HierHybNET: Cut-set upper bound of ad hoc networks with cost-effective infrastructure

This paper introduces an information-theoretic upper bound on the capacity scaling law for a hierarchical hybrid network (HierHybNET), consisting of both n wireless ad hoc nodes and m base stations (BSs) equipped with l multiple antennas per BS, where the communication takes place from wireless nodes to a remote central processor through BSs in a hierarchical way. We deal with a general scenario where m, l, and the backhaul link rate scale at arbitrary rates relative to n. Then, a generalized cut-set upper bound under the HierHybNET model is derived by cutting not only the wireless connections but also the wired connections. In addition, the corresponding infrastructure-limited regime is identified.     

Throughput and delay analysis for hybrid radio-frequency and free-space-optical (RF/FSO) networks

In this paper the per-node throughput and end-to-end delay of randomly deployed (i.e. ad-hoc) hybrid radio frequency - free space optics (RF/FSO) networks are studied. The hybrid RF/FSO network consists of an RF ad hoc network of n nodes, f(n) of them, termed ‘super nodes’, are equipped with an additional FSO transceiver with transmission range s(n). Every RF and FSO transceiver is able to transmit at a maximum data rate of W ₁ and W ₂ bits/sec, respectively. An upper bound on the per node throughput capacity is derived. In order to prove that this upper bound is achievable, a hybrid routing scheme is designed whereby the data traffic is divided into two classes and assigned different forwarding strategies. The capacity improvement with the support of FSO nodes is evaluated and compared against the corresponding results for pure RF wireless networks. Under optimal throughput scaling, the scaling of average end-to-end delay is derived. A significant gain in throughput capacity and a notable reduction in delay will be achieved if \(f(n) = \Upomega\left(\frac{1}{s(n)}\sqrt{\frac{n}{\log n}}\cdot \frac{W_1}{W_2} \right)\). Furthermore, it is found that for fixed W ₁, f(n) and n where f(n) < n, there is no capacity incentive to increase the FSO data rate beyond a critical value. In addition, both throughput and delay can achieve linear scaling by properly adjusting the FSO transmission range and the number of FSO nodes.     

Impact of deployment size on the asymptotic capacity for wireless ad hoc networks under Gaussian channel model

We study the throughput capacity and transport capacity for both random and arbitrary wireless networks under Gaussian Channel model when all wireless nodes have the same constant transmission power P and the transmission rate is determined by Signal to Interference plus Noise Ratio (SINR). We consider networks with n wireless nodes \(\{v_1,v_2,\ldots,v_n\}\) (randomly or arbitrarily) distributed in a square region B _a with a side-length a. We randomly choose n _s node as the source nodes of n _s multicast sessions. For each source node v _i , we randomly select k points and the closest k nodes to these points as destination nodes of this multicast session. We derive achievable lower bounds and some upper bounds on both throughput capacity and transport capacity for both unicast sessions and multicast sessions. We found that the asymptotic capacity depends on the size a of the deployment region, and it often has three regimes.     

An adaptive routing algorithm considering position and social similarities in an opportunistic network

An opportunistic network (OPPNET) is a wireless networks without an infrastructure. In OPPNET, communication intermittently occurs when one node meets with another node. Thus, a connected path between the source and destination nodes rarely exists. For this reason, nodes need not only to forward messages but are also to store and carry messages as relay nodes. In OPPNET, several routing algorithms that rely on relay nodes with appropriate behavior have been proposed. Some of these are referred to as context-ignorant routing algorithms, which manipulate flooding, and others are referred to as context-aware routing algorithms, which utilize the contextual information. We propose a routing algorithm that employs a novel similarity based on both position and social information. We combine the position similarity with the social similarity using the fuzzy inference method to obtain the enhanced performance. Through this method, the proposed algorithm utilizes more proper relay nodes in forwarding adaptively and achieves significant improvement on the performance especially under memory constrained environment. We analyze the proposed algorithm on the NS-2 network simulator with the home-cell community-based mobility model. Experimental results show that the proposed algorithm outperforms typical routing algorithms in terms of the network traffic and delivery delay.     

Weighted dominating set based routing for ad hoc communications in emergency and rescue scenarios

Disasters create emergency situations and the services provided must be coordinated quickly via a communication network. Mobile adhoc networks (MANETs) are suited for ubiquitous communication during emergency rescue operations, since they do not rely on infrastructure. The route discovery process of on-demand routing protocols consumes too much bandwidth due to high routing overhead. Frequent route changes also results in frequent route computation process. Energy efficiency, quick response time, and scalability are equally important for routing in emergency MANETs. In this paper, we propose an energy efficient reactive protocol named Weighted-CDSR for routing in such situations. This protocol selects a subset of network nodes named Maximum Weighted Minimum Connected Dominating Set (MWMCDS) based on weight, which consists of link stability, mobility and energy. The MWMCDS provides the overall network control and data forwarding support. In this protocol, for every two nodes u and v in the network there exists a path between u and v such that all intermediate nodes belong to MWMCDS. Incorporating route stability into routing reduces the frequency of route failures and sustains network operations over an extended period of time. With fewer nodes providing overall network control and data forwarding support, the proposed protocol creates less interference and consumes less energy. The simulation results show that the proposed protocol is superior to other protocols in terms of packet delivery ratio, control message overhead, transmission delay and energy consumption.     

Channel-quality-aware multihop broadcast for asynchronous multi-channel wireless sensor networks

In this paper, we propose Multi-channel EMBA (M-EMBA), efficient multihop broadcast for asynchronous multi-channel wireless sensor networks. Our scheme employs two channel-quality-aware forwarding policies of improved forwarder’s guidance and fast forwarding to improve multihop broadcast performance. The improved forwarder’s guidance allows forwarders to transmit broadcast messages with guidance to their receivers through channels with good quality. The guidance indicates how each receiver should forward the broadcast message to its neighbor nodes. The improved forwarder’s guidance tremendously reduces redundant transmissions and collisions. Fast forwarding allows adjacent forwarders to send their broadcast messages simultaneously through different channels that have good quality, which helps to reduce multihop broadcast latency and improve multi-channel broadcast utility. In this work, we evaluate the multihop broadcast performance of M-EMBA through theoretical analysis of the system design and empirical simulation-based analysis. We implement M-EMBA in ns-2 and compare it with the broadcast schemes of ARM, EM-MAC, and MuchMAC. The performance results show that M-EMBA outperforms these protocols in both light and heavy network traffic. M-EMBA reduces message cost in terms of goodput, total bytes transmitted, as well as broadcast redundancy and collision. M-EMBA also achieves a high broadcast success ratio and low multihop broadcast latency. Finally, M-EMBA significantly improves energy efficiency by reducing average duty cycle.     

Topology control in constant rate mobile ad hoc networks

Topology control is the problem of assigning power levels to the nodes of an ad hoc network so as to create a specified network topology while minimizing the energy consumed by the network nodes. While considerable theoretical attention has been given to the issue of topology control in wireless ad hoc networks, all of that prior work has concerned stationary networks. When the nodes are mobile, there is no algorithm that can guarantee a graph property (such as network connectivity) throughout the node movement. In this paper we study topology control in mobile wireless ad hoc networks (MANETs). We define a mobility model, namely the constant rate mobile network (CRMN) model, in which we assume that the speed and direction of each moving node are known. The goal of topology control under this model is to minimize the maximum power used by any network node in maintaining a specified monotone graph property. Network connectivity is one of the most fundamental monotone properties. Under the CRMN model, we develop general frameworks for solving both the decision version (i.e. for a given value p > 0, will a specified monotone property hold for the network induced by assigning the power value p to every node?) and the optimization version (i.e. find the minimum value p such that the specified monotone property holds for the network induced by assigning the power value p to every node) of the topology control problems. Efficient algorithms for specific monotone properties can be derived from these frameworks. For example, when the monotone property is network connectivity, our algorithms for the decision and optimization versions have running times of O(n ² log² n) and O(n ⁴ log² n), respectively. Our results represent a step towards the development of efficient and provably good distributed algorithms for topology control problems for MANETs.     

Link scheduling for throughput maximization in multihop wireless networks under physical interference

We consider the problem of link scheduling for throughput maximization in multihop wireless networks. Majority of previous methods are restricted to graph-based interference models. In this paper we study the link scheduling problem using a more realistic physical interference model. Through some key observations about this model, we develop efficient link scheduling algorithms by exploiting the intrinsic connections between the physical interference model and the graph-based interference model. For one variant of the problem where each node can dynamically adjust its transmission power, we design a scheduling method with O(g(E)) approximation to the optimal throughput capacity where g(E) denotes length diversity. For the other variant where each node has a fixed but possible different transmission powers for different nodes, we design a method with O(g(E))-approximation ratio when the transmission powers of all nodes are within a constant factor of each other, and in general with an approximation ratio of \(O(g(E)\log \rho )\) where \(\log \rho\) is power diversity. We further prove that our algorithm for fixed transmission power case retains O(g(E)) approximation for any length-monotone, sub-linear fixed power setting. Furthermore, all these approximation factors are independent of network size .     

Symptotics: a framework for estimating the scalability of real-world wireless networks

We present a framework for non-asymptotic analysis of real-world multi-hop wireless networks that captures protocol overhead, congestion bottlenecks, traffic heterogeneity and other real-world concerns. The framework introduces the concept of symptotic scalability to determine the number of nodes to which a network scales, and a metric called change impact value for comparing the impact of underlying system parameters on network scalability. A key idea is to divide analysis into generic and specific parts connected via a signature—a set of governing parameters of a network scenario—such that analyzing a new network scenario reduces mainly to identifying its signature. Using this framework, we present the first closed-form symptotic scalability expressions for line, grid, clique, randomized grid and mobile topologies. We model both TDMA and 802.11, as well as unicast and broadcast traffic. We compare the analysis with discrete event simulations and show that the model provides sufficiently accurate estimates of scalability. We show how our impact analysis methodology can be used to progressively tune network features to meet a scaling requirement. We uncover several new insights, for instance, on the limited impact of reducing routing overhead, the differential nature of flooding traffic, and the effect real-world mobility on scalability. Our work is applicable to the design and deployment of real-world multi-hop wireless networks including community mesh networks, military networks, disaster relief networks and sensor networks.     

A Contract-Based Model for Multiuser Cooperative Relay in Wireless Communication Networks

Cooperative communication utilizes multi-user spatial diversity to improve spectrum efficiency and channel capacity. However, due to the limited wireless network resource, the selfish relay nodes may be unwilling to offer their relay assistance without any extra incentive. In this paper, the incentive issue between multiple wireless nodes’ relay service and multiple sources’ relay selection is investigated. By modelling multi-user cooperative relay as a labour market, a contract model is proposed with the combination of relay power and basic wage. A relay factor is introduced to describe the contract-relay strategy in cooperative communication. To incentivize the relay nodes to participate in multiple sources’ relay efficiently and credibly, an optimization problem of multi-user relay incentive is formulated to obtain the sources’ maximum cooperative utility under the individually rational restraints. By exploiting the hidden convexity of the non-convex problems in both single-source and multi-source scenarios, the efficient iterative algorithms are developed. Numerical results show that the performance of our approach yields a significant enhancement compared with the equal relay-power and equal relay-factor strategies.     

