CANDIDATE REQUIREMENTS FOR MULTILATERATION AND ADS-B SYSTEMS TO SERVE AS ALTERNATIVES TO SECONDARY RADAR PatrickJ. Martone, US DOT Volpe Center, Cambridge, MA George E. Tucker, NASA Ames Research Center, Moffett Field, CA Abstract the ATCBI-6 secondary surveillance radar. These criteria were developed expressly for this The US Department of Transportation (DOT) evaluation. Volpe Center is currently involved in a National Aeronautics and Space Administration (NASA) Due to differences in the technologies, project to configure, deploy, and evaluate the comparing HITS and ATCBI-6 presents challenges. capabilities of a transponder multilateration and For example, radar measures target range and Automatic Dependent Surveillance-Broadcast azimuth, while multilateration measures time of (ADS-B) system that will perform aircraft tracking arrivals (TOAs) and provides a rectangular position, in the Gulf of Mexico offshore area. The and ADS-B utilizes GPS position. Assuming that Helicopter In-flight Tracking System (HITS) is the ground sites have the same coverage (which is being assessed for use in an offshore area where typically not the case), surveillance of a given several hundred petroleum industry helicopter volume using multilateration requires roughly three flights occur daily, and where there is currently times as many sites as SSR. On the other hand, little secondary surveillance radar coverage. There radar target report update rates are limited by the are also over-flights by aircraft to/from Mexico and radar antenna scan period (5 or 10 seconds), while CentraVSouth America. updates as frequent as once per second are achievable with multilateration. In contrast to the Although multilateration has been extensively requirements differences, testing procedures for tested for airport surface applications, there is SSR and multilateratiodADS-B are quite similar. limited experience in the tracking of airborne aircraft. The HITS project provides an opportunity The baseline radar standards upon which the to evaluate multilateration and ADS-B technologies HITS evaluation is based are those for the ATCBI- as potential alternatives to established secondary 6, as documented in [l]. In order to perform the surveillance radar (SSR) as air traffic control evaluation, many of the criteria listed in the surveillance systems. The project is described in ATCBI-6 specification are extracted from Section more detail in a separate paper [9]. 3.2, and corresponding criteria are developed for the HITS multilateration and ADS-B capabilities. This paper describes (1) the derivation of In many cases, the parameters have,been trans- multilateration and ADS-B system requirements, in formed to account for the technology differences order for these systems to provide equivalent capa- among the three technologies. In brief: bility to the Air Traffic Control Beacon Interrogator Model 6 (ATCBI-6) SSR system now being install- SSR measures aircraft range and azimuth ed in the National Airspace System; and (2) pro- relative to a single ground location; a ground- cedures being implemented to test the HITS multi- interrogatiordaircraft-transponder-response IateratiodADS-B systems against the requirements. methodology is employed; and ground sites have mechanically-scanned high-gain directional antennas. Evaluation Requirements Multilateration measures the times-of-arrival This section delineates the requirements - at three or more ground stations of both both capabilities and numerical parametershalues unelicited (squittered) or elicited transponder -that will be used to evaluate whether the HITS signals; aircraft location is computed in multilateration and ADS-B capabilities are rectangular coordinates with respect to the equivalent in function andperformance to those for geographic reference system used to define U.S. Government work not protected by U.S. Copyright. 7.C.2-1 the ground station locations; and ground sites are contained in FAA Order 1010.5 1.A [3], devel- have omni-directional low-gain stationary oped for the Identification Friend or Foe (IFF) Mark antennas. X system), FAA Order 6365.1A ([4], developed for 0 ADS-B avionics obtain aircraft position and Mode S), and International Civil Aviation Organ- velocity from an onboard GPS receiver, and ization (ICAO) Annex 10 [5]. ICAO Annex 10 has squitter this information to one or more precedence over FAA Order 63 65.1 A when con- ground stations over a digital data link; and flicts arise. ground sites use omni-directional low-gain Table 1 compares many of the ATCBI-6 stationary antennas. requirements of [ 11 with evaluation requirements In addition to the ATCBI-6 specification [ 11, developed below for the HITS multilateration and several documents were consulted in developing the ADS-B capabilities. Italicized numbers in the criteria herein. The Airport Surface Detection headings for entries in the first column refer to Equipment Model X (ASDE-X) specification [2] is sections in