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.

IR-UWB has been gaining attentions for its capability of providing high precision ranging and location-tracking. In responding to the changes of regulations, IR-UWB devices need to be implemented at UWB high band (6.0-10.6 GHz) instead of low band (3.14.9 GHz). To compensate the deficiency of high band in propagation, we propose an adaptive detection threshold at the receiver to improve receiving sensitivity. The proposed adaptive threshold is implemented by adding an additional circuit to a conventional detector. Evaluations are performed through measurements. The proposed structure improves receiving sensitivity by 7 dB compared to the conventional structure. Moreover, IR-UWB system with the proposed structure provides better positioning accuracy and precision than the conventional system.

We developed and deployed a testbed based on the concept of peer aware communication (PAC), where PAC is used to refer the fully distributed and self-coordinated device-to-device (D2D) wireless networks. The testbed was originally developed for information sharing at local community by employing in-operation community buses as main components. However, strong demands rise from the local community for obtaining bus location information. To enable the bus location features, a number of improvements are performed to the testbed such as increasing the robustness of wireless links, streamlining MAC frame format and data flow, etc. Examination is carried out on the improved testbed. The results show that the bus location information is obtained within acceptable time delay.

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.

Wireless networks formed by peer devices or device-to-device communications are drawing more and more attention recently. In IEEE 802 Standardization Committee, TG15.8 was set up to develop a new standard for peer aware communication (PAC). PAC is expected to provide fast neighbor discovery, offload traffic for infrastructure-based networks, provide emergency links without fixed central control, etc. In this paper, we propose procedures and protocols for using common channel for discovery and for forming group in PAC. Computer simulations are carried out with various combinations of devices and various device densities. Simulation results show that the proposed method is efficient for fast initial discovery and for accommodation of large number of PDs.

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.

Visualization of stomach and small intestine, nowadays can be done with wireless capsule endoscopy. However, the limitation of bandwidth at low frequencies such as Industrial, Scientific and Medical (ISM) band and Medical Implant Communication Service (MICS) band do not provide high resolution images. One of the possible frequency band to have clear images from digestive organs is the use of Ultra Wideband (UWB) at frequency of 3.1-10.6 GHz. To have high resolution wireless endoscopy at higher frame rate, we need to investigate the antenna, path-loss model and radio channel behavior at available higher frequency band such as UWB band. This paper discusses on UWB antennas and propagation for digestive organs implanted device.

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.

Two-dimensional communication system (2DCS) is a novel communication system which utilizes surface of sheet as communication medium. 2DCS provides wireless power supply as well as safely and high-speed data transmission to sensor devices. However, how to suppress the standing wave effect to a minimum is still an open issue for 2DCS. In this study, we explore how the power distribution on sheet medium changes by the location of input coupler, and then compose a scheme of the power provision with multiple single or compound couplers where shadowing effect is considered to suppress the standing wave effect. Through simulation experiments, we evaluate the performance of proposed scheme to improve the power provision efficiency over 2DCS.

The sheet medium communication sensor network (SMCSN) is a novel physical form of communication that utilizes the surface as a communication medium to provide both data and power transmission services to the sensor node placed atop it. To enable SMCSN to detect the position of sensor devices on the sheet medium, we developed a simple and highly accurate position identifying method that maps phase differences measured at electrode array corresponding to a pilot signal sent by a sensor node. When however an object other than a sensor node is placed on the sheet medium, it may have an influence on position estimation. In this paper, we thus evaluate the robustness of our proposed positioning scheme by performing the actual position measurement in which extraneous objects such as plastic, copper, water and aluminium, are put on the sheet medium. The experimental results reveal that the position estimation accuracy is slightly decreased in the case that extraneous objects are put on the sheet medium compared to the case of not placing extraneous objects as the interference.

In this paper, we propose a novel type of Impulse Radio Ultra-Wideband (IR-UWB) beamforming structure that we named a chirp beamformer. It represents an alternative to the well-known correlation beamforming paradigm. The chirp beamformer uses a chirp pulse as a symbol waveform. In comparison with a correlation beamformer, the chirp beamformer requires considerably lower timing resolution in cases where the IR-UWB symbol consists of a relatively long single uninterrupted waveform, as in the mandatory modes of two of the IEEE 802.15 IR-UWB standards, namely IEEE 802.15.4a-2007 and IEEE 802.15.6-2012. Furthermore, the bandwidth of the signal that the chirp beamformer generates in the baseband is considerably lower than in the case of the correlation beamformer. Hence, in the case of digital baseband signal generation, the chirp beamformer requires a considerably lower sampling rate than the correlation beamformer. A method for shaping the beam pattern of the chirp beamformer is also described. All concepts introduced are illustrated by numerical examples.

