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A Survey on Legacy and Emerging Technologies for Public Safety Communications

Abhaykumar Kumbhar, Farshad Koohifar, Ismail Guvenc, Bruce Mueller

arXiv:1509.08316v2cs.NI

TL;DR

Public safety communications must support mission-critical voice and data while addressing interoperability and coverage constraints. The paper compares LMRS and LTE-based public safety networks, examines their convergence, and reports higher LTE throughput but better LMRS coverage, supporting complementary roles for broadband data and voice connectivity.

  • Problem

    Public safety agencies face interoperability failures and need communication systems that support mission-critical voice and data efficiently.

  • Method

    The paper compares LMRS and LTE-based public safety networks, examines their convergence, and evaluates LTE band class 14 and LMRS performance through simulation and related system analysis.

  • Results

    LTE band class 14 provides significantly higher throughput than LMRS, while LMRS provides better cell coverage and range.

  • Takeaways & Limitations

    LMRS remains suited to mission-critical voice connectivity, while LTE can support mission-critical broadband data and converged public safety devices can combine their strengths.

  • Takeaways & Limitations

    Flexible integration of LTE enhancements, interoperable SDR-based public safety systems, and cybersecurity protections remain open research challenges.

Abstract

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Effective emergency and natural disaster management depend on the efficient mission-critical voice and data communication between first responders and victims. Land Mobile Radio System (LMRS) is a legacy narrowband technology used for critical voice communications with limited use for data applications. Recently Long Term Evolution (LTE) emerged as a broadband communication technology that has a potential to transform the capabilities of public safety technologies by providing broadband, ubiquitous, and mission-critical voice and data support. For example, in the United States, FirstNet is building a nationwide coast-to-coast public safety network based of LTE broadband technology. This paper presents a comparative survey of legacy and the LTE-based public safety networks, and discusses the LMRS-LTE convergence as well as mission-critical push-to-talk over LTE. A simulation study of LMRS and LTE band class 14 technologies is provided using the NS-3 open source tool. An experimental study of APCO-25 and LTE band class 14 is also conducted using software-defined radio, to enhance the understanding of the public safety systems. Finally, emerging technologies that may have strong potential for use in public safety networks are reviewed.

I. INTRODUCTION

Public safety communications must support reliable, interoperable voice and data exchange for emergency responders, while legacy systems face congestion, interoperability, and limited broadband capabilities. This survey compares legacy and LTE-based public safety networks, reviews convergence and emerging technologies, and reports simulation and SDR studies.

  • Emergency responders depend on seamless communication and critical information sharing to protect lives during natural and man-made disasters.
  • Emergency-driven traffic spikes can congest public safety and commercial networks, making reliable communication and congestion prevention critical.
  • The survey addresses a literature gap by comparatively analyzing legacy and emerging public safety technologies, including spectrum allocation across multiple regions.
  • It reviews FirstNet, LMRS-LTE convergence, mission-critical push-to-talk over LTE, and unified LMRS-LTE comparisons not covered by earlier surveys.
  • The paper studies LMRS and LTE band class 14 through NS-3 simulations and software-defined-radio measurement campaigns, while surveying emerging technologies and open problems.

1) APCO-25:

APCO-25 is a North American digital LMRS standard that evolved from narrowband analog-compatible operation toward improved capacity, interoperability, and data support. TETRA serves a similar role in Europe and Asia, while LTE provides broadband capabilities for public safety applications.

