Link Independence Assumption Research Articles

Energy-Efficient Smart Routing Based on Link Correlation Mining for Wireless Edge Computing in IoT

Modern Internet-of-Things (IoT) applications are heavily data driven and often require reliable data streams to achieve high-quality data mining. The concept of edge computing is introduced to reduce data latency and communication bandwidth between the cloud server and IoT edge devices. However, inefficient routing that may cause transmission failure or unnecessary data (re)transmission is still a key obstacle to obtain good and reliable data mining results. In this article, network coding combined with opportunistic routing is used to improve energy efficiency in wireless IoT infrastructure, considering the existence of link correlation. Studies have shown that packet receptions on wireless links are correlated, which is completely contrary to the assumption of link independence used in existing routing mechanisms. This assumption causes estimation errors in the calculation of expected number of transmissions for forwarders, which further affects the selection of forwarder set, and ultimately affects the performance of the protocol. We propose an intrasession network coding mechanism based on the mining of link correlation. A novel smart routing method is proposed to accurately estimate the number of transmissions required by forwarders, together with an algorithm for selecting a forwarder set with more optimal number of transmissions. Simulation results demonstrate that the proposed mechanism can achieve fewer transmissions and offer more energy-efficient communications for wireless edge IoT applications.

Computing approximate blocking probabilities for transparent waveband switching based WDM networks using hierarchical cross-connects

An analytical model is presented to study the dynamics of wavelength division multiplexing (WDM) networks with waveband switching (WBS). The reduced load approximation method is considered to compute approximated network blocking probabilities in WBS-based WDM networks. The analytical model considers the link blocking probability due to insufficient link capacity and an impact of the waveband granularity (G). The analytical model also considers the node blocking probability due to unavailability of a switch port at the wavelength cross connect (WXC) layer of an Hierarchical cross connect (HXC) switch node. The set of nonlinear equations is obtained with the link independence assumption and solved using repeated substitutions. The accuracy of the analytical model is examined by comparing with simulation results considering the random-fit algorithm for waveband and wavelength assignments in different network scenarios. Lightpaths are routed between source and destination (s-d) HXC switch nodes using shortest path first (SPF) routing. An impact of the switch parameter to limit the input and the output WXC switch ports of an HXC switching node is also being investigated using the analytical model as well as through simulation results.

Exploiting Spatiotemporal Correlation for Wireless Networks Under Interference

This paper starts from an empirical observation on the existence of spatiotemporal correlation among nearby wireless links within short time intervals. The phenomenon due to correlated interference has become pervasive with densely deployed wireless devices, causing potential errors in existing popular metrics built upon the assumption of link independence. To this end, we propose correlated ETX (cETX), which generalizes the widely-adopted ETX to maintain the accuracy under correlated links. To the best of our knowledge, this is the first work to introduce a unified metric embracing both temporal and spatiotemporal correlations. As a generalized metric, the highlight of our work is the broad applicability and effectiveness–extensive evaluations on ZigBee (802.15.4) and Wi-Fi (802.11b/g/n) testbeds deployed in a lab, corridor, and on a bridge reveal that: simply replacing ETX with cETX: 1) cuts down the error by 62.1%–70.2% and 2) saves averages of 22% and 37% communication cost in three unicast and nine broadcast protocols, respectively, under only 0.7% additional overhead.

Link-Correlation-Aware Opportunistic Routing in Wireless Networks

Recent empirical studies have shown clear evidence that wireless links are not independent and that the packet receptions on adjacent wireless links are correlated. This finding contradicts the widely held link-independence assumption in the calculation of the core metric, i.e., the expected number of transmissions to the candidate forwarder set, in opportunistic routing (OR). The inappropriate assumption may cause serious estimation errors in the forwarder set selection, which further leads to underutilized diversity benefits or extra scheduling costs. We thus advocate that OR should be made aware of link correlation. In this paper, we propose a novel link-correlation-aware OR scheme, which significantly improves the performance by exploiting the diverse low correlated forwarding links. We evaluate the design in a real-world setting with 24 MICAz nodes. Testbed evaluation and extensive simulation show that higher link correlation leads to fewer diversity benefits and that, with our link-correlation-aware design, the number of transmissions is reduced by 38%.

Achieving Efficient Flooding by Utilizing Link Correlation in Wireless Sensor Networks

Although existing flooding protocols can provide efficient and reliable communication in wireless sensor networks on some level, further performance improvement has been hampered by the assumption of link independence, which requires costly acknowledgments (ACKs) from every receiver. In this paper, we present collective flooding (CF), which exploits the link correlation to achieve flooding reliability using the concept of collective ACKs. CF requires only 1-hop information at each node, making the design highly distributed and scalable with low complexity. We evaluate CF extensively in real-world settings, using three different types of testbeds: a single-hop network with 20 MICAz nodes, a multihop network with 37 nodes, and a linear outdoor network with 48 nodes along a 326-m-long bridge. System evaluation and extensive simulation show that CF achieves the same reliability as state-of-the-art solutions while reducing the total number of packet transmission and the dissemination delay by 30%-50% and 35%-50%, respectively.

