LTE Communications Over 3.5 GHz Band for Broadband Public Safety Applications

1. 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 Source: Homeland Security, “Public Safety Communications Evolution”, Brochure, Nov 2011

3. Public Safety Network: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) Challenges: • Broad range of stakeholders and context • Efficient coordination and interoperability • Rich content based information • Existing spectrum allocation

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 Wireless@VT

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 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

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

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 • 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.

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).