  • 1) APCO-25:: APCO-25 supports analog, digital, or mixed-mode operation and maintains backward compatibility with legacy systems.
  • 1) APCO-25:: Phase 1 APCO-25 uses C4FM in 12.5 KHz channels and provides a 9600 bits/s bit rate.
  • 1) APCO-25:: Phase 2 introduces two-slot TDMA, doubling call capacity within a 12.5 KHz allocation while emphasizing interoperability, roaming, and spectral efficiency.
  • 1) APCO-25:: Project MESA planning addressed the need for high-speed public-safety data and broadband communication applications.
  • 2) TETRA:: TETRA Release 1 supports voice-plus-data, direct-operation, and packet-data-optimized modes, including direct voice and data without base stations.
  • 2) TETRA:: TETRA Release 2 expands data capacity through adaptive modulation, channel bandwidth, and coding, with user bit rates ranging from 10 Kbits/s to 500 Kbits/s.
  • LTE is a broadband technology intended to support high-data-rate public safety applications beyond LMRS capabilities.

C. Major Challenges in PSNs

Public safety networks face simultaneous challenges from heterogeneous technologies, congestion, limited bandwidth, interoperability failures, and the need for broadband mission-critical services. LTE spectrum allocation and convergence with existing systems are presented as responses to these constraints.

  • Large-scale disasters can combine network congestion, low data rates, interoperability problems, spectrum scarcity, and security problems.
  • Emergency traffic spikes can congest public safety and commercial networks, making reliable communication critical.
  • Emergency voice, video, telemetry, and situational-awareness applications require higher data rates and broadband spectrum.
  • Independent public safety agencies using non-interoperable systems can cause communication failures and risks to public lives.
  • The 700 MHz public safety allocation includes broadband, narrowband, and guard-band blocks, while D Block reallocation provided critical additional spectrum.

B. 800 MHz Public Safety Spectrum

The survey describes public safety spectrum across the 800 MHz, 900 MHz, and 4.9 GHz bands, including their users, allocations, and broadband applications. These bands support distinct combinations of narrowband radio, commercial services, and incident-scene connectivity.

  • The 800 MHz NPSPAC allocation uses uplink channels at 806–809 MHz and downlink channels at 851–854 MHz.
  • The 900 MHz spectrum plan includes SMR, industrial, scientific and medical, paging, and fixed-microwave radio bands.
  • Public safety and business-industrial LMRS operate as narrowband systems using 12.5 kHz technology.
  • The 700 MHz D Block was legislatively reallocated for public safety broadband, while public safety operations must vacate T-Band spectrum by 2023.
  • The 4.9 GHz band provides 50 MHz for fixed and mobile services, supporting incident-scene WLAN, mesh networks, Wi-Fi hotspots, VoIP, and video surveillance.

IV. LTE-BASED FIRSTNET PSN

FirstNet is presented as an LTE-based broadband public safety network using dedicated Band Class 14 spectrum and layered architecture. The survey also examines deployable coverage, LMRS-LTE convergence, and the complementary roles of legacy voice and broadband data.

  • FirstNet is an LTE-based broadband network dedicated to public safety services, with features including direct communication, PTT, group calls, emergency alerting, and audio quality.
  • FirstNet comprises distributed core, terrestrial mobile, mobile satellite, and deployable systems for public safety connectivity.
  • Deployable FirstNet categories are intended to extend coverage, capacity, connectivity, and flexibility outside terrestrial coverage or after disasters.
  • Band Class 14 uses LTE commercial standards and is dedicated to public safety in North America, with specified uplink and downlink frequencies.
  • LMRS-LTE convergence is described as supporting continuous mission-critical voice and data communication, interoperability, security, and robust coverage.

VI. MISSION-CRITICAL PTT OVER LTE

Mission-critical PTT over LTE aims to extend reliable group voice and data communication through proximity services, direct device links, and locally routed operation. The section contrasts these LTE capabilities with LMRS and commercial-network constraints.

  • Mission-critical voice requires fast call setup, group communication, PTT, high audio quality, emergency alerting, and secure voice communication.
  • LTE Release 12 introduced proximity services for optimized communication among nearby mobiles and group-call support for public safety.
  • Direct proximity communication can bypass the network, saving network resources and enabling mission-critical communication.
  • Release 13 was planned to enhance D2D/ProSe with advanced public safety discovery, relays, group communication, and locally routed operation without backhaul.
  • LMRS supplies wide-area mission-critical voice with restricted data rates, whereas FirstNet supplies high-speed connectivity and real-time updates.
  • Commercial networks can support public safety services through existing infrastructure but remain vulnerable to congestion and disrupted communications at incident scenes.

