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The performance of throughput, delay, and their tradeoff in mobile ad hoc networks (MANETs) has been investigated on different assumptions. Nevertheless, few papers consider the supportive infrastructure in MANETs. With the help of supportive infrastructure, i.e., cellular networks, the performance of throughput and delay in MANETs can be improved. The impact of supportive infrastructure on the throughput–delay tradeoff in MANETs is an open research point. In this paper, we are interested in the optimal throughput–delay tradeoff in MANETs with supportive infrastructure. We investigate the supportive infrastructure that only provides transmission pipes between distant nodes. We study the optimal throughput–delay tradeoff in MANETs on different assumptions such as different densities of nodes and base stations (BSs), discrete/continuous mobility models with various velocities, and the fast/slow mobility assumption. We obtain the asymptotically optimal throughput–delay tradeoff and propose transmission policies based on random linear coding (RLC) to achieve the optimal throughput–delay tradeoff asymptotically. From the obtained optimal throughput–delay tradeoff, we find that supportive infrastructure reduces the delay bound from velocity, which is a lower bound of delay caused by nodes' velocity. In particular, if supportive infrastructure can cover the entire network, then the delay bound from velocity vanishes when per-node throughput does not exceed a threshold. Moreover, we find that there also exists a delay bound from the transmission range of the instant transmission. In addition, we observe that, for the optimal throughput–delay tradeoff in the large throughput region, the case in the continuous mobility model outperforms the case in the discrete mobility model, and the case on the slow mobility assumption outperforms the case on the fast mobility assumption. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel approach to assess the performance in terms of end-to-end throughput of an ad hoc multi-hop wireless network, where each link is affected by interference coming from other multi-hop paths nearby. The approach captures the mutual impact of each path on all others. It can be applied to both, contention-based and scheduled, medium access control (MAC) protocols. Sources have data to send to destination nodes through $n$ relays. Nodes are assumed to be uniformly and randomly distributed in the 2-D infinite plane. The model shows the impact on the end-to-end throughput of $n$ ; it also captures the influence of node density, traffic generated, number of retransmissions, and other MAC parameters. Finally, the model provides the throughput-delay tradeoff. Unlike most previous approaches, the mathematical tool proposed appears to be scalable, allowing easy extension to any number of hops. Comparison with simulation results is provided to prove that the impact of the approximations introduced in the analysis is almost negligible. [ABSTRACT FROM PUBLISHER]

Security is the main concern and bottleneck for widely deployed wireless applications due to the fact that wireless channels are vulnerable to attacks and that wireless bandwidth is a constrained resource. In this sense, it is desirable to adaptively achieve security according to the available resource. In particular, mobile ad hoc networks (MANETs) based on cooperative communication (CC) present significant challenges to security issues, as well as issues of network performance and management. In this paper, we focus on authentication and topology control issues. Although authentication and topology control are separately studied in most existing works, they are, in fact, closely correlated in MANETs. For example, both authentication and topology control schemes have significant impacts on throughput. In this paper, we jointly consider authentication and topology control. Specifically, we analyze the effective throughput with upper layer authentication schemes and physical-layer schemes related to channel conditions and relay selections for CCs. A joint authentication and topology control (JATC) scheme is proposed to improve the throughput. JATC is formulated as a discrete stochastic optimization problem, which does not require prior perfect channel status but only channel estimate. We also mathematically prove the tracking convergence property and the convergence rate of the discrete stochastic optimization approach in this paper. Simulation results show that our scheme can substantially improve throughput in MANETs with CC. [ABSTRACT FROM PUBLISHER]

This paper studies the delay constrained multicast capacity of large-scale mobile ad hoc networks (MANETs). We consider a MANET that consists of ns multicast sessions. Each multicast session has one source and p destinations. Each source sends identical information to the p destinations in its multicast session, and the information is required to be delivered to all the p destinations within D .1 We then propose a joint coding/scheduling algorithm achieving a throughput of \Theta (\min \{1,{({D}/{n_{s}})}^{1/2}\}) . Our simulation results suggest that the same scaling law also holds under random walk and random waypoint models.1

Given non-negative functions f(n)$ and g(n)$ : f(n)=O(g(n))$ means there exist positive constants c$ and m$ such that f(n) \leq cg(n)$ for all n\geq m;~f(n)=\Omega (g(n))$ means there exist positive constants c$ and m$ such that f(n)\geq cg(n)$ for all n\geq m;~f(n)=\Theta (g(n)) ; and f(n)=\omega (g(n))$ means that \lim _{n\rightarrow \infty } g(n)/f(n)=0 . [ABSTRACT FROM PUBLISHER]

In this paper, we study the throughput and delay in wireless cognitive social networks. Specifically, we consider a common scenario for cognitive radio networks (CRNs) where the primary and secondary networks operate at the same time and space and share the spectrum. On this basis, we integrate a social relationship into the CRN where each source node selects its destination upon a rank-based model, which captures the social characteristic well. By applying a cellular time-division multiple-access scheduling scheme, we first characterize the distinct traffic pattern caused by the social relationships between nodes. Then, we derive the achievable throughput and delay for both primary and secondary networks under the new network setting. In addition, we also study the cognitive social networks with infrastructure where $l=o$ $(n)$ base stations are regularly deployed within the primary network. Given a probabilistic routing strategy, throughput of the proposed network is recalculated. Particularly, due to the social relationships between nodes, we reveal that a larger $l$ is required if we expect a significant capacity gain within the primary network compared with previous works. [ABSTRACT FROM PUBLISHER]

