Airborne Emergency Communications Node Technical Approaches

1. Airborne Emergency Communications Node Technical Approaches National Conference on Emergency Communications December 12-13, 2005 Dr. Chris Hawkins Chief Technologist of Unmanned Systems Northrop Grumman Corporation

2. High-Level Requirements for Airborne Relays • Support communications systems of all responders • Police, fire, medical, power, water, roads, National Guard, Coast Guard, etc. • Voice, text, and data communications for all appropriate communication systems • Possibly include commercial cellular • Interface to public telephone networks and internet • Provide regional coverage with large numbers of relayed communication channels • Regional areas spanning 200 miles or more • Will require far more comms channels than a single ground based repeater or base station • Potentially hundreds to thousands of simultaneously active relayed channels • Support channel frequency reuse over the region by dealing with inherent radio frequency interference problems • Support any geographic region on short notice • Self-deploying in all weather conditions is best, with sufficient speed to overcome headwinds • Ability to fly through national airspace on short notice • Best to not be dependent on a high data rate line-of-sight or satellite link to a ground station • Gateways, bridges, routers, and some data servers would need to be located on-board

3. System Solution Range • This briefing will focus on high capacity regional coverage approaches • Lower capacity solutions are subsets of this, and the technical issues are common to all Satellite High Capacity, Regional Coverage Low Capacity, Regional Coverage Airborne Node Airborne Node Low Capacity, Local Coverage Multiple Low Capacity, Local Coverage Airborne Node Airborne Node Airborne Node

4. Typical Signal Characteristics • Frequency Division Multiplexed (FDM) • A comms channel is a frequency of a specified bandwidth and modulation • The frequency is dedicated or dynamically allocated (trunked) • Base method for Project 25 • Well suited for long range relay • Time Division Multiple Access (TDMA) • Proprietary systems and in consideration for Phase 2 of Project 25 • Often not well suited for long range relay to due timing issues • Simplex: transmit and receive on same frequency • Transmit or receive (not both) at a given time • Direct handset to handset. No repeater involved • Half-duplex: transmit on one frequency, receive on another • Transmit or receive (not both) at a given time • Signal retransmitted by a repeater or base station • Typical land mobile radio used by public safety • Full-duplex: transmit on one frequency, receive on another • Transmit and receive at the same time • Signal retransmitted by a repeater or base station • Typical of cell phones

5. Typical Signal Characteristics (2) • Trunked systems • The communications channel is assigned dynamically to maximize spectrum usage efficiency. The user’s radio requests a comms channel via a known control channel when needed. All radios in the call group are sent the comms channel when it is assigned. • Common in Land Mobile Radio Systems, and included in Project 25 • Modern Commercial Cellular • CDMA • Well suited for long range operation – 185 km theoretical maximum • GSM and iDEN • Both are TDMA signal types – problems for long range operation due to timing issues • GSM is limited to 35 km maximum at normal rates, and 70 km at half rate • Military Comms • Of the types that would be used for disaster response, well suited to long range operation

6. High power repeater on a tall tower allows mobile units to communicate better Mobiles don’t need much power High tower gets over many obstacles F1: Mobile Transmit Frequency F2: Mobile Receive Frequency Gn: Group of transmit and receive frequencies assigned to a repeater Cellular pattern of frequency group assignments on a map (idealized) Same frequency groups are separated by enough distance that the signal loss is sufficiently great that no interference occurs. Cells are connected by landline or microwave backhaul links Allows greater total capacity than high power mobile radios G3 G1 G1 G6 G4 G2 G2 G7 G5 G3 Background: Land Mobile Radio Repeaters F1 “Help!” F2 “Help!” F2 “Coming” F1 “Coming” Repeater, (Relay, Base Station)

7. G3 G1 G1 G6 G4 G2 G2 G7 G5 G3 Airborne Repeater Frequency Reuse Challenge • Airborne repeater sees many cells at once • Signal loss is much higher near the ground than well above the ground, thus limiting range of ground based radios and repeaters, but the range for an airborne repeater can be very long • Radio path to airborne repeater also has fewer obstacles (buildings, mountains, etc.) • Airborne repeater must either • use a group of frequencies that is not repeated for a very long range (limiting the number of channels for the region – low capacity) Or • Create cells on the ground using directional antennas or antenna arrays (higher capacity)

8. Frequency Reuse using Beams Regional Coverage Area G3 G4 G3 G1 G2 G2 G1 Frequency Group Reuse in Different Beams Smaller (More) Beams = greater frequency reuse = higher regional capacity

