Green RF/FSO Communications in Cognitive Relay-Based Space Information Networks for Maritime Surveillance

In this paper, we provide an overview of a space-based network for the maritime surveillance information sharing and evaluate the coverage, the throughput and the real-time reception capacity of the presented systems. The focus is on the feeder link of a multi-hop geostationary satellite system. We propose a cognitive relay-based architecture for the inter-satellite and satellite-to-ground communication with a multi-band spectrum sensing operating on both free-space optical (FSO) and radio frequency (RF) bands. Furthermore, modeling the spectrum sensing energy as a Gamma distribution we derive the formula of the network energy consumption in presence of multipath fading and considering two different data relay schemes: amplify-and-forward (AF) and decode-and-forward (DF). We prove that the RF/FSO communication in the proposed relay-based architecture enhances the data transmission increasing the throughput and the real-time reception capacity and reducing the network energy consumption. The performance evaluation shows that the DF scheme overcomes the AF one in terms of energy consumption while the AF scheme overcomes the DF one in terms of probability detection, both experience the same throughput. Finally, the proposed novel architecture has been compared with existing ones showing that it enhances the current maritime surveillance systems by jointly optimizing communication functionalities.

I. Introduction

In next decade, the space information networks are expected to play a key role in accommodating the huge amount of traffic demanded by wireless communications, remote sensing, air traffic control, aviation/maritime communications, Internet of Things, and aerospace metrology. At the end of 2020 the predicted information volume for each Sentinel of the Copernicus system [1] is of 7 PB/year. The persistent trend for greater information volume proves that the traditional standalone Earth observation (EO) satellites are not capable of ensuring such a large traffic volume. A space information network (SIN) is an information network infrastructure based on: a) integrated networking of space platforms (e.g., GEO/NGEO satellites, high altitude platform stations); b) support of massive real-time data transmission and processing; c) realization of global information services. In this paper, we present an implementation of a SIN for the maritime surveillance aiming at improving the degree of integration between space and in situ maritime surveillance systems in order to realize a common interoperable spatial platform for maritime surveillance. We propose a novel architecture that enhances the current maritime surveillance systems based on Sentinel-1 of the Copernicus programme in terms of coverage area, throughput and delivery time. In order to enhance the data rate and the coverage area and to reduce the time between data acquisition and transmission from the satellite to a ground station, data relay systems have been introduced [2]–[4]. Contrarily to high throughput satellites (HTS) that enhance the channel capacity utilizing a multibeam architecture with frequency reuse, the data relay systems have no interference from adjacent frequencies [2].