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Tactical Data Links, Air Traffic Management, and Software Programmable Radios* B

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Tactical Data Links, Air Traffic Management, and Software Programmable Radios* B TACTICAL DATA LINKS, AIR TRAFFIC MANAGEMENT, AND SOFTWARE PROGRAMMABLE RADIOS* B. E. White, The MITRE Corporation, Bedford, MA (AC2ISRC) was: Why can’t civil aviation data Abstract link (CADL) requirements be satisfied by Link Background on Link 16, global air 16? Another question is whether a single traffic management (GATM), and the joint CADL can satisfy Air Force GATM needs. tactical radio system (JTRS) is provided. An objective of this paper is to answer Information addressing the ability of: 1) Link these questions. Section 2 briefly introduces 16 to handle evolving civil aviation data link the Link 16 program. CADLs and implications (CADL) waveforms; 2) a single data link to for DOD are discussed in Section 3. Section 4 satisfy Air Force GATM requirements; and 3) highlights difficulties of integrating Link 16 JTRS to incorporate data links of interest to and CADLs waveforms, and relying on a single aviation is offered. Relationships with layered data link to satisfy CNS/ATM data link communication architectures, the Global Grid, requirements. Section 5 discusses SPRs and and software programmable radios (SPRs) are the JTRS. Section 6 has concluding remarks also discussed. and suggested actions. 1. Introduction 2. Link 16 In October 1994 Link 16 was Link 16 is NATO terminology for an designated as the DOD’s primary tactical data anti-jam (AJ), secure, data and voice system, link for all military service and defense agency with standard waveforms and messages to 2 command, control and intelligence (C I) promote interoperability, supported by the Joint systems [1]. The Air Combat Command Tactical Information Distribution System (ACC) has already incorporated Link 16 into its (JTIDS) and Multifunctional Information 2 C and sensor systems and is now planning on Distribution System (MIDS) terminals. installing Link-16 in its fighters and bombers. This commitment entails an expenditure of Figure 1 shows how the number of billions of dollars. platforms to receive Link 16 rapidly rises starting in FY00, and the significant changes in However, there are other data link the increases from FY03 through FY15, based requirements competing for DOD resources, on various planning data [2]. notably those of the International Civil Aviation Organization (ICAO) for communications, navigation and surveillance/ 3. Civil Aviation Data Links air traffic management (CNS/ATM). In 1997 CADLs are primarily associated with the Air Force created a global air traffic ATM systems, and include fixed message sets management (GATM) function in a new built into upgraded but standard system program office (SPO) at Hanscom Air communication procedures to reduce pilot and Force Base (AFB) to include the certification of controller workload and lead to quieter cockpits avionics capabilities from a GATM and airwaves. Also, CADLs on military 2 perspective. A question asked by the aircraft could be used as a resource for C . commander of the Aerospace C2 Intelligence, ICAO’s CNS/ATM concept relies on data links _______________Surveillance, and Reconnaissance Center to be the primary means of routine * This work was sponsored by the Electronic Systems Center (AFMC), Hanscom Air Force Base, Massachusetts. 0-7803-5749-3/99/$10.00 © 1999 IEEE 5.C.5-1 communications for air traffic services (ATS) does not yet require dual redundant satellite [3]. Controller-pilot data link communications communication systems for ATC but probably (CPDLC) is the first comprehensive ATS data will. Many potential users, particularly the link application to be implemented. airlines, have advocated HF data link (HFDL) for over the ocean ATC instead of a second Line of Sight (LOS) Data Links satellite system because HFDL is less expensive to install. The author expects a The FAA is advocating a new digital SATCOM/HFDL configuration to become voice and data time division multiple access acceptable for ATC after some further FAA (TDMA) waveform for their next-generation effort to validate HFDL for this application. air-ground communications (NEXCOM) system. This waveform is known as Mode 3 of It is noted that Inmarsat’s geostationary the VHF digital link (VDL-3). In 1995 ICAO satellites do not provide polar coverage, a endorsed VDL-3 as the long-term solution to desirable feature for military applications. worldwide spectrum congestion in the VHF However, the narrowband ICO system will aeronautical band. VDL-3 operates at a 25- provide global coverage. Although there has kHz channel data rate of 31.5 kb/s. The VDL-3 been interest in providing aeronautical service end-to-end delay is no more than about 250 ms, with ICO, this capability is not yet realized. a latency suitable for ATS. HFDL may also support global coverage. Another future CADL, VDL-2, uses the same modulation scheme as VDL-3 but Implications for DOD employs carrier sense multiple access (CSMA) DOD must comply with civil standards instead of TDMA. VDL-2 is attractive to being developed by ICAO. With the assistance airlines for aeronautical