VIII. LMRS VS. LTE: SIMULATION RESULTS

The NS-3 comparison evaluates LTE band class 14 and APCO-25 using throughput and signal-quality measurements under increasing distance and interference. LTE provides substantially higher aggregate throughput, while signal quality declines toward cell edges and under adjacent-cell interference.

  • Simulation setup: The study uses NS-3 to compare LTE band class 14 and APCO-25 with similar user density, measuring throughput and signal quality as cell size increases.The LTE model is based on LENA, while the LMRS model follows APCO-25 definitions.
  • LTE throughput: 33 Mbit/s downlink and 11 Mbit/s uplink are the maximum aggregated LTE throughputs observed with 20 UEs.The LTE scenario uses a macro-eNodeB and a 10 MHz bandwidth.
  • LTE throughput: LTE throughput diminishes as UE distance from the macro-eNodeB increases.The throughput trend is reported for the aggregated uplink and downlink measurements.
  • LTE signal quality: LTE downlink SINR ranges from −10 dB to 50 dB across the simulated cell, with nearby UEs experiencing better signal quality.The measurements span cell-center through cell-edge regions.
  • Inter-cell interference: Cell-edge interference shifts LTE downlink SINR from −10–10 dB without interference to −15–10 dB with adjacent-cell interference.The scenario models two neighboring homogeneous cells and cell-edge UEs in one cell.

B. Setup for APCO-25

The APCO-25 setup models direct radio-to-radio communication among randomly distributed subscriber units using the APCO-25 common air interface. Throughput and SINR decrease as portable and mobile units become more distant, limiting direct-mode range and reuse.

  • Direct mode: Direct mode, or talk-around, bypasses repeater and base systems to enable radio-to-radio communication but limits distance and spectrum reuse.The mode is used by both portable and mobile subscriber units.
  • APCO-25 interface: The APCO-25 common air interface provides interoperability across vendors, with a 9600 bps control channel and IMBE voice digitization.The interface supports digital voice modulation for compliant radios.
  • Simulation setup: APCO-25 simulations use 20 randomly distributed subscriber units in direct communication mode with the APCO-25 common air interface and Friis propagation.Portable units transmit at 5 W and mobile units at 10 W.
  • Results: Maximum throughput occurs when subscriber units are nearby, while throughput decreases as geographical distance increases.The simulation evaluates data-only direct communication for portable and mobile devices.
  • Results: SINR decreases with increasing distance, ranging from −30 dB to 40 dB for portable devices and −20 dB to 40 dB for mobile devices.Poor link quality and increased distance are associated with dropped packets and lower aggregate throughput.
  • Comparison: The comparison identifies wider LMRS coverage but higher aggregate LTE throughput, supporting complementary use of the two technologies.The paper connects the coverage difference with the need for voice communication and the throughput difference with real-time multimedia.

IX. LMRS VS. LTE: SDR EXPERIMENTS

The SDR experiments capture and analyze APCO-25 and LTE band class 14 signals using low-cost software-defined-radio equipment. The LTE measurements identify cell parameters and channel transfer behavior that can support coverage and quality-of-service analysis.

