This research develops a method for trajectory planning of robotic systems with differential constraints based on hierarchical partitioning of a continuous state space. Unlike conventional roadmaps which is constructed in the configuration space, the proposed state roadmap also includes additional state information, such as velocity and orientation. A bounded domain of the additional state is partitioned into sub-intervals with multiple resolution levels. Each node of a state roadmap consists of a fixed position and an interval of additional state values. A valid transition is defined between a pair of nodes if any combination of additional states, within their respective intervals, produces a trajectory that satisfies a set of safety constraints. In this manner, a trajectory connecting arbitrary start and goal states subject to safety constraints can be obtained by applying a graph search technique on the state roadmap. The hierarchical nature of the state roadmap reduces the computational cost of roadmap construction, the required storage size of computed roadmaps, as well as the computational cost of path planning. The state roadmap method is evaluated in the trajectory planning examples of an omni-directional mobile robot and a car-like robot with collision avoidance and various types of constraints.

In this letter, we propose a lattice reduction (LR) aided joint precoding design for MIMO-relay broadcast communication with the average bit error rate (BER) criterion. We jointly design the signal process flow at both the base station (BS), and the relay station (RS), using the reduced basis of two-stage channel matrices. We further modify the basic precoding design with a novel shift method and a modulo method to improve the power efficiency at the BS and the RS respectively. In addition, the MMSE-SIC algorithm is employed to improve the performance of precoding. Simulations show that, the proposed schemes achieve higher diversity order than the traditional precoding without LR, and the modified schemes significantly outperform the basic design, proving the effectiveness of the proposed methods.

We developed an electrically driven near-infrared broadband light source based on self-assembled InAs quantum dots (QDs). By combining emissions from four InAs QD ensembles with controlled emission center wavelengths, electro-luminescence (EL) with a Gaussian-like spectral shape and approximately 85-nm bandwidth was obtained. The peak wavelength of the EL was blue-shifted from approximately 1230 to 1200 nm with increased injection current density (J). This was due to the state-filling effect: sequential filling of the discrete QD electron/hole states by supplied carriers from lower (ground state; GS) to higher (excited state; ES) energy states. The EL intensities of the ES and GS emissions exhibited different J dependence, also because of the state-filling effect. The point-spread function (PSF) deduced from the Fourier-transformed EL spectrum exhibited a peak without apparent side lobes. The half width at half maximum of the PSF was 6.5 µm, which corresponds to the estimated axial resolution of the optical coherence tomography (OCT) image obtained with this light source. These results demonstrate the effectiveness of the QD-based device for realizing noise-reduced high-resolution OCT.

Traffic is a key aspect of everyday life. Its study, as it happens with other complex phenomena, has found in simulation a basic tool. However, the use of simulations faces important limitations. Building them requires considering different aspects of traffic (e.g. urbanism, car features, and individual drivers) with their specific theories, that must be integrated to provide a coherent model. There is also a variety of simulation platforms with different requirements. Many of these problems demand multi-disciplinary teams, where the different backgrounds can hinder the communication and validation of simulations. The Model-Driven Engineering (MDE) of simulations has been proposed in other fields to address these issues. Such approaches develop graphical Modelling Languages (MLs) that researchers use to model their problems, and then semi-automatically generate simulations from those models. Working in this way promotes communication, platform independence, incremental development, and reutilisation. This paper presents the first steps for a MDE framework for traffic simulations. It introduces a tailored extensible ML for domain experts. The ML is focused on human actions, so it adopts an Agent-Based Modelling perspective. Regarding traffic aspects, it includes concepts commonly found in related literature following the Driver-Vehicle-Environment model. The language is also suitable to accommodate additional theories using its extension mechanisms. The approach is supported by an infrastructure developed using Eclipse MDE projects: the ML is specified with Ecore, and a model editor and a code generator tools are provided. A case study illustrates how to develop a simulation based on a driver's behaviour theory for a specific target platform using these elements.

Analog and digital collaborative design techniques for wireless SoCs are reviewed in this paper. In wireless SoCs, delicate analog performance such as sensitivity of the receiver is easily degraded due to interferences from digital circuit blocks. On the other hand, an analog performance such as distortion is strongly compensated by digital assist techniques with low power consumption. In this paper, a sensitivity recovery technique using the analog and digital collaborative design, and digital assist techniques to achieve low-power and high-performance analog circuits are presented. Such analog and digital collaborative design is indispensable for wireless SoCs.

