A New Algorithm for Improving the Remote Sensing Data Transmission

over the LEO Satellite Channels

Ali Payandeh and Mohammad Reza Aref Applied Science Research Association (ASRA) Department of Electrical Engineering, K.N. Toosi University of TechnologyTehran, Iran

International Conference on Engineering Education (ICEE) Silesian University of Technology, Gliwice, PolandJuly 2005

Outline

• Introduction

• LEO Satellite Channel Modeling

• Problem Statement

• Proposed Scheme Structure

• Simulation Results

• Conclusions

Introduction• Remote sensing imagery produces large amounts of data that needs to

be reliably transmitted over a band-limited channel.

• Today’s performance requirements of real time on-board satellite communication systems are demanding lower consumption energy.

• During the data transmit in the communications field of view area, distance between the LEO satellite and ground station changes.

• We derive an adaptive data protection method, which is based on the modeling of the channel and compensation change of distance between satellite and ground station.

LEO Satellite Channel ModelingSNR in ground receiver’s input is calculated by:

is the satellite transmitter power, is the satellite transmitter antenna’s gain, is the ground station antenna’s gain, is the total noise power and is the total path losses

We use the following approximation equation for LEO satellite channel modeling:

NEASUMSAST PGLGPSNR

STP SAG

EAG

NP

SUML

)log(10sin)log(sin20 BRBAPSNR dBST

Problem Statement•The distance between satellite and ground station has a

considerable effect on performance of the communications system.

•The distance in the LEO satellite’s configuration changes continuously.

•For access to the desirable image’s quality, a pre-specified bit error probability usually is enough. If bit error rate reduces from the pre-specified value, received image’s quality in practical doesn’t change considerably.

•Therefore, designing the on-board data transmit system for the worst case of communications channel, concludes to a wasteful use of communication system resources.

•To overcome this problem, we propose a variable error-

correction coding scheme.

R0 R180

Ri Ri+90R90

Distance Between LEO Satellite and Ground Station

Proposed Scheme Structure• We use a variable block coding, which its bit protection can be

varied in accordance with the distance, so that the bit error probability is fixed at a pre-specified value .

• The design constraint is a given total received data .

• Bit error probability for a block code in the case of AGWN is given by:

.

)(ePb

. 0VV

),,( mindnk

)()(

))((2

1)(

min

0min

ePn

deP

NEdRerfceP

wb

bcw

• For the assumed , an appropriate approximation is:

• We obtain:

• If varies based on above equation with elevation angle, bit error probability doesn’t change in the whole of communicate séance.

• The problem is to calculate the transmission rate and power, subject to .

,

)(ePb

min0 dRN

E

c

b 21 ))2(( erfc

sin)log(sin20)log(10 minBCdRc

mindRc

0VV

• A tradeoff must be done between three parameters: (coding complexity), (consumption energy) and (bandwidth).

• Two special cases:

A. Constant and known:

B. Constant and known:

mindRc

STP

BR

cR

10)(

0

0

sin102

10

min

10

10)(sin

10)(

CA

cST

c

B

c

C

TR

VP

TR

VBR

Rd

mind

10)(

0

0

sin102

min

10

10

)(

10)(sin

10)(

CA

ST

T

c

BC

c

BRP

dtR

VBR

dR

Simulation Results• Since the error-correction code with continuous variation

isn’t discovered yet, we use a method with discrete variation in simulation.

• In this method, a lookup table of various error-correction codes is used. In each step, one appropriate error-correction code is selected from table based on value.

• For implementation the improved remote sensing data transmission system, we use the standard BCH codes.

mindRc

mindRc

mindRc

)(wPST )(MbpsBR )(bitsV

49 3.5 91018.3

1.9 6.10 91055.3

1.6 1.7 91017.3

8.6 9.7 9102.3

Type

Basic system

Improved system

I

II

III

Performance Comparison of the Basic and Improved Data Transmission Systems

Theoretical improved system

Case III

Case I

Case II

Basic system

Bit Error Rates for the Basic and Improved Data Transmission Systems Versus Elevation Angle

Conclusions

• We proposed an analytical approach to determine an adaptive policy for selecting the error-correction code with bit protection proportional to change of distance between the LEO satellite and ground station.

• This method provides transmission rate and power better than traditional systems.

• The simulation results show that this scheme is a more effective tool for the LEO satellite data transmission.