GEOCAST Project Work Package WP2400:


TimeSeries Fade Prediction Error Model

Different footprint regions in a GEO Satellite system, operating at EHF, experience constantly changing weather patterns. Changes in weather conditions may cause either long link outages/fades (due to rain) or short outages/fades (due to scintillation). Prolonged link outages/fades often lead to significantly low data throughput, due to high data loss rate in the upper layers (i.e. transport layer and application layer).

In this work package WP2400, a fade prediction error model was implemented in ns Network Simulator. This enabled UoA to analyse and evaluate, using simulation, the performance of a selected set of reliable multicast transport protocols suited for GEO satellite systems. The fade prediction error model, implemented in ns, was based on a Packet Error Rate (PER) Time Series (TS) provided by ONERA and ALCATEL Space Industries (ASPI).

Packet Error Rate (PER) Time Series (TS)

  • The formula outlined below was used by ALCATEL Space Industries (ASPI) to convert Eb/N0 Time Series to Packet Error Rate (PER) time series, such that PER(t) = function(Eb/N0(t)), where t = time, assuming no memory from the past Eb/N0 values.

  • This formula assumes that synchronisation was OK and uses data for QPSK modulation with an interleaved (12 bit) Reed-Solomon (RS) coding 188/204 and convolutional coding rate of 3/4 with soft decision viterbi decoding on the downlink and turbo code 2/3 on the uplink. Number of packets in error on each sample was given by:

    where fd = payload data flow ((Bytes) transmitted and nbSamples = number of samples per second.

Fade Prediction Algorithm

  • Algorithm keeps track of fade_start_time, fade_duration and fade_start_time
  • No packet loss before fade_start_time
  • No packet loss after fade_end_time
  • Packet loss occurs during fade_duration

Extension and Integration in ns Network Simulator

  • Fade Error Model - simulates link fades
  • Queue - holds packets in a queue
  • Link Delay - models delay and bandwidth of link
  • TTL Checker - decrements TTL on eack packet on transit
  • Drop Target - target for dropped packets

Related Resources

  • Download ns source code for TimeSeries Fade Error Model used in this work. [tar, gz]
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