Broadcasting and communications networks can be used together to offer hybrid broadcasting services that incorporate a variety of personalized information from communications networks in TV programs. To enable these services, many different applications have to be run on a user terminal, and it is necessary to establish an environment where any service provider can create applications and distribute them to users. The danger is that malicious service providers might distribute applications which may cause user terminals to take undesirable actions. To prevent such applications from being distributed, we propose an application authentication protocol for hybrid broadcasting and communications services. Concretely, we modify a key-insulated signature scheme and apply it to this protocol. In the protocol, a broadcaster distributes a distinct signing key to each service provider that the broadcaster trusts. As a result, users can verify that an application is reliable. If a signed application causes an undesirable action, a broadcaster can revoke the privileges and permissions of the service provider. In addition, the broadcaster can update the signing key. That is, our protocol is secure against leakage of the signing key by the broadcaster and service providers. Moreover, a user terminal uses only one verification key for verifying a signature, so the memory needed for storing the verification key in the user terminal is very small. With our protocol, users can securely receive hybrid services from broadcasting and communications networks.

This paper proposes a novel cooperative scheme combining distributed space-time block code (STBC) at physical layer, multiple access protocol at medium access control (MAC) layer and opportunistic routing without complicated routing algorithm for achieving high reliability for vehicle-to-vehicle (V2V) communications. The proposed scheme can reduce interference and collision, and achieve reducing redundant broadcast of safety-related messages for multi-hop vehicular communications on highway. In particular, we propose a novel algorithm of relay selection based-on position, speed and direction of movement to select intermediate vehicle stations (VS) with high contribution according to the transmission direction. Furthermore, in order to reduce interference and collision, we install a new timer to select a master relay vehicle station (MVS) which manages a packet transmission of whole network to trigger and synchronize transmitting timing of relay VSs (RVSs) in each hop. From the results of simulations, we can confirm that the proposed method can achieve reducing the redundant broadcast safety-related messages with keeping the packet loss probability by limiting the retransmission at each VS.

Broadcasting is the process of sending a message from one node to all the other nodes in a network. Simple flooding is the simplest form of broadcasting in ad hoc wireless networks. Simple flooding provides important control, route discovery, and network information update functionality for unicast and multicast protocols. However, simple flooding generates too many broadcast message duplications in ad hoc wireless networks. Minimum spanning tree (MST)-based flooding has traditionally been used in networks to reduce the broadcast duplications by determining broadcast trees using global topology information. However, MST-based flooding still generates a lot of broadcast traffic duplications. In this paper, we propose an efficient type of flooding, called “minimizing re-transmissions” (MRT), to significantly reduce the broadcast duplications. The purpose of MRT is to minimize the number of retransmitting nodes in an ad hoc wireless network based on the network's link state information. This advantage of minimizing the number of retransmitting nodes significantly reduces broadcast message duplications in ad hoc wireless networks. The performance of MRT is analyzed, evaluated, and compared to that of the simple flooding and the MST-based flooding. Simulations are conducted using the OMNet++ Simulator in order to validate the traffic performance analysis. For our sample network, analytical and simulation results show that MRT reduces broadcast message duplications by about 80% compared to simple flooding and by about 68% compared to MST-based flooding, thus saving a significant amount of network bandwidth and energy. MRT can be used in static or mobile ad hoc wireless networks and in wired networks to implement scalable broadcast communications.

Two spanning trees T1,T2 of a graph G = (V,E) are independent if they are rooted at the same vertex, say r, and for each vertex v ∈ V, the path from r to v in T1 and the path from r to v in T2 have no common vertices and no common edges except for r and v. In general, spanning trees T1,T2,…,Tk of a graph G = (V,E) are independent if they are pairwise independent. A graph G = (V,E) is called a 2-chordal ring and denoted by CR(N,d1,d2), if V = {0,1,…,N-1} and E = {(u,v)|[v-u]N = 1 or [v-u]N = d1 or [v-u]N = d2, 2 ≤ d1 < d2 ≤ N/2}. CR(N,d1,N/2) is 5-connected if N ≥ 8 is even and d1 ≠ N/2-1. We give an algorithm to construct 5 independent spanning trees of CR(N,d1,N/2),N ≥ 8 is even and 2 ≤ d1 ≤ ⌈N/4⌉.