Most publications on the capacity and performance of wireless ad hoc networks share the underlying assumption of a uniform random distribution of nodes. In this paper, we study the effects of different node distributions on the local throughput of the slotted ALOHA MAC protocol. The throughput achieved in a network where the nodes are distributed according to a Poisson point process is used as a baseline performance measure for the comparison with other point distributions. We show that non-uniform random node distributions have a strong impact on the local throughput. This has also effects on the network capacity and performance. The results show that the node topology should be taken into account in more detailed analyses and simulations of ad hoc, sensor, and mesh networks. [ABSTRACT FROM AUTHOR]

The performance of existing coded caching schemes is sensitive to the worst channel quality, a problem which is exacerbated when communicating over fading channels. In this paper, we address this limitation in the following manner: in short-term, we allow transmissions to subsets of users with good channel quality, avoiding users with fades, while in long-term we ensure fairness among users. Our online scheme combines (i) the classical decentralized coded caching scheme with (ii) joint scheduling and power control for the fading broadcast channel, as well as (iii) congestion control for ensuring the optimal long-term average performance. We prove that our online delivery scheme maximizes the alpha-fair utility among all schemes restricted to decentralized placement. By tuning the value of alpha, the proposed scheme can achieve different operating points on the average delivery rate region and tune performance according to an operator’s choice. We demonstrate via simulations that our scheme outperforms two baseline schemes: (a) standard coded caching with multicast transmission, limited by the worst channel user yet exploiting the global caching gain; (b) opportunistic scheduling with unicast transmissions exploiting the fading diversity but limited to local caching gain. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of rate/distortion with side information available only at the decoder. For the case of jointly Gaussian source X and side information Y, and mean-squared error distortion, Wyner proved in 1976 that the rate/distortion function for this problem is identical to the conditional rate/distortion function RX∣Y, 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 high-correlation 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 per-node 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 large-scale wireless networks. [ABSTRACT FROM AUTHOR]

To improve the efficiency of wireless data communications, new physical-layer transmission methods based on known-interference cancelation (KIC) have been developed. These methods share the common idea that interference can be canceled when its content is known. Existing work on KIC mainly focuses on single-hop or two-hop networks, with physical-layer network coding and full-duplex communications as typical examples. This paper extends the idea of KIC to general multihop networks and proposes an end-to-end KIC (E2E-KIC) transmission method, together with its medium access control (MAC) design. With E2E-KIC, multiple nodes in a flow passing through a few nodes in an arbitrary topology can simultaneously transmit and receive on the same channel. We first present a theoretical analysis on the effectiveness of E2E-KIC in an idealized case. Then, to support E2E-KIC in multihop networks with an arbitrary topology, we propose an E2E-KIC-supported MAC protocol (E2E-KIC MAC), which is based on an extension of the Request-to-Send/Clear-to-Send mechanism in the IEEE 802.11 MAC. We also analytically analyze the performance of the proposed E2E-KIC MAC in the presence of hidden terminals. Simulation results illustrate that the proposed E2E-KIC MAC can improve network throughput and reduce end-to-end delay. [ABSTRACT FROM PUBLISHER]

The medium access probability (MAP) of a random access protocol can severely impact network throughput especially for delay-sensitive applications, since it determines whether a node should transmit packets in a given slot or not. This paper focuses on network throughput maximization through optimizing the MAPs of all users under delay quality-of-service constraints in wireless interference-limited networks. Specifically, first, the total delay for transmitting one packet for a user is analyzed and derived based on an M/G/1 model. Then, the stochastic property of the aggregated interference is analyzed and its distribution is modeled as a log-normal distribution. Based on the delay and interference models, an optimization problem is formulated to derive the optimal MAPs so that the network throughput is maximized under the delay constraints. Two network traffic scenarios, homogeneous and heterogeneous user traffic, are discussed, respectively. For the case of homogeneous traffic, a closed-form expression of the optimal MAP is derived; for the case of heterogeneous traffic, a global $\epsilon $ -optimal algorithm based on the branch-and-bound framework and convex relaxation technology is proposed with relatively low complexity. Simulations results show that the proposed algorithms can achieve superior network throughput performance over existing schemes. [ABSTRACT FROM PUBLISHER]

A substantial body of the literature exists addressing the capacity of wireless networks. However, it is commonly assumed that all nodes in the network are identical. The issue of heterogeneity has not been embraced into the discussions. In this paper, we investigate the throughput capacity of heterogeneous wireless networks with general network settings. Specifically, we consider an extended network with n normal nodes and m = n^b (0 \le b \le 1) more powerful helping nodes in a rectangular area with width s(n) and length n/s(n), where s(n) = n^w and 0 \le w \le 1/2. We assume that there are n flows in the network. All the n normal nodes are sources while only randomly chosen n^d (0 \le d \le 1) normal nodes are destinations. We further assume that the n normal nodes are uniformly and independently distributed, while the m helping nodes are either regularly placed or uniformly and independently distributed, resulting in two different kinds of networks called Regular Heterogeneous Wireless Networks and Random Heterogeneous Wireless Networks, respectively. We show that network capacity is determined by the shape of the network area, the number of destination nodes, the number of helping nodes, and the bandwidth of helping nodes. We also find that heterogeneous wireless networks can provide throughput higher in the order sense than traditional homogeneous wireless networks only under certain conditions. [ABSTRACT FROM AUTHOR]

