When a large-scale disaster happens, which causes catastrophic damage to terrestrial information/road traffic networks and forces a huge number of people to live as refugees in shelters, it is necessary to quickly check the safety of victims and damage state in the disaster-hit area. Unmanned Aerial Vehicles (UAVs) including drones are promised to play an essential role in such a disaster recovery process because of its infrastructureless workability.In this paper, we propose a message collection system using a drone for refugees in a disaster-hit area. In order to quickly and efficiently collect messages for all refugees dispersed in shelters, we try to solve a problem to create a flight plan in the form of the Vehicle Routing Problem (VRP), taking into consideration two major drawbacks of drone such as short time to fly and vulnerability to wind. Our numerical results for an area of Osaka, Japan, show that off-line pre-creation of drone routes assuming no wind is risky, because the drone cannot safely return to a depot, if it is used under some windy conditions.

In order to avoid the loss of separation or collision risk among unmanned aircrafts as well as manned aircrafts, we have developed a prototype system where the aircrafts autonomously exchange their location information obtained through the signal of the Global Positioning System (GPS) using device-to-device (D2D) communications. Based on the developed system, we have conducted an experiment that demonstrates its successful operation for maintaining the targeted separation between the drone and manned helicopter. This paper will report the details of our experimental results as well as describe our finding of the requirement in D2D communications so as to guarantee the sufficient separation among the aircrafts.

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.

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.

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.

This paper investigates the aerial networks where the two unmanned aerial vehicles (UAVs) with different altitudes communicate with each other using the same spectral resources as the ground communication links. We propose a spectral sharing approach based on power control for aerial communication link such that the interference observed by the ground communication links is maintained below a predetermined threshold. Through theoretical analysis based on Nakagami-Rice fading channel model, the trade- off relationship between the acceptable interference observed by the ground terminals and the information rate achieved by the aerial communication link is elucidated.

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.

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.

In this paper, we develop a wireless relay network model for an unmanned aircraft (UA) system, where an UA serves as a resilient moving relay among the ground stations with disconnected communication links in the event of disasters. A fixed-wing type is considered as our UA model, since it can operate longer than a rotary-wing UA without recharging battery, but the former can fly only in a circular manner and thus is difficult to stay at a fixed position. When the UA relays the received information to the destination with a conventional fixed-rate decode-and-forward protocol, the circular flight operation of a fixed-wing UA imposes a severe limitation on the achievable performance in terms of outage probability and information rate as they considerably depend on the location of the UA. Therefore, we propose a variable-rate relaying approach that enables us to optimize the achievable performance. Based on the theoretical derivation of the outage probability and formulation of its optimization process, we demonstrate that significant improvement over a conventional fixed-rate relaying can be achieved by the proposed rate optimization.

In this paper, we consider boolean network tomography to identify link failures in a network. In boolean network tomography, the relationship between end-to-end measurements and link states are represented with a system of boolean equations, and failure links are identified by solving the equations. In order to establish measurement paths efficiently, we propose an adaptive boolean network tomography scheme, where measurement paths are established sequentially according to a candidate set of failure links. Here, to derive the candidate set, we extend CBP (Combinatorial Basis Pursuit), a representative decoding algorithm in Combinatorial Group Testing, and utilize its property that it can identify failure links without false negative errors. We evaluate the performance of the proposed scheme in terms of the number of measurement paths and compare it with a non-adaptive boolean network tomography scheme. Furthermore, we propose mobility-assisted boolean network tomography, which can improve the ambiguity problem in boolean network tomography.

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.

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.

This paper proposes a virtual MIMO system model for the unmanned aircraft system (UAS) that consists of a small unmanned aircraft (UA) and multiple ground stations (GSs). Since it is difficult to equip a small UA with multiple antennas due to the limitation of its payload, the proposed system exploits a mobility of the single-antenna UA to realize virtual MIMO channels. The channel is assumed to be either Rayleigh or Rician fading, and in the case of Rician, we also investigate the case where the UA fails to receive the line-of-sight (LOS) path due to some turbulence as a probabilistic event. The comparison of the bit error rate (BER) performance through computer simulations shows that when the channel fading is severe or the LOS path is lost with non-negligible probability, a significant improvement of BER performance can be achieved by the diversity gain through the proposed virtual MIMO approach.

