Proceedings of the 16th Annual International Conference on Mobile Computing and Networking, MOBICOM 2010, Chicago, Illinois, USA, September 20-24, 2010. ACM 【DBLP Link】
【Paper Link】 【Pages】:1-12
【Authors】: Jung Il Choi ; Mayank Jain ; Kannan Srinivasan ; Philip Levis ; Sachin Katti
【Abstract】: This paper discusses the design of a single channel full-duplex wireless transceiver. The design uses a combination of RF and baseband techniques to achieve full-duplexing with minimal effect on link reliability. Experiments on real nodes show the full-duplex prototype achieves median performance that is within 8% of an ideal full-duplexing system. This paper presents Antenna Cancellation, a novel technique for self-interference cancellation. In conjunction with existing RF interference cancellation and digital baseband interference cancellation, antenna cancellation achieves the amount of self-interference cancellation required for full-duplex operation. The paper also discusses potential MAC and network gains with full-duplexing. It suggests ways in which a full-duplex system can solve some important problems with existing wireless systems including hidden terminals, loss of throughput due to congestion, and large end-to-end delays.
【Keywords】: wireless full-duplex
【Paper Link】 【Pages】:13-24
【Authors】: Kaishun Wu ; Haoyu Tan ; Yunhuai Liu ; Jin Zhang ; Qian Zhang ; Lionel M. Ni
【Abstract】: Interference is a critical issue in wireless communications. In a typical multiple-user environment, different users may severely interfere with each other. Coordination among users therefore is an indispensable part for interference management in wireless networks. It is known that, coordination among multiple nodes is a costly operation taking a significant amount of valuable communication resource. In this paper, we have an interesting observation that by generating intended patterns, some simultaneous transmissions, i.e., "interference", can be successfully decoded without degrading the effective throughput in original transmission. As such, an extra and "free" coordination channel can be built. Based on this idea we propose a DC-MAC to leverage this "free" channel for efficient medium access in a multiple-user wireless network. We theoretically analyze the capacity of this channel under different environments with various modulation schemes. USRP2-based implementation experiments show that compared with the widely adopted CSMA, DC-MAC can improve the channel utilization efficiency by up to 250%.
【Keywords】: coordination; interference; wireless network
【Paper Link】 【Pages】:25-36
【Authors】: Souvik Sen ; Romit Roy Choudhury ; Srihari Nelakuditi
【Abstract】: A wireless transmitter learns of a packet loss, infers collision, only after completing the entire transmission. If the transmitter could detect the collision early (such as with CSMA/CD in wired networks), it could immediately abort its transmission, freeing the channel for useful communication. There are two main hurdles to realize CSMA/CD in wireless networks. First, a wireless transmitter cannot simultaneously transmit and listen for a collision. Second, any channel activity around the transmitter may not be an indicator of collision at the receiver. This paper attempts to approximate CSMA/CD in wireless networks with a scheme called CSMA/CN (collision notification). Under CSMA/CN, the receiver uses PHY layer information to detect a collision and immediately notifies the transmitter. The collision notification consists of a unique signature, sent on the same channel as the data. The transmitter employs a listener antenna and performs signature correlation to discern this notification. Once discerned, the transmitter immediately aborts transmission. We show that the notification signature can be reliably detected at the listener antenna, even in the presence of a strong self-interference from the transmit antenna. A prototype testbed of 10 USRP/GNURadios demonstrates the feasibility and effectiveness of CSMA/CN
【Keywords】: collision detection; cross-layer; csma/cd; wireless
【Paper Link】 【Pages】:37-48
【Authors】: Lei Yang ; Ben Y. Zhao ; Haitao Zheng
【Abstract】: Guardbands are designed to insulate transmissions on adjacent frequencies from mutual interference. As more devices in a given area are packed into orthogonal wireless channels, choosing the right guardband size to minimize cross-channel interference becomes critical to network performance. Using both WiFi and GNU radio experiments, we show that the traditional "one-size-fits-all" approach to guardband assignment is ineffective, and can produce throughput degradation up to 80%. We find that ideal guardband values vary across different network configurations, and across different links in the same network. We argue that guardband values should be set based on network conditions and adapt to changes over time. We propose Ganache, an intelligent guardband configuration system that dynamically sets and adapts guardbands based on local topology and propagation conditions. Ganache includes three key mechanisms: an empirical model of guardband sizes based on power heterogeneity of adjacent links, network-wide frequency and guardband assignment, and local guardband adaptation triggered by real-time detection of cross-band interference. We deploy a Ganache prototype on a local 8-node GNU radio testbed. Detailed experiments on different topologies show that to minimize interference, traditional fixed-size configurations allocate more than 40% of available spectrum to guardbands, while Ganache does the same using only 10% of the spectrum, leading to a 150% gain in throughput.