operational control of Hanscom’s GATM SPO, the Air Mobility (AOC) where latency requirements for data are Command (AMC) is planning to integrate not so stringent, as compared to ATS. ADS-A, Aero-I, and HFDL, into its operational Any of the time-critical functions of airlift capabilities. CPDLC are more in the bailiwick of ATS, not ACC has been concerned about AOC, and at VHF should be handled by VDL- equipping all their aircraft with avionics 3, not VDL-2. However, VDL-2 could be equipment that would make them compliant around for a long time, and additional ATS with the emerging civil aviation standards. The uses for VDL-2 that do not require near-real- “heavy special use aircraft” that routinely fly as time latency performance could be attractive. general aviation traffic (GAT) aircraft, viz., the Automatic dependent surveillance E-3 (Airborne Warning and Control System broadcast (ADS-B), a CADL system critical to [AWACS]), E-4 (command post aircraft), E-8 “free flight”, is devoted to the LOS broadcast (Joint Surveillance Target Attack Radar System of position, velocity, and intent information. [JSTARS]), and the OC/RC/TC-135 Potential solutions to ADS-B are the Extended (reconnaissance and tanker aircraft) would be Squitter, Self-Organizing TDMA (S-TDMA) fully equipped. However, it was questionable (also known as VDL-4), and the Universal whether it would be necessary to equip fighters, Access Transceiver (UAT). bombers, and EC/HC-130s (transport aircraft). Overall, considerable progress has been Beyond Line of Sight (BLOS) Data Links made in the last two years. The number of GATM communications (comm) functional Inmarsat aeronautical (Aero) satellite units planned for various aircraft between 1999 communications (SATCOM) is certifiable for and 2016 are shown in Figure 2. CMU stands BLOS air traffic control (ATC) use. ICAO for communications management unit. 0-7803-5749-3/99/$10.00 © 1999 IEEE 5.C.5-2 4. Integration of Link 16 and CADLs resides in the JTIDS/MIDS terminal. A given Section 1 questions are now addressed. Link 16 platform's host computer contains the required databases, various controls, message processing, interface, input/output, and other Layered Communication Architecture functions. Thus, if a hardware or software A "layered" communication system change outside the terminal becomes necessary, architecture is advocated as a tool for analyzing all the host platforms must be modified. the integration problem. Ideas of a MITRE Although layering implies modularity, colleague, Mike Butler, are freely used. He has the reverse is not necessarily true. However, elaborated on several key attributes of layered two or more adjacent layers can be combined in architectures: 1) technology neutrality; 2) some situations to save space. One just has to functional encapsulation; 3) interface be careful that when layers are combined, standardization; 4) independent resources; and future flexibility is not precluded. 5) extensible systems. Layering facilitates performance vs. flexibility tradeoffs as Contrasts Among Link 16 and CADL technology and system needs change. This Waveforms helps ensure the architecture accommodates system evolution over a long period. As an exercise in preparing this paper, the author allocated some basic functions of An example of a general, layered Link 16 and VDL-3 to the ISO layers. In doing communication architecture is the 7-layer this, it became apparent that Link 16 and model of the International Standards CADLs of interest have many fundamental Organization (ISO). This model is well known differences. Link 16 employs an L-Band, 3 and has been applied successfully. MHz-bandwidth, fast-frequency-hopping, AJ- A tenet of layering is to partition the coded, multi-pulse waveform with encrypted implementation of functions so that each self- messages. VDL-3 is a VHF, 25 kHz-channel, contained physical entity within a system non-hopping, non-AJ, multi-mode, waveform realizes only functions within the same layer of with un-encrypted messages. The time slot and the architecture. An example is when a radio coding structures of the two schemes are very contains only the hardware and software different. Furthermore, the ground necessary for performing modulation/ infrastructure for interconnecting the two demodulation and coding/decoding associated systems does not exist. This does not bode with the physical layer and data link layer, well if Link 16 is to accomplish all the respectively, of the OSI model. The functionality of the CADLs becoming required JTIDS/MIDS radios (which are contained in by the FAA and civil aviation authorities the terminals) already follow that precept in (CAAs). There are too many practical hurdles part. to overcome that hinder the cost-effective integration of these waveforms. This answers However, in general, the Link 16 the first question of Section 1. system does not have a full layered architecture because the tenet of layering stated above is not always followed. First, portions of the network A Potentially Attractive Approach to and cryptographic management functions Accommodating Link 16 and CADLs reside within the message signal processor of Instead of attempting to have Link 16 the “radio”.
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