An Analytical Prediction Model of Time Diversity Performance for Earth-Space Fade Mitigation

Time diversity (TD) has recently attracted attention as a promising and cost-efficient solution for high-frequency broadcast satellite applications. The present work proposes a general prediction model for the application of TD by approximating the time dynamics of rain attenuation through the use of the joint lognormal distribution. The proposed method is tested against experimental data and its performance is investigated with respect to the basic parameters of a satellite link

MIMO Extension to DVB-SH

DVB-SH is a hybrid satellite-terrestrial system combining a satellite component and a complementary ground component to provide service in all types of environments, i.e., outdoor and indoor coverage in urban, sub-urban and rural. This paper reports the studies on multiple-input multiple-output (MIMO) extension to the existing DVB-SH standard. MIMO techniques are considered in this paper for achieving increased spectral efficiency and reliability in the challenging satellite and hybrid channel environment

Precoding, Scheduling and Link Adaptation in Mobile Interactive Multibeam Satellite Systems

This paper deals with the problem of precoding, scheduling and link adaptation in next generation mobile interactive multibeam satellite systems. In contrast to the fixed satellite services, when the user terminals move across the coverage area, additional challenges appear. Due to the time varying channel, the gateway has only access to a delayed version of the channel state information (CSI) which can eventually limit the overall system performance. However, in contrast to general multiuser multipleinput- multiple-output terrestrial systems, the CSI degradation in multibeam mobile applications has a very limited impact for typical fading channel and system assumptions. Under realistic conditions, the numerical results show that precoding can offer an attractive gain in the system throughput compared to conservative frequency reuse allocations

Precoding, Scheduling and Link Adaptation in Mobile Interactive Multibeam Satellite Systems

This paper deals with the problem of precoding, scheduling and link adaptation in next generation mobile interactive multibeam satellite systems. In contrast to the fixed satellite services, when the user terminals move across the coverage area, additional challenges appear. Due to the time varying channel, the gateway has only access to a delayed version of the channel state information (CSI) which can eventually limit the overall system performance. However, in contrast to general multiuser multipleinput- multiple-output terrestrial systems, the CSI degradation in multibeam mobile applications has a very limited impact for typical fading channel and system assumptions. Under realistic conditions, the numerical results show that precoding can offer an attractive gain in the system throughput compared to conservative frequency reuse allocations

Precoding in multibeam satellite communications: present and future challenges

Whenever multibeam satellite systems target very aggressive frequency reuse in their coverage area, inter-beam interference becomes the major obstacle for increasing the overall system throughput. As a matter of fact, users located at the beam edges suffer from a very large interference for even a moderately aggressive planning of reuse-2. Although solutions for inter-beam interference management have been investigated at the satellite terminal, it turns out that the performance improvement does not justify the increased terminal complexity and cost. In this article, we pay attention to interference mitigation techniques that take place at the transmitter (i.e. the gateway). Based on this understanding, we provide our vision on advanced precoding techniques and user clustering methods for multibeam broadband fixed satellite communications. We also discuss practical challenges to deploy precoding schemes and the support introduced in the recently published DVB-S2X standard. Future challenges for novel configurations employing precoding are also provided

Physical layer simulator of the deep space to ground high photon efficiency optical wireless communications link

This paper focuses on the implementation of the physical layer simulator for the deep space to ground high photon efficiency optical wireless communications link designed by NASA. The link employs the serially concatenated pulse position modulation (SCPPM) transmitted over a cloud free atmospheric and turbulent atmospheric link. The decoder is an iterative process based on the BCJR algorithm to achieve the optimum bit error rate (BER) performance. The results show that for the higher orders of SCPPM a lower signal to noise ratio is required to achieve the same BER as the lower orders. The effects of atmospheric turbulence on the link performance is also demonstrated as well as the combative technique of channel interleaving of the data

