Single-hop Case Research Articles

On the Benefits of Traffic “Reprofiling” the Single Hop Case

On the Benefits of Traffic “Reprofiling” the Single Hop Case

Connectivity Probability Analysis for Green Cooperative Cognitive Vehicular Networks

To meet the increasing demands of green communications for vehicular services, cognitive vehicular networks (CVNs) are expected to improve spectrum efficiency via cognitive radio (CR) technology. The connectivity of CVNs not only related to the communication between cognitive vehicles (CVs), but also detection of idle spectrum. Nevertheless, few existing works simultaneously consider the communication and cognitive probabilities on the road. In this paper, we use probability theory to deduce the connectivity probabilities of CVNs. The analysis scenario consists of two parts: single-hop scenario and multi-hop clustering scenario. Particularly, in multi-hop clustering scenario, we propose Inter-Cluster integration process and Intra-Cluster communication process respectively, and deduce the probability expressions for two cases. The relationships between connectivity and parameters of both channel circumstance and traffic factors are given via theoretical analysis. The simulation results show that connectivity in multi-hop clustering scenario is better than that in single-hop case and the effect of signal-to-noise ratio (SNR) on connectivity is prominent, which indicates that the cognitive probability deeply affects the connectivity probability in CVNs.

Level Crossing Rate and Average Outage Duration of Free Space Optical Links

The level crossing rate (LCR) and the average outage duration (AOD) are two important second order statistics that allow a deeper understanding of the behavior of the channel. In this paper, we study these metrics in order to assess the performance of free space optical (FSO) communication links in the presence of weak atmospheric turbulence and rice-induced pointing errors. More specifically, we derive an integral and a Gauss-Laguerre quadrature representation for both the LCR and the AOD in the single hop case and for their respective bounds in the multihop case. Selected numerical simulations are presented to show the accuracy of the derived results and to study the effect of certain system parameters on these two performance metrics.

State Estimation Over Delayed Mutihop Network

In this paper, we consider the properties for Kalman filtering in a multi-hop network. A time-homogeneous Markov chain is used to characterize the stochastic packet delay and loss phenomenon of each relay. Since, after several relays, the average expected estimation error covariance at the terminal is difficult to calculate, we derive lower and upper bounds for the average value. Using these bounds, it is found that the stability is related to one special entry in the channel's transition probability matrix, from which we obtain a necessary and sufficient condition for the stability of the single-hop case and extend the result to the multihop one.

Opportunistic broadcasting for low-power sensor networks with adaptive performance requirements

To reduce the energy waste caused by idle listening, sensor nodes in wireless sensor networks (WSNs) usually work with low-duty-cycle mode. However, such mode brings many new challenges, especially for broadcasting applications. This paper proposes to exploit the broadcast nature of wireless media to further save energy for broadcasting in low-duty-cycle WSNs, by adopting a novel opportunistic broadcasting transmission model. The key idea is to allow nodes to defer their wake-up time slots to opportunistically overhear the broadcasting messages sent by their neighbors, improving the energy efficiency at the cost of the increase of average broadcasting delay. Instead of regarding delay or energy as the single optimization objective, in this paper, we present a broadcasting cost function, which provides an adaptive control on the tradeoff between delay and energy to cover various performance requirements. Our target is thus to find the optimal broadcasting schedule to minimize the broadcasting cost, based on the opportunistic broadcasting transmission model. To this end, we first model the target problem under the single-hop case as a dynamic programming problem and prove it is solvable in polynomial time, then extend it to the multi-hop case and come up with an efficient solution. Extensive simulation results reveal that our solution always has a better performance over the other solutions under whatever configurations.

