Abstract — Studying transfer opportunities between wireless devices carried by humans, we observe that the distribution of the inter-contact time, that is the time gap separating two contacts of the same pair of devices, exhibits a heavy tail such as one of a power law, over a large range of value. This observation is confirmed on six distinct experimental data sets. It is at odds with the exponential decay implied by most mobility models. In this paper, we study how this new characteristic of human mobility impacts a class of previously proposed forwarding algorithms. We use a simplified model based on the renewal theory to study how the parameters of the distribution impact the delay performance of these algorithms. We make recommendation for the design of well founded opportunistic forwarding algorithms, in the context of human carried devices. I.

Abstract — We study data transfer opportunities between wireless devices carried by humans. We observe that the distribution of the inter-contact time (the time gap separating two contacts between the same pair of devices) may be well approximated by a power law over the range [10 minutes; 1 day]. This observation is confirmed using eight distinct experimental data sets. It is at odds with the exponential decay implied by the most commonly used mobility models. In this paper, we study how this newly uncovered characteristic of human mobility impacts one class of forwarding algorithms previously proposed. We use a simplified model based on the renewal theory to study how the parameters of the distribution impact the performance in terms of the delivery delay of these algorithms. We make recommendations for the design of well founded opportunistic forwarding algorithms, in the context of human carried devices. I.

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.

Since the original work of Grossglauser and Tse, which showed that the mobility can increase the capacity of an ad hoc network, there has been a lot of interest in characterizing the delay-capacity relationship in ad hoc networks. Various mobility models have been studied in the literature, and the delay-capacity relationships under those models have been characterized. The results indicate that there are trade-offs between the delay and the capacity, and that the nature of these trade-offs is strongly influenced by the choice of the mobility model. Some questions that arise are: (i) How representative are these mobility models studied in the lieterature? (ii) Can the delay-capacity relationship be significantly different under some other “reasonable ” mobility model? (iii) What would the delay-capacity trade-off in a real network be like? In this paper, we address these questions. In particular, we analyze, among others, some of the mobility models that have been used in the recent related works, under a unified framework. We relate the nature of the delay-capacity trade-off to the nature of the node motion, thereby providing a better understanding of the delay-capacity relationship in ad hoc networks than earlier works.

Gupta and Kumar (2000) introduced a random model to study throughput scaling in a wireless network with static nodes, and showed that the throughput per source-destination pair is Θ ( 1 / √ n log n). Grossglauser and Tse (2001) showed that when nodes are mobile it is possible to have a constant throughput scaling per source-destination pair. In most applications delay is also a key metric of network performance. It is expected that high throughput is achieved at the cost of high delay and that one can be improved at the cost of the other. The focus of this paper is on studying this trade-off for wireless networks in a general framework. Optimal throughput-delay scaling laws for static and mobile wireless networks are established. For static networks, it is shown that the optimal throughput-delay trade-off is given by D(n) = Θ(nT (n)), where T (n) and D(n) are the throughput and delay scaling, respectively. For mobile networks, a simple proof of the throughput scaling of Θ(1) for the Grossglauser-Tse scheme is given and the associated delay scaling is shown to be Θ(n log n). The optimal throughput-delay trade-off for mobile networks is also established. To capture physical movement in the real world, a random walk model for node mobility is assumed. It is shown that for throughput of O ( 1 / √ n log n) , which can also be achieved in static networks, the throughput-delay trade-off is the same as in static networks, i.e., D(n) = Θ(nT (n)). Surprisingly, for almost any throughput of a higher order, the delay is shown to be Θ(n log n), which is the delay for throughput of Θ(1). Our result, thus, suggests that the use of mobility to increase throughput, even slightly, in real-world networks would necessitate an abrupt and very large increase in delay.

