Abstract — The popularity of IEEE 802.11 WLANs has led to dense deployments in urban areas. High density leads to suboptimal performance unless the interfering networks learn how to optimally use and share the spectrum. This paper proposes two fully distributed algorithms that allow (i) multiple interfering 802.11 Access Points to select their operating frequency in order to minimize interference, and (ii) users to choose the Access Point they attach to, in order to get their fair share of the whole network bandwidth. The proposed algorithms rely on Gibbs sampler, and do not require explicit coordination among the wireless devices. They only require the participating wireless nodes to measure local quantities such as interference and transmission delay. The algorithms are shown to lead to optimal bandwidth sharing, where optimality is defined according to the minimal potential delay. We analytically prove the convergence of the proposed algorithms, and study their performance by simulation.

Dense deployments of WLANs suffer from increased interference and as a result, reduced capacity. There are three main functions used to improve the overall network capacity: a) intelligent frequency allocation across APs, b) load-balancing of user affiliations across APs, and c) adaptive power-control for each AP. Several algorithms

We study the impact on 802.11 networks of RF interference from devices such as Zigbee and cordless phones that increasingly crowd the 2.4GHz ISM band, and from devices such as wireless camera jammers and non-compliant 802.11 devices that seek to disrupt 802.11 operation. Our experiments show that commodity 802.11 equipment is surprisingly vulnerable to certain patterns of weak or narrow-band interference. This enables us to disrupt a link with an interfering signal whose power is 1000 times weaker than the victim’s 802.11 signals, or to shut down a multiple AP, multiple channel managed network at a location with a single radio interferer. We identify several factors that lead to these vulnerabilities, ranging from MAC layer driver implementation strategies to PHY layer radio frequency implementation strategies. Our results further show that these factors are not overcome by simply changing 802.11 operational parameters (such as CCA threshold, rate and packet size) with the exception of frequency shifts. This leads us to explore rapid channel hopping as a strategy to withstand RF interference. We prototype a channel hopping design using PRISM NICs, and find that it can sustain throughput at levels of RF interference well above that needed to disrupt unmodified links, and at a reasonable cost in terms of switching overheads. Categories and Subject Descriptors:

Today’s local-area, mesh and cellular networks assign a single narrow-band channel to a node, and this assignment remains fixed over long time scales. Using network traces, we show that the load within a network can vary significantly even over short time scales on the order of tens of seconds. Therefore, we make the case for allocating spectrum ondemand to nodes and regions of the network that need it. We present an architecture that shares the entire spectrum on-demand using spread-spectrum codes. If implemented, the system will achieve fine-grained spectrum allocation for bursty traffic without requiring inter-cell coordination. Preliminary experiments suggest a throughput improvement of 75 % over commodity 802.11b networks. By eschewing the notion of channelization, and matching demand bursts with spectrum dynamically, better wireless networks that sustain higher throughputs may be designed. 1

Abstract — Demand-driven spectrum allocation can drastically improve performance for WiFi access points struggling under increasing user demands. While their frequency agility makes cognitive radios ideal for this challenge, performing adaptive spectrum allocation is a complex and difficult process. In this work, we propose FLEX, an efficient spectrum allocation architecture that efficiently adapts to dynamic traffic demands. FLEX tunes network-wide spectrum allocation by access points coordinating with peers, minimizing network resets through local adaptations. Through detailed analysis and experimental evaluation, we show that FLEX converges quickly, provides users with proportional-fair spectrum usage and significantly outperforms existing spectrum allocation proposals.

Over the past few years a range of new Media Access Control (MAC) protocols have been proposed for wireless networks. This research has been driven by the observation that a single one-size-fits-all MAC protocol cannot meet the needs of diverse wireless deployments and applications. Unfortunately, most MAC functionality has traditionally been implemented on the wireless card for performance reasons, thus, limiting the opportunities for MAC customization. Software-defined radios (SDRs) promise unprecedented flexibility, but their architecture has proven to be a challenge for MAC protocols. In this paper, we identify a minimum set of core MAC functions that must be implemented close to the radio in a high-latency SDR architecture to enable high performance and efficient MAC implementations. These functions include: precise scheduling in time, carrier sense, backoff, dependent packets, packet recognition, fine-grained radio control, and access to physical layer information. While we focus on an architecture where the bus latency exceeds common MAC interaction times (tens to hundreds of microseconds), other SDR architectures with lower latencies can also benefit from implementing a subset of these functions closer to the radio. We also define an API applicable to all SDR architectures that allows the host to control these functions, providing the necessary flexibility to implement a diverse range of MAC protocols. We show the effectiveness of our splitfunctionality approach through an implementation on the GNU Radio and USRP platforms. Our evaluation based on microbenchmarks and end-to-end network measurements, shows that our design can simultaneously achieve high flexibility and high performance. 1

In this paper we describe specific challenges in virtualizing a wireless network and multiple strategies to address them. Among different possible wireless virtualization strategies, our current work in this domain is focussed on a Time-Division Multiplexing (TDM) approach. Hence, we we present our experiences in the design and implementation of such TDM-based wireless virtualization. Our wireless virtualization system is specifically targeted for multiplexing experiments on a large-scale 802.11 wireless testbed facility.

Abstract — Dynamic spectrum management can drastically improve the performance of wireless networks struggling under increasing user demands. However, performing efficient spectrum allocation is a complex and difficult process. Current proposals make the problem tractable by simplifying interference constraints as conflict graphs, but they face potential performance degradation from inaccurate interference estimation. In this paper, we show that conflict graphs, if optimized properly, can produce spectrum allocations that closely match those derived from the physical interference model. Thus we propose PLAN, a systematic framework to produce conflict graphs based on physical interference characteristics. PLAN first applies an analytical framework to derive the criterion for identifying conflicting neighbors, capturing the cumulative effect of interference. PLAN then applies a local conflict adjustment algorithm to address heterogeneous interference conditions and improve spectrum allocation efficiency. Through detailed analysis and experimental evaluations, we show that PLAN builds a conflict graph to effectively represent the complex interference conditions and allow the reuse of efficient graph-based spectrum allocation solutions. PLAN also significantly outperforms the conventional graph model based solutions. I.

Game-theoretic control is a promising new approach for distributed resource allocation. In this paper, we describe how game-theoretic control can be viewed as having an intrinsic layered architecture, which provides a modularization that simplifies the control design. We illustrate this architectural view by presenting details about one particular instantiation using potential games as an interface. This example serves to highlight the strengths and limitations of the proposed architecture while also illustrating the relationship between game-theoretic control and other existing approaches to distributed resource allocation. 1.

Jamming is a serious security problem in wireless networks. Recently, software-based channel hopping has received attention as a jamming countermeasure. In particular, proactive, or periodic, channel hopping has been studied more extensively than reactive hopping. In this paper, we address the question of which of the two defense strategies, namely proactive and reactive channel-hopping, provides better jamming resiliency than the other? in the context of singleand multi-radio wireless devices. In the single-radio context, we develop theoretical models to analyze the blocking probability for combinations of defense and attack strategies. In the multi-radio setting, we formulate the jamming problem as a max-min game and show through simulation that the game outcome depends on the payoff function. Our results show that reactive defense provides better jamming tolerance than proactive when considering communication availability. However, both reactive and proactive defenses have almost the same performance when energy efficiency is considered as a performance metric.