Wireless meshnet8Ex8 (WMNs)consist of meshrout6L and meshclient8 where meshroutfix have minimal mobilit and formtr backbone of WMNs. They provide netide access for bot mesh andconvent1)fi8 clientt TheintL gratLfl of WMNs wit ot8 net8866 such as t1Int6fiPx1 cellular, IEEE 802.11, IEEE 802.15, IEEE 802.16, sensor netsor1L ets can be accomplishedtccomp tc gatomp and bridging functng1 in t1 meshroutfijx Meshclient can be eit8fi st8fij1)6x or mobile, and can form aclient meshnet16S amongtng1fifiELj and wit meshroutLfifi WMNs are antLfifl1)6fl t resolvets limit18fiflfl andt significantfl improvetp performance of ad hocnetLEP8L wireless local area net1Pxx (WLANs), wireless personal areanet16fij (WPANs), and wirelessmetess1fifljfl areanet1LPS (WMANs). They are undergoing rapid progress and inspiring numerousdeploymentS WMNs will deliver wireless services for a largevariet ofapplicat6fifl in personal, local, campus, andmet8Lfix1)6fi areas. Despit recent advances in wireless mesh netjLfiP1)6 many research challenges remain in allprotjfiS layers. This paperpresent adetEfl81 stEonrecent advances and open research issues in WMNs. Syst1 architL881)6 andapplicat)68 of WMNs are described, followed by discussingts critssi factss influencingprotenc design.Theoret8fiL netore capacit and tdst1LLSjx tt1LL protLLSj for WMNs are exploredwit anobjectE1 t point out a number of open research issues. Finally,tnal beds,indust681 pract68 andcurrent strent actntx1) relatt t WMNs arehighlight8x # 2004 Elsevier B.V. Allrl rl KedI7-8 Wireless meshnet186flfl Ad hocnet8jEES Wireless sensornetor16fl Medium accessconts1fi Routs1 prots1fiS Transport protspor ScalabilitS Securiti Powermanagement andcontfi8fl Timingsynchronizat ion 1389-1286/$ - seefront matt # 2004 Elsevier B.V. Allright reserved. doi:10....

With the availability of multiple unlicensed spectral bands, and potential cost-based limitations on the capabilities of individual nodes, it is increasingly relevant to study the performance of multichannel wireless networks with channel switching constraints. To this effect, some constraint models have been recently proposed, and connectivity and capacity results have been formulated for networks of randomly deployed single-interface nodes subject to these constraints. One of these constraint models is termed random (c, f) assignment, wherein each node is pre-assigned a random subset of f channels out of c (each having bandwidth W c), and may only switch on these. Previous results for this model established bounds on network capacity, and proved that when c = O(logn), the per-prnd f flow capacity is O(W nlogn) and Ω(W cnlogn) (where prnd = 1 −(1 − f f f f 2 c)(1 − c−1)...(1 − c − f+1) ≥ 1 − e − c). In this paper we present a lower bound construction that matches the previous upper prnd bound. This establishes the capacity as Θ(W nlogn). The surprising implication of this result is that when f = Ω ( √ c), random (c, f) assignment yields capacity of the same order as attainable via unconstrained switching. The routing/scheduling procedure used by us to achieve capacity requires synchronized route-construction for all flows in the network, leading to the open question of whether it is possible to achieve capacity using asynchronous procedures.

The capacity of ad hoc wireless networks is constrained by the interference between concurrent transmissions from neighboring nodes. Gupta and Kumar have shown that the capacity of an ad hoc network does not scale well with the increasing number of nodes in the system when using omnidirectional antennas [6]. We investigate the capacity of ad hoc wireless networks using directional antennas. In this work, we consider arbitrary networks and random networks where nodes are assumed to be static. In arbitrary networks, due to the reduction of the interfer-

Multihop wireless mesh networks can provide Internet access over a wide area with minimal infrastructure expenditure. In this work, we present a measurement driven deployment strategy and a data-driven model to study the impact of design and topology decisions on network-wide performance and cost. We perform extensive measurements in a twotier urban scenario to characterize the propagation environment and correlate received signal strength with application layer throughput. We find that well-known estimates for pathloss produce either heavily overprovisioned networks resulting in an order of magnitude increase in cost for high pathloss estimates or completely disconnected networks for low pathloss estimates. Modeling throughput with wireless interface manufacturer specifications similarly results in severely underprovisioned networks. Further, we measure competing, multihop flow traffic matrices to empirically define achievable throughputs of fully backlogged, rate limited, and web-emulated traffic. We find that while fully backlogged flows produce starving nodes, rate-controlling flows to a fixed value yields fairness and high aggregate throughput. Likewise, transmission gaps occurring in statistically multiplexed web traffic, even under high offered load, remove starvation and yield high performance. In comparison, we find that well-known noncompeting flow models for mesh networks over-estimate network-wide throughput by a factor of 2. Finally, our placement study shows that a regular grid topology achieves up to 50 percent greater throughput than random node placement.

