This paper theoretically analyzes the usage of directional slotted Aloha schemes for managing the peer-to-peer random access in fifth and sixth generation (5G/6G) systems. To this aim, the physical layer is modeled by accounting for interference and noise, while a Markov chain approach is developed to investigate the network behavior in the presence and in the absence of a separate feedback channel, which provides information concerning the success or not of each transmission attempt. Closed-form expressions for the coverage probability and for the transition matrices with and without feedback are derived to then evaluate the corresponding throughput. The analytical results, which are validated by independent Monte Carlo simulations, are used to estimate the impact of the antenna gain, of the burst length, and of the node density on the achievable performance, as well as to discuss the directional random access benefit/complexity tradeoff.

This paper presents a method for estimating the time of arrival (ToA) of long term evolution (LTE) signals received on multiple separate transmission bands by the same base station (BS) mast. By exploiting the overall bandwidth occupied by the different signals and the correlation between the corresponding channel impulse responses, a higher precision is achieved with respect to the usually adopted single-band approach whenever the time-correlation among the bands is sufficiently high. The ToA estimation is carried out by generalizing the space-alternating generalized expectation-maximization (SAGE) algorithm to the multi-band context, proving that the availability of multiple bands provides a reduced standard deviation for the estimated ToA, with a limited increase of the computational cost. The main analyzed issue consists in the management of the asynchrony between transmitters belonging to distinct cellular operators, which is addressed by developing a suitable method to combine the contributions provided by the different bands. The method is validated by simulations in dual- and tri-band scenarios, and is further applied to real dual-band signals measured through a portable setup and experimentally acquired from an LTE BS mast covering multiple cells.

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.

Among the recently proposed non-orthogonal multiple access techniques, the Coded Slotted Aloha (CSA) scheme has been identified as one of the most efficient ones. This scheme relies on the subdivision of a packet into segments and of a slot into slices, in order to enable the transmission of different segments in different slices. With respect to SA, the CSA implementation is more sophisticated, since the header of each segment must contain proper pointers specifying the slices where the other segments of that packet lie. Purpose of this paper is to investigate the impact of these pointers on the CSA throughput by properly considering the capture effect at the receiver. To this aim, a capture analysis accounting for the modulation and the header coding rate in the presence of Rayleigh fading is developed. The numerical results, which also involve a realistic millimeter-wave channel, show that the beneficial interference diversity effect introduced by the segmentation process is not significantly reduced by the overhead due to the pointers, thus confirming the practical usefulness of the CSA scheme.

This paper presents a theoretical analysis for estimating the coverage probability in two-dimensional (2D) and three-dimensional (3D) peer-to-peer (P2P) millimeter-wave (mmWave) wireless networks. The analysis is carried out by adopting suitable link state models and realistic propagation conditions, involving path-loss attenuation, angular dispersion, mid- and small-scale fading, which comply with recent channel measurements. The presented framework accounts in detail for the actual shape of the transmitting/receiving antenna patterns and for the spatial statistic that describes the node location, by considering the widely adopted Poisson point process, the uniform distribution, and the random waypoint mobility model. Analytical expressions for the statistic of the received power and simple integral formulas for the coverage probability in the presence of interference and noise are derived. The accuracy of the obtained estimations and of the introduced approximations is checked by independent Monte Carlo validations. As possible applications in the 3D mmWave context, the conceived mathematical theory is used to discuss the impact of the interference model on the reliability of the noise-limited approximation, and to estimate the average link capacity of an interfered P2P communication.

This paper discusses the use of the Space-Alternating Generalized Expectation-maximization (SAGE) algorithm for Time of Arrival (ToA) estimation in Orthogonal Frequency Division Multiplexing (OFDM) systems. This algorithm, which is an extension of the expectation-maximization approach, can exploit the intrinsic properties of a multi-carrier OFDM system to achieve the estimation of a number of parameters of each incoming signal replica, such as its amplitude, ToA, Doppler shift, and angle of arrival. The SAGE method can also be easily tailored to estimate only a desired subset of these parameters. Accordingly, this study focuses on the sole ToA estimation, but extending the SAGE functionalities to dual-band OFDM systems. This extension is achieved by exploiting the availability at the receiver of more than one band from the same transmitter, and combining the derived channel information to increase the bandwidth available for estimation. It will be shown that, in highly correlated scenarios, the performance of the SAGE algorithm for ToA estimation in a dual-band system is comparable to that of a single-band system with equivalent total bandwidth.