In this paper, we characterize the information-theoretic capacity scaling of wireless ad hoc networks with n randomly distributed nodes. By using an exact channel model from Maxwell's equations, we successfully resolve the conflict in the literature between the linear capacity scaling by Özgür and the degrees of freedom limit given as the ratio of the network diameter and the wavelength \lambda by Franceschetti In dense networks where the network area is fixed, the capacity scaling is given as the minimum of n and the degrees of freedom limit \lambda^-1 to within an arbitrarily small exponent. In extended networks where the network area is linear in n, the capacity scaling is given as the minimum of n and the degrees of freedom limit \sqrtn\lambda^-1 to within an arbitrarily small exponent. Hence, we recover the linear capacity scaling by Özgür if \lambda=O(n^-1) in dense networks and if \lambda=O(n^-1/2) in extended networks. Otherwise, the capacity scaling is given as the degrees of freedom limit characterized by Franceschetti For achievability, a modified hierarchical cooperation is proposed based on a lower bound on the capacity of multiple-input multiple-output channel between two node clusters using our channel model. [ABSTRACT FROM AUTHOR]

This paper studies the bottleneck link capacity under the Gaussian channel model in strongly connected random wireless ad hoc networks, with n nodes independently and uniformly distributed in a unit square. We assume that each node is equipped with two transceivers (one for transmission and one for reception) and allow all nodes to transmit simultaneously. We draw lower and upper bounds, in terms of bottleneck link capacity, for homogeneous networks (all nodes have the same transmission power level) and propose an energy-efficient power assignment algorithm (CBPA) for heterogeneous networks (nodes may have different power levels), with a provable bottleneck link capacity guarantee of \Omega (B\log (1+1/\sqrtn\log^2n)), where B is the channel bandwidth. In addition, we develop a distributed implementation of CBPA with O(n^2) message complexity and provide extensive simulation results. [ABSTRACT FROM PUBLISHER]

Security always comes with a price in terms of performance degradation, which should be carefully quantified. This is especially the case for wireless ad hoc networks (WANETs), which offer communications over a shared wireless channel without any preexisting infrastructure. Forming end-to-end secure paths in such WANETs is more challenging than in conventional networks due to the lack of central authorities, and its impact on network performance is largely untouched in the literature. In this paper, based on a general random network model, the asymptotic behaviors of secure throughput and delay with the common transmission range rn and the probability pf of neighboring nodes having a primary security association are quantified when the network size n is sufficiently large. The costs and benefits of secure-link-augmentation operations on the secure throughput and delay are also analyzed. In general, security has a cost: Since we require all the communications operate on secure links, there is a degradation in the network performance when pf<1. However, one important exception is that when pf is \Omega(1/\log n), the secure throughput remains at the Gupta and Kumar bound of \Theta(1/\sqrtn\log n)~packets/time slot, wherein no security requirements are enforced on WANETs. This implies that even when the pf goes to zero as the network size becomes arbitrarily large, it is still possible to build throughput-order-optimal secure WANETs, which is of practical interest since pf is very small in many practical large-scale WANETs. [ABSTRACT FROM PUBLISHER]

This paper proposes a scheduling scheme for wireless mesh networks that are capable of multiple channel access and equipped with multiple radio interfaces. The proposed scheme is interference and traffic aware in that it increases the overall achievable throughput of the network by eliminating the interference between the wireless mesh routers and maximizes the satisfaction ratios of all active sessions by accounting for the sessions' data rate requirements. Simulation results show that the proposed scheme outperforms the Tabu-based scheduling scheme and yields good tradeoffs between the achievable throughput of the network and the satisfaction ratios of the sessions. [ABSTRACT FROM PUBLISHER]

In multihop ad hoc networks over 802.11, the real bandwidth-delay product (BDP) cannot reach a value as large as in wired networks due to contention through wireless shared channels. As a result, conventional congestion-control algorithms cause an overshooting window problem and result in poor throughput in ad hoc networks. In this paper, we split the real round-trip time (RTT) into two parts: 1) congestion RTT and 2) contention RTT. We reveal that the contention RTT has nothing to do with the BDP and that the BDP is determined by only the congestion RTT if a link with the worst contention status does not lead to link breakage. An inadequate use of contention RTT causes a Transmission Control Protocol (TCP) congestion window overshooting problem. We propose a novel mechanism called congestion window adaptation through contention detection, which provides a more accurate method of estimating the contention status. Based on this mechanism, we present a congestion window adaptation method to limit the window size from overshooting. Simulation results show that our proposed mechanism outperforms the conventional TCP and the enhanced mechanisms called TCP with contention control and TCP with a maximum window. [ABSTRACT FROM PUBLISHER]

The throughput of conventional wireless multicast systems is limited by the multicast user with the lowest channel quality, which leads to a low throughput, particularly if the number of multicast users is large. In this paper, we show that hybrid-automatic repeat request with Chase combining (HARQ-CC) is a promising technique to overcome this problem and optimize the corresponding transmission rate. We analyze the throughput of wireless multicast systems with HARQ-CC under various channel conditions and derive a closed-form approximation for the optimal rate. The numerical evaluation of our analytical expressions reveals that HARQ-aided multicast outperforms conventional multicast in most channel environments. To further improve performance, we propose a dynamic rate-allocation scheme that combines the advantages of conventional multicast and HARQ-aided multicast. [ABSTRACT FROM PUBLISHER]