【Keywords】: dynamic spectrum access; guard-band configuration; out-of-band emissions
【Paper Link】 【Pages】:49-60
【Authors】: Ruogu Zhou ; Yongping Xiong ; Guoliang Xing ; Limin Sun ; Jian Ma
【Abstract】: WiFi networks have enjoyed an unprecedent penetration rate in recent years. However, due to the limited coverage, existing WiFi infrastructure only provides intermittent connectivity for mobile users. Once leaving the current network coverage, WiFi clients must actively discover new WiFi access points (APs), which wastes the precious energy of mobile devices. Although several solutions have been proposed to address this issue, they either require significant modifications to existing network infrastructures or rely on context information that is not available in unknown environments. In this work, we develop a system called ZiFi that utilizes ZigBee radios to identify the existence of WiFi networks through unique interference signatures generated by WiFi beacons. We develop a new digital signal processing algorithm called Common Multiple Folding (CMF) that accurately amplifies periodic beacons in WiFi interference signals. ZiFi also adopts a constant false alarm rate (CFAR) detector that can minimize the false negative (FN) rate of WiFi beacon detection while satisfying the user-specified upper bound on false positive (FP) rate. We have implemented ZiFi on two platforms, a Linux netbook integrating a TelosB mote through the USB interface, and a Nokia N73 smartphone integrating a ZigBee card through the miniSD interface. Our experiments show that, under typical settings, ZiFi can detect WiFi APs with high accuracy (<5% total FP and FN rate), short delay (~780 ms), and little computation overhead
【Keywords】: digital signal processing; interference; power management; stochastic signal detection; wifi network discovery
【Paper Link】 【Pages】:61-72
【Authors】: Ji-Hoon Yun ; Kang G. Shin
【Abstract】: Femtocell technology has been drawing considerable attention as a cost-effective means of improving cellular coverage and capacity. However, under co-channel deployment, femtocells may incur high uplink interference to existing macrocells, and vice versa. To alleviate this interference, we propose a distributed and self-organizing femtocell management architecture, called CTRL Complementary TRi-control Loops), that consists of three control loops. First, for protection of macrocell users' uplink communications, CTRL controls the maximum TX power of femtocell users based on the fedback macrocell's load margin so as to keep, on average, the macrocell load below a certain threshold. Second, CTRL determines the target SINRs of femtocell users, conditioned on the maximum TX power, to reach a Nash equilibrium based on their utility functions, thus achieving efficient coordination of uplink usage among femtocells. Third, for protection of femtocell users' uplink communications, the instantaneous TX power of each femtocell user is controlled to achieve the target SINR against bursty interference from nearby macrocell or femtocell users. Our in-depth evaluation has shown CTRL to successfully preserve the macrocell users' service quality from femtocells' interference and converge to an optimal point under highly dynamic user TX conditions. CTRL is also shown to limit the effects of the estimation errors of channel gains and feedback delay.
【Keywords】: co-channel deployment; femtocell; home base station; interference mitigation; self-organizing networks
【Paper Link】 【Pages】:73-84
【Authors】: Brett D. Higgins ; Azarias Reda ; Timur Alperovich ; Jason Flinn ; Thomas J. Giuli ; Brian Noble ; David Watson
【Abstract】: Mobile devices face a diverse and dynamic set of networking options. Using those options to the fullest requires knowledge of application intent. This paper describes Intentional Networking, a simple but powerful mechanism for handling network diversity. Applications supply a declarative label for network transmissions, and the system matches transmissions to the most appropriate network. The system may also defer and re-order opportunistic transmissions subject to application-supplied mutual exclusion and ordering constraints. We have modified three applications to use Intentional Networking: BlueFS, a distributed file system for pervasive computing, Mozilla's Thunderbird e-mail client, and a vehicular participatory sensing application. We evaluated the performance of these applications using measurements obtained by driving a vehicle through WiFi and cellular 3G network coverage. Compared to an idealized solution that makes optimal use of all aggregated available networks but that lacks knowledge of application intent, Intentional Networking improves the latency of interactive messages from 48% to 13x, while adding no more than 7% throughput overhead.
【Keywords】: application-aware networking; wireless network selection
【Paper Link】 【Pages】:85-96
【Authors】: Aaron Schulman ; Vishnu Navda ; Ramachandran Ramjee ; Neil Spring ; Pralhad Deshpande ; Calvin Grunewald ; Kamal Jain ; Venkata N. Padmanabhan
【Abstract】: Cellular radios consume more power and suffer reduced data rate when the signal is weak. According to our measurements, the communication energy per bit can be as much as 6x higher when the signal is weak than when it is strong. To realize energy savings, applications must preferentially communicate when the signal is strong, either by deferring non-urgent communication or by advancing anticipated communication to coincide with periods of strong signal. Allowing applications to perform such scheduling requires predicting signal strength, so that opportunities for energy-efficient communication can be anticipated. Furthermore, such prediction must be performed at little energy cost. In this paper, we make several contributions towards a practical system for energy-aware cellular data scheduling called Bartendr. First, we establish, via measurements, the relationship between signal strength and power consumption. Second, we show that location alone is not sufficient to predict signal strength and motivate the use of tracks to enable effective prediction. Finally, we develop energy-aware scheduling algorithms for different workloads - syncing and streaming - and evaluate these via simulation driven by traces obtained during actual drives, demonstrating energy savings of up to 60%. Our experiments have been performed on four cellular networks across two large metropolitan areas, one in India and the other in the U.S.