This paper investigates the throughput of a Framed Slotted Aloha (FSA) random access scheme, called Segmented FSA (SFSA), in which each packet is encoded and subdivided into segments before the transmission, and where Interference Cancellation (IC) is adopted to improve the success probability in case of collision between segments. The overall system performance is estimated by considering a decoding criterion based on the average information rate that is experienced during each communication. This criterion, which enables to properly consider the capture effect in the presence of interference, noise, and fading, is compared to the classic packet erasure channel model, with the aim of identifying the reliability of the two decoding approaches in different network scenarios. The final purpose of the presented study is to discuss the benefits of the interference diversity mechanism that is triggered by the combination of segmentation and IC in a capture channel.

This paper presents a theoretical model for estimating the uplink capacity of a communication in a three-dimensional(3D) millimeter-wave (mmWave) scenario. The model is developed considering realistic channel conditions, including path-loss attenuation, shadowing, and angular dispersion, which comply with recent measurement campaigns carried out in mmWave environment. The analysis also incorporates the effects of interference and noise, additionally accounting in detail for the actual shapes of the transmitting/receiving antenna patterns. Analytical expressions for the statistics of the interference power are derived, in order to enable a low-complexity evaluation of the capture probability and of the Shannon capacity for an interfered uplink communication. The conceived 3D mathematical framework, whose reliability is verified by Monte Carlo validations, is used to investigate some insights concerning the application of beamforming in dense mmWave scenarios.

Advanced antenna systems enable spatial multiplexing through beamforming, allowing the coexistence of multiple, asynchronous, peer-to-peer communications at the medium access control layer, thus introducing multi-packet communication (MPC). The result of each communication is usually established adopting a receiving threshold on the signal-to-interference ratio (SIR). However, more sophisticated reception criteria would be desirable, since the instantaneous SIR of a packet may change because of the asynchrony of the scenario. This paper investigates this partly unexplored issue moving from the exploration of some analytically tractable situations and then performing a comprehensive investigation carried out by a suitable simulation platform. The aim is to realistically estimate the combined effect of the channel access strategy, of the acknowledgement packet, and of the channel code rate, on the throughput, the drop probability, and the packet delay of an MPC network.

This paper presents a mathematical framework for including the angular domain beside the radial one in the theoretical modeling of wireless networks, in which spatial reuse enables the coexistence of multiple single-hop peer-to-peer communications inside a finite region. The proposed model analyzes a scenario where the transmitting sources are uniformly distributed over a disk and the communications are subjected to path-loss attenuation and multipath-fading, considering the actual location of each destination and its antenna system. Different from most of the previous theories in which the coverage probability of a destination is estimated assuming that the destination itself is positioned at the center of the network, in the proposed analysis, the destination location is generic. This generalization, together with the consideration of the spatial channel model and of the actual receiving pattern, allows one to investigate the influence of the angular domain on the statistic of the interference power and on the coverage probability. The conceived theory, which is further verified by Monte Carlo validations, is finally exploited to derive the network transmission capacity, with the purpose to illustrate the possible advantages that may derive from a reliable modeling of the non-isotropic context, in which each destination has to operate realistically.

Video quality assessments represent useful tools not only to evaluate the quality of the received video, but also to enable unequal error protection mechanisms. The computational cost of these quality assessments is however a relevant limitation to their use, mainly in the presence of time constraints, such as in live streaming applications. This paper proposes an algorithm capable to estimate, with a very low computational cost, the distortion due to the loss of a frame on videos encoded using the H.264 Scalable Video Coding (SVC) standard, by adopting one of the most reliable video quality assessments: the Structural SIMilarity (SSIM) index. The results show that the proposed solution allows one to obtain a satisfactory approximation of the exact SSIM-based distortion, simultaneously reducing the time required by the estimation process. The approximated SSIM distortion values are finally applied to an 802.11e distributed network with energy constraints, in order to test the effectiveness of the conceived algorithm in a practical scenario.

This letter characterizes the error performance of realistically modelled orthogonal frequency division multiplexing (OFDM) signals, when their time of arrival has to be estimated in an additive white Gaussian noise channel. In particular, different power distributions on the available sub-carriers of the OFDM signal are considered, and bounds on the corresponding root mean square estimation error (RMSEE) are evaluated. The tools used for such purpose are the widely adopted Cramér-Rao bound and the Ziv-Zakai bound, which is tight in a wide range of signal-to-noise ratio (SNR) values. The presented analysis reveals that, for a given signal bandwidth, a proper power distribution on the OFDM sub-carriers is crucial for achieving a good performance in the low to medium SNR region, where the RMSEE curve exhibits the typical threshold behavior. Moreover, a trade-off between asymptotic and threshold performance is identified, thanks to the adoption of a novel performance figure, which directly describes the threshold RMSEE behavior.

