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Distributed Non-Stochastic Experts [article]

Varun Kanade, Zhenming Liu, Bozidar Radunovic
2012 arXiv   pre-print
We consider the online distributed non-stochastic experts problem, where the distributed system consists of one coordinator node that is connected to k sites, and the sites are required to communicate with each other via the coordinator. At each time-step t, one of the k site nodes has to pick an expert from the set 1, ..., n, and the same site receives information about payoffs of all experts for that round. The goal of the distributed system is to minimize regret at time horizon T, while
more » ... taneously keeping communication to a minimum. The two extreme solutions to this problem are: (i) Full communication: This essentially simulates the non-distributed setting to obtain the optimal O(√((n)T)) regret bound at the cost of T communication. (ii) No communication: Each site runs an independent copy : the regret is O(√(log(n)kT)) and the communication is 0. This paper shows the difficulty of simultaneously achieving regret asymptotically better than √(kT) and communication better than T. We give a novel algorithm that for an oblivious adversary achieves a non-trivial trade-off: regret O(√(k^5(1+ϵ)/6 T)) and communication O(T/k^ϵ), for any value of ϵ∈ (0, 1/5). We also consider a variant of the model, where the coordinator picks the expert. In this model, we show that the label-efficient forecaster of Cesa-Bianchi et al. (2005) already gives us strategy that is near optimal in regret vs communication trade-off.
arXiv:1211.3212v1 fatcat:ozgcr4q4rfc6rl4jaef2wz4gwa

Communication complexity of approximate maximum matching in the message-passing model [article]

Zengfeng Huang, Bozidar Radunovic, Milan Vojnovic, Qin Zhang
2017 arXiv   pre-print
We consider the communication complexity of finding an approximate maximum matching in a graph in a multi-party message-passing communication model. The maximum matching problem is one of the most fundamental graph combinatorial problems, with a variety of applications. The input to the problem is a graph G that has n vertices and the set of edges partitioned over k sites, and an approximation ratio parameter α. The output is required to be a matching in G that has to be reported by one of the
more » ... ites, whose size is at least factor α of the size of a maximum matching in G. We show that the communication complexity of this problem is Ω(α^2 k n) information bits. This bound is shown to be tight up to a n factor, by constructing an algorithm, establishing its correctness, and an upper bound on the communication cost. The lower bound also applies to other graph combinatorial problems in the message-passing communication model, including max-flow and graph sparsification.
arXiv:1704.08462v1 fatcat:bvjfnlx5mne7fo6df2nxpgbdom

Performance of Ultra-Wideband Impulse Radio in Presence of Impulsive Interference [article]

Bozidar Radunovic, Jean-Yves Le Boudec, Raymond Knopp
2007 arXiv   pre-print
We analyze the performance of coherent impulsive-radio (IR) ultra-wideband (UWB) channel in presence of the interference generated by concurrent transmissions of the systems with the same impulsive radio. We derive a novel algorithm, using Monte-Carlo method, to calculate a lower bound on the rate that can be achieved using maximum-likelihood estimator. Using this bound we show that such a channel is very robust to interference, in contrast to the nearest-neighbor detector.
arXiv:cs/0702084v1 fatcat:ph46a3dcdveptid5ffjxu22lr4


Božidar Radunović, Ranveer Chandra, Dinan Gunawardena
2012 Proceedings of the 8th international conference on Emerging networking experiments and technologies - CoNEXT '12  
One of the key distinctive requirements of white-space networks is the power asymmetry. Static nodes are allowed to transmit with 15dB-20dB higher power than mobile nodes. This poses significant coexistence problems, as high-power nodes can easily starve lowpower nodes. In this paper, we propose Weeble, a novel distributed and state-less MAC protocol that solves the coexistence problem. One of the key building blocks is an adaptive preamble support, an add-on to the PHY layer that allows
more » ... wer nodes to detect a low-power transmission even when the difference in transmit power is as high as 20dB. The other key building block is a MAC protocol that exploits the adaptive preambles functionality. It implements a virtual carrier-sensing and automatically adapts the preamble size to optimize network performance. We extensively evaluate our system in a test-bed and in simulations. We show that we can prevent starvation of low-power nodes in almost all existing scenarios and improve the data rates of low-power links several-fold over existing MACs, and as a trade-off we decrease the throughput of the rest of the system by 20%-40%.
doi:10.1145/2413176.2413201 dblp:conf/conext/RadunovicCG12 fatcat:gaaubnelsjainkskvhucelddsu


