Alessandro Vanelli-Coralli

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).

Introducing the QEST broker: Scaling the IoT by bridging MQTT and REST

In the “Internet of Things” (IoT) vision the physical world blends with virtual one, while machine-to-machine interaction improve our daily life. Clearly, how these virtual objects are exposed to us is critical, so that their user interface must be designed to support the easiness of usage that is driven by the users needs, which is different from what machines requires. These two requirements must be solved, and an integrated solution should emerge, if we want to bring the IoT to the 50 billions network that is predicted to became in the next years. We believe that these requirements cannot be met by the same communication protocol, and so we propose a new kind of broker, named QEST that can bridge the two worlds, represented by their state-of-the-art protocols: MQTT and REST. In this paper, we demonstrate that our approach allows rapid development of user-facing IoT systems, while grating machines all the performance they need.

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.

Internet of Things application layer protocol analysis over error and delay prone links

Internet of Things (IoT) application layer protocols are gaining popularity in a wide range of scenarios, where low-cost, low-power or resource constrained devices are present. The most diffused protocols are the Constrained Application Protocol (CoAP) and MQTT. In order to ensure message delivery, CoAP features a retransmission mechanism based on exponential back-off and a finite number of retransmissions, while MQTT relies on TCP. In remote areas lacking fixed terrestrial network infrastructure, the only available Internet access technology is often represented by wireless or satellite links, usually affected by losses and significant delay. At this time, there is no information about MQTT and CoAP performance over high delay links in the literature. The goal of this paper is to provide a quantitative performance analysis of the mentioned IoT protocols over various conditions of offered traffic, packet loss probability and delay. Our findings show that, with default protocol parameters, MQTT offers better performance in terms of throughput in any of the considered scenarios. As far as latency is concerned, CoAP slightly outperforms MQTT in case of low offered traffic, low loss probability and high delay. We suggest to tune CoAP parameters in order to cope with high traffic and high loss probability: the new parameters result in improved latency and throughput in those conditions.

An interference estimation technique for Satellite cognitive radio systems

The increasing request of communication capacity for the introduction of modern multimedia services has collided with the problem of the spectrum shortage. One of the most known approach is represented by cognitive radios, which are supposed to exploit already deployed frequency bands in use by an incumbent system. Among other cognitive radio features, detection and estimation of the incumbent user are essential for implementing the cognitive radio system avoiding any interference. This is particularly important in SatCom cognitive scenarios due to transmission power impairments. In this paper, we focus on a joint interference and noise estimation algorithm aiming at detecting and estimating incumbent interference, for allowing the coexistence of the two systems. The behavior of the algorithm is analytically derived, and numerical results obtained through computer simulations confirm the effectiveness of the proposed approach.

Adaptive coding and modulation techniques for next generation hand-held mobile satellite communications

In the last years we are seeing the increasing presence of multimedia applications together with a wide variety of terminals, from the PCs to the notebooks, from the smartphones to the tablets. In order to exploit such advanced services, ubiquitous and broadband connections are required. While urban or suburban areas can be covered by using terrestrial wireless broadband networks, there are several rural or low populated areas with narrowband access. To this aim, satellite community has developed in the last years two communications standards specifically suited for mobile communications, i.e., DVB-SH and DVB-RCS NG. Among others they consider adaptive waveforms techniques for increasing the system reliability and throughput aiming to exploit the variable channel behavior. Adaptive coding and modulation (ACM) belongs to this family of algorithms, by adapting the modulation and coding scheme based on the channel behavior. In this paper we focus on a state adaptive algorithm suited for mobile applications.

An energy detector based radio environment mapping technique for cognitive satellite systems

The increasing request of bandwidth for multimedia advanced services is one of the major issues of modern wireless systems. The spectrum shortage has been faced in several ways; among others the cognitive radio approach, aiming to exploit the unused spectrum resources already assigned to incumbent users, is maybe the most known. However, even if its application has been extensively proposed for wireless terrestrial communications, it remains a still unexplored area concerning Satellite Communications. The aim of this paper is to propose an Energy Detector based Radio Environment Mapping for the spectrum awareness functionality of a hybrid terrestrial/satellite scenario where the satellite components aim at exploiting the resources unused by terrestrial communications. The proposed approach allows to take advantage of cooperation between multiple sensing nodes evaluating spatial detection and false alarm probabilities besides their relationship with device detection and false alarm probabilities.

Coarse beamforming techniques for multi-beam satellite networks

Coarse beamforming is a space processing scheme which allows for efficient use of the available spectral resources on the feeder link of a multi-beam broadband satellite system. In this framework, spectral occupancy of the multiplexed antenna signals that must be exchanged between the satellite and the gateway is a critical issue, up to the point that a costly multiple gateway infrastructure could be required to restrain bandwidth usage. Alternatively, a hybrid on board/on ground processing architecture is desirable, where the effect of space processing allows to project feed signals on a subspace, thus reducing the required feeder link bandwidth. This foresees a fixed processing scheme on board the satellite, which we refer to as Coarse Beamforming, yielding an overall system which relies on reasonable payload complexity, together with on ground processing flexibility. We explore two Coarse Beamforming techniques for the return link of a multi beam satellite system, and we evaluate the effect of compression in terms of reconstructed signal degradation. We show how, without significant distortion, bandwidth occupancy can be considerably reduced.

Adaptive coding and modulation techniques for mobile satellite communications: A state estimation approach

In the last years we are witnessing the increasing presence of multimedia application, in a wide variety of terminals, from the PC to the notebook, from the smartphone to the tablet. In order to exploit such advanced services the requirement is to have an ubiquitous and broadband connection. While urban or suburban areas can be covered by using terrestrial wireless broadband networks, there are several rural or low populated areas with narrowband access. To this aim, satellite technologies allow to cover very large areas. However, they still have some issues in covering mobile users with broadband connections. One of the most important approaches is to develop adaptive waveforms techniques able to exploit the variable channel behavior. Adaptive coding and modulation (ACM) belongs to this family of algorithms, by adapting the modulation and coding scheme based on the channel behavior. In this paper a comparison among three different techniques is proposed by focusing on a state approach for increasing the user throughput, and considering different mobile speeds.

Energy efficient CPM waveforms for satellite mesh networks

This papers addresses the design of new energy-efficient Continuous Phase Modulation (CPM) waveforms suitable for being adopted in satellite mesh networks that are characterized by the absence of the Hub, and by small antennas and power amplifiers with moderate to low output saturated power at the user terminal. In particular, a CPM modulation format concatenated with a proper convolutional code for low spectral efficiency values has been selected to implement an efficient waveform for power-limited scenarios. Performance results show the gain obtained with respect to the DVB-RCS2 CPM waveforms at higher spectral efficiency also when transmission techniques, such as Burst Repetition, are considered, and confirm the suitability of the new designed CPM waveforms for satellite hub-less scenarios.