As fifth-generation wireless networks aim to meet the growing demand for enhanced mobile broadband (eMBB), while ensuring ultra-reliable and low-latency communication (URLLC), efficient resource-allocation strategies have become a critical research focus. Puncturing and superposition are promising techniques to satisfy the high data rate of eMBB, as well as the strict latency and high reliability of URLLC. In this study, we extend conventional puncturing and superposition techniques, originally applied in single-cell environments, to multi-antenna environments such as centralized radio access network (C-RAN) systems. Multi-antenna coordination facilitates puncturing across antennas and enables superposition by reusing the frequencies across antennas. However, puncturing and superposition for URLLC cause the degradation of eMBB data rates, and the superiority of either scheme depends on the effect on ongoing eMBB transmissions and the effect of interference. We provide a system model for resource allocation of puncturing and superposition in C-RAN where eMBB and URLLC coexist and formulate the optimization problem of minimizing the degradation of the eMBB data rate due to URLLC transmission by puncturing and superposition, respectively. Through computer simulations, we revealed the performance differences between puncturing and superposition techniques under various conditions. The results showed that dynamic selection between puncturing and superposition techniques based on real-time network conditions can enhance resource-allocation efficiency in C-RAN systems.

Large-scale disasters such as earthquakes and tsunamis have a history of affecting people’s lives and social activities, and there is a growing demand for creating a more disaster-resilient society. Terrestrial communication infrastructure such as base stations may be heavily damaged during a disaster, rendering it unable to provide people with network connectivity. Using an unmanned aerial vehicle (UAV) as an aerial base station is a notable solution to this problem because it can move quickly in the air and be deployed immediately after a disaster, regardless of road conditions. However, a moving UAV creates a lack of fairness when there are multiple pieces of ground-based user equipment (UE) due to two causes: some UEs have relatively fewer opportunities to communicate with the base station due to their locations, and the link rate of the UE is lower the further away the equipment is from the UAV’s flight trajectory. To solve this problem, we propose a bandwidth allocation algorithm designed to make adjustments after quantifying the unfairness arising from these causes. We then use computer simulations to confirm its effectiveness.

With the proliferation of Internet of Things (IoT) devices, the load caused by network demands has been increasing. This has direct consequences in terms of increased network requests and thus significantly higher energy consumption. To this end, this paper focuses on network power saving. In a cloud-radio access network with fiber-wireless, we propose a power saving method based on the optical line terminals (OLTs) and optical network units (ONUs), the equipment responsible for data transmission to and from the devices. Our proposed method is based on the novel idea of dividing the sleep phase of the ONUs into time slots, which facilitates synchronization and coordination in the whole system, thus increasing resource efficiency and bringing power economy not only to the ONUs, but also to the OLTs and the network as a whole. This is in contrast to the existing literature, which considers only ONUs or OLTs separately, without focusing on the cooperation within the system. Additionally, our proposed method was created with IoT traffic in mind. and it was designed to guarantee a maximum delay in order to make it applicable to mobile and real-time IoT. Finally, our proposed method allows the network to operate without external power sources for the ONUs by using power over fiber in conjunction with the OLT. Mathematical analyses show that our proposed method can successfully decrease the system’s energy consumption.

Unmanned aircraft systems (UASs) have attracted considerable attention in various industries. Furthermore, the use of unmanned aircrafts (UAs) is expected to spread rapidly and change our daily lives, in the future. However, while the number of UAs is increasing, the available frequency allocated to the UASs remains limited. Thus, when numerous UAs are used at high densities, the wireless communication between the UAs and the ground stations (GSs) may fail because of interference. To solve this issue, a time-division multiple access scheme can be adopted in the UASs. For efficient use of the allocated frequency, it is desirable that the UAs free from interference communicate simultaneously. Therefore, in this paper, we propose an efficient resource allocation scheme that increases the number of UAs that communicate simultaneously and improves the throughput. Our proposed scheme is based on the concept of multilayer virtual cells, and can increase the number of UAs that communicate simultaneously by considering the distance between the UAs and the GSs. The effectiveness of our proposed resource allocation scheme is evaluated through simulations. Our proposed scheme is found to be more efficient than other existing schemes, in terms of the number of UAs that can communicate simultaneously.

The evolution of cellular networks under Long Term Evolution (LTE) has paved the path for LTE-Advanced (LTE-A) Pro that proposes forward LTE enhancements for Machine Type Communications (MTC) and meets the stringent requirements for realization of the Internet-of-Things (IoT). This paper identifies possible improvements in LTE-A Pro's existing group paging scheme, which is more expedient for human-to-human communications and inadequate for IoT applications. We propose a novel energy efficient group paging scheme by considering diverse IoT characteristics including Quality of Service considerations. Simulation results reveal that our proposed approach can significantly reduce energy consumption of IoT devices over existing group paging schemes.

Recently, Wi-Fi Direct (WFD) enabled mobile Device-to-Device (D2D) communication emerged as a promising technique to carry out communication in disaster affected areas by exploiting its ability to operate without existing communication infrastructures. However, existing methods utilizing WFD randomly select communication partners, and therefore, are not effective in diffusing safety information pertaining to disaster victims over a wide coverage area. We address this issue in this paper, and propose a novel and efficient information diffusion method exploiting WFD by designing special virtual cells comprising the location information of the mobile devices. Our designed virtual cell enables information diffusion by allocating the same time to multiple areas without interference. We also evaluate the effectiveness of our proposed method through computer-based simulations. The simulation results demonstrate that the scheduling control of our proposal outperforms those of the conventional methods.

Mobile devices have several restrictions due to design choices that guarantee their mobility. A way of surpassing such limitations is to utilize cloud servers called cloudlets on the edge of the network through Mobile Edge Computing. However, as the number of clients and devices grows, the service must also increase its scalability in order to guarantee a latency limit and quality threshold. This can be achieved by deploying and activating more cloudlets, but this solution is expensive due to the cost of the physical servers. The best choice is to optimize the resources of the cloudlets through an intelligent choice of configuration that lowers delay and raises scalability. Thus, in this paper we propose an algorithm that utilizes Virtual Machine Migration and Transmission Power Control, together with a mathematical model of delay in Mobile Edge Computing and a heuristic algorithm called Particle Swarm Optimization, to balance the workload between cloudlets and consequently maximize cost-effectiveness. Our proposal is the first to consider simultaneously communication, computation, and migration in our assumed scale and, due to that, manages to outperform other conventional methods in terms of number of serviced users.

Unmanned aircraft systems (UASs) have attracted worldwide attention in recent years because of their potential applicability in a multitude of fields such as environmental monitoring and the communication provisioning environment. These applications enable data to be remotely collected from distant places through unmanned aerial vehicles (UAVs) equipped with communication devices. However, the communication range of a single UAV is limited because of the restrictions of the wireless transceiver as a result of the payload limitation. Therefore, UASs consisting of relay-based UAVs in which data are transferred via multiple UAVs have been studied to achieve long-distance communication with a high throughput. The time division long-term evolution advanced (TD-LTE-A) relaying technique may be applicable to UASs as it offers a reasonable solution. However, this technique is currently ineffective for UASs due to the limitation caused by its frame configuration. To alleviate this issue, in this paper, we propose a method to optimize radio resources based on the TD-LTE-A frame structure, which is capable of realizing efficient relay communication. Our proposed method considers a flexible frame configuration and updates cycle of control information to overcome the shortcoming of the conventional scheme. The effectiveness of the proposed radio resource optimization is demonstrated through simulation under varying environments.

Near real time monitoring system utilizing earth observation satellite constellation is expected for disaster management. However, these satellites may not have sufficient time to transmit all of their observed data to a ground station because low earth orbit (LEO) satellites pass over a ground station for a few minutes. Therefore, if the satellite stores more data than the size of transmission data to a ground station, it needs to transmit residual data after approaching other ground stations. As a result, it causes lack of timeliness due to the overhead time for fine tracking between a satellite and a new target of ground station. To deal with above mention, this paper proposes novel routing method to improve transfer ratio of whole observed data in a contact time. Relative to the conventional method which transmits data to a ground station, the proposed method divides observed data and modulates them as multi-carrier signals so as to distribute to two or more ground stations by multi-hop relaying. Furthermore, the satellite of this system switches inter-satellite link and satellite-to-ground link for own data and other satellite''''s data utilizing channelizer dynamically. The effectiveness of our proposal is verified through simulation results.

High Throughput Satellite (HTS), which has large communication capacity, is being developed to meet the rising demand for satellite communication system at the time of disaster. However, HTS adopts static frequency resource allocation, hence it is difficult to effectively utilize frequency resources. Therefore, many technologies for effectively utilizing frequency resources have been developed. However, the effectiveness of such technologies was not revealed clearly, because there was no quantitative evaluation method to measure their effectiveness. To create such method of evaluation, it is essential to consider the flexibility of frequency resource allocation. Thus, the construction of an evaluation method for flexibility is an important research issue. Therefore, in this research, we aim to construct a system analysis model to measure the effectiveness of frequency flexibility of satellite communication systems. Furthermore, we evaluate the effectiveness of frequency flexibilization technologies and quantitatively show the validity of such technologies.

Unmanned aircraft systems are expected to open pathways towards the development of many new services. Owing to their airborne flexible mobility, systems using unmanned aircraft (UA) have a significant potential to change our daily lives. However, several issues with such systems need to be addressed. In particular, wireless transmission of data such as high quality video from a UA to Ground Stations (GSs) is a major challenge affecting how airborne UAs are controlled. In this paper, we attempt to construct a base model of data transmission from UA to GSs in order to most efficiently use communication resources. To do this, we propose a method to allocate resources for individual UA missions that takes differences in requirements and surroundings into account. In this method, time division multiple access (TDMA)-based resource allocation is performed by anticipating the effective throughput according to the surrounding radio wave propagation environment. The effectiveness of this proposed resource allocation method is evaluated through simulation.

Mobile devices are naturally limited due to their portable sizes and will therefore never be equal to their desktop counterparts. To overcome this, Edge Cloud Computing can be utilized to execute tasks on behalf of the devices, allowing them to run applications that would normally be too demanding. In this service model, it is important to maintain a low Service Delay to keep the service transparent to the user. This can be achieved by focusing on lowering the Transmission Delay and Processing Delay. While existing approaches in the literature focus on one of those two, we postulate that only when considering both delays you can efficiently lower Service Delay and provide quality to all applications. In order to do that while being feasible, we propose a method based on Particle Swarm Optimization for lowering Service Delay in Edge Cloud Computing. Our proposal is shown to be close to optimality while still maintaining a low execution time for multiple cloudlets scenarios. Moreover, our proposal outperforms existing approaches from the literature with single focus on computation or communication, even in situations with high processing and transmission burdens, proving the superiority of a dual focus approach.