Abstract — In this paper we study the broadcast capacity of multihop wireless networks which we define as the maximum rate at which broadcast packets can be generated in the network such that all nodes receive the packets successfully within a given time. To asses the impact of topology and interference on the broadcast capacity we employ the Physical Model and Generalized Physical Model for the channel. Prior work was limited either by density constraints or by using the less realistic but manageable Protocol model [1], [2]. Under the Physical Model, we find that the broadcast capacity is within a constant factor of the channel capacity for a wide class of network topologies. Under the Generalized Physical Model, on the other hand, the network configuration is divided into three regimes depending on how the power is tuned in relation to network density and size and in which the broadcast capacity is asymptotically either zero, constant or unbounded. As we show, the broadcast capacity is limited by distant nodes in the first regime and by interference in the second regime. In the second regime, which covers a wide class of networks, the broadcast capacity is within a constant factor of the bandwidth. I.

We study the connectivity and capacity of finite area ad hoc wireless networks, with an increasing number of nodes (dense networks). We find that the properties of the network strongly depend on the shape of the attenuation function. For power law attenuation functions, connectivity scales, and the available rate per node is known to decrease like 1/ # n.Onthe contrary, if the attenuation function does not have a singularity at the origin and is uniformly bounded, we obtain bounds on the percolation domain for large node densities, which show that either the network becomes disconnected, or the available rate per node decreases like 1/n.

Abstract—The presence of heterogeneous nodes (i.e., nodes with an enhanced energy capacity or communication capability) in a sensor network is known to increase network reliability and lifetime. However, questions of where, how many, and what types of heterogeneous resources to deploy remain largely unexplored. We focus on energy and link heterogeneity in ad hoc sensor networks and consider resource-aware MAC and routing protocols to utilize those resources. Using analysis, simulation, and real testbed measurements, we evaluate the impact of number and placement of heterogeneous resources on performance in networks of different sizes and densities. While we prove that optimal deployment is very hard in general, we also show that only a modest number of reliable, long-range backhaul links and linepowered nodes are required to have a significant impact. Properly deployed, heterogeneity can triple the average delivery rate and provide a 5-fold increase in the lifetime (respectively) of a large battery-powered network of simple sensors. ∗� I.

In this paper we study the transport capacity of a data-gathering wireless sensor network under di#erent communication organizations. In particular, we consider using a flat as well as a hierarchical/clustering architecture to realize many-to-one communications. The capacity of the network under this many-to-one data gathering scenario is reduced compared to random one-to-one communication due to the unavoidable creation of a point of tra#c concentration at the data collector/receiver. We introduce the overall throughput bound of # = per node, where W is the transmission capacity, and show under what conditions it can be achieved and under what conditions it cannot. When those conditions are not met, we constructively show how # = # is achieved with high probability as the number of sensors goes to infinity. We also show how the introduction of clustering can improve the throughput. We discuss the trade-o#s between achieving capacity and energy consumption, how transport capacity might be a#ected by considering in-network processing and the implications this study has on the design of practical protocols for large-scale data-gathering wireless sensor networks.

Wide-spread deployment of infrastructure WLANs has made Wi-Fi an integral part of today’s Internet access technology. Despite its crucial role in affecting end-to-end performance, past research has focused on MACprotocol enhancement, analysis and simulation-based performance evaluation without sufficient consideration for modeling inaccuracies stemming from inter-layer dependencies, including physical layer diversity, that significantly impact performance. We take a fresh look at IEEE 802.11 WLANs, and using a combination of experiment, simulation, and analysis demonstrate its surprisingly agile performance traits. Our main findings are two-fold. First, contention-based MACthroughput degrades gracefully under congested conditions, enabled by physical layer channel diversity that reduces the effective level of MACcontention. In contrast, fairness and jitter significantly degrade at a critical offered load. This duality obviates the need for link layer flow control for throughput improvement but necessitates traffic control for fairness and QoS. Second, TCP-over-WLAN achieves high throughput commensurate with that of wireline TCP under saturated conditions, challenging the widely held perception that TCP throughput fares poorly over WLANs when subject to heavy contention. We show that TCP-over-WLAN prowess is facilitated by the self-regulating actions of DCF and TCP congestion control that jointly drive the shared physical channel at an effective load of 2–3 wireless stations, even when the number of active stations is very large. Our results highlight subtle inter-layer dependencies including the mitigating influence of TCP-over-WLAN on dynamic rate shifting.

There is a critical need for new thinking regarding overload traffic management in sensor networks. It has now become clear that experimental sensor networks (e.g., mote networks) and their applications commonly experience periods of persistent congestion and high packet loss, and in some cases even congestion collapse. This significantly impacts application fidelity measured at the physical sinks, even under light to moderate traffic loads, and is a direct product of the funneling effect; that is, the many-to-one multi-hop traffic pattern that characterizes sensor network communications. Existing congestion control schemes are effective at mitigating congestion through rate control and packet drop mechanisms, but do so at the cost of significantly reducing application fidelity measured at the sinks. To address this problem we propose to exploit the availability of a small number of all wireless, multi-radio virtual sinks that can be randomly distributed or selectively placed across the sensor field. Virtual sinks are capable of siphoning off data events from regions of the sensor field that are beginning to show signs of high traffic load. In this paper, we present the design, implementation, and evaluation of Siphon, a set of fully distributed algorithms that support virtual sink discovery and selection, congestion detection, and traffic redirection in sensor networks. Siphon is based on a Stargate implementation of virtual sinks that uses a