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85
Allocating Dynamic TimeSpectrum Blocks In Cognitive Radio Networks
, 2007
"... A number of studies have shown the abundance of unused spectrum in the TV bands. This is in stark contrast to the overcrowding of wireless devices in the ISM bands. A recent trend to alleviate this disparity is the design of Cognitive Radios, which constantly sense the spectrum and opportunistically ..."
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Cited by 95 (2 self)
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A number of studies have shown the abundance of unused spectrum in the TV bands. This is in stark contrast to the overcrowding of wireless devices in the ISM bands. A recent trend to alleviate this disparity is the design of Cognitive Radios, which constantly sense the spectrum and opportunistically utilize unused frequencies in the TV bands. In this paper, we introduce the concept of a timespectrum block to model spectrum reservation, and use it to present a theoretical formalization of the spectrum allocation problem in cognitive radio networks. We present a centralized and a distributed protocol for spectrum allocation and show that these protocols are close to optimal in most scenarios. We have implemented the distributed protocol in QualNet and show that our analysis closely matches the simulation results.
A Measurement Study of Interference Modeling and Scheduling in LowPower Wireless Networks
"... Accurate interference models are important for use in transmission scheduling algorithms in wireless networks. In this work, we perform extensive modeling and experimentation on two 20node TelosB motes testbeds – one indoor and the other outdoor – to compare a suite of interference models for their ..."
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Cited by 71 (1 self)
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Accurate interference models are important for use in transmission scheduling algorithms in wireless networks. In this work, we perform extensive modeling and experimentation on two 20node TelosB motes testbeds – one indoor and the other outdoor – to compare a suite of interference models for their modeling accuracies. We first empirically build and validate the physical interference model via a packet reception rate vs. SINR relationship using a measurement driven method. We then similarly instantiate other simpler models, such as hopbased, rangebased, protocol model, etc. The modeling accuracies are then evaluated on the two testbeds using transmission scheduling experiments. We observe that while the physical interference model is the most accurate, it is still far from perfect, providing a 90percentile error about 2025 % (and 80 percentile error 712%), depending on the scenario. The accuracy of the other models is worse and scenariospecific. The second best model trails the physical model by roughly 1218 percentile points for similar accuracy targets. Somewhat similar throughput performance differential between models is also observed when used with greedy scheduling algorithms. Carrying on further, we look closely into the the two incarnations of the physical model – ‘thresholded ’ (conservative, but typically considered in literature) and ‘graded ’ (more realistic). We show via solving the one shot scheduling problem, that the graded version can improve ‘expected throughput ’ over the thresholded version by scheduling imperfect links. Categories and Subject Descriptors C.2.1 [Network architecture and design]: Wireless communication;
Multicast capacity for large scale wireless ad hoc networks
 In ACM Mobicom
, 2007
"... In this paper, we study the capacity of a largescale random wireless network for multicast. Assume that n wireless nodes are randomly deployed in a square region with sidelength a and all nodes have the uniform transmission range r and uniform interference range R> r. We further assume that eac ..."
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Cited by 68 (23 self)
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In this paper, we study the capacity of a largescale random wireless network for multicast. Assume that n wireless nodes are randomly deployed in a square region with sidelength a and all nodes have the uniform transmission range r and uniform interference range R> r. We further assume that each wireless node can transmit/receive at W bits/second over a common wireless channel. For each node vi, we randomly pick k − 1 nodes from the other n − 1 nodes as the receivers of the multicast session rooted at node vi. The aggregated multicast capacity is defined as the total data rate of all multicast sessions in the network. In this paper we derive matching asymptotic upper bounds and lower bounds on multicast capacity of random wireless networks. We show that the total multicast capacity is Θ( � n log n · W √ k) when k = O ( n log n
TDMA Scheduling Algorithms for Wireless Sensor Networks
, 2009
"... Algorithms for scheduling TDMA transmissions in multihop networks usually determine the smallest length conflictfree assignment of slots in which each link or node is activated at least once. This is based on the assumption that there are many independent pointtopoint flows in the network. In se ..."
