Pedro Henrique Juliano Nardelli

On the Joint Impact of Beamwidth and Orientation Error on Throughput in Directional Wireless Poisson Networks

We introduce a model for capturing the effects of beam misdirection on coverage and throughput in a directional wireless network using stochastic geometry. In networks employing ideal sector antennas without sidelobes, we find that concavity of the orientation error distribution is sufficient to prove monotonicity and quasi-concavity (both with respect to antenna beamwidth) of spatial throughput and transmission capacity, respectively. Additionally, we identify network conditions that produce opposite extremal choices in beamwidth (absolutely directed versus omni-directional) that maximize the two related throughput metrics. We conclude our paper with a numerical exploration of the relationship between mean orientation error, throughput-maximizing beamwidths, and maximum throughput, across radiation patterns of varied complexity.

Efficiency of Wireless Networks under Different Hopping Strategies

In this work we investigate whether it is preferable to have a large number of short single-hop links or a small number of long single-hops in a multi-hop wireless network. We derive analytical expressions to compute the metric aggregate multi-hop information efficiency under different hopping strategies, and analyze the trade-off involving robustness of single-hop links, interference and hopping strategy.

Optimal Transmission Capacity of Ad Hoc Networks with Packet Retransmissions

In this paper we investigate the transmission capacity of wireless networks when packet retransmissions are allowed. We consider networks modeled as a homogeneous Poisson point process operating under different medium access control schemes, namely unslotted and slotted ALOHA, and CSMA with carrier sensing at the transmitter and with carrier sensing at the receiver. For these scenarios, we derive analytical expressions to compute the maximum number of retransmissions attempts that leads to the optimal transmission capacity. Numerical results based on our formulation show that CSMA with carrier sensing at the receiver (asynchronous transmissions) reaches the highest maximum transmission capacity when traffic intensity is low, while slotted ALOHA (synchronous transmissions) is the best choice when traffic intensity is high.

Models for the modern power grid

This article reviews different kinds of models for the electric power grid that can be used to understand the modern power system, the smart grid. From the physical network to abstract energy markets, we identify in the literature different aspects that co-determine the spatio-temporal multilayer dynamics of power system. We start our review by showing how the generation, transmission and distribution characteristics of the traditional power grids are already subject to complex behaviour appearing as a result of the the interplay between dynamics of the nodes and topology, namely synchronisation and cascade effects. When dealing with smart grids, the system complexity increases even more: on top of the physical network of power lines and controllable sources of electricity, the modernisation brings information networks, renewable intermittent generation, market liberalisation, prosumers, among other aspects. In this case, we forecast a dynamical co-evolution of the smart grid and other kind of networked systems that cannot be understood isolated. This review compiles recent results that model electric power grids as complex systems, going beyond pure technological aspects. From this perspective, we then indicate possible ways to incorporate the diverse co-evolving systems into the smart grid model using, for example, network theory and multi-agent simulation.

Throughput Optimization in Wireless Networks Under Stability and Packet Loss Constraints

The problem of throughput optimization in decentralized wireless networks with spatial randomness under queue stability and packet loss constraints is investigated in this paper. Two key performance measures are analyzed, namely the effective link throughput and the network spatial throughput. Specifically, the tuple of medium access probability, coding rate, and maximum number of retransmissions that maximize each throughput metric is analytically derived for a class of Poisson networks, in which packets arrive at the transmitters following a geometrical distribution. Necessary conditions so that the effective link throughput and the network spatial throughput are stable and achievable under bounded packet loss are determined, as well as upper bounds for both cases by considering the unconstrained optimization problem. Our results show in which system configuration stable achievable throughput can be obtained as a function of the network density and the arrival rate. They also evince conditions for which the per-link throughput-maximizing operating points coincide or not with the aggregate network throughput-maximizing operating regime.

Aggregate Information Efficiency and Packet Delay in Wireless Ad Hoc Networks

In this paper we evaluate the effects of modulation and coding schemes on the performance of ad hoc networks. The analysis is based on analytical expressions derived for the aggregate information efficiency and the average packet delay in ad hoc networks. Modulation and error correcting coding directly affect the trade-offs involving spectral efficiency, interference immunity and channel reuse in a wireless network. Results of numerical analysis show that lower modulation orders and high coding rates are preferable when one wants to maximize the aggregate information efficiency and minimize the average packet delay.

Full-duplex communications in interference networks under composite fading channel

In this paper, we investigate how highly dense deployments of small cells perform when full-duplex nodes communicate under composite fading channels. With regard to an arbitrary user of interest, we first identify the impact of the extra interference from co-channel users and how that compares to the intrinsic self-interference. The performance of full-duplex networks is compared to a traditional half-duplex benchmark scenario where the only source of down-link inference is originated by simultaneous transmissions of surrounding base stations. A mathematical framework based on stochastic geometry is used to carry out our investigations. Here, the system performance is assessed by considering various network configurations and distinct fading channel conditions, namely log-normal shadowing and Nakagami-m fading. Using the aforesaid framework, we approximate the aggregate interference at the user of interest and then derive closed-form expressions for the corresponding signal to interference ratio and outage probability. Results show that users in full-duplex mode achieve higher rates even though they are subject to higher interference. It is also shown that the extent of these gains depends on the self-interference cancellation value that can be achieved and how that compares to the inference from other users.

Throughput analysis of cognitive wireless networks with Poisson distributed nodes based on location information

This paper provides a statistical characterization of the individual achievable rates in bits/s/Hz and the spatial throughput of bipolar Poisson wireless networks in bits/s/Hz/m

On the Secrecy of Interference-Limited Networks under Composite Fading Channels

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Multi-Hop Aggregate Information Efficiency in Wireless Ad Hoc Networks

. We assume that all transmitters have a cognitive ability to know the distance to their receivers closest interferers so they can individually tune their coding rates to avoid outage events for each spatial realization. Considering that the closest interferer approximates the aggregate interference of all transmitters treated as noise, we derive closed-form expressions for the probability density function of the achievable rates under two decoding rules: treating interference as noise, and jointly detecting the strongest interfering signals treating the others as noise. Based on these rules and the bipolar model, we approximate the expected maximum spatial throughput, showing the best performance of the latter decoding rule. These results are also compared to the reference scenario where the transmitters do not have cognitive ability, coding their messages at predetermined rates that are chosen to optimize the expected spatial throughput -- regardless of particular realizations -- which yields outages. We prove that, when the same decoding rule and network density are considered, the cognitive spatial throughput always outperforms the other option.