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80
Power law and exponential decay of inter contact times between mobile devices
, 2007
"... We examine the fundamental properties that determine the basic performance metrics for opportunistic communications. We first consider the distribution of intercontact times between mobile devices. Using a diverse set of measured mobility traces, we find as an invariant property that there is a cha ..."
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Cited by 195 (2 self)
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We examine the fundamental properties that determine the basic performance metrics for opportunistic communications. We first consider the distribution of intercontact times between mobile devices. Using a diverse set of measured mobility traces, we find as an invariant property that there is a characteristic time, order of half a day, beyond which the distribution decays exponentially. Up to this value, the distribution in many cases follows a power law, as shown in recent work. This power law finding was previously used to support the hypothesis that intercontact time has a power law tail, and that common mobility models are not adequate. However, we observe that the time scale of interest for opportunistic forwarding may be of the same order as the characteristic time, and thus the exponential tail is important. We further show that already simple models such as random walk and random waypoint can exhibit the same dichotomy in the distribution of intercontact time asc in empirical traces. Finally, we perform an extensive analysis of several properties of human mobility patterns across several dimensions, and we present empirical evidence that the return time of a mobile device to its favorite location site may already explain the observed dichotomy. Our findings suggest that existing results on the performance of forwarding schemes based on powerlaw tails might be overly pessimistic.
On the Broadcast capacity in multihop wireless networks: Interplay of power, . . .
, 2007
"... 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 t ..."
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Cited by 103 (5 self)
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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.
Scaling Laws for Overlaid Wireless Networks: A Cognitive Radio Network vs. a Primary Network
, 2008
"... We study the scaling laws for the throughputs and delays of two coexisting wireless networks that operate in the same geographic region. The primary network consists of Poisson distributed legacy users of density n, and the secondary network consists of Poisson distributed cognitive users of densit ..."
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Cited by 41 (7 self)
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We study the scaling laws for the throughputs and delays of two coexisting wireless networks that operate in the same geographic region. The primary network consists of Poisson distributed legacy users of density n, and the secondary network consists of Poisson distributed cognitive users of density m, with m> n. The primary users have a higher priority to access the spectrum without particular considerations for the secondary users, while the secondary users have to act conservatively in order to limit the interference to the primary users. With a practical assumption that the secondary users only know the locations of the primary transmitters (not the primary receivers), we first show that both networks can achieve the same throughput scaling law as what Gupta and Kumar [1] established for a standalone wireless network if proper transmission schemes are deployed, where a certain throughput is achievable for each individual secondary user (i.e., zero outage) with high probability. By using a fluid model, we also show that both networks can achieve the same delaythroughput tradeoff as the optimal one established by El Gamal et al. [2] for a standalone wireless network. Index Terms — Ad hoc networks, overlaid wireless networks, throughput, delay, cognitive radio networks.
Improved Capacity Scaling in Wireless Networks With Infrastructure
, 2008
"... This paper analyzes the impact and benefits of infrastructure support in improving the throughput scaling in networks of n randomly located wireless nodes. The infrastructure uses multiantenna base stations (BSs), in which the number of BSs and the number of antennas at each BS can scale at arbitra ..."
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Cited by 19 (9 self)
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This paper analyzes the impact and benefits of infrastructure support in improving the throughput scaling in networks of n randomly located wireless nodes. The infrastructure uses multiantenna base stations (BSs), in which the number of BSs and the number of antennas at each BS can scale at arbitrary rates relative to n. Two schemes are introduced in this study: a BSbased singlehop routing protocol with multipleaccess uplink and broadcast downlink and a BSbased multihop routing protocol. Then, the throughput scaling laws of each are analyzed here. These schemes are compared against two conventional schemes without BSs: the multihop (MH) transmission and hierarchical cooperation (HC) schemes. It is shown that the BSbased routing schemes do not improve the throughput scaling in dense networks. In contrast, the proposed BSbased routing schemes can, under realistic
1 ThroughputDelay Tradeoff for Hierarchical Cooperation in Ad Hoc Wireless Networks
"... Abstract — Hierarchical cooperation has recently been shown to achieve better throughput scaling than classical multihop schemes under certain assumptions on the channel model in static wireless networks. However, the endtoend delay of this scheme turns out to be significantly larger than those of ..."
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Cited by 18 (1 self)
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Abstract — Hierarchical cooperation has recently been shown to achieve better throughput scaling than classical multihop schemes under certain assumptions on the channel model in static wireless networks. However, the endtoend delay of this scheme turns out to be significantly larger than those of multihop schemes. A modification of the scheme is proposed here that achieves a throughputdelay tradeoff D(n) = (log n) 2 T(n) for T(n) between Θ ( √ n/log n) and Θ(n/log n), where D(n) and T(n) are respectively the average delay per bit and the aggregate throughput in a network of n nodes. This tradeoff complements the previous results of El Gamal et al., which show that the throughputdelay tradeoff for multihop schemes is given by D(n) = T(n) where T(n) lies between Θ(1) and Θ ( √ n). Meanwhile, the present paper considers the network multipleaccess problem, which may be of interest in its own right.
GarciaLunaAceves, “The capacity and energy efficiency of wireless ad hoc networks with multipacket reception
 in MobiHoc’08, 2008
"... We address the cost incurred in increasing the transport capacity of wireless ad hoc networks over what can be attained when sources and destinations communicate over multihop paths and nodes can transmit or receive at most one packet at a time. We define the energy efficiency η(n) as the bitmeters ..."
