In the light of latest intrusions into satellite data the demand to protect the sensitive and valuable data transmitted from satellites to ground has increased and hence the need to use encryption on-board. The Advanced Encryption Standard (AES), which is a very popular choice in terrestrial communications, is slowly emerging as the preferred option in the aerospace industry including satellites. Computing systems on-board satellites have limited power and computational resources as in terrestrial embedded systems. With these constraints in mind various implementations of the AES algorithm using different optimization techniques have been carried out on FPGAs and the implementations have been evaluated in terms of power, throughput and device area. Satellites operate in a harsh radiation environment and consequently any electronic system used on board, including the encryption processor, is susceptible to radiationinduced faults. Hence, in addition to consuming limited resources, the encryption processor should be immune to radiation induced faults to avoid faulty data transmission to ground station. Most of the faults that occur in satellite on-board electronic devices are radiation induced bit flips called single event upsets (SEUs). A detailed novel analysis of the effect of faults on imaging and telemetry data during onboard encryption is carried out. Also the impact of faults in the data which occur during transmission to the ground station due to noisy channels is discussed and compared. In order to avoid data corruption due to SEUs a novel fault-tolerant model of the AES is presented, which is based on the Hamming error correction code. Implementation of the proposed model is carried out on FPGAs and measurements of the power and throughput overhead are presented.

Η παρούσα εργασία περιλαμβάνει την μελέτη και τον χαρακτηρισμό του καναλιού ενός δορυφορικού καναλιού καθώς και την επίγεια διάδοση Αρχικά γίνεται μια εισαγωγή στα ασύρματα συστήματα τηλεπικοινωνιών . Ειδικά παρουσιάζεται το δορυφορικό σύστημα και αναλύονται τα μέρη αυτού. Γίνεται παρουσίαση των δορυφορικών ζεύξεων και μελετάται το περιβάλλον μέσα στο οποίο λαμβάνει χώρα μια σύνδεση. Αρχικά αναλύονται οι μέθοδοι διάδοσης της ηλεκτρομαγνητικής ακτινοβολίας και οι διάφορες εξασθενήσεις που υφίσταται το σήμα λόγω φαινομένων της ατμόσφαιρας καθώς και άλλων επιδράσεων. Γίνεται έπειτα μια εκτενής αναφορά στις διαλείψεις και στην ταξινόμησή τους. Στη συνέχεια γίνεται μια κατηγοριοποίηση των διαλείψεων αυτών με βάση τα χαρακτηριστικά τους. Ακολουθεί η στατιστική αναπαράσταση των καναλιών με διαλείψεις χρησιμοποιώντας τις βασικότερες κατανομές που συναντώνται στα τηλεπικοινωνιακά συστήματα. / This work includes the study and channel characterization for a satellite signal and also its terrestrial propagation. First we introduce the wireless telecommunications systems. We focus on the satellite system and its components are analyzed. A presentation of the satellite links follows and the propagation environment is studied. We analyze the propagation methods of electromagnetic radiation and the various losses that the signal endures due to atmospheric phenomena and other effects. There is then a reference to the fading channel and and its analysis. Then there is categorization of the fading according to its characteristics. The statistical representation of the fading channel follows, with the use of the key distributions found in telecommunication systems. Lastly, the satellite transmission is simulated for various orbit heights and conditions