Results 1  10
of
67
Network Information Flow with Correlated Sources
 TO APPEAR IN THE IEEE TRANSACTIONS ON INFORMATION THEORY
, 2005
"... Consider the following network communication setup, originating in a sensor networking application we refer to as the “sensor reachback ” problem. We have a directed graph G = (V, E), where V = {v0v1...vn} and E ⊆ V × V. If (vi, vj) ∈ E, then node i can send messages to node j over a discrete memor ..."
Abstract

Cited by 93 (7 self)
 Add to MetaCart
(Show Context)
Consider the following network communication setup, originating in a sensor networking application we refer to as the “sensor reachback ” problem. We have a directed graph G = (V, E), where V = {v0v1...vn} and E ⊆ V × V. If (vi, vj) ∈ E, then node i can send messages to node j over a discrete memoryless channel (Xij, pij(yx), Yij), of capacity Cij. The channels are independent. Each node vi gets to observe a source of information Ui (i = 0...M), with joint distribution p(U0U1...UM). Our goal is to solve an incast problem in G: nodes exchange messages with their neighbors, and after a finite number of communication rounds, one of the M + 1 nodes (v0 by convention) must have received enough information to reproduce the entire field of observations (U0U1...UM), with arbitrarily small probability of error. In this paper, we prove that such perfect reconstruction is possible if and only if H(USUS c) < i∈S,j∈S c for all S ⊆ {0...M}, S = ∅, 0 ∈ S c. Our main finding is that in this setup a general source/channel separation theorem holds, and that Shannon information behaves as a classical network flow, identical in nature to the flow of water in pipes. At first glance, it might seem surprising that separation holds in a
A Scalable Model for Channel Access Protocols in Multihop Ad Hoc Networks
, 2004
"... A new modeling framework is introduced for the analytical study of medium access control (MAC) protocols operating in multihop ad hoc networks. The model takes into account the e#ect of physicallayer parameters on the success of transmissions, the MAC protocol on the likelihood that nodes can acces ..."
Abstract

Cited by 84 (6 self)
 Add to MetaCart
(Show Context)
A new modeling framework is introduced for the analytical study of medium access control (MAC) protocols operating in multihop ad hoc networks. The model takes into account the e#ect of physicallayer parameters on the success of transmissions, the MAC protocol on the likelihood that nodes can access the channnel, and the connectivity of nodes in the network. A key feature of the model is that nodes can be modeled individually, i.e., it allows a pernode setup of many layerspecific parameters. Moreover, no spatial probability distribution or a particular arrangement of nodes is assumed; the model allows the computation of individual (pernode) performance metrics for any given network topology and radio channel model. To show the applicability of the modeling framework, we model multihop ad hoc networks using the IEEE 802.11 distributed coordination function and validate the results from the model with discreteevent simulations in Qualnet. The results show that our model predicts results that are very close to those attained by simulations, and requires seconds to complete compared to several hours of simulation time.
Capacity of a wireless ad hoc network with infrastructure
 LEMMA 31 (HOEFFDING’S INEQUALITY). Let X1, x2, · · · , Xn
, 2004
"... We study the capacity of a wireless ad hoc network with infrastructure, where wellconnected base stations are placed in an ad hoc network to relay data traffic for wireless nodes. This network architecture presents a tradeoff between a cellular network and an ad hoc network in that data may be forw ..."
Abstract

Cited by 65 (0 self)
 Add to MetaCart
(Show Context)
We study the capacity of a wireless ad hoc network with infrastructure, where wellconnected base stations are placed in an ad hoc network to relay data traffic for wireless nodes. This network architecture presents a tradeoff between a cellular network and an ad hoc network in that data may be forwarded in a multihop fashion or through the infrastructure. It has been shown that the capacity of ad hoc network does not scale well with the number of nodes in the system [1]. In this work, we investigate the potential benefit of infrastructure network to improve ad hoc network capacity. Analytical expressions are obtained for the capacity of an ad hoc networks with infrastructure. For an ad hoc network of £ nodes with ¤ base stations, the results show that, if ¤ grows asymptotically slower than ¥ £ , the benefit of infrastructure network is insignificant. However, if ¤ grows faster than ¥ £ , the capacity increases linearly with the number of base stations, providing an effective improvement over ad hoc networks. Therefore, in order to achieve nonnegligible capacity gain, the investment in the wired infrastructure should be sufficiently high.
The Distance2 Matching Problem and its Relationship to the MACLayer Capacity of Ad Hoc Wireless Networks
 IEEE Journal on Selected Areas in Communications
, 2004
"... Abstract—We consider the problem of determining the maximum capacity of the media access (MAC) layer in wireless ad hoc networks. Due to spatial contention for the shared wireless medium, not all nodes can concurrently transmit packets to each other in these networks. The maximum number of possible ..."
Abstract

