Luis J. de la Cruz Llopis

A centrality-based topology control protocol for wireless mesh networks

Nodes in wireless multi-hop networks establish links with their neighbors, which are used for data transmission. In general, in this kind of networks every node has the possibility of acting as a router, forwarding the received packets when they are not the final destination of the carried data. Due to the routing protocol procedures, when the network is quite dense the overload added by the routing management messages can be very high. To reduce the effects of this overload a topology control mechanism can be used, which can be implemented using different techniques. One of these techniques consists of enabling or disabling the routing functionality in every node. Many advantages result from selecting just a subset of nodes for routing tasks: reduction of collisions, protocol overhead, interference and energy consumption, better network organization and scalability. In this paper, a new protocol for topology control in wireless mesh networks is proposed. The protocol is based on the centrality metrics developed by social network analysts. Our target network is a wireless mesh network created by user hand-held devices. For this kind of networks, we aim to construct a connected dominating set that includes the most central nodes. The resulting performance using the three most common centrality measures (degree, closeness and betweenness) is evaluated. As we are working with dynamic and decentralized networks, a distributed implementation is also proposed and evaluated. Some simulations have been carried out to analyze the benefits of the proposed mechanism when reactive or proactive routing protocols are used. The results confirm that the use of the topology control contributes to a better network performance.

A game-theoretic multipath routing for video-streaming services over Mobile Ad Hoc Networks

The number of portable devices capable of maintaining wireless communications has increased considerably in the last decade. Such mobile nodes may form a spontaneous self-configured network connected by wireless links to constitute a Mobile Ad Hoc Network (MANET). As the number of mobile end users grows the demand of multimedia services, such as video-streaming, in such networks is envisioned to increase as well. One of the most appropriate video coding technique for MANETs is layered MPEG-2 VBR, which used with a proper multipath routing scheme improves the distribution of video streams. In this article we introduce a proposal called g-MMDSR (game theoretic-Multipath Multimedia Dynamic Source Routing), a cross-layer multipath routing protocol which includes a game theoretic approach to achieve a dynamic selection of the forwarding paths. The proposal seeks to improve the own benefits of the users whilst using the common scarce resources efficiently. It takes into account the importance of the video frames in the decoding process, which outperforms the quality of the received video. Our scheme has proved to enhance the performance of the framework and the experience of the end users. Simulations have been carried out to show the benefits of our proposal under different situations where high interfering traffic and mobility of the nodes are present.

Dynamic buffer sizing for wireless devices via maximum entropy

Buffer overflow is an important phenomenon in data networks that has much bearing on the overall network performance. Such overflow critically depends on the amount of storage space allotted to the transmission channels. To properly dimension this buffering capacity a detailed knowledge of some set of probabilities is needed. In real practice, however, that information is seldom available, and only a few average values are at the analyst disposal. In this paper, the use of a solution to this quandary based on maximum entropy is proposed. On the other hand, when wireless devices are taken into account, the transmission over a shared medium imposes additional restrictions. This paper also presents an extension of the maximum entropy approach for this kind of devices. The main purpose is that wireless nodes become able to dynamically self-configure their buffer sizes to achieve more efficient memory utilization while keeping bounded the packet loss probability. Simulation results using different network settings and traffic load conditions demonstrate meaningful improvement in memory utilization efficiency. This could potentially benefit devices of different wireless network technologies like mesh routers with multiple interfaces, or memory constraint sensor nodes. Additionally, when the available memory resources are not a problem, the buffer memory reduction also contributes to prevent the high latency and network performance degradation due to overbuffering. And it also facilitates the design and manufacturing of devices with faster memory technologies and future all-optical routers.

A Multi-User Game-Theoretical Multipath Routing Protocol to Send Video-Warning Messages over Mobile Ad Hoc Networks

The prevention of accidents is one of the most important goals of ad hoc networks in smart cities. When an accident happens, dynamic sensors (e.g., citizens with smart phones or tablets, smart vehicles and buses, etc.) could shoot a video clip of the accident and send it through the ad hoc network. With a video message, the level of seriousness of the accident could be much better evaluated by the authorities (e.g., health care units, police and ambulance drivers) rather than with just a simple text message. Besides, other citizens would be rapidly aware of the incident. In this way, smart dynamic sensors could participate in reporting a situation in the city using the ad hoc network so it would be possible to have a quick reaction warning citizens and emergency units. The deployment of an efficient routing protocol to manage video-warning messages in mobile Ad hoc Networks (MANETs) has important benefits by allowing a fast warning of the incident, which potentially can save lives. To contribute with this goal, we propose a multipath routing protocol to provide video-warning messages in MANETs using a novel game-theoretical approach. As a base for our work, we start from our previous work, where a 2-players game-theoretical routing protocol was proposed to provide video-streaming services over MANETs. In this article, we further generalize the analysis made for a general number of N players in the MANET. Simulations have been carried out to show the benefits of our proposal, taking into account the mobility of the nodes and the presence of interfering traffic.Finally, we also have tested our approach in a vehicular ad hoc network as an incipient start point to develop a novel proposal specifically designed for VANETs.