  • Experimental approach: The experiments use RTL-SDR and HackRF receivers to capture and analyze public safety LMRS and LTE signals.SDR shifts radio functions such as filtering, mixing, and modulation into software.
  • APCO-25 experiment: A HackRF and SDRSharp setup observes unencrypted APCO-25 voice spectrum, including an 851.68 MHz signal with −36.59 dB strength.The setup functions as a radio scanner for the APCO-25 experiment.
  • Band class 14 experiment: The band class 14 experiment uses Motorola infrastructure and an LTE-LMR converged APX7000L as the UE.The base station operates over 758–768 MHz downlink and 788–798 MHz uplink ranges.
  • Channel behavior: The LTE channel transfer function varies in magnitude and phase as the SDR-equipped user terminal moves.The experiment reports instantaneous magnitude and phase transfer functions for cell 27.
  • Band class 14 results: LTE-Tracker detects band class 14 cell 27 with center frequency 765.5 MHz, receive power −33.6 dB, two transmit antennas, and 25 occupied resource blocks.The detected cell uses a 5 MHz channel bandwidth.
  • Implication: These band class 14 analyses can help researchers detect public safety network coverage holes and assess UE quality of service.The paper presents the SDR work as a way to improve understanding of public safety signals.

A. Multimedia Broadcast Multicast Service (MBMS)

The survey reviews emerging technologies for extending public safety communication capacity, coverage, and service flexibility. It highlights eMBMS, mmWave, massive MIMO, heterogeneous networks, and LTE small cells, while noting propagation and estimation limitations.

  • Multimedia Broadcast Multicast Service: eMBMS groups LTE cells into an MBSFN so they simulcast the same bearer information across cells.This point-to-multipoint design supports broadcast and multicast delivery.
  • Multimedia Broadcast Multicast Service: eMBMS can support public safety group calls, PTT, emergency video, surveillance video, and other multimedia services using one resource set for multiple devices.The paper also associates simulcast with improved cell-edge performance and LMRS-like coverage improvement.
  • Millimeter wave: mmWave offers large bandwidth for congestion and high-data-rate needs, but atmospheric, rain, and vegetation losses limit its propagation range.The survey identifies beamforming, high transmit power, receiver sensitivity, and high antenna gains as mitigation approaches.
  • Massive MIMO: Massive MIMO is constrained by pilot contamination during channel estimation in time-division-duplex systems.The paper attributes this impairment to non-orthogonal pilots from neighboring cells and notes mitigation techniques.
  • Massive MIMO: Massive MIMO is reported to provide 100× radiated energy efficiency and 10× capacity over traditional MIMO.The survey also associates it with lower latency, spectrum efficiency, reliability, and robustness.
  • Small cells: LTE small cells can provide portable or deployable emergency hotspots that improve public safety capacity and reduce competition for macro-eNodeB resources.Backhaul may use a nearby eNodeB, satellite link, or dedicated connection.
  • Small cells: Indoor LTE coverage remains a concern because locations such as building basements may have weak coverage, although LTE minitowers are proposed as a remedy.The survey identifies indoor coverage as an unresolved LTE pitfall.

E. Unmanned Aerial Vehicles (UAVs)

UAVs are presented as deployable complements to public safety networks, helping restore coverage and relay communications in emergencies, while spectrum, mobility, energy, and policy challenges remain.

  • Emergency deployment: UAVs can provide voice and data coverage or operate as relay nodes when disasters disrupt terrestrial communications.They can share public safety broadband bandwidth and backhaul traffic from the UAV.
  • Challenges: UAV-based public safety networking faces challenges involving mobility models, topology formation, energy constraints, multi-UAV cooperation, spectrum scarcity, and cognitive-radio integration.
  • Emergency deployment: UAVs can operate in public safety spectrum, connect with the nearest functioning eNodeB, and extend coverage into high-risk areas.These capabilities position UAVs as complements to PSNs and as relay nodes for emergency first responders.
  • Challenges: Clearer civilian UAV rules and policies are identified as necessary for integrating UAVs into PSNs and filling coverage holes.
  • Spectrum and broadband support: LTE-U and licensed-assisted access are discussed as complementary approaches that can supplement downlink capacity and support seamless mobility for public safety applications.The paper connects these approaches to improved network performance and enhanced emergency responder capabilities.
  • Spectrum and broadband support: Cognitive radio can sense and learn spectrum use, enabling operation in unused licensed-spectrum portions or whitespaces without interfering with primary users.The paper also associates cognitive radio with heterogeneity, reconfigurability, self-organization, and interoperability in disaster scenarios.

