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					  Link Analysis and Rain Attenuation
      Considerations in AI3-AIT
        Satellite Link Project
                           by

               Birat Bahadur Mishra

Examination Committee : Dr. K.M. Ahmed (Chairman)
                        Dr. R.M.A.P. Rajatheva
                        Dr. Kanchana Kanchanasut


              Asian Institute of Technology
                   Bangkok, Thailand
                  Nov. 27, 1997
Link Analysis and Rain Attenuation
Considerations in AI3-AIT
Satellite Link Project

                                       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 continuously, without properly analyzing the effect of rain on the satellite
 l                           i                           n                            k.
                             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
• Rain attenuation calculated for uplink frequency approached

   to higher value
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 (Bangkok-Japan) and Outbound (Japan-Bangkok) satellite communication
                                        Inbound link            Outbound link
                Parameter             (Bangkok-Japan)         (Japan-Bangkok)
                                      Uplink Downlin          Uplink Downlin
                                                   k                       k
           Threshold rain rate         38         49            21         75
                (mm/h)
         Threshold % of a year 0.070436 0.006327 0.048904 0.018889
          outage        hour     6.17     0.55     4.28     1.65
           time         min.      370      33       257      99


•    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
                     Parameter                              Rain Location
                                                       Bangkok           Japan
              Threshold rain rate                        38                21
                    (mm/h)
                                 % of a year           0.070436         0.048904
         Threshold outage
               time                 hour                  6.17            4.28
                                         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

Inbound Link (Bangkok-Japan)

 • Bit Error rate
    BER is calculated for the satellite link, operating with transmission rates of H1,
    H11, H12, T1 and E1 at different rain rates
    BER 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, which
    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 satellite link at different transmission rates for
inbound communication (Bangkok-Japan)
               Outbound Link (Japan-Bangkok)
Threshold rain rate and threshold outage time of AI3 satellite link at different
transmission rates for outbound communication (Japan-Bangkok)
            Bi-directional satellite communication
• Threshold rain rate and threshold outage time of AI3-AIT satellite link, operating
  at different transmission rate for bi-directional communication.




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