Analysis of UAT performance in the terminal environment in ...



Analysis of UAT Performance in the Terminal Environment in Core Europe 2015

Larry Bachman, JHU-APL

Mike Castle, JHU-APL

|SUMMARY |

|This working paper examines the performance of the UAT ADS-B data link in the Core Europe 2015 traffic scenario (CE2015), in the |

|terminal environment at Brussels airport in the presence of a DME/TACAN at the airport operating at a frequency of 979 MHz. Three |

|situations are analyzed: air-to-ground reception of UAT ADS-B transmissions; two air transport aircraft on a final parallel |

|approach (air-to-air); and aircraft-to-aircraft reception of UAT transmissions on the airport surface. |

Introduction

This working paper discusses the performance of the UAT ADS-B data link in the Brussels airport terminal region in the Core Europe 2015 traffic scenario (CE2015). This is intended to be a worst case analysis of the state in which all aircraft are equipped with UAT transmitters. Three situations will be analyzed:

• Air-to-ground reception performance will be examined and compared with current air traffic requirements.

• UAT performance between two air transport aircraft on final parallel approach will be evaluated.

• Performance of aircraft-to-aircraft communications on the airport surface will be investigated.

The assumptions for this worst-case environment are listed below in section 2, followed by a description of the results for each of the three situations in the following sections.

Assumptions

The following assumptions were used in this analysis:

• Unless otherwise stated, the baseline for all assumptions is to be found in the RTCA UAT MOPS (DO-282), specifically the modeling and simulation sections of Appendix K in that document.

• The ground station antenna gain is omni-directional in azimuth (0dB), and the elevation gain is based on measured values of a TACAN antenna.

• The sensitivity of the ground station receiver is -96 dB at the antenna, and a 2 dB cable loss is assumed.

• The DME/TACAN is located at the site of a current DME on the airport surface at a distance of 2 NM from the center, where the UAT ground station is assumed to be. The DME location is around 0.75 NM from the end of a runway.

• All aircraft and ground vehicles are assumed to be UAT-equipped and transmitting.

• Link 16 Baseline B, co-site (in aircraft), and the appropriate DME interference are all assumed to be present.

Air-to-Ground Performance

Approximately 1000 aircraft are in line of sight of the ground receiver in this scenario, so all of these aircraft provided UAT self-interference to the probe aircraft that were used to evaluate the air-to-ground performance. Since all aircraft are assumed to be equipped with UAT, it was assumed that the ground station was not transmitting during the ADS-B segment of the UAT frame. The probe aircraft transmitted at the usual rate of one UAT message per second, in a Message Start Opportunity (MSO) chosen randomly each second. Since each UAT message contains the information for a state vector update, each successfully received message provides a state vector update. The 95-95 update time interval was calculated for each 10 NM bin for each case that was simulated. Since it was established in DO-282 that there was little altitude dependence in air-to-ground performance, each aircraft equipage class was run at a single altitude appropriate for that class.

1 Effect of Closely Located DME/TACAN

Error! Reference source not found.1-5 show the air-ground performance for all levels of UAT equipped aircraft as received by an omni-directional antenna at the ground station. Some of the curves indicate that they include the effects of a nearby DME/TACAN on reception. The location of the DME/TACAN transmitted is 2 NM from the UAT receiver, corresponding to the current location of a DME at the Brussels airport. The curve labeled “No TACAN” represents the baseline case, where there is no co-located DME/TACAN at the Brussels airport. The other curves show the effect of inserting an adjacent channel DME/TACAN and increasing the power from 100 W to 10 kW, while also increasing the number of pulse pairs per second as the interferer transforms from DME to TACAN. The Figures show that increasing the power and pulse rate of the nearby DME/TACAN results in decreasing levels of performance. The stair-step black curve represents current approximate update rates as provided by radars and seen by air traffic controllers.

[pic]

Figure 1 - 95th Percentile State Vector Update Times vs. Range in CE 2015 for DME/TAC Configurations at Brussels for A3 Transmissions

[pic]

Figure 2 - 95th Percentile State Vector Update Times vs. Range in CE 2015 for DME/TAC Configurations at Brussels for A2 Transmissions

[pic]

Figure 3 - 95th Percentile State Vector Update Times vs. Range in CE 2015 for DME/TAC Configurations at Brussels for A1H Transmissions

[pic]

Figure 4 - 95th Percentile State Vector Update Times vs. Range in CE 2015 for DME/TAC Configurations at Brussels for A1L Transmissions

[pic]

Figure 5 - 95th Percentile State Vector Update Times vs. Range in CE 2015 for DME/TAC Configurations at Brussels for A0 Transmissions

Eurocontrol has specified that it feels that the radar update rate requirement should be met to 150 NM. These Figures show that, even for the baseline case of no DME/TACAN present, an omni-directional antenna may not provide adequate reception for some classes of aircraft. The next section will provide an analysis of the effect of installing a three-sector antenna instead of an omni-directional antenna.

