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 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 work presents our effort in developing a complete, real-time, Software-Defined Radio implementation of an OFDM transceiver, compliant with the IEEE 802.11 Physical Layer specifications. All the baseband components in both the transmitter and the receiver are implemented with fast software functions, running on a General Purpose CPU. Real-time operation is achieved on a modern CPU by means of extensive code optimization, mostly using the SIMD instruction sets which are widely available on almost every modern CPU.

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 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.