Topology control for wireless mesh networks based on centrality metrics

In this paper, a new mechanism for topology control in wireless mesh networks is proposed. We evaluate the application to this problem of the centrality metrics developed by social network analysts. Our target network is a wireless mesh network created by user hand-held devices. For this kind of networks, we aim to construct a connected dominating set that includes the most central nodes. Many advantages result from selecting just a subset of stations for routing tasks: reduction of collisions, protocol overhead, interference and energy consumption, better network organization and scalability. The resulting performance using the three most common centrality measures (degree, closeness and betweenness) is evaluated. As we are working with dynamic and decentralized networks, a distributed implementation is also proposed and evaluated.

Dynamic framework with adaptive contention window and multipath routing for video-streaming services over mobile ad hoc networks

The number of portable electronic devices capable of maintaining wireless communications increases day by day. Such mobile nodes may easily self-configure to form a Mobile Ad Hoc Network (MANET) without the help of any established infrastructure. As the number of mobile devices grows, the demand of multimedia services such as video-streaming from these networks is foreseen to increase as well. This paper presents a proposal which seeks to improve the experience of the end users in such environment. The proposal is called dCW-MMDSR (dynamic Contention Window-Multipath Multimedia Dynamic Source Routing), a cross-layer multipath routing protocol which includes techniques to achieve a dynamic assignment of the Contention Window of the IEEE 802.11e MAC level. In addition, it includes multipath routing suitable for layered coded video to improve the performance of the service. The operation is simple and suitable for low capacity wireless devices. Simulations show the benefits under different scenarios.The number of portable electronic devices capable of maintaining wireless communications increases day by day. Such mobile nodes may easily self-configure to form a Mobile Ad Hoc Network (MANET) without the help of any established infrastructure. As the number of mobile devices grows, the demand of multimedia services such as video-streaming from these networks is foreseen to increase as well. This paper presents a proposal which seeks to improve the experience of the end users in such environment. The proposal is called dCW-MMDSR (dynamic Contention Window-Multipath Multimedia Dynamic Source Routing), a cross-layer multipath routing protocol which includes techniques to achieve a dynamic assignment of the Contention Window of the IEEE 802.11e MAC level. In addition, it includes multipath routing suitable for layered coded video to improve the performance of the service. The operation is simple and suitable for low capacity wireless devices. Simulations show the benefits under different scenarios.

MAX-MIN based buffer allocation for VANETs

Many proposals have studied the optimization of the EDCA mechanism used by the IEEE 802.11p MAC layer to provide QoS. In this work, we focus on the queuing process done by the different Access Categories (ACs). We propose the use of a single common buffer with a prioritized buffer allocation algorithm inspired on the MAX-MIN principle for a fair sharing of a common resource. We test the proposed algorithm with a fixed and a dynamic guaranteed queue size for each AC. Results obtained from simulations in a multihop VANET scenario show that our approach outperforms traditional queuing system used in MAC 802.11p.

Load splitting in clusters of video servers

Nowadays, video on demand is one of the services more highly appreciated and demanded by customers. As the number of users increases, the capacity of the system that provides these services must also be increased to guarantee the required quality of service. An approach to that end is to have available several video servers at various distribution points in order to satisfy the different incoming demands (video server cluster). When a movie demand arrives to such a cluster, a load balancing device must assign the request to a specific server according to a procedure that must be fast, easy to implement and scalable. In this article we consider the problem of appropriately splitting this load to improve on the system performance. After an analysis of the video packet generation, we point out the similarity between this problem and that of optimally routing packets in data networks. With this similarity in mind, a new mechanism to select the appropriate video server is proposed. The purpose of this mechanism is to minimize the average packet transfer time (waiting time plus transmission time) at the video server cluster. In this way, we are able to obtain a dynamic load balancing policy that performs satisfactorily and that is very easy to implement in practice. The results of several experiments run with real data are shown and commented to substantiate our claims. A description of a practical implementation of the system is also included.

Multi Channel Allocation and Congestion Control for Smart Grid Neighborhood Area Networks

The evolution of traditional electricity distribution infrastructures towards Smart Grid networks has generated the need to carry out new research. There are many fields that have attracted the attention of researchers, among which is the improvement of the performance of the so-called Neighborhood Area Networks (NAN). In this paper, three mechanisms for these kind of networks are proposed, implemented and evaluated: traffic differentiation, multichannel allocation and congestion control. These proposals have been evaluated in the context of a wireless mesh networks (WMN) made up by a set of smart meter devices, where various smart grids (SG) applications are sending their data traffics. Each SG application must meet its unique quality of service (QoS) requirements, such as reliability and delay. To evaluate the proposals, we have built some NAN scenarios by using the ns-3 simulator and its 802.11s basic model, which we have modified to implement our techniques. Compared with the basic Hybrid Wireless Mesh Protocol (HWMP), our modifications, multiple channel (M-HWMP) and congestion control (MC-HWMP), show improvements in terms of packet delivery ratio and transit time.

Efficient deployment of gateways in multi-hop ad-hoc wireless networks

This paper proposes a mixed linear and integer optimization model for multi-hop ad-hoc networks to select the positions of the gateways over a certain area. This model mimics the routing behavior of such network and takes into account the maximum bandwidth capacity of the network gateways. We also include a suboptimal solution for the cases in which the complexity or the amount of the data make the optimal solution infeasible. Results in a pedestrian mesh network and in a VANET scenarios show that the model locates gateways in an efficient way and that the suboptimal solution is close to the optimal one in terms of the number of required gateways or the common selected gateways.