2 Effect of Three-Sector Antenna

As a result of the performance analysis of section 3.1, identical simulation runs were made with a single modification, the use of a three-sector antenna for ground reception, rather than an omni-directional antenna. The results of this series of simulations are shown in Figures 6-10 below. The Figures only show the results for the modified baseline case and the case with the 10 kW TACAN at two miles from the ground station, which is the worst case DME/TACAN. All of the aircraft equipage classes meet the ADS-B update requirements to at least 150 NM. Therefore, in a high-density UAT environment, especially in the presence of an adjacent channel DME/TACAN, it may be necessary to utilize a three-sector antenna in order to meet the update requirements.

[pic]

Figure 6 – 95th Percentile State Vector Update Times vs. Range for a 3-sector Antenna in CE 2015 at Brussels for A3 Transmissions

[pic]

Figure 7 - 95th Percentile State Vector Update Times vs. Range for a 3-sector Antenna in CE 2015 at Brussels for A2 Transmissions

[pic]

Figure 8 - 95th Percentile State Vector Update Times vs. Range for a 3-sector Antenna in CE 2015 at Brussels for A1H Transmissions

[pic]

Figure 9 - 95th Percentile State Vector Update Times vs. Range for a 3-sector Antenna in CE 2015 at Brussels for A1L Transmissions

[pic]

Figure 10 - 95th Percentile State Vector Update Times vs. Range for a 3-sector Antenna in CE 2015 at Brussels for A0 Transmissions

Two Air Transport Aircraft on Final Parallel Approach

Simulations were run to investigate the effect of a high power TACAN at the airport on air-to-air ADS-B performance for two air transport aircraft on final parallel approach. The scenario is the same as for the air-ground analysis of section 3, with a 10 kW TACAN located at 2 NM from the airport, and the aircraft passing right over the TACAN in their approach path. The two aircraft were assumed to be 2500’ apart, traveling at 150 knots. The starting point for the approach was 9.5 NM from the center of the airport at an altitude of 3000’, and the ending point was 0.5 NM away at 200’. This corresponds to a glide slope of 3o.

Error! Reference source not found.11 shows both the 95th and 99th percentile update times for the closely spaced parallel approach scenario into Brussels airport in Core Europe 2015 in the presence of a 10 kW TACAN. These plots indicate that the update times are essentially unaffected by the presence of the TACAN, and that the update rate is around 1.7 seconds for closely spaced parallel approaches. A check of this result for the case where the aircraft are separated by 4000’ (rather than 2500’) showed nearly identical results. The dark line at 2 seconds on the Figure indicates the preliminary estimate of the requirement for this application as specified in the ASA MASPS, recently approved at the SC-186 plenary at RTCA.

[pic]

Figure 111 - State Vector Update Times between Two A3 Aircraft on Parallel Approach into Brussels in the Presence of a 10 kW TACAN

Aircraft-to-Aircraft on the Airport Surface

Direct aircraft-to-aircraft ADS-B link performance on the surface of the Brussels airport in Core Europe 2015 in the presence of a 10 kW adjacent channel TACAN is the subject of this section. The receiving aircraft was placed at the end of the runway nearest the TACAN, a distance of 0.7 NM, while the transmitting aircraft was located at three ranges from the receiver: 1, 3, and 5 NM. The metric that was used in the analysis is the standard 95-95 update time (T95). Results were calculated for both the case with no multipath fading on the signal, and a worst-case severe horizontal multipath degradation based on the MITRE model developed in conjunction with the work on DO-282 and described in Appendix M of the TLAT report. The anticipated performance of the UAT datalink on the surface is expected to fall somewhere between these two extremes.

Below in Table 1 and

Table 2, the values in dB for the worst-case fading due to multipath on the surface, based on the MITRE model, are shown in tabular form. Fading values are shown for each of the three ranges used in the simulation for each combination of transmitter and receiver antenna (top and bottom). These values were added to each signal incident on the receiving aircraft on the airport surface.

