Intelligent reflecting surfaces (IRS) are emerging as a promising technology for establishing adaptable links and addressing the limitations of direct line-of-sight (LOS) in underwater optical wireless communication (UOWC) systems. In challenging underwater environments where direct LOS is often disrupted, the IRS can provide alternative paths for stable and reliable communication. In this paper, we consider an IRS-assisted UOWC system with an autonomous surface vehicle (ASV) and autonomous underwater vehicles (AUVs) operating in realistic, dynamic conditions. To enable adaptive link switching between LOS and IRS-based paths, we apply a reinforcement learning approach using a deep$\mathbf{Q}$network (DQN). We conduct simulations over gamma-gamma channels, taking into account key degrading factors, including underwater attenuation, pointing errors, turbulence, and obstruction. System performance is evaluated in terms of both average reward and cumulative reward. Based on the obtained results, we demonstrate that the proposed method effectively maintains transmission reliability in the presence of obstacles, improving performance across various scenarios, particularly under obstruction, low attenuation, and minimal pointing error conditions.

This paper proposes an extension of CNN-based demodulation in image sensor-based visible light communication from single-color to multi-color processing. Conventional CNN-based demodulation methods mainly focus on a single color space, limiting the utilization of chromatic information. In this study, we introduce a multiplexed chromatic modulation by incorporating both Cr and Cb components into the demodulation process. To evaluate the proposed method, we conducted fundamental experiments using 24 different monochromatic backgrounds. The performance of our approach was compared with the conventional cell averaging method in terms of bit error rate (BER). Experimental results demonstrate that the proposed CNN-based demodulation with multi-color processing achieves a lower BER than conventional methods, indicating improved communication quality in image sensor-based visible light communication.

This study focuses on an uplink terminal cooperative wireless communication system that provides high-speed and stable communications in Beyond 5G/6G technologies. This system involves sharing mobile station (MS) information among multiple cooperating terminals (Helpers) using millimeter wave (mmWave) wireless communication with directional antennas. We evaluated the influence of directional antennas on the number of Helpers. Simulation results show that directional antennas can increase the number of Helpers as the number of MSs increases. In addition, for a larger number of MSs, directional antennas enable increased inter-terminal distances.

This research addresses challenges in visible light communication (VLC) systems that use two orthogonally aligned rolling shutters (RS) image sensors as receivers and an LED array as a transmitter. The study focuses on overcoming burst signal loss caused by unsensed periods between frames in RS image sensors. To improve VLC performance, we propose and compare three different schemes. The first is a conventional approach that superimposes a Barker code synchronization signal on the transmission signal using pulse width modulation (PWM). The second introduces a new method of spatial synchronization by dedicating specific LEDs in an array for synchronization signals. The third scheme extends this spatial approach by incorporating a 4 -level PWM for information transmission to increase data rates. The study aims to evaluate and compare the error rate characteristics of these three schemes, assessing their effectiveness in mitigating burst errors and enhancing overall VLC system performance. This research has potential applications, including vehicle communication, Internet of Things devices, and smartphones.

Underwater optical wireless communication (UOWC) systems are attracting attention in the context of beyond 5G/6G networks for their capacity to ensure reliable and high-data-rate communications. The system under consideration consists of underwater nodes communicating with an onshore base station through relay nodes. In such scenarios, system performance can be affected by pointing errors resulting from the movements of both underwater and relay nodes. In this paper, we investigate the end-to-end performance of a UOWC-free space optical (FSO) system under the influence of pointing errors while considering the depth-dependent characteristics of the underwater link. We present a comprehensive mathematical model that accounts for relevant impairments, including attenuation, turbulence, and pointing errors. A closed-form expression for the outage probability is derived by applying the cascaded underwater turbulence model. The results obtained highlight the validity of using a cascaded turbulence model. We also show that it is possible to determine an optimal system configuration, specifically the beam radius at the receiver, to alleviate the induced fading caused by pointing errors, thereby enhancing the end-to-end system performance.

This study focuses on visible light communications using a high-speed display and rolling-shutter camera of a smartphone. We aim to achieve high-quality communication imperceptible to the human eye through the high-speed display. The capture rate of an image sensor is generally slow. Then, the image sensor cannot obtain some parts of a transmitted data image because of the high-speed display rate. We employ the rolling shutter camera that reads pixels row by row and propose a receiving scheme in which the camera obtains some transmitted data images in a captured image. The proposed scheme can acquire transmitted data, even if the display rate is higher than the capture rate. We experimentally evaluate the proposed scheme in terms of the quality of the visual information and the communication quality to clarify its superiority.

This study proposes a flight algorithm for delay-tolerant networks using unmanned aerial vehicles (UAVs) that cooperatively serve users on the ground. Information from a ground user is relayed across UAVs in a store-and-forward manner before transferring to another user. The network performance considerably depends on how UAVs move because of this feature. In this study, two types of intermittent communication between UAVs and between a UAV and a user are jointly considered to a varying degree in the UAV operation. The measure and optimization problem for UAVs to move are devised, and this measure is heuristically maximized. Simulation results demonstrated the effectiveness of the proposed algorithm in terms of information delivery with certain insights in the UAV movement based on UAV-to-user and UAV-to-UAV communication concepts.

In imperfect communication environments, such as those with high packet loss, systems using remote videos to perform robot teleoperations exhibit video quality degradation and reduced operability, which deteriorates work quality. In this study, we proposed using a video transmission method to suppress video quality degradation and associated reduction in work quality. Instead of using video compression and transmission, we combined motion JPEG, which compresses individual frames and transmits them sequentially, with erasure correction using parity, to reduce video freezing in remote video transmission and improve work quality. To validate this method, we measured the reception rates of video frames with and without erasure correction. We conducted subjective evaluations using an industrial robot that erasure correction was effective in teleoperation environments with sufficient bandwidth. However, in environments with limited bandwidth, the increase in data volume should be considered because of erasure probability and parity assignment. Furthermore the selection of an appropriate strength of erasure correction is necessary.

This paper proposes an industrial robot system that interpolates data loss due to imperfect communication. Most wireless communication standards adopt Carrier Sense Multiple Access protocol. This protocol may introduce intentional delay in packet transmissions to avoid interference, on top of the delay caused by transmission failure and retransmission. This delay can vary the reception timing of commands to the robot, and affect the behavior of the robot. To overcome this problem, we develop an algorithm that interpolates the data not received appropriately at the robot side. Our findings demonstrate that the proposed method reduces unnecessary behavior (vibration) compared to the conventional one, thus improving the operability robot.

Intelligent reflecting surfaces (IRSs) are an emerging technology that can be used to alleviate the requirements of a strict line of sight in free-space optical communication (FSO) systems. This paper investigates the performance of an IRS-assisted FSO system under the conditions of strong atmospheric turbulence fluctuations, taking into account the impact of the spatial jitter at the transmitter and the IRS. A closed-form for the bit-error rate (BER) has been derived. The impact of the strong atmospheric turbulence is characterized using the K-distribution. The obtained results demonstrate that the performance depends on the system configuration as well as the transmitter and IRS jitter. Furthermore, we show that optimal placement of the IRS can improve the BER.

This paper presents a high-speed uplink optical wireless communication system using multiuser multiple-input multiple-output (MIMO) technique. The proposed system is composed of multiple photodetectors installed on the ceiling and multiple transmitters located near the floor with multiple light-emitting diodes (LEDs). To improve the quality of the uplink channel, we apply angle diversity for each transmitter consisting of multiple LEDs with different orientations. The performance evaluation with one transmitter fixed and the other randomly moving is conducted. Based on the obtained results, we show that the proposed system achieves a BER of each transmitter better than 10−4over most locations while maintaining a data rate of 100 Mbps.