In this paper, we study cross-layer design and dynamic selection trade-offs between settings of the transmission data rate, the transmission power and the forwarding range in both single hop and multihop IEEE 802.11 based ad hoc wireless networks while taking the effect of capture into account. We present an approximate mathematical model for calculating throughput and packet delay performance and show that it can be effectively used to dynamically select the nodal cross-layer parameters. We present simulation results that have been used to validate the precision of our analytical model. We demonstrate the performance behavior of such networks under a multitude of settings applied to the nodal cross-layer parameters by employing data rate and power level settings that are present in commercially available IEEE 802.11 b radios. Under such settings, we show that in networks with lower nodal spatial density, operations that select higher nodal transmit power values along with higher data rate level settings, using relatively longer distance forwarding ranges, tend to exhibit enhanced delay-throughput performance characteristics. Our performance analyses show that the throughput-capacity level tends to increase as the nodal transmit power level used in the network increases. Our results also show that operating at the lowest transmit power value that keeps the network connected often yields distinct degradation in the throughput and the delay performance. This is mainly due to the fact that the higher spatial re-use factors introduced by operating at lower nodal transmit power levels is typically not sufficient to offset the resulting increase in the average path length of a flow's route. This increase in path length increases the intensity of the internal traffic process, and thus induces higher access contention and packet delays. By using a free space attenuation model, we study the effect of the attenuation factor of this propagation model on the selection of the transmit data rate and observe that, depending on the value of the underlying propagation factor, an increase in nodal transmit data rate does not always yield a consequent increase in the system's throughput-capacity level. We demonstrate the underlying performance tradeoffs that are realized through the selection of the nodal cross layer parameters by considering illustrative multihop network topologies. Our analytical methods can be employed to determine the effective settings of the corresponding transmit power, data rate and forwarding range levels for general CSMA/CA based multihop ad hoc wireless network systems. [ABSTRACT FROM AUTHOR]

Recently, performance analysis for large-scale content-centric mobile ad hoc networks (MANETs) has received intense attention. In content-centric MANETs, content delivery consists of two operations, i.e., content placement and content retrieval, which may involve different network costs. However, the existing performance studies in content-centric MANETs mainly focus on content retrieval, and hence may not reflect the impact of content placement. In this paper, we investigate the asymptotic throughput and delay performance by considering the two operations of possibly different network costs. In particular, we introduce a general weighted sum delay cost of content placement and content retrieval as the delay performance metric. We consider an arbitrary content popularity distribution and study two mobility models in different time scales, i.e., fast and slow mobility. For each mobility model, we characterize the impacts of the network parameters on the network performance. By optimizing the content placement and retrieval for contents of different popularities, we design a general near-optimal scheme, the parameters of which reflect the delay weights of the two phases. We show that the network performance improves as the number of cached replicas increases until the number reaches a threshold. Finally, we show that our results are general and can incorporate some existing results as special cases. [ABSTRACT FROM AUTHOR]

We study distributed queueing games in interference-limited wireless networks. We formulate the throughput maximization problem via distributed selection of users' transmission thresholds as a Nash Equilibrium Problem (NEP). We first focus on the solution analysis of the NEP and derive sufficient conditions for the existence and uniqueness of a Nash Equilibrium (NE). Then, we develop a general best-response-based algorithmic framework wherein the users can explicitly choose the degree of desired cooperation and signaling, converging to different types of solutions, namely: 1) a NE of the NEP when there is no cooperation among users and 2) a stationary point of the Network Utility Maximization (NUM) problem associated with the NEP, when some cooperation among the users in the form of (pricing) message passing is allowed. Finally, as a benchmark, we design a globally optimal but centralized solution method for the nonconvex NUM problem. Our experiments show that in many scenarios the sum-throughput at the NE of the NEP is very close to the global optimum of the NUM problem, which validates our noncooperative and distributed approach. When the gap of the NE from the global optimality is non negligible (e.g., in the presence of “high” coupling among users), exploiting cooperation among the users in the form of pricing enhances the system performance. [ABSTRACT FROM AUTHOR]

We analyze throughput–delay scaling laws of mobile ad hoc networks under a content-centric traffic scenario, where users are mainly interested in retrieving contents cached by other nodes. We assume limited buffer size available at each node and Zipf-like content popularity. We consider nodes uniformly visiting the network area according to a random-walk mobility model, whose flight size varies from the typical distance among the nodes (quasi-static case) up to the edge length of the network area (reshuffling mobility model). Our main findings are: 1) the best throughput–delay tradeoffs are achieved in the quasi-static case: increasing the mobility degree of nodes leads to worse and worse performance; ii) the best throughput–delay tradeoffs can be recovered by power control (i.e., by adapting the transmission range to the content) even in the complete reshuffling case. [ABSTRACT FROM AUTHOR]

We analyze a novel architecture for caching popular video content to enable wireless device-to-device (D2D) collaboration. We focus on the asymptotic scaling characteristics and show how they depend on video content popularity statistics. We identify a fundamental conflict between collaboration distance and interference and show how to optimize the transmission power to maximize frequency reuse. Our main result is a closed form expression of the optimal collaboration distance as a function of the model parameters. Under the common assumption of a Zipf distribution for content reuse, we show that if the Zipf exponent is greater than 1, it is possible to have a number of D2D interference-free collaboration pairs that scales linearly in the number of nodes. If the Zipf exponent is smaller than 1, we identify the best possible scaling in the number of D2D collaborating links. Surprisingly, a very simple distributed caching policy achieves the optimal scaling behavior. [ABSTRACT FROM AUTHOR]