Cited by 60 (6 self)
 Add to MetaCart
Abstract—We consider the problem of determining the maximum capacity of the media access (MAC) layer in wireless ad hoc networks. Due to spatial contention for the shared wireless medium, not all nodes can concurrently transmit packets to each other in these networks. The maximum number of possible concurrent transmissions is, therefore, an estimate of the maximum network capacity, and depends on the MAC protocol being used. We show that for a large class of MAC protocols based on virtual carrier sensing using RTS/CTS messages, which includes the popular IEEE 802.11 standard, this problem may be modeled as a maximum Distance2 matching (D2EMIS) in the underlying wireless network: Given a graph @ A, find a set of edges such that no two edges in are connected by another edge in. D2EMIS is NPcomplete. Our primary goal is to show that it
Capacity bounds for three classes of wireless networks: Asymmetric, cluster and hybrid
 Proc. of ACM Mobihoc 2004
, 2004
"... We present capacity results for three classes of wireless ad hoc networks, using a general framework that allows their unified treatment. The results hold with probability going to 1 as the number of nodes in the network approaches infinity, and under a general model for channel fading. We first stu ..."
Abstract

Cited by 45 (0 self)
 Add to MetaCart
(Show Context)
We present capacity results for three classes of wireless ad hoc networks, using a general framework that allows their unified treatment. The results hold with probability going to 1 as the number of nodes in the network approaches infinity, and under a general model for channel fading. We first study asymmetric networks that consist of n source nodes and around n d destination nodes, communicating over a wireless channel. Each source node creates random. When 1 2 data traffic that is directed to a destination node chosen at <d<1, an aggregate throughput that increases with n as n 1 2 is achievable. If, however, 0 <d< 1 2, bottlenecks are formed and the aggregate throughput can not increase faster than n d. We also consider cluster networks, that consist of n client nodes and around n d cluster heads, communicating over a wireless channel. Each of the clients wants to communicate with one of the cluster heads, but the particular choice of cluster head is not important. In this setting, the maximum aggregate throughput is on the order of n d,anditcanbe achieved with no transmissions taking place between client nodes. We conclude with the study of hybrid networks. These consist of n wireless nodes and around n d access points. The access points are equipped with wireless transceivers, but are also connected with each other through an independent network of infinite capacity. Their only task is to support < d < 1, an aggregate throughput on the order of n d is achievable, through the use of the infrastructure. If, however, 0 <d< 1, using the infrastructure offers no significant gain, and the the operation of the wireless nodes. When 1 2 2 wireless nodes can achieve an aggregate throughput on the order of n 1 2 by using the wireless medium only.
How does randomized beamforming improve the connectivity of ad hoc networks
 in In Proceedings of the IEEE International Conference on Communications (ICC), Seoul, Korea
, 2005
"... Abstract—This paper analyzes the impact of beamforming antennas on the topological connectivity of multihop wireless networks. As a metric for the connectivity of the network, we use the percentage P (path) of nodes that are connected via a multihop path. We show that simple randomized beamforming — ..."
Abstract

Cited by 28 (2 self)
 Add to MetaCart
(Show Context)
Abstract—This paper analyzes the impact of beamforming antennas on the topological connectivity of multihop wireless networks. As a metric for the connectivity of the network, we use the percentage P (path) of nodes that are connected via a multihop path. We show that simple randomized beamforming — i.e., each node adjusts its main beam into a randomly chosen direction for transmission and reception — significantly improves P (path) compared to networks with omnidirectional antennas employing the same power and sensitivity. The study is performed using accurate, analytical antenna models for uniform linear and circular antenna arrays. Already small arrays with four antenna elements give high gains of P (path). These gains are achieved although the nodes ’ average number of neighbors does not necessarily increase. Index Terms — Wireless multihop networks, beamforming, adaptive antennas, antenna arrays, connectivity, path probability.
ThroughputDelay Analysis of Mobile Adhoc Networks with a MultiCopy Relaying Strategy
 in Proceedings of IEEE SECON
, 2004
"... Multiuser diversity has been shown to increase the throughput of mobile adhoc wireless networks (MANET) when compared to fixed wireless networks. This paper addresses a multiuser diversity strategy that permits one of multiple onetime relays to deliver a packet to its destination. We show that the ..."
Abstract