In free space optics (FSO) communication, one of the main challenges consists in ensuring a line of sight (LOS) link between the transmitter and the receiver. To overcome this stringent requirement, intelligent reflecting surfaces (IRSs) are considered as a promising solution to provide more controllable links and increase communication coverage. In this paper, we investigate the performance of an IRS-assisted FSO system considering the most degrading factors, including atmospheric turbulence and pointing error induced fading due to both the transmitter jitter and the IRS jitter angles. A closed-form expression of outage probability has been derived. Based on the obtained results, it is shown that the system performance depends on the placement of the IRS and the atmospheric turbulence. Furthermore, we show that it is possible to determine the optimal link distance depending on the placement of the IRS.

A wireless relay network using unmanned aerial vehicles (UAVs) to deliver messages, such as damage reports and safety confirmation, in wide areas affected by large-scale disasters is proposed. In this system, UAVs move autonomously following a predetermined flight method and deliver a message in a delay-tolerant manner by transmitting it hop by hop to other UAVs within the communication range. In this study, we propose a UAV flight method for non-uniform-user-distribution environments. The proposed method is based on coverage control and utilizes the Voronoi cell with a density function. We considered cases where the user distribution was available in advance and also where it was not. Simulation results showed that the proposed method could improve effectiveness in terms of average message delivery delay, especially when the user distribution was considerably non-uniform.

This study considers an autonomous inspection system of power transmission lines using multicopter-type un-manned aerial vehicles (UAVs). In this system, base stations (BSs) are placed on power transmission towers, and the control information for autonomous flight of UAVs is exchanged between the BSs and UAVs through wireless transmissions. In this study, we conduct transmission experiments between the transmitter of a UAV and a receiver placed on the power transmission tower. In the transmission experiments, we employ LoRa in 920 MHz band and measure the received signal strength indicator (RSSI) to investigate propagation characteristics. From the measured results, we calculate the mean and standard deviation of RSSI and discuss the feasibility of the system.

This paper discusses the uplink performance of an indoor data collection system. A base station (BS) collects information sent asynchronously from multiple transmitters using the optical code division multiple access (CDMA) technique. The communication performance may degrade because of the near-far problem caused by variations in the propagation path length between each transmitter and the BS receiver. We apply spatial diversity to mitigate the interference and improve the error rate performance. In our proposed method, the correlation values are normalized at each photodetector, and the largest value is selected for symbol estimation. The obtained results show that a performance improvement can be achieved using the proposed method for a small number of users.

This paper investigates underwater optical wireless communication (UOWC) systems. We introduce a system model including the main factors impairing the optical signal intensity, i.e., light absorption, scattering, together with water turbulence, which have not been thoroughly investigated in other UOWC studies. The optimal receiver design is based on maximum a posteriori (MAP) estimation while considering not only thermal noise but also shot noise. In addition to the MAP-based receiver, a simplified configuration of the receiver is also examined. The symbol error rate (SER) is analytically calculated for 3 different modulation schemes, i.e., pulse-position modulation (PPM), pulse-amplitude modulation (PAM), and pulse-amplitude-and-position modulation (PAPM). The obtained results show that a SER of $10^{-3}$ is achieved at a distance of 20 m for all the modulation schemes. The superiority of PPM over PAM and PAPM in terms of the SER is also shown. We demonstrate that the simplified receiver obtains almost the same SER performance as the MAP receiver.

Visible light communication based intelligent transportation systems (ITS-VLC) show great potential for future urban mobility. This study presents a performance evaluation of range estimation between vehicles and infrastructures in an ITS-VLC system. In the proposed ITS-VLC system, it is easy to simultaneously conduct communication and ranging using stereo cameras. However, the stereo camera calibration becomes a problem during simultaneous communication and ranging due to vehicle vibration. Using the data from LED transmitters and stereo cameras, it can obtain multiple measurements of distance. The monocular-stereo fusion algorithm is applied to visible light ranging in the proposed scheme using particle swarm optimization. We employed real data from the field trial experiment and achieved a ranging accuracy of 60 ± 1.0 m.

A wireless LAN relay system is designed to extend the transmission range while maintaining stable communication. In this paper, we propose a wireless LAN relay system using multicopter unmanned aerial vehicles (UAVs) and evaluate the communication performance. For the demonstration experiment, we employ air-to-air and ground-to-air communications, where the former is a link between UAVs, and the latter is a link between a UAV and ground node. We measure the throughput and the received signal strength indicator, and clarify the communication performance of the wireless LAN relay system.

This paper presents an image sensor communication (ISC) using a digital micromirror device (DMD) projector as a transmitter. In particular, we focus on ISC for intelligent transport systems (ITSs) because DMD projectors are expected to be used in road traffic, such as vehicle headlights, street lights, and traffic signs. The DMD projector controls light patterns by switching tilt of micromirrors at high speed. Compared to the conventional LED array transmitter, DMD projector can design and alter the shape of the light pattern and data rate of transmission more easily. In the proposed system, the data rate can be easily increased by increasing the number of multiplexes. However, as the number of multiplexes is increased, the number of received pixels on the image sensor is decreased, and thus the performance of symbol detection deteriorates. Therefore, the purpose of this paper is to examine the relation between the number of received pixels per cell and communication performance for transmission pattern design. Hence, we experimentally clarify this relation using our prototype system via a DMD projector and a high-speed camera.

Wireless communication in an intelligent transport system (ITS) requires high quality and low latency vehicle-to-infrastructure (V2I) transmission. However, fading occurs because of vehicle movements and this results in transmission errors, leading to frequent retransmission requests that require long delay times. Furthermore, in suburban areas, the distance between base stations (BSs) and vehicles tends to be long and the quality of wireless transmission degrades. To address this problem, we employ diversity transmission schemes, particularly frequency diversity, because these schemes are effective to increase the throughput. In this paper, we propose a frequency scheduling-based cooperative V2I uplink transmission scheme using vehicle-to-vehicle (V2V) side link (SL) communication in LTE-V2X to achieve improvements in far vehicle transmission from a BS, including efficient frequency use. To verify the proposed scheme, we execute traffic simulation in a suburban road model and apply the proposed transmission scheme to several vehicles. The simulation results demonstrate that the proposed scheme can improve the performance of uplink far-vehicle transmission to the BS compared with conventional schemes.

In a large-scale indoor environment such as an industrial one, a multiple-input-multiple-output optical wireless communication (MIMO-OWC) system represents a flexible and easy-to-deploy solution to achieve point-to-point long-distance and high-speed data transmission. The majority of imaging MIMO-OWC systems have mainly targeted high data rate communication over short distances, not exceeding 10 m. In this work, on the contrary, we focus on longer-distance links providing high-speed transmission data rate. For this purpose, we propose an imaging MIMO-OWC system that features an improved optical modulator array with a one-dimensional element arrangement, and a new imaging receiver using long focal length lenses placed in front of the receiving photo-detector array. The performance of the proposed system is then experimentally evaluated. The obtained results show that the measured MIMO channel matrices have sparse patterns, which means that the elements not corresponding to the emitted beams are nearly zero. We successfully demonstrate the transmission at a high data rate of 100 Mbps over a long distance of 50 m. This result surpasses the achieved distance corresponding to the conventional MIMO-OWC system using an independent optical system for each light-receiving element. Consequently, the experimental results confirm that our proposed system has the potential for higher speed with longer distances.

