Ilaria Thibault

Phase synchronization algorithms for distributed beamforming with time varying channels in wireless sensor networks

In a wireless sensor network, distributed beamforming is a cooperative technique that enables a group of nodes to emulate a virtual array and to steer a beam in a particular direction in space. This allows for shared message delivery to a distant receiver in a condition where typically communication range is limited due to power consumption constraints. Potential gains in terms of received power are compelling, but one of the main challenges is to achieve coherence of the transmitted signals at the destination in such a distributed scenario. This work presents innovative phase synchronization algorithms for a wireless sensor network that not only prove to be very efficient in terms of energy consumption, but also present good channel tracking capabilities in a time varying scenario.

Random, deterministic, and hybrid algorithms for distributed beamforming

Distributed beamforming is a form of cooperation among nodes in a wireless network to efficiently deliver a common message to a distant receiver. The critical requirement to achieve electromagnetic coherence is to synchronize the initial phases of all local oscillators, introducing minimal overhead and complexity. In the paper we introduce random, deterministic and hybrid algorithms, all based on feedback from the common receiver as the driving force, but with different phase update strategies. Our numerical results show that these algorithms achieve faster convergence time than previously proposed approaches.

Design and Analysis of Deterministic Distributed Beamforming Algorithms in the Presence of Noise

This paper presents a new deterministic closed-loop phase-alignment algorithm based on quantized feedback from the receiver for distributed beamforming. In contrast with previously proposed methods, which entailed repeated transmissions from all the nodes in the network, this new algorithm requires each node to transmit only once during the synchronization cycle. This drastically reduces the amount of power consumed to achieve phase alignment, yet the new algorithm converges at least as fast as all other existing schemes. In contrast with previous analyses of distributed beamforming based on random phase updates, where noise had been disregarded, here it is explicitly included in the models and shown to have a considerable effect that cannot be ignored. With and without noise, analytical expressions that characterize the performance of the new algorithm are provided, with emphasis on various limiting regimes of interest.

A Survey on Infrastructure-Based Vehicular Networks

The infrastructure of vehicular networks plays a major role in realizing the full potential of vehicular communications. More and more vehicles are connected to the Internet and to each other, driving new technological transformations in a multidisciplinary way. Researchers in automotive/telecom industries and academia are joining their effort to provide their visions and solutions to increasingly complex transportation systems, also envisioning a myriad of applications to improve the driving experience and the mobility. These trends pose significant challenges to the communication systems: low latency, higher throughput, and increased reliability have to be granted by the wireless access technologies and by a suitable (possibly dedicated) infrastructure. This paper presents an in-depth survey of more than ten years of research on infrastructures, wireless access technologies and techniques, and deployment that make vehicular connectivity available. In addition, we identify the limitations of present technologies and infrastructures and the challenges associated with such infrastructure-based vehicular communications, also highlighting potential solutions.

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.

Beaconing from connected vehicles: IEEE 802.11p vs. LTE-V2V

In a near future, vehicles will be equipped with wireless communications technologies to periodically broadcast information to their neighbors on their position and speed. The messages carrying such information, normally denoted as beacons, will reduce the probability of accidents and improve the safety of drivers and passengers. The main candidate technologies for this scope today are IEEE 802.11p and LTE-Advanced with device-to-device communications (LTE-D2D), which is now evolving into vehicle-to-vehicle communications features (LTE-V2V). The aim of this paper is thus to compare the performance in terms of scalability of these two technologies when used for beacon transmission. The comparison is made analytically, through the definition of common scenario and metrics.

Multi-user interference mitigation techniques for broadband multi-beam satellite systems

This paper presents a comprehensive evaluation of multi-user interference mitigation techniques for a broadband multi-beam satellite system.

Joint feeder-link bandwidth compaction and interference mitigation based on a hybrid space/ground processing architecture for a broadband multi-beam satellite system

SUMMARY In a broadband multi-beam satellite system, a hybrid space/ground processing has the potential to allow for a more efficient use of the feeder-link spectral resources when the payload is equipped with a multi-fed reflector antenna and the number of feeds exceeds the number of users to be served on-ground. In conventional systems, where the processing burden is kept on-ground to minimize payload complexity, the on-ground and the space segments have to engage in extensive communication efforts on the feeder-link to exchange the whole set of multiplexed feed signals. When spectral resources are scarce, an expensive multiple-gateway (GW) infrastructure is required to cope with these communication efforts. As an alternative, this work suggests a hybrid architecture where the satellite and the GW are able to exchange a set of intermediate signals called feedlets, whose cardinality is smaller than the number of feeds. When this occurs, the satellite implements a fixed non-adaptive processing called Coarse Beamforming (CB) to reconstruct feed signals from the subset of feedlets. Non-adaptive processing keeps the payload complexity acceptable, while a gain is obtained in terms of feeder-link bandwidth reduction. The objective of this paper is to study the implications of introducing a fixed processing scheme on-board, the satellite for the Forward Link (FL) of a broadband multi-beam satellite network. The first part of this work studies the effect of bandwidth compression on the quality of on-board reconstructed feed signals.The second part focuses on the effect of coarse beamforming on the systems spectral efficiency and availability when adaptive precoding is implemented at the GW to allow for a full-frequency-reuse scheme. Copyright

3GPP C-V2X and IEEE 802.11p for Vehicle-to-Vehicle communications in highway platooning scenarios

Abstract The focus of this study is the performance of high-density truck platooning achieved with different wireless technologies for vehicle-to-vehicle (V2V) communications. Platooning brings advantages such as lower fuel consumption and better traffic efficiency, which are maximized when the inter-vehicle spacing can be steadily maintained at a feasible minimum. This can be achieved with Cooperative Adaptive Cruise Control, an automated cruise controller that relies on the complex interplay among V2V communications, on-board sensing, and actuation. This work provides a clear mapping between the performance of the V2V communications, which is measured in terms of latency and reliability, and of the platoon, which is measured in terms of achievable inter-truck spacing. Two families of radio technologies are compared: IEEE 802.11p and 3GPP Cellular-V2X (C-V2X). The C-V2X technology considered in this work is based on the Release 14 of the LTE standard, which includes two modes for V2V communications: Mode 3 (base-station-scheduled) and Mode 4 (autonomously-scheduled). Results show that C-V2X in both modes allows for shorter inter-truck distances than IEEE 802.11p due to more reliable communications performance under increasing congestion on the wireless channel caused by surrounding vehicles.

Full-Duplex MIMO in Cellular Networks: System-Level Performance

This paper characterizes, through a stochastic geometry analysis, the increase in spectral efficiency that full-duplex transmission brings about in wireless networks. While, on isolated links, full-duplex promises a doubling of the spectral efficiency, in the context of a network this is weighted down by the corresponding rise in interference, and our characterization captures the balance of these effects. The analysis encompasses both the forward link (FL) and the reverse link (RL) with single-user and multiuser transmissions. And, as a complement to the analysis, Monte-Carlo simulations on a Vodafone LTE field test network are also presented. In the FL, the rise in interference is found to have minor impact and a doubling in spectral efficiency can indeed be approached, especially in microcellular networks. In the RL, however, a major difficulty arises in the form of exceedingly strong interference among base stations. This renders full-duplex transmission all but unfeasible in macrocellular networks (unless major countermeasures could be implemented) and undesirable in dense microcellular networks. Only in microcells with sufficient spacing among base stations does RL full-duplex pay off. Thus, full-duplex is seen not to blend easily with densification.