Charalampos Tsourakakis, Christos Gkantsidis, Bozidar Radunovic, Milan Vojnovic
2014 Proceedings of the 7th ACM international conference on Web search and data mining - WSDM '14  
Radunović (, and M. Vojnović ( are with Microsoft Research, Cambridge, United Kingdom.  ...  Radunović (, and M. Vojnović ( are with Microsoft Research, Cambridge, United Kingdom.  ... 
doi:10.1145/2556195.2556213 dblp:conf/wsdm/TsourakakisGRV14 fatcat:wh5soym5xbfspaobgolmvkktsa


Saravana Rathinakumar, Bozidar Radunovic, Mahesh K. Marina
2016 Proceedings of the 12th International on Conference on emerging Networking EXperiments and Technologies - CoNEXT '16  
OFDM is currently the most popular PHY-layer carrier modulation technique, used in the latest generations of cellular, Wi-Fi and TV standards. OFDM systems use cycle prefix to mitigate inter-symbol interference. However, most of the existing systems over-provision the size of the cycle prefix considering the worst case scenarios which rarely occur. We propose a novel OFDM PHY receiver design, called CPRecycle , that exploits the redundant cycle prefix to reduce the effects of interference from
more » ... eighboring nodes. CPRecycle is based on the key observation that the starting position of the FFT window within the cyclic prefix at the OFDM receiver does not affect the received signal but can substantially reduce interference from concurrent transmissions. We further develop an algorithm that is able to find the optimal starting position of the FFT window for each subcarrier using a Gaussian kernel density function and a fixed sphere maximum likelihood detector. Through implementation and extensive evaluations using USRP and offthe-shelf IEEE 802.11g transmitters/interferers, we show the effectiveness of CPRecycle in significantly mitigating interference. CPRecycle only requires local modifications at the receiver and does not require changes in standards, making it incrementally deployable.
doi:10.1145/2999572.2999577 dblp:conf/conext/RathinakumarRM16 fatcat:2pjfthumdbb2xc6mmqoc2ujqwy


Souvik Sen, Bozidar Radunovic, Jeongkeun Lee, Kyu-Han Kim
2013 Proceedings of the 19th annual international conference on Mobile computing & networking - MobiCom '13  
Wireless performance depends directly on the quality of the channel. A wireless transmitter can improve its performance by estimating and transmitting on only the strongest channel, which can be of significantly higher quality than a weak channel (yielding up to 100% rate improvement). It is considered impossible to predict the quality of the unseen channels. Thus, the only way to identify the strongest channel is by probing each channel individually, incurring large overheads. The key
more » ... ion of this paper is a discovery of previously unobserved properties of the wireless channel that makes it possible to predict the the strongest of a set of channels from the measurements collected only on a single channel. We confirm the properties through measurements and present a theoretical analysis that explains their nature. Our proposed system, CSpy, utilizes these observations to predict the strongest channel. CSpy is the first to reliably estimate the strongest channel by utilizing channel responses extracted from off-the-shelf wireless chipsets, without probing any additional channels. By tracking the strongest channel, CSpy improves performance by up to 100% in comparison to channel agnostic schemes.
doi:10.1145/2500423.2500452 dblp:conf/mobicom/SenRLK13 fatcat:t6z6iqt3ybd4jme2pvubdkoqtu


Saravana Manickam Rathinakumar, Bozidar Radunovic, Mahesh K. Marina
2015 Proceedings of the 2nd International Workshop on Hot Topics in Wireless - HotWireless '15  
Adjacent channel interference (ACI) in wireless systems is commonly mitigated through the use of guard bands and filters. Guard bands are not used for any transmissions and are therefore wasted spectrum. The use of sharp filters can reduce the size of required guard bands but they are costly and often not present in devices that are already deployed. We focus on OFDM wireless systems, which form the basis for almost all modern wireless networks, and propose a novel technique called ShiftFFT
more » ... can be deployed at an OFDM receiver to mitigate ACI from legacy OFDM transmitters. ShiftFFT exploits the presence of over-provisioned cyclic prefixes in most OFDM wireless standards to optimize the starting time of the FFT operation at the receiver, which we show to have significant potential to reduce the amount of guard band required to avoid ACI and thereby enable efficient spectrum use. We evaluate ShiftFFT with a SDR testbed and using simulations across diverse settings, and show that using it can significantly reduce the guard band required by at least 10MHz in most cases while maintaining the same packet error rate performance.
doi:10.1145/2799650.2799658 dblp:conf/mobicom/RathinakumarRM15 fatcat:7m2jwibuy5hszj6qki6o5mncuy