This paper focuses on high-speed stereo camera receivers for visible light communication (VLC) in intelligent transport systems (ITSs), contrary to conventional studies where a single (high-speed) camera is used. An advantage of high-speed stereo cameras as VLC receivers is that both front-facing ranging and wireless communication can be achieved in one device. In this paper, utilizing features of VLC, we consider stereo ranging with high accuracy. Moreover, it is known that an LED transmitter for VLC has specific features, high-luminance and high- speed blinking. This paper proposes stereo ranging by applying LED transmitter detection (utilizing these features) to disparity estimation. Additionally, we introduce subpixel estimation using equiangular line fitting to obtain more accurate disparity. Finally, we experimentally demonstrate that the proposed stereo ranging achieves an accuracy of 60 m ± 0.1 m.

This study considers a power line communication (PLC) based multi-machine feedback control system. In PLC, channel characteristics have cyclostationary features synchronous to the mains voltage, and based on the multiple access schemes, the communication performance significantly differs. In this situation, previous work has evaluated the system which uses time division multiple access (TDMA) and found that the controlled quality of each machine becomes unequal. This manuscript thus proposes employing synchronous code division multiple access (SCDMA) and compares the control performance with the system using TDMA. As a result, using the proposed SCDMA, it is observed that all the machines achieve the same control quality, and the control quality itself is better than that with TDMA when the signals are much stronger than noise.

In this paper, we examine wireless relay networks using drones as emergency communication systems during large-scale disasters. Flying drones are inclined in the direction of their movement. This inclination causes a reduction in the received power when taking into account the effects of antenna directivity in the vertical plane and the polarization plane deviation. In this paper, we model the relationship between the inclination and flying speed of drones and derive the received power taking into account the inclination. We evaluate the influence of the drone's inclination on the delay time through simulation. The results indicate that the speed of the drone that achieves the shortest delay time is dependent on the number of drones.

For efficient collection of the leaf temperature data over the entire farm, we simultaneously use a drone in the sky and sensor nodes on the ground that are both equipped with infrared thermometers. In this study, we propose a communication protocol for wireless sensor network (WSN). The preliminary results of a prototype experiment show that the measurements are sufficiently synchronized for collecting useful leaf temperature data.

In-vehicle cameras can be used as receivers for visible light communication in addition to their primary functions: for viewing assistance and object recognition. Most studies with this design perform tests via a single high-speed camera that is used as the receiver, but this study employs a receiver that uses a high- speed stereo camera. The reception method developed in this paper effectively utilizes left and right stereo images to improve communication performance. Although the selective diversity reception method proposed in previous work improved communication performance, it cannot deal with cases wherein both the left and right cameras introduce errors. To further improve the communication performance of this system, maximal ratio combining (MRC) diversity is applied to the high-speed stereo camera in this study. Communication performance is then evaluated comparing to the selective diversity reception and conventional single-camera reception by experimental tests conducted under static and driving conditions.

For large-scale disasters, it is important to ensure communications to confirm the information about safety and disaster situation. Then, this paper focuses on an emergency communication system using drones. In this system, an important issue is to shorten the delay time of transmitting information. Since delay time depends highly on a flight scheme of the drones, we propose two flight schemes: a rebounding-flight scheme and a common-flight-path scheme. Moreover, we consider breaks of drones due to their battery exhaustion because it is impossible for the drones to fly permanently. We evaluate the delay time with and without drones' breaks for the proposed flight schemes. Our results show that the proposed flight schemes are effective to reduce the delay time even if the drones' breaks are considered.

In this paper, a cross-layer design for communication and control layers for wireless feedback control systems is considered, and an optimized receiver design for state feedback is proposed. The proposed receiver is designed on the basis of a maximum à posteriori probability decision and utilizes the control layer's information, namely, the estimated state information of a Kalman filter-based state observer, as the à priori information of the transmitted state feedback. In addition, the proposed receiver provides the error covariance information of the received state feedback for the control layer. The recursive structure of the receiver and state observer is simple and suitable for the feedback control loop. The improvement in the channel error probability is supported by the control accuracy and vice versa. Numerical results show that the proposed receiver can effectively reduce the number of channel errors in the received state feedback and improve the control performance.

In cooperative intelligent transport systems, local dynamic maps (LDMs) are used to achieve safe and efficient transport systems. To transmit LDM data, a reliable, low-latency wireless communication is required. However, the transmission quality between base stations and distant vehicles often degrades, resulting in delays due to retransmission requested by upper-layer protocols. To solve it, in this paper, we propose an uplink cooperative relay transmission scheme using two timeslots in the physical layer, where a vehicle close to a base station relays data from a more distant vehicle. The scheme uses non-orthogonal superposition relaying at the close vehicle and maximum ratio combining at the base station, and improves quality of the data received by the distant vehicle. In addition, high-latency retransmission can be avoided using this scheme. The performance of the proposed scheme is evaluated with link budget calculations and numerical simulations, and it is shown that the proposed scheme greatly enhances a throughput of the distant vehicle.

Packet losses degrade the performance of wireless feedback control systems. The use of channel coding may decrease the packet loss rate; however, its redundancy decreases the packet transmission rate under the same bit rate and thus degrades the control quality. In this paper, we propose a variable length channel coding scheme for state feedback without decreasing the packet transmission rate. The proposed scheme reduces the number of state variables to be fed back and instead adds redundant bits of channel coding on the basis of state estimation error. We show that the proposed scheme improves the control quality without decreasing the packet transmission rate.

In wireless feedback control systems with multiple plants, state information and control information are sent over a shared communication channel. The IEEE 802.15.4 beaconenabled mode has a contention access period (CAP) and a contention free period (CFP). In the CAP, carrier sense multiple access/collision avoidance (CSMA/CA) is used. In the CFP, time division multiple access (TDMA) is used. This paper considers wireless control over the IEEE 802.15.4 beacon-enabled mode and discusses how to use the CAP and the CFP. We propose two schemes that assign the plants to the CAP and the CFP; one is based on communication success/failure and the other is based on control error between state information and the target value. We show that the proposed assignment schemes improve the quality of an overall plant control compared with random assignment. In addition, the scheme based on the control layer achieves better control quality than that based on the communication layer.

Multiple access communication is required to control multiple plants via wireless communication channels. This study discusses time division multiple access (TDMA) schemes to improve control quality for feedback control of multiple plants. To improve the control quality, time slot allocation of the TDMA should be based on information of the control layer, i.e., control objective and plant's state. In wireless control of multiple plants, there are different target values for the plants and different packet losses on communication channels. This leads to different tracking performances among the controlled plants. Therefore, a flexible time slot allocation scheme that considers the tracking performances is required. In this paper, we propose time slot allocation schemes to minimize predicted tracking error on the controlled plants. One minimizes the predicted tracking error in all time slots, and the other sequentially minimizes that in each time slot. Numerical results show that the proposed schemes can improve an overall control quality under packet loss.

In this paper, we consider the reduction of the amount of transmission data in wireless feedback control systems. Because available frequency bandwidth is limited in wireless communication, the amount of control data that can be transmitted in a sampling period is limited. A source coding scheme that has variable length codes can efficiently reduce the amount of transmission data; however, a variation in packet loss rate due to the variable code length highly affects the control quality. If control data are assigned to long codes, packet loss rate of the data becomes large. Therefore, the control quality deteriorates if control data of high importance are assigned to long codes. From this view point, we propose a source coding scheme that considers the importance of control data. We evaluate the performance of the proposed coding scheme under a data-rate constraint and show that the proposed coding suppresses the deterioration of the control quality and reduces the amount of transmission control data.