Due to the lack of a centralized coordinator for wireless resource allocation, the design of medium access control (MAC) protocols is considered crucial for throughput enhancement in the wireless ad hoc networks. The receiver blocking problem, which has not been studied in most of the MAC protocol design, can lead to severe degradation on the throughput performance. In this paper, the multiple receiver transmission (MRT) and the fast NAV truncation (FNT) mechanisms are proposed to alleviate the receiver blocking problem without the adoption of additional control channels. The adaptive receiver transmission (ART) scheme is proposed to further enhance the throughput performance with dynamic adjustment of the selected receivers. Analytical model is also derived to validate the effectiveness of the proposed ART protocol. Simulations are performed to evaluate and compare the proposed three protocols with existing MAC schemes. It can be observed that the proposed ART protocol outperforms the other schemes by both alleviating the receiver blocking problem and enhancing the throughput performance for the wireless multihop ad hoc networks. [ABSTRACT FROM PUBLISHER]

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 the hybrid protocol model to analyze the occurrence of transmission opportunities for secondary nodes. We show that if the primary network operates in a generalized TDMA fashion, or employs a routing scheme such that traffic flows choose relays independently, then the hybrid protocol model suffices to guide the secondary network to achieve the same throughput and delay scaling as a standalone network without harming the performance of the primary network, as long as the secondary transmission range is smaller than the primary range in order. Our approach is general in the sense that we only make a few weak assumptions on both networks, and therefore it obtains 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, multicast networks, CSMA networks, networks with general mobility, or clustered networks. Our work presents a relatively complete picture of the performance scaling of cognitive networks and provides fundamental insight on the design of them. [ABSTRACT FROM AUTHOR]

Synchronization among primary users (PUs) and secondary users (SUs) is either explicitly or implicitly assumed in the literature to allow reliable dynamic spectrum access (DSA) and cognitive radio (CR) networking. However, in realistic DSA that supports ad-hoc transmissions, perfect synchronization is not attainable in the absence of a centralized control mechanism, particularly among SUs. Current efforts either ideally assume perfect synchronization among PUs and SUs or consider medium access that does not require network synchronization based on a single SU. In this paper, we propose an implementable asynchronous DSA scheme by practically considering the timing misalignment with multiple SUs competing for the spectrum opportunity. We further employ a game theoretical framework in asynchronous DSA to thoroughly predict the competition among SUs. Based on the equilibrium concept, we identify the feasible operating region, achieving optimal equilibrium that is not only reaching a win–win situation in the sense of PU throughput and spectrum utilization maximization but is robust to potential selfish behavior of SUs as well. Both low-complexity one-shot and sequential-decision access schemes are analyzed. We demonstrate that, when operating in the proposed feasible region, contrary to intuitive conjecture, the asynchronous DSA achieves surprising improvement in spectrum utilization. [ABSTRACT FROM PUBLISHER]

In this paper, we propose Period-Controlled Medium Access Control (PC-MAC), which can operate in pseudo-TDMA manner and achieves high throughput and fairness in simple networks. PC-MAC works like CSMA/CA initially and becomes a pseudo-TDMA scheme in a few seconds due to the periodic backoff mechanism along with the contention control that tries to maintain the number of idle slots to an optimal level. Simulation results show 10%–50% higher throughput than distributed coordination function (DCF), depending on the number of nodes, while maintaining nearly perfect fairness. Furthermore, we also show how PC-MAC can successfully be applied to complex networks. [ABSTRACT FROM PUBLISHER]

In this paper, we characterize analytically the multi-access interference in wireless code-division multiple-access sensor networks with uniformly random distributed nodes and study the tradeoff between interference and connectivity. To provide a guideline for improving system behavior, three competitive deterministic topologies are evaluated along with the random topology in terms of link-level and network-level (routing) performance. The impact of signature code length and receiver design on the network performance for different topologies is also studied. [ABSTRACT FROM AUTHOR]

The widespread of smart phones has brought new social-aware features to wireless networks. Users prefer to forward traffic to their social contacts in social-aware networks, which is highly different from the traditional uniform traffic pattern. To this end, we analyze a social-aware wireless network, which is modeled by the social contacts between nodes, and explore its impact on network throughput capacity. We present that it can refine social contacts, thus improving the network capacity. Moreover, directional antennas are applied to further enhance the capacity performance, which can reduce the interference brought by other simultaneous communications. We derive the throughput capacity for social-aware networks with single-beam and multi-beam directional antenna, respectively. For single-beam directional antenna, we prove that when wireless networks are dominated by traffics of short-distance social contact, the throughput capacity can be promoted from order of (\Theta (1/\theta ^2n\,\text log\,n)^1/2) to \Theta (1/\theta ^2 \text log\,n) . In addition, when the beamwidth \theta is at order of \Omega ({1}/{({\log {n}})^{1/2}}) , the throughput capacity is a constant. Thus, the wireless network is scalable. For multi-beam antennas, we prove that when sidelobe gain G_{s} is at order of o(Gm) , where Gm is main lobe gain, compared with the single-beam case, the network capacity can achieve the order of \Theta (1/\theta ^2\text log\,n) . [ABSTRACT FROM AUTHOR]

The cost-effective impact and fundamental limits of infrastructure support with rate-limited wired backhaul links (i.e., GreenInfra support), directly connecting base stations (BSs), are analyzed in a large-scale hybrid network of unit node density, where multiantenna BSs are deployed. We consider a general scenario such that the rate of each BS-to-BS link scales at an arbitrary rate relative to the number of randomly located wireless nodes n. For the operating regimes with respect to the number of BSs and the number of antennas at each BS, we first analyze the minimum rate of each backhaul link C_{\text{BS}}, required to guarantee the same throughput scaling as in the infinite-capacity backhaul link case. We then identify the operating regimes in which the required rate C_{\text{BS}}$ scales slower than n^\epsilon$ for an arbitrarily small \epsilon > 0$ (i.e., the regimes where does not need to be infinitely large). We also show the case where our network with GreenInfra is fundamentally in the infrastructure-limited regime, in which the performance is limited by the rate of backhaul links. In addition, we derive a generalized throughput scaling law including the case where the rate of each backhaul link scales slower than C_{\text{BS}}. To validate the throughput scaling law for finite values of system parameters, numerical evaluation is also shown via computer simulations. [ABSTRACT FROM AUTHOR]