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Cited by 14 (3 self)
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We address the cost incurred in increasing the transport capacity of wireless ad hoc networks over what can be attained when sources and destinations communicate over multihop paths and nodes can transmit or receive at most one packet at a time. We define the energy efficiency η(n) as the bitmeters of information transferred in the network for each unit energy. We compute the energy efficiency of many different techniques aimed at increasing the capacity of wireless networks and show that, in order to achieve higher transport capacity, a lower energy efficiency must be attained. Using the physical model, we compute the throughput capacity of random wireless ad hoc networks in which nodes are endowed with multipacket reception (MPR) capabilities. We
Optimal delay scheduling in networks with arbitrary constraints
 In SIGMETRICS
, 2008
"... We consider the problem of designing an online scheduling scheme for a multihop wireless packet network with arbitrary topology and operating under arbitrary scheduling constraints. The objective is to design a scheme that achieves high throughput and low delay simultaneously. We propose a scheduli ..."
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Cited by 13 (1 self)
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We consider the problem of designing an online scheduling scheme for a multihop wireless packet network with arbitrary topology and operating under arbitrary scheduling constraints. The objective is to design a scheme that achieves high throughput and low delay simultaneously. We propose a scheduling scheme that – for networks operating under primary interference constraints – guarantees a perflow endtoend packet delay bound of 5d j/1−ρ j, at a factor 5 loss of throughput, where dj is the path length (number of hops) of flow j and ρj is the effective loading along the route of flow j. Clearly, dj is a universal lower bound on endtoend packet delay for flow j. Thus, our result is essentially optimal. To the best of our knowledge, our result is the first one to show that it is possible to achieve a perflow endtoend delay bound of O( # of hops) in a constrained
Throughput and Delay Scaling of General Cognitive Networks
 in Proceedings of IEEE INFOCOM
, 2011
"... Abstract—There has been recent interest within the networking research community to understand how performance scales in cognitive networks with overlapping n primary nodes and m secondary nodes. Two important metrics, i.e., throughput and delay, are studied in this paper. We first propose a simple ..."
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Cited by 13 (4 self)
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Abstract—There has been recent interest within the networking research community to understand how performance scales in cognitive networks with overlapping n primary nodes and m secondary nodes. Two important metrics, i.e., throughput and delay, are studied in this paper. We first propose a simple and extendable decision model, i.e., the hybrid protocol model, for the secondary nodes to exploit spatial gap among primary transmissions for frequency reuse. Then a framework for general cognitive networks is established based on it to analyze the occurrence of transmission opportunities for secondary nodes. We show that in the case that the transmission range of the secondary network is smaller than that of the primary network in order, as long as the primary network operates in a roundrobin TDMA fashion or employs a routing scheme that flows independently choose relays, the hybrid protocol model suffice to guide the secondary network to achieve the same throughput and delay scaling as a standalone network, without harming the transmissions of the primary network. Our approach is general in the sense that we only make a few weak assumptions on both networks, and therefore obtain a wide variety of results. We show secondary networks can obtain the same order of throughput and delay as standalone networks when primary networks are classic static networks, networks with random walk mobility, hybrid networks, CSMA networks or networks with general mobility. Our work presents a relatively complete picture of the performance scaling of cognitive networks and provides fundamental insight on the design of them. I.
Buffer Scalability of Wireless Networks
 in Proc. of IEEE INFOCOM
, 2006
"... Abstract—This paper investigates the existence of scalable protocols that can achieve the capacity limit of per sourcedestination pair in a large wireless network of nodes when the buffer space of each node does not grow with the size of the network. It is shown that there is no endtoend protocol ..."
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Cited by 11 (2 self)
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Abstract—This paper investigates the existence of scalable protocols that can achieve the capacity limit of per sourcedestination pair in a large wireless network of nodes when the buffer space of each node does not grow with the size of the network. It is shown that there is no endtoend protocol capable of carrying out the limiting throughput of with nodes that have constant buffer space. In other words, this limit is achievable only with devices whose buffers grow with the size of the network. On the other hand, the paper establishes that there exists a protocol which realizes a slightly smaller throughput of log when devices have constant buffer space. Furthermore, it is shown that the required buffer space can be very small, capable of storing just a few packets. This is particularly important for wireless sensor networks where devices have limited resources. Finally, from a mathematical perspective, the paper furthers our understanding of the difficult problem of analyzing large queueing networks with finite buffers for which, in general, no explicit solutions are available. Index Terms—Ad hoc wireless networks, finitebuffer queueing networks, largescale networks, local cooperation, scaling laws, wireless sensor networks. I.
Optimal RateReliabilityDelay Tradeoff in Networks with Composite Links 1
"... Networks need to accommodate diverse applications with different QualityofService (QoS) requirements. New ideas at the physical layer are being developed for this purpose, such as diversity embedded coding, which is a technique that combines high rates with high reliability. We address the problem ..."
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Cited by 9 (1 self)
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Networks need to accommodate diverse applications with different QualityofService (QoS) requirements. New ideas at the physical layer are being developed for this purpose, such as diversity embedded coding, which is a technique that combines high rates with high reliability. We address the problem of how to fully utilize different ratereliability characteristics at the physical layer to support different types of traffic over a network and to jointly maximize their utilities. We set up a new framework based on utility maximization for networks with composite links, meaning that each link consists of sublinks that can attain different ratereliability characteristics simultaneously. We incorporate delay, in addition to rate and reliability, into the utility functions. To accommodate different types of traffic, we propose distributed algorithms converging to the optimal ratereliabilitydelay tradeoff based on capacity division and priority queueing. Numerical results show that compared with traditional codes, the new codes can provide higher network utilities for all traffic types simultaneously. The results also show that priority queueing achieves higher network utility than capacity division.