HVE-mobicast: a hierarchical-variant-egg-based mobicast routing protocol for wireless sensornets

In this paper, we propose a new mobicast routing protocol, called the HVE-mobicast (hierarchical-variant-egg-based mobicast) routing protocol, in wireless sensor networks (WSNs). Existing protocols for a spatiotemporal variant of the multicast protocol called a “mobicast” were designed to support a forwarding zone that moves at a constant velocity, \(\stackrel{\rightarrow}{v}\), through sensornets. The spatiotemporal characteristic of a mobicast is to forward a mobicast message to all sensor nodes that are present at time t in some geographic zone (called the forwarding zone) Z, where both the location and shape of the forwarding zone are a function of time over some interval (t _start ,t _end ). Mobicast routing protocol aims to provide reliable and just-in-time message delivery for a mobile sink node. To consider the mobile entity with the different moving speed, a new mobicast routing protocol is investigated in this work by utilizing the cluster-based approach. The message delivery of nodes in the forwarding zone of the HVE-mobicast routing protocol is transmitted by two phases; cluster-to-cluster and cluster-to-node phases. In the cluster-to-cluster phase, the cluster-head and relay nodes are distributively notified to wake them up. In the cluster-to-node phase, all member nodes are then notified to wake up by cluster-head nodes according to the estimated arrival time of the delivery zone. The key contribution of the HVE-mobicast routing protocol is that it is more power efficient than existing mobicast routing protocols, especially by considering different moving speeds and directions. Finally, simulation results illustrate performance enhancements in message overhead, power consumption, needlessly woken-up nodes, and successful woken-up ratio, compared to existing mobicast routing protocols.     

On routing with guaranteed delivery in three-dimensional ad hoc wireless networks

We study the problem of routing in three-dimensional ad hoc networks. We are interested in routing algorithms that guarantee delivery and are k-local, i.e., each intermediate node v’s routing decision only depends on knowledge of the labels of the source and destination nodes, of the subgraph induced by nodes within distance k of v, and of the neighbour of v from which the message was received. We model a three-dimensional ad hoc network by a unit ball graph, where nodes are points in three-dimensional space, and for each node v, there is an edge between v and every node u contained in the unit-radius ball centred at v. The question of whether there is a simple local routing algorithm that guarantees delivery in unit ball graphs has been open for some time. In this paper, we answer this question in the negative: we show that for any fixed k, there can be no k-local routing algorithm that guarantees delivery on all unit ball graphs. This result is in contrast with the two-dimensional case, where 1-local routing algorithms that guarantee delivery are known. Specifically, we show that guaranteed delivery is possible if the nodes of the unit ball graph are contained in a slab of thickness \(1/\sqrt{2}.\) However, there is no k-local routing algorithm that guarantees delivery for the class of unit ball graphs contained in thicker slabs, i.e., slabs of thickness \(1/\sqrt{2} + \epsilon\) for some \( \epsilon > 0.\) The algorithm for routing in thin slabs derives from a transformation of unit ball graphs contained in thin slabs into quasi unit disc graphs, which yields a 2-local routing algorithm. We also show several results that further elaborate on the relationship between these two classes of graphs.     

Lower bounds on lifetime of ultra wide band wireless sensor networks

The asymptotic lower bounds on the lifetime of time hopping impulse radio ultra wide band (TH-IR UWB) wireless sensor networks are derived using percolation theory arguments. It is shown that for static dense TH-IR UWB wireless sensor network, which sensor nodes are distributed in a square of unit area according to a Poisson point process of intensity n, the lower bound on the lifetime is \( \Upomega \left( {\left( {{{\sqrt n } \mathord{\left/ {\vphantom {{\sqrt n } {\log \sqrt n }}} \right. \kern-\nulldelimiterspace} {\log \sqrt n }}} \right)^{\alpha - 2} } \right) \), where α > 2 is the path loss exponent, thus dense TH-IR UWB wireless sensor network is fit to be employed in large-scale network. For static extended TH-IR UWB wireless sensor network which sensor nodes are distributed in a square \( \left[ {0,\sqrt n } \right] \times \left[ {0,\sqrt n } \right] \) according to a Poisson point process of unit intensity, the lower bound on the lifetime is \( \Upomega \left( {{{\left( {\log \sqrt n } \right)^{2 - \alpha } } \mathord{\left/ {\vphantom {{\left( {\log \sqrt n } \right)^{2 - \alpha } } n}} \right. \kern-\nulldelimiterspace} n}} \right) \), therefore large-scale extended network will lead to shorten network lifetime. The results also indicate that the lower bound on the lifetime in the ideal case is longer than that of a static network by a factor of \( n^{1/2} \left( {\log \sqrt n } \right)^{\alpha - 4} \). Hence mobility of sensor nodes can improve network lifetime.     

