Konstantinos Liolis

Cognitive spectrum utilization in Ka band multibeam satellite communications

Multibeam satellite networks in Ka band have been designed to accommodate the increasing traffic demands expected in the future. However, these systems are spectrum limited due to the current spectrum allocation policies. This paper investigates the potential of applying cognitive radio techniques in satellite communications (SatCom) in order to increase the spectrum opportunities for future generations of satellite networks without interfering with the operation of incumbent services. These extra spectrum opportunities can potentially amount to 2.4 GHz of bandwidth in the downlink and 2 GHz of bandwidth in the uplink for high density fixed satellite services (HDFSS).

Cognitive radio scenarios for satellite communications: The CoRaSat approach

This paper presents initial results of the recently kicked-off FP7 ICT STREP project “CoRaSat” (Cognitive Radio for Satellite Communications) [1]. Focus is put on the preliminary identification of the scenarios which are suitable for the applicability of Cognitive Radio technology over Satellite Communications (SatCom). The considered frequency bands include Ka-band, Ku-band, C-band and S-band, where regulatory and coordination constraints exist. An initial mapping of broadband and narrowband SatCom use cases on each identified scenario is also provided. Moreover, several challenges associated to the applicability of Cognitive Radio over SatCom in the identified scenarios are presented, which form the basis of the market/business, regulatory, standardization and technological framework of CoRaSat. Furthermore, ongoing and future work of the CoRaSat project is outlined.

Spatial multiplexing in optical feeder links for high throughput satellites

Optical feeder links are an attractive alternative to the RF feeder links in satellite communications (SatCom). In this paper, we present initial results from an optical feeder link study. We discuss the architecture of a geostationary earth orbit (GEO) satellite system based on optical feeder links. To mitigate the effects of cloud coverage, which is the main availability-limiting factor, Optical Ground Station (OGS) diversity is employed. Moreover, a spatial multiplexing scheme is considered. Assuming an ON-OFF channel model, the number of required OGSs to ensure availability and throughput requirements is analyzed.

Cognitive Zone for Broadband Satellite Communications in 17.3–17.7 GHz Band

Deploying high throughput satellite systems in Ka band to accommodate the ever increasing demand for high data rates hits a spectrum barrier. Cognitive spectrum utilization of the allocated frequency bands to other services is a potential solution. Designing a cognitive zone around incumbent broadcasting satellite service (BSS) feeder links beyond which the cognitive fixed satellite service (FSS) terminals can freely utilize the same frequency band is considered in this paper. In addition, we show that there is a rain rate called rain wall, above which cognitive downlink communications become infeasible.

Simultaneous Sensing and Transmission for Cognitive Radios With Imperfect Signal Cancellation

In conventional cognitive radio systems, the secondary user employs a “listen-before-talk” paradigm, where it senses if the primary user is active or idle, before it decides to access the licensed spectrum. However, this method faces challenges, with the most important one being the reduction of the secondary user’s throughput, as no data transmission takes place during the sensing period. In this context, the idea of simultaneous spectrum sensing and data transmission is proposed. This paper studies a system model where this concept is obtained through the collaboration of the secondary transmitter with the secondary receiver. First, the secondary receiver decodes the signal from the secondary transmitter, removes it from the total received signal, and then carries out spectrum sensing in the remaining signal in order to determine the presence/absence of the primary user. Different from the existing literature, this paper considers the imperfect signal cancellation, evaluating how the decoding errors affect the sensing reliability, and derives the analytical expressions for the probability of false alarm. Finally, numerical results are presented illustrating the accuracy of the proposed analysis.

Cognitive radio for Ka band satellite communications

The satellite communication data traffic is increasing dramatically over the coming years. High throughput multibeam satellite networks in Ka band are potentially able to accommodate the upcoming high data rate demands. However, there is only 500 MHz of exclusive band for download and the same amount for upload. This spectrum shortage impose a barrier in order to satisfy the increasing demands. Cognitive satellite communication in Ka band is considered in this paper in order to potentially provide an additional 4.4 GHz bandwidth for downlink and uplink fixed-satellite-services. In this way, it is expected that the problem of spectrum scarcity for future generation of satellite networks is alleviated to a great extent. The underlying scenarios and enabling techniques are discussed in detail, and finally we investigate the implementation issues related to the considered techniques.

Sensitivity Analysis of Multicarrier Digital Pre-distortion/ Equalization Techniques for Non-linear Satellite Channels

Sensitivity Analysis of Multicarrier Digital Pre-distortion/ Equalization Techniques for Non-linear Satellite Channels

SatCom systems in the context of Future Internet-enabled smart infrastructures

This paper aims at forecasting the role of Satellite Communications (SatCom) in the context of Future Internet and particularly of the future Internet-enabled smart infrastructures in support of some European Societal Grand Challenges. It also aims at identifying the necessary technological enablers which need to be developed by the European SatCom industry for the emerging SatCom solutions.

Monthly and Seasonal CFLOS Statistics for Optical GEO Feeder Links Design

A methodology for the generation of seasonal and monthly cloud-free-line of sight (CFLOS) statistics for single optical satellite slant paths and joint CFLOS statistics for multiple spatially separated optical satellite links is proposed and evaluated with numerical results. It is assumed that the blockage of the satellite link is considered with the occurrence of clouds. The reported methodology is based on the stochastic dynamic modeling of Integrated Liquid Water Content (ILWC) and uses as inputs monthly statistical parameters of the logarithm of (ILWC) to produce CFLOS statistics. This methodology is an extension of an existing model that captures very well both the seasonal and monthly variability of clouds. The proposed model takes into account the temporal and spatial correlation of clouds, the elevation angle and the altitude of the ground station among others. The numerical results are concentrated on for hypothetical satellite links with optical gateways located in North and South hemisphere respectively are presented. The numerical results are compared with the corresponding annual results.