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Multicast is an efficient paradigm for transmitting data from a sender to a group of receivers. The IEEE 802.11 wireless LANs standards specify how to send multicast frames with no ACK and using one of the Basic Service Set (BSS) rates. This situation has led many researchers to design techniques aiming to improve reliability of a multicasting mechanism. The Leader-Base Protocol (LBP) is one such mechanism proposed in the literature that is the most promising approach. The main idea behind the design of the LBP mechanism is to reduce the probability of collision of the feedback messages sent by the multicast group members. However, the LBP mechanism falls short by not considering the varying conditions characterizing the wireless channels. In this paper, we introduce a novel auto rate selection multicast mechanism for multi-rate wireless LANs, namely ARSM (Auto Rate Selection for Multicast), capable of adapting the data transmission to the varying conditions of the channel. Our simulation results show that our new scheme outperforms the IEEE 802.11 and the LBP mechanisms.

Co-channel interference and contention at shared medium access may significantly degrade the performance of a CSMA/CA-based wireless LAN. While this phenomenon may be controlled within a single administrative domain by choosing appropriate access point installation sites and assigning operating channels intelligently, there is little that can be done against interference by access points from other nearby administrative domains. This problem becomes paramount in so-called , as each access point is operated by a different owner and can be viewed as a separate domain. In this paper we propose a from different domains based solely on knowledge about the immediate neighborhood. We show that our distributed coordination algorithm may lower contention by around 19% compared to standard WLAN.

Opportunistic scheduling monitors the receivers’ channel states and schedules packets to the receivers in relatively good channel conditions. Opportunistic scheduling can be easily implemented in cellular networks such as the 1xEVDO system because the channel state report function is embedded in the system. To apply opportunistic scheduling to WLANs, deficient of channel report functions, we first devise efficient channel probing mechanisms. Several opportunistic scheduling methods for WLANs have been proposed recently. These previous methods limit the candidate receivers and may not fully realize the potential multiuser diversity gains. In this paper, we develop new opportunistic scheduling called WDOS (Wireless LAN Distributed Opportunistic Scheduling). That is based on a modified RTS/CTS exchange scheme. In WDOS, a sender broadcasts a BRTS (Broadcast RTS) to all receivers. A receiver responds with a CTS after a backoff delay. The value of the backoff delay is determined such that the receivers in relatively better channel conditions acquire channel accesses. We evaluate the performance of WDOS both via an analytic method and via computer simulations. Our performance study shows that WDOS achieves the performance near optimal.

Two dual-printed dipole antennas for WLAN applications operating in the 802.11 a/b/g (2.4-2.5 Ghz and 4.9-5.875 GHz) frequency bands are presented. Genetic Algorithm optimization (GA) is applied first, to a classical dual band printed dipole antenna schema. Later on, a pre-fractal technique is proposed on the larger strip and electromagnetic parameters are re-optimized to achieve a more compact radiator. Frequency performance of both antennas is introduced showing a VSWR<1.5 for a input impedance of 50 Ohms. Finally, the mean effective gain (MEG) is worked out considering several scenarios. Results for both antennas for typical indoor and outdoor environments are given using the statistical angle of arrival behavior of such environments.

WLAN, printed dipole antennas, genetic algorithms, Mean Effective Gain.

Future wireless communication scenarios will be characterized by the heterogeneity in terms of coexisting wireless access technologies. Many mobile terminals will support different air interfaces and in order to provide true multi-mode operation, the sole use of IP protocol is not enough. We present in this document the Universal Convergence Layer that residing on top of the different air interfaces offers a single interface to IP while supporting the cross-layer optimization of user data flows as well as many other key functionalities in personal networks communications. This document describes and discusses the implementation of this framework over real platforms. Furthermore, the results of the measurement campaign carried out to assess the benefits introduced by the dynamic interface selection mechanism implemented at the UCL will be also presented. The results obtained will allow us to extract conclusions about the appropriateness of the solution adopted.

