CSE Journal Articles Copyright (c) 2013 University of Nebraska - Lincoln All rights reserved. http://digitalcommons.unl.edu/csearticles Recent documents in CSE Journal Articles en-us Sun, 17 Feb 2013 01:41:33 PST 3600 Upstream-Downstream Relationships in Terms of Annual Streamflow Discharges and Drought Events in Nebraska http://digitalcommons.unl.edu/csearticles/107 http://digitalcommons.unl.edu/csearticles/107 Fri, 15 Feb 2013 13:10:55 PST Upstream-downstream relationships of annual streamflow discharges and severity and frequency of stream-flow drought events are critical in understanding how streamflow droughts propagate over time and space. Such information can be used to resolve water disputes, trigger mitigation strategies, and understand how streamflow changes due to changes in the environment. During drought years, such information is even more critical as water resources are contested. The objective of this research is to study the upstream-downstream relationships of streamflow in Nebraska along four major river systems with diverse hydrologic characteristics and human activities: North Platte, Big Blue, Republican, and Niobrara. The relationships among the upstream and downstream stations along the four rivers are investigated by comparing several statistics de-rived from the annual flow discharge and on drought events. Trend analysis and coefficient of variation are applied to annual flow discharge values, and a host of drought-related parameters (e.g., annual maximum drought duration, annual accumulated drought duration, number of drought events) are also computed with respect to five different levels of streamflow drought events: water shortage, mild drought, moderate drought, significant drought, and extreme drought. The paired-t test and ANOVA with MIXED procedure are subsequently applied to the statistics to observe whether there is a significant difference between upstream and downstream stations along a river. The analysis allows us to characterize the upstream-downstream relation-ships of the four river systems, laying the groundwork for further investigations to identify the reasons for some of the trends and observations. These findings will be essential in water resources management during or prior to hydrological droughts.

]]> Hong Wu et al. Cross-Layer Analysis of the End-to-End Delay Distribution in Wireless Sensor Networks http://digitalcommons.unl.edu/csearticles/106 http://digitalcommons.unl.edu/csearticles/106 Tue, 02 Oct 2012 14:14:57 PDT Emerging applications of wireless sensor networks (WSNs) require real-time quality-of-service (QoS) guarantees to be provided by the network. Due to the nondeterministic impacts of the wireless channel and queuing mechanisms, probabilistic analysis of QoS is essential. One important metric of QoS in WSNs is the probability distribution of the end-to-end delay. Compared to other widely used delay performance metrics such as the mean delay, delay variance, and worst-case delay, the delay distribution can be used to obtain the probability to meet a specific deadline for QoS-based communication in WSNs. To investigate the end-to-end delay distribution, in this paper, a comprehensive cross-layer analysis framework, which employs a stochastic queueing model in realistic channel environments, is developed. This framework is generic and can be parameterized for a wide variety of MAC protocols and routing protocols. Case studies with the CSMA/CAMAC protocol and an anycast protocol are conducted to illustrate how the developed framework can analytically predict the distribution of the end-to-end delay. Extensive test-bed experiments and simulations are performed to validate the accuracy of the framework for both deterministic and random deployments.Moreover, the effects of various network parameters on the distribution of end-to-end delay are investigated through the developed framework. To the best of our knowledge, this is the first work that provides a generic, probabilistic cross-layer analysis of end-to-end delay in WSNs.

]]> Yunbo Wang et al. Exploring the Design Space of Multichannel Peer-to-Peer Live Video Streaming Systems http://digitalcommons.unl.edu/csearticles/105 http://digitalcommons.unl.edu/csearticles/105 Tue, 02 Oct 2012 14:12:08 PDT Most of the commercial peer-to-peer (P2P) video streaming deployments support hundreds of channels and are referred to as multichannel systems. Recent research studies have proposed specific protocols to improve the streaming quality for all channels by enabling cross-channel cooperation among multiple channels. In this paper, we focus on the following fundamental problems in designing cooperating multichannel systems: 1) what are the general characteristics of existing and potential designs? and 2) under what circumstances should a particular design be used to achieve the desired streaming quality with the lowest implementation complexity? To answer the first question, we propose simple models based on linear programming and network-flow graphs for three general designs, namely Naive Bandwidth allocation Approach (NBA), Passive Channel-aware bandwidth allocation Approach (PCA), and Active Channel-aware bandwidth allocation Approach (ACA), which provide insight into understanding the key characteristics of cross-channel resource sharing. For the second question, we first develop closed-form results for two-channel systems. Then, we use extensive numerical simulations to compare the three designs for various peer population distributions, upload bandwidth distributions, and channel structures. Our analytical and simulation results show that: 1) the NBA design can rarely achieve the desired streaming quality in general cases; 2) the PCA design can achieve the same performance as the ACA design in general cases; and 3) the ACA design should be used for special applications.