This paper considers H∞control for wireless networked control systems with data packet loss. In wireless networked control systems, the control performance deteriorates due to packet loss. Therefore, packet loss is one of major weakness in the wireless networked control systems. To overcome this weakness, this paper proposes a new control design that considers the influence of packet loss as a disturbance. Our new control design belongs to the H∞control design and can reduce the influence of disturbances acting on the controlled object. Numerical examples show that the proposed H∞control design can more effectively reduce control performance deterioration due to packet loss. This paper provides not only the proposal of the new control design but also control performance comparisons of the proposed control design and the Linear Quadratic (LQ) control design. Numerical examples show that the control performance of the proposed H∞control design is better than that of the LQ control design.

Digital signage, which is advertising media using a liquid crystal display (LCD), is increasing in popularity. One possible application is wireless communications between digital signage and viewers. We focus on image-sensor-based visible light communication (VLC). Image-sensor-based VLC requires only an image sensor (IS), which is common equipment in smart phones. In the proposed method, an information signal is displayed on LCD. However, embedding the information signal into an advertisement may decrease the quality. We propose blue color difference modulation to make such signals imperceptible. We implemented a VLC system between digital signage and IS to demonstrate, the effectiveness of the proposed modulation in a real environment.

We focus on MIMO mesh networks, which consist of wireless nodes supporting MIMO transmission. Communication quality of a wireless link using MIMO spatial streams is sensitive to change in its channel, and performance will be unstable. For stable operation of MIMO mesh networks, a method analyzing the MIMO mesh networks is needed. In this paper, we aim to propose an analyzing method of MIMO mesh networks. We measure the time variation of throughput and Received Signal Strength Indicator (RSSI) as feature values of a link in our testbed of the MIMO mesh network, and analyze the measurement results by using Self-Organizing Map. As a result, we confirm that it is possible to find the links that have correlation with time variation of throughput and RSSI by applying SOM to the measured feature values.

Our goal is the improvement of the data collection in solar-powered wireless sensor networks. One of the methods to improve the data collection is cooperative transmission by which a node relays data from a source node to a base station. However, the cooperative transmission is not enough to prevent the data collection performance from the decline in low power generation, such as in a cloudy day and at night. We tackled this problem by introducing a repeater role to same nodes, which only relays data from the other nodes without transmitting its own data. Our proposal improves the data collection performance in the low power generation. Numerical examples compare and show the effectiveness of the conventional method and three assignment methods of the repeater role: one is to assign the repeater role to some nodes fixed in place around the farthest nodes, one is to assign the repeater role uniformly randomly to some nodes, and another is to assign the repeater role to some nodes that do not have sufficient battery levels.

An emergency node-combined wireless network that uses balloons, electric vehicles, and unmanned aerial vehicles (UAVs) was proposed. We discuss the construction and specific issues of this network. The communication area is evaluated by changing the node elevation. In this network, the elevations of balloon and UAV nodes vary, and the communication area changes with elevation. In addition, the network may be temporarily disconnected by changes of the communication area. To solve this problem, we employ a delay-tolerant network technique. We evaluate the number of nodes and node density according to the desired application and regional characteristics.

A distributed and expansible architecture for providing message communication service to nodes, which are typically shelters, in a wide disaster-affected area is presented. The large disaster-affected area is divided into a number of sub-areas, to each of which a pair of electric and unmanned aerial vehicles (EVs and UAVs) is assigned. Message files are sent and received through a wireless link between each node and the UAV flying over the node. They are also carried by this UAV (end-to-end-transfer) or carried/relayed by multiple UAVs (relay transfer) from/to the center station in the area. For simple square area modeling, sub-area formation methods such as time-uniform, space-uniform, and hybrid-uniform divisions are established for end-to-end transfer. The relay can be performed synchronously or asynchronously in relay transfer. Several observations are made through numerical examples.

In this paper, we propose area transmission efficiency to evaluate the performance of single-user multiple-input multiple-output (SU-MIMO) and multi-user MIMO (MU-MIMO) in wireless mesh networks (WMNs). The area transmission efficiency is the number of packets that can be transmitted per unit time and per area, and is calculated by considering the multiplexing effect of MIMO and the density of transmitting nodes. The performance of SU-MIMO and MU-MIMO is evaluated and compared in term of the area transmission efficiency in WMNs. As a result, the area transmission efficiency of MU-MIMO can be superior to that of SU-MIMO when the number of queueing packets is small. Conversely, this relationship is reversed when the number of queueing packets is enough large. In addition, by selecting the transmission packets so as to reduce the number of receiving nodes, MU-MIMO is always superior to SU-MIMO.

Channel modeling is critical for the design and performance evaluation of visible light communication (VLC). Although a considerable amount of research has focused on indoor VLC systems using single-element photodiodes, there remains a need for channel modeling of VLC systems for outdoor mobile environments. In this paper, we describe and provide results for modeling image sensor based VLC for automotive applications. In particular, we examine the channel model for mobile movements in the image plane as well as channel decay according to the distance between the transmitter and the receiver. Optical flow measurements were conducted for three VLC situations for automotive use: infrastructure to vehicle VLC (I2V-VLC); vehicle to infrastructure VLC (V2I-VLC); and vehicle to vehicle VLC (V2V-VLC). We describe vehicle motion by optical flow with subpixel accuracy using phase-only correlation (POC) analysis and show that a single-pinhole camera model successfully describes these three VLC cases. In addition, the luminance of the central pixel from the projected LED area versus the distance between the LED and the camera was measured. Our key findings are twofold. First, a single-pinhole camera model can be applied to vehicle motion modeling of a I2V-VLC, V2I-VLC, and V2V-VLC. Second, the DC gain at a pixel remains constant as long as the projected image of the transmitter LED occupies several pixels. In other words, if we choose a pixel with highest luminance among the projected image of transmitter LED, the value remains constant, and the signal-to-noise ratio does not change according to the distance.

In wireless feedback control systems, reducing packet loss is critical. The use of channel coding may decrease such packet loss; however, redundancy in channel coding also decreases the packet transmission rate although the bit rate remains the same. Thus, control systems are highly affected by disturbances. To improve control system quality, channel coding should be adaptively employed on the basis of packet loss and disturbances. Herein, an on-off error control coding scheme based on the communication and control layers is proposed. In this scheme, channel coding is adaptively used to minimize tracking errors in a controlled plant. Results demonstrate that the proposed on-off error control coding scheme improves the control system's reference tracking performance compared with that when using a fixed-rate coding scheme.

The present paper proposes a novel multiple-LED-arrays acquisition for an infrastructure-to-vehicle visible light communication (I2V-VLC) using LED arrays (transmitter) and an in-vehicle high-speed image sensor (receiver). In order to achieve a robust detection of LED arrays, we employ the block matching algorithm, which is a way of finding a corresponding position between two successive frames. The proposed method divides a captured image into a number of small domains (blocks) and determines if the LED array is present or absent using the block matching. We perform I2V-VLC experiments with multiple-LED arrays and evaluate the acquisition capability of the proposed method.

Packet loss is the major weakness of wireless feedback control systems. In this paper, we discuss the improvement of the control quality of wireless feedback control systems with Forward Error Correction (FEC) coding. If FEC coding is used, packet losses may decrease. But its redundancy decreases the packet transmission rate under the same bit rate, so that the control quality will be worse. Therefore, we propose an adaptive coding scheme to improve the control quality. In this scheme, FEC coding is used adaptively based on a predicted state of the controlled plant. Our proposal is the first approach in the field of adaptive channel coding for wireless feedback control systems because this scheme adapts channel coding to the quality of the control layer (application layer). In this paper, we show that the proposed adaptive coding scheme improves the control quality more than that of the fixed rate coding in Rayleigh fading channels.

