Link Analysis and Rain AttenuationConsiderations in AI3-AIT

Satellite Link Project

by

Birat Bahadur Mishra

Examination Committee : Dr. K.M.

Ahmed (Chairman) Dr. R.M.A.P.Rajatheva Dr. Kancha

na Kanchanasut

Asian Institute of Technology Bangkok, Thailand

Nov. 2 7 , 1 9 9 7

Abstract

AI3 satellite link may be downed in case of heavy rain around AI3 earth stations of south east Asia. The satellite link is operating round the year at lower rate than designed to avoid frequent failure. It is nor worthful to operate the satellite link at lower rate c

ontinuously, without properly analyzing the effect of rain on the satellite link.

Link Analysis and Rain Attenuation

Considerations in AI3-AIT

Satellite Link Project

Introduction

• Asian Internet Interconnection Initiative (AI3) is a series of research activities performed on a testbed, constructed using Ku band star VSAT network provided by JCSAT-3 communication satellite.

• Goals of AI3 project:

– Promote internet technologies on Asian countries

– Develop an efficient Internet topology for Asian countries.

– Develop recommendations and requirements for Internet connection among Asian countries

• From hub station in Nara, Japan, 2 Mbps satellite links are connected to earth stations at the AI3 partners' site in several Asian contries.

Problem Statement

• AI3 satellite link may be downed in case of heavy rain around AI3 earth stations of south east Asia.

• The satellite link is operating round the year at lower rate than designed to avoid frequent failure.

• It is nor worthful to operate the satellite link at lower rate continuously

, without properly analyzing the effect of rain on the satellite link.

Objectives

• Study of different rain attenuation prediction models

• Selection of appropriate rain attenuation model for Thailand

• Analysis of AI3-AIT satellite link, operating with different compatible transmission rates, at various rain rates.

• Assessment of AI3-AIT satellite link, operating with different coding schemes, at various rain rates.

Scope and Limitations

• Selection of link bit rates required for AI3-AIT satellite link at different rain rates will enable the efficient operation of such link.

• Shut down of the satellite link due to heavy rain can be avoided.

• Stable operation of link is greatly desired for countries where only AI3 project provides Internet connectivity.

• Such study would be useful to assess other VSAT networks also.

• Rain in only uplink and downlink of the satellite link is considered i.e. effects of simultaneous rain in uplink and downlink are not considered.

• The result of this study, however, cannot be verified by other measurement procedure.

Methodology .. (1)

• H channels of ISDN server higher data rate user for the purpose

– Video conferencing

– Digital program

– Fast facsimile

– Internet

• H channel transmission rates are

– 0.384 Mbps (H0)

– 1.536 Mbps (H11)

– 1.920 Mbps (H12)

• Primary Rate Interface (PRI) transmission rate of ISDN are

– 2.488 Mbps (E1)

– 1.544 Mbps (T1)

Methodology .. (2)

• Modem of AI3 satellite earth stations is compatible to H0, H11, H12, E1 and T1 transmission rates

• Currently, AI3-AIT satellite link is operating at H11 transmission rate.

• Also, AI3 earth stations are equipped with convolutional encoder and Viterbi decoder.

• Modem of the ground stations is equipped with convolutional encoders of rates' 3/4, 1/2 and 7/8

• Currently, AI3-AIT is operating with convolutional encoder of rate 3/4

Procedures .. (1)

• Rain attenuation : Garcia Model

– Reasons for selecting Garcia Model

• Simple in use

• gives similar accuracy in different regions of earth

• applicable to different regions of earth.

• Experimental results have verified that this model provides more accurate results than CCIR (1986) model.

• Rain rate exceeded percentage of a year calculation : CCIR Report 563

Procedures .. (2)

• Threshold rain rate and threshold outage time of designed AI3-AIT satellite link

• Analyzing AI3-AIT satellite link with compatible transmission rates of H0, H11, H12, E1 and T1

– Calculation of bit error rate (BER) at different rain rates

– Determination of threshold rain rate and threshold outage time

• Analyzing AI3-AIT satellite link with its applicable codind rates of 3/4, 1/2 and 7/8

– Calculation of BER

– Determination of threshold rain rate and threshold rain rate.