]]> Miao Wang et al. Palantir: Early Detection of Development Conflicts Arising from Parallel Code Changes http://digitalcommons.unl.edu/csearticles/104 http://digitalcommons.unl.edu/csearticles/104 Tue, 02 Oct 2012 14:09:00 PDT The earlier a conflict is detected, the easier it is to resolve—this is the main precept of workspace awareness. Workspace awareness seeks to provide users with information of relevant ongoing parallel changes occurring in private workspaces, thereby enabling the early detection and resolution of potential conflicts. The key approach is to unobtrusively inform developers of potential conflicts arising because of concurrent changes to the same file and dependency violations in ongoing parallel work. This paper describes our research goals, approach, and implementation of workspace awareness through Palantır and includes a comprehensive evaluation involving two laboratory experiments. We present both quantitative and qualitative results from the experiments, which demonstrate that the use of Palantır, as compared to not using Palantir 1) leads to both earlier detection and earlier resolution of a larger number of conflicts, 2) leaves fewer conflicts unresolved in the code base that was ultimately checked in, and 3) involves reasonable overhead. Furthermore, we report on interesting changes in users’ behavior, especially how conflict resolution strategies changed among Palantır users.

]]> Anita Sarma et al. SimCoL: A Simulation Tool for Computer-Supported Collaborative Learning http://digitalcommons.unl.edu/csearticles/103 http://digitalcommons.unl.edu/csearticles/103 Tue, 02 Oct 2012 14:06:13 PDT Researchers designing the multiagent tools and techniques for computer-supported collaborative learning (CSCL) environments are often faced with high cost, time, and effort required to investigate the effectiveness of their tools and techniques in large scale and longitudinal studies in a real-world environment containing human users. Here, we propose SimCoL, a multiagent environment that simulates collaborative learning among students and agents providing support to the teacher and the students. Our goal with SimCoL is to provide a comprehensive test bed for multiagent researchers to investigate 1) theoretical multiagent research issues, e.g., coalition formation, multiagent learning, and communication, where humans are involved and 2) the impact and effectiveness of the design and implementation of various multiagent-based tools and techniques (e.g., multiagent-based human coalition formation) in a real world, distributed environment containing human users. Our results show that SimCoL 1) closely captures the individual and collective learning behaviors of the students in a CSCL environment; 2) identify the impact of various key elements of the CSCL environment (e.g., student attributes and group formation algorithm) on the collaborative learning of students; 3) compare and contrast the impact of agent-based versus non agent-based group formation algorithms; and 4) provide insights into the effectiveness of agent-based instructor support for the students in a CSCL environment.

]]> Nobel Khandaker et al. Lessons Learned from Comprehensive Deployments of Multiagent CSCL Applications I-MINDS and ClassroomWiki http://digitalcommons.unl.edu/csearticles/102 http://digitalcommons.unl.edu/csearticles/102 Tue, 02 Oct 2012 14:04:18 PDT Recent years have seen a surge in the use of intelligent computer-supported collaborative learning (CSCL) tools for improving student learning in traditional classrooms. However, adopting such a CSCL tool in a classroom still requires the teacher to develop (or decide on which to adopt) the CSCL tool and the CSCL script, design the relevant pedagogical aspects (i.e., the learning objectives, assessment method, etc.) to overcome the associated challenges (e.g., free riding, student assessment, forming student groups that improve student learning, etc). We have used a multiagent-based system to develop a CSCL application and multiagent frameworks to form student groups that improve student collaborative learning. In this paper, we describe the contexts of our three generations of CSCL applications (i.e., I-MINDS and Classroom Wiki) and provide a set of lessons learned from our deployments in terms of the script, tool, and pedagogical aspects of using CSCL. We believe that our lessons would allow 1) the instructors and students to use intelligent CSCL applications more effectively and efficiently, and help to improve the design of such systems, and 2) the researchers to gain additional insights into the impact of collaborative learning theories when they are applied to real-world classrooms.