In wireless feedback control systems, it is important how to reduce packet losses. If channel coding is used, packet losses may decrease. But its redundancy decreases the packet transmission rate under the same bit rate, so that disturbances in the controlled plant may deteriorate the quality of the control system. To improve the quality of the control system, the channel coding should be used adaptively based on packet losses and disturbances. In this paper, we propose an adaptive coding scheme based on the quality of the communication layer and the control (application) layer. In this scheme, the channel coding is used adaptively based on a predicted state of the controlled plant under a packet loss rate. We show that the proposed adaptive coding improves the control quality compared with that of the fixed rate coding.

This paper proposes a joint coding scheme for information advertisement in wireless mesh networks. Random network coding is a technique that can mitigate the effect of a broadcast storm problem. However, it cannot correct bit errors, and it should forward more and more packets to recover bit errors. On the other hand, multi-route coding was proposed to reduce bit errors on wireless channels. This coding scheme can obtain a diversity gain by transmitting multiple coded packets on multiple routes. This paper proposes the joint coding scheme by using random network and multi-route coding to reduce the effect of the broadcast storm problem and bit errors. We evaluate the performance of the proposed coding scheme by simulation. The results show that the proposed scheme improves the transmission delay and packet delivery failure ratio compared with the conventional schemes.

In this paper, we focus on a road-to-vehicle visible light communication (VLC) system using LED traffic lights. In this system, an LED traffic light consists of a 2-dimensional LED array (2D LED array), and cars are equipped with high-speed 2-dimensional cameras (2D image sensors). An important issue of this system is frame loss. Sometimes, 2D image sensor in a car fails to get a frame. So as to mitigate the influence of frame loss, we propose to apply erasure coding to the road-to-vehicle VLC system. In the proposed system, a data sequence is encoded by LDPC code whose length is much longer than the size of 2D LED array. In addition, code synchronization is required for the proposed system. We also propose a code synchronization scheme, which makes use of error detection capability of LDPC code. We evaluate the performance of our proposed system, and show that it can recover frame loss for high SNR when less than 8 frames among total 18 frames are lost. In addition, we show that our proposed code synchronization scheme can ignore its errors.

Network coding has been studied as a solution to mitigate traffic concentration at a bottleneck node in wireless multihop networks. When network coding is applied to a unicast flow, the decoding nodes overhear packet transmissions, receive all packets which are headed for not only themselves but also the other nodes, and store them. The reception of undesired packets is, however, unreliable, and this unreliability causes the decoding failure for network coding. In this case, the encoding node has to retransmit the packet somehow. In this paper, we discuss an ARQ scheme using a negative acknowledgement (NACK). By simple model simulation, our proposed scheme can improve overflow rate, compared with no network coding. Furthermore, a realistic protocol for our proposed scheme is developed, and its simulation results show that our proposed scheme is very effective to mitigate the degradation at the bottleneck node.

This paper introduces a Visible Light Communication (VLC) system using an LED sign panel, which allows the provision of broadcast-type information in public spaces. This system provides an additional function to an LED advertisement panel; the panel not only displays an advertisement, but also transmits wirelessly to other devices. We suggest its use in benefit of the visually impaired. They can obtain local information by using this system, named i-LightHouse (i-LH). For this purpose, i-LH transmits a long-range navigation signal to direct users to the LED sign panel and a short-range signal to download content information to the users' devices. We propose its modulation scheme which can multiplex the navigation and content information at the same time. In this system, the interruption by a passerby and ambient lights may degrade the communication performance. On these issues, we propose an error correcting method and a filter to mitigate the interference of them and evaluate the effectiveness.

IEEE802.11a/b/g Wireless LAN (WLAN) supports multiple transmission rates for packet transmission. In a mesh network backbone using WLAN, it is desirable to select and use an optimum transmission rate in order to achieve high throughput. Transmission rate can be set fixedly or adaptively. The former is further classified to link-based and node-based. In this paper, three transmission rate selection methods, link-based fixed optimum rate transmission, node-based fixed rate transmission and adaptive rate transmission are experimentally evaluated. It is shown that the link-based fixed optimum rate transmission method outperforms the other methods in the average throughput.

IEEE 802.11 wireless interface supports multiple transmission rates. It is an important problem how to select the transmission rate so that the throughput is maximized. In a wireless mesh network (WMN), nodes are stationary placed in general. The characteristic of each link will not change significantly over relatively long time. It is effective to assign fixed transmission rate which achieves the best transmission performance at each link while link quality does not change significantly. There are two of for fixed transmission rate assignment schemes. One type assigns a transmission rate at each link (link-fixed), and the other assigns it at each node (node-fixed). In this paper, we propose a novel node-fixed transmission rate assignment scheme. Our proposed scheme tries to increase throughput on the condition that the network connectivity of all nodes in the WMN is kept. We evaluate the proposed scheme by experimental measurement using our testbed. Compared with the scheme that the same transmission rate is assigned to all nodes, our proposed scheme can improve the minimum throughput although the average throughput of both schemes is almost the same.

As one of ITS technique, a new visible light road-to-vehicle communication system at intersections is proposed. In this system, the communication between a vehicle and an LED traffic light is conducted using an LED traffic light as a transmitter, and an on-vehicle high-speed camera as a receiver. The LEDs in the transmitter emit light in high frequency and those emitting LEDs are captured by the high-speed camera for making communication. Here, the luminance value of LEDs in the transmitter should be captured in consecutive frames to achieve effective communication. For this purpose, first the transmitter should be found, then it should be tracked in consecutive frames by processing the images from the high-speed camera. In this paper, we propose new effective algorithms for finding and tracking the transmitter, which result in a increased communication speed, compared to the previous methods. Experiments using appropriate images showed the effectiveness of the proposals.

A wireless mesh network (WMN) is one of important applications for mobile ad hoc networks (MANETs). Most researches about WMN employ IEEE 802.11 wireless LAN in wireless links. IEEE 802.11 supports multiple channels. Performance improvement strategies by using multiple interfaces and multiple channels were discussed. In this paper, we propose to apply a 3-sector antenna system to multi-interface and multi-channel WMN. In cellular networks, the 3-sector antenna system is widely used for enhancement of user capacity. Further improvement will be obtained if the 3-sector antenna system is applied to WMN. WMN has different features from cellular networks. In particular, the hidden node and exposed node problems are very important in WMN. The 3-sector antenna system is compared with the omni-directional antenna systems in terms of contention and collision rates. As a result, both rates of the 3-sector antenna system is smaller than or equal to those of the omni-directional antenna systems. The throughput is also analyzed with the consideration of hidden and exposed node problems. From the numerical results of the throughput analysis, the 3-sector antenna system achieves much better throughput performance than those of the omni-directional antenna systems.

Wireless Mesh Networks (WMN) is an essential technology based on mobile ad hoc networks (MANETs). A three sector antenna system applied to WMN was proposed in early 2010, and system performance was analyzed. In this paper, we introduce a real-world three sector antenna system set up in the current WMN test bed in Niigata University, which employs IEEE 802.11 wireless LAN and supports multi-interface and multi-channel. Channel assignment is performed to the system, and two network patterns are acquired. A series of real-world single-flow and multi-flow throughput measuring experiments are performed to the two network patterns using three sector antenna system. The performance and characteristics of the system are discussed. The test bed node has the exchange function of three sector antenna and omni directional antenna. We discuss a preliminary comparison between the two antenna system. And the three sector antenna system achieves much better throughput performance than the omni directional antenna system on the basis of the one-hop throughput measuring experiment.

In this paper, we consider visible light communication systems using LED array as a transmitter and high-speed camera as a receiver for Intelligent Transport System (ITS). Previously, we have proposed the hierarchical coding scheme which allocates data to spatial frequency components of the image depending on the priority. This scheme is possible to receive information of the high-priority even if communication distance is long. However, we need to distinguish multi-valued data from the received image by using a hierarchical coding. In this paper, we propose two improved decoding methods, and demonstrate to distinguish multi-valued data more correctly in the experiment.