Unmanned aerial vehicles (UAVs) can be used for a wide variety of applications, including agriculture, infrastructure maintenance, and disaster response. In this paper, we focus on the use of UAVs for disaster response. Multiple UAVs equipped with communication terminals can be deployed to construct an airborne network connecting isolated areas. Another use is for real-time video transmission from a UAV to a ground station, using multiple UAVs operating simultaneously by different organizations, e.g., rescue teams, fire departments, broadcasting companies, and so forth. In both cases, frequency resources must be shared efficiently among adjacent UAVs. Thus, we describe a radio resource management system for UAVs. The focus of this paper is data communications, rather than the broader issue of command and control communications. First, we present experimental results from field experiments using WiFi communication terminals that do not have centralized radio resource management functionality. Then, we propose a centralized resource allocation technique that assumes an orthogonal frequency division multiplexing (OFDM)-based communication system, using resource blocks consistent with the long-term evolution (LTE) standard.

Unmanned aerial vehicles (UAVs) have attracted attention as a means of monitoring the environment because of their ability to remotely collect data from distant places. However, due to the payload limitations, the communication range of UAVs is limited. Therefore, UAVs need to cooperate with other UAVs in order to achieve high speed and long distance communication. In this paper, we construct a base model of data transmission over multi-hop UAV networks. Time Division, Long Term Evolution Advanced (TD-LTE-A) relaying is a technique that may be applicable to such networks. However, it is currently not suitable for UAV networks due to the limitation caused by its frame structure. Therefore, in this study, we propose a TD- LTE-A based radio access scheme that can realize efficient relay communication. The effectiveness of this proposed radio access scheme is evaluated through simulation.

The development of technologies related to the Internet of Things (IoT) provides a new perspective on applications pertaining to smart cities. Smart city applications focus on resolving issues facing people in everyday life, and have attracted a considerable amount of research interest. The typical issue encountered in such places of daily use, such as stations, shopping malls, and stadiums is crowd dynamics management. Therefore, we focus on crowd dynamics management to resolve the problem of congestion using IoT technologies. Real-time crowd dynamics management can be achieved by gathering information relating to congestion and propose less crowded places. Although many crowd dynamics management applications have been proposed in various scenarios and many models have been devised to this end, a general model for evaluating the control effectiveness of crowd dynamics management has not yet been developed in IoT research. Therefore, in this paper, we propose a model to evaluate the performance of crowd dynamics management applications. In other words, the objective of this paper is to present the proof-of-concept of control effectiveness of crowd dynamics management. Our model uses feedback control theory, and enables an integrated evaluation of the control effectiveness of crowd dynamics management methods under various scenarios. We also provide extensive numerical results to verify the effectiveness of the model.

Due to physical limitations, mobile devices are restricted in memory, battery, processing, among other characteristics. This results in many applications that cannot be run in such devices. This problem is fixed by Edge Cloud Computing, where the users offload tasks they cannot run to cloudlet servers in the edge of the network. The main requirement of such a system is having a low Service Delay, which would correspond to a high Quality of Service. This paper presents a method for minimizing Service Delay in a scenario with two cloudlet servers. The method has a dual focus on computation and communication elements, controlling Processing Delay through virtual machine migration and improving Transmission Delay with Transmission Power Control. The foundation of the proposal is a mathematical model of the scenario, whose analysis is used on a comparison between the proposed approach and two other conventional methods; these methods have single focus and only make an effort to improve either Transmission Delay or Processing Delay, but not both. As expected, the proposal presents the lowest Service Delay in all study cases, corroborating our conclusion that a dual focus approach is the best way to tackle the Service Delay problem in Edge Cloud Computing.

A concept of Cloud Radio Access Networks (C-RANs) with Power over Fiber (PoF) is expected to work as a post- disaster access network architecture. In this architecture, since external power is supplied to Remote Radio Heads (RRHs) through the optical-fiber cable for data communication, RRHs can operate even when power cables are disrupted due to disasters. This network, however, needs to reduce the power consumption for RRH operation and consider Quality of Experience (QoE) to provide sustainable service with enough user satisfaction. To this end, we propose user position guidance approaches which give advices of the best position to users. Our proposed approaches are able to achieve high sustainability while satisfying the QoE constraint. Furthermore, the effectiveness of our proposed approaches is evaluated by numerical calculation.

Recently, unmanned aerial vehicles (UAVs) have attracted attention as a means to observe a terrain due to their ability to fly above the place to be observed and collect information (e.g., picture, video and sensor data) easily. Moreover, UAVs can transmit data through equipped wireless transceivers. However, because the payload of UAVs is limited, the performance of the transceiver is limited as well. Therefore, UAVs need to cooperate with other UAVs for high speed and long distance data transmission. In this article, we suppose a network model for transmitting in real time observed data in a multihop relay communication; then we take into account parameters related to the observation area (e.g., area size, distance between a base station and observation area) and signal attenuation by obstacles (e.g., buildings, trees). Finally, we propose a way to maximize the network performances affected by those parameters in the network.

Wireless communication devices have spread widely in our society. However, they usually depend heavily on communication infrastructure, leaving them vulnerable to disasters or congestion of base stations. In these situations, a method to send out data without the support of infrastructure is required. Data transmission by D2D communication is a reliable method that does not rely on infrastructure. In this paper, we aim to improve the data dissemination using D2D transmission by applying the concept of assigning “modes” to devices according to their own mobility. In our study, we assume a multi-channel environment, where devices will be allocated different amounts of frequency channels according to their modes. We propose a mode selection function that uses velocity information of the devices to assign modes. By using this function, it is possible to allocate more frequency channels to devices of high mobility, so that they can transmit their data to more devices as they move through a wide area. By mathematical analysis, we evaluate the fairness of disseminated data density among devices of various velocities and the obtained results indicate the effectiveness of the proposed method for improving the efficiency of data dissemination.

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.

The earth observation missions have improved its sensor performance, it results in a huge amount of data to be stored and transmitted to a ground station. Although, satellite to ground transmitter had been usually used X band, migration to Ka band has been studied in recent years for broadband transmission. Relative to X band, higher frequency has severe atmospheric effects, site diversity is one of the popular technique to mitigate rain attenuation. However, if Signal to Noise power Ratio (SNR) is different between receivers because of receiving antenna gain and rain attenuation, diversity gain decreases. This paper proposes novel beam controlling method to improve SNR performance for satellite to ground transmission. The proposed method estimates SNR in each of candidate transmitting antenna boresight, and update boresight in order to be equal SNR between receivers. Simulation results show that, proposed method improves SNR especially at a low elevation angle.

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.

There are many applications which cannot be executed by mobile devices due to their limitations in memory, processing, battery, among others. One solution to this would be offloading heavy tasks to cloud servers in the edge of the network, in a service model called Edge Cloud Computing. The main Quality of Service requirement of this model is a low Service Delay, which can be achieved by lowering Transmission Delay and Processing Delay. Works in literature focus on either one of those two types of delay. This paper, however, argues that an approach which combines transmission and processing technologies to lower Service Delay would be more efficient. This idea is defended by an analysis of the service model and existing stochastic modeling of the Edge Cloud Computing system. We conclude that a dual focus approach would be the only way of truly minimizing the Service Delay, therefore being the desired method to improve Quality of Service. We conclude by laying the foundation for a future model that follows such concept.

Both the variety of communication devices and their options in connecting to the Internet are continuously increasing due to the advances in numerous attractive network applications. These trends make designing the network much more complex. Legacy network design only had to consider predefined applications using common end-point devices such as plain old telephone system. On the other hand, the current and future network, especially in the access part, is expected to be universal so as to cover not only residential users, but also mobile users, and the huge number Internet of Things devices for the sake of cost efficiency. The key issue is the difficulty of designing a complex network that is also extremely energy efficient, particularly the future access system. Although many studies have attempted to improve the bandwidth utilization or energy efficiency in multiple-wavelength systems, little is known about how it will be impacted by the divergence among these multiple concrete services. In order to solve this energy issue, we propose a service multiplexing method with a profile-based network architecture, where each device declares its traffic profile. Our concept provides the feasible and practical control of complex network. It differs markedly from the methods that control the traffic at the packet or session level as it is easy to apply in actual networks.

In the era of the Internet of Things (IoT), the access network should provide Internet connectivity to huge numbers of wireless sensor nodes that are collecting data. For most sensor nodes, the macro cells of cellular networks provide cost-effective connectivity. However, covering the remaining nodes, which are either in the out-of-service state or have short-range wireless interfaces only, is a difficult issue. For example, when deploying small cells densely to provide fuller node coverage, the cost of the small cells should be well considered. From the perspective of economy, small cells that use the passive optical network (PON) and moderately priced wireless interfaces, called fiber-wireless (Fi-Wi) in this paper, seem the most promising candidates. However, the flexibility in Fi-Wi system deployment is strictly constrained by the need for a stable power source. Because most of the PON systems have been developed for fiber to the home (FTTH), the gateway node on the customer premise continuously consumes power and thus requires a stable power source. Therefore, the key issue is how to reduce the power consumption of the Fi-Wi gateway node drastically enough to run continuously with only battery and/or solar power. Additionally, the power-saving approach must meet the requirements of the IoT applications at the same time. We focus on the deep sleep approach, which turns OFF almost all the components, with significant power savings at the cost of a drop in quality of service (QoS). This paper proposes methods to control the deep sleep while assuring successful packet reception.

In this paper, we study the outage probability of device-to-device (D2D)-communication-enabled cellular networks from a general threshold-based perspective. Specifically, a mobile user equipment (TIE) transmits in D2D mode if the received signal strength (RSS) from the nearest base station (BS) is less than a specified threshold β ≥ 0; otherwise, it connects to the nearest BS and transmits in cellular mode. The RSS-threshold-based setting is general in the sense that by varying β from β = 0 to β = ∞, the network accordingly evolves from a traditional cellular network (including only cellular mode) toward a wireless ad hoc network (including only D2D mode). We provide a unified framework to analyze the downlink outage probability in a multichannel environment with Rayleigh fading, where the spatial distributions of BSs and TIEs are well explicitly accounted for by utilizing stochastic geometry. We derive closed-form expressions for the outage probability of a generic TIE and that in both cellular mode and D2D mode and quantify the performance gains in outage probability that can be obtained by allowing such RSS-thresholdbased D2D communications. We show that increasing the number of channels, although able to support more cellular TIEs, may result in an increase of outage probability in the D2D-enabled cellular network. The corresponding condition and reason are also identified by applying our framework.