This paper discusses the design requirements for enabling multiple simultaneous peer-to-peer communications in IEEE 802.11 asynchronous networks in the presence of adaptive antenna arrays, and proposes two novel access schemes to realize multipacket communication (MPC). Both presented solutions, which rely on the information acquired by each node during the monitoring of the network activity, are suitable for distributed and heterogeneous scenarios, where nodes equipped with different antenna systems can coexist. The first designed scheme, called threshold access MPC (TAMPC), is based on a threshold on the load sustainable by the single-node, while the second protocol, called signal-to-interference ratio (SIR) access MPC (SAMPC), is based on an accurate estimation of the SIR and on the adoption of low density parity check codes. Both protocols, which are designed to be backward compatible with the 802.11 standard, are numerically tested in realistic scenarios. Furthermore, the performance of the two schemes is compared to the theoretical one and to that of the 802.11n extension in a mobile environment.

This paper presents an approximated, but accurate and fast to compute, mathematical framework for evaluating the capture probability and the number of sustainable communications in a mobile wireless network where spatial reuse enables the coexistence of multiple traffic flows. The proposed study focuses on a particular multi-packet approach, known as multi-packet communication, in which different communicating pairs are simultaneously active. Within this context, the statistics of the received power, of the interference power, and of the signal-to-interference ratio are derived accounting for the antenna system and the network topology in the presence of Nakagami fading. The theoretical results, which are validated by independent Monte Carlo simulations, are used to discuss the impact of mobility on the result of each transmission attempt. The purpose of the developed theory is to provide an alternative analysis, including the spatial domain, for modeling the capture probability and the number of concurrent peer-to-peer communications that can be sustained in a mobile ad-hoc network.

Multiple‐input multiple‐output (MIMO) techniques have received a considerable attention from the research community for their promising performance in faded environments, and particular interest has been given to the physical (PHY) layer implications of the tradeoff between multiplexing and diversity. This study discusses this tradeoff extending the analysis to the medium access control (MAC) layer. To this purpose, a theoretical model for assessing the performance of an 802.11 network that relies on a MIMO‐enabled PHY layer is presented. The proposed model characterises the different MIMO systems in terms of their multiplexing gain and bit error rate performance, considering both the diversity gain of the specific MIMO scheme and the impact of the spatial distribution of the nodes. The results compare, from a MAC layer perspective, the benefits of multiplexing and diversity, providing some analytic insights on the tradeoff between increasing the system's reliability and enhancing the data rate of the single link.

This paper analyzes the performance of an 802.11 network in which spatial reuse enables the simultaneous coexistence of multiple asynchronous communications between different node pairs. This scenario, defined multi-packet communication (MPC), is theoretically investigated by deriving the capture probability for the single communication and by evaluating the network throughput using a Markov chain approach. The mechanisms introduced in the analysis for MPC operations enable the development of an improved version of the 802.11 access scheme, whose performance is evaluated using a reliable simulation platform. The main purpose of this study is to directly compare the throughput obtained from the completely theoretical analysis of an MPC scenario with that obtained from a protocol implementation, discussing some issues related to the accuracy of the collision model in realistic network topologies.

This paper has the objective of identifying the application domain of a particular multi-packet strategy enabled by spatial reuse, which allows the simultaneous coexistence of multiple traffic flows in 802.11 wireless networks and is known as multi-packet communication (MPC). More precisely, this study outlines the differences between MPC and the widely investigated multi-packet reception (MPR) and multi-packet transmission (MPT) techniques, proposing extensions to the existing MPC theoretical models that aim to reliably estimate the throughput, the average successful packet delay, and the drop probability. The presented discussion involves the channel coding rate and the stochastic collision model, which determines the throughput-delay behavior of the network. Moving from the derived results, some open issues are identified as possible topics for the future research in the field of MPC.

This paper analyzes the problem of modeling the collisions in a distributed and heterogeneous fixed wireless network in which spatial reuse enables multi-packet communication (MPC), thus allowing the coexistence of multiple peer to peer communications. The objective is to present a completely theoretical model that provides closed form expressions for the capture probability, and for the statistics of the interference power and of the signal-to-interference ratio (SIR) experienced by a receiving node. The presented theory aims in particular to investigate the impact on the capture probability of the heterogeneity introduced by the network topology and by the use of different antenna systems. All theoretical results are validated by independent Monte Carlo simulations. Finally, this study discusses the possible analogies between the developed and the existing frameworks for homogeneous scenarios, and presents a preliminary application of the developed capture analysis by evaluating the throughput-delay behavior of a homogeneous 802.11 MPC network.

