Ruben Merz

Towards programmable enterprise WLANS with Odin

We present Odin, an SDN framework to introduce programmability in enterprise wireless local area networks (WLANs). Enterprise WLANs need to support a wide range of services and functionalities. This includes authentication, authorization and accounting, policy, mobility and interference management, and load balancing. WLANs also exhibit unique challenges. In particular, access point (AP) association decisions are not made by the infrastructure, but by clients. In addition, the association state machine combined with the broadcast nature of the wireless medium requires keeping track of a large amount of state changes. To this end, Odin builds on a light virtual AP abstraction that greatly simplifies client management. Odin does not require any client side modifications and its design supports WPA2 Enterprise. With Odin, a network operator can implement enterprise WLAN services as network applications. A prototype implementation demonstrates Odins feasibility.

Trade-off analysis of PHY-Aware MAC in low-rate low-power UWB networks

We are interested in the design of physical-layer-aware medium access control for self-organized low-power low-data-rate impulse radio ultra-wideband (IR-.UWB) networks.. In such networks energy consumption is much more of a concern than achieved data rates. So far, a number of different solutions have been proposed in the context of data rate efficiency for IR-UWB. However, the choices made for rate-efficient designs are not necessarily optimal when considering energy efficiency. Hence, there is a need to understand the design trade-offs in very low-power networks, which is the aim of this article. To this end, we first identify what a PHY-aware MAC design has to achieve: interference management, access to a destination, and sleep cycle management. Second, we analyze how these functions can be implemented, and provide a list of the many possible building blocks that have been proposed in the literature. Third, we use this classification to analyze fundamental design choices. We propose a method for evaluating energy consumption already in the design phase of IR-UWB systems. Last, we apply this methodology and derive a set of guidelines; they can be used by system architects to orientate fundamental choices early in the design process.

Distributed spectrum assignment for home WLANs

We consider the problem of jointly allocating channel center frequencies and bandwidths for IEEE 802.11 wireless LANs (WLANs). The bandwidth used on a link affects significantly both the capacity experienced on this link and the interference produced on neighboring links. Therefore, when jointly assigning both center frequencies and channel widths, there is a trade-off between interference mitigation and the potential capacity offered on each link. We study this tradeoff and we present SAW (spectrum assignment for WLANs), a decentralized algorithm that finds efficient configurations. SAW is tailored for 802.11 home networks. It is distributed, online and transparent. It does not require a central coordinator and it constantly adapts the spectrum usage without disrupting network traffic. A key feature of SAW is that the access points (APs) need only a few out-of-band measurements in order to make spectrum allocation decisions. Despite being completely decentralized, the algorithm is self-organizing and provably converges towards efficient spectrum allocations. We evaluate SAW using both simulation and a deployment on an indoor testbed composed of off-the-shelf 802.11 hardware. We observe that it dramatically increases the overall network efficiency and fairness.

What details are needed for wireless simulations? - A study of a site-specific indoor wireless model

The wireless networking community continuously questions the accuracy and validity of simulation-based performance evaluations. The main reason is the lack of widely-accepted models that represent the real wireless characteristics, especially at the physical (PHY) layer. Hence, the trend in wireless networking is to rely more and more on testbeds, which on one hand bring more realism to network and protocol evaluation, but on the other hand present a high implementation barrier before an idea is ready to be tested. Therefore, realistic network simulators are still very much needed to reduce the time and effort for “concept testing” of novel ideas. In this case, the main question is how detailed should wireless simulators be to evaluate network and protocol performance. In this paper, we attempt a first answer to this question by using the Berlin Open Wireless Lab (BOWL) indoor model (BIM) in the ns-3 simulator. BIM includes several measurement-based models to characterize wireless communication such as frame detection ratio (FDR), frame error ratio (FER), capture and interference models. Through extensive measurements, we analyze the accuracy that we obtain with these PHY-layer models. Our experiments also show whether the detailed models at the PHY layer play an important role to represent transport layer performance in simulations.

Performance of LTE in a high-velocity environment: a measurement study

The performance of LTE at high velocities (larger than

Synchronization for Impulse-Radio UWB With Energy-Detection and Multi-User Interference: Algorithms and Application to IEEE 802.15.4a

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Performance evaluation of OFDMA femtocells link-layers in uncontrolled deployments

km/h) is badly understood. Operators have largely deployed LTE in urban environments where velocities are low and the benefits of LTE core features, for instance MIMO, are well demonstrated. With the proliferation of smartphones and tablets, mobile Internet access became ubiquitous and the pressure of rising traffic demands on operator infrastructures is increasing. Furthermore, mobile users now expect access to audio and HD video streams or IPTV while traveling in cars, public transports or intercity trains. Expectations evolve and high-quality connectivity is desired anywhere. To address these demands, operators are expanding their LTE deployments to semi-urban and rural areas of importance, typically along main transportation axes. However, it is unclear (1) how much LTE still benefits from MIMO spatial multiplexing or link adaptation at velocities above a few tens of kilometer per hours; and (2) how overall performance degrades with higher velocities. This paper presents results of a measurement study of a live LTE system at velocities up to

Enhance & explore: an adaptive algorithm to maximize the utility of wireless networks

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Demo: programming enterprise WLANs with odin

km/h. The results show that while velocity has an effect on performance, its influence remains limited if the SNR coverage is well dimensioned. The percentage of spatial multiplexing usage can exceed 65% from

Experimental Analysis of Backpressure Scheduling in IEEE 802.11 Wireless Mesh Networks

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