ENRI Int. Workshop on ATM/CNS. Tokyo, Japan. (EIWAC 2010)[EN­105] Evaluation Results of Airport Surface Multilateration(EIWAC 2010)+H. Miyazaki*, T. Koga**, E. Ueda*, Y. Kakubari*, S. Nihei**Communication, Navigation and Surveillance Department**Airborne System Technology Department
Electronic Navigation Research Institute (ENRI)
Tokyo, Japanhiro@enri.go.jp

Abstract: The Multilateration (MLAT) is a new surveillance system which has been introduced worldwide for air trafficcontrol. Electronic Navigation Research Institute has conducted evaluation tests of MLAT by using an evaluation system atsome Japanese major airports. (1) This paper describes evaluation results of MLAT for airport surface surveillance
conducted at Kansai International airport. The evaluation results indicated that performance satisfied requirement values atalmost area of the airport. A main point of this paper is to share our experiences obtained from the evaluation results withthe lessons learned from the evaluation.
Keywords: Airport Surface Surveillance, Multilateration
1. INTRODUCTION

2. Overview of MLAT

Air traffic controllers have usually usedconventional Surface Movement Radar (SMR) for groundcontrol. However, the SMR has some problems, such as
no display of identification data, performance degradation
in bad weather condition, and blind area by construction.

Figure 1 represents a conceptual figure of MLAT
positioning. MLAT detects SSR “squitter” signals (2)transmitted from aircraft transponder by ground Receiver
Units (RUs), and measures the aircraft position by using
TDOA technique. This means, the time differences ofarrival among ground RUs are transformed to the distancedifferences between the aircraft and RUs. Then the aircraft
position is fixed as the intersection of the two hyperboliclines.

On the other hand, the Multilateration (MLAT) is a
new surveillance system which is capable of resolving theSMR problems. Therefore, it is expected that surface
surveillance system can achieve advanced functions andhigher performance by operating MLAT in combination
with SMR. From this reason, Japan Civil Aviation Bureau
decided to introduce Multilateration system to someJapanese airports.

Main advantages of MLAT are as follows; displayof identification information on radar screen, noperformance degradation in bad weather condition,complement to SMR blind area, and no additional
equipment to aircraft.

In order to achieve high performance in MLAT,
one of important factors is to select appropriate antenna
installation positions based on the airport layout. However,Kansai international airport (Kansai A/P) has specificrestrictions for antenna installation positions. Therefore,
Electronic Navigation Research Institute (ENRI)
conducted evaluation tests of MLAT by using anevaluation system at Kansai international airport. Main
purposes of the evaluation are to verify performances of
MLAT and to propose the appropriate antenna allocation
based on the test results.

TbTa
RU ABTdTc

This paper describes test results of the evaluation
at Kansai international airport. In addition, causes ofperformance degradation and their mitigation means arealso described in this paper.

CTd - TaTc - Tb

DFigure 1 Conceptual figure of MLAT positioning

41

Position accuracy of MLAT mainly depends on
precision of signal detection time and positional relation
among the aircraft and RUs, which is GDOP (GeometricalDilution of Precision). The GDOP becomes fine if RUs
surround the aircraft. Also precise time synchronization
among RUs is important, because MLAT measuresaircraft position by TDOA.

4. Kansai International Airport
Kansai A/P is a main international airport for west
part of Japan and exists in Osaka prefecture, actually on
the Osaka bay. Figure 3 represents location of Kansai A/P.
Figure 4 represents overview of the airport. There are two
runways and a sophisticated terminal building at theairport. Figure 5 represents a picture of the terminalbuilding. This terminal building was designed by a famousarchitect.

On the other hand, one of main causes ofperformance degradation is signal corruption by multipath.
It is highly required to avoid the multipath, because it
brings undetected signal or false detection. From above
facts, it is important to select the antenna layout andantenna positions appropriately based on the airport layout
and the signal environment.

Osaka

3. Evaluation SystemTokyo

Figure 2 represents system architecture of theevaluation system. The evaluation system consists of RUs,
Reference Transmitter (RefT), and Central Processing
Station (CPS). The RU detects SSR signal and transfers
the CPS signal information with detection time as target
reports. There are two types of RU. One is Receiver only(Ro); another one is Receiver/Transmitter (R/T). R/Tinterrogates aircraft to get additional information(Identification, Altitude) and to measure ranges between
R/T and aircraft for selecting the best solution. The RefTtransmits squitters for time synchronization among RUs
and for monitoring of the whole system. And the CPS
calculates target positions from target reports including
detection time and conducts tracking for updating target
positions.

KobeOsakaKansai A/PFigure 3 Location of Kansai A/PCentral Processing StationLANFigure 4 Overview of the airport.

Receiver Unit
1Reference
Transmitter 1

Receiver Unit
NReference
Transmitter NFigure 2 System architecture of the evaluation system

Figure 5 picture of the terminal building

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ENRI Int. Workshop on ATM/CNS. Tokyo, Japan. (EIWAC 2010)
5.3 Antenna Installations
Based on our concept and the specific restrictions,
we designed the antenna layout for Kansai A/P. Figure 6represents the antenna layout of the evaluation system.
The evaluation system consists of 13 Ro units, 5 RT units,
and one RefT. Figure 7 shows pictures of some antenna
installations. We installed antennas on existing facilities,
such as ILS middle marker, glide slope, A/G radio tower,
and roof of Cargo building. 2 antennas were installed on
top of ATC tower. Top of ATC tower is the most ideal
place, due to taking fine line-of-sight to whole airport.

