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Networking researchers have long faced a fundamental tension between the experimental realism of wireless testbeds on one hand, and the control and repeatability of simulation on the other hand. To overcome the stark tradeoff of these traditional alternatives, we have developed a wireless network emulator that enables both realistic and repeatable...
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... Not only must the emulator simulate the channel losses accurately but it must also preserve the integrity of the transmitted signals . The process of mixing and sampling will add some distortion to the transmitted signals [20]. This distortion is only a concern if the performance of the radios in the emulator is not consistent with the performance of the same radios communicating through the air. ...
The evaluation of wireless research is challenging because signals traveling through the ether are affected by the physical environment, including movement by people and objects. As a result, testbed experiments are hard to control and are non-repeatable. We have developed a wireless networking testbed based on digital signal propagation emulation that provides control over the signal propagation environment. The testbed has been in regular use for research and education since early 2007. In this paper we present measurements illustrating the properties of the emulator testbed. We also compare the results of various experiments on the emulator with simulation results to shed some light on when the increased accuracy of the emulator testbed is important. Finally, we use the experience gained on the emulator to identify classes of experiments for which the emulator is well suited, compared with other evaluation platforms.
... • A second approach is to use a channel emulator (FPGA or otherwise based), for example, as Judd et al. describe on [90]. Channel emulators change wireless conditions artificially to simulate different kinds of environments with high repeatability. ...
... The Physical layer is the most elusive for controlling, since to the extreme would require total isolation and controlled interference generation. Work on this area has been developed by Judd et al. [90], where the wireless channel is emulated based on the modification of the signal characteristics using a dedicated FPGA for digital signal processing . MAC layer access for controlling purposes is as available as the wireless card vendor and drivers allow, for example, for Atheros-based cards under Linux, certain parameters (as the transmission rate, the ACK timeout or the output power) can be controlled as a standard feature. ...
Since the inception of the 802.11 standard in 1999, WLANs, which used to be exceptional, became a massive phenomena together with the evolution of portable devices. At the same pace, research on wireless networks, where both simulation and experimentation are used to validate protocols, has evolved rapidly. Nevertheless, the models used in this area were adapted from the wired paradigm, which has led to a significant gap between the simulated and the experimental results. Therefore, to validate wireless protocols or algorithms, wireless experimentation remains as an important resource. This thesis explores the improvements to experimentation on WLANs, from a methodological point of view. The main contributions of this thesis are: First, the new model for data abstraction to represent network events and aggregated data logs; second, the methodology to manage data in order to support a database model; and third the replacement of custom made processing scripts with data-oriented filter modules. These three key points converge to a proposal of a wireless experimentation methodology in order to attain reproductible experiments. We implement this methodology within a Wireless Experimentation Tool, and furthermore we show the improvement results through a wireless multicast experimentation use case.
... The emulator can work in different bands but requires a new RF front end. The design of the RF front end for the emulator system was studied in [6]. ...
... The emulator can work in different bands but requires a new RF front end. The design of the RF front end for the emulator system was studied in [6]. The downconverted signal is sampled at 180MHz by an AD9430 12 bit ADC so the entire 80MHz of the 802.11b/g band can be emulated. ...
Wireless channel emulators are important tools for testing radio devices, especially in mobile environments. Wireless network emulators give the same accuracy and control for testing radio network systems that traditional channel emulators give to point to point radio links. Network emulators require many more independent channels than traditional channel emulators. This problem is particularly challenging for the real time channel simulator in the emulator. The challenges of designing a wireless network channel simulator are discussed and a design is presented on a Xilinx Virtex-II Pro FPGA. This channel simulator can model 210 independent channels between 15 nodes with a bandwidth of 90 MHz. The performance of the design was verified by measuring transport-layer throughput between 802.11b radios transmitting through the channel simulator.
... • A second approach is to use a channel emulator (FPGA or otherwise based), for example, as Judd et al. describe on [90]. Channel emulators change wireless conditions artificially to simulate different kinds of environments with high repeatability. ...
... The Physical layer is the most elusive for controlling, since to the extreme would require total isolation and controlled interference generation. Work on this area has been developed by Judd et al. [90], where the wireless channel is emulated based on the modification of the signal characteristics using a dedicated FPGA for digital signal processing . MAC layer access for controlling purposes is as available as the wireless card vendor and drivers allow, for example, for Atheros-based cards under Linux, certain parameters (as the transmission rate, the ACK timeout or the output power) can be controlled as a standard feature. ...