A broadband mode transition between grounded coplanar waveguide (GCPW) and post-wall waveguide (PWW) is proposed. The transition is composed of GCPW, microstrip line (MSL) and PWW, where the GCPW and PWW are connected via the MSL. The transition is fabricated on liquid crystal polymer (LCP) substrate because of its low dielectric loss and cost effectiveness based on a roll-to-roll fabrication process. Center strip of the GCPW is sandwiched by two ground pads in each of which two through-holes and a rectangular slit are structured. Broadband impedance matching is achieved by this structure thanks to an addition of lumped inductance and capacitance to the transition. A part of the MSL is tapered for the broadband operation. A 25% impedance bandwidth for |S11| less than -15dB is achieved in measurement of a fabricated transition. Loss of the GCPW ground-signal-ground (GSG) pad of 0.12dB and that of the MSL-PWW transition of 0.29dB at 60GHz are evaluated from the measurement. Fabrication error and the caused tolerance on performance are also evaluated and small variation in production is confirmed. The mode transition can be used for low loss antenna-in-package in millimeter-wave applications.

The tree-based routing approach has been known as an efficient method for node mobility management and data packet transmission between two long-distance parties; however, its parameter adjustment must balance control overhead against the convergence speed of topology information according to node mobility. Meanwhile, location-based routing works more efficiently when the distance between the source and destination is relatively short. Therefore, this paper proposes a roadside unit (RSU) based hybrid routing protocol, called RSU-HRP that combines the strengths of both protocols while offsetting their weaknesses. In RSU-HRP, the tree construction is modified to take into account the link and route quality to construct a robust and reliable tree against high node mobility, and an optimized broadcast algorithm is developed to reduce control overhead induced by the advertisement message periodically sent from a roadside unit. In addition, the two routing methods are selectively used based on the computed distance in hops between a source and a destination. Simulation results show that RSU-HRP far outperforms TrafRoute in terms of packet delivery ratio, end-to-end delay, and control overhead in both Vehicle-to-Infrastructure and Vehicle-to-Vehicle communication models.

DTNs (Delay/Disruption-Tolerant Networks) composed of mobile nodes in low node-density environments have attracted considerable attention in recent years. In this paper, we propose a CD-BCAST (Contact Duration BroadCAST) mechanism that can reduce the number of message forwardings while maintaining short message delivery delays in DTNs composed of mobile nodes. The key idea behind CD-BCAST is to increase the probability of simultaneous forwarding by intentionally delaying message forwarding based on the contact duration distribution measured by each node. Through simulations, we show that CD-BCAST needs substantially less message forwardings than conventional mechanisms and it does not require parameter tuning under varieties of communication ranges and node densities.

The pilot symbols in the broadband Air-to-Ground (A/G) communications system, e.g., L-band Digital Aeronautical Communications System (L-DACS1), are expected to be also utilized for navigation. In order to identify the co-channel signals from different Ground Stations (GSs), the N-Shift Zero Correlation Zone (NS-ZCZ) sequences are employed for pilot sequences. The ideal correlation property of the proposed pilot sequence in ZCZ can maintain the signal with less co-channel interference. The simulation confirms that the more co-channel GSs are employed, the higher navigation accuracy can be achieved.

The iterative random subdivision of rectangles is used as a generation model of networks in physics, computer science, and urban planning. However, these researches were independent. We consider some relations in them, and derive fundamental properties for the average lifetime depending on birth-time and the balanced distribution of rectangle faces.

In the case of a disaster such as an earthquake or a tsunami, the city, town, and village administration usually issues an evacuation advisory and other information through the Outdoor Public Address Speakers for the disaster reduction broadcasting system covering its area of jurisdiction. However, in areas those have previous experience of a disaster, people frequently voice the lack of audibility of the disaster reduction broadcast. In this research, we conducted a questionnaire survey on the residents in the central area of Ishinomaki City, Miyagi Prefecture, who are the victims of the Great East Japan Earthquake Disaster, on the audible quality of outdoor public address (PA) speakers of the disaster reduction broadcasting system so as to understand the current state of such broadcasts and to propose ideal methods of sending and receiving information at the time of a future disaster.

