Intermittent Communication Links Research Articles

Communication-Aware Flight Algorithms for UAV-Based Delay-Tolerant Networks

In this paper, a wireless communication network that uses unmanned aerial vehicles (UAVs) in the sky to transmit information between ground users is considered. We highlight a delay-tolerant network, where information is relayed in a store-and-forward fashion by establishing two types of intermittent communication links: between a UAV and a user (UAV-to-user) and between UAVs (UAV-to-UAV). Thus, a flight algorithm that controls the movement of the UAVs is crucial in achieving rapid information transmission. Our study proposes new flight algorithms that simultaneously consider the two types of communication links. In UAV-to-UAV links, the direct information transmission between two UAVs and the indirect transmission through other UAVs are considered separately. The movement of the UAVs is controlled by solving an optimization problem at certain time intervals, with a variable consideration ratio of the two types of links. In addition, we investigate not only the case where all UAVs move cooperatively but also the case where each UAV moves autonomously. Simulation results show that the proposed algorithms are effective. Moreover, they indicate the existence of an optimal consideration ratio of the two types of communication and demonstrate that our approach enables the control of frequencies of establishing the communication links. We conclude that increasing the frequency of indirect communication between UAVs improves network performance.

Software-Defined Coexisting UAV and WiFi: Delay-Oriented Traffic Offloading and UAV Placement

Software-defined networking (SDN) is a cutting-edge technology, featuring a centralized control that facilitates, e.g., flexible deployment of unmanned aerial vehicles (UAVs). On the other hand, UAV-enabled communication is a promising technology due to its numerous traits such as the ability of on-demand deployment and the high likelihood of strong line-of-sight (LoS) communication links. However, UAV-enabled communication suffers non-perpetual nodes and intermittent communication links. Fortunately, SDN provisions an unparalleled global vision on such dynamic network architecture to overcome the challenges of loose links and disappearing nodes. On the other hand, there are catastrophic or remote regions where a UAV-mounted base station (BS) potentially functions without a terrestrial BS, albeit a WiFi access point (AP) may still exist. Therefore, this paper considers software-defined coexisting UAV-mounted BS (UBS) and WiFi AP, and investigates the queuing delay behavior via the UBS positioning and the AP traffic offloading. The subscribers (users) are divided into cellular subscribers (CSs) and WiFi subscribers (WSs). A CS is connected to the UBS and is possibly granted simultaneous access to the AP, leading to WiFi traffic offloading. Leveraging the software-defined global view, the objective of a software-defined controller (SDC) is to minimize the average M/M/1 queuing delay of the CSs, while guaranteeing the delay performance for the WSs, via optimizing the spectrum allocation, the UBS position, the CS association to the AP, and the CS traffic offloading. The optimization problem is non-convex, comprising binary variables, for which we use the block coordinate descent and successive convex approximation methods to find a high-quality solution. Numerical results verify that our solution achieves significant performance gains over benchmark schemes.

Coordination of Marine Robots Under Tracking Errors and Communication Constraints

This paper presents the development and the experimental validation of a centralized coordination control scheme that is robust to communication constraints and individual tracking errors for a team of possibly heterogeneous marine vehicles. By assuming the existence of a lower level target tracking control layer, a centralized potential-field-based coordination scheme is proposed to drive a team of robots along a path that does not necessarily need to be defined a priori. Furthermore, the formation is allowed to hold its position (the vehicles hold their positions with regard to a static virtual leader), which is particularly appreciated in several marine applications. As it is important to guarantee stability and mission completion in adverse environments with limited communications, the centralized control scheme for coordination is constructed in a way that makes it robust to tracking errors and intermittent communication links. The study and developments presented in this paper are complemented with field experiments in which vehicles have coordinated their operation to keep in formation over a dynamic path and static points. This work considers two types of communication technologies. Firstly, standard high rate radio communications are used to drive the formation and, secondly, acoustic communications are employed to assess the performance and the robustness of the proposed approach to degraded and highly variable conditions.

Service Oriented Robotic Architecture for Space Robotics: Design, Testing, and Lessons Learned

This paper presents the lessons learned from six years of experiments with planetary rover prototypes running the Service Oriented Robotic Architecture (SORA) developed by the Intelligent Robotics Group (IRG) at the NASA Ames Research Center. SORA relies on proven software engineering methods and technologies applied to space robotics. Based on a service oriented architecture and robust middleware, SORA encompasses onboard robot control and a full suite of software tools necessary for remotely operated exploration missions. SORA has been field‐tested in numerous scenarios of robotic lunar and planetary exploration. The experiments conducted by IRG with SORA exercise a large set of the constraints encountered in space applications: remote robotic assets, flight‐relevant science instruments, distributed operations, high network latencies, and unreliable or intermittent communication links. In this paper, we present the results of these field tests in regard to the developed architecture, and we discuss its benefits and limitations.

Push selling—Multicast messages to wireless devices based on the publish/subscribe model

Push technology automates the information delivery process by not requiring users to request for the information they need. Wireless has experienced explosive growth in recent years, and “ push” will be the predominant wireless service delivery paradigm of the future. A wide variety of services, alerts and messages, such as promotional content, will be delivered to consumers’ phones or PDA. However, to push information to a wireless device can be a challenge because of the problem of intermittent communication links and resource constraints on wireless devices as well as limited bandwidth. This paper explores an efficient multicasting mechanism that “pushes” pre-specified information to groups of wireless devices. The mechanism operates with limited bandwidth and also overcomes the connectivity problem. Based on the above concept, we have designed and implemented a system to multicast sales information via wireless technology. The system is message-oriented and JMS compliant.

Proposal of design method for fixed wireless telecommunication in 400-MHz band and measurements of propagation inside office buildings

There is no clear design guide for fixed wireless links for instrumentation in office buildings. In fact, there are no quantitative data for the propagation and fading characteristics to be utilized in link design. This article intends to provide a design guide for intermittent communication links for instrumentation in office buildings. The approach is as follows. The case where only instantaneous variation with time exists is considered. The receiver power level required to satisfy the specified transmission quality is determined. The variation of the central value depending on the site is represented as a function of the distance between the transmitter and the receiver. By superposing the variation of the central value of the site on the specified distance and variation of the instantaneous value, the zone periphery outage probability is derived, based on the case where the required transmission quality is not maintained. Then, a design guide based on the communication distance is proposed so that the outage probability is kept below the specified value. The communication completion rate is measured quantitatively by a long-term check of communication incompletion cases. The propagation characteristics of electromagnetic waves are measured for the 400-MHz band in an actual office environment. It is shown by experiments that the variation of the received power level follows the Rayleigh distribution and the distance attenuation follows an exponential function, as in a waveguide. Design of a link is attempted for an air-conditioner wireless telecontrol system, using the proposed communication distance estimation based on coefficients determined by experiment. The communicable distance is estimated as 21 m on the same floor with a seven-fold code redundant selective SD antenna. It is estimated that the required transmission quality cannot be realized in communication to adjacent floors. The communicable distance is estimated as up to 14 on in the same floor by the selective SD antenna, when the seven-fold extended code is not used. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(8): 42–52, 2000