Optimal Tradeoff Between Exposed and Hidden Nodes in Large Wireless Networks

Wireless networks equipped with the CSMA protocol are subject to collisions due to interference. For a given interference range we investigate the tradeoff between collisions (hidden nodes) and unused capacity (exposed nodes). We show that the sensing range that maximizes throughput critically depends on the activation rate of nodes. For infinite line networks, we prove the existence of a threshold: When the activation rate is below this threshold the optimal sensing range is small (to maximize spatial reuse). When the activation rate is above the threshold the optimal sensing range is just large enough to preclude all collisions. Simulations suggest that this threshold policy extends to more complex linear and non-linear topologies

Balancing exposed and hidden nodes in linear wireless networks

Wireless networks equipped with the CSMA protocol are subject to collisions due to interference. For a given interference range, we investigate the tradeoff between collisions (hidden nodes) and unused capacity (exposed nodes). We show that the sensing range that maximizes throughput critically depends on the activation rate of nodes. For infinite line networks, we prove the existence of a threshold: When the activation rate is below this threshold, the optimal sensing range is small (to maximize spatial reuse). When the activation rate is above the threshold, the optimal sensing range is just large enough to preclude all collisions. Simulations suggest that this threshold policy extends to more complex linear and nonlinear topologies. Keywords: Carrier-sensing range; Markov processes; collisions; exposed nodes; hidden nodes; random-access; throughput; wireless network

An Enhanced Source Location Privacy based on Data Dissemination in Wireless Sensor Networks (DeLP)

open access articleWireless Sensor Network is a network of large number of nodes with limited power and computational capabilities. It has the potential of event monitoring in unattended locations where there is a chance of unauthorized access. The work that is presented here identifies and addresses the problem of eavesdropping in the exposed environment of the sensor network, which makes it easy for the adversary to trace the packets to find the originator source node, hence compromising the contextual privacy. Our scheme provides an enhanced three-level security system for source location privacy. The base station is at the center of square grid of four quadrants and it is surrounded by a ring of flooding nodes, which act as a first step in confusing the adversary. The fake node is deployed in the opposite quadrant of actual source and start reporting base station. The selection of phantom node using our algorithm in another quadrant provides the third level of confusion. The results show that Dissemination in Wireless Sensor Networks (DeLP) has reduced the energy utilization by 50% percent, increased the safety period by 26%, while providing a six times more packet delivery ratio along with a further 15% decrease in the packet delivery delay as compared to the tree-based scheme. It also provides 334% more safety period than the phantom routing, while it lags behind in other parameters due to the simplicity of phantom scheme. This work illustrates the privacy protection of the source node and the designed procedure may be useful in designing more robust algorithms for location privac

Hidden Terminal-Aware Contention Resolution with an Optimal Distribution

Achieving low-power operation in wireless sensor networks with high data load or bursty traffic is challenging. The hidden terminal problem is aggravated with increased amounts of data in which traditional backoff-based contention resolution mechanisms fail or induce high latency and energy costs. We analyze and optimize Strawman, a receiver-initiated contention resolution mechanism that copes with hidden terminals. We propose new techniques to boost the performance of Strawman while keeping the resolution overhead small. We finally validate our improved mechanism via experiments

Approaching Throughput-optimality in Distributed CSMA Scheduling Algorithms with Collisions

It was shown recently that CSMA (Carrier Sense Multiple Access)-like distributed algorithms can achieve the maximal throughput in wireless networks (and task processing networks) under certain assumptions. One important, but idealized assumption is that the sensing time is negligible, so that there is no collision. In this paper, we study more practical CSMA-based scheduling algorithms with collisions. First, we provide a Markov chain model and give an explicit throughput formula which takes into account the cost of collisions and overhead. The formula has a simple form since the Markov chain is "almost" time-reversible. Second, we propose transmission-length control algorithms to approach throughput optimality in this case. Sufficient conditions are given to ensure the convergence and stability of the proposed algorithms. Finally, we characterize the relationship between the CSMA parameters (such as the maximum packet lengths) and the achievable capacity region.Comment: To appear in IEEE/ACM Transactions on Networking. This is the longer versio

An adaptive approach on the carrier sensing range of CSMA/CA multi-hop wireless networks.