【Keywords】: bartendr; cellular; energy; evdo; hsdpa; mobile
【Paper Link】 【Pages】:97-104
【Authors】: Danilo De Donno ; Fabio Ricciato ; Luca Catarinucci ; Angelo Coluccia ; Luciano Tarricone
【Abstract】: Current Radio-Frequency Identification (RFID) technology involves two types of physical devices: tags and reader. The reader combines in a single physical device transmission (to the tags) and reception (from the tags) functions. In this paper we discuss an alternative approach, where receive functions are performed by a separate device called "RFID listener". This allows distributed tag-sensing schemes where one transmitter coexists with multiple listeners. We discuss pros and cons of both approaches and present our implementation of a passive RFID listener on GNU Radio. Our implementation is a basis for experimenting with future distributed listener-based systems, but it can be also used as a cheap and flexible protocol analyzer for currently available commercial RFID readers.
【Keywords】: gnu-radio; rfid; software-defined radio; wsn
【Paper Link】 【Pages】:105-112
【Authors】: Ashwin Ashok ; Marco Gruteser ; Narayan B. Mandayam ; Jayant Silva ; Michael Varga ; Kristin J. Dana
【Abstract】: Mobile optical communications has so far largely been limited to short ranges of about ten meters, since the highly directional nature of optical transmissions would require costly mechanical steering mechanisms. Advances in CCD and CMOS imaging technology along with the advent of visible and infrared (IR) light sources such as (light emitting diode) LED arrays presents an exciting and challenging concept which we call as visual-MIMO (multiple-input multiple-output) where optical transmissions by multiple transmitter elements are received by an array of photodiode elements (e.g. pixels in a camera). Visual-MIMO opens a new vista of research challenges in PHY, MAC and Network layer research and this paper brings together the networking, communications and computer vision fields to discuss the feasibility of this as well as the underlying opportunities and challenges. Example applications range from household/factory robotic to tactical to vehicular networks as well pervasive computing, where RF communications can be interference-limited and prone to eavesdropping and security lapses while the less observable nature of highly directional optical transmissions can be beneficial. The impact of the characteristics of such technologies on the medium access and network layers has so far received little consideration. Example characteristics are a strong reliance on computer vision algorithms for tracking, a form of interference cancellation that allows successfully receiving packets from multiple transmitters simultaneously, and the absence of fast fading but a high susceptibility to outages due to line-of-sight interruptions. These characteristics lead to significant challenges and opportunities for mobile networking research
【Keywords】: computer vision; line of sight(los); optical communication; rf communication; visual mimo
【Paper Link】 【Pages】:113-124
【Authors】: Aditya Dhananjay ; Ashlesh Sharma ; Michael Paik ; Jay Chen ; Trishank Karthik Kuppusamy ; Jinyang Li ; Lakshminarayanan Subramanian
【Abstract】: While the cellular revolution has made voice connectivity ubiquitous in the developing world, data services are largely absent or are prohibitively expensive. In this paper, we present Hermes1, a point-to-point data connectivity solution that works by modulating data onto acoustic signals that are sent over a cellular voice call. The main challenge is that most voice codecs greatly distort signals that are not voice-like; furthermore, the backhaul can be highly heterogeneous and of low quality, thereby introducing unpredictable distortions. Hermes modulates data over the extremely narrow-band approximately 3kHz bandwidth) acoustic carrier, while being severely constrained by the requirement that the resulting sound signals are voice-like, as far as the voice codecs are concerned. Hermes uses a robust data transcoding and modulation scheme to detect and correct errors in the face of bit flips, insertions and deletions; it also adapts the modulation parameters to the observed bit error rate on the actual voice channel. Through real-world experiments, we show that Hermes achieves approximately 1.2 kbps goodput which when compared to SMS, improves throughput by a factor of 5× and reduces the cost-per-byte by over a factor of 50x
【Keywords】: cellular; codec; modulation
【Paper Link】 【Pages】:125-136
【Authors】: Jay Chen ; Lakshminarayanan Subramanian ; Eric A. Brewer
【Abstract】: Short Messaging Service (SMS) based mobile information services have become increasingly common around the world, especially in emerging regions among users with low-end mobile devices. This paper presents the design and implementation of SMSFind, an SMS-based search system that enables users to obtain extremely concise (one SMS) message of 140 bytes) and appropriate search responses for queries across arbitrary topics in one round of interaction. SMSFind is designed to complement existing SMS-based search services that are either limited in the topics they recognize or involve a human in the loop. Given an unstructured search query, SMSFind, uses a conventional search engine as a back-end to elicit several search responses and uses a combination of information retrieval techniques to extract the most appropriate 140-byte snippet as the final SMS search response. We show that SMSFind returns appropriate responses for 57.3% of ChaCha search queries in our test set; this accuracy rate is high given that ChaCha employs a human to answer the same questions. We have also deployed a pilot version of SMSFind for use with a small focus group in Kenya to explore the interaction issues of such a system and share our experience.