Loss Differentiation Algorithms (LDA) are currently used to determine the cause of packet losses with an aim of improving TCP performance over wireless networks. In this work, we propose a cross-layer solution based on two LDA in order to classify the loss origin on an 802.11 link and then to react consequently. The first LDA scheme, acting at the MAC layer, allows differentiating losses due to signal failure caused by displacement or by noise from other loss types. Moreover, in case of signal failure, it adapts the behavior of the MAC layer to avoid a costly end-to-end TCP resolution. The objective of the second LDA scheme, which acts at the TCP layer, is to distinguish a loss due to interferences from those due to congestions and to adapt consequently the TCP behavior. The efficiency of each LDA scheme and of the whole cross-layer solution are then demonstrated through simulations.

When TCP is carried over 3G links, overbuffering and buffer overflow at the RLC layer degrades its performance. AQM techniques at the RLC buffer can bring noticeable enhancements to TCP performance without introducing changes in 3G specifications. We show that the optimum parameter setting of AQM algorithms in RLC buffers is strongly related to the radio bearer rate, which can be changed dynamically by control layer protocols. By means of extensive simulation experiments we propose, for each specified nominal rate, optimum configurations that keep the goodput near the maximum while the delay is reduced up to 50%. We consider two AQM schemes, an adapted RED algorithm and a novel deterministic one, SBD described in this paper. We illustrate how an automatic reconfiguration of AQM parameters avoids the degradation caused by sudden changes in the radio bearer rate.

Mobile ad hoc networks (MANETs) appear nowadays as one of the most promising architectures to flexibly provide multimedia services in multiple wireless scenarios. However, the dynamic nature of this environment complicates the supporting of the heavily demanded QoS. Since cooperation in MANETs is required to establish multihop communications, designing efficient QoS Routing algorithms mainly concentrates the technical efforts to guarantee QoS. This work presents a cross-layer architecture that performs a practical solution to solve the trade-off between the QoS provision and the efficient resource utilization thanks to different layers sharing network status information to cooperate in the network resource management. The cooperation between Routing and MAC levels allows to select End-to-End QoS paths according to the bandwidth availability measured in a realistic interference scenario, and appropriately react to mobility in a QoS context.

This paper proposes an enhanced B-MAC (ENBMAC), a carrier sense Medium Access Control (MAC) protocol with ultra low power operations for wireless sensor networks. Due to battery-operated computing and sensing devices in wireless sensor networks, the development of MAC protocols that efficiently reduce power consumption is an important issue. B-MAC provides bidirectional interfaces such as Clear Channel Assessment (CCA), Low Power Listening (LPL) and uses an adaptive preamble sampling scheme to optimize performance and conserve energy. This reduces the amount of energy by comparing to other MAC protocols in WSNs. However, B-MAC can not achieve the overhearing avoidance. To solve this problem, we propose Node Recognition (NR) algorithm using the next hop address in MAC layer. Because this mechanism tries to handle the overhearing avoidance, ENBMAC makes it possible to extend the lifetime of the wireless sensor networks that contain a large number of nodes. The experiment results show that ENBMAC protocol reduces the energy consumed by receiving up to 90 percent comparing to B-MAC.

For the latest ten years, many authors have focused their investigations in wireless sensor networks. Different researching issues have been extensively developed: power consumption, MAC protocols, self-organizing network algorithms, data-aggregation schemes, routing protocols, QoS management, etc. Due to the constraints on data processing and power consumption, the use of artificial intelligence has been historically discarded. However, in some special scenarios the features of neural networks are appropriate to develop complex tasks such as path discovery. In this paper, we explore the performance of two very well known routing paradigms, and , and our routing algorithm, named , which has the novelty of being based on the introduction of neural networks in every sensor node. Extensive simulations over our wireless sensor network simulator, OLIMPO, have been carried out to study the efficiency of the introduction of neural networks. A comparison of the results obtained with every routing protocol is analyzed. This paper attempts to encourage the use of artificial intelligence techniques in wireless sensor nodes.