9. Antennas

10. Antenna Arrays • VHF Frequency Bands (30 to 300 MHz = 1m to 10m wavelength) • Blade antennas mounted over a large area on bottom of aircraft • Antennas combined with amplitude and phase weighting to create directional beams • Needed only if frequency reuse in VHF bands is desired • UHF • Antenna arrays would only be used in the low end of UHF (300 to 500 MHz) only if frequency reuse is desired and if the directional antennas for that band are too large to be mounted on the selected aircraft. • Advanced Electronically Steered Arrays (AESA) • Panel of individual antenna elements that are electronically controlled and weighted with amplitude and phase offsets to create multiple steerable beams from a single array • Very advanced and flexible, but also expensive

11. Some Frequency Management Issues • If beams used, need to steer and/or switch antennas to keep each frequency group on the same ground cell location. • Airborne relay can’t reproduce the same cellular pattern of the ground stations • Must coordinate frequency sets with local authorities to avoid interference • Desirable to have well separated blocks of uplink frequencies (mobile to repeater) from blocks of downlink frequencies (repeater to mobile) • Same as commercial cellular does • Allows for an overall smaller, lighter weight equipment package on the aircraft by using wideband technology • Fewer analog filters and power combiners • Allows many more relay channels than individual narrowband transceivers

12. Servers (Information Databases, Chat, Imagery, etc.) Commercial Cellular Base Stations Wideband Data Links (e.g., Ku SATCOM, TCDL, video links, etc.) LMRS Radios/Repeaters (Project 25 Compliant) Military Narrowband Radios/Repeaters High-Level Architecture Concept Airborne Comms Node Comms Node Controller Network Manager Voice/Data Routing Data Traffic Bridging Gateways Ethernet Switch Voice Digitization and Packetization (VoIP) Commercial Cellular Switch/Controller Non-Ethernet Control and Data Analog Audio VHF/UHF Antenna Interfaces (Diplexers, Filters, Low Noise Amplifiers, Splitters, RF Switch Matrix, High Power Amplifiers as needed, etc.) Wideband Link Antenna Interfaces VHF/UHF Antenna Group Wideband Link Antenna Group Voice and lower-rate data users (data can include imagery at limited download speed) High Data Rate Users & Networks (Command Centers, imagery and video users, public telephone network interfaces, Internet Interface, backhaul relays, etc.)

13. Concept Points • Recommend using a federated architecture • Integrate multiple vendors’ radio and controller systems rather than try to build a tightly integrated custom system that “does it all” • Keeps development and upgrade costs lower overall • Focus on Project 25 standards for public safety land mobile radio • Support of proprietary systems would be very complicated or cost prohibitive due to the number of types • Rapid add-on proprietary systems could be considered to deal with specific regions • Use Ethernet with Internet Protocol (IP) as the backbone for the system • Bridge all comms gear to Ethernet/IP (Voice using Voice over IP) • On-board controllers should be capable of operating the node without high-rate data links to the ground • For example, the commercial cellular system should be able to operate as a stand-alone network if necessary, and dynamically reconnect to the ground network as data links are available. • Encryption units and trusted gateways/filters were not shown in the high-level block diagram, but can be included • Caution: encryption can cause communications problems if not setup carefully, and it must not jeopardize disaster response

14. Sharing with the Military • Only those military radios and comms systems that might be needed for disaster response operations need to be accomodated • However, the military also has needs for airborne communications nodes, but with additional military comms equipment • An experimental comms relay node program is in progress, but with a limited number of simultaneous channels • Sharing with the military could offset the cost of the aircraft(s) and maintenance

15. Aircraft Considerations • High flying (> 50,000 feet) (e.g., Global Hawk, Proteus, U2, WB-57, etc.) • Advantages: • Above the weather allows for constant comms coverage during hurricanes and thunderstorms • Above commercial air traffic means no conflict with other aircraft and hence optimal comms relay flight paths • Better angle of incidence to the ground radios reduces radio signal blockage by obstacles and reduces ground signal loss • Disadvantages: • Generally more costly than low flying aircraft • Exposed to more radio interference • Long endurance (24+ hours) recommended • Reduces the number of aircraft needed due to less time spent flying to and from airbase • Reduces how often comms interrupts occurs when aircraft are swapped • Velocity > 250 mph recommended • Can self deploy from long distances if also long endurance • No local airbase required (airbase could be 2000 miles away) • Can combat high velocity headwinds • Weight and Power: A high capacity system will likely weigh 1000 to 3000 pounds, and consume 5,000 to 15,000 Watts.

16. Summary • High capacity airborne comms relay nodes are possible • High capacity can be achieved using directional antennas and frequency reuse • Low capacity has the same node architecture and radio interference issues, but simply to a lesser degree • Rapid response and all weather operations are achievable • Communications node should be standards based with a flexible interconnect backbone • Project 25 standard for public safety and public works systems • Commercial cell phone support • CDMA best suited due to long distance relay issues • Standard military radios for National Guard, Coast Guard and other military support • Commercial and military standard wideband data links • Ethernet/IP backbone using Voice over IP and data bridges