Abstract—We consider the problem of throughput-optimal routing over large-scale wireless ad-hoc networks. Gupta and Kumar (2000) showed that a throughput capacity (a uniform 1) is achievable n log n rate over all source-destination pairs) of Θ( in random planar networks, and the capacity is achieved by straight-line routes. In reality, both the network model and the traffic demands are likely to be highly non-uniform. In this paper, we first propose a randomized forwarding strategy based on geographic routing that achieves near-optimal throughput over random planar networks with an arbitrary number of routing holes (regions devoid of nodes) of varying sizes. Next, we study a random planar network with arbitrary source-destination pairs with arbitrary traffic demands. For such networks, we demonstrate a randomized local load-balancing algorithm that supports any traffic load that is within a poly-logarithmic factor of the throughput region. Our algorithms are based on geographic routing and hence inherit their advantageous properties of lowcomplexity, robustness and stability. I.

Recent years have seen significant interest in using the multihop wireless networking paradigm for building mesh networks, ad hoc networks, and sensor networks. A key challenge in multihop wireless networks is to provision for sufficient network capacity to meet user requirements. Several approaches have been proposed to improve the network capacity in multihop networks, ranging from approaches that improve the efficiency of existing protocols, to approaches that use additional resources. In this dissertation, we propose to use additional frequency spectrum, as well as improve the efficiency of using existing frequency spectrum, for improving network capacity. Widely used wireless technologies, such as IEEE 802.11, provision for multiple frequencyseparated channels in the available frequency spectrum. Commercially available wireless network interfaces can typically operate over only one channel at a time. Due to cost and complexity constraints, the total number of interfaces at each node is expected to be fewer than the total number of channels available in the network. Under this scenario with fewer interfaces per node than channels, several challenges have to be addressed before all the channels can be utilized. In this dissertation, we have established the asymptotic capacity of multichannel wireless networks with varying number of channels and interfaces. Capacity analysis has shown that it is feasible

Abstract—We consider the question of obtaining tight delay guarantees for throughout-optimal link scheduling in arbitrary topology wireless ad-hoc networks. We consider two classes of scheduling policies: 1) a maximum queue-length weighted independent set scheduling policy, and 2) a randomized independent set scheduling policy where the independent set scheduling probabilities are selected optimally. Both policies stabilize all queues for any set of feasible packet arrival rates, and are therefore throughput-optimal. For these policies and i.i.d. packet arrivals, we show that the average packet delay is bounded by a constant that depends on the chromatic number of the interference graph, and the overall load on the network. We also prove that this upper bound is asymptotically tight in the sense that there exist classes of topologies where the expected delay attained by any scheduling policy is lower bounded by the same constant. Through simulations we examine the scaling of the average packet delay with respect to the overall load on the network, and the chromatic number of the link interference graph. I.

Abstract—Routing to mobile nodes in a wireless network is conventionally performed by associating a static IP address (or a geographic location) to each node, and routing to that address using routing tables at intermediate nodes that are updated periodically to reflect mobility-induced network topology changes. This mode of routing works when the mobiles ’ speeds as well as the number of mobiles are small. However, in the presence of large number of fast-moving mobiles, such approaches are infeasible and can lead to excessive overheads, routing failures and hence, throughput loss. In this paper, we consider a wireless network over a domain with a collection of static nodes (that form a connected cover of the domain) and mobile nodes, where the mobile nodes can move in an arbitrary (non-ergodic) manner over sub-domains of the network. For such a system, we develop new routing algorithms (based on a spatial multi-resolution search) that we show are efficient both in terms of routing overheads and throughput. In particular, we show that the achievable rate region of the proposed algorithm is within a poly-logarithmic constant of the optimal rate region with non-ergodic mobility. I.

Abstract This paper considers dynamic wireless networks where messages arriving randomly (in time and space) are collected by a mobile receiver. The messages are transmitted to the mobile receiver according to a random access scheme and the receiver dynamically adjusts its position in order to receive these messages in the least amount of time. We study utilizing a combination of wireless transmission and controlled mobility to improve the delay performance in such networks. In particular, we analytically characterize the tradeoff between wireless transmission and physical movement of the mobile receiver. We derive a fundamental lower bound for the delay in the system and show how its effected by different communication parameters. We show that the combination of mobility and wireless transmission results in a significant improvement in delay as compared to a system where wireless transmission is not used. 1