In this paper, we propose an analysis of broadcasting in the IEEE 802.11p MAC protocol. We consider multi-channel operation which is specifically designed for VANET (Vehicular Ad hoc Networks) applications. This protocol supports channel switching; the device alternates between the CCH (Control Channel) and the SCH (Service Channel) during the fixed synchronization interval. It helps vehicles with a single transceiver to access the CCH periodically during which time they acquire or broadcast safety-related messages. Confining the broadcasting opportunity to the deterministic CCH interval entails a non-typical approach to the analysis. Our analysis is carried out considering 1) the time dependency of the system behavior caused by the channel switching, 2) the mutual influence among the vehicles using a multi-dimensional stochastic process, and 3) the generation of messages distributed over the CCH interval. The proposed analysis enables the prediction of the successful delivery ratio and the delay of the broadcast messages. Furthermore, we propose a refinement of the analysis to take account of the effects of hidden nodes on the system performance. The simulation results show that the proposed analysis is quite accurate in describing both the delivery ratio and delay, as well as in reflecting the hidden node effects. The benefits derived from the distributed generation of traffic are also evidenced by the results of experiments.

Providing images captured by an on-board camera to surrounding vehicles is an effective method to achieve smooth road traffic and to avoid traffic accidents. We consider providing images using WiFi technology based on the IEEE802.11p standard for vehicle-to-vehicle (V2V) communication media. We want to compress images to suppress communication traffic, because the communication capacity of the V2V system is strictly limited. However, there are difficulties in image compression and transmission using wireless communication especially in a vehicular broadcast environment, due to transmission errors caused by fading, packet collision, etc. In this letter, we propose an image transmission technique based on compressed sensing. Through computer simulations, we show that our proposed technique can achieve stable image reconstruction despite frequent packet error.

RC4 is a widely-used stream cipher, adopted in many standard protocols, such as WEP, WPA and SSL/TLS, as a standard encryption algorithm. Isobe et al. proposed a plaintext recovery attack on RC4 in the broadcast setting, where the same plaintext is encrypted with different secret keys. Their attack is able to recover the first 257bytes by exploiting the biases of the initial bytes of a keystream. In this paper, we propose two types of full plaintext recovery attacks that are able to recover all the bytes, even after the 258th byte, of a plaintext, unlike Isobe et al.'s attack. To achieve this, we combine the use of multiple keystream biases appropriately. The first attack utilizes the initial byte biases and Mantin's long-term bias. This attack can recover the first 1000 terabytes of a plaintext from 234 ciphertexts with a probability of almost one. The second attack is based on two long-term biases. Since this attack does not rely on the biases of the initial bytes of the RC4 keystream, it can recover any byte of a plaintext, even if the initial bytes are disregarded. Given 235 ciphertexts encrypted by different keys, any byte of a target plaintext can be recovered with a probability close to one.

To support the processing of spatial window queries efficiently in a non-flat wireless data broadcasting system, we propose a Two-Tier Spatial Index (TTSI) that uses a two tier data space to distinguish hot and regular data items. Unlike an existing index which repeats regular data items located near hot items at the same time as the hot data items during the broadcast cycle, TTSI makes it possible to repeat only hot data items during a cycle. Simulations show that the proposed TTSI outperforms the existing scheme with respect to access time and energy consumption.

We propose a cyclic sleep control technique for backup resources in reconfigurable optical add/drop multiplexer (ROADM) systems to simultaneously achieve power savings and high-speed recovery from failures. Processes to check the reliability of backup resources, backup transponders and paths, are also provided in the control technique. The proposed technique uses sleep mode where backup transponders are powered down to minimize power for power savings. At least one of the backup transponders is always activated after self-checking using the loopback fiber connection in the ROADM and it becomes a shared backup for working transponders to enable high-speed recovery from failures. This activated backup transponder is powered down again after the next transponder is activated. These state transitions are cyclically applied to each backup transponder. This “cyclic” aspect of operation enables network operators to continuously monitor the reliability for all backup resources with the sleep mode. The activated backup transponders at both ends of the path are used in checking the reliability of backup paths. Therefore, all backup resources, both transponders and paths, can be regularly checked with the sleep mode to ensure data are stably forwarded. We estimated the power consumption with this technique under various conditions and found a trade-off between power reduction and the recovery capabilities from failures. We achieved more than 34% power saving of backup transponders maintaining the failure recovery time within 50ms in experiments. Furthermore, we confirmed the reliability of backup paths in experiments using backup transponders with the cyclic sleep control technique. These results indicated that the proposed control technique is promising in dramatically and reliably reducing the power consumption of backup resources.