Table 1 - Worst-Case Signal Loss in dB due to Multipath Added to Received Signal for A3/A2 Receivers on the Surface

|Range (NM) ( |A3/A2 Transmitters |A1/ A0 Transmitters |

| |1 |3 |5 |1 |3 |5 |

|Top-Top |0 |-9 |-19 |-4 |-16 |-24 |

|T-B / B-T |-4 |-16 |-24 |-10 |-21 |-31 |

|Bottom-Bottom |-9 |-21 |-29 |-18 |-30 |-41 |

Table 2 -Worst-Case Signal Loss in dB due to Multipath Added to Received Signal for A1/A0 Receivers on the Surface

|Range (NM) ( |A3/A2 Transmitters |A1/ A0 Transmitters |

| |1 |3 |5 |1 |3 |5 |

|Top-Top |-7 |-17 |-27 |-12 |-25 |-36 |

|T-B / B-T |-10 |-21 |-31 |-18 |-30 |-41 |

|Bottom-Bottom |-18 |-30 |-41 |-23 |-35 |-44 |

Note that a DO-282 requirement (2.2.6.1.3) states that if the transmitting aircraft is determined to be in the ON-GROUND state (DO-282, Section 2.2.4.5.2.5.1), the top antenna is used to transmit. This will hold true for all transmitters except for the A0, which has no top antenna. Assumptions used in this analysis about the receive system for each type of aircraft equipage are as follows:

• A3 is the only equipage that has a 0.8 MHz filter. It also uses receiver diversity as specified in DO-282 in Section 2.2.8.1.

• The A2 receiver uses a 1.2 MHz filter and receiver diversity.

• The A1 receiver is typically a switched receiver, although when in the ON-GROUND state, only uses the top antenna for reception (DO-282 2.2.8.1) and transmission. The bottom antenna does not contribute to the reception of messages on the surface.

• The A0 receiver has one antenna, which is on the bottom of the aircraft.

In order to provide a baseline for comparison, Tables 3-6 show the results for the T95 times for the case of surface-to-surface aircraft UAT ADS-B performance in Core Europe 2015, with no multipath effects, both with and without a 10 kW TACAN present. In each data cell in the tables, the number on the top is the value of T95 with no TACAN included, and the number on the bottom is the value for T95 in the presence of a 10 kW TACAN at a distance of 0.7 NM from the receiver. Values for T95 are calculated for each type of aircraft receiver, for each of the three ranges, and each transmitter equipage (the results for A2 and A1H equipages are grouped together because these equipages are identical in terms of transmit power and antenna configuration). A dash is indicated when T95 could not be calculated due to insufficient data, indicating a very large value for T95.

Table 3 - T95 Surface-to-Surface Update Times for an A3 Receiver at Brussels in Core Europe 2015 (No Multipath)

|Range (NM) | |Transmitters |

| | |A3 |A2 / A1H |A1L |A0 |

|1 |No TAC |1.2 |1.2 |1.2 |1.2 |

| |TAC |1.2 |1.2 |1.2 |1.2 |

|3 |No TAC |1.2 |2.0 |2.0 |2.0 |

| |TAC |1.2 |2.0 |2.0 |2.1 |

|5 |No TAC |1.5 |2.0 |2.1 |2.1 |

| |TAC |1.9 |2.1 |2.1 |2.2 |

Table 4 - T95 Surface-to-Surface Update Times for an A2 Receiver at Brussels in Core Europe 2015 (No Multipath)

| Range (NM) | |Transmitters |

| | |A3 |A2 / A1H |A1L |A0 |

|1 |No TAC |1.2 |1.2 |1.2 |1.2 |

| |TAC |1.2 |1.2 |1.6 |1.7 |

|3 |No TAC |1.2 |1.8 |2.0 |1.9 |

| |TAC |1.2 |2.0 |2.0 |2.0 |

|5 |No TAC |1.2 |2.0 |2.0 |2.0 |

| |TAC |1.9 |2.0 |2.1 |2.1 |

Table 5 - T95 Surface-to-Surface Update Times for an A1 Receiver at Brussels in Core Europe 2015 (No Multipath)

|Range (NM) | |Transmitters |

| | |A3 |A2 / A1H |A1L |A0 |

|1 |No TAC |1.2 |1.2 |1.2 |1.2 |

| |TAC |1.2 |1.9 |2.0 |2.0 |

|3 |No TAC |1.2 |2.0 |2.0 |2.0 |

| |TAC |2.0 |2.1 |2.1 |2.1 |

|5 |No TAC |1.9 |2.1 |2.1 |2.1 |

| |TAC |2.0 |2.3 |2.5 |2.8 |

Table 6 - T95 Surface-to-Surface Update Times for an A0 Receiver at Brussels in Core Europe 2015 (No Multipath)

|Range (NM) | |Transmitters |

| | |A3 |A2 / A1H |A1L |A0 |

|1 |No TAC |1.2 |1.2 |1.2 |1.2 |

| |TAC |1.2 |1.7 |2.0 |2.0 |

|3 |No TAC |1.2 |2.0 |2.0 |2.0 |

| |TAC |1.9 |2.0 |2.1 |2.1 |

|5 |No TAC |1.6 |2.0 |2.1 |2.1 |

| |TAC |2.0 |2.1 |2.3 |2.6 |

The tables show that, in the absence of multipath, the presence of a 10 kW TACAN at close range (0.7 NM) does not appreciable affect the update times to be expected for surface-to-surface aircraft UAT ADS-B performance. The addition of the TACAN results in at most an increase in the update time of less than a second.