the ATCBI-6 specification. The para- the standard for multilateratiod ADS-B systems graphs that follow address some, but not all, of the designed for airport surface surveillance. The primary requirements included in the table, in primary standards by which all Federal Aviation greater detail, along with the rational used to Administration (FAA) beacon radars are designed develop them. Table 1. Summ ~ryof HITS Evaluation Criteria ATCBI-6 HITS (Heading Number = Ref. 1 Section Number) I Multilateration ADS-B 3.1.1 Coverage Volume Altiude: 0 to 100,000 feet AGL Elevation Angle: Horizon to 40 deg Slant Range: 125 and 250 nmi Azimuth Angle: 360 deg I 3.1.2 Probability of Target Detection and Probability of False Target Detection 99% detection of all targets; ATCRBS false target detected 0.1%; No false Mode S targets Processing for a minimum of 64 non-fixed and 64 fixed reflectors 3.1.5 Interrogation Modes 0.2 Hz average rate Same One target report per scan I 3.1.3Accuracy 3.2.4 Target Plot Report Position Accuracy Range bias: f30 ft; Bias: k30 R Not applicable. Range jitter: 25 ft rms; Jitter: 25 R rms Azimuth bias: f0.033 deg; Azimuth jitter: 0.066 deg rms I 3.1.4 Target Resolution Target Resolution 2 ATCRBS targets with <I.7 nmi slant range 2 ATCRBS targets with cl.7 nmi slant range Two closely spaced separation: separation: Mode S targets 1.2 deg az c 2.4 deg, detected 98%; Detected 98%; resolvable 100% Az 1.2 deg, detected 90%; Correct codes available 90% Correct codes available 90% All other target combinations resolvable 100% Two closely spaced Mode S targets resolvable 100% 7.C.2-2 ATCBI-6 (Heading Number = Ref. 1 Section Number) Multilateration ADS-B 3.1.5 Interrogation Modes Interrogate and process replies from ATCRBS and Same requirement. I Not applicable. Mode S targets. I 3.1.6 Multiple ATCRBS Reply Processing 3.2.7 Multiple A TCRBS Reply Processing Decode at least four replies simultaneously. Same requirement. Not applicable. 3. I.7 Code Reliability and Validity Modes 31A codes correct 99%; Correct Mode 31A codes validated 99%; Incorrect Mode 3/A codes validated 1%; Mode S ID correct 99.9% 3.1.8 Altitude Report Reliability & Validation Altitude Report Reliabilityand Validation Mode C code correct 99%; Mode C code correct 99%; ADS-B altitude Correct Mode C code validated 95%; Correct code validated 95%; correct 99.9% Incorrect Mode C code validated 1% Incorrect code validated 1% Not applicable Not applicable ADS-B nav correct I 99.9% 3.1.9 Spectrum / PRF Spectrum / PRF Max PRF 300 Hz (3 mode interlace); ATCRBS waveform and spectrum per FAA Order ATCRBS waveform & spectrum per FAA Order 1010.51A Section 2.4; 1010.51A Section 2.4; Mode S waveform and spectrum per FAA Order Mode S waveform & spectrum per FAA Order 6365.1A. Section 2.4.1 6365.1A, Section 2.4.1 3.1.10 Target Capacity/Overload Processing Target Capacity Process returns for Each RU must process messages from 1400 transponders (all types) 1400 beacon targets I360 degree scan; in 5 sec Peak 32 beacon targets 12.4 deg wedge; Full HITS must process: Primary radar reports (standards are not relevant to Average Itarget per 35 nmi2 in entire coverage area HITS) Peak 1 target per 10 nmi2in 1% of coverage area 3.1.10 Target Capacity/Overload Processing Overload processing Detect overload condition and report to remote system Detect overload condition and report via CPS. Targets discriminately control terminal and the National Airspace System and dynamically reduced for optimum operational capability Infrastructure Management System (NIMS). Targets discriminately and dynamically reduced for optimum operational capability 3.1.11 Data Timeliness Data Latency For terminal use, detect, process and display Detect, process and output transponder replies within 0.450 sec of transponder replies between min 5/64 and max 3132 of each transponder's transmission time. a scan period (approx. 0.375 sec min and 0.450 sec mad 3.2.IO. 7 Beacon Pamt RU Clock Calibration System shall include a beacon parrot transponder Multilateration subsystem shall include a Not applicable capability to be located at two fixed locations means to synchronize the time of arrival clocks of the RUs 3.2.12 System Calibration Continuous Certification Shall have beacon transponders within coverage Continuously certify that the multilateration I Similar criterion volume for automatic subsystem is operating properly North mark alignment (true or magnetic) I Calibration of range and azimuth measurements 7.C.2-3 Coverage Volume least one RT which interrogates transponders ATCBI-6 ([ 11, Subsection 3.1.1, “Coverage that comply with [6] and [7]. Volume”) - The ATCBI-6 shall provide surveil- The “geometry subcriterion” (first item) is lance coverage for the area defined as follows: taken from the ASDE-X specification ([2], Sub- a. an altitude of 0 to 100,000 feet above ground section 3.3.5), and is similar to requirements for level (AGL) as limited by the system most area navigation systems.