]]> Nobel Khandaker et al. Redistricting Using Constrained Polygonal Clustering http://digitalcommons.unl.edu/csearticles/101 http://digitalcommons.unl.edu/csearticles/101 Tue, 02 Oct 2012 14:01:42 PDT Redistricting is the process of dividing a geographic area consisting of spatial units—often represented as spatial polygons—into smaller districts that satisfy some properties. It can therefore be formulated as a set partitioning problem where the objective is to cluster the set of spatial polygons into groups such that a value function is maximized [1]. Widely used algorithms developed for point-based data sets are not readily applicable because polygons introduce the concepts of spatial contiguity and other topological properties that cannot be captured by representing polygons as points. Furthermore, when clustering polygons, constraints such as spatial contiguity and unit distributedness should be strategically addressed. Toward this, we have developed the Constrained Polygonal Spatial Clustering (CPSC) algorithm based on the A* search algorithm that integrates cluster-level and instance-level constraints as heuristic functions. Using these heuristics, CPSC identifies the initial seeds, determines the best cluster to grow, and selects the best polygon to be added to the best cluster. We have devised two extensions of CPSC—CPSC* and CPSC*-PS—for problems where constraints can be soft or relaxed. Finally, we compare our algorithm with graph partitioning, simulated annealing, and genetic algorithm-based approaches in two applications—congressional redistricting and school districting.

]]> Deepti Joshi et al. Investigating adaptive, confidence-based strategic negotiations in complex multiagent environments http://digitalcommons.unl.edu/csearticles/100 http://digitalcommons.unl.edu/csearticles/100 Fri, 16 Dec 2011 12:36:08 PST We propose an adaptive 1-to-many negotiation strategy for multiagent coalition formation in complex environments that are dynamic, uncertain, and real-time. Our strategy deals with how to assign multiple issues to a set of concurrent negotiations based on an initiating agent’s confidence in its profiling of its peer agents. When an agent is confident, it uses a packaged approach—conducting multiple multi-issue negotiations—with its peers. Otherwise, it uses a pipelined approach—conducting multiple single-issue negotiations—with its peers. The initiating agent is also capable of using both approaches in a hybrid, dealing with a mixed group of responding peers. An agent’s confidence in its profile or view of another agent is crucial, and that depends on the environment in which the agents operate. To evaluate the proposed strategy, we use a coalition formation framework in a complex environment. Results show that the proposed strategy outperforms the purely pipelined strategy and the purely packaged strategy in both efficiency and effectiveness.

]]> Leen-Kiat Soh et al. Exploiting redundancy to boost performance in a RAID-10 style cluster-based file system http://digitalcommons.unl.edu/csearticles/99 http://digitalcommons.unl.edu/csearticles/99 Fri, 12 Aug 2011 09:00:28 PDT While aggregating the throughput of existing disks on cluster nodes is a cost-effective approach to alleviate the I/O bottleneck in cluster computing, this approach suffers from potential performance degradations due to contentions for shared resources on the same node between storage data processing and user task computation. This paper proposes to judiciously utilize the storage redundancy in the form of mirroring existed in a RAID-10 style file system to alleviate this performance degradation. More specifically, a heuristic scheduling algorithm is developed, motivated from the observations of a simple cluster configuration, to spatially schedule write operations on the nodes with less load among each mirroring pair. The duplication of modified data to the mirroring nodes is performed asynchronously in the background. The read performance is improved by two techniques: doubling the degree of parallelism and hot-spot skipping. A synthetic benchmark is used to evaluate these algorithms in a real cluster environment and the proposed algorithms are shown to be very effective in performance enhancement.

]]> Yifeng Zhu et al. CEFT: A cost-effective, fault-tolerant parallel virtual file system http://digitalcommons.unl.edu/csearticles/98 http://digitalcommons.unl.edu/csearticles/98 Thu, 11 Aug 2011 12:03:09 PDT The vulnerability of computer nodes due to component failures is a critical issue for cluster-based file systems. This paper studies the development and deployment of mirroring in cluster-based parallel virtual file systems to provide fault tolerance and analyzes the tradeoffs between the performance and the reliability in the mirroring scheme. It presents the design and implementation of CEFT, a scalable RAID-10 style file system based on PVFS, and proposes four novel mirroring protocols depending on whether the mirroring operations are server-driven or client-driven, whether they are asynchronous or synchronous. The comparisons of their write performances, measured in a real cluster, and their reliability and availability, obtained through analytical modeling, show that these protocols strike different tradeoffs between the reliability and performance. Protocols with higher peak write performance are less reliable than those with lower peak write performance, and vice versa. A hybrid protocol is proposed to optimize this tradeoff.

