Catálogo de publicaciones - libros

Within Ad hoc networks, IP connectivity is achieved with the help of multi-hop routing; nodes are supposed to cooperate and act as routers for the benefit of the others. However, this cooperation-based paradigm has limitations, because nodes do not always make their resources available, properly. We propose a reputation-based routing protocol, called MOOR, for application to hybrid Ad hoc networks. MOOR aims at improving the reliability of communications between Ad hoc nodes and the gateway to an infrastructure-based network. We present an application–motivated performance analysis of our protocol MOOR, which allows to quantify the benefit in terms of radio network coverage increase. The impact of non-cooperative nodes on a MOOR protected network remains rather low, even for nodes located 5 hops away from the gateway.

To achieve high protocol efficiency is one of the primary goals in designing routing protocols for mobile ad hoc networks (MANETs), because high protocol efficiency implies low additional control overhead and power cost, which are two key issues in MANETs due to the inherited bandwidth and power-constrained characteristic. In this paper, an AODV improvement protocol with the Hello message mechanism is presented based on wireless link availability prediction. The simulation results demonstrate that the improved AODV improves the performance in terms of latency and protocol efficiency greatly, compared to the standard AODV with the periodic Hello message broadcast mechanism.

This paper investigates the sink positioning problem in Wireless Sensor Networks(WSNs) with the consideration of the energy-latency trade-offs. Energy-efficiency and low-latency are two major objectives in most researches on WSNs. Positioning the sink properly and exploiting its mobility can improve the two performances. A novel linear programming model is proposed to solve the sink positioning problem. Its objective function represents the overall performance of the network lifespan and the average packet latency. We can get not only the position pattern of the sink but also the sojourn time ratio for each possible position according to the optimization results. Simulations are accomplished on NS-2. The results show that compared with a static sink approach or a positioning approach which only concerns the energy-efficiency, our approach can greatly shorten the average packet latency and prolong the network lifespan, especially when the sensor nodes are distributed asymmetrically or the traffic load is unbalanced.

There are many applications of large scale sensor networks in which both the stimulus and the data collection stations are mobile (i.e. animal tracking, battlefield chasing). TTDD is a scalable and energy-efficient data dissemination model designed for this type of scenarios. However, TTDD only focused on handling mobile sinks. In this paper, we extend TTDD to deal with both mobile sources and sinks and evaluate the effectiveness of two potential extended TTDD schemes. Simulation results are presented to compare their performance in terms of energy consumption, delay and success rate. It is shown that the two schemes have similar performance when the moving speeds of the phenomena objects are slow. However, when the phenomena objects moving exceed certain speed, the advantages of one scheme over the other become unneglectable.

Many routing protocols for wireless sensor networks based on location information have been proposed such as GPSR, LAR, IGF, etc. When these routing protocols are used with existing MAC protocols, however, the sleep and wake-up scheduling of many MAC protocols degrades the routing protocol performance because of the long latency for periodic scheduling and synchronization overhead. In this paper, a cross layered routing and MAC protocol, CBT(Cell Back-off Time) protocol, has been proposed for the enhancement of successful routing in the Wireless Sensor Network environment considering the mobility of sensor nodes. Analysis and Simulation shows that CBT shows good performance when network density is high and nodes have mobility.

In wireless sensor networks, it is necessary and important to send information to all nodes. In some situation, every node has its own data to send to all the other nodes. The communication patterns are all-to-all broadcasting, which is called data exchange problem. In this paper, we present an efficient data exchange protocol using improved star trees. We divide the sensor area into four equal grids and each sensor node associates itself with a virtual grid based on its location information. These grids can be divided again if necessary. In each grid, we calculate the position of root node with location information of sensor nodes. Then, an efficient data exchange Star-Tree was constructed and used to achieve the exchange behavior in the grid. The fused data of each grid was sent to the center node. Simulations show that our protocol can prolong the lifetime about 69% to the multiple-chain protocols, and the delay can be reduced at least 35%.

IEEE 802.11-based wireless local area networks (WLANs) have been set up in many public places in recent years. It provides convenient network connectivity to mobile nodes (MNs) and allows users moving from one wireless network to another. With mobility protocol support, such as Mobile IPv6 (MIPv6), people can roam across wireless IP subnets without loss of network-layer connectivity. However, the handover latency may make users uncomfortable in MIPv6. To support seamless handover, an enhanced MIPv6 scheme, Fast Handovers for Mobile IPv6 (FMIPv6) [1], was been proposed. In order to further reduce the handover latency, integration IEEE 802.11 and MIPv6 is necessary. Unfortunately, when integrating the IEEE 802.11-based standard with FMIPv6, FMIPv6 always fails to perform predictive handover procedure and results in reactive handover. It is because of the protocol nature of IEEE 802.11 and the weak relationship between IEEE 802.11 and FMIPv6. Furthermore, a MN can not receive packets destined to it as it sends the FBU to the original access router (OAR). This would cause unnecessary packet loss and make the predictive handover have more packet loss then reactive. Those issues will cause quality of services degradation and make real-time application unreachable. In this paper, a low-latency MIPv6 handover scheme will be proposed. It is a FMIPv6-based scheme, which is based on an active-scan scheme link layer assistance. It has the advantage of FMIPv6 and can reduce the unnecessary packet loss when the handover occurs. Also, with the active scheme assistance, it can avoid the longest phase that IEEE 802.11 will enter, and can lower the handover latency.

Fair allocation of bandwidth and maximization of channel utilization are two important issues when designing a contention-based wireless medium access control (MAC) protocol. However, fulfilling both design goals at the same time is very difficult. Considering the problem in the IEEE 802.11 wireless local area networks (WLANs), in this work we propose a method using a p-persistent enhanced DCF, called , to achieve the weighted fairness among multiple priority classes in a WLAN. The key idea of this method is that when the back-off timer of a node reaches zero, the transmission probability is properly controlled to reflect the relative weights among data traffic flows so as to maximize the aggregate throughput and to minimize the frame delay at the same time. In particular, we obtain the optimal transmission probability based on a theoretical analysis, and also provide an approximation to this probability. The derived optimal and approximation are all evaluated numerically and simulated with different scenarios. The results show that the proposed method can fulfill our design goals under different numbers of priority classes and different numbers of hosts.

In this paper, a dynamic hierarchical location management scheme for Host Identity Protocol called DH-HIP is proposed to support micro-mobility. DH-HIP has a three-layer architecture which is managed by Rendezvous Server (RVS), Gate RVS and Local RVS (LRVS) respectively. The host selects its LRVS and computes the optimal size of administrative domain according to its current mobility and packet arrival rate. Furthermore, an analytical model to study the performance of DH-HIP and HIP is presented. Analytical results show that the signaling cost is significantly reduced through DH-HIP compared with the IETF HIP scheme under various conditions.

data storage is a fundamental paradigm for data management in wireless ad-hoc networks. It guarantees that data is stored at network nodes near specific geometric reference locations in the region where the network is deployed. In mobile ad-hoc networks, maintaining spatial proximity between data and its associated location requires explicit migration mechanisms in order to “keep the data in place”. In this paper we propose comprehensive policies for data migration that effectively maintain the spatial coherence of data given the particular characteristics of mobile ad-hoc networks. Using extensive simulations we show how the proposed policies outperform related migration approaches over a wide range of system parameter settings, in particular, node density, network dynamics, and migratable data size.