I. Wireless Sensor Networks

Wireless sensor networks can extend public safety situational awareness and deliver real-time information through LTE-based PSNs, but large-scale deployment and security remain constrained.

  • Network foundations: Wireless sensor networks use distributed autonomous sensors and gateway nodes to monitor and control physical environments cooperatively.
  • Situational awareness: WSNs can support large-scale situational awareness, early detection of catastrophic events, and location-aware protocols.Localization algorithms can enhance situational awareness, although large deployments face traffic-pattern and node-convergence vulnerabilities.
  • Spectrum adaptation: Cognitive-radio-enabled WSNs can use dynamic spectrum access, while channel bonding can improve bandwidth utilization and channel capacity.
  • LTE integration: Connecting sensor gateways to LTE-based PSNs allows real-time data to reach public safety data centers, raising situational awareness and reducing responder response time.
  • Security constraints: WSN integration with IP-based networks introduces security vulnerabilities, including threats to public safety data and cloud-connected IoT devices.The paper identifies complex IoT threats and lists eavesdropping, corrupt information, insecure interfaces, data exfiltration, and denial-of-service attacks among PSN concerns.
  • Security constraints: Public safety agencies must define technical and policy requirements for identification, authentication, and authorization according to security-technique scope and context.
  • Deployment context: Public safety broadband deployments vary across regions, creating interoperability and spectrum-harmonization requirements for nationwide and cross-border operations.The paper describes differing frequency ranges and plans including band class 14 in Canada, LTE-based ESN in the United Kingdom, and European 400 MHz and 700 MHz considerations.

XII. ISSUES AND OPEN RESEARCH DIRECTIONS

The section identifies open research directions spanning converged public safety networks, advanced radio technologies, IoT, and cybersecurity. It also concludes that LMRS and LTE will likely coexist, with LMRS supporting mission-critical voice and LTE supporting real-time data.

  • LMRS-LTE convergence: Full-fledged mission-critical LTE-based public safety deployment is not commercially attainable in the short term, motivating LMRS-LTE convergence.The convergence can provide mission-critical voice and broadband data, but optimizing converged devices remains an open engineering challenge.
  • Advanced network technologies: Integrating and optimizing eMBMS, HetNets, LAA, LTE-based V2X, D2D/ProSe, small cells, mmWave, massive MIMO, and UAVs remains an open research agenda.Specific challenges include flexible MBSFN resources, interference avoidance, handover, backhauling, and convergence of advanced technologies with small cells.
  • Spectrum technologies: SDR and cognitive radio improve spectrum flexibility and efficiency, but interoperable SDRs, regulatory compliance, and energy-efficient spectrum sensing require further research.The paper also identifies spectrum sharing, prioritized access, and LAA applications as areas needing additional investigation.
  • IoT and wearables: Public safety wearables, wireless sensor networks, and IoT require advances in infrastructure, design, cost, interoperability, data aggregation, regulation, policy, and information security.The section connects these issues to real-time data aggregation and situation analysis for emergency first responders.
  • Cybersecurity and policy: Securing public safety infrastructures, devices, and data remains an open cybersecurity issue because emergency responders access sensitive medical, site, and multimedia information.The paper also identifies policy requirements for public safety devices and information as a major concern for agencies and regulators.
  • Concluding comparison: LTE band class 14 provides significantly higher throughput than LMRS, while LMRS provides better cell coverage and range.The paper concludes that LMRS is expected to remain primary for mission-critical voice while LTE provides mission-critical real-time data.

APPENDIX

The appendix lists the acronyms used throughout the survey. These definitions are collected in Table XI.

  • APPENDIX: Table XI lists the definitions of acronyms used in the survey article.
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