Tables 7-10 show the results for the same two basic cases (with and without the TACAN), with the addition of signal degradation due to the presence of severe horizontal multipath. The performance of UAT as a surface-to-surface system is expected to fall somewhere between the two multipath cases represented by Tables 3-6 as compared to Tables 7-10.

Table 7 - T95 Surface-to-Surface Update Times for an A3 Receiver at Brussels in Core Europe 2015 (Severe Horizontal Multipath)

|Range (NM) | |Transmitters |

| | |A3 |A2 / A1H |A1L |A0 |

|1 |No TAC |1.2 |1.2 |2.0 |2.0 |

| |TAC |1.2 |1.2 |2.0 |2.1 |

|3 |No TAC |2.0 |2.3 |5.2 |8.2 |

| |TAC |2.0 |3.0 |7.1 |15.5 |

|5 |No TAC |3.4 |7.6 |- |- |

| |TAC |4.4 |10.8 |- |- |

Table 8 - T95 Surface-to-Surface Update Times for an A2 Receiver at Brussels in Core Europe 2015 (Severe Horizontal Multipath)

|Range (NM) | |Transmitters |

| | |A3 |A2 / A1H |A1L |A0 |

|1 |No TAC |1.2 |1.2 |1.9 |2.0 |

| |TAC |1.2 |1.2 |2.0 |2.1 |

|3 |No TAC |1.8 |2.1 |4.9 |8.6 |

| |TAC |2.0 |2.8 |6.5 |18.5 |

|5 |No TAC |3.0 |6.9 |- |- |

| |TAC |3.9 |10.1 |- |- |

Table 9 - T95 Surface-to-Surface Update Times for an A1 Receiver at Brussels in Core Europe 2015 (Severe Horizontal Multipath)

|Range (NM) | |Transmitters |

| | |A3 |A2 / A1H |A1L |A0 |

|1 |No TAC |1.2 |1.7 |2.1 |2.7 |

| |TAC |1.5 |2.0 |2.8 |3.1 |

|3 |No TAC |2.1 |4.0 |115.5 |- |

| |TAC |2.9 |5.1 |148.6 |- |

|5 |No TAC |8.0 |- |- |- |

| |TAC |13.3 |- |- |- |

Table 10 - T95 Surface-to-Surface Update Times for an A0 Receiver at Brussels in Core Europe 2015 (Severe Horizontal Multipath)

|Range (NM) | |Transmitters |

| | |A3 |A2 / A1H |A1L |A0 |

|1 |No TAC |1.2 |1.3 |2.8 |3.1 |

| |TAC |1.4 |2.0 |3.1 |4.1 |

|3 |No TAC |2.4 |5.3 |- |- |

| |TAC |3.1 |6.9 |- |- |

|5 |No TAC |- |- |- |- |

| |TAC |- |- |- |- |

Tables 7-10 demonstrate that, in the presence of severe horizontal multipath, a nearby 10 kW TACAN can have a greater affect on surface-to-surface UAT ADS-B performance than when no multipath effects are present. For the severe multipath case, the update times may vary by more than for the no multipath case, depending on the aircraft equipage type and range between transmitter and receiver. The only requirement guidance that could be found is in the ASA MASPS, which places a 2 second update time requirement for surface probing applications. On first inspection, the results presented above do not appear to be affected by the presence of the TACAN; i.e., if the UAT ADS-B link meets the 2-second requirement at a particular range for the transmit-receive pair in one of the tables, the introduction of the TACAN does not appear to cause the system to fail to meet the requirement at that same range (if 2.1 seconds is allowed). This study provides a basis for examining the terminal environment and understanding the potential performance expectations and limitations for a high-density situation.

Summary

This analysis looked at the performance of the UAT ADS-B link in the presence of a 10 kW TACAN on the airport surface in three different situations:

• Air-to-ground performance: In a high-density UAT environment, it may be necessary to provide for a three-sector ground station receive antenna, in order to achieve radar-type update rates at the 95th percentile level out to 150 NM.

• Closely spaced parallel approach air-to-air: The presence of the TACAN does not appear to affect the air-to-air UAT ADS-B performance in the CSPA situation.

• Surface-to-surface: While the presence of the TACAN may affect aircraft-to-aircraft UAT ADS-B performance on the airport surface for certain aircraft equipage and range combinations, it does not appear for the cases examined that the TACAN causes a failure to meet the 2-second requirement for cases that are compliant in the absence of the TACAN.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download