Recently, many large-scale natural disasters, such as earthquake and tsunami occur all over the world. One of the major problems after a disaster is the damage caused to the communication and power infrastructure, such as damaged base station and power grid. As a result, disaster victims are unable to communicate with outside area for an extended period of time. Therefore, it is essential to deploy a communication network, which can operate even without power supply or infrastructure. In this paper, we focus on Wireless Mesh Networks (WMNs), which consists of Solar Powered Base Station (SPBS) equipped with air interfaces. These WMNs can be promptly setup. However, because the power generated from solar panel is easily affected by weather condition, it is insufficient and unstable. Additionally, because the power consumption is affected by the distance between the SPBSs and the number of wireless links in each SPBS, it is difficult to maintain network connectivity in the WMNs that are consisted of SPBSs. Therefore, to address the network connectivity problem in the assumed network, we aim to reduce the power consumption of the wireless links by controlling the on-off cycle of air interfaces. We first analyze the network connectivity issue in disaster area and formulate this problem, and propose the on-off scheme of controlling the wireless links of air interfaces based on graph theory. Simulation results of our proposal show that our proposed scheme can ensure the network connectivity.

With the development of wireless communication technology, the utilization of the ambient information that the network users observe has attracted much attention. In this paper, we focus especially on the utilization of observed environmental signals for authentication systems. Ambient information taken as unique data at a particular time and place can be utilized to construct stronger authentication systems. However, since the environmental condition of the network is different for each location, which has a huge effect on the observed ambient information in the area, required data are also different for each place. Thus, in this paper, we propose an efficient data collection method which dynamically changes the way data is collected according to the requirements and the network condition. More specifically, our proposal aims to collect uniform amount of fresh data from areas with varying population density. Additionally, an algorithm to improve the efficiency of our proposal regarding the accommodation of the environmental condition of the network is introduced. Moreover, numerical results verify the effectiveness of our proposal.

After a disaster strikes, the disaster victims usually become isolated and unable to utilize communication services for an extended period of time. Therefore, it is essential to establish a communication network that can operate when there is no power or infrastructure. In this paper, we focus on Satellite/Solar-powered Mesh Integrated Networks (SMIN), which are composed of a communication satellite, Earth Stations (ESs) and solar-powered Mesh Routers (MRs). A SMIN can connect to external networks via satellite and provide communication services in a large area through the wireless mesh network (WMN). To maximize the amount of communication traffic from the WMN, we aim to optimize the number of ESs and its deployment. When the number of ESs increases, the hop count between a MR and its closest ES decreases, thus resulting in an improved connectivity in the route. However, since the ESs share the bandwidth of satellite, allocated bandwidth to each ES decreases as the number of ESs increases. Therefore, we aim to optimize the number and deployment pattern of ESs. Additionally, we validate the amount of aggregated traffic that can be sent to the satellite through numerical analysis.

Based on the tool of stochastic geometry, we present in this paper a framework for analyzing the coverage probability and ergodic rate in a D2D overlaying multi-channel downlink cellular network. Different from previous works, 1) we consider a flexible new scheme for mobile UEs to select operation mode individually, under which a mobile UE decides to establish a cellular link (with a BS) or a D2D link (with a neighboring UE) based on the pilot signal strength received from its nearest BS; 2) we allow a mobile UE which is located far from BSs to connect to a nearby BS via another intermediate UE in a two-hop manner. Our results indicate that the developed framework is very helpful for network designers to efficiently determine the optimal network parameters at which the optimum system performance can be achieved. Furthermore, as corroborated by extensive numerical results, enabling the D2D link based two-hop connection can significantly improve the network coverage performance, especially for the low SIR regime.

Wireless Data Center Network (Wi-DCN) is considered one of the most promising future data center architectures due to its low installation and management cost and high flexibility of network design. However, the existing Wi-DCN is, still, not capable of providing an efficient big data mining service such as MapReduce because its topology (i.e., Cayley graph with same degree) cannot achieve enough connectivity on the breakdown of servers and spectrum efficiency, which are important factors to improve the performance of big data mining. Therefore, in order to modify the existing Wi-DCN for big data mining, this paper proposes a spherical rack architecture based on a bimodal degree distribution that improves both failure tolerance and spectrum efficiency. Extensive computer simulations demonstrate the effectiveness of our proposed rack architecture in terms of data transmission time required for MapReduce under a failure-prone environment.

The development of technologies for realizing “Internet of Things” inspire many applications which utilize the things' network. Additionally, the ambient information of the things including various information collected via the network has attracted much attention as useful data for novel applications. By collecting the ambient information from things and constructing databases of them, it is expected to make our lives smarter and more convenient. On the other hand, to maximize the advantage of such a database, it is important to keep the information in the database as fresh as possible. However, in order to keep the freshness of the database, periodically collecting data with short interval is needed, which causes heavy traffic congestion when we use the traditional access control schemes in the existing communication network technologies. Thus, in this paper, we propose a novel access control scheme to keep the freshness of the database while avoiding traffic congestion. Additionally, an optimization to improve the efficiency of our proposed method is provided with mathematical expressions. Moreover, numerical results verify the effectiveness of our proposal.

A concept of cloud radio access networks (C-RANs) is becoming a popular solution to support the required communication quality for new emerging service in the future network environment, i.e., more than 10 Gbps capacity, less than 1 ms latency, and connectivity for numerous devices. In this paper, we envision a C-RAN based on passive optical network (PON) exploiting power over fiber (PoF), which achieves low installation and operation costs since it is capable of providing communication services without external power supply for large amount of remote radio heads (RRHs). This network, however, needs to reduce the optical transmission power of PoF due to the fiber fuse issue. Additionally, the diversification of services, devices, and personality indicates the need to improve user satisfaction, i.e., quality of experience (QoE), based on the user's perspective, which is different from previous approaches that aim to guarantee quality of services (QoS). Therefore, we propose a QoE-guaranteed and power-efficient network operation strategy. Our proposed operation is able to reduce the transmission power while satisfying the QoE constraint by controlling both the schedule of RRH's sleep and optical transmission power of PoF. Furthermore, the effectiveness of our proposed operation scheme is evaluated through extensive computer simulations.

Fiber-Wireless (FiWi) network is a classification of network that combines the massive bandwidth of the optical network and the reach of the wireless network. FiWi networks are usually composed of an optical and a wireless component. Since both components are designed to work independently, some mechanisms, such as the different power saving methods in both components, may not cooperate with each other and this may result in an undesirable performance. In this paper, we identify that the conflicting power saving mechanisms cause unnecessary energy consumption and introduce additional delay to the overall FiWi network. To cope with this problem, we propose a novel ONU sleep method, which dynamically control the ONU sleep period based on the STAs energy control mechanism. Finally, we demonstrate that our proposed method has shorter latency and is more efficient in term of energy consumption than the existing method.

Delay-tolerant networks (DTNs) are a promising network architecture which can provide reliable multi-hop message transmission between participating mobile nodes in an unfavorable environment that is prone to link disruption and disconnection by replicating and relaying messages without any need of physical infrastructure. Additionally, DTNs can also operate as cooperative DTNs to extend the coverage of other type of networks by carrying the messages that originate from farther away base station in a multi-hop fashion to the base station. In this paper, we focus on these cooperative DTNs and propose a novel routing scheme, ring distribution routing (RDR), that controls the replication and forwarding based on the source node surroundings. This paper also analyzes the reliability and buffer efficiency in RDR. Furthermore, we show that RDR provides the reliable and immediate message delivery in any environment through extensive computer simulations.

Recent technological advances in electronics, sensors, and communications have accelerated the widespread deployment of Unmanned Aircraft System (UAS)-aided applications. Nevertheless, networks composed of multiple UAS and ground stations, referred to as UAS-aided communications networks, have yet to receive sufficient research attention. In this paper, we address a fundamental research challenge stunting such networks, which is how to fairly maximize the energy efficiency (throughput per energy) in networks comprising adaptive modulation-capable ground nodes. For the mobility pattern intrinsic to the UASs, we demonstrate how adaptive modulation is affected. Furthermore, we formulate the problem of maximizing fair energy efficiency as a potential game that is played between the multiple ground nodes and substantiate its stability, optimality, and convergence. Based on the formulated potential game, a data collection method is proposed to maximize the energy efficiency with a fairness constraint. Additionally, we analyze the Price of Anarchy of our proposed game-theoretic data collection method. Extensive simulations exhibit the effectiveness of our proposal under varying environments.

In recent years, tremendous amount of traffic is delivered by the Internet. However, ground networks cannot provide communication environment to disaster areas and isolated areas such as mountain and sea. Thus, as the next generation networks, optical satellite networks have attracted much attention because of many advantages such as high capacity, disaster resistance, and large coverage. Since optical communication can increase traffic rate in comparison with radio wave, the optical satellite networks can provide high speed communication. On the other hand, optical communication is greatly influenced by the atmospheric condition, which can lead to traffic congestion. Thus, we focus on utilizing satellites with embedded mass storage device to manage large amount of traffic in the network. Since satellites embedded mass storage device can store the traffic temporary, it is possible to deliver the data when the downlink condition is more favorable. However, there are no traffic control method that effectively use mass storage device embedded in satellite while taking into account optical link between satellite and optical ground station. Therefore, in this article, we propose a new traffic control method to effectively use mass storage device embedded in satellite according to optical downlink condition between satellite and optical ground station.

The design of a wireless network is often critically affected by issues such as determining the optimal density of Access Points (APs) and the optimal channel assignment by exploiting partially overlapped channels (POCs) for significantly improving the network performance in terms of maximizing the overall network capacity. Contemporary research works have traditionally dealt with these two problems in an isolated manner though they should be considered within the same problem formulation. Furthermore, even though deployment of additional APs can improve the network capacity in case there are a few APs in a given area, the APs cannot be indefinitely added to the wireless network. This means that there is an upper bound to the network capacity maximization with respect to the number of APs. In fact, the network capacity starts to dramatically decrease when the number of deployed APs becomes excessive. This performance decrease can be accredited to the substantial interference among the high number of deployed APs. In order to address this challenge, in this paper, we propose an approach to jointly optimize the number of APs and POCs assignment. Our proposal derives the existence of the optimal density of APs with POCs, and models the POC assignment to the deployed APs from a novel perspective. Computer-based simulations are conducted to demonstrate the effectiveness of our proposal.

The recent increase of wireless devices (i.e., STAtions (STAs)) brings forward an increase of energy consumption. We address the energy consumption issues for STAs in Wireless Mesh Networks (WMNs). One of the available techniques for power-saving is the sleep technique. However, since the common transmission mode from the STA to the server is performed based on end-to-end transmission, this results in increase of energy consumption of the STAs since they cannot enter sleep mode until end-to-end communications are completed. To cope with the issue, we focus on an Access Point equipped with External Storage (APES), which provide end-to-end communication instead of STAs. Using this, STAs can shorten the transmission time and decrease the energy consumption since they communicate with neighboring APES. In this paper, we propose a novel method to select the adequate APES as a proxy server based on the number of STAs and the amount of traffic from STAs. The proposed method effectively transmits data and reduces the energy consumption of the STAs. Moreover, we validate the efficiency of the proposed APES selection method through numerical analysis.

Recent technological advances in electronics, sensors, and communications devices have facilitated the proliferation of Unmanned Aircraft System (UAS)-aided applications. However, the UAS-aided communications networks are yet to receive sufficient research endeavor. In this paper, we address one of the most important research challenges pertaining to UAS-aided networks comprising adaptive modulation-capable nodes, namely how to fairly maximize the energy efficiency (throughput per energy). For the mobility pattern innate to the UAS, we demonstrate how the adaptive modulation behaves. Furthermore, we formulate the problem as a potential game that is played between the UAS and the network-nodes, and prove its stability, optimality, and convergence. Based upon the potential game, a data collection method is envisioned to maximize the energy efficiency with the fairness constraint. Additionally, we analyze the Price of Anarchy (PoA) of our proposed game. Extensive simulations exhibit the effectiveness of our proposal under varying environments.

Reference Point Group Mobility (RPGM) has been a practical mobility model used to efficiently capture the potential correlation among mobile nodes in many important applications. In this paper, we explore the throughput-delay tradeoff in a mobile ad hoc network (MANET) operating under the RPGM model and also a general setting of node moving speed. In particular, we consider a MANET with unit area and n nodes being divided evenly into Θ(nα) groups, a Є [0,1], where the center of each group moves according to a random direction model with speed no more than v e [0,1]. We determine the regions of per node throughput, average delay and their tradeoffs that can be achieved (in order sense) in such a network. For the regime of v =0, we first prove that the per node throughput capacity is Θ(n−α/2), and then develop a routing scheme to achieve this capacity, resulting an average delay of Θ (max1/2, n1-α) for any α Є [0,1]. Regarding the regime of v > 0, we prove that the per node throughput capacity there can be improved to Θ(1), which is achievable by adopting a new routing scheme with an average delay of Θ(max{n1-α, na/2/v}) for v = o(l) and Θ(n) for v = Θ(1). The results in this paper help us to have a deep understanding on the fundamental performance scaling laws and also enable an efficient throughput-delay tradeoff to be achieved in MANETs with correlated mobility.

MapReduce architecture has been considered as one of the most promising candidates for efficient and reliable big data mining. While current MapReduce is basically designed for data center and enterprise networks, in which a number of servers are interconnected with optical fiber cables, prospective MapReduce would be applied in optical-wireless environment such as optical-wireless data center network, fiber-wireless (FiWi) access network, and so forth. To modify MapReduce for opticalwireless hybrid network, we need to answer the fundamental research problem, “How does MapReduce architecture use optical and wireless resources for task allocation?” To answer this question, this paper reveals some challenging issues and proposes a context-aware task allocation scheme that is designed by considering characteristics of both optical and wireless communications. Our proposed task allocation scheme can minimize the completion time of big data processing. Numerical results are presented to demonstrate the effectiveness of our proposed method compared with existing task allocation schemes.

In recent years, disasters happened in many places, and resulted in power shortage and communication interruption. The Wireless Mesh Networks (WMNs) constituted by Renewable Energy-enabled Base Station (REBS) is regarded as a powerful solution in post-disaster recovery, for its energy harvesting ability and the ready-made facilities. However, this solution needs to address several challenges such as unstable power supply, limited bandwidth and long-term optimization. In this paper, we focus on the issue of energy efficiency when realizing the maximal network throughput in a period of time, by the combination of energy usage and network data distribution. To this end, we firstly analyze the unique features of REBS and its associated network in disaster area. Then a throughput-maximization problem is proposed in order to figure out the maximal network throughput. Based on the maximal value, we count out the most energy-efficiency result while guaranteeing the maximal network throughput. We formulate the proposed model into a two-stage Mixed-Integer Linear Programming (MILP) problem and solve it by branch-and-bound algorithm. Simulation results demonstrate our considered two-stage energy efficient scheme strikes a balance between network throughput and its associated energy consumption, and outperforms the existing schemes.

Since communications services become much more demanded after disaster strikes, it is necessary to promptly set up a temporary communications infrastructure to provide services to those in need. The Movable and Deployable Resource Unit (MDRU) based Wireless Mesh Network (WMN) is an attractive candidate to achieving this goal. In MDRU based WMN, the MDRU is transported to the disaster affected area by either ground or air transportation like truck or helicopter. After arriving at the disaster area, it configures any remaining wireless Access Points (AP) in the area to provide connectivity services. This work provides an insight on the performance of MDRU based WMN under the situation where multiple MDRUs are deployed within close region to increase the overall coverage and performance of the network. A simulation is conducted to estimate the performance of the network under both scenarios where mesh tier operates under a single channel and where a channel assignment scheme is applied. We show that the performance of MDRU based WMN can be greatly enhanced by deploying multiple MDRUs to the area. However, since the number of available MDRUs is limited, using more MDRUs than necessary is not efficient. We discuss some of the factors that should be taken into account when selecting an appropriate number of MDRUs for a single area.

By combining optical networks and wireless networks, Fiber Wireless (FiWi) networks are able to provide broadband and flexible communication. In order to reduce energy consumption of STAtions (STAs) and Optical Network Units (ONUs), there are several power saving mechanisms in optical networks and wireless networks. Generally, power saving mechanisms lead to delay. The delay problem becomes more critical in FiWi networks where multiple power saving mechanisms are used at the same time to reduce energy consumption. In this paper, we analyze the delay by considering the relationship between the power saving mechanisms, which independently control the STAs and the ONUs in FiWi networks, and point out the problem that two delays can occur at the same time. In order to address the problem, we propose a novel power saving mechanism of STAs, which controls the STAs by synchronizing two power saving mechanisms for ONUs and STAs. Through mathematical analysis and numerical evaluation, we confirm that the proposed method can significantly reduce energy consumption without any increase in latency.

In recent years, HETerogeneous NETworks (HET-NET) arises as a promising network technique to manage a large number of mobile devices. By using the networks having different coverage size in the HETNET, it enables to increase the network capacity drastically. However, sometimes variations in user distribution causes inhomogeneous traffic load among the networks having different coverage size in the HETNET. On the other hand, Device-to-Device (D2D) communication technologies have attracted much attention as another solution to increase the network capacity. The direct communication between user devices creates flexible networks. Thus, we focus on utilizing D2D communication technologies in HETNET to avoid the inhomogeneous load among the networks having different coverage size. In this paper, a traffic detouring method is proposed and the advantage of the proposed method is analyzed with some mathematical expressions. Additionally, numerical results demonstrate the effectiveness of our proposal.

Due to the increasing popularity of multimedia streaming applications and services in recent years, the issue of trusted video delivery to prevent undesirable content-leakage has, indeed, become critical. While preserving user privacy, conventional systems have addressed this issue by proposing methods based on the observation of streamed traffic throughout the network. These conventional systems maintain a high detection accuracy while coping with some of the traffic variation in the network (e.g., network delay and packet loss), however, their detection performance substantially degrades owing to the significant variation of video lengths. In this paper, we focus on overcoming this issue by proposing a novel content-leakage detection scheme that is robust to the variation of the video length. By comparing videos of different lengths, we determine a relation between the length of videos to be compared and the similarity between the compared videos. Therefore, we enhance the detection performance of the proposed scheme even in an environment subjected to variation in length of video. Through a testbed experiment, the effectiveness of our proposed scheme is evaluated in terms of variation of video length, delay variation, and packet loss.

Mobile Ad-hoc Network (MANET) has drawn attention of many researchers due to its ability to construct a network without any infrastructure. In MANET, mobile nodes can transmit packets by using multi-hop paradigm. However, with the high probability of link disruption, the performance of this network decreases with the increase of hop count between the source and destination. On the other hand, Delay- and Disruption-Tolerant Network (DTN) is more tolerant to the link disruption. These two types of networks can have different advantages depending on communication environments. Therefore, we focus on a system which is able to switch the routing method, i.e., DTN or MANET, in conformity with the change of communication environment. In this paper, we provide an adequate comparison between the performances of two transmission methods of MANET and DTN. With the aim of reducing the number of transmissions, we propose a routing method which combines both transmission methods. Simulation results show that our proposed method can significantly reduce the number of transmissions and it leads to lowering message delivery delay.

Satellite-Routed Sensor System (SRSS) has attracted attentions as a next generation sensor network system to realize data gathering from a large scale sensors deployment. In this system, a large number of sensor terminals send sensed data to the monitoring stations which are located in the different area via a satellite. With the help of satellite, it is possible to collect data from sensor terminals that are located in an area that has no physical infrastructure. Thus, SRSS is expected to provide many services such as real-time traffic control system and disaster detection systems by utilizing gathered data from large area. However, an efficient access control method is required to accommodate a large number of sensor terminals trying to transmit their sensed data to the satellite. Therefore, this paper proposes a novel data gathering method that can efficiently allocate bandwidth to the sensor terminals in need to transmit their sensed data. Additionally, an optimization to improve the efficiency of our proposed method is provided with mathematical expressions. The effectiveness of our proposal is evaluated through numerical results.

In the last decade, there has been a tremendous increase in both the number of mobile devices and the consumer demand for mobile data communication. As a general network architecture, ad hoc mobile networks are expected to offload a large amount of mobile traffic in lots of promising application scenarios. However, how to achieve a good balance between delivery performances (like delivery delay and delivery probability) and network resource consumptions (like power energy and buffer storage) remains an extremely challenging problem. In this paper, we focus on the general k-hop relay routing, which covers a lot of popular routing schemes as special cases, such as the direct transmission (k = 1), the two-hop relay algorithm (k = 2), and the epidemic routing (k = n - 1). We first develop absorbing continuous-time Markov chain models to characterize the complicated message delivery process under the general k-hop relay routing, and then conduct Markovian analysis to derive all the above important performance metrics. Finally, extensive numerical results are presented to illustrate the achievable delivery performances under the general k-hop relay and the possible performance trade-offs there.

