Comparison of advanced modulation schemes for LEO satellite downlink communications

Belce, O
The M.Sc. degree project, whose one major part is explained in this paper, has been accomplished at the University of Surrey by the financial support of TUBITAK-BILTEN inclusive to the remote sensing satellite project BILSAT-1*, which was carried out by Surrey Satellite Technology Limited in UK, collaboration with TUBITAK-BILTEN. This paper explains the methodology and the simulation results of the performances of advanced modulation techniques under the implications of highly dynamic LEO satellite downlink. Modulation schemes that can possibly serve the objectives are the phase shift keying type modulations. Hence, the performance of binary phase shift keying (BPSK), quadriphase shift keying (QPSK), offset QPSK (OQPSK), pi/4 shifted QPSK, octaphase shift keying (8PSK), and 3pi/8 shifted 8PSK have been deeply investigated through simulations considering the LEO satellite communication downlink channel properties. The modulators and demodulators were synthesised using computer programs. The simulations demonstrated the necessity of applying non-coherent demodulators in order to fight with the multipath fading present in the downlink channel. The non-coherent limiter discriminator demodulator of pi/4 shifted QPSK, which turned out to have the best performance in fading simulations, was an evidence of the above observation. 3pi/8 shifted 8PSK was also demodulated with a similar system. However, implementation of 3pi/8 shifted 8PSK is not recommended because of the fact that higher power with respect to pi/4 shifted QPSK modulation is necessary to have identical BER performances. Although the data rate could be increased even more with implementation of 3pi/8 shifted 8PSK than pi/4 shifted QPSK scheme, power limited 'little' LEO satellites prevent using this higher order modulation for downlink.
International Conference on Recent Advances in Space Technologies


A Comparative study for the production of recombinant intracellular glucose isomerase by escherichia coli and pichia pastoris
Yaman, Sena; Çalık, Pınar; Özdamar, Tunçer H.; Department of Biotechnology (2014)
In this M.Sc. study, intracellular thermostable glucose isomerase (EC production capacities of two metabolically engineered microorganisms, Escherichia coli and Pichia pastoris, were investigated. In this context, to construct intracellular glucose isomerase (GI) producing recombinant P. pastoris, the cells were transfected with pPICZ-A expression vector containing GI coding gene (xylA) of Thermus thermophilus. After the confirmation of the transfection, effects of co-carbon source sorbitol were in...
Investigation of thermostable recombinant glucose isomerase production by sucrose utilizing escherichia coli
Akdağ, Burcu; Çalık, Pınar; Özdamar, Tunçer H.; Department of Biotechnology (2013)
The aim of this M.Sc. thesis is to investigate the production of thermostable glucose isomerase (GI; EC by metabolically engineered sucrose-utilizing Escherichia coli in the designed molasses-based production media. Throughout the experiments the cell growth, sucrose consumption, recombinant GI activity, and by-product concentrations were analyzed. For this purpose, in the first part of this thesis, pRSETA plasmid carrying the thermostable GI encoding gene from Thermus thermophilus (xylA) was isola...
The Firewall paradox
Dündar, Furkan Semih; Tekin, Bayram; Department of Physics (2014)
In this MSc. thesis, we have attempted to give an overview of the firewall paradox and various approaches towards its resolution. After an introductory chapter on some basic concepts in quantum field theory in curved spacetimes such as Hawking radiation, we introduce the paradox. It arises out of application of principles each of which is thought or assumed to be correct: 1) unitary black hole evaporation, 2) validity of quantum field theory in curved spacetime, 3) a measure of the number of black hole quan...
Aerothermodynamic modeling and simulation of gas turbines for transient operating conditions
Koçer, Gülru; Uzol, Oğuz; Department of Aerospace Engineering (2008)
In this thesis, development of a generic transient aero-thermal gas turbine model is presented. A simulation code, gtSIM is developed based on an algorithm which is composed of a set of differential equations and a set of non-linear algebraic equations representing each gas turbine engine component. These equations are the governing equations which represents the aero-thermodynamic process of the each engine component and they are solved according to a specific solving sequence which is defined in the simul...
Recombinant human growth hormone production under double promoters by Pichia pastoris
Yalçınkaya, Duygu; Çalık, Pınar; Özdamar, Tunçer H.; Department of Chemical Engineering (2017)
The aim of the M.Sc. thesis is expression of recombinant human growth hormone (rhGH) by Pichia pastoris under the double-promoters, namely, glyceraldehyde-3-phosphate dehydrogenase and pyruvate decarboxylase, engineered and constructed by metabolic- and genetic- engineering methods. The DNA fragment including the promoter region of the P. pastoris pyruvate decarboxylase (PPDC), Saccharomyces cerevisiae α-mating factor (α-MF1) secretion signal sequence, and hGH gene, was amplified from the pPDCZαA::hGH plasm...
Citation Formats
O. Belce, “Comparison of advanced modulation schemes for LEO satellite downlink communications,” Istanbul, TURKEY, 2003, p. 432, Accessed: 00, 2020. [Online]. Available: