University of BrasíliaLaboratory of Array Signal Processing

1

Improved Landing Radio Altimeter for Unmanned Aerial Vehicles based on an Antenna Array

Ronaldo S. Ferreira Júnior, Marco A. M. Marinho, Kefei Liu, João Paulo C. Lustosa da Costa, Arthur V. Amaral , and Hing Cheung So

University of Brasília (UnB)Department of Electrical Engineering (ENE)Laboratory of Array Signal Processing

PO Box 4386Zip Code 70.919-970, Brasília - DF

University of BrasíliaLaboratory of Array Signal Processing

2

Outline

Motivation

Traditional radio altimeter

Antenna array based radio altimeter

Simulation results

Conclusions

University of BrasíliaLaboratory of Array Signal Processing

3

Outline

Motivation

Traditional radio altimeter

Antenna array based radio altimeter

Simulation results

Conclusions

University of BrasíliaLaboratory of Array Signal Processing

4

Motivation (1)

ApplicationsÞ Landing and approaching of Unmanned Aerial VehiclesÞ Detect dangerous obstaclesÞ Manned operations where life can be put in risk

DrawbackÞ Only the main power component reflected component

• Multipath components are not taken into account Antenna array based Radio Altimeter

Þ The multipath components are estimated.Þ The ground can be mapped.

University of BrasíliaLaboratory of Array Signal Processing

5

Motivation (2)

Example with 3 MPCs

Which one is detected?

University of BrasíliaLaboratory of Array Signal Processing

6

Motivation (3)

By detecting only the red component:Þ A crash is prevented.

How to detect all multipath components?Þ By detecting the Direction of Arrival (DoA) and the Time

Delay of Arrival (TDoA) of the MPCs

University of BrasíliaLaboratory of Array Signal Processing

7

Motivation (4)

Solution for Direction of Arrival (DOA) estimation Another candidate solution: Rotating antenna

Þ Advantage• DOA detection according to the antenna position

Þ Drawback:• Heavy weighted, large sized and slow scanning

Proposed solution: Antenna arraysÞ Advantages:

• Compact, power saving and light weightedÞ Drawback:

• Complex software and complex hardware

University of BrasíliaLaboratory of Array Signal Processing

8

Outline

Motivation

Traditional radio altimeter

Antenna array based radio altimeter

Simulation results

Conclusions

University of BrasíliaLaboratory of Array Signal Processing

9

Traditional Radio Altimeter (1)

General informationÞ Frequency Modulated–Continuous Wave (FM-CW) radio

altimeterÞ Uses saw-tooth or triangle wave as the modulating signalÞ Altitude-to-frequency conversion

• the time-delayed wave mixed with the transmitted wave

Þ Not possible to distinguish the MPCs

University of BrasíliaLaboratory of Array Signal Processing

10

Simplified block diagram of a traditional radio altimeter for UAVs

Traditional Radio Altimeter (2)

University of BrasíliaLaboratory of Array Signal Processing

11

Outline

Motivation

Traditional radio altimeter

Antenna array based radio altimeter

Simulation results

Conclusions

University of BrasíliaLaboratory of Array Signal Processing

12

Simplified block diagram of an antenna array based radio altimeter

Antenna Array based Radio Altimeter (1)

University of BrasíliaLaboratory of Array Signal Processing

13

Antenna Array based Radio Altimeter (2)

Candidate solutions for the signal processing block

Þ MUSIC• High-resolution • More computational effort

Þ ESPRIT• Closed-form solution • Worse resolution than MUSIC • Array with shift invariance structure

University of BrasíliaLaboratory of Array Signal Processing

14

Antenna Array based Radio Altimeter (3)

[1]: J. P. C. L. da Costa, A. Thakre, F. Roemer, and M. Haardt, “Comparison of model order selection techniques for high-resolution parameter estimation algorithms”, in. Proc. 54 th International Scientific Colloquium (IWK), Ilmenau, Germany, Sept. 2009.

The model order d can be estimated based on [1].

We consider it as known.

Matrix data model

University of BrasíliaLaboratory of Array Signal Processing

15

Antenna Array based Radio Altimeter (4)

Selection matrices and Þ To estimate the spatial frequencies (ESPRIT)

University of BrasíliaLaboratory of Array Signal Processing

Estimation of Signal Parameters via Rotation Invariance Techniques

ESPRIT

16

The steering matrix A and the first d eigenvectors U of the covariance matrix generate the same subspace

Note that Us is related to the low-rank approximation.

Spatial frequencies

Antenna Array based Radio Altimeter (5)

University of BrasíliaLaboratory of Array Signal Processing

17

Outline

Motivation

Traditional radio altimeter

Antenna array based radio altimeter

Simulation results

Conclusions

University of BrasíliaLaboratory of Array Signal Processing

18

Simulation Results (1)

University of BrasíliaLaboratory of Array Signal Processing

19

Simulation Results (2)

University of BrasíliaLaboratory of Array Signal Processing

20

Simulation Results (3)

University of BrasíliaLaboratory of Array Signal Processing

21

Outline

Motivation

Traditional radio altimeter

Antenna array based radio altimeter

Simulation results

Conclusions

University of BrasíliaLaboratory of Array Signal Processing

22

Conclusions

The antenna array based radio altimeterÞ Ground mapping and imagingÞ Ground inclination and obstacle detectionÞ Electronic receiving lobe sweep Þ Light weight and small sized compared to a mechanical

scanning radar

University of BrasíliaLaboratory of Array Signal Processing

23

Thank you for your attention!

Prof. Dr.-Ing. João Paulo C. Lustosa da Costa

University of Brasília (UnB)Department of Electrical Engineering (ENE)Laboratory of Array Signal Processing

PO Box 4386Zip Code 70.919-970, Brasília – DF

E-mail: joaopaulo.dacosta@ene.unb.br