1. Munawwar M. Sohul Dr. Taeyoung Yang Dr. Jeffrey H. Reed a
LTE Communications Over 3.5 GHz Band for Broadband Public Safety Applications
Munawwar M. Sohul
Dr. Taeyoung Yang
Dr. Jeffrey H. Reed a

2. 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
Greater interoperability and enhanced interagency cooperation
Unprecedented broadband capabilities
High reliability and security
Cost effective
Better performance, low latency
Source: Homeland Security, “Public Safety Communications Evolution”, Brochure, Nov 2011

3. Public Safety Network: Future Direction
Challenges:
Broad range of stakeholders and context
Efficient coordination and interoperability
Rich content based information
Existing spectrum allocation
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)
law enforcement, response to fire, natural and man-made disasters, medical emergencies, threats to public order and a host of other situations.
14,000 police departments,
3,000 sheriff’s offices,
more than 6, centers,
1.2 million employees in city, county, state, and Federal law enforcement
and 800,000 in private-sector security in the United States
To design and develop an efficient and coordinated system to facilitate this gigantic workforce is a challenging task and the effectiveness of such a system is heavily dependent on the accuracy and detailed nature of the information shared within this complex topology.
The use of 700 MHz spectrum for public safety applications is attractive because of its propagation and penetration characteristics. However, there is practically no room available in 700 MHz band to extend the spectrum further for future broadband PS applications.

4. 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

5. Phase 2: Mobile Platform with Repeater
Setting up the phase-1 repeater in a mobile platform:
Easy to access emergency scenario
Useful for non-emergency 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

6. Phase 2: Application Scenario

7. 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

8. 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

9. 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

10. FDD LTE Repeaters UE side repeater Two separate RF path
Attaches to UE through Band-14 LTE duplexer
Designed and developed by
eNB side repeater
Two separate RF path
Two ports to attach to the UL and DL port of CMW500
Designed and developed by

11. Result: Impact of interference on the LTE Link
Downlink at 3.5 GHz band
Max Throughput: 5.74 Mbps
Downlink at 3.5 GHz band
Max Throughput: 5.74 Mbps
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
3.85 Mbps
32.93%
LTE link moved to avoid Interference
3.75 Mbps
34.70%

12. Impact of Interference (without DSA)
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

13. Impact of DSA
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

14. Observations and Recommendations
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.

15. 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 non-emergency scenario
Enable spectrum sharing: use NTIA identified shared bands

16. Thank You
Acknowledgements: This work is supported by the office of the Vice President for Information Technology, VT; Center for Innovative Technologies (CIT).