Blocking probability evaluation of end-to-end dynamic WDM networks

Two mathematical methods for blocking probability evaluation of end-to-end dynamic WDM networks are proposed. The first method can be applied to networks operating with static (fixed) routes. By diminishing the impact of the link independence assumption, the method proposed improves a recently proposed mathematical procedure that assumes link blocking independency and non-Poisson traffic. To do so, the so-called streamline effect is taken into account in the equations. As a result, values closer to that of simulation are obtained. The second method applies to networks operating with alternate routing. In this case, the method simultaneously relaxes three non-realistic assumptions of previous works: the link blocking independence, the Poisson traffic arrival and the homogeneity of the traffic load offered to the network links. Both methods were applied to different network topologies, and their results were compared to those of simulation. Results show that the match between simulation and the proposed methods is excellent, and better than assuming link blocking independence, in all the topologies studied.

An analytical framework to infer multihop path reliability in MANETs

Due to complexity and intractability reasons, most of the analytical studies on the reliability of communication paths in mobile ad hoc networks are based on the assumption of link independence. In this paper, an analytical framework is developed to characterize the random behavior of a multihop path and derive path metrics to characterize the reliability of paths. This is achieved through the modeling of a multihop path as a PDMP (piecewise deterministic Markov process). Two path based metrics are obtained as expectations of functionals of the process: the mean path duration and the path persistence. We show that these metrics are the unique solution of a set of integro-differential equations and provide a recursive scheme for their computation. Finally, numerical results illustrate the computation of the metrics; these results are compared with independent link approximation results.

Reduced load approximation for WDM rings with wavelength continuity constraint

A reduced load approximation for WDM rings with a wavelength continuity constraint under Poissonian, homogeneous traffic with any spatial profile is presented. The model accounts for interactions among successive links in a linear network, correcting the overestimation of the blocking probability caused by the link independence assumption. Comparisons with simulation results show that the proposed reduced load approximation is a better substitute for the well-known reduced load approximation that uses the link independence assumption for blocking computation. It is shown that the proposed model provides accurate estimates of blocking probabilities in WDM rings with a wavelength continuity constraint.

Asymptotic blocking probabilities in rings with single-circuit links

We present a better substitute for the classical link independence assumption of the Lee approximation and we prove it to be asymptotically valid for rings with unit capacity links. A simple asymptotic expression is derived for increasing ring size. The asymptotic probability is shown to be a very good approximation for finite-size rings.

Call blocking probabilities in a traffic-groomed tandem optical network

In this paper, we consider an optical network consisting of N nodes arranged in tandem. We assume traffic grooming, which permits multiple sub-rate traffic streams to be carried on the same wavelength. This optical network is modeled by a tandem queueing network of multi-rate Erlang loss nodes with simultaneous resource possession, with a view to calculating call blocking probabilities. The queueing network is analyzed by decomposition using a modified version of Courtois' algorithm. Numerical comparisons of the decomposition algorithm against simulation show that the algorithm has good accuracy. Also, it is shown that the proposed algorithm is an improvement over the well-known single-node decomposition algorithm based on the link-independence assumption.

Call blocking probabilities in a traffic-groomed tandem optical network

In this paper, we consider an optical network consisting of N nodes arranged in tandem. We assume traffic grooming, which permits multiple sub-rate traffic streams to be carried on the same wavelength. This optical network is modeled by a tandem queueing network of multi-rate Erlang loss nodes with simultaneous resource possession, with a view to calculating call blocking probabilities. The queueing network is analyzed by decomposition using a modified version of Courtois' algorithm. Numerical comparisons of the decomposition algorithm against simulation show that the algorithm has good accuracy. Also, it is shown that the proposed algorithm is an improvement over the well-known single-node decomposition algorithm based on the link-independence assumption.

Blocking Probability Approximations and Revenue Optimization in Multirate Loss Networks

For the end-to-end (Originator-Destination pair) call blocking probability computation in multirate loss networks the so-called reduced load approximation under link independence assumption is often used, because it allows the derivation of analytical and numerical results. Its accuracy and extendibility to multirouting or multicasting networks (like me B-ISDN), however, is seldom studied. This paper attempts to generalize this assumption and to assess the usefulness of this generalization by comparing simulation and approximation results on link, route, and end-to-end blocking probability evaluation for these kinds of networks. The accuracy of the approximation is examined by a simulation tool called Flexible Simulation Platform for ATM Networks. An important application example of this generalized link-, route- and Originator-Destination pair blocking measure is the formulation of an optimization model for multirate loss networks, which optimizes carried traffic and network revenue.

Fixed Point Approximations for Retrial Networks

Fixed point approximations for blocking probabilities arising from a link independence assumption and a light retrial rate limit are derived for circuitswitched network models that incorporate caller retrials. This approximation is a generalization of the well-known reduced load approximation for loss networks, which retains much of the versatility of this approximation.