This paper presents a performance evaluation on path diversity introduced in a wireless network established by unmanned aerial vehicles or unmanned aircrafts (UAs). One of usage scenarios of the wireless network established by UAs is establishment of a temporal communications instead of disrupted terrestrial networks due to a massive disaster. In order to evaluate system performance based on this usage scenario, we have conducted the following simulations; first, radio propagation characteristics between UAs flying over different two conditions have been simulated, after that, system simulations have been carried out over radio channels derived by simulations. Results regarding radio propagation reveal that characteristics including path loss and RMS delay are highly depend on not only altitude of the deployed UAs, but also its polarization of radio signal. System simulations based on the channel impulse responses obtained by propagation simulations, in which IEEE802.11g is utilized as specifications of the radio system, show that path diversity introduced by deploying multiple UAs brings remarkable improvement on achievable throughputs.

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.

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.

This paper investigates possible amendment of the IEEE 802.15.6 standard for Body Area Network (BAN). Particularly, we study amending the IEEE 802.15.6 Impulse-Radio Ultra-Wideband (IR-UWB) DPSK Physical Layer (PHY) through adding data rates lower than what is currently both the lowest and mandatory data rate of this PHY. The motivation for this study is enhancing link margin and, more importantly, enhancing PHY's multi-BAN interference resistivity, crucial in medical applications of IEEE 802.15.6 BAN. Three different possibilities of adding lower data rates are considered. The first is increasing transmitted waveform duration and thus symbol rate; the second is introducing a spreading sequence and using current mandatory data rate symbols as chips; the third is introducing an inner convolution code for concatenation with the existing BCH(63,51) block code. Performances of these communication schemes are studied in multi-BAN interference.

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.

Network coding is an effective method to improving relay efficiency by reducing the number of transmissions. However, its performance is limited by several factors such as packet length mismatch and rate mismatch. Although the former may be solved by re-framing, the latter remains a challenge and is likely to greatly degrade the efficiency of network coding. In this paper, we re-interpret network coding as a mapping of modulation constellation. On this basis, we extend such mapping to enable simultaneous use of different modulations by nesting the low-level constellation as a subset of the high level constellation. When relay links have different qualities, the messages of different flows are combined together in such a way that for each relay link its desired message is transmitted at its own highest rate. Compared with previous solutions to rate mismatch, the proposed scheme achieves the full rate of all relay links on the broadcast channel.

Carrier sense multi-access (CSMA) is a typical method to share the common channel in a wireless LAN (WLAN). It works fairly well in times of light traffic. However as the number of nodes in a WLAN increases quickly, severe collision greatly degrades network performance. In this paper we propose a distributed multi-user scheduling (DMUS) scheme to solve this problem, taking time-variant link quality and rate adaptation into account. Instead of all nodes, only nodes with high instantaneous link quality are allowed to contend for the channel. By setting a suitable SNR threshold, at any instance only a small percentage of nodes join the contention. As a result, collision is mitigated, fairness is retained by independent fading, and the total throughput is increased since transmissions are finished at higher rates. Simulation results show when there are 40 nodes in a WLAN, the DMUS scheme improves total throughput by up to 49.6% compared with the contention-free scheme, and by up to 194.6% compared with the CSMA/CA scheme.

Safety driving support is one of the most attractive applications of an inter-vehicle communications system. Real-time and reliable packet exchange among vehicles is a key to offering timely warnings to drivers in order to avoid fatal accidents. In this paper, we introduce the multi-carrier multi-code spread ALOHA (MM-SA) system, an inter-vehicle communications system developed for satisfying challenging requirements on supporting safety driving. MM-SA is based on code division multiple access (CDMA) technology, and has inherent robustness to the increase of node density as well as the hidden terminal problem. This paper presents an overview of MM-SA system including protocol design and prototyping as well as graphical user interface (GUI) tool, which are all developed for avoiding intersection collisions.

Network coding is an effective method to improve forwarding efficiency in multi-hop wireless networks. Previous network coding schemes proposed for unicast transmissions focus on scheduling where paths are already established, and assume a fixed rate for all links, neglecting link rate heterogeneity. In this paper we study a network coding based pseudo bidirectional relay scheme for wireless LAN, taking link quality into account. We first show when network coding based relay improves channel efficiency and how to select such a relay in a distributed way. Then we enhance network coding based transmissions from three aspects: (i) Coordinated rate adaptation is adopted to reduce the probability with which a priori packet is missing in times of network decoding. (ii) The retransmission scheduling completely solves the lack-of-a-priori problem. (iii) Piggybacking receiving status in ACK/NAK further enables opportunistic reception and avoids unnecessary transmissions. Simulation results confirm that compared with direct transmissions, the proposed relay scheme can reduce per-packet transmission time by up to 39% in Rayleigh fading environment.

