OPTIMISATION OF DATA THROUGHPUT FOR LEO SATELLITE DOWNLINK USING TRELLIS CODED MODULATION

OPTIMISATION OF DATA THROUGHPUT FOR LEO SATELLITE DOWNLINK USING TRELLIS CODED MODULATION

ABSTRACT

The line of sight communication between an orbiting LEO satellite and its Ground Station is time constrained by duration of visibility and number of visible passes in a day. In Equatorial region like Nigeria, the average duration is short and number of passes is very few. In most cases, the satellite size is small and therefore power generated on-board is also small, consequently the downlink budget is power constrained.  Transmission bandwidth is also constrained by Regulations and need for cost effective RF design. High resolution remote sensing LEO satellite that acquires large data to be downloaded to a Ground station requires high capacity downlink at minimum power that guarantee BER of 10-6. Application of high level MPSK for high data rate requires more power to reduce transmission errors. Convolution or Block codes when used for Error Correction adds overhead bits to the detriment of the link capacity and without significant coding gain for a power limited downlink. Trellis Coded Modulation (TCM) developed in 1982 by Ungerboeck et el, though still adds overhead bits, but generates significant coding gain that can be extended up to 6dB.This Thesis seeks to optimise LEO Satellite Downlink that is Time, Power and Bandwidth constrained, through trade-off between the coding gains of TCM for bandwidth efficient high level MPSK schemes.