Thuan Ngo

Disaster-resilient networking: a new vision based on movable and deployable resource units

During the great east Japan earthquake on March 11, 2011, a lot of ICT resources - telecom switching offices, optical fiber links, and so forth - were completely or partially damaged due to the tremor and the resultant tsunami. As a consequence, the demand for ICT services explosively increased, mainly because the people of the affected areas were trying desperately to communicate with the outside world that led to a phenomenal rise in the network traffic. In the Nippon Telegraph and Telephone (NTT) East Corporation alone, 385 telephone offices stopped operating immediately following the earthquake because of power outages and disruption of facilities. Approximately 1.5 million users were cut off from using fixed-line telephone service. The demand for fixed-line and mobile telephone services jumped up to 10-50 times the usual. This gave rise to serious traffic congestion, and the emergency ICT networks and services could not deal with this issue sufficiently. This article proposes a network architecture that is resilient even through devastating disasters by effectively exploiting specially designed movable and deployable resource units, which we refer to as MDRUs. An MDRU having the ability to accommodate communication and information processing functions can be rapidly transported or moved to the disaster zone, and can be deployed within a reasonably short time to establish the network at the disaster site and launch ICT services. The concept and configuration of the network architecture based on the MDRU and its features are described in this article. Some preliminary simulation results are also reported to evaluate the performance of our adopted MDRU-based disaster resilient network.

On Minimizing the Impact of Mobility on Topology Control in Mobile Ad Hoc Networks

Although topology control has received much attention in stationary sensor networks by effectively minimizing energy consumption, reducing interference, and shortening end-to-end delay, the transience of mobile nodes in Mobile Ad hoc Networks (MANETs) renders topology control a great challenge. To circumvent the transitory nature of mobile nodes, k-edge connected topology control algorithms have been proposed to construct robust topologies for mobile networks. However, uniformly using the value of k for localized topology control algorithms in any local graph is not effective because nodes move at different speeds. Moreover, the existing k-edge connected topology control algorithms need to determine the value of k a priori, but moving speeds of nodes are unpredictable, and therefore, these algorithms are not practical in MANETs. A dynamic method is proposed in this paper to effectively employ k-edge connected topology control algorithms in MANETs. The proposed method automatically determines the appropriate value of k for each local graph based on local information while ensuring the required connectivity ratio of the whole network. The results show that the dynamic method can enhance the practicality and scalability of existing k-edge connected topology control algorithms while guaranteeing the network connectivity.

On the throughput evaluation of wireless mesh network deployed in disaster areas

After disasters such as earthquakes and tsunamis, the network infrastructures might be extremely damaged or destroyed while Internet connection becomes much more necessary. Therefore, deploying networks in disaster areas has received much attention especially after the great earthquake in Japan on March 11, 2011. Among many kinds of networks, Wireless Mesh Network (WMN) is considered as one of the most suitable solutions because it can easily configure a network without any wired infrastructure. In our national project on disaster recovery network, we attempt to build a WMN connecting remaining routers (i.e., the routers that remain functional after the disaster) by using a Movable and Deployable Resource Unit (MDRU) as a base station, which has processing servers, storage servers, and Internet connectivity. However, in order to have a good network design, many experiments such as simulations need to be done beforehand. In this paper, we provide an adequate throughput evaluation of the deployed network with many configurations, which are close to reality. The results demonstrate that the network can, at the same time, provide basic Internet access to a significantly large population of users.

Relay by Smart Device: Innovative Communications for Efficient Information Sharing Among Vehicles and Pedestrians

The combination of vehicles and mobile computers, such as smartphones and wearable devices, has provided many applications in our daily life. However, it is still limited to the applications in personal use. In fact, by utilizing the device-to-device technologies, which make use of the mobile device resources, vehicle-to-pedestrian (V2P), vehicle-to-vehicle (V2V), and pedestrian-to-pedestrian (P2P) communications can be more effective and convenient. In this article, we present a concept of relay by smart device that aims at information dissemination by smart communication devices, which can contribute to efficient information sharing among vehicles and pedestrians. We propose a novel technique for effectively forming and disbanding the groups of vehicles and pedestrians for their communications. The proposed mechanism is based on three criteria, namely, the stability of the group, the activity of the group, and the qualification as a group leader. Procedures for group forming and disbanding are introduced. We develop a prototype as a smartphone application using Wi-Fi technology, referred to as the second generation of relay by smartphone, which is the smartphone type of relay by smart device. The results of the field experiment show that the proposed group-based information sharing technology has a good potential to be utilized in V2P, V2V, and P2P communications.

A Spectrum- and Energy-Efficient Scheme for Improving the Utilization of MDRU-Based Disaster Resilient Networks

The movable and deployable resource unit (MDRU)-based network provides communication services in disaster-struck areas where the lack of spectrum and energy resources is intensified due to the high demand from users and the power outages after a disaster. The MDRU-based network attempts to apply spectrum- and energy-efficient methods to provide communications services to users. However, existing works in this field only consider spectrum efficiency or energy efficiency separately, in spite of the tradeoff relationship between them. Thus, we propose a scheme to improve the utilization of both spectrum and energy resources for better system performance. The considered MDRU-based network is composed of gateways deployed in the disaster area, which can replenish their energy by using solar panels. Our proposed scheme constructs a topology based on the top k spectrum-efficient paths from each sender and applies a max flow algorithm with vertex capacities, which are the number of transmissions that each gateway can send, which is referred to as transmission capability. The transmission capability of each gateway is determined by its energy resource and distances to its neighbors. Furthermore, we show that the proposal can be used for multisender-multireceiver topologies. A new metric named spectrum-energy efficiency to measure both spectrum efficiency and energy efficiency of the network is defined. Through analyses, we prove that a value of k exists such that the spectrum-energy efficiency of a given topology is maximized. Furthermore, our simulation results show that, by dynamically selecting appropriate value of k, the proposed scheme can provide better spectrum-energy efficiency than existing approaches. Moreover, our experimental results verify the findings of our analysis.

