Catálogo de publicaciones - libros

This paper describes a new algorithm based on the Binary Decision Diagrams (BDDs) to solve the reliable communication network design problem (RCND). In this NP-hard problem, a subset of communication links must be chosen such that the network cost is minimized given a network reliability constraint. This problem is closely related to the network reliability computation problem.

Adequate coverage is very important for sensor networks to fulfill the issued sensing tasks. In traditional sensor networks, the sensors are based on omni-sensing model. However, directional sensing sensors are with great application chances, typically in video sensor networks. Toward this end, this paper addresses the problem of enhancing coverage in a directional sensor network. First, based on a rotatable directional sensing model, we present a method to deterministically estimate the amount of directional nodes for a given coverage rate. We also employ Sensing Connected Sub-graph (SCSG) to divide a directional sensor network into several parts in a distributed manner, in order to decrease time complexity. Moreover, the concept of convex hull is introduced to model each sensing connected sub-graph. According to the characteristic of adjustable sensing directions of directional nodes, we study a coverage-enhancing algorithm to minimize the overlapping sensing area of directional sensors only with local topology information. Extensive simulation is conducted to verify the effectiveness of our solution and we give detailed discussions on the effects of different system parameters.

Some sensor network applications require -coverage to ensure the quality of surveillance. Meanwhile, energy is another primary concern for sensor networks. In this paper, we investigate the Sensor Scheduling for -Coverage (SSC) problem which requires to efficiently schedule the sensors, such that the monitored region can be -covered throughout the whole network lifetime with the purpose of maximizing network lifetime. The SSC problem is NP-hard and we propose a heuristic algorithm for it. In addition, we develop a guideline for users to better design a sensor deployment plan to save energy by employing density control. Simulation results are presented to evaluate our proposed algorithm.

This paper proposes a Media Access Control protocol,called CT-MAC, for ad-hoc wireless sensor networks. It is a contention-based TDMA scheme, which assimilates the valuable design philosophies of CSMA and TDMA while offsetting their weaknesses. Inspired by S-MAC[1], CT-MAC proposes a novel conception of contention/doze and communication/dormancy duty cycle. Unlike S-MAC where the durations of each cycle are fixed, CT-MAC makes these durations self-adaptive for energy efficiency. More importantly, CT-MAC originally adopts the protocol interference model to contend the noninterference channels for each time-slot, and extends the conventional IEEE 801.11 RTS-CTS scheme with stronger functions to successfully solve the exposed terminal problem, which is not well addressed before. We believe that the initial high overhead in the contention period would be eventually compensated by the improved throughput and energy efficiency subsequently. Simulations are performed among CT-MAC, S-MAC and simplified 802.11 DCF to demonstrate the efficiency and effectiveness of the proposed CT-MAC.

IEEE 802.11 has employed distributed coordination function (DCF) adopting carrier sense multiple access with collision avoidance (CSMA/CA). To effectively resolve collisions, DCF uses binary exponential backoff (BEB) algorithm with three parameters, i.e., backoff stage, backoff counter and contention window. If a collision occurs, stations involving in the collision increase their backoff stages by one and double their contention window sizes. However, DCF with BEB wastes wireless resource when there are many contending stations. Therefore, in this paper, we propose a binary negative-exponential backoff (BNEB) algorithm which maintains a maximum contention window size during collisions and reduces a contention window size half after successful transmission of a frame without retransmissions. We also compare the performance of DCF with BEB to that with BNEB. From the results, BNEB yields better performance than BEB when the number of contending stations is larger than 4.

In this paper, we design and implement an application-aware, event-oriented MAC protocol (App-MAC) for event-driven multimodality WSN applications. We leverage the advantages of contention-based and reservation-based MAC protocols to coordinate the channel access, and propose channel contention and reservation algorithms to adaptively allocate channel time slots according to application requirements and current events status. To evaluate the proposed App-MAC, we have implemented App-MAC using Berkeley TelosB motes and compared with three state-of-the-art MAC protocols, i.e., S-MAC, TDMA, and TRAMA. We found that App-MAC outperforms other protocols tremendously, including decreasing the average event delivery latency from 3% to 75%, improving the channel utilization efficiency from 12% to 58%, while improving the energy consumption efficiency from 46% to 59%.

Localization is crucial to many applications in wireless sensor networks. This article presents a range-free anchor-based localization algorithm for mobile wireless sensor networks that builds upon the Monte Carlo Localization algorithm. We improve the localization accuracy and efficiency by making better use of the information a sensor node gathers and by drawing the necessary location samples faster. Namely, we constrain the area from which samples are drawn by building a box that covers the region where anchors’ radio ranges overlap. Simulation results show that localization accuracy is improved by a minimum of 4% and by a maximum of 73%, on average 30%, for varying node speeds when considering nodes with knowledge of at least three anchors. The coverage is also strongly affected by speed and its improvement ranges from 3% to 55%, on average 22%. Finally, the processing time is reduced by 93% for a similar localization accuracy.

Mobile sinks pose several challenges for network protocol design. While moving, a sink should continuously update its topological position information in the sensor nodes to maintain paths. This may require large signaling overhead, resulting in excessive energy consumption. Various schemes have been proposed to reduce the path management overhead. In many of these schemes, the sinks only maintain paths from active sources to reduce the overhead. While reducing the path management overhead, this approach introduces other problems. In this paper, a novel path management scheme, Net Cast Routing (NCR), is proposed. NCR provides ceaseless connection from every sensor node to every sink in an efficient manner. Since it does not distinguish active sources from other sensor nodes, its performance is not affected by the number or movement of the sensing targets. In addition, unlike multicast based schemes [2,3,4], NCR does not require any subscription procedure to active sources.

In this paper, we propose cost-reduced binding update scheme (CRBU) which further reduces signaling traffic for location updates by employing virtual mobility anchor point (VMAP) on top of overlapped MAP in Hierarchical Mobile IPv6 (HMIPv6). This proposed scheme significantly improves performance compared to HMIPv6, in terms of binding update rate per user and average handoff latency. Also it makes the mobile nodes (MNs) moving around the boundary access routers (ARs) of adjacent MAPs and they become to move within a VMAP. It is certain that our scheme uses the network resources efficiently by the removal of global binding updates for MNs in boundary ARs inside MAPs. And we explain an analytic model for performance analysis of HMIPv6 networks, which is based on the random walk mobility model. Based on this analytic model, we formulate binding update cost and analyze it as the probability that an MN stays in the current cell (). As a result, our proposed scheme can greatly reduce the packet loss and delay by eliminating Inter-MAP handoff.

With the spread of mobile phones, the use of Mobile Ad- hoc NETworks (MANETs) for disaster recovery finally becomes feasible. Information retrieval from the catastrophic place is attended in an energy-efficient manner using the Geographically Bound Mobile Agent (GBMA) model. The GBMA, which is a mobile agent on MANETs that retrieves geographically bound data, migrates to remain in a designated region to maintain low energy consumption for data retrieval, and provides location based migration scheme to eliminate needless migration to reduce energy consumption. In the data retrieval using the GBMA model, survivability of the agent is important. In a MANET, a GBMA with retrieved data may be lost due to its host’s death. The lost of the agent causes re-execution of the retrieval process, which depraves energy efficiency. We propose migration strategies of the GBMA to improve its survivability. In the migration strategies, the selection of the next host node is parameterized by node location, speed, connectivity, and battery level. Moreover, in the strategies, multiple migration trigger policies are defined to escape from a dying node. We present the implementation of migration strategies and confirm the achievements with several simulations. This finally leads to the adaptive Geographically Bound Mobile Agent model, which consumes even less energy.