【Keywords】: cell phones; question/answering; search; sms
【Paper Link】 【Pages】:137-148
【Authors】: Samuel David Perli ; Nabeel Ahmed ; Dina Katabi
【Abstract】: Given the abundance of cameras and LCDs in today's environment, there exists an untapped opportunity for using these devices for communication. Specifically, cameras can tune to nearby LCDs and use them for network access. The key feature of these LCD-camera links is that they are highly directional and hence enable a form of interference-free wireless communication. This makes them an attractive technology for dense, high contention scenarios. The main challenge however, to enable such LCD-camera links is to maximize coverage, that is to deliver multiple Mb/s over multi-meter distances, independent of the view angle. To do so, these links need to address unique types of channel distortions, such as perspective distortion and blur. This paper explores this novel communication medium and presents PixNet, a system for transmitting information over LCD-camera links. PixNet generalizes the popular OFDM transmission algorithms to address the unique characteristics of the LCD-camera link which include perspective distortion, blur, and sensitivity to ambient light. We have built a prototype of PixNet using off-the-shelf LCDs and cameras. An extensive evaluation shows that a single PixNet link delivers data rates of up to 12 Mb/s at a distance of 10 meters, and works with view angles as wide as 120 degree°.
【Keywords】: camera; ofdm; optical links; perspective distortion
【Paper Link】 【Pages】:149-160
【Authors】: Ionut Constandache ; Xuan Bao ; Martin Azizyan ; Romit Roy Choudhury
【Abstract】: Finding a person in a public place, such as in a library, conference hotel, or shopping mall, can be difficult. The difficulty arises from not knowing where the person may be at that time; even if known, navigating through an unfamiliar place may be frustrating. Maps and floor plans help in some occasions, but such maps may not be always handy. In a small scale poll, 80% of users responded that the ideal solution would be "to have an escort walk me to the desired person". This paper identifies the possibility of using mobile phone sensors and opportunistic user-intersections to develop an electronic escort service. By periodically learning the walking trails of different individuals, as well as how they encounter each other in space-time, a route can be computed between any pair of persons. The problem bears resemblance to routing packets in delay tolerant networks, however, its application in the context of human localization raises distinct research challenges. We design and implement Escort, a system that guides a user to the vicinity of a desired person in a public place. We only use an audio beacon, randomly placed in the building, to enable a reference frame. We do not rely on GPS, WiFi, or war-driving to locate a person - the Escort user only needs to follow an arrow displayed on the phone. Evaluation results from experiments in parking lots and university buildings show that, on average, the user is brought to within 8m of the destination. We believe this is an encouraging result, opening new possibilities in mobile, social localization.
【Keywords】: localization; mobile phones; navigation; sensors
【Paper Link】 【Pages】:161-172
【Authors】: Swati Rallapalli ; Lili Qiu ; Yin Zhang ; Yi-Chao Chen
【Abstract】: Localization is a fundamental operation for many wireless networks. While GPS is widely used for location determination, it is unavailable in many environments either due to its high cost or the lack of line of sight to the satellites (e.g., indoors, under the ground, or in a downtown canyon). The limitations of GPS have motivated researchers to develop many localization schemes to infer locations based on measured wireless signals. However, most of these existing schemes focus on localization in static wireless networks. As many wireless networks are mobile (e.g., mobile sensor networks, disaster recovery networks, and vehicular networks), we focus on localization in mobile networks in this paper. We analyze real mobility traces and find that they exhibit temporal stability and low-rank structure. Motivated by this observation, we develop three novel localization schemes to accurately determine locations in mobile networks: (i) Low Rank based Localization (LRL), which exploits the low-rank structure in mobility, (ii) Temporal Stability based Localization (TSL), which leverages the temporal stability, and (iii) Temporal Stability and Low Rank based Localization (TSLRL), which incorporates both the temporal stability and the low-rank structure. These localization schemes are general and can leverage either mere connectivity (i.e., range-free localization) or distance estimation between neighbors (i.e., range-based localization). Using extensive simulations and testbed experiments, we show that our new schemes significantly outperform state-of-the-art localization schemes under a wide range of scenarios and are robust to measurement errors.
【Keywords】: localization; low-rank structure; mobility; temporal stability
【Paper Link】 【Pages】:173-184
【Authors】: Krishna Chintalapudi ; Anand Padmanabha Iyer ; Venkata N. Padmanabhan
【Abstract】: While WiFi-based indoor localization is attractive, the need for a significant degree of pre-deployment effort is a key challenge. In this paper, we ask the question: can we perform indoor localization with no pre-deployment effort? Our setting is an indoor space, such as an office building or a mall, with WiFi coverage but where we do not assume knowledge of the physical layout, including the placement of the APs. Users carrying WiFi-enabled devices such as smartphones traverse this space in normal course. The mobile devices record Received Signal Strength (RSS) measurements corresponding to APs in their view at various (unknown) locations and report these to a localization server. Occasionally, a mobile device will also obtain and report a location fix, say by obtaining a GPS lock at the entrance or near a window. The centerpiece of our work is the EZ Localization algorithm, which runs on the localization server. The key intuition is that all of the observations reported to the server, even the many from unknown locations, are constrained by the physics of wireless propagation. EZ models these constraints and then uses a genetic algorithm to solve them. The results from our deployment in two different buildings are promising. Despite the absence of any explicit pre-deployment calibration, EZ yields a median localization error of 2m and 7m, respectively, in a small building and a large building, which is only somewhat worse than the 0.7m and 4m yielded by the best-performing but calibration-intensive Horus scheme [29] from prior work.