This paper proposes a relaying protocol which combines a network coding with a mobility of small unmanned aircraft (UA) for wireless relay networks. We consider the scenario where the UA circles above around the networks automatically and bridges the signals between ground access points (GAPs) of the distant networks. Such wireless relay networks using UA can be considered particularly useful for emergencies e.g., when the communication networks are partially or completely interrupted after the disaster or power failure. The proposed protocol using network coding and UA can provide a significant diversity gain in contrast to conventional relay protocol. In this paper, simulation results are presented to demonstrate the reliability of the proposed protocol. The bit error rate of the proposed protocol can be lower than that of the conventional relay protocol. This paper also reveals that the diversity gain can be achieved by the proposed protocol.

To realize the high data transmission rate in the optical wireless communications effectively, a Repeated-permutation Multi-pulse Pulse Position Modulation (RMPPM) system with interference avoidance is considered. The RMPPM system can transmit the bit data by using the repeated-permutation of the slot positions of the orthogonal codes, whereas the conventional Multi-pulse Pulse Position Modulation (MPPM) system can transmit the bit data by using the combination of the slot positions of the orthogonal codes. To avoid Multiple Access Interference (MAI), we consider Reduction Rule (RR) of orthogonal codes at a transmitter. We analyze the Bit Error Rate (BER) performance theoretically. As results, BER can be greatly improved by RR. RR is effective to the RMPPM system in the multi-user case of optical wireless communication.

To achieve the full data rate and diversity gain with low decoding complexity in a multi-hop network, a space time block coded MIMO network coding (STBC-MIMO) with dual polarization antennas is proposed. Each node has two vertical polarized antennas and two horizontal polarized antennas and each node receives or transmits the STBC signal from or to forward and backward links. In this paper, the effect of polarized orthogonal STBC-MIMO network coding is evaluated by numerical results. As results, STBC-MIMO network coding can supply about 2.0 times higher performance than the conventional STBC-MIMO network coding by using dual polarization antennas.

This paper proposes data collection schemes with two mobile sinks for wireless sensor networks. The proposed schemes use eigenvectors of an adjacency matrix of the networks. Eigenvectors of adjacency matrix mean the strength of the connection between sensors so that data collection takes into account the wireless links can be achieved by eigenvectors. In this paper, the disjoint rate among routes for two mobile sinks, the number of hops from sensors to the gateway on the route and the total travel time of mobile sinks are evaluated. The total travel time of the proposed scheme is shorter than that of conventional scheme, and it is found that the proposed scheme can achieve effective data collection.

This paper introduces a node centrality as multipath routing metric for wireless multihop networks. The node centrality is an eigenvector centrality. This paper also proposes two route selection method using an eigenvector centrality. The disjoint rate of the proposed methods are 30% to twice larger than that of the conventional methods. Therefore, it is found that the eigenvector centrality is an effective metric to achieve the high reliability routes in the disjoint multipath routing.

Wireless mesh networks, consist of mesh routers and clients, have attracted researchers in the field of sensor network or wireless plant control for its potential to achieve high connectivity and wide area coverage in an ad-hoc way. The mesh routers should supply the backbone of the network with high capacity to support accumulated traffic from or to mesh clients. In the conventional mesh network it is a biggest problem of inefficient network channel capacity due to multiple access interference among the mesh routers. In this paper we will propose a novel MIMO mesh network, where the mesh routers support multiple antennas, to avoid multiple access interference and to supply higher network capacity via link multiplexing. As a MIMO transmission scheme, linear (such as Zero-Forcing) and nonlinear (such as Dirty Paper Coding / Successive Interference Cancellation) MIMO algorithm are developed for the proposed mesh network. It is found from numerical analysis that the proposed MIMO mesh network achieves extremely higher channel capacity than that of conventional mesh network.