We propose a novel communication system for evacuees of shelters, termed "Shelter Communication System (SCS)". SCS is composed of a computer (termed Shelter Server) connected to the Internet and a set of personal computers (termed shelter PCs), one in each shelter, connected to Shelter Server through a temporal link and the Internet. SCS provides a message communication service between shelters as well as between shelters and outside the disaster area. Neither computer terminals nor cellular phones are required for those in the shelters. They write messages on specially-designed message sheets by hand. They receive messages on the sheets of paper printed by Shelter PCs. A prototype of SCS has been developed. A simple evaluation shows that SCS could provides service for 15,000 shelters and 750,000 people there, using 10 earth stations and wireless mesh networks.

An inter-vehicle communication system, called vehicular ad hoc network (VANET), is one of the most promising applications of a mobile ad hoc network (MANET). One of the important issues in VANET is scalability. Compared with topology-based routing protocols, a routing protocol using position information may alleviate the issues of scalability or control overhead. Car navigation systems using a global positioning system (GPS) are widespread, and position-based routing is a useful approach in VANETs. A next-hop forwarding method is a type of position-based routing protocol, wherein a selection scheme for the next-hop node is very important. In this paper, we propose a novel selection scheme for the next-hop node in the next-hop forwarding method in VANET. In the proposed scheme, a new link metric, expected progress distance, is introduced in order to consider both forwarding distance and transmission quality of the wireless link. We evaluate the performance of our proposed scheme, and show that it can achieve much higher throughput and a better packet delivery ratio than existing conventional schemes.

One of the important issues in Mobile Ad Hoc NETworks (MANETs) is assignment of Internet Protocol (IP) addresses to nodes. Several address assignment schemes are discussed in Autoconf working group in Internet Engineering Task Force (IETF). These schemes are based on autonomously decentralized manner, and it may cause duplication of assigned IP addresses. The duplication of IP addresses disturbs route computation because routing protocols assume uniqueness of IP addresses. Therefore, a Duplicate Address Detection (DAD) scheme is needed. Weak DAD uses a unique key for the detection of duplicated IP addresses. This key is advertised together with the IP address in control messages for routing. By finding the conflict of keys, duplicated IP addresses are detected. This scheme can use a simple rule, but it requires large overhead because key size should be large enough to satisfy the uniqueness. In this paper, we propose a partial-key DAD for the reduction of control overhead. In the partial-key DAD, the original key is divided into several partial keys, and one of them is attached to each control message. We evaluate the performance of the partial-key DAD, and show that it can reduce the control overhead although the resolution time of duplicated IP addresses increases slightly.

One of the solutions to mitigate degradation due to traffic concentration on certain nodes is network coding in ad hoc networks. When network coding is applied to unicast traffic, it is necessary to satisfy two condition; (a) an encoding node has to know which packets the neighbor node stores, and (b) decoding nodes have to hold all native packets encoded in the received packet except for the desired native packet. Because of these conditions, some retransmission schemes can be considered. In our study, we propose three retransmission schemes for network coding in ad hoc networks, and compare the performance. From the result, it is found that the scheme in which decoding nodes that fail in decoding the received packet and return NACK to the encoding node decreases the overflow rate the most.

We study the connectivity in vehicular ad-hoc networks, where the motion of vehicles is constrained on a lattice-shaped road network. First, we theoretically investigate the connectivity under the Poisson-positioning assumption, where vehicles are positioned according to a Poisson process on each road at any arbitrary instants. We find that the Poisson-positioning assumption allows the existence of the finite critical-vehicle density; that is, if (and only if) the density of vehicles is greater than the finite critical density, then there exists a large (theoretically infinite) cluster of vehicles and an arbitrary pair of vehicles in the set is connected in single or multiple hops. We obtain an analytical expression for the critical density as a function of the transmission range of each vehicle and the distance between intersections. Next, we consider the connectivity under more realistic movement patterns of vehicles where the Poisson-positioning assumption does not hold. We numerically find that, even in non-Poisson-positioning cases, there exists the critical vehicle density. The critical density in non-Poisson-positioning cases is, however, larger than the one under the Poisson-positioning assumption. We also gain some insight on the efficiency of roadside-relay-station deployment to provide better connectivity between vehicles.

In a sensor network, a lot of distributed sensor nodes observe a certain area or environment, and transmit the observed data to a sink. The observed data sequences may have space- and/or time-dependent correlation. This correlation is regarded as redundant information and can be used for error correction by the joint decoding. In this paper, we propose the joint decoding scheme using the time-dependent correlation between the continuous data sequences generated by a sensor node. We also propose a power control scheme using the time- dependent correlation for saving energy consumption. The packet error rate and the energy consumption ratio are evaluated and the effect of our proposed schemes are clarified.

Wireless sensor networks (WSNs) usually have a regular lattice structure and can be considered as multi-hop multi-route networks. In multi-route transmissions, even if the link quality of several routes decreases, the whole performance of the communication would be compensated by the help of the other routes, which is referred to "the route diversity effect". As generally known, forward error correction (FEC) techniques can enhance the route diversity gain. In this paper, route diversity effect in WSNs using turbo codes is investigated. We introduce a WSN having a triangle lattice structure. BER performances of an additive white Gaussian noise channel and a slow Rayleigh fading channel are evaluated in order to show the route diversity effect.

We propose a contention-free medium access control (MAC) protocol for inter-vehicle communication systems that share information for the improvement of safety drive on the highway. In the proposed system, contention-free medium access is achieved by periodical one-way token transmissions. The token contains the frame information about the transmission/reception phase. While the token is relaid by one-way, the vehicle which has the token can send a packet to both up- and down-link. The token transmission interval is set not to be interfered from other transmit vehicles at a receive vehicle. In addition, multiple channels are used and allocated dynamically for every token transmission to reduce the transmission waiting time. We also evaluate the maximum end-to-end transmission delay of the proposed protocol, and clarify that the proposed protocol can guarantee the transmission within allowable delay time.

VANET is an application of a mobile ad hoc network to inter-vehicle communication. Each vehicle is aware of its position information by GPS or other methods. Position-based routing is a useful approach in VANET. The Position-based routing protocol can be classified roughly into a next-hop forwarding method and a directed flooding method. We evaluate performance of both methods by analysis and simulation and compare them in this paper.

A wireless mesh network has much attention for various applications such as home networks or hot spot services, and its standardization is now progressing at the IEEE 802.11s task group. One of the most important issues of the wireless mesh network is how to handle the association information of huge number of legacy user stations (STAs). In this paper, we propose a low-overhead handling scheme of the STA association information in order to solve this issue. In the proposed scheme, we introduce an on-demand approach to handle the STA association information. We also evaluate the overhead of the proposed scheme, and clarify its superiority.

In this manuscript, a decode-and-forward cooperative diversity scheme for wireless packet transmission network with large and undetermined set of relay terminals is considered. Correctly received signals at some relay terminals are retransmitted to the receiver with the STBC-based cooperative relaying scheme. For large and undetermined set of relay terminals, performance of the conventional STBC-based cooperative diversity is known to be degraded due to the loss of the diversity gain and increasement of decoding complexity. In this manuscript, we propose a signaling scheme to reduce the performance loss. Our proposed scheme is based on the linear transformation of the STBC matrix by a signature vector, which has more degrees of freedom for the assignment of signals compared to the conventional STBC-based cooperative diversity.