Depuis la création de la norme 802.11, en 1999, les réseaux locaux sans fil, qui était exceptionnelle à l'époque, sont devenus un phénomène incontournable après la l'évolution des appareils mobiles. Au même rythme, la recherche sur les réseaux sans-fil a rapidement évolué suivant des modèles adaptés du paradigme des réseaux filaires, qui a conduit un écart significatif entre la simulation et les résultats expérimentaux. En conséquence, afin de valider les protocoles sans fil ou des algorithmes, l'expérimentation sans fil devient un ressource importante. Cette thèse étudie les améliorations sur l'expérimentation sur les réseaux locaux sans fil, d'un point de vue méthodologique.
Dans cette thèse, nous avons d'abord créé un nouveau modèle d'abstraction de données pour représenter les événements de réseau et de l'agrégation de données statistiques, en deuxième lieu, nous élaborons une méthodologie pour la gestion des données en vue de supporter un modèle de base de données et enfin on remplace le traitement avec scripts sur mesure avec des modules de filtrage et traitement. Ces trois principaux éléments convergent dans une méthodologie d'expérimentation qui pointe sur les conditions d'expérience et d'amélioration de la reproductibilité. Après, nous présentons Wextool, la mise en oeuvre d'un outil d'expérimentation sans fil qui applique la méthodologie et enfin, nous montrons les améliorations à travers une étude du multicast dans un scenario sans fil comme un cas d'utilisation, et nous évaluons la performance du processus.
... Carnegie Mellon University Wireless Emulator. Supports real devices, applications, MAC and PHY layers on a networkwide scale while maintaining experimental control and repeatability [19]. The disadvantages of this emulator are that it does not use commercial off-the-shelf devices, using a FPGA for digital emulation instead. ...
Mobile Ad Hoc Network solution testing is typically done using simulation. The simulated code is generally a simplified version of the real code, and thus code porting to actual operating systems lacks a strong validation. In this work we present Castadiva, a test-bed architecture that allows validating software solutions for real ad hoc network environments using low-cost, off-the-shelf devices and open source software. Castadiva is also compatible with the ns-2 simulator, allowing a combined and more complete evaluation. In this work we present our tool and the results obtained when evaluating videocalls in different scenarios, both static and dynamic.
... A test-bed is a platform for experimentation which allows for rigorous, transparent and replicable testing of scientific theories, computational tools, and other new technologies . Several prototypes for generating a real ad hoc network test-bed can also be founded in the literature, like mLab [6] , the wireless emulator from Carnegie Mellon Uni- versity [7], and test emulators like ORBIT [8] or MobiEmu [9]. Test-beds also have some disadvantages: the test-bed called mLab can only generate network topologies and capture packets, Carnegie Mellon University's emulator does not use commercial off-the-shelf devices, while ORBIT or MobiEmu use expensive equipment to do their tests, being limited in terms of radio signal modelling as occurs with simulators. ...
... A test-bed is a platform for experimentation which allows for rigorous, transparent and replicable testing of scientific theories, computational tools, and other new technologies. Several prototypes for generating a real ad hoc network test-bed can also be founded in the literature, like mLab [6], the wireless emulator from Carnegie Mellon University [7], and test emulators like ORBIT [8] or MobiEmu [9]. Test-beds also have some disadvantages: the test-bed called mLab can only generate network topologies and capture packets, Carnegie Mellon University's emulator does not use commercial off-the-shelf devices, while ORBIT or MobiEmu use expensive equipment to do their tests, being limited in terms of radio signal modelling as occurs with simulators. ...
The validation of new video protocols and applications for mobile ad hoc networks in a real environment is an important task. In this work we present Castadiva, a test-bed architecture that allows validating software solutions for ad hoc networks using low-cost, off-the-shelf devices and open source software. We use this tool to test a videocall using the OLSR protocol in different scenarios, varying the number of hops between the caller and the receiver. The results obtained in this paper show that, for an ad hoc network with a large number of hops, the quality of videocalls suffers a significant degradation even in the absence of mobility.