Vehicular Ad Hoc Networks (VANETs) with base stations are called hybrid VANET, where base stations are deployed to improve the throughput capacity. In this paper, we study the multicast throughput capacity for hybrid wireless VANET with a directional antenna on each vehicle and the end-to-end delay is constrained. In the hybrid VANET, there are n mobile vehicles (or nodes) distributed in a unit area with m strategically deployed base stations connected using high-bandwidth wire links. There are n_s multicast sessions and each multicast session has one source which transmits identical data to its associated p destinations. We investigate the multicast throughput capacity for two mobility models with two mobility scales, respectively, while each vehicular node is equipped with a directional antenna and with a tolerant delay D. That is, a source node transmits to its p destinations only with the help of normal nodes within D consecutive time slots. Otherwise, the transmission will be performed with in the infrastructure mode, i.e., with the help of base stations. We demonstrate that the one dimensional i.i.d. slow mobility pattern catch the main feature of VANETs. And we find that the multicast throughput capacity of the hybrid wireless VANET greatly depends on the delay constraint D, the number of base stations m, and the beamwidth of directional antenna θ. In the order of magnitude, we obtain the closed form of the multicast throughput capacity of the hybrid directional VANET, where the impact of D, m and θ on the multicast throughput capacity is analyzed. Moreover, we derive the lower bound of the muticast throughput using a similar raptor coding approach. [ABSTRACT FROM PUBLISHER]

We consider a multicast scenario that involves an ad hoc network of cochannel multiple-input–multiple-output (MIMO) nodes in which a source node attempts to share a streaming message with all nodes in the network through some predefined multihop routing tree. The message is assumed to be broken down into packets, and the transmission is conducted over multiple frames. Each frame is divided into time slots, and each link in the routing tree is assigned one time slot in which to transmit its current packet. We present an algorithm for determining the number of time slots and the scheduling of the links in these time slots to optimize the connectivity of the network, which we define to be the probability that all links can achieve the required throughput. In addition to time multiplexing, the MIMO nodes also employ beamforming to manage interference when links are simultaneously active, and the beamformers are designed with the maximum connectivity metric in mind. The effects of outdated channel-state information are taken into account in both the scheduling and the beamforming designs. We also derive bounds on the network connectivity and sum transmit power to illustrate the impact of interference on network performance. Our simulation results demonstrate that the choice of the number of time slots is critical in optimizing network performance and illustrates the significant advantage provided by multiple antennas in improving network connectivity. [ABSTRACT FROM PUBLISHER]

This work studies the throughput scaling laws of ad hoc wireless networks in the limit of a large number of nodes. A random connections model is assumed in which the channel connections between the nodes are drawn independently from a common distribution. Transmitting nodes are subject to an on--off strategy, and receiving nodes employ conventional single-user decoding. The following results are proven: 1) for a class of connection models with finite mean and variance, the throughput scaling is upper-bounded by O(n1/3) for single-hop schemes, and O(n½) for two-hop (and multihop) schemes; 2) the Θ (n½) throughput scaling is achievable for a specific connection model by a two-hop opportunistic relaying scheme, which employs full, but only local channel state information (CSI) at the receivers, and partial CSI at the transmitters; 3) by relaxing the constraints of finite mean and variance of the connection model, linear throughput scaling Θ (n) is achievable with Pareto-type fading models. [ABSTRACT FROM AUTHOR]

We study the capacity of a large clustered wireless ad hoc network in which clusters of nodes are scattered in a sea of relatively low-density nodes. We fix the density of nodes and clusters and study behavior as we increase the total network area (or, equivalently, the total number of nodes), which we call the network size. The main result is that the capacity switches behavior at a critical network size, which depends on the cluster size and the density of clusters within the network. Thus, the clustering parameters of the network allow us to quantify the meaning of a ‘large’ network, i.e., such that further size increase entails degradation of throughput capacity. [ABSTRACT FROM AUTHOR]

Throughput maximization is a key challenge for wireless applications in cognitive Vehicular Ad-hoc Networks (C-VANETs). As a potential solution, cooperative communications, which may increase link capacity by exploiting spatial diversity, has attracted a lot of attention in recent years. However, if link scheduling is considered, this transmission mode may perform worse than direct transmission in terms of end-to-end throughput. In this paper, we propose a cooperative communication aware link scheduling scheme and investigate the throughput maximization problem in C-VANETs. Regarding the features of cooperative communications and the availability of licensed spectrum, we extend the links into cooperative links/general links, define extended link-band pairs, and form a 3-dimensional (3-D) cooperative conflict graph to characterize the conflict relationship among those pairs. Given all cooperative independent sets in this graph, we mathematically formulate an end-to-end throughput maximization problem and near-optimally solve it by linear programming. Due to the NP-completeness of finding all independent sets, we also develop a heuristic pruning algorithm for cooperative communication aware link scheduling. Our simulation results show that the proposed scheme is effective in increasing end-to-end throughput for the session in C-VANETs. [ABSTRACT FROM PUBLISHER]