Wireless Mesh Network (WMN) is a promising networking architecture because of its useful characteristics such as low deployment cost, ease of maintenance, network robustness and reliable coverage. Each node in the network is referred to either as Mesh Router (MR), Mesh Client (MC), or Mesh Gateway (MG) depending on its role in the network. MRs are interconnected to form a mesh backbone network, which can relay communications service from MCs to the MG. In many situations, MRs deployment are uncontrollable, and thus deployed MRs may not have ideal locations. In addition, in a dense network, using all available MRs that are deployed randomly to form mesh backbone network would results in a lower performance than what could be achieved. Therefore, our goal aims to select a set of working MRs that would yield an improved upper bound throughput, while still preserving connectivity. Our contributions include using graphs to represent multi-tier WMN and utilizing them to determine the set of MRs that can be safely removed from the network without severing any connectivity of the network. Furthermore, we proposed algorithm that goes through those set of MRs to determine the MRs which should be removed from the network to improve the overall performance, and we demonstrate capacity improvement brought by our scheme through simulations.

Available works either explore the order sense capacity scaling laws or derive closed-form throughput results for mobile ad hoc networks (MANETs) where a transmitter randomly probes only once a neighboring node for possible transmission. Obviously, such single probing strategy may result in a significant waste of the precious transmission opportunities in highly dynamic MANETs since the randomly selected node may already get the packets that the transmitter hopes to deliver. In this paper, we consider a two-hop relay MANET where each transmitter may conduct multiple rounds of probing so as to identify a possible receiver. We first develop closed-form expressions for per node throughput capacity in such probing-based network, with a careful consideration of the time cost taken to probe for an eligible receiver in each time slot. Extensive numerical results are further presented to explore the possible maximum per node throughput capacity, the corresponding optimum setting of probing round limit, and also their relationships with the network control parameters, like the probing time limit, the redundancy limit and the number of users, etc.

In order to realize environmentally friendly networks, energy-efficient technologies are essential. In Fiber Wireless (FiWi) networks that consists of optical and wireless networks, there are two main power saving mechanisms, namely, Power Saving Mode (PSM) and Optical Network Unit (ONU) sleep. PSM works in wireless networks, and ONU sleep works in optical networks. These two mechanisms work independently in FiWi networks. Since both PSM and ONU sleep turn off the node's transmission device to save energy, the throughput of the network decreases. Thus, a trade-off relationship between throughput and energy consumption exists. Therefore, taking account of this relationship is essential when discussing energy efficiency in these networks. In this paper, we focus on the effect of PSM and ONU sleep on throughput and energy consumption. We analyze both the energy consumption and the throughput in FiWi networks. Through analysis, we point out energy and throughput inefficiencies in FiWi networks and propose a novel method that determines the optimal ONU sleep period and behavior in order to increase throughput and decrease the energy consumption. Furthermore, we validate our proposed method through numerical analysis, and confirm that it improves both throughput and energy consumption.

Next generation satellite-routed sensor system (SRSS) is expected to provide disaster detection system with high real-time performance. By using satellite networks, SRSS realizes data collection from multiple sensor terminals deployed in a wide area. However, an efficient access control scheme is needed to achieve multiple access from numerous sensor terminals to the satellite with its limited bandwidth. Conventional research works propose a countermeasure to avoid data collisions at the satellite. However, they do not consider the situation that a significantly large number of sensor terminals communicate with the satellite anytime, which cause data collisions and decrease real-time performance. Therefore, in order to efficiently resolve these problems, we propose a new scheme which utilizes a divide and conquer approach for efficient bandwidth allocation. The effect of the scheme on the amount of time for allocating satellite bandwidth is also analyzed. The analysis clearly shows the advantage of our proposed scheme. Furthermore, numerical results demonstrate the effectiveness of our proposal.

A common complication for routing in mobile sensor networks is how to efficiently control the forwarding behaviors of relay nodes so as to save their energy consumption and buffer usage while simultaneously satisfy the specified delivery performance requirement. Available works either assign each message with a lifetime, a maximum number of copies, or a sequence number, or flush special feedback information among the whole network after the message reception. In the former case, a relay node has no idea of the message reception status and will carry and forward the message until meeting the destination, while the latter could efficiently notify all relay nodes but demands extra communication resources. Different from previous studies, we consider in this paper an explicit probabilistic stopping mechanism for relay nodes. Under such mechanism, a relay node that is actively disseminating a message will stop spreading the message with a certain probability, after meeting another node having already received the message. We first develop a two-dimensional Markov chain framework to characterize the highly complicated dynamics until the end of message propagation, then conduct Markovian analysis to derive the associated important performance metrics, including the average time required for the completion of message propagation, the expectation and variance of the fraction of nodes finally receiving the message, and the probability that a given number of nodes end up with the message, etc. Finally, extensive numerical results are provided to analytically explore how the network parameter settings may affect these performance metrics.

Recently, since many kinds of wireless devices have been widely used and a large amount of contents is available on the Internet, a network system that provides adequate services anytime and anywhere is required. In this research, we focus on satellite networks using mass storage devices to provide the above mentioned services. In this kind of network, multiple satellites are used to cover the whole surface of the earth, and each satellite is equipped with a mass storage device. By using mass storage devices, the satellite network can manage a high buffer capacity to handle large amounts of data. However, no routing method has been developed for such kind of satellite network that can utilize the storage devices and manage the large amount of data in the network effectively. In this paper, we propose a novel routing scheme for the efficient utilization of the mass storage on satellites to mitigate network congestion. The proposed method is analyzed mathematically. The numerical results validate the effectiveness of our proposed method.

Multi-Layered Satellite Networks (MLSNs) have many advantages such as extensive coverage, lower delay performance, and disaster resistance. Moreover, the networks permit load distribution by bypassing traffic efficiently from lower layers to upper layers. In the future, the MLSNs should play an important role to provide global communication services. However, sometimes traffic congestion happens in these networks since the distribution of users is unbalanced heavily depending on geographical restrictions, which causes bad effects on the networks such as increasing delay. Therefore, we focus on network design to avoid traffic congestion. There are many constitution elements to design these networks. One of the most significant elements is the altitude of satellites because it affects propagation distance and number of links between layers in MLSNs, and thus the packet transfer delay of the networks. Therefore, we analyze the relationship between the altitude of satellites and the packet transfer delay with network-wide equalization. Furthermore, the existence of the optimal altitude of satellites is denoted in this paper. Our analyses are validated by simulation experiments.

We study a novel distributed storage system integrated Data Centers (DCs) and satellite networks. This integrated system is expected as distributed storage system that can keep the storage service even if disasters strike because satellite is tolerant to link disruption caused by disasters. In this paper, we focus on data distribution method in the integrated system, and assume an erasure coding and a simple replication as data distribution method. We evaluate the storage volume and transmission time on each method which are required to restore lost data when some DCs are damaged by disasters. The storage volume of the erasure coding becomes lower than that of the replication while the transmission time becomes higher. A data transfer method is proposed in this paper to shorten the transmission time of the erasure coding. The proposed method can reduce the transmission volume on downlink communication by using network coding technologies. The numerical results show that the proposed method can restore the lost data in less time.

In wireless sensor networks with mobile sink, mobile sink traverse the sensing area and aggregate the data from nodes near the mobile sink. In this scheme, mobile sink can reduce the total energy consumption by dividing the network to the multiple clusters. Since, energy consumption is proportional to the sum of square of communication distance, dividing the network into smaller clusters can reduce the amount of energy required for transmission. Previous researches concluded that increasing number of the cluster reduces energy required for data transmission. However, these ideas do not take into account the energy consumption due to data request message flooding in dense networks. In this paper, we focus on the data request flooding problem which is the massive energy consumption for data request message in dense network. Moreover, we point out that energy consumption of data transmission and data request message are controlled by the number of clusters in the network.

A significant amount of works has been done to model the delivery performances in Intermittently Connected Mobile Networks (ICMNs). However, available works considered either the two-hop relay routing or the epidemic routing, which actually represent two extreme cases of the message delivery process in ICMNs. In this paper, we take one step ahead and focus on the three-hop relay routing where each message travels at most three hops to reach the destination. Under such a scheme, besides that the source can send a message copy to each node it meets, a relay which receives the message directly from the source can also replicate the message to other nodes, while a relay node which receives the message from another relay can only forward the message to the destination. In order to characterize the complicated message delivery process under the three-hop relay routing, a multidimensional Markov chain theoretical framework is developed. Based on the Markov chain framework and block matrix theory, closed-form expressions are further derived for the important message delivery delay and delivery cost. Extensive numerical results are also provided to explore the achievable delivery performances under the three-hop relay.

Hierarchical unstructured peer-to-peer (P2P) networks for file sharing systems such as Gnutella and Kazaa have made a tremendous achievement in the last decade. However, while these P2P networks can be tolerant to churn, i.e., the dynamics of peer participation and departure (or fault), there still remains the issue of vulnerability to Denial of Service (DoS) attacks, i.e., when the highest degree peers are removed. In order to overcome this shortcoming, we focus on a bimodal degree distribution, which is tolerant to both churn and DoS attacks. However, the network topology affects the network stability that was not taken into considered in the previous works. Therefore, we analyze the optimal network topology for DoS attack tolerance, and accordingly develop the peer joining procedure to construct and maintain the proposed network topology. Our proposed scheme is dubbed THUP (churn/DoS Tolerant, Hierarchical, Unstructured, P2P network). Performance evaluation conducted through computer simulations shows that THUP substantially improves the stability and communication efficiency compared with other existing P2P networking structures.

This paper focuses on the delivery probability performance in a two-hop relay mobile ad hoc network (MANET) with erasure coding. Available works in this line either considered a simple extreme case of achieving the delivery probability 1, or assumed a simple traffic pattern with only one source-destination pair, or studied a very special MANET scenario (i.e., the sparsely distributed MANET) by assuming that whenever two nodes meet together they can transmit to each other. Obviously, such models cannot be applied for an accurate delivery probability analysis in the general MANETs where the interference, medium contention and traffic contention issues are of significant importance. In this paper, a general finite-state absorbing Markov chain theoretical framework is first developed to model the complicated message spreading process in the challenging MANETs. Based on the theoretical framework, closed-form expressions are further derived for the corresponding message delivery probability under any given message lifetime and message size, where all the above important issues in MANETs are carefully incorporated into analysis. As verified through extensive simulation studies, the new framework can be used to accurately predict the message delivery probability behavior and characterize its relationship with the message size, replication factor and node density there.