This paper analyzes the problem of modeling the collisions in a wireless network supporting multi-packet communication by spatial reuse. Typically, in a multi-packet scenario, the result of a transmission attempt is established using two main approaches: one, more idealized but suitable for theoretical analyses, based on the success probability or on the threshold on the number of sustainable communications, and another one, more realistic, relying on the signal-to-interference ratio (SIR) experienced by the receiving node. The two approaches may lead to considerably different results, since the number of allowed communications is often estimated neglecting many physical aspects. This study investigates this issue by presenting a mathematical model, validated by simulations, which relates the number of active communications with the statistic of the SIR. Moving from the developed framework, this paper discusses how some assumptions usually adopted for analyzing multi-packet networks exploiting spatial reuse may be revised in presence of a more detailed characterization of the spatial domain.

This paper proposes a novel Medium Access Control (MAC) protocol for enabling multiple simultaneous communications in 802.11 networks where the nodes can use adaptive antenna arrays. The presented scheme is backward compatible with the 802.11 standard and is designed for heterogeneous scenarios, where legacy and non-legacy nodes equipped with different antenna systems can coexist. The access rules are based on a local but accurate Signal-to-Interference Ratio (SIR) estimation and on the adoption of Low Density Parity Check (LDPC) codes, which enable each node to reliably estimate the result of the transmission attempt of all active nodes. The proposed scheme is compared to a previously developed one in noisy and multipath-fading environments.

Abstract This paper describes an experimental setup for measuring the throughput of an 802.11 network that supports Quality of Service (QoS) mechanisms, addressing some issues concerning the comparison between experimental and theoretical results. The setup is an ad hoc network in which the nodes implement the Multiband Atheros Driver for Wireless Fidelity (MADWiFi). There are three main contributions of this study. The first one describes the adjustments to the MADWiFi source code that guarantee the control of the QoS parameters in ad hoc mode. The second contribution aims to provide a practical method for verifying if the backoff generated by a given wireless card is uniformly distributed, as dictated by the 802.11 standard. This represents a key point when theoretical and experimental results must be compared, since many vendors adopt nonuniform backoff distributions in their commercial cards. As a third contribution, this paper presents a theoretical nonsaturated analysis that provides the throughput and the successful packet delay of an 802.11 network supporting QoS in presence of nonuniform backoff. The throughput derived from this analysis using a uniform backoff, which is included in the proposed model as a particular case, is compared to the measurements provided by the deployed setup. Copyright © 2010 John Wiley & Sons, Ltd.

This paper presents a novel Medium Access Control (MAC) protocol for 802.11 networks in which the nodes can adopt smart antenna systems. The presented protocol is designed to satisfy two fundamental requirements: the exploitation of adaptive arrays to increase the network throughput and the backward compatibility of the novel scheme with the 802.11 MAC layer. The developed solution allows the simultaneous coexistence of multiple communications, while maintaining, for the legacy nodes, the same throughput levels achievable in the 802.11 standard. The performance and the backward compatibility of the proposed MAC protocol are tested in multipath-fading environment and considering heterogeneous scenarios, including 802.11 legacy stations together with nodes implementing the novel scheme and equipped with different antenna systems.

This paper proposes a PHYsical (PHY) layer de sign that enables Multi-Packet Reception (MPR) in distributed wireless networks using advanced antenna systems. The main objective of this work is to present a backward compatible solution that is able to exploit the capabilities of adaptive arrays, allowing the coexistence of non-legacy and legacy 802.11g nodes. The proposed scheme is designed for an asynchronous scenario, in which a node can access to the medium as long as the number of ongoing communications lies within a given threshold, and considering an heterogeneous network, in which the antenna system can be different for each node. The developed solution is implemented in an hybrid discrete-time discrete-event simulation platform obtained integrating MATLAB and network simulator 2 (ns-2), in order to explore the system performance for different network topologies and in presence of multipath-fading.

Recent studies have revealed that many vendors implement nonuniform backoff distributions in their commercial 802.11 Network Interface Cards (NICs) in order to obtain a better performance in particular scenarios. Therefore, in many cases, the backoff behavior of the cards can be not adherent to the 802.11 standard specifications. By consequence, the theoretical and the experimental performance of an 802.11 distributed network, including throughput and packet delay, may not coincide because the real backoff behavior of the adopted cards is different from the expected one. This paper presents a practical method for verifying if the backoff generated by a given 802.11 NIC is uniformly distributed, as dictated by the 802.11 standard, or not. The proposed method is based on the comparison between the theoretical and the experimental statistics of the time between two successfully transmitted packets. Thus it does not require intrusive measurements inside the chipset and can be performed using a simple open source software platform.

