Munawwar M. Sohul
Dr. Taeyoung Yang
Dr. Jeffrey H. Reed
a
Public Safety Network:
•
Future Direction
PS network is moving
towards a broadband
system
•
LTE for public safety
• Priority access to network
resources
•
Desired services
•
data, voice, and video
communication, access to
Internet
• Push-To-Talk (PTT) or
Device-to-Device (D2D)
comm.
• Group calling
Source: Homeland Security, “Public Safety Communications Evolution”, Brochure,
Nov 2011
Public Safety Network:
Challenges:
 Broad range of stakeholders
and context
 Efficient coordination and
interoperability
 Rich content based
information
 Existing spectrum allocation
Future Direction
Enabling concept: Spectrum sharing
 Calls for a paradigm shift in
 sharing and managing the spectrum
 designing the radio architecture.
Enabling technologies:
 Dynamic Spectrum Access (DSA)
 Carrier aggregation (CA)
 Self-organizing networks (SON)
Phase 1: Frequency Translating LTE Repeater
 Low-cost way to demonstrate the feasibility of spectrum sharing for
broadband PS applications.
 Enables f1/f2 band (700 MHz/3.5 GHZ band) communication
 DSA enabled repeaters
 Designed and developed by Wireless@VT
Phase 2: Mobile Platform with Repeater
 Setting up the phase-1
repeater in a mobile
platform:
 Easy to access
emergency scenario
 Useful for nonemergency scenario
 Mobile platform equipped
with LTE repeater
 Wireless services in the
disaster affected area
over licensed and
unlicensed bands
 Self-sustainable in terms
of power
Phase 2: Application Scenario
Impact and Significance
 Mobile infrastructure for broadband PS applications in rural areas
 Data, voice, and video communication, Access to internet
 Communication to the central PS command center
 Scalable and rapidly deployable small cell infrastructure
 Improve situational awareness
 Rapid dissemination of information to the deployed forces
 Option to provide some wireless service to non-PS users
 Backhaul connection even if the original link is faltered
 Attractive business opportunity for non-disaster scenarios
 Cellular communications, broadband internet connectivity, wireless
services (WiFi, bluetooth)
 Operational data collection for future reference and analysis
Proof of Concept Demonstration
 Demonstrate
 The feasibility of broadband PS applications over the 3.5 GHz band
 The frequency agility provided by the repeater to use any of the
NTIA identified shared bands
 Generate interest among the stakeholders
 Shared bands to achieve broadband PS services
 Scalable and rapidly deployable PS radio coverage

Off-the-shelf equipments, Frequency translating LTE repeater
 Description
 Tentative timeline: October, 2014
 LTE PS-UE and eNB (works in the PS band)
 DAS capability to identify spectrum opportunity
 Proof of communication between UE and eNB over 3.5 GHz band
Demo in the Indoor Environment
 Use available PS devices (Band 14)
 Ensure successful operation of the FD-LTE repeaters (Band
14 to 3.5 GHz)
 Communicate over the 3.5 GHz band
 DAS capability to identify
spectrum opportunity
 Observe
 The successful SU
hopping to avoid PU
 The impact of PU
interference on the SU
LTE link performance
System Setup
FDD LTE Repeaters
UE side repeater
 Two separate RF path
 Attaches to UE through
Band-14 LTE duplexer
 Designed and developed
by Wireless@VT
eNB side repeater
 Two separate RF path
 Two ports to attach to
the UL and DL port of
CMW500
 Designed and developed
by Wireless@VT
Result: Impact of interference on the LTE Link
• Downlink at 3.5 GHz band
• Max Throughput: 5.74 Mbps
Scenario
UE-eNB Attachment
throughput
BLER
• Interference not hitting the LTE link
• Attached
• 4.61 Mbps
• 19.72%
• Interference hitting the LTE link
• Attached
• 3.85 Mbps
• 32.93%
• LTE link moved to avoid Interference • Attached
• 3.75 Mbps
• 34.70%
Impact of Interference (without DSA)
Impact of inteference power on the FDD LTE system performance
100
6
90
BLER (%)
70
4
60
50
3
40
2
30
20
1
10
0
-10
-5
0
5
10
15
20
25
30
0
35
SINR (dB)
 SINR calculated for Band14
 Throughput and BLER shows flat regions
 LTE link tries to compensate through CQI adjustment
 The UE remains attached to the eNB for small SINR values
 Link performance is severely degraded
Throughput (Mbps)
5
80
Impact of DSA
Impact of DSA on the FDD LTE system performance
Impact of DSA on the FDD LTE system performance
100
no DSA
with DSA
no DSA
with DSA
5
Throughput (Mbps)
BLER (%)
80
60
40
20
0
1
4
3
2
1
2
3
4
5
6
Time (minute)
7
8
9
10
0
1
2
3
4
5
6
Time (minute)
7
 Employing the DSA algorithm improves the LTE link performance
 The LTE link avoids interference:
 The external spectrum monitor detects the PU
 The LTE eNB switches to another channel that is reported empty
 Recovery time is smaller when DSA is employed
 LTE link is interfered by the PU for only a fraction of the time
 Similar performance is expected for multiple PU
8
9
10
Observations and Recommendations
 Observations
 UE and eNB communicated over the 3.5GHz band using the
repeaters
 Resilient: Even for low SINR values UE remained attached
 Once interfered


The link recovers through CQI adjustment
Long period of un-interfered state is required for recovery
 Recommendations
 Modifying LTE protocols to address strong and pulsating signal

To ensure faster recovery through faster SINR to CQI mapping
 Observe the impact of interfering with different control channels
 Demonstrate successful communication using the repeaters in the
outdoor environment
 Compare the performance of TD-LTE with the FD-LTE results.
Conclusion
 Public Safety Network
 Mobile infrastructure for broadband PS service
 Scalable and rapidly deployable wireless network
 Operational data
collection for future
reference and analysis
 Over the air hardware
and software reconfig
capability
 Useful in nonemergency scenario
 Enable spectrum
sharing: use NTIA
identified shared
bands
Acknowledgements:
This work is supported by the office of the Vice President for
Information Technology, VT; Center for Innovative Technologies (CIT).