This paper investigates throughput and delay based on a traffic pattern, called convergecast, where each of the n nodes in the network acts as a destination with k randomly chosen sources corresponding to it. Adopting Multiple-Input-Multiple-Output (MIMO) technology, we devise two many-to-one cooperative schemes under convergecast for both static and mobile ad hoc networks (MANETs), respectively. We call them Convergimo Schemes. In static networks, our Convergimo scheme highly utilizes hierarchical cooperation MIMO transmission. This feature overcomes the bottleneck which hinders convergecast traffic from yielding ideal performance in traditional ad hoc network, by turning the originally interfering signals into interference-resistant ones. It helps to achieve an aggregate throughput up to \Omega (n^1-\epsilon ) for any \epsilon >0. In the mobile ad hoc case, our Convergimo scheme characterizes on joint transmission from multiple nodes to multiple receivers. With optimal network division where the number of nodes per cell is constantly bounded, the achievable per-node throughput can reach \Theta (1) with the corresponding delay reduced to \Theta (k). The gain comes from the strong and intelligent cooperation between nodes in our scheme, along with the maximum number of concurrent active cells and the shortest waiting time before transmission for each node within a cell. This increases the chances for each destination to receive the data it needs with minimum overhead on extra transmission. Moreover, our converge-based analysis well unifies and generalizes previous work since the results derived from convergecast in our schemes can also cover other traffic patterns. Last but not the least, our schemes are of interest not only from a theoretical perspective but also provide useful theoretical guidelines to future design of MIMO schemes in wireless networks. [ABSTRACT FROM AUTHOR]

Providing quality of service (QoS) assurances in a mobile ad hoc network (MANET) is difficult due to node mobility, contention for channel access, a lack of centralized co-ordination, and the unreliable nature of the wireless channel. A QoS-aware routing (QAR) protocol and an admission control (AC) protocol are two of the most important components of a system attempting to provide QoS guarantees in the face of the above mentioned difficulties faced. Many QAR and AC-based solutions have been proposed, but such network layer solutions are often designed and studied with idealized lower layer models in mind. This means that existing solutions are not designed for dealing with practical phenomena such as shadow fading and the link quality-dependent fluctuation of link transmission rates. This paper proposes and evaluates new solutions for improving the performance of QAR and AC protocols in the face of mobility, shadowing, and varying link SINR. It is found that proactively maintaining backup routes for active sessions, adapting transmission rates, and routing around temporarily low-SINR links can noticeably improve the reliability of assured throughput services. [ABSTRACT FROM PUBLISHER]

We study the scaling properties of a georouting scheme in a wireless multi-hop network of n mobile nodes. Our aim is to increase the network capacity quasi-linearly with n , while keeping the average delay bounded. In our model, we consider mobile nodes moving according to an independent identically distributed random walk with velocity v and transmitting packets to randomly chosen fixed and known destinations. The average packet delivery delay of our scheme is of order 1/v . This shows a practical throughput-delay tradeoff, in particular when compared with the seminal result of Gupta and Kumar, which shows network capacity of order {(n/\log n)}^{1/2} and negligible delay and the groundbreaking result of Grossglauser and Tse, which achieves network capacity of order n$ but with an average delay of order \sqrt {n}/v . The foundation of our improved capacity and delay tradeoff relies on the fact that we use a mobility model that contains straight-line segments, a model that we consider more realistic than classic Brownian motions. We confirm the generality of our analytical results using simulations under various interference models. [ABSTRACT FROM AUTHOR]

We study the capacity scaling laws for the cognitive network that consists of the primary hybrid network (PhN) and secondary ad hoc network (SaN). PhN is further comprised of an ad hoc network and a base station-based (BS-based) network. SaN and PhN are overlapping in the same deployment region, operate on the same spectrum, but are independent with each other in terms of communication requirements. The primary users (PUs), i.e., the ad hoc nodes in PhN, have the priority to access the spectrum. The secondary users (SUs), i.e., the ad hoc nodes in SaN, are equipped with cognitive radios, and have the functionalities to sense the idle spectrum and obtain the necessary information of primary nodes in PhN. We assume that PhN adopts one out of three classical types of strategies, i.e., pure ad hoc strategy, BS-based strategy, and hybrid strategy. We aim to directly derive multicast capacity for SaN to unify the unicast and broadcast capacities under two basic principles: 1) The throughput for PhN cannot be undermined in order sense due to the presence of SaN. 2) The protocol adopted by PhN does not alter in the interest of SaN, anyway. Depending on which type of strategy is adopted in PhN, we design the optimal-throughput strategy for SaN. We show that there exists a threshold of the density of SUs according to the density of PUs beyond which it can be proven that: 1) when PhN adopts the pure ad hoc strategy or hybrid strategy, SaN can achieve the multicast capacity of the same order as it is stand-alone; 2) when PhN adopts the BS-based strategy, SaN can asymptotically achieve the multicast capacity of the same order as if PhN were absent, if some specific conditions in terms of relations among the numbers of SUs, PUs, the destinations of each multicast session in SaN, and BSs in PhN hold. [ABSTRACT FROM AUTHOR]

We extend the analysis of the scaling laws of wireless ad hoc networks to the case of correlated nodes movements, which are commonly found in real mobility processes. We consider a simple version of the Reference Point Group Mobility model, in which nodes belonging to the same group are constrained to lie in a disc area, whose center moves uniformly across the network according to the i.i.d. model. We assume fast mobility conditions and take as a primary goal the maximization of per-node throughput. We discover that correlated node movements have a huge impact on asymptotic throughput and delay and can sometimes lead to better performance than the one achievable under independent nodes movements. [ABSTRACT FROM PUBLISHER]