Although the near-far effect has been considered to be the major issue preventing CDMA from being used in ad-hoc networks, in this paper, we show that the near-far effect is not a severe issue in inter-vehicle networks for safety driving support, where packet transmissions are performed in the broadcast manner. Indeed, the near-far effect provides extremely reliable transmissions between near nodes, regardless of node density, which can not be achieved by CSMA/CA. However, CDMA can not be directly applied in realistic traffic accident scenarios, where highly reliable transmissions are required between far nodes as well. This paper proposes to apply packet forwarding and transmission scheduling methods that try to expand the area, where reliable transmissions are achievable. Simulation results show that the proposed scheme achieves approximately 100% of delivery ratio and 4 milliseconds of delay in a realistic traffic accident scenario, where CSMA/CA achieves approximately 60% of delivery ratio and 80 milliseconds of delay.

A multi-player video game via wireless connections using portable devices is one of the most popular applications of ad-hoc networks. Broadcast transmissions can be used for many- to-many communications in multi-player games. However, reliable broadcast communications are hard to realize because of the lack of retransmissions in the medium access control (MAC) layer. In this paper, we propose a broadcast method using random linear network coding in order to enhance the reliability of many-to-many and real-time communications. Exploiting the periodic nature of game traffic as well as inherent robustness offered by random network coding, the proposed method can provide reliable packet deliveries between 2 nodes which have a link under constant fade or even under temporary loss. Our simulation results show that the proposed method can provide higher reliability than the other schemes using multi point relay (MPR) or redundant transmissions such as forward error correction (FEC). We also implement the proposed method in a wireless testbed, and show that the proposed method achieves high reliability in a real-world environment with practical degree of complexity when installed on current wireless devices.

A mobile terminal localization experiment using an unmanned aerial vehicle (UAV) carrying an angle-of-arrival array antenna was conducted in 2006. The UAV was a prototype stage in the development of a high-altitude long endurance platform (HALE). This UAV was used for the mobile terminal localization experiment because detecting the positions of mobile terminals is considered to be one of the fundamental applications for future High Altitude Platform (HAP) systems. The localization experiment is described in this paper, and the post-processing results obtained to date are given and discussed.

Abstract R&D on new generation mobile network has attracted a growing interest over the world on the background of rapid market growth for 2nd and 3rd generation cellular networks and wireless LANs/MANs. The National Institute of Information and Communications Technology (NICT) started the New Generation Mobile Network Project in April 2002, and has developed fundamental technologies to enable seamless and secure integration of various wireless access networks such as existing cellular networks, wireless LANs, home networks, intelligent transport systems (ITS), the Beyond‐3G (B3G) cellular and other wireless access systems. This paper overviews the achievements of the project focusing on network and access technologies. Copyright © 2007 John Wiley & Sons, Ltd.

In June and July 2002, we conducted the world's first experiments on digital TV broadcasting and third-generation mobile communications system (IMT-2000) by radio-relay at an altitude of 20 km using unmanned stratospheric-flying solar-powered aircraft. These experiments demonstrated that future broadcasting/telecom systems by high altitude platform station (HAPS) are feasible and useful. This paper describes the experimental and analytical results of the IMT-2000 experiment.

A novel radio resource management approach composed of the space division multiple access (SDMA) strategy and the dynamic resource assignment for the stratospheric platform (SPF) communication system is proposed. Since the whole channel resource is shared with each beam of the digital beamforming (DBF) multibeam onboard antenna, it realizes our objective by making good use of the spectrum resource to meet the increasing demand of mobile communications and broadband fixed wireless access (FWA) services within the limited spectrum. Computer simulation result illustrate that the communication capacity of an SPF communication system increases significantly.

A Japanese national project for the development of stratospheric platforms (SPF) started in 1998 with the goal of constructing a new communications infrastructure. This paper describes this project, including the purpose, organizational structure, and current R and D activities. It focuses on the SPF-based broadband wireless access systems including the system scenario, system configuration, and services to be supported. Key technologies, such as the onboard multibeam antenna system and channel access schemes, are described.

A digital signal processor (DSP) for a digital beam forming antenna (DBF antenna) in the L-band has been implemented using a field programmable gate array (FPGA). The DSP has 16 channel processors, where each processor calculates both I and Q data in one channel. The DSP provides multi-beam synthesis and beam selection for the DBF antenna, which has 16 element antennas.>