【Keywords】: calibration-free; indoor localization; wifi
【Paper Link】 【Pages】:185-196
【Authors】: Chris Y. T. Ma ; David K. Y. Yau ; Nung Kwan Yip ; Nageswara S. V. Rao
【Abstract】: Mobility traces of people and vehicles have been collected and published to assist the design and evaluation of mobilee networks, such as large-scale urban sensing networks. Although the published traces are often made anonymous in that the true identities of nodes are replaced by random identifiers, the privacy concern remains. This is because in real life, nodes are open to observations in public spaces, or they may voluntarily or inadvertently disclose partial knowledge of their whereabouts. Thus, snapshots of nodes' location information can be learned by interested third parties, e.g., directly through chance/engineered meetings between the nodes and their observers, or indirectly through casual conversations or other information sources about people. In this paper, we investigate how an adversary, when equipped with a small amount of the snapshot information termed as side information, can infer an extended view of the whereabouts of a victim node appearing in an anonymous trace. Our results quantify the loss of victim nodes' privacy as a function of the nodal mobility (captured in both real and synthetic traces), the inference strategies of adversaries, and any noise that may appear in the trace or the side information. Generally, our results indicate that the privacy concern is significant in that a relatively small amount of side information is sufficient for the adversary to infer the true identity (either uniquely or with high probability) of a victim in a set of anonymous traces.
【Keywords】: entropy; location privacy
【Paper Link】 【Pages】:197-208
【Authors】: Ehsan Aryafar ; Narendra Anand ; Theodoros Salonidis ; Edward W. Knightly
【Abstract】: Multi-User MIMO promises to increase the spectral efficiency of next generation wireless systems and is currently being incorporated in future industry standards. Although a significant amount of research has focused on theoretical capacity analysis, little is known about the performance of such systems in practice. In this paper, we present the design and implementation of the first multi-user beamforming system and experimental framework for wireless LANs. Using extensive measurements in an indoor environment, we evaluate the impact of receiver separation distance, outdated channel information due to mobility and environmental variation, and the potential for increasing spatial reuse. For the measured indoor environment, our results reveal that two receivers achieve close to maximum performance with a minimum separation distance of a quarter of a wavelength. We also show that the required channel information update rate is dependent on environmental variation and user mobility as well as a per-link SNR requirement. Assuming that a link can tolerate an SNR decrease of 3 dB, the required channel update rate is equal to 100 and 10 ms for non-mobile receivers and mobile receivers with a pedestrian speed of 3 mph respectively. Our results also show that spatial reuse can be increased by efficiently eliminating interference at any desired location; however, this may come at the expense of a significant drop in the quality of the served users.
【Keywords】: beamforming; channel information; interference suppression; mobility; multi-user mimo; wireless lan
【Paper Link】 【Pages】:209-220
【Authors】: Xi Liu ; Anmol Sheth ; Michael Kaminsky ; Konstantina Papagiannaki ; Srinivasan Seshan ; Peter Steenkiste
【Abstract】: Recent work demonstrates that directional antennas have significant potential to improve wireless network capacity in indoor environments. This paper provides a broader exploration of the design space of indoor directional antenna systems along two main dimensions: antenna configuration and antenna control. Studying a number of alternative configurations, we find that directionality on APs and clients can significantly improve performance, even over other configurations with stronger directionality. Moreover, it is sufficient to have a small number of narrow beam antennas to achieve such gains, thus making such a solution practical for actual deployment. Designing systems with directional APs and clients for increased spatial reuse comes, however, with a number of challenges in the way the directional antennas are controlled. Antenna control needs to encompass antenna orientation algorithms, an appropriate MAC layer protocol, and novel client-AP association solutions. To overcome these challenges, we propose Speed, a distributed directional antenna control system that is easy to deploy and significantly improves network capacity over existing solutions.
【Keywords】: directional antenna; indoor wireless capacity
【Paper Link】 【Pages】:221-232
【Authors】: Ardalan Amiri Sani ; Lin Zhong ; Ashutosh Sabharwal
【Abstract】: We report a first-of-its-kind realization of directional transmission for smartphone-like mobile devices using multiple passive directional antennas, supported by only one RF chain. The key is a multi-antenna system (MiDAS) and its antenna selection methods that judiciously select the right antenna for transmission. It is grounded by two measurement-driven studies regarding 1) how smartphones rotate during wireless usage in the field and 2) how orientation and rotation impact the performance of directional antennas under various propagation environments. We implement MiDAS and its antenna selection methods using the WARP platform. We evaluate the implementation using a computerized motor to rotate the prototype according to traces collected from smartphone users in the field. Our evaluation shows that MiDAS achieves a median of 3dB increase in link gain. We demonstrate that rate adaptation and power control can be combined with MiDAS to further improve goodput and power saving. Real-time experiments with the prototype show that the link gain translates to 85% goodput improvement for a low SNR scenario. The same gain translates to 51% transmit power reduction for a high SNR scenario. Compared to other methods in realizing directional communication, MiDAS does not require any changes to the network infrastructure, and is therefore suitable for immediate or near-future deployment.