Mobile ad hoc networks (MANETs) have attracted much attention due to their mobility and ease of deployment. However, the wireless and dynamic natures render them more vulnerable to various types of security attacks than the wired networks. The major challenge is to guarantee secure network services. To meet this challenge, certificate revocation is an important integral component to secure network communications. In this paper, we focus on the issue of certificate revocation to isolate attackers from further participating in network activities. For quick and accurate certificate revocation, we propose the Cluster-based Certificate Revocation with Vindication Capability (CCRVC) scheme. In particular, to improve the reliability of the scheme, we recover the warned nodes to take part in the certificate revocation process; to enhance the accuracy, we propose the threshold-based mechanism to assess and vindicate warned nodes as legitimate nodes or not, before recovering them. The performances of our scheme are evaluated by both numerical and simulation analysis. Extensive results demonstrate that the proposed certificate revocation scheme is effective and efficient to guarantee secure communications in mobile ad hoc networks.

This paper studies the exact per node throughput capacity of a MANET, where the transmission power of each node can be controlled to adapt to a specified transmission range υ and a generalized two-hop relay with limited packet redundancy f is adopted for packet routing. Based on the concept of automatic feedback control and the Markov chain model, we first develop a general theoretical framework to fully depict the complicated packet delivery process in the challenging MANET. With the help of the framework, we are then able to derive the exact per node throughput capacity for a fixed setting of both υ and f. Based on the new throughput result, we further explore the optimal throughput capacity for any f but a fixed υ and also determine the corresponding optimum setting of f to achieve it. This result helps us to understand how such optimal capacity varies with υ (and thus transmission power) and to find the maximum possible throughput capacity of such a network for any f and υ. Interestingly, our results show that increasing the transmission power of the nodes improves the capacity, which is the same as that proved in fixed networks.

This paper focuses on the per node throughput capacity in mobile ad hoc networks (MANETs) with the general group-based two-hop relay algorithm. Under such an algorithm with packet redundancy limit f and group size g (2HR-(f, g) for short), each packet is delivered to at most f distinct relay nodes and can be accepted by its destination if it is a fresh packet to the destination and also it is among g packets of the group the destination is currently requesting. A general Markov chain-based theoretical framework is first developed to characterize the complicated packet delivery process in the challenging MANET environment. With the help of the new theoretical framework, closed-form expressions are further derived for the throughput capacity of the 2HR-(f, g) algorithm, from which one can easily recover the available throughput capacity results by proper settings of the redundancy limit f and group size g.

Due to their simplicity and efficiency, the two-hop relay algorithm and its variants serve as a class of attractive routing schemes for mobile ad hoc networks (MANETs). With the available two-hop relay schemes, a node, whenever getting an opportunity for transmission, randomly probes only once a neighbor node for the possible transmission. It is notable that such single probing strategy, although simple, may result in a significant waste of the precious transmission opportunities in highly dynamic MANETs. To alleviate such limitation for a more efficient utilization of limited wireless bandwidth, this paper explores a more general probing-based two-hop relay algorithm with limited packet redundancy. In such an algorithm with probing round limit τ and packet redundancy limit f, each transmitter node is allowed to conduct up to τ rounds of probing for identifying a possible receiver and each packet can be delivered to at most f distinct relays. A general theoretical framework is further developed to help us understand that under different setting of τ and f, how we can benefit from multiple probings in terms of the per node throughput capacity.

Non-Geostationary satellite networks have many advantages to enable ubiquitous wireless environments such as, extensive coverage, disaster-resistance, and efficient power consumption. Furthermore, to use these networks more efficiently, multi-layered satellite networks are a promising approach, due to their ability to achieve increases in network capacity and to detour traffic efficiently, while maintaining the advantages of each layer. However, they suffer from high delay. In this paper, we focus on constellation design of two-layered satellite networks, in particular on the satellite altitude that minimizes the total packet delivery delay of the network. We express the relationship between the total packet delivery delay and the satellite altitude in mathematical form and develop an expression for determining the altitude to minimize total packet delivery delay. Simulation results validate our analyses.

A lot of works have been dedicated towards understanding the relationship between throughput capacity and packet delay in mobile ad hoc networks (MANETs). However, nearly all these works either assume a localized transmission range, or report the relationship between throughput capacity and packet delay only in terms of the number of users. It remains largely unknown for such a fundamental relationship in terms of other network parameters, like the packet redundancy and node transmission range. As a first step towards this end, in this paper we derive closed-from expressions for throughput capacity and delivery delay under a general setting of node transmission range and also a generalized two-hop relay with limited packet redundancy. Extensive numerical results are further provided to explore how throughput capacity varies with delivery delay in terms of various network parameters, such as the number of users, the packet redundancy limit, and the node transmission range, etc.

A lot of work has been done to model and analyze the performances of two-hop relay algorithm and its variants. However, the delivery ratio, especially under limited message lifetime, has been largely neglected in literature, which is not only of significant importance for delay sensitive applications (where a message beyond some delay limit will typically be dropped) but also of practical interests for general MANET scenarios (where mobile nodes are usually both energy-constrained and buffer storage-limited). In this paper, we study the delivery ratio of a generalized two-hop relay with limited message lifetime and redundancy. In particular, a finite-state absorbing Markov chain-based theoretical framework is first developed to model the complicated message delivery process under the considered relay algorithm. Closed-form expressions are then derived for the message delivery ratio under any given message lifetime, where the important interference, medium contention and traffic contention issues are carefully incorporated into analysis. Finally, extensive simulations are conducted to validate the theoretical framework and corresponding delivery ratio results.

Topology control is a powerful solution to reduce power consumption and the number of collisions by minimizing the transmission range of each node by maintaining a certain level of network connectivity. Although many topology control algorithms have been developed for static networks, e.g., sensor and ad hoc networks with less topology change, where nodes are fixed and the network topology never changes, the topology control technologies can also be adopted for dynamic networks such as Mobile Ad hoc NETworks (MANETs) with an aim to efficiently construct reliable networks. However, in order to apply topology control technologies into MANETs, it is essential to address the issue of performance degradation due to node mobility. Topology information in each node needs to be frequently and appropriately updated according to its moving speed so as to maintain the connectivity with neighbors. In our proposed mechanism, each node determines an appropriate value of topology control update interval according to the mobility information of its neighbors. The proposed mechanism with an adopted topology control technique, based on a localized algorithm, can maintain local connectivity which results in keeping global network connectivity although the network is dynamic. This is a significant advantage of our approach. Simulation results demonstrate that our scheme can ensure a certain level of network connectivity even in MANETs.

The lack of a general capacity theory on mobile ad hoc networks (MANETs) is still a challenging roadblock stunting the application of such networks. The available works on this line mainly focus on deriving order sense results, which are helpful for us to explore the general scaling laws of throughput capacity but tell us little about the exact achievable throughput. This paper studies the exact per node throughput capacity of a MANET, where the transmission power of each node can be controlled to adapt to a specified transmission range v and a generalized two-hop relay with limited packet redundancy f is adopted for packet routing. Based on the concept of automatic feedback control and the Markov chain model, we first develop a general theoretical framework to fully depict the complicated packet delivery process in the challenging MANET environment. With the help of the framework, we are then able to derive the exact per node throughput capacity for a fixed setting of both v and f. Based on the new throughput result, we further explore the optimal throughput capacity for any f but a fixed v and also determine the corresponding optimum setting of f to achieve it. This result helps us to understand how such optimal capacity varies with v (and thus transmission power) and to find the maximum possible throughput capacity of such a network for any f and v. Surprisingly, our results here indicate that usually such maximum throughput capacity can not be achieved through the local transmission, a fact different from what is generally believed in literature.

Many important real networks can be modeled as intermittently connected mobile networks (ICMNs), like the vehicular ad hoc networks, wildlife tracking and habitat monitoring sensor networks, military networks, etc. However, the fundamental performance limits of ICMNs are still largely unknown so far. This paper explores the capability of these networks to support multicast traffic, where each source node desires to send packets to k distinct destinations and all nodes move according to the generalized hybrid random walk mobility model. We show how the network capacity and related delay/delay jitter for supporting multicast in such ICMNs are scaling with the basic network parameters under three transmission protocols: one-hop relay, two-hop relay without packet redundancy and two-hop relay with packet redundancy.

Since Wireless Mesh Networks (WMNs) can be easily deployed without wirelines among wireless mesh routers, they allow us to quickly recover network access services in disaster areas even if the existing network infrastructures have been enormously destroyed by terrible earthquake, tsunami, and so on. However, the performance of wireless mesh networks is largely affected by many factors, e.g., wireless mesh routers' locations, channel assignment, transmission scheduling, etc. In particular, the method of selecting gateways which has a connection to external networks significantly impacts on the network performance when the topology and routing have been fixed in the wireless mesh network. In this paper, we suppose a wireless mesh network which consists of wireless mesh routers and a base station directly connected to external networks. The base station is located at the center of the wireless mesh network chooses a certain number of wireless mesh routers as gateways, and establishes a connection with each of them. Our goal is to easily and quickly find the candidate gateways that maximize the system throughput without solving a complex optimization problem which includes a large number of parameters and involves heavy computation load. The performance of the proposed scheme is evaluated by numerical analysis, and demonstrated through computer simulations. The results show that our proposed scheme can determine the appropriate candidate gateway with high accuracy when there is a certain variance in the amount of traffic generated by users at each wireless mesh router.

In this paper, we focus on the bandwidth allocation issue in wireless access networks, which are made up of Ethernet Passive Optical Network (EPON) and Worldwide Interoperability for Microwave Access (WiMAX) networks, i.e., Fiber-Wire (FiWi) networks. Since the bandwidth allocation scheme largely determines the performance of the entire wireless access network, in the past decades, researchers have dedicated much effort to design bandwidth allocation algorithms based on different criteria in order to satisfy various performance requirements. Various types of bandwidth allocation scheme based on Max-Min Fairness (MMF) or Proportional Fairness (PF) criteria have been developed to increase not only system throughput but also user fairness. However, in general, there is a tradeoff relationship between maximizing system throughput and increasing the fairness among users in throughput, and the users satisfaction in their Quality of Service (QoS) cannot always be maximized by adopting fair bandwidth allocation methods. To cope with this issue, we propose a bandwidth allocation method which improves the QoS satisfaction of all users while maintaining the system throughput similar to standard schemes, such as MMF and PF. In our method, users satisfaction is quantified by using utility functions which can be different among users according to their applications and services. By transferring portions of bandwidth from fully filled users to others so as not to decrease the system throughput, the proposed scheme is able to eventually converge to a compromised point. The results of performance evaluation through computer simulations have demonstrated that our proposed scheme can successfully enhance the performance of wireless access networks.