Bringing movable and deployable networks to disaster areas: development and field test of MDRU

Communication demand is paramount for disaster-affected people to confirm safety, seek help, and gather evacuation information. However, the communication infrastructure is likely to be crippled due to a natural disaster, which makes disaster response excruciatingly difficult. Although traditional approaches can partially fulfill the most important requirements from the user perspective, including prompt deployment, high capacity, large coverage, useful disaster-time application, and carrier-free usability, a complete solution that provides all those features is still required. Our collaborative research and development group has developed the Movable and Deployable Resource Unit, which is referred to as the MDRU and has been proven to have all those required features. Via extensive field tests using a compact version of an MDRU (i.e., the van-type MDRU), we verify the effectiveness of the MDRU-based disaster recovery network. Moreover, we demonstrate the further improvement of the MDRUs performance when it is complemented by other technologies such as relay-by-smartphone or satellites.

An efficient method for minimizing energy consumption of user equipment in storage-embedded heterogeneous networks

Recently, the issue of energy consumption of the UEs in heterogeneous networks has rapidly become a research focus area of the entire telecommunications community. This issue is obviously critical because the energy consumption of UEs can severely degrade their already limited battery capacity. In this article, we consider a heterogeneous network environment comprising base stations (each of which is also referred to as an eNB) with embedded storage that can serve as an effective cache-based traffic offloading technology in scenarios where many UEs simultaneously want to access popular contents of sports matches, live music events, and so forth. However, if many UEs are connected to only a few eNBs, they suffer from degraded throughput and increased transmission time. This longer transmission time eventually leads to increased energy consumption of UEs. To deal with this challenge, we propose an algorithm to reassign UEs to eNBs to minimize the total energy consumption of UEs with the constraint that their throughput is guaranteed. The effectiveness of our proposed algorithm is evaluated through computer-based simulations.

An Efficient Safety Confirmation Method Using Image Database in Multiple-MDRU-Based Disaster Recovery Network

Safety confirmation is one of the most important applications of disaster-resilient networking based on the movable and deployable resource unit (MDRU). With an embedded image database, a single MDRU can provide the safety confirmation application that allows users to search for the images that look similar to the people they are looking for. However, a network with multiple MDRUs may increase the image searching time of the safety confirmation application because the image databases are distributed and the capacity of the backbone wireless network constructed by connecting the MDRUs is also limited. Therefore, in this paper, we propose a safety confirmation method that guarantees the minimum searching time of users. The method includes four phases, namely, resizing and storing images, broadcasting small-size images, routing, and deciding image size to deliver to users. Based on mathematical analysis using the absorbing Markov chain, we estimate the expected searching time for each different size of images and choose the most appropriate size. Furthermore, we conduct extensive computer-based simulations to verify the findings of our analysis. The simulation results prove the existence of the optimal image size that minimizes the searching time and demonstrate the effectiveness of our proposed method.

A Novel Graph-Based Topology Control Cooperative Algorithm for Maximizing Throughput of Disaster Recovery Networks

Deployment of portable access points (APs) in disaster affected areas has been heralded by many contemporary researchers as a key technique to formulate disaster recovery networks. However, existing research works do not effectively address one of its key problems, i.e., the low capacity of the backbone network (constructed by the APs) which is unable to satisfy the high user demands emanating from the users in the local network of each AP. We consider cooperative communications to be a promising candidate to alleviate this problem, and formulate the trade-off relationship between the gained throughput and the network complexity. Also, we propose a novel graph-based topology control algorithm to solve the problem by exploiting cooperative communications to increase the inter-AP throughput gain. We first model the network by using a logical graph, where any two nodes are connected by a logical link if they are within the transmission range of each other. After that, k best paths, in terms of throughput gain, via mobile terminals, are found to connect any pair of APs. The constructed topology based on the resulted paths is used for cooperative communications. An in-depth analysis of the effect of the value of k on the network complexity and throughput gain is presented. Also, by introducing cooperative throughput gain speed as the utility of our proposal, we prove that there is an optimal value of k that maximizes the utility. Furthermore, extensive simulations are conducted to validate the analytical findings and demonstrate the effectiveness of our proposal.

GHAR: Graph-based hybrid adaptive routing for cognitive radio based disaster response networks

Although the importance of Disaster Response Networks (DRNs) has been highlighted in many researches, the requirement of spectrum agility has not been well addressed. In this paper, we focus on using all-spectrum cognitive radio for DRNs to fulfill this requirement. We consider a DRN constructed by Cognitive Radio Base Stations (CRBSs), which are deployed in the disaster affected area. Each CRBS is equipped with multiple antennas to support different frequency bands available in the area. Based on the considered DRN, we propose a Graph-based Hybrid Adaptive Routing scheme, which we refer to as GHAR. There are two phases in GHAR, centralized phase for topology formation and distributed phase for adaptive routing. In the centralized phase, we propose an algorithm that unites k non-overlapping minimum spanning trees to construct the topology for the next phase. We provide an analysis on the relationship between k and the adaptability with cognitive radio as well as the complexity of routing process. We also provide an analysis on the optimality of k. Furthermore, extensive simulations are conducted to validate our analysis. Simulation results confirm the effectiveness of our proposal and the existence of the optimal value of k.