Ruan, Sichao.Thesis (M.Phil.)--Chinese University of Hong Kong, 2008.Includes bibliographical references (leaves 62-65).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Multihop Ad Hoc Wireless Networks --- p.1Chapter 1.1.1 --- Introduction to Multihop Ad Hoc Networks --- p.2Chapter 1.1.2 --- Scalability of Ad Hoc Wireless Networks --- p.3Chapter 1.2 --- Hidden Terminal Problem --- p.3Chapter 1.3 --- Exposed Terminal Problem --- p.5Chapter 1.4 --- Overview of the Thesis --- p.6Chapter 2 --- Background --- p.8Chapter 2.1 --- MAC Protocols for Wireless Networks --- p.8Chapter 2.1.1 --- Aloha --- p.8Chapter 2.1.2 --- CSMA/CA --- p.9Chapter 2.1.3 --- IEEE 802.11 DCF Standard --- p.10Chapter 2.2 --- Related Work --- p.12Chapter 2.2.1 --- Schemes for Hidden Node Problem --- p.12Chapter 2.2.2 --- Schemes for Exposed Node Problem --- p.13Chapter 2.3 --- Tradeoff between Hidden and Exposed Nodes --- p.14Chapter 2.4 --- The Effect of Carrier Sensing Range --- p.17Chapter 3 --- Analysis on Carrier Sensing Range --- p.18Chapter 3.1 --- Analysis Model --- p.18Chapter 3.1.1 --- Terminal Configurations --- p.18Chapter 3.1.2 --- Timing/Packet Parameters --- p.19Chapter 3.1.3 --- Protocol Approximation --- p.20Chapter 3.1.4 --- Throughput Measurement --- p.21Chapter 3.2 --- Derivation of Throughput --- p.21Chapter 3.2.1 --- Channel Modeling --- p.22Chapter 3.2.2 --- Actual Transmission Rate --- p.24Chapter 3.2.3 --- Case One --- p.24Chapter 3.2.4 --- Case Two --- p.26Chapter 3.2.5 --- Mathematical Form of Throughput --- p.28Chapter 3.2.6 --- Analysis Results --- p.30Chapter 3.3 --- Implications --- p.31Chapter 3.3.1 --- Value of Sensing Range in CSMA/CA --- p.31Chapter 3.3.2 --- Need for New MAC Protocols --- p.32Chapter 4 --- MAC Protocols by Congestion Control --- p.34Chapter 4.1 --- Motivations and Principles --- p.34Chapter 4.1.1 --- Balancing Hidden and Exposed Nodes --- p.35Chapter 4.1.2 --- Controlling Carrier Sensing Range --- p.36Chapter 4.1.3 --- Non-homogenous Sensing Range --- p.36Chapter 4.2 --- Algorithm Descriptions --- p.38Chapter 4.2.1 --- Core Concept --- p.38Chapter 4.2.2 --- LDMI Control Scheme --- p.40Chapter 4.2.3 --- Tahoe Control Scheme --- p.41Chapter 5 --- Simulation Analysis --- p.44Chapter 5.1 --- Simulation Configurations --- p.44Chapter 5.1.1 --- Geometric Burst Traffic Model --- p.45Chapter 5.1.2 --- Network Topology --- p.46Chapter 5.1.3 --- Simulation Parameters --- p.47Chapter 5.2 --- Throughput Comparisons --- p.48Chapter 5.3 --- Fairness Comparisons --- p.50Chapter 5.3.1 --- Situation of Unfairness --- p.50Chapter 5.3.2 --- Fairness Measurement --- p.52Chapter 5.4 --- Convergence Comparisons --- p.54Chapter 5.5 --- Summary of Performance Comparison --- p.55Chapter 6 --- Conclusions --- p.56Chapter A --- Categories of CSMA/CA --- p.58Chapter A.1 --- 1-persistent CSMA/CA --- p.58Chapter A.2 --- non-persistent CSMA/CA --- p.58Chapter A.3 --- p-persistent CSMA/CA --- p.59Chapter B --- Backoff Schemes --- p.60Chapter B.1 --- Constant Window Backoff Scheme --- p.60Chapter B.2 --- Geometric Backoff Scheme --- p.60Chapter B.3 --- Binary Exponential Backoff Scheme --- p.61Bibliography --- p.6