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Cited by 27 (0 self)
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Algorithms for scheduling TDMA transmissions in multihop networks usually determine the smallest length conflictfree assignment of slots in which each link or node is activated at least once. This is based on the assumption that there are many independent pointtopoint flows in the network. In sensor networks however often data are transferred from the sensor nodes to a few central data collectors. The scheduling problem is therefore to determine the smallest length conflictfree assignment of slots during which the packets generated at each node reach their destination. The conflicting node transmissions are determined based on an interference graph, which may be different from connectivity graph due to the broadcast nature of wireless transmissions. We show that this problem is NPcomplete. We first propose two centralized heuristic algorithms: one based on direct scheduling of the nodes or nodebased scheduling, which is adapted from classical multihop scheduling algorithms for general ad hoc networks, and the other based on scheduling the levels in the routing tree before scheduling the nodes or levelbased scheduling, which is a novel scheduling algorithm for manytoone communication in sensor networks. The performance of these algorithms depends on the distribution of the nodes across the levels. We then propose a distributed algorithm based on the distributed coloring of the nodes, that increases the delay by a factor of 10 − 70 over centralized algorithms for 1000 nodes. We also obtain upper bound for these schedules as a function of the total number of packets generated in the network. 1
How to Correctly Use the Protocol Interference Model for Multihop Wireless Networks
 IN PROC. OF ACM MOBIHOC
, 2009
"... This paper tries to reconcile the tension between physical model and protocol model that have been used to characterize interference relationship in a multihop wireless network. The physical model (a.k.a. SINR model) is widely considered as a reference model for physical layer behavior but its appl ..."
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Cited by 27 (1 self)
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This paper tries to reconcile the tension between physical model and protocol model that have been used to characterize interference relationship in a multihop wireless network. The physical model (a.k.a. SINR model) is widely considered as a reference model for physical layer behavior but its application in multihop wireless networks is limited by its complexity. On the other hand, the protocol model (a.k.a. unified disk graph model) is simple but there have been doubts on its validity. This paper explores the following fundamental question: How to correctly use the protocol interference model? We show that in general, solutions obtained under the protocol model may be infeasible in practice and thus, results based on blind use of protocol model can be misleading. We propose a novel concept called “reality check ” and present a method of using protocol model with reality check for wireless networks. Subsequently, we show that by appropriate setting of the interference range in the protocol model, it is possible to narrow the solution gap between the two models. Our simulation results confirm that this gap is indeed small (or even negligible). Thus, our methodology of joint reality check and interference range setting retains the protocol model as a viable approach to analyze multihop wireless networks.
InterferenceAware Joint Routing and TDMA Link Scheduling for Static Wireless Networks
, 2007
"... We study efficient interferenceaware joint routing and TDMA link scheduling for a multihop wireless network to maximize its throughput. Efficient link scheduling can greatly reduce the interference effect of closeby transmissions. Unlike the previous studies that often assume a unit disk graph m ..."
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Cited by 23 (3 self)
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We study efficient interferenceaware joint routing and TDMA link scheduling for a multihop wireless network to maximize its throughput. Efficient link scheduling can greatly reduce the interference effect of closeby transmissions. Unlike the previous studies that often assume a unit disk graph model, we assume that different terminals could have different transmission ranges and different interference ranges. In our model, it is also possible that a communication link may not exist due to barriers or is not used by a predetermined routing protocol, while the transmission of a node always result interference to all nonintended receivers within its interference range. Using a mathematical formulation, we develop interference aware joint routing and synchronized TDMA link schedulings that optimize the networking throughput subject to various constraints. Our linear programming formulation will find a flow routing whose achieved throughput is at least a constant fraction of the optimum, and the achieved fairness is also a constant fraction of the requirement. Then, by assuming known link capacities and link traffic loads, we study link scheduling under the RTS/CTS interference model and the protocol interference model with fixed transmission power. For both models, we present both efficient centralized and distributed algorithms that use time slots within a constant factor of the optimum. We also present efficient distributed algorithms whose performances are still comparable with optimum, but with much less communications. We prove that the timeslots needed by our faster distributed algorithms are only at most O(min(log n, log ψ)) for RTS/CTS interference model and protocol interference model. Our theoretical results are corroborated by extensive simulation studies.
Local Broadcasting in the Physical Interference Model
, 2008
"... In this work we analyze the complexity of local broadcasting in the physical interference model. We present two distributed randomized algorithms: one that assumes that each node knows how many nodes there are in its geographical proximity, and another, which makes no assumptions about topology know ..."
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Cited by 22 (2 self)
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In this work we analyze the complexity of local broadcasting in the physical interference model. We present two distributed randomized algorithms: one that assumes that each node knows how many nodes there are in its geographical proximity, and another, which makes no assumptions about topology knowledge. We show that, if the transmission probability of each node meets certain characteristics, the analysis can be decoupled from the global nature of the physical interference model, and each node performs a successful local broadcast in time proportional to the number of neighbors in its physical proximity. We also provide worstcase optimality guarantees for both algorithms and demonstrate their behavior in average scenarios through simulations.