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 evaluating the throughput of an 802.11 Distributed Wireless Network (DWN) when the system allows Multi-Packet Reception (MPR) in asynchronous operating mode. Differently from previous studies on MPR, which assume a certain synchronization between the different sources at the beginning of the respective transmissions, this work analyzes a fully distributed scenario, where each node can access to the medium in a completely asynchronous way. More precisely, a new transmission may begin in an already busy channel, as long as the current channel load is within a given threshold. The presented 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.

This paper compares the theoretical and the experimental throughput of an 802.11 adhoc network implementing quality of service (QoS) mechanisms. The theoretical model provides the throughput of each access category (AC) of each node in saturated and non-saturated traffic conditions. The experimental setup is described in detail to enable the reproduction of the presented measurements. This setup adopts the widely used multiband atheros driver for wireless fidelity (MADWiFi), which, however, provides the QoS option for centralized operations only. Hence, this study describes the adjustments to the MADWiFi source code that guarantee the control of the QoS parameters in adhoc mode.

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 proposes a mathematical framework for evaluating, in saturated and non-saturated traffic conditions, the performance of an 802.11 wireless network in which the nodes are equipped with adaptive antenna systems. The analysis, validated by simulations, adopts detailed models for the antenna behavior and the propagation environment, taking into account multipath and interference. The developed model is used to investigate the proper parameter settings that lead to throughput maximization, providing a simplified method to obtain the optimum contention window when adaptive arrays are employed.

This paper investigates the influence of channel coding on the performance of a distributed wireless network in which the nodes are equipped with multiple antennas. Different coded modulation techniques and antenna systems are taken into consideration and compared, assuming an outdoor environment. More precisely, the proposed study compares the performance of wireless networks adopting convolutional codes, already adopted in the 802.11a physical layer standard, with the performance that may be achieved by adopting more efficient coding techniques. A realistic channel model including Rayleigh fading and Laplacian power azimuth spectrum is adopted, and code performance comparison is performed using both simple switched-beam antenna (SBA) systems and more complex fully adaptive smart antennas (FASAs).

This paper investigates the behavior of a wireless mesh network in which the nodes are equipped with a multiple antenna system. The objective of this study is the comparison of the low-cost switched-beam antennas with the more expensive fully adaptive smart antennas. The analysis and the simulations are performed together with some considerations regarding the advantages and the practical possibilities of employing multi-antenna systems on mesh routers. The analytical and the numerical results are derived employing realistic antenna radiation patterns and a proper spatial channel model.

This paper investigates the performance of a distributed wireless network in which the nodes are equipped with fully adaptive smart antennas. The main goal is the evaluation of the influence that the geometrical configuration of the antenna array has on network throughput and packet delay. Analysis and simulations are performed to study the relationship between the geometry of the antenna array and the network topology. In this paper, the performance degradation due to both the small-channel angular spreads and the speed of mobile nodes is investigated. The results, which hold for the low-rank channel model only, extend to this specific case previous results obtained in ideal channel conditions. The study adopts an access scheme, previously proposed for ad-hoc networks, which is able to exploit the interferer suppression capabilities of smart antennas, together with realistic models for the antenna and the channel behaviors.

This paper proposes three methods to estimate the distortion deriving from packet losses in wireless video communication. The proposed models take into account the short-term properties of the encoded video sequences and the properties of the wireless links. A suitable set of functions is adopted to model the distortion envelope resulting from multiple losses. The performance of the employed models, which depends on the average packet loss rate (PLR), is compared with the actual distortion, evaluated by decoding the received sequence with a properly designed, robust decoder. Numerical results confirm the accuracy of the proposed models, that are able to closely approximate the actual mean square error (MSE) behavior for a wide range of loss rates. Some applications of the proposed algorithms are also presented in the paper.

This paper analyzes the maximum number of simultaneous communications that can be sustained by an ad-hoc network in which the nodes are equipped with fully adaptive smart antennas. The study proposes an analytical model for the evaluation of the performance of ad hoc networks which includes multipath together with some characteristics of the access scheme. The main goal is the analysis of the relationship between the angular spread of the channel and the transmission policy ruled at MAC layer. Moreover, in the paper, it is examined the influence of the spatial channel model on network performance.