We investigate, both theoretically and experimentally, the stability of CSMA-based wireless mesh networks, where a network is said to be stable if and only if the queue of each relay node remains (almost surely) finite. We identify two key factors that impact stability: the network size and the so-called “stealing effect,” a consequence of the hidden-node problem and nonzero transmission delays. We consider the case of a greedy source and prove, by using Foster's theorem, that three-hop networks are stable, but only if the stealing effect is accounted for. We also prove that four-hop networks are, on the contrary, always unstable (even with the stealing effect) and show by simulations that instability extends to more complex linear and nonlinear topologies. To tackle this instability problem, we propose and evaluate a novel, distributed flow-control mechanism called EZ-flow. EZ-flow is fully compatible with the IEEE 802.11 standard (i.e., it does not modify headers in packets), can be implemented using off-the-shelf hardware, and does not entail any communication overhead. EZ-flow operates by adapting the minimum congestion window parameter at each relay node, based on an estimation of the buffer occupancy at its successor node in the mesh. We show how such an estimation can be conducted passively by taking advantage of the broadcast nature of the wireless channel. Real experiments, run on a nine-node test-bed deployed over four different buildings, show that EZ-flow effectively smooths traffic and improves delay, throughput, and fairness performance. [ABSTRACT FROM PUBLISHER]

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 (IEEE Trans. Inf. Theory, vol. 46, no. 2, pp. 388–404, Mar. 2000) 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 delay-throughput tradeoff as the optimal one established by El Gamal (IEEE Trans. Inf. Theory, vol. 52, no. 6, pp. 2568–2592, Jun. 2006) for a standalone wireless network. [ABSTRACT FROM PUBLISHER]

Relay networks having n source-to-destination pairs and m half-duplex relays, all operating in the same frequency band and in the presence of block fading, are analyzed. This setup has attracted significant attention, and several relaying protocols have been reported in the literature. However, most of the proposed solutions require either centrally coordinated scheduling or detailed channel state information (CSI) at the transmitter side. Here, an opportunistic relaying scheme is proposed that alleviates these limitations, without sacrificing the system throughput scaling in the regime of large n. The scheme entails a two-hop communication protocol, in which sources communicate with destinations only through half-duplex relays. All nodes operate in a completely distributed fashion, with no cooperation. The key idea is to schedule at each hop only a subset of nodes that can benefit from multiuser diversity. To select the source and destination nodes for each hop, CSI is required at receivers (relays for the first hop, and destination nodes for the second hop), and an index-valued CSI feedback at the transmitters. For the case when n is large and m is fixed, it is shown that the proposed scheme achieves a system throughput of m/2 bits/s/Hz. In contrast, the information-theoretic upper bound of (m/2) log log n bits/s/Hz is achievable only with more demanding CSI assumptions and cooperation between the relays. Furthermore, it is shown that, under the condition that the product of block duration and system bandwidth scales faster than log n log log n, the achievable throughput of the proposed scheme scales as θ (log n). Notably, this is proven to be the optimal throughput scaling even if centralized scheduling is allowed, thus proving the optimality of the proposed scheme in the scaling law sense. Simulation results indicate a rather fast convergence to the asymptotic limits with the system's size, demonstrating the practical importance of the scaling results. [ABSTRACT FROM AUTHOR]

We propose a new model of wireless networks which we refer to as "two-scale networks." At a local scale, characterised by nodes being within a distance r, channel strengths are drawn independently and identically from a distance-independent distribution. At a global scale, characterised by nodes being further apart from each other than a distance r, channel connections are governed by a Rayleigh distribution, with the power satisfying a distance-based decay law. Thus, at a local scale, channel strengths are determined primarily by random effects such as obstacles and scatterers whereas at the global scale channel strengths depend on distance. For such networks, we propose a hybrid communications scheme, combining elements of distance-dependent networks and random networks. For particular classes, of two-scale networks with N nodes, we show that an aggregate throughput that slightly sublinear in N, for instance, of the form N/log4N is achievable. This offers a significant improvement over throughput scaling behaviour of O(√N) that is obtained in other work. [ABSTRACT FROM AUTHOR]

We address the problem of how throughput in a wireless network scales as the number of users grows. Following the model of Gupta and Kumar, we consider n identical nodes placed in a flied area. Pairs of transmitters and receivers wish to communicate but are subject to interference from other nodes. Throughput is measured in bit-meters per second. We provide a very elementary deterministic approach that gives achievability results in terms of three key properties of the node locations. As a special case, we obtain &Ohm; (√n) throughput for a general class of network configurations in a fixed area. Results for random node locations in a fixed area can also be derived as special cases of the general result by verifying the growth rate of three parameters. For example,as a simple corollary of our result we obtain a stronger (almost sure) version of the √n/√log n throughput for random node locations in a fixed area obtained by Gupta and Kumar. Results for some other interesting non-independent and identically distributed (i.i.d.) node distributions are also provided. [ABSTRACT FROM AUTHOR]

We study routing overhead due to location information collection and retrieval in mobile ad-hoc networks employing geographic routing with no hierarchy. We first provide a new framework for quantifying overhead due to control messages generated to exchange location information. Second, we compute the minimum number of bits required on average to describe the locations of a node, borrowing tools from information theory. This result is then used to demonstrate that the expected overhead is \Omega (n^1.5 \log (n)), where n is the number of nodes, under both proactive and reactive geographic routing, with the assumptions that 1) nodes' mobility is independent, and 2) nodes adjust their transmission range to maintain network connectivity. Finally, we prove that the minimum expected overhead under the same assumptions is \Theta (n \log (n)). [ABSTRACT FROM AUTHOR]