Gordon Stewart, Mahanth Gowda, Geoffrey Mainland, Bozidar Radunovic, Dimitrios Vytiniotis
2014 Proceedings of the 2014 ACM workshop on Software radio implementation forum - SRIF '14  
Software-defined radio (SDR) brings the flexibility of software to the domain of wireless protocol design, promising an ideal platform both for research and innovation and the rapid deployment of new protocols on existing hardware. However, existing SDR programming platforms require either careful hand-tuning of low-level code, negating many of the advantages of software, or are too slow to be useful in the real world. In this demo we present Ziria, the first software-defined radio programming
more » ... latform that is both easily programmable and performant. Ziria introduces a novel programming model tailored to wireless physical layer tasks and captures the inherent and important distinction between data and control paths in this domain. We show the capabilities of Ziria by demonstrating a real-time implementation of WiFi PHY running at 20 MHz.
doi:10.1145/2627788.2627799 dblp:conf/sigcomm/StewartGMRV14 fatcat:mohvkk5ufvhuxmikmmgul5bjbi


Božidar Radunović, Christos Gkantsidis, Dinan Gunawardena, Peter Key
2008 Proceedings of the 14th ACM international conference on Mobile computing and networking - MobiCom '08  
There has been extensive work on network architectures that support multi-path routing to improve performance in wireless mesh networks. However, previous work uses ad-hoc design principles that cannot guarantee any network-wide performance objectives such as conjointly maximizing resource utilization and improving fairness. In parallel, numerous theoretical results have addressed the issue of optimizing a combined metric of network utilization and fairness using techniques based on
more » ... e scheduling, routing and flow control. However, the proposed theoretical algorithms are extremely difficult to implement in practice, especially in the presence of 802.11 MAC and TCP. We propose Horizon , 1 a novel system design for multipath forwarding in wireless meshes, based on the theoretical results on back-pressure. Our design works with an unmodified TCP stack and on the top of the existing 802.11 MAC. We modified the back-pressure approach to obtain a simple 802.11-compatible packet-forwarding heuristic and a novel, light-weight path estimator, while maintaining global optimality properties. We propose a delayed reordering algorithm that eliminates TCP timeouts while keeping TCP packet reordering at a minimum. We have evaluated our implementation on a 22-node testbed. We have shown that Horizon effectively utilizes available resources (disjoint paths). In contrast to previous work our design can not only avoid bottlenecks but also optimally load-balances traffic across them when needed, improving fairness among competing flows. To our knowledge, Horizon is the first practical system based on back-pressure.
doi:10.1145/1409944.1409973 dblp:conf/mobicom/RadunovicGGK08 fatcat:tu4smz2ohne5rp4jpddp5uobeq


Gordon Stewart, Mahanth Gowda, Geoffrey Mainland, Bozidar Radunovic, Dimitrios Vytiniotis, Doug Patterson
2014 Proceedings of the 2014 ACM conference on SIGCOMM - SIGCOMM '14  
Software-defined radios (SDR) have the potential to bring major innovation in wireless networking design. However, their impact so far has been limited due to complex programming tools. Most of the existing tools are either too slow to achieve the full line speeds of contemporary wireless PHYs or are too complex to master. In this demo we present our novel SDR programming environment called Ziria. Ziria consists of a novel programming language and an optimizing compiler. The compiler is able to
more » ... synthesize very efficient SDR code from high-level PHY descriptions written in Ziria language. To illustrate its potential, we present the design of an LTE-like PHY layer in Ziria. We run it on the Sora SDR platform and demonstrate on a test-bed that it is able to operate in real-time.
doi:10.1145/2619239.2631427 dblp:conf/sigcomm/StewartGMRVP14 fatcat:lgawb4med5cgpeyhl25kzs7epu


Eugenio Magistretti, Krishna Kant Chintalapudi, Bozidar Radunovic, Ramachandran Ramjee
2011 Proceedings of the 17th annual international conference on Mobile computing and networking - MobiCom '11  
The increase in WiFi physical layer transmission speeds from 1 Mbps to 1 Gbps has reduced transmission times for a 1500 byte packet from 12 ms to 12 µs. However, WiFi MAC overheads such as channel access and acks have not seen similar reductions and cumulatively contribute about 150 µs on average per packet. Thus, the efficiency of WiFi has deteriorated from over 80% at 1 Mbps to under 10% at 1 Gbps. In this paper, we propose WiFi-Nano, a system that uses 800 ns slots to significantly improve
more » ... Fi efficiency. Reducing slot time from 9 µs to 800 ns makes backoffs efficient, but clear channel assessment can no longer be completed in one slot since preamble detection can now take multiple slots. Instead of waiting for multiple slots for detecting preambles, nodes speculatively transmit preambles as their backoff counters expire, while continuing to detect premables using self-interference cancellation. Upon detection of preambles from other transmitters, nodes simply abort their own preamble transmissions, thereby allowing the earliest transmitter to succeed. Further, receivers speculatively transmit their ack preambles at the end of packet reception, thereby reducing ack overhead. We validate the effectiveness of WiFi-Nano through implementation on an FPGA-based software defined radio platform, and through extensive simulations, demonstrate efficiency gains of up to 100%.
doi:10.1145/2030613.2030619 dblp:conf/mobicom/MagistrettiCRR11 fatcat:s7n2m7rvs5eh7p3ts74eg6atd4