Recently, Non-Geostationary Earth Orbit (NGEO) satellite networks have gained research attention. Since they offer many features, e.g., extensive coverage, disaster-resistance, and efficient power consumption, they are considered as a good candidate for providing global communication services. Moreover, Multi-Layered Satellite Networks (MLSNs), which consist of layered NGEO satellite networks, have attracted much attention since they achieve excellent load distribution through bypassing traffic from the lower layer to upper layer. However, there is a possibility that traffic congestion may exist at a satellite on the upper layer because each satellite on the upper layer usually covers more than one satellite on lower layers in MLSNs. In this paper, we focus on traffic control in two-layered networks, especially on distributing the packet flow between the two layers in order to minimize the transfer delay of the network. Simulation results demonstrate the correctness of our analyses about delay in the network.

In Rayleigh block fading channels which represent fast-varying channels, long-term rate adaptation is required instead of instantaneous rate adaptation because the channel information fed back may be outdated. We maximize the long-term average transmission rate (LATR) in a two-hop relay network which adopts Chase combining (CC) type Hybrid Automatic-Repeat-reQuest (HARQ). The round transmission rate, i.e. the transmission rate of each HARQ round in each hop, is optimally selected based on the channel statistics of two hops. Two constraints are considered: the outage probability and the maximum number of HARQ rounds, L. In an infinite L case, we show that the optimal round transmission rate of one hop is determined only by the channel statistics of that hop, and can be expressed as a Lambert W function. In a finite L case, we propose a numerical search algorithm to find the optimal round transmission rate. If HARQ is not adopted, the LATR performance becomes very poor. As L increases in the two-hop relay with CC-based HARQ, the LATR performance becomes close to the LATR performance in the infinite L case. We also show the benefits of the proposed rate selection method compared to a non-optimal rate selection method in terms of the LATR.

One of the challenging roadblocks stunting the development and commercialization of mobile ad hoc networks (MANETs), is the lack of a thorough understanding of the fundamental performance limits in MANETs. Distinguished from available works which mainly focused on deriving order sense scaling laws of the delay performance in MANETs and usually assumed a localized transmission range, this paper examines the MANET packet delay from a much more detailed perspective. Specifically, we assume for each node a general transmission power control such that the transmission range can be flexibly adapted and adopt a generalized two-hop relay with limited packet redundancy for packet routing. For a tagged traffic flow in the MANET, we first develop a theoretical framework based on two correlated FIFO queues to fully characterize the complicated packet delivery process. Then for any feasible traffic input rate there, we derive closed-form expressions for the corresponding expected end-to-end packet delay. Extensive simulations are further conducted to validate our theoretical results.

This paper examines the optimal forwarding problem in mobile ad hoc networks (MANETs) based on a generalized two-hop relay with limited packet redundancy f (f-cast) for packet routing. We formulate such problem as a forwarding game, where each node i individually decides a probability τi(i.e., a strategy) to deliver out its own traffic and helps to forward other traffic with probability 1-τi, τi∈[0,1], while its payoff is the achievable throughput capacity of its own traffic. We derive closed-form result for the per node throughput capacity (i.e., payoff function) when all nodes play the symmetric strategy profiles, identify all the possible Nash equilibria of the forwarding game, and prove that there exists a Nash equilibrium strategy profile that is strictly Pareto optimal. Finally, for any symmetric profile, we explore the possible maximum per node throughput capacity and determine the corresponding optimal setting of f to achieve it.

Recently, the demand for content delivery in wired/wireless heterogeneous networks is increasing at a rapid pace. Content Distribution/Delivery Networks (CDNs) are considered to be one of the best solutions for dealing with this increasing demand. In this paper, we point out that the performance of a CDN typically degrades in such heterogeneous environments due to the changes in not only user demand but also wireless mobility, which triggers unexpected fluctuations in traffic. Wireless users, roaming between different access networks, may contribute to sudden and unexpected demand spikes in certain parts of the content delivery system. To address this issue, we develop a cooperative server selection scheme, which is designed to maximize robustness to such changes with the cooperation between the content delivery system and its users. The performance of our proposal is evaluated by extensive computer simulations. The evaluation results demonstrate that our proposed scheme effectively makes the considered content delivery system resilient against request fluctuations while minimizing system overloading.

The available two-hop relay protocols with out-of-order or strictly in-order reception cannot provide a flexible control for the packet delivery delay, which may significantly limit their applications to the future mobile ad hoc networks (MANETs) with different delay requirements. This paper extends the conventional two-hop relay and proposes a general group-based two-hop relay algorithm with packet redundancy. In such an algorithm with packet redundancy limit$f$and group size$g$(2HR-$(f,g)$for short), each packet is delivered to at most$f$distinct relay nodes and can be accepted by its destination if it is a fresh packet to the destination and also it is among$g$packets of the group the destination is currently requesting. The 2HR-$(f,g)$covers the available two-hop relay protocols as special cases, like the in-order reception ones$(f\geq 1,g=1)$, the out-of-order reception ones with redundancy$(f>1,g=\infty)$, or without redundancy$(f=1,g=\infty)$. A Markov chain-based theoretical framework is further developed to analyze how the mean value and variance of packet delivery delay vary with the parameters$f$and$g$, where the important medium contention, interference, and traffic contention issues are carefully incorporated into the analysis. Extensive simulation and theoretical results are provided to illustrate the performance of the 2HR-$(f,g)$algorithm and the corresponding theoretical framework, which indicate that the theoretical framework is efficient in delay analysis and the new 2HR-$(f,g)$algorithm actually enables both the mean value and variance of packet delivery delay to be flexibly controlled in a large region.

Power-aware routing in Wireless Sensor Networks (WSNs) is designed to adequately prolong the lifetime of severely resource-constrained ad hoc wireless sensor nodes}. Recent research has identified the energy hole problem in single sink-based WSNs, a characteristic of the many-to-one (convergecast) traffic patterns. In this paper, we propose HYbrid Multi-hop routiNg (HYMN) algorithm, which is a hybrid of the two contemporary multi-hop routing algorithm architectures, namely, flat multi-hop routing that utilizes efficient transmission distances, and hierarchical multi-hop routing algorithms that capitalizes on data aggregation. We provide rigorous mathematical analysis for HYMN-optimize it and model its power consumption. In addition, through extensive simulations, we demonstrate the effective performance of HYMN in terms of superior connectivity.

Due to their simplicity and efficiency, the two-hop relay algorithm and its variants serve as a class of attractive routing schemes for mobile ad hoc networks (MANETs). With the available two-hop relay schemes, a node, whenever getting an opportunity for transmission, randomly probes only once a neighbor node for the possible transmission. It is notable that such single probing strategy, although simple, may result in a significant waste of the precious transmission opportunities in highly dynamic MANETs. To alleviate such limitation for a more efficient utilization of limited wireless bandwidth, this paper proposes a more general probing-based two-hop relay algorithm with limited packet redundancy. In such an algorithm with probing round limit τ and packet redundancy limit f, each transmitter is allowed to conduct up to τ rounds of probing for identifying a possible receiver and each packet can be delivered to at most f distinct relays. A general theoretical framework is further developed to help us understand that under different setting of τ and f, how we can benefit from multiple probings in terms of the per node throughput capacity and the expected end-to-end packet delay.

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.

Among the "store-carry-forward" kind of protocols, the two-hop relay and its variants have become a class of attractive routing protocols for the mobile ad hoc networks (MANETs) due to its efficiency and simplicity. This paper focuses on the performance modeling for two-hop relay with erasure coding, a promising technique for improving the delay performance of conventional two-hop relay with simple replication. A general Markov chain-based theoretical framework is first developed to model the complicated message delivery process in such a network, based on which not only the mean value but also the variance of message delivery delay are derived analytically. The important medium contention, interference and traffic contention issues are carefully incorporated into our analysis, so the new theoretical framework can be used to precisely predicate the message delivery delay performance of two-hop relay with erasure coding, as verified by extensive simulation results.

Two-hop relay is a class of attractive routing protocols for mobile ad hoc networks (MANETs) due to its efficiency and simplicity. This paper extends the conventional two-hop relay and proposes a more general group-based two-hop relay algorithm with redundancy. In such an algorithm with redundancy f and group size g (2HR-(f, g) for short), each packet is delivered to at most f distinct relay nodes and can be accepted by its destination if it is among the group of g packets the destination is currently requesting. The 2HR-(f, g) covers the available two-hop relay protocols as special cases, like the in-order protocols (f ≥ 1, g = 1), the out-of-order protocols with redundancy (f >; 1, g = ∞) or without redundancy (f = 1, g = ∞), and it enables a more flexible control of packet delivery process to be made in the challenging MANET environment. A general theoretical framework is further developed to explore how the control parameters f and g affect the expected packet delivery delay in an 2HR-(f, g) MANET, where the important medium contention, interference and traffic contention issues are carefully incorporated into the analysis. Finally, extensive simulation and theoretical results are provided to demonstrate the efficiency of the 2HR-(f, g) scheme and the corresponding theoretical framework.

The 2-hop relay algorithm and its variants have been attractive for ad hoc mobile networks, because they are simple yet efficient, and more importantly, they enable the capacity and delay to be studied analytically. This paper considers the 2-hop relay with f-cast (2HR-f) under i.i.d. mobility model, a general 2-hop relay algorithm that allows one packet to be delivered to at most f distinct relay nodes. The 2HR-f algorithm covers the available 2-hop relay algorithms (f = 1,√n) as special cases. Closed-form analytical models rather than order sense ones are developed for the 2HR-f algorithm with a careful consideration of important medium contention and queuing delay issues, which enable an accurate delay and capacity analysis to be performed for ad hoc mobile networks employing 2HR-f. Based on our models and some typical settings of f (say, f = 1,√n), one can easily derive the corresponding order sense results.

Certificate revocation is an important security component in mobile ad hoc networks (MANETs). Owing to their wireless and dynamic nature, MANETs are vulnerable to security attacks from malicious nodes. Certificate revocation mechanisms play an important role in securing a network. When the certificate of a malicious node is revoked, it is denied from all activities and isolated from the network. The main challenge for certificate revocation is to revoke the certificates of malicious nodes promptly and accurately. In this paper, we build upon our previously proposed scheme, a clustering-based certificate revocation scheme, which outperforms other techniques in terms of being able to quickly revoke attackers' certificates and recover falsely accused certificates. However, owing to a limitation in the scheme's certificate accusation and recovery mechanism, the number of nodes capable of accusing malicious nodes decreases over time. This can eventually lead to the case where malicious nodes can no longer be revoked in a timely manner. To solve this problem, we propose a new method to enhance the effectiveness and efficiency of the scheme by employing a threshold based approach to restore a node's accusation ability and to ensure sufficient normal nodes to accuse malicious nodes in MANETs. Extensive simulations show that the new method can effectively improve the performance of certificate revocation.

