic exchange over group and 

direct link via GUI, including push-to-talk, image transfer, and text message

• Tested and demoed over cabled and wireless testbed indoor and outdoor

DDPS achievements – details (1/2)

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• Synchronization study 

• Simulated the VL “Array-Assisted Cross-Ambiguity Function (AACAF)” synchronization algorithm on 

MatLab for D2D indoor and outdoor environments 

• Compared the performance of multiple synchronization search algorithms including three variants of 

AACAF and four variants of direct correlation detector, under the variables of frequency offset, 

Gaussian noise, and pedestrian multipath channel conditions 

• Showed feasibility with respect to stringent SNR and frequency offset

• Resource management study 

• Investigated methods for reducing collision rates for off-net D2D operations 

• Proposed new algorithms and compared performance with the baseline 3GPP D2D resource 

assignment procedure. 

• Studied two variants of the resource assignment algorithm. Both achieved an improvement of ~25% 

reduction in collision rate. Further study will compare implementation complexity.

DDPS achievements details (2/2)

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Off-network call flow

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Service continuity Ccall flow

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OAI RAN and CN additional extensions (in progress)

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