Physical and MAC layer issuesd of fixed broadband wireless networks

The present thesis deals with a number of issues related to the physical and MAC layers of fixed broadband wireless access (BWA) networks operating in the 10-66GHz spectral range. The recent release of the broadband wireless standards IEEE 802.16 and ETSI BRAN HIPERACCESS signified a growth period for these networks to profit from the advantages of wireless communications in metropolitan area networks (MAN). Chapter 1 of the thesis provides an introduction on the recent technological and standardization developments of broadband wireless access technologies. Next, propagation in frequency bands above 10GHz is studied by separating the influence of the atmosphere and the environment a fixed wireless network is deployed. This is supplemented by many prediction models reproduced from the literature and the ITU-R Recommendations. Emphasis is given on describing a physical statistical model for rain fading, which constitutes the dominant factor degrading the performance of the high frequency segment of fixed BWA systems. Furthermore, Chapter 3 investigates the various fade mitigation techniques (FMT) to combat channel fading. FMTs are separated into three general categories, that is, power control, adaptive modulation and coding and diversity. For the latter, two new methods are described for predicting its performance under heavy and stratiform rain, respectively. The rest of the chapters offer a radiocommunication analysis on intercell interference with respect to the multiple access scheme selected. Specifically, Chapter 4 is focused on conventional TDMA based BWA networks in the frame of the distinct cellular characteristics this type of networks exhibit. Despite that multipath is less important for the system under study, Chapter 5 introduces CDMA as an alternative access option for the 10-66GHz segment of BWA networks motivated by the improved performance in terms of intercell interference, at least for the link from the subscriber to the base station (upstream). In both cases, a statistical assessment of intercell interference is carried out by taking into account rain fading for the desired and the interfering signals. For the opposite direction of transmission (downstream), Chapter 6 proposes a combination of multirate techniques including multicode-CDMA and variable spreading factor-CDMA employed in a modified fashion to control the interference throughout the sector. The performance of the proposed code assignment scheme is tested both analytically and through a comprehensive simulation of the dynamic properties of the channel.Στην παρούσα διατριβή αντιμετωπίζονται διάφορα ζητήματα που άπτονται του φυσικού στρώματος και του στρώματος MAC των σταθερών ευρυζωνικών ασύρματων δικτύων πρόσβασης που λειτουργούν στο φασματικό εύρος 10-66GHz. Η πρόσφατη δημοσίευση των ευρυζωνικών ασύρματων προτύπων IEEE 802.16 και ETSI BRAN HIPERACCESS σηματοδότησε μια περίοδο ανάπτυξης των συγκεκριμένων δικτύων με εκμετάλλευση των πλεονεκτημάτων της ασύρματης επικοινωνίας σε μητροπολιτικά δίκτυα (MAN). Το Κεφάλαιο 1 της διατριβής παρέχει μια εισαγωγή στις πρόσφατες εξελίξεις από τεχνολογικής και κανονιστικής σκοπιάς της σταθερής ασύρματης ευρυζωνικής τεχνολογίας. Στη συνέχεια, μελετώνται τα "θέματα διάδοσης σε ζώνες συχνοτήτων άνω των 10GHz διαχωρίζοντας την επίδραση της ατμόσφαιρας και του περιβάλλοντος εγκατάστασης του σταθερού ασύρματου δικτύου. Η μελέτη αυτή συνοδεύεται από πολυάριθμα μοντέλα πρόβλεψης που αναπαράγονται από τη διεθνή βιβλιογραφία και τις Συστάσεις της ITU-R. Ιδιαίτερη έμφαση δίδεται στην περιγραφή ενός φυσικού στατιστικού μοντέλου των διαλείψεων λόγω βροχής, ο οποίος αποτελεί τον κυρίαρχο παράγοντα υποβάθμισης της επίδοσης στο υψηλής συχνότητας τμήμα των σταθερών συστημάτων BWA. Επιπλέον, το Κεφάλαιο 3 διερευνά τις διάφορες μεθόδους άμβλυνσης των διαλείψεων (FMT) για την αντιμετώπιση των διαλείψεων του διαύλου. Οι τεχνικές FMT διαχωρίζονται σε τρεις γενικές κατηγορίες και, συγκεκριμένα, τον έλεγχο ισχύος, την προσαρμοστική διαμόρφωση και κωδικοποίηση και τη διαφορική λήψη. Για την τελευταία, από τη διατριβή περιγράφονται δύο νέες μέθοδοι για την πρόβλεψη της επίδοσής της υπό ισχυρή και στρωσιγενής βροχή, αντίστοιχα. Στα υπόλοιπα κεφάλαια πραγματοποιείται μια ανάλυση της διακυψελικής παρεμβολής ως προς το σχήμα πολλαπλής πρόσβασης που επιλέγεται. Ειδικότερα, το Κεφάλαιο 4 επικεντρώνεται σε συμβατικά δίκτυα BWA που βασίζονται στη διαίρεση TDMA λαμβάνοντας υπόψη τα διαφορετικά χαρακτηριστικά κυψέλης που διακρίνει αυτού του είδους τα δίκτυα. Καίτοι οι πολυδιαδρομικές διαλείψεις έχουν σαφώς μικρότερη βαρύτητα για τα υπό μελέτη συστήματα, το Κεφάλαιο 5 εισάγει την τεχνική CDMA ως εναλλακτικό σχήμα πρόσβασης στο τμήμα των BWA δικτύων που λειτουργεί στο εύρος 10-66GHz, με κίνητρο τη βελτίωση ως προς τη διακυψελική παρεμβολή, τουλάχιστον για τη ζεύξη από το σταθμό συνδρομητή προς το σταθμό βάσης (upstream). Και στις δύο περιπτώσεις, πραγματοποιείται μια στατιστική εκτίμηση της διακυψελικής παρεμβολής λαμβάνοντας υπόψη τις διαλείψεις λόγω βροχής τόσο για την επιθυμητή όσο και για τις παρεμβάλλουσες ζεύξεις. Για την αντίθετη κατεύθυνση μετάδοσης (downstream), το Κεφάλαιο 6 προτείνει ένα συνδυασμό τεχνικών πολλαπλών ρυθμών μετάδοσης συμπεριλαμβανομένης της τεχνικής CDMA πολλαπλών κωδίκων και μεταβλητού κέρδους εξάπλωσης, των οποίων υιοθετείται μια τροποποιημένη εκδοχή για τον έλεγχο της παρεμβολής σε ολόκληρη την έκταση του τομέα. Η επίδοση του προτεινόμενου σχήματος ανάθεσης κωδίκων ελέγχεται τόσο με αναλυτικό τρόπο όσο και μέσω μιας ενδελεχούς εξομοίωσης των δυναμικών ιδιοτήτων του διαύλου