Throughput and Delay Analysis of IEEE 802.11 DCF in the Presence of Hidden Nodes for Multi-hop Wireless Networks

Hidden node collision in a contention-based medium access control protocol contributes to poor wireless network performance. This paper extended the Bianchi’s study and introduces a mathematical model that can be used to calculate throughput and delay for the IEEE 802.11 distributed coordination function of a multihop wireless network infrastructure assuming the presence of hidden node collision. This research investigates three essential parameters of multi-hop wireless networks. More specifically, this paper aims to analyze the effect of hidden nodes, network size, and maximum backoff stage on the overall system throughput and packet delay. Results clearly reveal the effect of large wireless network size, maximum backoff stage, and collision probability on throughput and packet delay. On one hand, throughput does not depend on the maximum backoff stage (m) for a small network size (e.g., n \(=\) 10). On the other hand, throughput does not strongly depend on the number of nodes when the backoff stage values are high. Comparing our proposed model in case single-hop with the Bianchi model, the analysis results indicate that the throughput values in our model when the numbers of nodes are 10, 50, and 100 are 0.6031, 0.4172 and 0.3433 respectively; whereas the throughput values are respectively 0.8370, 0.8317 and 0.8255 at the same number of nodes for the Bianchi model. The difference can be attributed to several assumptions made in our proposed model that were not considered in the Bianchi model.     

Computationally Efficient Motion Estimation Algorithm for HEVC

In this paper, we present a novel computationally efficient motion estimation (ME) algorithm for high-efficiency video coding (HEVC). The proposed algorithm searches in the hexagonal pattern with a fixed number of search points at each grid. It utilizes the correlation between contiguous pixels within the frame. In order to reduce the computational complexity, the proposed algorithm utilizes pixel truncation, adaptive search range, sub-sampling and avoids some of the asymmetrical prediction unit techniques. Simulation results are obtained by using the reference software HM (e n c o d e r_l o w d e l a y_P_m a i n and e n c o d e r_r a n d o m a c c e s s_m a i n profile) and shows 55.49% improvement on search points with approximately the same PSNR and around 1% increment in bit rate as compared to the Test Zonal Search (TZS) ME algorithm. By utilizing the proposed algorithm, the BD-PSNR loss for the video sequences like B a s k e t b a l l P a s s_416 × 240@50 and J o h n n y_1280 × 720@60 is 0.0804 dB and 0.0392 dB respectively as compared to the HM reference software with the e n c o d e r_l o w d e l a y_P_m a i n profile.     

Secure Relay Selection of Cognitive Two-Way Denoise-and-Forward Relaying Networks

In this paper, secrecy performance of a cognitive two-way denoise-and-forward relaying network consisting of two primary user (PT and PD) nodes, two secondary source (SA and SB) nodes, multiple secondary relay (\({\textit{SR}}_i\)) nodes and an eavesdropper (E) node is considered, where SA and SB exchange their messages with the help of one of the relays using a two-way relaying scheme. The eavesdropper tries to wiretap the information transmitted between SA and SB. To improve secrecy performance of the network, two relay selection schemes called maximum sum rate and maximum secrecy capacity based relay selection (MSRRS and MSCRS) are proposed and analyzed in terms of intercept probability. It is proved that the MSRRS and MSCRS schemes have the same secrecy performance. Two parameters called average number gain and average cost gain are proposed to show the performance of the proposed relay selection schemes. Numerical results demonstrated that with 10 relay nodes, the proposed relay selection schemes can achieve, respectively, 3.7 dB and 1.9 dB’s improvements in terms of the reduced intercept probability and the enhanced secrecy capacity compared to the traditional round-robin scheme.     