Contention techniques for opportunistic communication in wireless mesh networks

Auf dem Gebiet der drahtlosen Kommunikation und insbesondere auf den tieferen Netzwerkschichten sind gewaltige Fortschritte zu verzeichnen. Innovative Konzepte und Technologien auf der physikalischen Schicht (PHY) gehen dabei zeitnah in zelluläre Netze ein. Drahtlose Maschennetzwerke (WMNs) können mit diesem Innovationstempo nicht mithalten. Die Mehrnutzer-Kommunikation ist ein Grundpfeiler vieler angewandter PHY Technologien, die sich in WMNs nur ungenügend auf die etablierte Schichtenarchitektur abbilden lässt. Insbesondere ist das Problem des Scheduling in WMNs inhärent komplex. Erstaunlicherweise ist der Mehrfachzugriff mit Trägerprüfung (CSMA) in WMNs asymptotisch optimal obwohl das Verfahren eine geringe Durchführungskomplexität aufweist. Daher stellt sich die Frage, in welcher Weise das dem CSMA zugrunde liegende Konzept des konkurrierenden Wettbewerbs (engl. Contention) für die Integration innovativer PHY Technologien verwendet werden kann. Opportunistische Kommunikation ist eine Technik, die die inhärenten Besonderheiten des drahtlosen Kanals ausnutzt. In der vorliegenden Dissertation werden CSMA-basierte Protokolle für die opportunistische Kommunikation in WMNs entwickelt und evaluiert. Es werden dabei opportunistisches Routing (OR) im zustandslosen Kanal und opportunistisches Scheduling (OS) im zustandsbehafteten Kanal betrachtet. Ziel ist es, den Durchsatz von elastischen Paketflüssen gerecht zu maximieren. Es werden Modelle für Überlastkontrolle, Routing und konkurrenzbasierte opportunistische Kommunikation vorgestellt. Am Beispiel von IEEE 802.11 wird illustriert, wie der schichtübergreifende Entwurf in einem Netzwerksimulator prototypisch implementiert werden kann. Auf Grundlage der Evaluationsresultate kann der Schluss gezogen werden, dass die opportunistische Kommunikation konkurrenzbasiert realisierbar ist. Darüber hinaus steigern die vorgestellten Protokolle den Durchsatz im Vergleich zu etablierten Lösungen wie etwa DCF, DSR, ExOR, RBAR und ETT.In the field of wireless communication, a tremendous progress can be observed especially at the lower layers. Innovative physical layer (PHY) concepts and technologies can be rapidly assimilated in cellular networks. Wireless mesh networks (WMNs), on the other hand, cannot keep up with the speed of innovation at the PHY due to their flat and decentralized architecture. Many innovative PHY technologies rely on multi-user communication, so that the established abstraction of the network stack does not work well for WMNs. The scheduling problem in WMNs is inherent complex. Surprisingly, carrier sense multiple access (CSMA) in WMNs is asymptotically utility-optimal even though it has a low computational complexity and does not involve message exchange. Hence, the question arises whether CSMA and the underlying concept of contention allows for the assimilation of advanced PHY technologies into WMNs. In this thesis, we design and evaluate contention protocols based on CSMA for opportunistic communication in WMNs. Opportunistic communication is a technique that relies on multi-user diversity in order to exploit the inherent characteristics of the wireless channel. In particular, we consider opportunistic routing (OR) and opportunistic scheduling (OS) in memoryless and slow fading channels, respectively. We present models for congestion control, routing and contention-based opportunistic communication in WMNs in order to maximize both throughput and fairness of elastic unicast traffic flows. At the instance of IEEE 802.11, we illustrate how the cross-layer algorithms can be implemented within a network simulator prototype. Our evaluation results lead to the conclusion that contention-based opportunistic communication is feasible. Furthermore, the proposed protocols increase both throughput and fairness in comparison to state-of-the-art approaches like DCF, DSR, ExOR, RBAR and ETT