【Keywords】: mobile devices; orientation estimation; passive directional antennas; smartphone rotation
【Paper Link】 【Pages】:233-244
【Authors】: Ravi Kokku ; Rajesh Mahindra ; Honghai Zhang ; Sampath Rangarajan
【Abstract】: This paper describes the design and implementation of a network virtualization substrate NVS) for effective virtualization of wireless resources in WiMAX networks. Virtualization fosters the realization of several interesting deployment scenarios such as customized virtual networks, virtual services and wide-area corporate networks, with diverse performance objectives. In virtualizing a basestation's uplink and downlink resources into slices, NVS meets three key requirements - isolation, customization, and efficient resource utilization - using two novel features: (1) NVS introduces a provably-optimal slice scheduler that allows existence of slices with bandwidth-based and resource-based reservations simultaneously, and (2) NVS includes a generic framework for efficiently enabling customized flow scheduling within the basestation on a per-slice basis. Through a prototype implementation and detailed evaluation on a WiMAX testbed, we demonstrate the efficacy of NVS. For instance, we show for both downlink and uplink directions that NVS can run different flow schedulers in different slices, run different slices simultaneously with different types of reservations, and perform slice-specific application optimizations for providing customized services.
【Keywords】: cellular networks; customization; isolation; mvno; network virtualization; scheduling; wimax; wireless resource provisioning
【Paper Link】 【Pages】:245-256
【Authors】: Giacomo Bernardi ; Matt Calder ; Damon Fenacci ; Alex Macmillan ; Mahesh K. Marina
【Abstract】: Stix is a platform managing emerging large-scale broadband wireless access (BWA) networks. It has been developed to make it easy to manage such networks for community deployments and wireless Internet service providers while keeping the network management infrastructure scalable and flexible. Stix is based on the notions of goal-oriented and in-network management. With Stix, administrators graphically specify network management activities as workflows, which are deployed at a distributed set of agents within the network that cooperate in executing those workflows and storing management information. We implement the Stix system on embedded boards and show that the implementation has a low memory footprint. Using real topology and logging data from a large-scale BWA network operator, we show that Stix is significantly more scalable (via reduction in management traffic) compared to the commonly employed centralized management approach. Finally we use two case studies to demonstrate the ease with which Stix platform can be used for carrying out network reconfiguration and performance management tasks, thereby also showing its potential as a flexible platform to realize self-management mechanisms.
【Keywords】: broadband wireless access networks; community networks; distributed management; heterogeneity; network management; rural internet access; scalability; self management; visual programming; workflows
【Paper Link】 【Pages】:257-268
【Authors】: Ioannis Pefkianakis ; Yun Hu ; Starsky H. Y. Wong ; Hao Yang ; Songwu Lu
【Abstract】: This paper studies MIMO based rate adaptation (RA) in 802.11n wireless networks. Our case study shows that existing RA algorithms offer much lower throughput than even a fixed-rate scheme. The fundamental problem is that, all such algorithms are MIMO oblivious; they do not consider the characteristics of diversity-oriented, single-stream mode and the spatial multiplexing driven, double-stream mode. We propose MiRA, a novel MIMO RA scheme that zigzags between intra- and inter-mode rate options. Our experiments show that MiRA consistently outperforms three representative RA algorithms, SampleRate, RRAA and Atheros MIMO RA, in static, mobility and collision settings.
【Keywords】: ieee 802.11n; mimo; rate adaptation
【Paper Link】 【Pages】:269-280
【Authors】: Domenico Giustiniano ; Eduard Goma Llairo ; Alberto López Toledo ; Ian Dangerfield ; Julián David Morillo-Pozo ; Pablo Rodriguez
【Abstract】: Aggregating multiple 802.11 Access Point (AP) backhauls using a single-radio WLAN card has been considered as a way of bypassing the backhaul capacity limit. However, current AP aggregation solutions greedily maximize the individual station throughput without taking fairness into account. This can lead to grossly unfair throughput distributions, which can discourage user participation and severely limit commercial deployability. Motivated by this problem, we present THEMIS, a single-radio station that performs multi-AP backhaul aggregation in a fair and distributed way, without requiring any change in the network. We implement THEMIS on commodity hardware, evaluate it extensively through controlled experimental tests, and validate it in a deployment spanning 3 floors of a multistory building. THEMIS is being used in a commercial trial by a major broadband provider to its customers.
【Keywords】: adsl; fairness; multi-ap aggregation; wlan
【Paper Link】 【Pages】:281-292
【Authors】: Erran L. Li ; Kun Tan ; Harish Viswanathan ; Ying Xu ; Yang Richard Yang
【Abstract】: Collisions in overlapping channels can be a major problem in the deployment of high-speed OFDM networks. In this paper, we present Remap, a simple, novel paradigm for handling collisions in overlapping OFDM channels. Remap introduces a novel concept of retransmission permutation that permutes the bit-to-subcarrier assignment after each transmission, departing from the traditional, simply-repeat paradigm. Remap is simple to implement and able to exploit collision-free subcarriers to decode frames despite successive collisions in overlapping channels. We apply Remap to 802.11g to demonstrate that the diversity created by remapped frames can substantially improve decoding efficiency and improve wireless throughput. We implement our technique in software radio and demonstrate that it has potential to be deployed with simple software and firmware updates.