]]> Yifeng Zhu et al. A Method for Estimating Fractal Dimension of Tree Crowns from Digital Images http://digitalcommons.unl.edu/csearticles/97 http://digitalcommons.unl.edu/csearticles/97 Thu, 17 Feb 2011 07:38:35 PST A new method for estimating fractal dimension of tree crowns from digital images is presented. Three species of trees, Japanese yew (Taxus cuspidata Sieb & Zucc), Hicks yew (Taxus × media), and eastern white pine (Pinus strobus L.), were studied. Fractal dimensions of Japanese yew and Hicks yew range from 2.26 to 2.70. Fractal dimension of eastern white pine range from 2.14 to 2.43. The difference in fractal dimension between Japanese yew and eastern white pine was statistically significant at 0.05 significance level as was the difference in fractal dimension between Hicks yew and eastern white pine. On average, the greater fractal dimensions of Japanese yew and Hicks yew were possibly related to uniform foliage distribution within their tree crowns. Therefore, fractal dimension may be useful for tree crown structure classification and for indexing tree images.

]]> Dongsheng Zhang et al. Special section on the algorithmics of software model checking — Introductory paper http://digitalcommons.unl.edu/csearticles/96 http://digitalcommons.unl.edu/csearticles/96 Fri, 28 Jan 2011 14:46:50 PST The term “software model checking” has recently been coined to refer to a flourishing area of research in software verification – the formal, automated analysis of program source code. Software model checking is considered an important application of classical model checking, where the model of a software system is analyzed in an automated fashion for compliance with a property specification. While classical model checking assumes the existence of an abstract model of the software system to be analyzed, in software model checking the emphasis is on directly analyzing program code given in a standard programming language, such as Java or C. This introduces a variety of significant obstacles, chief among them the efficient treatment of the complex data, e.g., heap structured data, and control constructs, e.g., procedure calls and exception handling, found in modern programming languages. These obstacles can also be viewed as opportunities for adapting traditional model checking data structures and algorithms to exploit the particular semantics of programming language constructs to gain improved performance. Moreover, while classical model checking emphasizes proving a model correct as the primary objective, an increasingly widely held view is that model checkers can function effectively as anomaly detectors or bug finders, i.e., they locate and explain undesired behavior of the software.

This special section is the second devoted to publishing revised versions of contributions first presented at the International SPIN Workshop Series on Model Checking Software. In recent years this series of workshops has broadened its scope from focusing on the model checker SPIN to covering software model checking technology in general. The editorial introduction by Havelund and Visser to the first STTT special section devoted to SPIN papers [11] provides an excellent overview of the foundational ideas underlying software model checking. That special section was based on papers presented at the 7th International SPIN Workshop held at Stanford University (USA) in August/September 2001. Authors of well-regarded papers from the 8th International SPIN Workshop held in Toronto (Canada), colocated with ICSE 2001 on May 10–11, 2001, and the 9th International SPIN Workshop on Model Checking Software, held April 11–13, 2002 in Grenoble (France) as a satellite event of ETAPS 2002,were invited to submit to this special issue. All three of the papers included here have been extended to include significant new content and have undergone an independent round of reviewing.

]]> Matthew Dwyer et al. An Analysis of Sexual Dimorphism in the Human Face http://digitalcommons.unl.edu/csearticles/95 http://digitalcommons.unl.edu/csearticles/95 Mon, 13 Dec 2010 08:53:03 PST Abstract Human beings can distinguish between a male and a female face without much difficulty. The science of recognizing and differentiating different faces by humans is not completely understood and is still under research. Sexual dimorphism is common in humans and indeed in other species of animals as well. Significant differences between males and females exist in many aspects like size, color, body shapes, and weight. In this research, we characterize and analyze the sexual dimorphism in the human face as a function of age and of face features. Features are grouped into six categories: head, eyes, orbits, nose, lips, and mouth, and ears. We demonstrate that the face of adult males is significantly different from adult females. We also identify the features that significantly contribute to the dimorphism of the face. This provides a basis for gender-based classification of faces.