In this paper, an architecture of MIMO mesh network which avoids co-channel interference and supplies link multiplexing simultaneously is proposed. As a MIMO transmission scheme, linear (such as zero-forcing) and nonlinear (such as dirty paper coding and successive interference cancellation) MIMO algorithm are developed for the proposed mesh network. It is found from numerical analysis that the proposed MIMO mesh network achieves extremely higher channel capacity than that of conventional mesh network.

In this paper, we propose a soft decision based cooperative sensing method for cognitive radio (CR) in ad-hoc networks. A CR can sense a surrounding radio environment and adapt to the environment by the reconfigurability to achieve more effective frequency utilization. Observing the environment, CR should detect presence or absence of primary user and exploits this information to opportunistically provide communication among secondary users while performance of primary user should not be deteriorated by the secondary users. Because of multi- path fading or shadowing, the detection of primary users may be significantly difficult. For this problem, cooperative sensing (CS), where gathered observations obtained by multiple users is utilized to achieve higher performance of detection, has been investigated. We propose a soft decision based CS where test statistic used in traditional single user energy detection is treated as soft decision information. The detector is designed analytically, i.e., the statistic of the performance, detection probability and given false alarm, can be obtained analytically. By computer simulations, we have presented as follows; validity of analysis and that the CS has better performance compared to non-cooperative sensing. In addition, we have presented the detection performance of cooperative sensing when there are considerable differences regarding signal to noise ratio among users.

In this paper, a system based on pulse spacing modulation and code shift keying is considered. The system uses quadriphase even-shift orthogonal sequences (E-sequences) as orthogonal sequence. The auto-correlation value of the quadriphase sequence is better than that of the biphase E-sequence. In this paper, the probability of block error and efficiency are shown. The probability of block error can improve and the efficiency is greater than that of the SS-PPM system

In this paper, a code selecting/spacing ALOHA system is proposed. The proposed system not only use Nmspreading codes but also M time slots. The proposed system varies in packet size from KNmTcto KMNmTc, where K is the number of symbols per packet and Tcis the chip duration. So, the length of the packet for the proposed system changes according to the source data although the message bits per packet are constant. The number of symbols per packet of the proposed system is smaller than that of the conventional direct sequence spread spectrum multiple access (DS/SSMA) ALOHA system. Therefore, the proposed system is expected for improving the throughput performance of the conventional DS/SSMA ALOHA system. In the result of the throughput performance evaluation on the additive white Gaussian noise (AWGN) channel, it is shown that the throughput performance of the proposed system is about 2 times higher than that of the DS/SSMA ALOHA system

A time hopping modified PSM system using pseudo-noise (PN) codes is proposed. The time hopping modified PSM system uses the several PN codes, and it transmits information by the interval between the successive PN codes. The bit error rate performance and the synchronization performance of the proposed system on the additive white Gaussian noise (AWGN) channel are evaluated by theoretical analysis. As a result, there is the optimum preamble pattern for bringing the probability of block error that takes into account the synchronization performance close to the lower bound. The efficiency of the time hopping modified PSM system is greater than that of the conventional SS-PPM system.

A spread spectrum pulse spacing modulation (SS-PSM) system using E-sequences and a preamble is considered. The preamble signal is used for block synchronization. The following performances are evaluated by theoretical analysis: (1) the data transmission rate; (2) the block error rate when the receiver detects the preamble correctly; (3) the synchronization performances (the probability of detection and the probability of false alarm); (4) the block error rate considering the synchronization performances; and (5) the efficiency. Consequently, the data transmission rate of the SS-PSM system is much higher than that of the conventional spread-spectrum pulse position modulation (SS-PPM) system. The block error rate considering the synchronization performance can reach the lower bound by making use of the preamble. The efficiency of the SS-PSM system is 2 times greater than that of the conventional SS-PPM system.

The spread spectrum pulse spacing modulation (SS-PSM) system using even-shift orthogonal sequences (E-sequences) and a preamble is considered. The probability of block error that takes into account the synchronization performance is evaluated by theoretical analysis. In particular, the effects of the probability of detection of a preamble and the probability of false alarm on the probability of block error are discussed. Consequently, it is found that the probability of detection and the probability of false alarm depend on the pattern of preamble. The probability of block error considering the synchronization performance can reach the lower bound by making use of the preamble with good correlation function.