For safety applications, automotive radar networks show an interesting potential. Apart from long range radars, networked short range radar systems are under development. Additional applications can be accomplished, such includes precrash detection, parking aid and blind spot surveillance. We research the automotive radar networks using short range radars. The network is built with multiple radars. In this paper, we consider data processing using measured ranges provided by the radars in order to estimate multiple target positions with high accuracy. Firstly, we derive a method based on MAP estimation. Secondly, we propose a method which reduces the calculation complexity compared to the above MAP method. Finally, we introduce a method which can detect targets with low undetected targets. The case often happens when the measured ranges are lost because of miss-detections. We evaluate the performance with computer simulations.

In the multihop cellular networks, multiple routes from a user station to a base station can be established because of the flexibility of network topology. In order to reduce packet errors of wireless transmissions, we proposed the multi-route coding scheme, in which packets are encoded and divided into subpackets, and they are transmitted on several routes from the user station to the base station. In order to improve the performance of the multi-route coding, a route selection scheme is very important issue. In this paper, we propose the route selection scheme for the multi-route coding in multihop cellular networks. The proposed scheme is based on the bit error rate of wireless links. We also apply the proposed route selection scheme to a hybrid routing protocol and evaluate its performance.

In sensor networks, because of densely deployment of sensor nodes, sensing area of each sensor node is overlapped with each other and its observed data sequence is correlated. The joint decoding scheme that uses the correlation between the observed data sequences can reduce bit errors in the wireless channel. In this paper, we extend the joint decoding to the case of more than two-hop transmission. For such extension, selection of fusion scheme is very important issue. If the global fusion scheme is employed and the observed data sequence of each sensor node is transmitted on an independent route, route diversity effect could be obtained by using the correlation between observed data sequences. We compare the bit error rate performance of local and global fusion schemes and clarify the route diversity effect

Pulse-shaping OFDM is well-known that it performs well in a mobile environment comparing with conventional OFDM. However, in highly mobile environment intersymbol and intercarrier interferences (ISI/ICIs) increase and can no longer be neglected. These ISI/ICIs deteriorate the performance of the systems. Proper channel equalization is needed for further improvement of the systems. In this paper, more general case, namely biorthogonal frequency division system based on offset QAM (BFDM/OQAM) is considered. We propose a multi-input multi-output (MIMO) transversal filter to equalize the time- frequency dispersive channel. Tap weights are calculated using the zero-forcing (ZF) algorithm. We also propose maximum- likelihood channel estimator and its low-complexity version. The proposed system can significantly improve the performance of BFDM/OQAM systems in the highly mobile environment.

Recently, sensor networks have been drawing many attentions. The networks can be applicable to many communication systems such as emergency communications, intelligent transportation systems, and so on. They could have a multi-route multi-hop structure by the signal relaying via multiple sensor nodes. Since the wireless links have very severe condition for the communications, a method which can maintain the quality of the links is required. Forward error correction techniques and turbo codes are effective ways to prevent performance degradation by the wireless links. In the multi-hop multi-route structure, the route diversity can be enhanced by using the error correction codes. For the decoding process of the turbo codes, the receiver should estimate the channel information to obtain high decoding performance. Although many channel information estimation methods are not applicable to the multi-hop structure, the channel information estimation method utilizing parity bits can be applied. In this paper, we investigate the route diversity effect of the channel information estimation scheme. We also provide performance comparison between the proposed scheme and the pilot aided scheme. The results suggest that the proposed scheme is effective in obtaining the route diversity.

Multi-hop multi-route networks are promising candidate for achieving the high channel capacity. The networks have high applicability to various new communications. Especially sensor networks are one of the attractive applications of the multihop multi-route networks. When the signals are transmitted over multiple routes, a route diversity effect would be possible. The effect can help to prevent performance degradation caused by quality loss of every route. Forward error correction schemes and turbo coding can be expected to enhance the route diversity. As it would be well known, a turbo encoder generates one message stream and two parity streams and the message stream is more important than the parity streams for reliable communications. Thus by allocating the message stream to a reliable route, the performance degradation could be prevented. In this paper, we examine the effect of the route diversity on multi-hop networks using turbo codes. The diversity effect against the quality loss of the multiple routes is investigated. The results suggest that the multi-route transmissions have high diversity effect. They also suggest that large performance degradation can be prevented by appropriate route assignment of the streams even though the link quality of the multiple routes can not be guaranteed.

This paper examines multihop cellular networks. There are some issues in these networks, such as route loss due to topological change and packet errors due to wireless nodes relay. To overcome these issues, we use a multiple route coding scheme in which packets are transmitted on multiple routes from a user node to multiple base stations. This scheme can achieve a diversity gain by combining packets that are transmitted along multiple routes. Some challenges must be met to establish multiple routes for this scheme. In this paper, we propose a routing protocol for multiple route coding. The key idea of this proposed scheme is using a hybrid routing protocol. This can mitigate an increase in control packets and multiple disjoint routes can be constructed. We evaluate the performance of this proposed scheme

For reduction in transmission errors on wireless links, we proposed the multi-route coding on multiple routes for wireless multi-hop networks. In the proposed coding, a source node encodes a packet, divides it into sub packets, and transmits them on multiple routes. A destination node combines and decodes the arriving sub packets to get coding and diversity gain. In this paper, we propose a hybrid ARQ scheme for the multiroute coding. In a hybrid ARQ, important information is firstly transmitted, and redundant information is retransmitted later. On the other hand, in the multiroute coding, all sub packets should have the same importance because of efficient diversity combining. We investigate the trade-off between hybrid ARQ and multi-route coding

For reduction in bit errors on wireless channels, we proposed the multi-route coding scheme on multiple routes for wireless multi-hop networks. In this paper, we introduce ARQ to the multi-route coding. In the multi-route coding, the destination node combines and decodes sub packets which are encoded and divided by the source node. The intermediate node relays a sub packet, that is, only a part of a packet. Therefore, the intermediate node cannot detect packet errors, and only the destination node can do after combining and decoding sub packets. We propose the ARQ scheme between the source node and the destination node. We analyze the proposed ARQ scheme and evaluate the throughput performance

This manuscript introduces a mathematically tractable and accurate model of narrowband power line noise based on experimental measurements. In this paper, the noise is expressed as a Gaussian process whose instantaneous variance is a periodic time function. With this assumption and representation, the cyclostationary features of power line noise can be described in close form. The periodic function that represents the variance is then approximated with a small number of parameters. The noise waveform generated with this model shows good agreement with that of actually measured noise. Noise waveforms generated by different models are also compared with that of the proposed model.

One technique to provide high data transmission for large number of users in mobile cellular networks is to arrange the network in a multi-hop structure. Multi-hop networks have large channel capacity and can achieve multi-route transmissions. When the information bit streams are transmitted over multiple routes, a route diversity effect would also be possible. In multiroute transmission, we usually require the routing protocols which can make every route condition be equal. The requirement, however, makes the routing algorithm be complex and causes large power consumption. Forward error correction schemes and turbo coding can be far from the strict requirement although they enhance the effect of route diversity. When applying the turbo codes, the receiver should know the channel condition for iterative decoding. Thus we have to consider how to obtain the channel information over the multi-route multi-hop network. Furthermore, the performance would improve when the destination knows the difference of the route reliability. In this paper, we propose the turbo coded multi-route multi-hop networks using parity check bits. By using parity bits, we can easily estimate the channel information in multi-route multi-hop networks. Using numerical examples we show that the proposed scheme improves the performance in additive white Gaussian noise and slow fading channel conditions

