This paper proposes a mathematical framework for evaluating the throughput of an 802.11 distributed wireless network when the system allows multi-packet reception in asynchronous operating mode. Differently from previous studies on multi-packet reception, which assume a certain synchronization between the different sources at the beginning of the respective transmissions, this work theoretically analyzes a fully distributed scenario, where each node can access to the medium in a completely asynchronous way. More precisely, a new transmission can begin in a channel where other nodes are already communicating as long as the current channel load is within a given threshold. The proposed framework consists of a single source, 802.11 specific model, which generalizes a previously presented analytical model, and a novel network model, which is adopted to evaluate the theoretical performance in terms of throughput. The novel model, which includes the synchronous scenario as a particular case, is employed to investigate the influence of the number of allowed communications, of the load threshold, and of the minimum contention window on the network performance. Furthermore, the theoretical analysis is used to evaluate the throughput in presence of Rayleigh fading and noise when error correcting codes are adopted.

This paper proposes a mathematical framework for comparing the performance of wireless networks based on the IEEE 802.11 standard, employing switched-beam, directional and adaptive antennas. The analysis adopts detailed models for the antenna system behavior and the propagation environment, taking into account multipath and interference. The purpose of this study is to determine the number of simultaneous communications that may be sustained by adopting advanced antenna systems, and to investigate, by analysis and simulation, the resulting performance improvements, in terms of throughput and packet delay. Both saturated and non-saturated traffic conditions are treated. Suitable 802.11 Medium Access Control (MAC) layer parameter settings, able to exploit smart and directional antenna capabilities for maximizing the throughput, are also discussed.

This paper presents a novel network architecture for an integrated nanosatellite (nSAT)-5G system operating in the millimeter-wave (mmWave) domain. The architecture is realized adopting a delay/disruption tolerant networking (DTN) approach allowing end users to adopt standard devices. A buffer aware contact graph routing algorithm is designed to account for the buffer occupancy of the nSATs and for the connection planning derived from their visibility periods. At the terrestrial uplink, a coded random access is employed to realize a high-capacity interface for the typically irregular traffic of 5G users, while, at the space uplink, the DTN architecture is combined with the contention resolution diversity slotted Aloha protocol to match the recent update of the DVB-RCS2 standard. To achieve a reliable testing of the introduced functionalities, an accurate analysis of the statistic of the signal to interference-plus-noise ratio and of the capture probability at each mmWave link is developed by including interference, shadowing, fading, and noise. The application of the designed architecture to data transfer services in conjunction with possible delay reduction strategies, and an extension to inter-satellite communication, are finally presented by estimating the resulting loss/delay performance through a discrete-time discrete-event platform based on the integration of Matlab with Network Simulator 3.

This paper presents a fast method for conformal antenna arrays that enables the synthesis of 3D co-polar and cross-polar patterns, simultaneously reducing the dynamic range ratio (DRR) of the array excitations. The power synthesis problem is reduced to a field synthesis one by introducing two auxiliary phase patterns: one for the co-polar pattern and the other for the cross-polar pattern. The problem is then iteratively solved with respect to the two auxiliary phase patterns and to the array excitations. A modified version of the method is also proposed, for the particular case where the DRR reduction is not required, obtaining a further strong reduction of the computational time.

The resonant behaviour and the size reduction capabilities of the Minkowski fractal dipole antenna are investigated. The antenna is analysed at each resonant frequency by considering the radiation efficiency and the fractional bandwidth. Besides, a method for deriving the approximate positions of the resonant frequencies of the Minkowski dipole at each fractal iteration is proposed. The presented analysis is based on the inductive circuit model and is validated by simulations. Moreover, in order to quantify the advantages provided by the Minkowski geometry, the proposed study performs a comparison with the generalised Koch dipole in terms of fractal dimension and lacunarity.

One of the main targets of the forthcoming fifth-generation (5G) cellular network will be the support of the communications for billions of sensors and actuators, so as to finally realize the Internet of things (IoT) paradigm. This pervasive scenario unavoidably requires the design of cheap antenna systems with beamforming capabilities for compensating the strong attenuations that characterize the millimeter-wave (mmWave) channel. To address this issue, this paper proposes an iterative algorithm for sparse antenna arrays that enables to derive the number of elements, their amplitudes, phases, and positions in the presence of constraints on the far-field pattern. The algorithm, which relies on the compressive sensing approach, is formulated by transforming the original nonconvex optimization problem into a convex one. To prove the suitability of the conceived solution for 5G IoT mmWave applications, numerical examples and comparisons with other existing methods are provided, considering synthesis problems with different pattern and aperture specifications.