]]> Ashok Samal et al. Smart Templates for peak pattern matching with comprehensive two-dimensional liquid chromatography http://digitalcommons.unl.edu/csearticles/94 http://digitalcommons.unl.edu/csearticles/94 Fri, 29 Oct 2010 13:44:40 PDT Comprehensive two-dimensional liquid chromatography (LC × LC) generates information-rich but complex peak patterns that require automated processing for rapid chemical identification and classification. This paper describes a powerful approach and specific methods for peak pattern matching to identify and classify constituent peaks in data from LC × LC and other multidimensional chemical separations. The approach records a prototypical pattern of peaks with retention times and associated metadata, such as chemical identities and classes, in a template. Then, the template pattern is matched to the detected peaks in subsequent data and the metadata are copied from the template to identify and classify the matched peaks. Smart Templates employ rule-based constraints (e.g., multispectral matching) to increase matching accuracy. Experimental results demonstrate Smart Templates, with the combination of retention-time pattern matching and multispectral constraints, are accurate and robust with respect to changes in peak patterns associated with variable chromatographic conditions.

]]> Stephen E. Reichenbach et al. Techniques for Computing Fitness of Use (FoU) for Time Series Datasets with Applications in the Geospatial Domain http://digitalcommons.unl.edu/csearticles/93 http://digitalcommons.unl.edu/csearticles/93 Mon, 11 Oct 2010 11:26:26 PDT Time series data are widely used in many applications including critical decision support systems. The goodness of the dataset, called the Fitness of Use (FoU), used in the analysis has direct bearing on the quality of the information and knowledge generated and hence on the quality of the decisions based on them. Unlike traditional quality of data which is independent of the application in which it is used, FoU is a function of the application. As the use of geospatial time series datasets increase in many critical applications, it is important to develop formal methodologies to compute their FoU and propagate it to the derived information, knowledge and decisions. In this paper we propose a formal framework to compute the FoU of time series datasets. We present three different techniques using the Dempster-Shafer belief theory framework as the foundation. These three approaches investigate the FoU by focusing on three aspects of data: data attributes, data stability, and impact of gap periods, respectively. The effectiveness of each approach is shown using an application in hydrological datasets that measure streamflow. While we use hydrological information analysis as our application domain in this research, the techniques can be used in many other domains as well.

]]> Lei Fu et al. Computation of a Face Attractiveness Index Based on Neoclassical Canons, Symmetry, and Golden Ratios http://digitalcommons.unl.edu/csearticles/92 http://digitalcommons.unl.edu/csearticles/92 Wed, 06 Oct 2010 13:01:44 PDT Analysis of attractiveness of faces has long been a topic of research. Literature has identified many different factors that can be related to attractiveness. In this research we analyze the role of symmetry, neoclassical canons, and golden ratio in the determination of attractiveness of a face. We focus on the geometry of a face and use actual faces for our analysis. We find there are some differences in the criteria used by males and females to determine attractiveness. The model we have developed to predict the attractiveness of a face using its geometry is accurate with low residual errors.

]]> Kendra Schmid et al. Error Control in Wireless Sensor Networks: A Cross Layer Analysis http://digitalcommons.unl.edu/csearticles/91 http://digitalcommons.unl.edu/csearticles/91 Thu, 16 Sep 2010 08:43:13 PDT Error control is of significant importance for Wireless Sensor Networks (WSNs) because of their severe energy constraints and the low power communication requirements. In this paper, a cross-layer methodology for the analysis of error control schemes in WSNs is presented such that the effects of multi-hop routing and the broadcast nature of the wireless channel are investigated. More specifically, the cross-layer effects of routing, medium access, and physical layers are considered. This analysis enables a comprehensive comparison of forward error correction (FEC) codes, automatic repeat request (ARQ), and hybrid ARQ schemes in WSNs. The validation results show that the developed framework closely follows simulation results.
Hybrid ARQ and FEC schemes improve the error resiliency of communication compared to ARQ. In a multi-hop network, this improvement can be exploited by constructing longer hops (hop length extension), which can be achieved through channel-aware routing protocols, or by reducing the transmit power (transmit power control). The results of our analysis reveal that for hybrid ARQ schemes and certain FEC codes, the hop length extension decreases both the energy consumption and the end-to-end latency subject to a target packet error rate (PER) compared to ARQ. This decrease in end-to-end latency is crucial for delay sensitive, real-time applications, where both hybrid ARQ and FEC codes are strong candidates. We also show that the advantages of FEC codes are even more pronounced as the network density increases. On the other hand, transmit power control results in significant savings in energy consumption at the cost of increased latency for certain FEC codes. The results of our analysis also indicate the cases where ARQ outperforms FEC codes for various end-to-end distance and target PER values.