Vehicle-to-Vehicle Forwarding in Green Roadside Infrastructure

Smart scheduling can be used to reduce infrastructure-to-vehicle energy costs in delay-tolerant vehicular networks. In this paper, we show that, by combining this with vehicle-to-vehicle (V2V) forwarding, downlink (DL) traffic schedules can be generated, whose energy costs are lower than that in the single-hop case. This is accomplished by having the roadside units (RSUs) dynamically forward packets through vehicles, which are in energy-favorable locations. This paper considers both constant bit rate (CBR) and variable bit rate (VBR) air-interface options. We first derive offline schedulers for the DL RSU energy usage when V2V forwarding is added to RSU-to-vehicle communication. Both in-channel and off-channel forwarding cases are considered. The CBR and VBR cases are obtained using integer linear programming (ILP) and time-expanded graph (TEG) formulations, respectively. These schedulers provide lower bounds on energy performance and are used for comparisons with a variety of proposed online scheduling algorithms. The first algorithm is based on a greedy local optimization (GLOA). A version of this algorithm, which uses a minimum-cost flow graph (MCFG) scheduler, is also introduced. A more sophisticated algorithm is then proposed, which is based on a finite-window group optimization (FWGO). Results from various experiments show that the proposed algorithms can generate traffic schedules with much improved DL energy requirements compared with the case where V2V packet forwarding is not used. The performance improvements are particularly strong when under heavy loading conditions and when the variation in vehicle communication requirements or vehicle speed is high. Results that compare the proposed algorithms with conventional nonenergy-aware schedulers are also presented.

Analysis of eavesdropping attack in mmWave-based WPANs with directional antennas

This paper explores the benefits of using directional antennas in an eavesdropping attack in millimeter-wave (mmWave)-based wireless personal area networks (WPANs) and the security enhancement of mmWaves. The detection and protection probabilities are analyzed for the eavesdropper's and transmitter's perspectives, respectively. The analysis is based on the probability density function of distance between devices (DEVs), the exposure region, and the interference free (limited) exposure region of a DEV. Four cases, in which all target DEVs and an eavesdropper are equipped with either a directional antenna or an omni-directional antenna, are considered in a single-hop and a multi-hop communications. The expected lower bound of an eavesdropper's detection probability and the relative detection rate are presented. Numerical results show that there exists a number of DEVs such that an eavesdropper can detect DEVs maximally. The detection probability tends to zero in a single-hop case, while it is saturated in a multi-hop case, as the number of DEVs increases. A DEV can communicate safely in one hop, while the communication is not secure anymore after several hops. Based on these results, we can conclude that the use of a directional antenna enables the better protection from an eavesdropping attack in mmWave-band communication and mmWave band can improve the security in communication.

Dynamic Control Policy for Delay Guarantees in Multi-hop Wireless Networks

This paper considers the dynamic control of stochastic networks for the guaranteed delay with network utility maximization in multi-hop wireless networks. On contrary to single hop case, the delay is difficult to predict in multi-hop scenarios due to their unpredictable traffic pattern and variable queuing time in intermediate nodes. We present here a control policy for joint flow control and scheduling which can achieve high network utility and guarantees delay constraints. In addition, we derive the capacity region of the network under a given delay condition. Simulation results show that the proposed policy achieves near optimal network utility with delay guaranteed compare to exiting algorithms.

Energy-Optimum Throughput and Carrier Sensing Rate in CSMA-Based Wireless Networks

We propose a model for the energy consumption of a node as a function of its throughput in a wireless CSMA network. We first model a single-hop network, and then a multi-hop network. We show that operating the CSMA network at a high throughput is energy inefficient since unsuccessful carrier sensing attempts increase the energy consumption per transmitted bit. Operating the network at a low throughput also causes energy inefficiency because of increased sleeping duration. Achieving a balance between these two opposite operating regimes, we derive the energy-optimum carrier-sensing rate and the energy-optimum throughput which maximize the number of transmitted bits for a given energy budget. For the single-hop case, we show that the energy-optimum total throughput increases as the number of nodes sharing the channel increases. For the multi-hop case, we show that energy-optimum throughput decreases as the degree of the conflict graph corresponding to the network increases. For both cases, the energy-optimum throughput reduces as the power required for carrier-sensing increases. The energy-optimum throughput is also shown to be substantially lower than the maximum throughput and the gap increases as the degree of the conflict graph increases for multi-hop networks.

Robust cross layer optimization in relay aided cellular networks

A robust optimization framework for cross layer optimization is proposed to deal with time varying channels, reducing the required channel state feedback overhead and giving strong QoS guarantees. Lower bounds for the achieved goodput when robust scheduling is used are derived and through simulation we study the impact in terms of blocked calls and QoS achieved by the robust solution for two different cell topology layouts: when 2-hop relaying is allowed and when only direct base station to user transmissions are allowed. The results reveal that the price of robustness is lower for the 2-hop case than the single hop case.

Centralised resource allocation policies for meshed high data rate wireless personal area networks

Multi-media applications with demanding throughput requirements often raise issues of capacity limitations in wireless networks. High data rate (HDR) wireless personal area networks (WPANs) can operate in a mesh configuration to extend from the legacy single-hop communication to multiple hops. Although the range of WPANs is increased in a mesh configuration, there are capacity constraints because the superframe time is shared by multiple piconet clusters instead of being dedicated for a single piconet cluster just like in the legacy single-hop case. Furthermore, the distributed superframe sharing can cause fairness issues because there is no mechanism to determine the requirement of each mesh piconet coordinator (MPNC) and monitor a fair allocation to each MPNC. Here, the authors propose a centralised resource allocation approach and define three resource allocation policies for meshed HDR WPANs. The proposed approach is augmented by a traffic estimation strategy to predict a suitable fraction of superframe time for each cluster. Simulation results prove the effectiveness of the proposed resource allocation policies and the fairness index is shown to increase upto 42% with the proposed approach in some cases.

The delay-constrained information coverage problem in mobile sensor networks: single hop case

In this paper, we study the delay-constrained information coverage problem in mobile sensor networks. Motivated by real application needs, our formulation takes advantage of the sensor mobility for sensing information collection, which takes place when a sensor moves into the proximity (single hop) of stationary sink nodes. To the best of our knowledge, we present the first formulation for the delay-constrained information coverage problem, which targets at optimal sink nodes placement with the objective of maximizing sensing information collection within a constrained time. We prove that this problem is NP-hard even under finite search space approximation and we develop theoretical analysis to derive its upper and lower performance bounds. We then develop approximation techniques and use simulations to verify their effectiveness.

Optimal Transmission Power for Single- and Multi-Hop Links in Wireless Packet Networks With ARQ Capability

In this paper, we rigorously investigate the energy minimization problem for wireless packet networks with automatic repeat request (ARQ) capability. We first formulate the problem for the single-hop case under constrained packet delay and reliability and derive the necessary and sufficient condition for the optimal transmission power at each ARQ stage. We formulate a global rule of optimal transmission power control that achieves optimality regardless of the delay and reliability constraints. Then we extend it to encompass the multi-hop case by dividing the overall problem into two subproblems-energy determination for each ARQ stage and energy distribution among the constituent nodes. We show that the optimality condition established for the single-hop case is also applicable to solve the energy determination problem in the multi-hop case, rendering an optimal solution to the energy distribution problem. Numerical examples reveal that a significant amount of energy is saved by adopting the optimal transmission power and the performance gain is strongly correlated with the decreasing property of the frame error rate

Adding definition to active probing

Active probing techniques have overwhelmingly been based on a few key heuristics. To progress to the next level a more powerful approach is needed, which is capable of filtering noise effectively, designing (and defining) optimal probing strategies, and understanding fundamental limitations. We provide a probabilistic, queueing-theoretic treatment that contributes to this program in the single hop case. We provide an exact inversion method for cross traffic distributions, rigorous system identifiability results to help determine what active probing can and can't achieve, a new approach for treating queueing theoretic 'noise' based on conditioning, and cross traffic estimators with enhanced properties

Stochastic analysis of packet-pair probing for network bandwidth estimation

In this paper, we perform a stochastic analysis of the packet-pair technique, which is a widely used method for estimating the network bandwidth in an end-to-end manner. There has been no explicit delay model of the packet-pair technique primarily because the stochastic behavior of a packet pair has not been fully understood. Our analysis is based on a novel insight that the transient analysis of the G/D/1 system can accurately describe the behavior of a packet pair, providing an explicit stochastic model. We first investigate a single-hop case and derive an analytical relationship between the input and the output probing gaps of a packet pair. Using this single-hop model, we provide a multi-hop model under an assumption of a single tight link. Our model shows the following two important features of the packet-pair technique: (i) The difference between the proposed model and the previous fluid model becomes significant when the input probing gap is around the characteristic value. (ii) The available bandwidth of any link after the tight link is not observable. We verify our model via ns-2 simulations and empirical results. We give a discussion on recent packet-pair models in relation to the proposed model and show that most of them can be regarded as special cases of the proposed model.

Conformance deterioration in QoS networks: Phenomenon, analysis and elimination

To verify conformance consistency of a previously regulated flow in QoS networks, two token buckets with identical token rate ( r) and bucket size ( b) are employed at the ingress and the egress nodes as the traffic shaper and policer respectively. In the presence of variable packet length, it has been found that an originally conformant packet may become non-conformant even transmitted at a constant speed. This non-intuitive phenomenon is referred to as conformance deterioration. After illustrating how conformance deterioration happens, the paper analyzes the probability of conformance deterioration for the single-hop case, both in general and for a special case. The analytical results are enriched by discussions and examples. To further understand the phenomenon, a set of simulations is carried out based on a generic multi-hop network model, for both individual and aggregated traffic flows. Finally, measures to eliminate conformance deterioration are also studied and compared in the paper.

An efficient deadline-credit-based transport scheme for prerecorded semisoft continuous media applications

In this paper, an efficient scheme is proposed based on the introduced deadline-credit-based (DC) policy. This scheme is appropriate for any prerecorded media, but is particularly relevant for prerecorded semisoft continuous media (CM) applications. Semisoft are applications with very small initial delay tolerance and, thus, for which very small amount of content may be sent in advance. The proposed policy pushes content toward the end user during the session by taking advantage of any bandwidth underutilization periods, exploiting available storage, and building up fairly a deadline credit to be consumed during periods of overutilization. The scheduling policy is studied for the single-hop case (applicable to the server of the content), as well as for the multihop case (applicable to the server and network nodes). The derived results demonstrate the ability of the proposed scheme to decrease the amount of required bandwidth (or equivalently induced losses) with respect to alternative schemes without requiring large initial delay, which is not acceptable for semisoft CM applications.

Improved approaches for cost-effective traffic grooming in WDM ring networks: ILP formulations and single-hop and multihop connections

Traffic grooming is the term used to describe how different traffic streams are packed into higher speed streams. In a synchronous optical network-wavelength division multiplexing (SONET-WDM) ring network, each wavelength can carry several lower-rate traffic streams in time division (TDM) fashion. The traffic demand, which is an integer multiple of the timeslot capacity, between any two nodes is established on several TDM virtual connections. A virtual connection needs to be added and dropped only at the two end nodes of the connection; as a result, the electronic add-drop multiplexers (ADMs) at intermediate nodes (if there are any) will electronically bypass this timeslot. Instead of having an ADM on every wavelength at every node, it may be possible to have some nodes on some wavelength where no add-drop is needed on any timeslot; thus, the total number of ADMs in the network (and, hence, the network cost) can be reduced. Under the static traffic pattern, the savings can be maximized by carefully packing the virtual connections into wavelengths. In this work, we allow arbitrary (nonuniform) traffic and we present a formal mathematical definition of the problem, which turns out to be an integer linear program (ILP). Then, we propose a simulated-annealing-based heuristic algorithm for the case where all the traffic is carried on directly connected virtual connections (referred to as the single-hop case). Next, we study the case where a hub node is used to bridge traffic from different wavelengths (referred to as the multihop case). We find the following main results. The simulated-annealing-based approach has been found to achieve the best results, so far, in most cases, relative to other comparable approaches proposed in the literature. In general, a multihop approach can achieve better equipment savings when the traffic-grooming ratio is large, but it consumes more bandwidth.

Optimal Transmission Ranges for Randomly Distributed Packet Radio Terminals

In multihop packet radio networks with randomly distributed terminals, the optimal transmission radii to maximize the expected progress of packets in desired directions are determined with a variety of transmission protocols and network configurations. It is shown that the FM capture phenomenon with slotted ALOHA greatly improves the expected progress over the system without capture due to the more limited area of possibly interfering terminals around the receiver. The (mini)slotted nonpersistent carrier-sense-multiple-access (CSMA) only slightly outperforms ALOHA, unlike the single-hop case (where a large improvement is available), because of a large area of "hidden" terminals and the long vulnerable period generated by them. As an example of an inhomogeneous terminal distribution, the effect of a gap in an otherwise randomly distributed terminal population on the expected progress of packets crossing the gap is considered. In this case, the disadvantage of using a large transmission radius is demonstrated.