Comparision between CCIR method and Garcia method for worldwide

Comparision between CCIR and Garcia Methods for tropical region

Parameters Given for Link VSAT (AIT) Parameters .. (1)

Parameters Given for Link VSAT (AIT) Parameters .. (2)

Source: JCSAT Corporation

Satellite (JCSAT-3) Parameters

Satellite Parameters.. (1)

Satellite Parameters.. (2)

Source : JCSAT Corporation.

Hub (Nara, Japan) Parameters

Parameters of Nara earth station

Source: JCSAT Corporation

Interference Parameters (assumed)

Interference Parameters

Source : (Ha, 1990) and (CCIR 1988)

Results

• Rain attenuation calculated for uplink frequency approached

to higher value

Rain attenuation

Rain rate exceeded percentage

• It is higher for Bangkok rain than Japan rain, as Bangkok and Japan are situated in tropical and temperate regions of CCIR rain climate zone respectively.

Rain attenuation for different uplink and downlink rain rate

for inbound link (Bangkok-Japan)

Rain attenuation for both uplink and downlink of AI3-AIT satellite link for outbound (

Japan-Bangkok)

Outage time of designed AI3-AIT satellite link

Inbound link(Bangkok-Japan)

Outbound link(Japan-Bangkok)Parameter

Uplink Downlink

Uplink Downlink

Threshold rain rate(mm/h)

38 49 21 75

% of a year 0.070436 0.006327 0.048904 0.018889hour 6.17 0.55 4.28 1.65

Thresholdoutagetime min. 370 33 257 99

• Inbound (Bangkok-Japan) and Outbound (Japan-Bangkok) satellite communicati

on

• Figure shows the outage time contributed by different rain rates on total outage time corresponding to threshold rain rate of 38 mm/h of Bangkok rain and 21 mm/h of Japan rain.

Bi-directional communication

Rain LocationParameter

Bangkok Japan

Threshold rain rate(mm/h)

38 21

% of a year 0.070436 0.048904

hour 6.17 4.28Threshold outage

time

min. 370 257

• threshold rain rate is the rain rate up to which reliable opeartion

of satellite link be maintained • threshold outage time is total outage time of the satellite link.

Cumulative link outage time

AI3-AIT satellite link at different transmission rate

• Bit Error rate

Inbound Link (Bangkok-Japan)

BER is calculated for the satellite link, operating with transmission rates of H1, H11, H12, T1 and E1 at different rain ratesBER of 10-7 is specified as criterion for reliable operation of satellite link Rain rate corresponds to BER of 10-7 is determined, which is a threshold rain rate. Percentage of a year, in which the threshold rain rate is exceeded, is determined, whic

h is a threshold outage time.

BER at different uplink and downlink rain rates for inbound link at transmission bit rate of 1.920 Mbps (H12).

threshold rain rates: 31 mm/h of uplink (Bangkok) only rain and

36 mm/h of downlink (Japan) only rain. threshold outage time: 0.094334 and 0.015111 percentage of a year for the case

of uplink only and downlink only rain.

BER at different uplink and downlink rain rates for inbound link at transmission bit rate of 2.0488 Mbps (E1)

threshold rain rate: 29 mm/h of Bangkok rain and 33 mm/h of downlink rain threshold outage time: 0.0103049 and 0.018747 percentage of a

year in the case of Bangkok rain and Japan rain respectively.

Inbound Link (Bangkok-Japan) Threshold rain rate and threshold outage time of AI3 sa

tellite link at different transmission rates for inbound c - ommunication (Bangkok Japan)

Outbound Link (Japan-Bangkok)

Threshold rain rate and threshold outage time o f AI3 satellite link at different transmission rate

-sforout bound communi cat i on (J apan Bangkok)

Bi-directional satellite communication

• Threshold rain rate and threshold outage tim - e of AI3 AIT satellite link, operating

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