Francisco Trujillo

An adaptive gateway discovery for mobile ad hoc networks

One of the main aspects that affect the performance of hybrid ad hoc networks is the discovery and selection of Internet gateways. Similar to conventional ad hoc route discovery, this procedure could be accomplished employing three different strategies: proactive, reactive and hybrid. In the proactive gateway discovery, the gateway periodically generates Modified Router Advertisement (MRA) messages. The election of the time between two consecutive MRAs (T) may greatly impact on the network performance (a low T could lead to unnecessary control packets meanwhile a high T could induce nodes keep invalid routes to external hosts). The optimum value of T depends on the network conditions as the load, the node density or the node mobility. In order to dynamically adjust the T interval, in this work we present a new adaptive scheme which is supported by a control system based on a genetic algorithm. The simulation results show that the proposed algorithm is able to decrease the network congestion and achieve lower end-to-end delay.

Improved Scheme for Adaptive Gateway Discovery in Hybrid MANET

This paper presents an adaptive scheme for gateway discovery in MANETs connected to the Internet. Basically, the proposed scheme reduces the flooding processes related to gateway discovery. To do so, the algorithm dynamically adjusts the interval of emission of the gateway advertisement messages to the need for updated routes to the gateway. The tuning is supported by the analysis of the spatial distribution of nodes in the MANET and by the impact that the relative position of nodes has on the route lifetimes. The simulations show that the proposed adaptive mechanism outperforms the conventional schemes: it decreases network saturation while it achieves lower end-to-end delay and it minimizes the routing overhead.

Adaptive gateway discovery for mobile ad hoc networks based on the characterisation of the link lifetime

Mobile ad hoc networks (MANETs) connected to the Internet require a gateway to operate. The gateway is responsible for providing the configuration parameters to the nodes by means of message exchanges. These messages are also necessary to create and/or update the route to the gateway in the mobile nodes. As MANET nodes move freely, these messages are generated at the beginning of the connections (to obtain the configuration parameters), when the route to the gateway breaks or when the gateway proactively sends them. This message exchange, also known as the gateway discovery procedure, has to be optimised in order to release wireless resources for the data transmissions. In this sense, this study proposes a novel technique by which the messages that the gateway periodically generates are exclusively forwarded in the areas where the links are expected to remain stable. By this, nodes are able to learn stable routes and, in turn, the messages generated because of the breakages of used links are avoided. From this parameter setting, the network performance is improved. The main difficulty of the technique is to determine the paths that are stable. For this purpose, the statistical characterisation of link duration in MANETs is employed in this study. The simulation results show the goodness of applying the proposed technique in terms of packet delivery ratio, protocol overhead and end-to-end delay.

Regional differences in personal saving rates in Spain

Abstract. The aim of this article is to analyze, from an aggregate perspective, the differences in personal saving rates among the Spanish regions at the NUTS II level from 1986 to 1994. In accordance with the postulates of the life cycle hypothesis, we present the main economic determinants for personal saving rates obtained from an aggregate personal saving model. Correcting for temporal and spatial dependence in the empirical model, the analysis suggests the existence of a significant and negative relationship between aggregate personal saving rates and wealth, access to credit and direct tax burdens. Likewise, a nearly significant positive relationship between personal saving rates and per capita gross disposable personal income has been detected.

An Adaptive Genetic Fuzzy Control Gateway Discovery to Interconnect Hybrid MANETs

In wireless communication, Mobile Ad Hoc NETwork (MANET) is a set of mobile nodes that are dynamically and randomly located in such a manner that the wireless link among nodes are often changing due to MANET dynamic features. In this MANET environment, if a device wants to connect to Internet, it must establish a communication with an Internet Gateway. The network performance between mobile nodes and Internet Gateway is affected by the stability, connectivity and network traffic load. The complex interactions among these parameters can be modelled using fuzzy set theory. This paper uses Artificial Intelligence (genetic algorithm and fuzzy system) to tune, adaptively, the control system that uses the gateway discovery schemes. The performance of fuzzy control is evaluated using simulation, and it is compared to others adaptive schemes explained in literature.

Interconnecting MANET and the internet a mobility approach

When a wireless node in an ad hoc network needs Internet access, it must select one gateway from the information sent in the Modified Router Advertisement (MRA) messages. In this paper, we propose an adaptive gateway discovery scheme that dynamically adjusts the frequency of MRA messages. This tuning is related to the mobility of the ad hoc network. The proposed tuning technique is supported by a control system which is configured by means of a new mobility factor obtained from the information contained in the MRA messages forwarded by the mobile nodes. Simulation results show that the proposed adaptive mechanism improves the conventional proactive schemes.

A stability approach to improve MANET-internet connection

Nowadays, there is an important effort in the research community to connect mobile devices in ad hoc networks with the Internet. In order to allow the connectivity to the Internet, a gateway that supports the wired single-hop and wireless multi-hop approaches is necessary. The wireless node, as laptops or personal digital assistants, must select the best gateway from the information that these elements send in the modified router advertisement (MRA) messages. The frequency of MRA messages generation by the Internet gateway clearly affects the network performance. In this paper, we propose an adaptive Gateway discovery scheme that dynamically adjusts the frequency of MRA messages and improves the conventional proactive schemes. The proposed scheme makes use of the mobility and connectivity properties of the network to tune the control system that sends the MRA messages.

An Optimized MANET Gateway Discovery Based on Fuzzy Logic

The interconnection of Mobile ad hoc networks (MANETs) and the Internet is supported by a Gateway. The gateway is responsible for informing about some configuration parameters as well as for facilitating the creation of the routes to the Internet in the MANET nodes. For these tasks, several control messages are generated. The way in which these messages are originated differentiates the integration supports for MANETs. In particular, in the hybrid Global Connectivity support the Gateway generates periodic Modified Router Advertisements (MRA) which are broadcast in an area close to the Gateway. The optimum values to define the periodicity of these messages and the area in which they are propagated depend on the network conditions. Therefore, an automatic and dynamic algorithm is recommended to be implemented in the Gateway to adjust these two parameters. In this sense, this paper presents a technique by which the interval of emission of the MRA messages is controlled by a fuzzy system. The fuzzy system captures several network conditions such as the link stability or the number of sources. The simulation results show that the proposed scheme outperforms other adaptive approaches for the gateway discovery in MANETs.