Fumie Ono

A Wireless Relay Network Based on Unmanned Aircraft System With Rate Optimization

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.

Throughput maximization for long-distance real-time data transmission over multiple UAVs

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.

Reflective Network Tomography Based on Compressed Sensing

Abstract Network tomography means to estimate internal link states from end-to-end path measurements. In conventional network tomog- raphy, to make packets transmissively penetrate a network, a cooperation between transmitter and receiver nodes is required, which are located at different places in the network. In this paper, we propose a reflective network tomography, which can totally avoid such a cooperation, since a single transceiver node transmits packets and receives them after traversing back from the network. Fur- thermore, we are interested in identification of a limited number of bottleneck links, so we naturally introduce compressed sensing technique into it. Allowing two kinds of paths such as (fully) loopy path and folded path, we propose a computationally-efficient algorithm for constructing reflective paths for a given network. In the performance evaluation by computer simulation, we confirm the effectiveness of the proposed reflective network tomography scheme.

C-band aircraft-to-ground (A2G) radio channel measurement for unmanned aircraft systems

This paper presents a summary of a measurement campaign on radio propagation channels in air-to-ground (A2G) links based on a usage scenario of unmanned aircraft services (UASs). In order to reveal their propagation characteristics, a measurement setup has been established that transmits a designed FMCW signal continuously from a small manned airplane with frequency bandwidth of 20 MHz at center frequency of 5060 MHz, and records the transmitted signals on ground as IQ waveforms by using a vector signal analyzer. Metrics on radio propagation characteristics including received signal strength (RSS) and channel impulse responses (CIRs) are obtained from the recorded data. The results on obtained RSS have shown that the trends of RSS change in the A2G links is expressed by free-space pathloss with a shadowing component encountered in mobile radio communications. Regarding the CIR in A2G links, it is observed that the radio propagation channels are expressed by a direct path and a ground reflection with scatter components; however, the direct path has margin of more than 20 dB in signal level against the other components.

Multi-Dimensional Wireless Tomography Using Tensor-Based Compressed Sensing

Wireless tomography is a technique for inferring a physical environment within a monitored region by analyzing RF signals traversed across the region. In this paper, we consider wireless tomography in a two and higher dimensionally structured monitored region, and propose a multi-dimensional wireless tomography scheme based on compressed sensing to estimate a spatial distribution of shadowing loss in the monitored region. In order to estimate the spatial distribution, we consider two compressed sensing frameworks: vector-based compressed sensing and tensor-based compressed sensing. When the shadowing loss has a high spatial correlation in the monitored region, the spatial distribution has a sparsity in its frequency domain. Existing wireless tomography schemes are based on the vector-based compressed sensing and estimates the distribution by utilizing the sparsity. On the other hand, the proposed scheme is based on the tensor-based compressed sensing, which estimates the distribution by utilizing its low-rank property. With simulation experiments, we reveal that the tensor-based compressed sensing has a potential for highly accurate estimation as compared with the vector-based compressed sensing. In order to show the possibility of the wireless tomography schemes in practical environments, we also show an experimental result in an anechoic chamber.

Virtual Cell Based Resource Allocation for Efficient Frequency Utilization in Unmanned Aircraft Systems

Recently, unmanned aircraft systems (UASs) have attracted attention as a new avenue for commercial services. Using the flexible mobility of unmanned aircrafts (UAs), commercial services can be operated in wide areas. However, there is a problem in the wireless communication between the UA and its ground station. When several UASs are operated within the neighboring airspace, wireless-communication conflicts occur. One of the most effective solutions for this issue is to decide the communication schedule using a time-division multiple access (TDMA) scheme. Furthermore, by spatially reusing the time slot, numerous UAs can be operated within the neighboring airspace, in a limited frequency band. In this paper, we propose an efficient time-slot allocation for enhancing the frequency resource utilization. Our proposed scheme determines the time-slot allocation considering the time-slot spatial reuse, using a virtual cell based space partitioning method. In addition, we consider the influence of the UA mobility on the network to decide the parameters for the proposed resource allocation system. The effectiveness of our proposed resource allocation is evaluated through computer-based simulation.

Measurements on C-band air-to-air channel for coexistence among multiple unmanned aircraft systems

The measurements of air-to-air channel at C-band for coexistence among multiple unmanned aircraft (UA) systems are presented. The measurement campaign was performed to clarify the channel characteristic of the air-to-air radio propagation between small UAs. This paper presents a measurement result of our campaign on radio channel characteristics in C-band held in Japan in March 2016. The received signal consisting of the line-of-sight (LOS) component and multi-path component formed predominately by the single ground reflected wave was observed. These results can be used to model the statistical channel characteristics in order to assist an efficient sharing of the airspace with multiple UAs.

An efficient throughput-aware resource allocation technique for data transmission in unmanned aircraft systems

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.

Adaptive boolean network tomography for link failure detection

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.

Demonstrations of combined small-UAV with satellite system for large-scale disaster

This paper describes overviews on two demonstration experiments of combinedxed- wing unmanned aircraft (UA) with satellite telecommunicatio systems for a large-scale disaster. Therst demonstration experiment is for video image delivery of disaster area even immediately after the occurrence of damage. To understand the situation in disaster area, the camera mounted on a small-UA is used in this demonstration experiment. The small-UA can photograph the moving picture during the circling, and the pictures are deliv- ered to non-isolated areas via ground station (GS) and satellite telecommunicatio system in an almost real time. The second demonstration is for providing temporal communication lines rapidly deployable to the isolated areas of disaster area until the recovery of ground infrastructures. To achieve temporal communication lines, small UA equipped with on- board transceiver (or repeater) is used to communicate with the GSs. The small UA-based wireless bridge system and satellite communication systems are serially concatenated to extend the network. This paper presents the successful results of these demonstrations and the effects of this combined system for large-scale disasters.