Cited by 24 (5 self)
 Add to MetaCart
(Show Context)
Multiuser diversity has been shown to increase the throughput of mobile adhoc wireless networks (MANET) when compared to fixed wireless networks. This paper addresses a multiuser diversity strategy that permits one of multiple onetime relays to deliver a packet to its destination. We show that the (1) throughput of the original single onetime relay strategy is preserved by our multicopy technique. The reason behind achieving the same asymptotic throughput is the fact that, as we demonstrate in this paper, interference for communicating among closest neighbors is bounded for different channel path losses, even when n goes to infinity.
On the Feasibility of LargeScale Wireless Sensor Networks
 In Proc. 40th Allerton Conf. on Communication, Control and Computing
, 2002
"... We consider the problem of rate/distortion with side information available only at the decoder. For the case of jointlyGaussian source X and side information Y, and meansquared error distortion, Wyner proved in 1976 that the rate/distortion function for this problem is identical to the conditional ..."
Abstract

Cited by 19 (2 self)
 Add to MetaCart
(Show Context)
We consider the problem of rate/distortion with side information available only at the decoder. For the case of jointlyGaussian source X and side information Y, and meansquared error distortion, Wyner proved in 1976 that the rate/distortion function for this problem is identical to the conditional rate/distortion function RXY, assuming the side information Y is available at the encoder. In this paper we construct a structured class of asymptotically optimal quantizers for this problem: under the assumption of high correlation between source X and side information Y, we show there exist quantizers within our class whose performance comes arbitrarily close to Wyner’s bound. As an application illustrating the relevance of the highcorrelation asymptotics, we also explore the use of these quantizers in the context of a problem of data compression for sensor networks, in a setup involving a large number of devices collecting highly correlated measurements within a confined area. An important feature of our formulation is that, although the pernode throughput of the network tends to zero as network size increases, so does the amount of information generated by each transmitter. This is a situation likely to be encountered often in practice, which allows us to cast under new—and more “optimistic”—light some negative results on the transport capacity of largescale wireless networks. Index terms: Rate/distortion, rate/distortion with side information, quantization, vector quantization, lattice quantization, lattice codes, hexagonal lattice, source coding, network information theory, adhoc networks, sensor networks, multihop radio networks, wireless networks, throughput, capacity.
On the Fundamental Capacity and Lifetime Limits of EnergyConstrained Wireless Sensor Networks
"... Energy constraints on sensor nodes pose significant challenges towards extending operational lifetimes and sustainable capacities of wireless sensor networks. In this paper, we seek to answer two fundamental questions with respect to energyconstrained sensor networks. First, what is the operational ..."
Abstract

Cited by 19 (0 self)
 Add to MetaCart
Energy constraints on sensor nodes pose significant challenges towards extending operational lifetimes and sustainable capacities of wireless sensor networks. In this paper, we seek to answer two fundamental questions with respect to energyconstrained sensor networks. First, what is the operational lifetime of a particular wireless sensor network under the control of optimal power management schemes? With an adequate definition of operational lifetimes, our asymptotic analysis shows that, with fixed node densities, operational lifetime of sensor networks decreases in the order of 1/n as the number of initially deployed nodes n grows. Second, what is the impact of constrained energy levels on the maximum sustainable throughput in sensor networks? Even with renewable energy sources on each of the sensors (e.g., solar energy sources), our analysis concludes that the maximum sustainable throughput in energyconstrained sensor networks scales worse than the capacity based on interference among concurrent transmissions as long as the high, the energyconstrained network capacity dominates. These verdicts are reached after examining the propositions with a broad spectrum of traffic patterns, ranging from data aggregation to directed diffusion.
On mobility–capacity–delay trade–off in wireless ad hoc networks
 in Proc. of IEEE/ACM MASCOTS, Volendam, The
, 2004
"... We show that there is a trade off among mobility, capacity, and delay in ad hoc networks. More specifically, we consider two schemes for mobility of nodes in ad hoc networks. We divide the entire network by cells whose sizes can vary with the total number of nodes n, or whose size is independent of ..."
Abstract

Cited by 15 (2 self)
 Add to MetaCart
We show that there is a trade off among mobility, capacity, and delay in ad hoc networks. More specifically, we consider two schemes for mobility of nodes in ad hoc networks. We divide the entire network by cells whose sizes can vary with the total number of nodes n, or whose size is independent of the number of nodes. By restricting the movement of nodes within these cells, we calculate throughput and delay for randomly chosen pairs of sourcedestination nodes, and show that mobility is an entity that can be exchanged with capacity and delay. We also investigate the effect of directional antennas in a static network in which packet relaying is done through the closest neighbor and verify that this approach attains better throughput than static networks employing omnidirectional antennas.