【Keywords】: collision decoding; interference cancellation; loss of orthogonality; ofdm; time-frequency decoding
【Paper Link】 【Pages】:293-304
【Authors】: Kyu-Han Kim ; Alexander W. Min ; Kang G. Shin
【Abstract】: Information on site-specific spectrum characteristics is essential to evaluate and improve the performance of wireless networks. However, it is usually very costly to obtain accurate spectrum-condition information in heterogeneous wireless environments. This paper presents a novel spectrum-survey system, called Sybot (Spectrum survey robot), that guides network engineers to efficiently monitor the spectrum condition (e.g., RSS) of WiFi networks. Sybot effectively controls mobility and employs three disparate monitoring techniques - complete, selective, and diagnostic - that help produce and maintain an accurate spectrum-condition map for challenging indoor WiFi networks. By adaptively triggering the most suitable of the three techniques, Sybot captures spatio-temporal changes in spectrum condition. Moreover, based on the monitoring results, Sybot automatically determines several key survey parameters, such as site-specific measurement time and space granularities. Sybot has been prototyped with a commodity IEEE 802.11 router and Linux OS, and experimentally evaluated, demonstrating its ability to generate accurate spectrum-condition maps while reducing the measurement effort (space, time) by more than 56%.
【Keywords】: adaptive spectrum survey; measurement; spectrum map; spectrum site-survey; wireless network
【Paper Link】 【Pages】:305-316
【Authors】: Eugenio Magistretti ; Omer Gurewitz ; Edward W. Knightly
【Abstract】: In 802.11 managed wireless networks, the manager can address under-served links by rate-limiting the conflicting nodes. In order to determine to what extent each conflicting node is responsible for the poor performance, the manager needs to understand the coordination among conflicting nodes' transmissions. In this paper, we present a management framework called MIDAS (Management, Inference, and Diagnostics using Activity Share). We introduce the concept of Activity Share which characterizes the coordination among any set of network nodes in terms of the time they spend transmitting simultaneously. Unfortunately, the Activity Share cannot be locally measured by the nodes. Thus, MIDAS comprises an inference tool which, based on a combined physical, protocol, and statistical approach, infers the Activity Share by using a small set of passively collected, time-aggregate local channel measurements reported by the nodes. MIDAS uses the estimated Activity Share as the input of a simple model that predicts how limiting the transmission rate of any conflicting node would benefit the throughput of the under-served link. The model is based on the current network conditions, thus representing the first throughput model using online measurements. We implemented our tool on real hardware and deployed it on an indoor testbed. Our extensive validation combines testbed experiments and simulations. The results show that MIDAS infers the Activity Share with an average normalized relative error below 12% in all testbed experiments.
【Keywords】: 802.11; coordination; inference; interference; wlans
【Paper Link】 【Pages】:317-328
【Authors】: Kannan Srinivasan ; Mayank Jain ; Jung Il Choi ; Tahir Azim ; Edward S. Kim ; Philip Levis ; Bhaskar Krishnamachari
【Abstract】: This paper explores metrics that capture to what degree packet reception on different links is correlated. Specifically, it explores metrics that shed light on when and why opportunistic routing and network coding protocols perform well (or badly). It presents a new metric, κ that, unlike existing widely used metrics, has no bias based on the packet reception ratios of links. This lack of bias makes κ a better predictor of performance of opportunistic routing and network coding protocols. Comparing Deluge and Rateless Deluge, Deluge's network coding counterpart, we find that κ can predict which of the two is best suited for a given environment. For example, irrespective of the packet reception ratios of the links, if the average κ of the link pairs is very high (close to 1.0), then using a protocol that does not code works better than using a network coding protocol. Measuring κ on several 802.15.4 and 802.11 testbeds, we find that it varies significantly across network topologies and link layers. κ can be a metric for quantifying what kind of a network is present and help decide which protocols to use for that network.
【Keywords】: 802.15.4; low power wireless networks; wireless measurement study; wireless protocol design
【Paper Link】 【Pages】:329-340
【Authors】: Fan Bai ; Daniel D. Stancil ; Hariharan Krishnan
【Abstract】: IEEE 802.11p-based Dedicated Short Range Communications (DSRC) is considered a promising wireless technology for enhancing transportation safety and improving highway efficiency. Here, using a large set of empirical measurement data taken in a rich variety of realistic driving environments, we attempt to characterize communication properties of DSRC as well as to analyze the causes of communication loss. Specifically, from a perspective of vehicular network engineers, the fundamental characteristic of DSRC communications is Packet Delivery Ratio (PDR). We investigate the impact of both uncontrollable environmental factors and controllable radio parameters on DSRC characteristics. Moreover, we also examine temporal correlation, spatial correlation and symmetric correlation of DSRC characteristics under realistic vehicular environments.