]]> Mehmet C. Vuran et al. A-MAC: Adaptive Medium Access Control for Next Generation Wireless Terminals http://digitalcommons.unl.edu/csearticles/90 http://digitalcommons.unl.edu/csearticles/90 Thu, 16 Sep 2010 08:36:59 PDT Next Generation (NG) wireless networks are envisioned to provide high bandwidth to mobile users via bandwidth aggregation over heterogeneous wireless architectures. NG wireless networks, however, impose challenges due to their architectural heterogeneity in terms of different access schemes, resource allocation techniques as well as diverse quality of service requirements. These heterogeneities must be captured and handled dynamically as mobile terminals roam between different wireless architectures. However, to address these challenges, the existing proposals require either a significant modification in the network structure and in base stations or a completely new architecture, which lead to integration problems in terms of implementation costs, scalability and backward compatibility. Thus, the integration of the existing medium access schemes, e.g., CSMA, TDMA and CDMA, dictates an adaptive and seamless medium access control (MAC) layer that can achieve high network utilization and meet diverse Quality of Service (QoS) requirements.
In this paper, an adaptive medium access control (A-MAC) layer is proposed to address the heterogeneities posed by theNG wireless networks. A-MAC introduces a two-layered MAC framework that accomplishes the adaptivity to both architectural heterogeneities and diverse QoS requirements. A novel virtual cube concept is introduced as a unified metric to model heterogeneous access schemes and capture their behavior. Based on the Virtual Cube concept, A-MAC provides architecture-independent decision and QoS based scheduling algorithms for efficient multi-network access. A-MAC performs seamless medium access to multiple networks without requiring any additional modifications in the existing network structures. It is shown via extensive simulations hat A-MAC provides adaptivity to the heterogeneities in NG wireless networks and achieves high performance.

]]> Mehmet C. Vuran et al. Spatial Correlation-Based Collaborative Medium Access Control in Wireless Sensor Networks http://digitalcommons.unl.edu/csearticles/89 http://digitalcommons.unl.edu/csearticles/89 Thu, 16 Sep 2010 08:33:01 PDT Wireless Sensor Networks (WSN) are mainly characterized by dense deployment of sensor nodes which collectively transmit information about sensed events to the sink. Due to the spatial correlation between sensor nodes subject to observed events, it may not be necessary for every sensor node to transmit its data. This paper shows how the spatial correlation can be exploited on the Medium Access Control (MAC) layer. To the best of our knowledge, this is the first effort which exploits spatial correlation in WSN on the MAC layer. A theoretical framework is developed for transmission regulation of sensor nodes under a distortion constraint. It is shown that a sensor node can act as a representative node for several other sensor nodes observing the correlated data. Based on the theoretical framework, a distributed, spatial Correlation-based Collaborative Medium Access Control (CC-MAC) protocol is then designed which has two components: Event MAC (E-MAC) and Network MAC (N-MAC). E-MAC filters out the correlation in sensor records while N-MAC prioritizes the transmission of route-thru packets. Simulation results show that CC-MAC achieves high performance in terms energy, packet drop rate, and latency.

]]> Mehmet C. Vuran et al. XLP: A Cross-Layer Protocol for Efficient Communication in Wireless Sensor Networks http://digitalcommons.unl.edu/csearticles/88 http://digitalcommons.unl.edu/csearticles/88 Tue, 14 Sep 2010 10:51:43 PDT Severe energy constraints of battery-powered sensor nodes necessitate energy-efficient communication in Wireless Sensor Networks (WSNs). However, the vast majority of the existing solutions is based on classical layered protocols approach, which leads to significant overhead. It is much more efficient to have a unified scheme which blends common protocol layer functionalities into a cross-layer module. In this paper, a cross layer protocol (XLP) is introduced, which achieves congestion control, routing, and medium access control in a cross-layer fashion. The design principle of XLP is based on the cross-layer concept of initiative determination, which enables receiver-based contention, initiative-based forwarding, local congestion control, and distributed duty cycle operation to realize efficient and reliable communication in WSNs. The initiative determination requires simple comparisons against thresholds, and thus is very simple to implement, even on computationally impaired devices. To the best of our knowledge, XLP is the first protocol that integrates functionalities of all layers from PHY to transport into a cross-layer protocol. A cross-layer analytical framework is developed to investigate the performance of the XLP. Moreover, in a cross-layer simulation platform, the state-of-the- art layered and cross-layer protocols have been implemented along with XLP for performance evaluations. XLP significantly improves the communication performance and outperforms the traditional layered protocol architectures in terms of both network performance and implementation complexity.

]]> Mehmet C. Vuran et al.