Fiber-Wireless (FiWi) access networks, have rapidly matured as a last mile Internet access network solution due to their novel combination of Ethernet Passive Optical Networks (EPON) as a backhaul and Wireless Mesh Networks (WMN) as an access network. The high bandwidth provided by the optical lines, as well as the flexibility offered by the wireless network, offers a great degree of cost-efficiency in terms of sharing an optical line with a number of simultaneous users. In a FiWi network, Gateways (GWs) located between the EPON and WMN serve both the function of an Optical Network Unit (ONU) in the EPON and a mesh router in WMN. Since all of the downstream from the EPON to the WMN and all of the upstream from the WMN to the EPON must be exchanged at GWs, traffic distribution technique between GWs is necessary to achieve efficient utilization of the network resources. Controlling the downstream traffic is a significant issue in preventing performance degradation due to network congestion at the GWs, because the bandwidth of WMN is generally narrower than that of the EPON. In addition, the number of hops from a GW to an end-user in the WMN needs to be taken into account in the traffic distribution process, because the increased number of hops results in lower communication efficiency due to mutual interferences between adjacent links and effects of cross traffic. Therefore, in this paper, we focus on the downstream controlling of FiWi networks, and propose a traffic distribution scheme which utilizes an aspect of EPON to properly distribute traffic load among GWs. A hop count limitation mechanism is adopted to avoid throughput degradation caused by increased wireless interference and effects of cross traffic in the WMN. Simulation results show a trade-off relationship between fair load balancing among GWs and high throughput for end-users, and the proposed scheme can accommodate it by regulating hop count limitation.

While GEostationary Orbit (GEO) satellite systems provide us with a wide coverage area, their long delay serves as a significant constraint for real-time applications. On the other hand, Low Earth Orbit (LEO) satellite systems are best suited to delay sensitive applications. However, the coverage and mobility issues of LEO satellites lead to relatively high management costs. In this paper, we devise a new load balancing and quality of service (QoS) provisioning scheme to accommodate both real-time and non-real-time traffic based on a new congestion-prediction scheme. The effect of this new scheme is expected to improve the efficiency of the GEO/LEO hybrid satellite networks and the QoS satisfaction of end users.

Owing to the heterogeneity and high degree of connectivity of various networks, there likely exist multiple available paths between a source and a destination. An effective model of delay-controlled load distribution becomes essential to efficiently utilize such parallel paths for multimedia data transmission and real-time applications, which are commonly known to be sensitive to packet delay, packet delay variation, and packet reordering. Recent research on load distribution has focused on load balancing efficiency, bandwidth utilization, and packet order preservation; however, a majority of the solutions do not address delay-related issues. This paper proposes a new load distribution model aiming to minimize the difference among end-to-end delays, thereby reducing packet delay variation and risk of packet reordering without additional network overhead. In general, the lower the risk of packet reordering, the smaller the delay induced by the packet reordering recovery process, i.e., extra delay induced by the packet reordering recovery process is expected to decrease. Therefore, our model can reduce not only the end-to-end delay but also the packet reordering recovery time. Finally, our proposed model is shown to outperform other existing models, via analysis and simulations.

The two-hop relay algorithm and its variants have been attractive for ad hoc mobile networks, because they are simple yet efficient, and more importantly, they enable the capacity and delay to be studied analytically. This paper considers a general two-hop relay with f-cast (2HR-f), where each packet is delivered to at most f distinct relay nodes and should be received in order at its destination. We derive the closed-form theoretical models rather than order sense ones for the 2HR-f algorithm with a careful consideration of the important interference, medium contention, traffic contention and queuing delay issues, which enable an accurate delay and capacity analysis to be performed for an ad hoc mobile network employing the 2HR-f. Based on our models, one can directly get the corresponding order sense results. Extensive simulation studies are also conducted to demonstrate the efficiency of these new models.

Power aware routing in Wireless Sensor Networks (WSNs) focuses on the crucial issue of extending the network lifetime of WSNs, which are limited by low capacity batteries. However, most of the previously proposed power aware routing algorithms have an inherent problem, which is the isolation of the sink node due to the quick power exhaustion of nodes that are close to the sink. In this paper, we propose a solution, referred to as HYbrid Multi-hop routiNg (HYMN), which addresses this problem by combining two routing strategies, namely flat multi-hop routing and hierarchical multi-hop routing. The former method aims at minimizing the total power consumption in the network while the latter attempts to decrease the amount of transferred data traffic by utilizing data compression. We present a mathematical analysis on the effect of the hybrid location on the performance of HYMN, and also demonstrate the effectiveness of HYMN through extensive simulations.

Recently, much effort aiming at achieving ubiquitous networks has been made. A ubiquitous network refers to a network environment, which enables anytime and anywhere access, by possibly any given device or by any user. In a ubiquitous network, applications require many types of information such as temperature and so forth. A great deal of attention has been paid to aggregate this information in Wireless Sensor Networks (WSNs). A WSN consists of tiny nodes comprising sensing and communication devices. The information sensed by each node is relayed via other nodes in the WSN to the destination node called the ``sink''. One of the most significant challenges pertaining to any WSN is to reduce the energy consumption of its nodes, which run on scarce battery resources. An effective scheme to reduce this energy consumption is to exploit the sink node's mobility, which however presents new challenges to the sink node's routing and information aggregation. In this paper, we propose a new routing and data aggregation scheme based on clustering. Simulation results demonstrate that our scheme can provide better energy efficient data aggregation as compared to the KAT (K-means And Traveling salesman path) mobility.

Along with the rapid deployment of video streaming applications and services over the networks, prevention of undesirable leakage of streaming contents have become a serious issue, which needs substantial attention. Our research group had previously proposed streaming content leakage detection technology based on the fact that different contents exhibit different traffic patterns when they are being delivered over the networks. By comparing traffic patterns obtained near the content server with those measured at egress nodes, these conventional systems are able to detect the stream leakage to the external network. Although our earlier works demonstrated that the performance of our detection method in delayed and lossy networks can be enhanced by adopting an advanced traffic pattern generation algorithm, their robustness to reordered or encrypted streams requires further investigation. In this paper, we first verify, through experiments, that the packet reordering does not significantly degrade the performance of the detection scheme while the packet encryption technologies substantially affect the conventional systems regardless of the employed traffic pattern generators. In order to address this problem, we envision an enhanced mechanism for dealing with encrypted traffic. We also empirically evaluate the performance of the proposed scheme and validate its effectiveness.

In Mobile Ad hoc NETworks (MANETs), certification systems play an important role in maintaining network security because attackers can freely move and repeatedly launch attacks against different nodes. By adopting certification systems, it becomes possible to exclude identified attackers from the network permanently by revoking the certifications of the attackers. A simple way to identify attackers is to collect information on attackers from nodes in the network. However, in this approach, it is difficult to differentiate valid accusations made by legitimate nodes from false accusations made by malicious nodes. In addition, the amount of traffic in order to exchange information on attackers and the necessary time to gather the information increases as the network size becomes larger. In this paper, we propose a certificate revocation scheme which can revoke the certification of attackers in a short time with a small amount of operating traffic. By clustering nodes and introducing multi-level node reliability, the proposed scheme can mitigate the improper certificate revocation due to false accusations by malicious users.

Energy consumption and network connectivity are two of the important research issues that are yet to be resolved in mobile ad hoc networks (MANETs). As taken advantage of in static networks, reliable topology control algorithms are also considered to be a good approach for mobile networks. However, a more adequate evaluation of these algorithms regarding mobility is still needed. In this paper, we evaluate the performance of some well-known topology control algorithms with various scenarios and measurements. The results show that Local Tree-based Reliable Topology (LTRT), a recently proposed algorithm, is the most scalable method and provides the most benefit in terms of redundant connectivity.

While Transmission Control Protocol (TCP) is the most popular transport protocol used in terrestrial networks, its performance is not adequate in wireless networks with long delay, e.g., satellite networks. Though some improvements of TCP and new transport protocols have been proposed, we focus on Variable-structure congestion Control Protocol (VCP) designed for high Bandwidth Delay Product (BDP) networks. In VCP, Explicit Congestion Notification (ECN) is used to generate the feedback signal from routers to sources in order to notify the utilization ratio of a bottleneck link. By adjusting its congestion window according to the network traffic conditions, VCP is able to achieve high link utilization even in high BDP networks. However, VCP requires a long time to fill the link capacity due to its more conservative window control mechanism than the slow start phase in TCP. In addition, throughput is unnecessarily degraded in VCP due to packet losses in wireless environments. In this paper, to address these issues, we propose two extensions of VCP, namely Bandwidth-Independent Start-up Extension (BISE) and Wireless Loss Tolerant Extension (WLTE). BISE can quickly increase its congestion window in the start-up phase. WLTE can maintain high throughput in wireless environments. The performance of the proposed schemes is evaluated through computer simulations. The results demonstrate that the proposed schemes dramatically improve the performance of VCP in the initial phase and also in wireless environments.

Over the past few years, a number of private networks have emerged. In these private networks, a server provides its subscribed clients with Internet services, forming a one-to-many network topology. Given the fact that users are located at different distances from the server, usage of the Transmission Control Protocol (TCP) for communication results in drastically unfair bandwidth allocations among the users. In this regard, this paper addresses the fairness and efficiency issues of TCP in such one-to-many IP (Internet Protocol) networks. The efficiency of TCP is controlled by matching the aggregate traffic rate of all TCP connections to the sum of the link capacity and total buffer size. On the other hand, its unfairness issue is mitigated by allocating bandwidth among individual flows in relative proportion with their RTTs. Simulation results elucidate that the proposed method makes better utilization of the network resources, reduces the number of packet drops, and provides a fair service to users.

Protection of mobile IP networks from denial-of-service (DoS) attacks, a serious security threat in today's Internet, is a one major step toward making this paradigm a reality. The paper proposes a method to detect DoS attacks, issued from mobile users, in the vicinity of flooding sources and in early stages before they cripple the targeted system. The fundamental challenge in attack detection consists in distinguishing between simple flash events and DoS attacks so as not to deprive innocent users from having legitimate accesses. In the proposed mechanism, this distinction is based on the fact that legitimate TCP flows obey the congestion control protocol, whereas misbehaving sources remain unresponsive. Suspicious flows are sent a test feedback and are required to decrease their sending rates. Legitimacy of such flows is decided based on their responsiveness. The scheme performance is evaluated through a set of simulations and encouraging results are obtained: short detection latency and high detection accuracy