【Keywords】: dedicated short range communication (dsrc); empirical measurement; vehicular ad hoc network (vanet)
【Paper Link】 【Pages】:341-352
【Authors】: Ram Keralapura ; Antonio Nucci ; Zhi-Li Zhang ; Lixin Gao
【Abstract】: With widespread popularity of smart phones, more and more users are accessing the Internet on the go. Understanding mobile user browsing behavior is of great significance for several reasons. For example, it can help cellular (data) service providers (CSPs) to improve service performance, thus increasing user satisfaction. It can also provide valuable insights about how to enhance mobile user experience by providing dynamic content personalization and recommendation, or location-aware services. In this paper, we try to understand mobile user browsing behavior by investigating whether there exists distinct "behavior patterns" among mobile users. Our study is based on real mobile network data collected from a large 3G CSP in North America. We formulate this user behavior profiling problem as a "co-clustering" problem, i.e., we group both users (who share similar browsing behavior), and browsing profiles (of like-minded users) simultaneously. We propose and develop a scalable co-clustering methodology, Phantom, using a novel hourglass model. The proposed hourglass model first reduces the dimensions of the input data and performs divisive hierarchical co-clustering on the lower dimensional data; it then carries out an expansion step that restores the original dimensions. Applying Phantom to the mobile network data, we find that there exists a number of prevalent and distinct behavior patterns that persist over time, suggesting that user browsing behavior in 3G cellular networks can be captured using a small number of co-clusters. For instance, behavior of most users can be classified as either homogeneous (users with very limited set of browsing interests) or heterogeneous (users with very diverse browsing interests), and such behavior profiles do not change significantly at either short (30-min) or long (6 hour) time scales.
【Keywords】: hierarchical coclustering; hourglass model; phantom bi-clustering
【Paper Link】 【Pages】:353-364
【Authors】: Davide Zanetti ; Boris Danev ; Srdjan Capkun
【Abstract】: In this work, we study physical-layer identification of passive UHF RFID tags. We collect signals from a population of 70 tags using a purpose-built reader and we analyze time domain and spectral features of the collected signals. We show that, based on timing features of the signals, UHF RFID tags can be classified, independently of the location and distance to the reader (evaluated up to 6 meters), with an accuracy of approx. 71% (within our population). Additionally, we show that is possible to uniquely identify a maximum of approx. 26 UHF RFID tags independently of the population size. We analyze the implications of these results on tag holder privacy. We further show that, in controlled environments, UHF RFID tags can be uniquely identified based on their signal spectral features with an Equal Error Rate of 0% (within our population); we discuss the application of those techniques to cloning detection in RFID-enabled supply chains.
【Keywords】: fingerprinting; physical-layer identification; privacy; rfid; tracking; wireless security
【Paper Link】 【Pages】:365-376
【Authors】: Jung Ryu ; Vidur Bhargava ; Nick Paine ; Sanjay Shakkottai
【Abstract】: We study a network composed of multiple clusters of wireless nodes. Within each cluster, nodes can communicate directly using the wireless links; however, these clusters are far away such that direct communication between the clusters is impossible except through "mobile" contact nodes. These mobile contact nodes are data carriers that shuffle between clusters and transport data from source to destination clusters. There are several applications of our network model (e.g., clusters of mobile soldiers connected via unmanned aerial vehicles). At the same time, much interest has been garnered by cross-layer design for wireless networks in order to improve efficiency and better allocate resources. In this paper, we focus on queue based cross-layer technique known as back-pressure algorithm. The algorithm is known to be throughput optimal, as well as resilient to disruptions in the network, making it an ideal place to start when designing communication protocols for our intermittently connected network. In this paper, we design a back-pressure routing/rate control algorithm for intermittently connected networks (ICNs). We implement a modified back-pressure routing algorithm on a 16-node experimental test bed, discuss some of the issues regarding design and implementation, and present our experimental results.
【Keywords】: back-pressure routing; intermittently connected networks
【Paper Link】 【Pages】:377-388
【Authors】: Rik Sarkar ; Jie Gao
【Abstract】: Consider mobile targets moving in a plane and their movements being monitored by a network such as a field of sensors. We develop distributed algorithms for in-network tracking and range queries for aggregated data (for example returning the number of targets within any user given region). Our scheme stores the target detection information locally in the network, and answers a query by examining the perimeter of the given range. The cost of updating data about mobile targets is proportional to the target displacement. The key insight is to maintain in the sensor network a function with respect to the target detection data on the graph edges that is a differential one-form such that the integral of this one-form along any closed curve C gives the integral within the region bounded by C. The differential one-form has great flexibility making it appropriate for tracking mobile targets. The basic range query can be used to find a nearby target or any given identifiable target with cost O(d) where d is the distance to the target in question. Dynamic insertion, deletion, coverage holes and mobility of sensor nodes can be handled with only local operations, making the scheme suitable for a highly dynamic network. It is extremely robust and capable of tolerating errors in sensing and target localization. Due to limited space, we only elaborate the advantages of differential forms in tracking of mobile targets. The same routine can be applied for organizing many other types of informations, for example streaming scalar sensor data (such as temperature data field), to support efficient range queries. We demonstrate through analysis and simulations that this scheme compares favorably with existing schemes that use location services for answering aggregated range queries of target detection data.
【Keywords】: differential forms; multi-target tracking; range queries; sensor networks