WiFi-NC : WiFi Over Narrow Channels

Krishna Chintalapudi, Bozidar Radunovic, Horia Vlad Balan, Michael Buettener, Srinivas Yerramalli, Vishnu Navda, Ramachandran Ramjee
2012 Symposium on Networked Systems Design and Implementation  
The quest for higher data rates in WiFi is leading to the development of standards that make use of wide channels (e.g., 40MHz in 802.11n and 80MHz in 802.11ac). In this paper, we argue against this trend of using wider channels, and instead advocate that radios should communicate over multiple narrow channels for efficient and fair spectrum utilization. We propose WiFi-NC, a novel PHY-MAC design that allows radios to use WiFi over multiple narrow channels simultaneously. To enable WiFi-NC, we
more » ... ave developed the compound radio, a single wideband radio that exposes the abstraction of multiple narrow channel radios, each with independent transmission, reception and carrier sensing capabilities. The architecture of WiFi-NC makes it especially suitable for use in white spaces where free spectrum may be fragmented. Thus, we also develop a frequency band selection algorithm for WiFi-NC making it suitable for use in white spaces. WiFi-NC has been implemented on an FPGAbased software defined radio platform. Through real experiments and simulations, we demonstrate that WiFi-NC provides better efficiency and fairness in both common WiFi as well as future white space scenarios.
dblp:conf/nsdi/ChintalapudiRBBYNR12 fatcat:mjjh4x337rgxvbhdkfw4y66r5q

Communication Complexity of Approximate Matching in Distributed Graphs

Zengfeng Huang, Bozidar Radunovic, Milan Vojnovic, Qin Zhang, Marc Herbstritt
2015 Symposium on Theoretical Aspects of Computer Science  
In this paper we consider the communication complexity of approximation algorithms for maximum matching in a graph in the message-passing model of distributed computation. The input graph consists of n vertices and edges partitioned over a set of k sites. The output is an αapproximate maximum matching in the input graph which has to be reported by one of the sites. We show a lower bound on the communication complexity of Ω(α 2 kn) and show that it is tight up to poly-logarithmic factors. This
more » ... wer bound also applies to other combinatorial problems on graphs in the message-passing computation model, including max-flow and graph sparsification. A model of computation for mapreduce. pages 938-948, 2010. 21 Hartmut Klauck, Danupon Nanongkai, Gopal Pandurangan, and Peter Robinson. The distributed complexity of large-scale graph processing. CoRR, abs/1311.6209, 2013. 22 Christian Konrad, Frédéric Magniez, and Claire Mathieu. Maximum matching in semistreaming with few passes. In APPROX-RANDOM, pages 231-242, 2012.
doi:10.4230/lipics.stacs.2015.460 dblp:conf/stacs/HuangRVZ15 fatcat:lgmbp2qmdfef5h5ard7w3qtvyi

Multipath code casting for wireless mesh networks

Christos Gkantsidis, Wenjun Hu, Peter Key, Bozidar Radunovic, Pablo Rodriguez, Steluta Gheorghiu
2007 Proceedings of the 2007 ACM CoNEXT conference on - CoNEXT '07  
Designing high throughput wireless mesh networks is a challenge, and involves solving interrelated scheduling, routing, and interference problems. In this paper, we exploit the fundamental properties of broadcast medium and path diversity in wireless meshes to implement multipath routing between a source and destination pair. We use network coding for a given unicast source-destination flow to ease the scheduling problem, exploit diversity, and deal with unreliable transmissions. We describe
more » ... tipath-forwarding algorithms, and show their performance benefits over existing proposals, using simulation, analysis, and a prototype implementation on a small testbed. We propose a ratescheduling protocol that relies on network coding, which gives over 30% performance improvement for a realistic topology and can double the throughput in certain cases.
doi:10.1145/1364654.1364667 dblp:conf/conext/GkantsidisHKRRG07 fatcat:yyeaatvlqzc7pmewit7ij6fswi
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