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 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 applies three low complexity methods, previously proposed by the authors, to estimate the distortion deriving from packet losses in error-prone video communication systems. In a first application scenario, the distortion estimated by the encoder is encapsulated in each video packet and used as side information by a modular router, in which the architecture is properly modified for taking into account the distortion impact produced by the loss of each packet. Computational complexity considerations, compared with traditional rate distortion optimization (RaDiO) techniques, are also discussed, showing that the proposed distortion estimation algorithms may be easily used and integrated in a wireless router with limited CPU resources. In the paper a multi-hop scenario is also considered as possible application environment, in which the prioritization and selective discarding policy are based on the estimated distortion and on the loss pattern deriving form previous hop transmissions.

This article proposes three methods to estimate the distortion deriving from packet losses in wireless video communication. The proposed methods take into account the short-term properties of the encoded video sequences. A suitable set of functions is adopted to model the distortion envelope resulting from multiple losses. The estimated performance is compared with the actual distortion, evaluated by decoding the received sequence with a properly designed decoder. Numerical results confirm the accuracy of the proposed models in approximating the actual Mean Square Error (MSE) for a wide range of loss rates. Some applications of the proposed algorithms are presented.

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.