Large Scale Transmit Diversity in Q/V Band Feeder Link with Multiple Gateways

Exploiting transmit diversity amid a high number of multiple gateways (GW) is a new research challenge in Q/V band satellite communication providing data rates of hundreds of Gbit/s. In this paper, we propose a practical switching strategy in a scenario with N +P GWs (N active and P redundant GWs) towards achieving GW transmit diversity. Differently from other works, the treatment in this paper is analytical and explores two key factors: outage performance and switching rate in detail. Further, the interplay between the number of redundant and active GWs on the availability is illustrated highlighting the contribution of the work towards system sizing

Space-Frequency Coding for Dual Polarized Hybrid Mobile Satellite Systems

An increasing number of hybrid mobile systems comprising a satellite and a terrestrial component are becoming standardized and realized. The next generation of these systems will employ higher dimensions adopting multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) techniques. In this work, we build upon recent studies of dual polarization MIMO for each component and propose the use of full-rate full-diversity (FRFD) codes adopting a space-frequency paradigm. We also propose a scheme taking advantage of the separation between the subcarriers to enhance the coding gain. By critically assessing the different options for the 4 transmit, 2 receive hybrid scenario taking into account system and channel particularities, we demonstrate that the proposed scheme is a solution for enhancing the performance of next generation hybrid mobile satellite systems

Golden Codes for Dual Polarized MIMO-OFDM Transmissions in Hybrid Satellite/Terrestrial Mobile Systems

This paper discusses the performance of Golden codes in a hybrid satellite/terrestrial system framework employing dual polarized MIMO-OFDM transmissions. Although the use of Golden codes in satellite and terrestrial scenarios has been studied independently, a realistic performance assessment must involve both components taking into account the relative delay between their reception. In fact, this work exploits the relative delay to create a multipath scenario and further improve the coding gain of the Golden codes, which is otherwise fixed. This is made possible by utilizing the Golden code in a Space-Frequency coding framework instead of the traditional Space-Time paradigm. The separation between the subcarriers constituting a Golden code is shown to be central to the coding gain enhancement and an algorithm to choose this separation is provided