Distributed Coordination with Deaf Neighbors: Efficient Medium Access for 60 GHz Mesh Networks
 in Proc. IEEE INFOCOM 2010
, 2010
"... Abstract—Multigigabit outdoor mesh networks operating in the unlicensed 60 GHz “millimeter (mm) wave ” band, offer the possibility of a quickly deployable broadband extension of the Internet. We consider mesh nodes with electronically steerable antenna arrays, with both the transmitter and receiver ..."
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Cited by 19 (7 self)
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Abstract—Multigigabit outdoor mesh networks operating in the unlicensed 60 GHz “millimeter (mm) wave ” band, offer the possibility of a quickly deployable broadband extension of the Internet. We consider mesh nodes with electronically steerable antenna arrays, with both the transmitter and receiver synthesizing narrow beams that compensate for the higher path loss at mmwave frequencies, achieving ranges on the order of 100 meters using the relatively low transmit powers attainable with lowcost silicon implementations. Such highly directional networking differs from WiFi networks at lower carrier frequencies in two ways that have a crucial impact on protocol design: (1) directionality drastically reduces spatial interference, so that pseudowired link abstractions form an excellent basis for protocol design; (2) directionality induces deafness, which makes medium access control (MAC) based on carrier sensing infeasible. Interference analysis in our prior work shows that, in such a setting, coordination between transmitters and receivers, rather than interference management, becomes the key MAC performance bottleneck. However, the question of whether such coordination can be achieved in a distributed fashion while achieving high medium utilization, was left open. In this paper, we answer this question in the affirmative, presenting a distributed MAC protocol that employs memory to achieve approximate time division multiplexed (TDM) schedules without explicit coordination or resource allocation. The efficacy of the protocol is demonstrated via packet level simulations, while a Markov chain fixedpoint analysis provides insight into the effect of parameter choices.
An Adaptive, High Performance MAC for LongDistance Multihop Wireless Networks
"... We consider the problem of efficient MAC design for longdistance WiFibased mesh networks. In such networks it is common to see long propagation delays, the use of directional antennas, and the presence of interlink interference. Prior work has shown that these characteristics make traditional CSM ..."
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Cited by 18 (6 self)
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We consider the problem of efficient MAC design for longdistance WiFibased mesh networks. In such networks it is common to see long propagation delays, the use of directional antennas, and the presence of interlink interference. Prior work has shown that these characteristics make traditional CSMAbased MACs a poor choice for longdistance mesh networks, prompting several recent research efforts exploring the use of TDMAbased approaches to media access. In this paper we first identify, and then address, several shortcomings of current TDMAbased proposals, which exhibit inefficienct throughput and delay charactersistics as they use fixedlength transmission slots that cannot adapt to dynamic variations in traffic load. We show that throughput achieved by existing solutions falls far short of the optimal achievable network throughput. Current TDMAbased solutions also only apply to bipartitie network
Energy efficient tdma sleep scheduling in wireless sensor networks
 in INFOCOM ’09
, 2009
"... Abstract—Sleep scheduling is a widely used mechanism in wireless sensor networks (WSNs) to reduce the energy consumption since it can save the energy wastage caused by the idle listening state. In a traditional sleep scheduling, however, sensors have to start up numerous times in a period, and thus ..."
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Cited by 15 (3 self)
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Abstract—Sleep scheduling is a widely used mechanism in wireless sensor networks (WSNs) to reduce the energy consumption since it can save the energy wastage caused by the idle listening state. In a traditional sleep scheduling, however, sensors have to start up numerous times in a period, and thus consume extra energy due to the state transitions. The objective of this paper is to design an energy efficient sleep scheduling for low datarate WSNs, where sensors not only consume different amounts of energy in different states (transmit, receive, idle and sleep), but also consume energy for state transitions. We use TDMA as the MAC layer protocol, because it has the advantages of avoiding collisions, idle listening and overhearing. We first propose a novel interferencefree TDMA sleep scheduling problem called contiguous link scheduling, which assigns sensors with consecutive time slots to reduce the frequency of state transitions. To tackle this problem, we then present efficient centralized and distributed algorithms that use time slots at most a constant factor of the optimum. The simulation studies corroborate the theoretical results, and show the efficiency of our proposed algorithms.