5. Antenna Layout
5.1 Concept
As mentioned above, antenna layout is mostimportant to achieve good performance in MLAT. On theother hand, one of main causes of performancedegradation is signal corruption by multipath. To resolve
this problem, it is typically effective to put antennas asmuch as higher. In addition, high installation cost is also
big problem to introduce MLAT system. This problem
inhibits installing antennas to ideal place. From thesematters, our concept is to install antennas on existing
facility, as much as possible. Furthermore, we keep anumber of antennas as low as possible.
5.2 Specific Restrictions
There are specific restrictions for antenna
installation at Kansai A/P. As mentioned above, Kansai
A/P is surrounded on all four sides by sea. So it is difficult
to install antennas widely around the airport. This means
antenna height is restricted by the regulation of transition
surface. This is a strong limitation for MLAT to achieve
high performance at runway/taxiway area. In addition, it isrestricted to install antennas on the roof of the terminalbuilding due to structural problem. This is a strong
limitation for MLAT to achieve high performance atterminal apron area. From these restrictions, some ideas
were required to select the antenna installation positions.

(a)ILS Middle marker(b) A/G radio tower(C) ILS Glide slope (d) Cargo building

B runway
ATC tower

J3 taxiway

Terminal building

CargoA runway
Ro：13units(e) ATC tower

Figure 7 Antenna installations

R/T：5units
Figure 6 Antenna layout of the evaluation system

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RefT：1unit6.2 Test Results
Evaluation tests were conducted from September toDecember 2009. Figure 9 represents test tracks withperformance values at each runway/taxiway areas. Redlines and blue lines mean tracks by MLAT and KinematicGPS, respectively. It was confirmed that the performanceat runway/taxiway areas satisfied the requirement values.

6. Evaluation Tests
6.1 Evaluation Method
The tests were conducted by using a test vehicle
equipping a transponder. Figure 8 shows a picture of thetest vehicle. Evaluation items are position accuracy anddetection rate. European standard (3) was used as theperformance requirement. Table 1 shows requirement
values for position accuracy and detection rate. Kinematic
GPS data was used as reference points to calculate position
accuracy.

Transponder
AntennaFigure 10 and Figure 11 represent test tracks withperformance values at cargo area and terminal building
area, respectively. It was confirmed that performancevalues satisfied performance requirements at almost apron
area. However, certain area has not yet satisfied therequirement values. main cause of this performancedegradation was signal corruption by multipath. This area
where the performance degradation occurred was mostdifficult area for signal environment.

2m

The picture within figure 11 shows the mostdifficult area. This area is surrounded on all four sides bybuilding. In order to improve performance in such difficult
area, ENRI has developed advanced techniques for signal
detection and processing. The advanced techniques include
to apply sophisticated pulse detection methods and bit
demodulation methods that are effective against corruption
by multipath,

Figure 8 Picture of the test van
Table 1 requirement values for accuracy and detection rate

Position
Accuracy

Detection
Rate

Runway/Taxiway

7.5m

99.9% (2sec)

Apron (Stand)

20m

99.9% (5sec)

Area

6.3 The Lessons Learned from the Evaluation
An apron area where is surrounded on all four sides
by building is most difficult area to achieve goodperformance. In order to improve performance in suchdifficult area, some advanced techniques are required forsignal detection and signal processing.

B runway area
J3 taxiway area
Accuracy:6.5m
Detectin:100%

Accuracy:6.8m
Detectin:100%

Accuracy:6.3m
Detectin:100%

A runway area

Figure 9 Test tracks with performance values at each runway/taxiway areas

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ENRI Int. Workshop on ATM/CNS. Tokyo, Japan. (EIWAC 2010)

Accuracy:15m
Detectin:100%
Accuracy:13m
Detectin:100%

Accuracy:17m
Detectin:100%

Accuracy:9.6m
Detectin:100%

Accuracy:13m
Detectin:100%

Figure 10 Test tracks with performance values at cargo area

Accuracy:5.9m
Detectin:100%

Accuracy:11m
Detectin:100%
Accuracy:57m
Detectin:41%

Accuracy:14m
Detectin:100%
Accuracy:6.3m
Detectin:100%

Accuracy:6.4m
Detectin:100%
Accuracy:6.4m
Detectin:100%

Accuracy:6.7m
Detectin:100%

Performance
Degradation
The Most difficult area

Figure 11 Test tracks with performance values at terminal building area45

7. Conclusion
This paper described evaluation results of MLAT
conducted at Kansai A/P. MLAT is an advanced
surveillance system which is capable of improving
functions and performance of airport surface surveillance.
It was confirmed in the evaluation tests that performancevalues satisfied performance requirements to almost areaof the airport. Actually, there are some restrictions for
installing antennas to airports. And the restrictions bringperformance degradation. In order to avoid performancedegradation, the most important factor is to select antennalayout appropriately. From these matters, it is consideredthat our lessons learned from the evaluation are effective.
MLAT operation at Kansai A/P will start next year.
8. ACKNOWLEDGMENTS
The evaluation at Kansai A/P was commissioned
by Japan civil Aviation Bureau.
9. REFERENCES[1] Miyazaki, et al.: Evaluation Results of Multilateration

at Narita international airport, IAIN 2009, November
2009.
[2] ICAO: Aeronautical Telecommunications ANNEX 10

Volume IV, Fourth Edition, July 2007.
[3] EUROCAE:

Minimum Operational Performance
Specification for Mode S Multilateration Systems for
Use in A-SMGCS, ED-117, November 2003.

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