Analog/RF Study of Self-aligned In<Subscript>0.53</Subscript>Ga<Subscript>0.47</Subscript>As MOSFET with Scaled Gate Length

This study presents the impact of gate length scaling on analog and radio frequency (RF) performance of a self- aligned multi-gate n-type In_0.53Ga_0.47As metal oxide semiconductor field effect transistor. The device is fabricated using a self-aligned method, air-bridge technology, and 8 nm thickness of the Al₂O₃ oxide layer with different gate lengths. The transconductance-to-normalized drain current ratio (g _m/I _D) method is implemented to investigate analog parameters. Moreover, g _m and drain conductance (g _D) as key parameters in analog performance of the device are evaluated with g _m/I _D and gate length variation, where g _m and g _D are both showing enhancement due to scaling of the gate length. Early voltage (V _EA) and intrinsic voltage gain (A _V) value presents a decreasing trend by shrinking the gate length. In addition, the results of RF measurement for cut-off and maximum oscillation frequency for devices with different gate lengths are compared.     

Incentive Mechanisms for Cooperative Wireless Networks with Adverse Selection and Moral Hazard

Cooperative communication is a promising technique to improve utilization of the wireless spectrum resource. However, due to the limited wireless network resource, the selfish relay nodes may be unwilling to offer their relay help without any extra incentive. In this work, we study a contract-based mechanism for incentivizing cooperative relay in the presence of the dual asymmetric information. By modelling multi-user cooperative relay as a labour market, a principal-agent model is proposed with the combination of relay power, basic wage and relay bonus in the continuous type scenario. And an optimization problem of multi-user relay incentive is formulated to achieve the twin objectives of ability-discrimination and effort-incentive. Numerical results show that the optimal contract design scheme is effective in improving the performance of cooperative communication.     

Mesoscopic fluctuations in the conductance of silicon-based MOS structures with a doped surface layer

In n-Si-based metal-oxide-semiconductor structures with a boron-doped surface layer, at the temperature T = 77 K, mesoscopic fluctuations in nondiagonal resistance-tensor component R _xy are discovered under hole depletion of the Si: B layer caused by the field effect. A sharp increase in the fluctuation in R _xy is discovered during the study of a shift from the 3D weakly perturbed hole transport to the quasi-2D percolation conduction on the back boundary of the Si: B layer. The fluctuations in R _xy are due to the restructuring that occurs in the percolation cluster when the hole shielding of the fluctuation potential of ionized acceptors is weakened. Correlation length L _c of the percolation cluster, which determines the boundary of the transition from the macroscopic to the mesoscopic system, has been estimated experimentally. Good agreement between the estimates and the computational results is observed for L _c ranging from ≈ 10 nm to ≈ 1 μm.     

Algebraic connectivity aided energy-efficient topology control in selfish ad hoc networks

Topology control is a technique to assign per-node’s transmit parameters so as to get the network topology with the best possible network performance given some optimization criteria, such as energy-efficient connectivity. In this paper, we investigate energy-efficient topology control for wireless ad-hoc networks in the presence of selfish nodes. A non-cooperative game aided topology control approach is developed for minimizing the potential transmit power, whilst maintaining the network connectivity. The utility function is conceived by virtue of algebraic connectivity, which is a fine metric to measure the connectivity redundancy of a network. We prove the existence of Nash Equilibrium (NE) and demonstrate that the NE is Pareto optimal as well. Specifically, two fully distributed topology controls—algebraic connectivity-based Max-Improvement (ACMI) algorithm and \(\delta\)-Improvement (ACDI) algorithm—are proposed to find the NE topologies. Both ACMI and ACDI can easily construct the stable topologies with a low information-overhead of the order O(n), where n is the number of nodes. Simulations demonstrate that our algorithms observably eliminate the redundancy of the maximum power topology and embrace several other attractive topological features.