In this manuscript, wireless communication system for reliable wireless control of industrial machines in indoor environment is considered. In indoor environment, transmitted signal fluctuates due to fading and shadowing. To combat the fading and shadowing, macro/micro spatial diversity can be used as an effective countermeasure. In this manuscript, macro/micro diversity is achieved by multiple wireless relay terminals, which is convenient in setting and moving the macro diversity branches. In the proposed scheme, channel between the transmitter and the receiver through relay terminals is considered as a MIMO channel and separation of the signals re-transmitted from the relay terminals is not required. This feature makes it possible to have higher order diversity without the cost of bandwidth inefficiency. In numerical examples, the performance of the proposed scheme is evaluated by average frame-error rate and outage probability of frame-error rate. With two relay terminals, the diversity gain of the proposed scheme is about 5-6 dB, which is 1 dB higher than that of conventional macroscopic diversity

In real-time packet communications, packet retransmission is generally not used because it may produce undesired delays. In this case, however, packet errors caused by a channel may lead directly to a loss of transmitted information. Then it is necessary to employ a technique which can reduce the influence of packet errors. We propose to employ a multiple-route packet combining scheme in realtime communications on wireless multihop networks. The scheme, which we proposed previously (Nakagawa, N. et al., IEICE Commun. Soc. Conf., vol.B-5-119, p.496, 2003), can achieve diversity gain by combining multiple copies of the same packet that are transmitted along different routes. We analyze two characteristics of the proposed system. One is the average packet error probability, which is obtained as a function of the elapsed time after generating copied packet transmission requests. The other is the required time for achieving a required packet error probability. The results are evaluated from a quality of service (QoS) point of view. From numerical results, it is shown that for a given tolerable delay, there exists a number of multiple routes that minimizes the achievable average packet error probability. Moreover, if the number of multiple routes is selected appropriately, the required time for achieving a required packet error probability can be minimized.

In multimedia wireless communications, various types of traffic are handled. Generally, each type of this traffic has a different stochastic property. An access control protocol for multimedia wireless communications, therefore, are required to adopt a stochastic property of multimedia traffic. Conventional access control protocols, however, do not consider such characteristics of multimedia traffic. In this paper, we propose an access control protocol for multimedia CDMA packet communications. The proposed protocol controls the data packet transmissions based on the estimation of the instantaneous number of simultaneously transmitted voice and video packets. This estimation exploits the stochastic property of multimedia traffic. To carry out such estimation, we employ an adaptive algorithm as an estimation method. We evaluate the performance of the proposed protocol by comparing it with the performance in the case where the stochastic property of traffic is not considered.

A CDMA unslotted ALOHA system is a connectionless-type of CDMA packet communication system. In this system, a user station can transmit a packet asynchronously and randomly, and so the packet birth/death event is one of the most important problems for multiuser detection. We have proposed the CDMA unslotted ALOHA system using an adaptive filter receiver based on minimum mean square error criterion of Okada, Grant, Band and Ogawa (see IEEE International Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), Sep. 2000), and shown the improvement in the throughput performance even considering the effect of birth/death event. The ensemble-averaged squared error, however, increases at the point of packet birth. In this paper, we employ interleaving and forward error correction (FEC) coding techniques to mitigate the momentary increase in ensemble-averaged squared error. The use of FEC, however, causes the increase in MAI due to redundancy bits of FEC. Moreover, signal power is reduced under the condition that the energy of an information bit is the same. In such cases, whether an adaptive filter can operate effectively or not interests us. We evaluate the system performance and show that the improvement in throughput is achieved with interleaving and FEC techniques.

In this paper, we propose a new packet recognition and signal acquisition scheme with an adaptive linear filter based on a least mean square (LMS) algorithm for code-division multiple access (CDMA) packet systems. In CDMA systems, conventional receivers with matched filtering suffer from the near-far problem due to multiple access interference (MAI). In general, closed-loop power control is used in order to reduce the influence of the near-far problem. However, closed-loop power control is unsuitable for packet systems. Hence, in order to eliminate the influence of the near-far problem, we focus on an adaptive receiver based on an LMS algorithm for packet recognition and signal acquisition in CDMA packet systems.

Packet detection is one of the most important problems in packet communication systems. In a CDMA Unslotted ALOHA system, which is one of the wireless packet communication systems, multiple access interference (MAI) makes the performance of the packet detection worse. To reduce the effect of MAI, we propose a new packet detection scheme in this paper. In this scheme, Successive Interference Cancellation(SIC) is applied. The packet's signal is detected after the cancellation of MAI using SIC. This proposed scheme gives good performance of the packet detection.

We compare CDMA and FDMA (or TDMA) schemes in multibeam non-geostationary satellite systems, taking the effects of antenna patterns on inter-cell interference into consideration. The maximum acceptable number of users per cell in the uplink is employed as a measure of the system capacity. We have found that in FDMA (or TDMA) systems the maximum acceptable number of users varies according to the altitude of the satellites. While the performance is insensitive to the altitude in CDMA systems. For this reason, the altitude of the satellites is found to be an important factor for selecting multiple access schemes in non-geostationary satellite systems.

In wireless communication systems, as one of the effective techniques for combating fading, transmit diversity has attracted much attention, especially when receive diversity is expensive or impractical due to the constraint of terminal size. In this study we consider an adaptive carrier-by-carrier basis antenna selection scheme for transmit diversity in OFDM systems under the assumption that a transmitter has priori knowledge of the channel state information (CSI). In the proposed schemes transmit antennas are selected adaptively for each subcarrier according to CSI.

A CDMA unslotted ALOHA system using MMSE multi-user detection is proposed. In the CDMA unslotted ALOHA system, a user station can transmit a packet asynchronously, and so the number of simultaneously transmitted packets fluctuates moment by moment. This fluctuation affects the performance of the MMSE multi-user detection. At first, we employ the Wiener filter detector assuming perfect information as an upper bound of the performance of the proposed system. Then, we apply an adaptive filter to CDMA unslotted ALOHA to compensate for the birth/death of a packet.

In this paper, we propose a CDMA slotted-ALOHA (CDMA S-ALOHA) system with low-bit rate and high-bit-rate classes of data users applying the multi code CDMA (MC-CDMA) scheme. Performance evaluation is obtained in the respect of the throughput. Contrary to one might expect, we show that the throughput of the class with higher bit rate can be improved by the MC-CDMA scheme. Moreover, we show that applying the modified channel load sensing protocol (MCLSP) to the system gives further improvement in the throughput of the higher bit rate class, as well as to the total throughput of the channel.

In this paper, we analyze the CDMA slotted ALOHA systems with finite buffer and finite population assumptions by expanding the linear approximate solution based on restricted occupancy urn models. We evaluate the system performance in terms of throughput, average delay, and rejection probability. Moreover, we clarify the effect of buffer capacity by changing the buffer size.

In this paper, we present the throughput performance of CDMA slotted ALOHA systems with modified channel load sensing protocol (MCLSP). In MCLSP, a hub station continuously senses channel load for a certain number of slots, and computes the probability with which each user station should transmit its packet, then broadcasts the computed value. As the access control is based on this probability, we can apply it to slotted system. We show that MCLSP can achieve significant improvement in throughput performance of CDMA slotted ALOHA systems even in large offered load. One of the issues in such a protocol is the access timing delay, which is the sum of process time and propagation time for the packet access control. We also show the effect of the access timing delay on the throughput performance.

Throughput analysis of direct-sequence spread spectrum multiple access (DS/SSMA) unslotted ALOHA with fixed packet length is presented. As the levels of multi-user interference fluctuate during the packet transmission, we calculate the packet error probability and the throughput by considering not only the number of overlapped packets but also the amount of time overlap. On the assumption that packet generation is Poisson, the system can be thought as the queueing system M/D//spl infin/. With Gaussian approximation of multi-user interference, we obtain the throughput as the function of the number of chips in a bit, the packet length, and the offered load of the system. We also analyze the channel load sensing protocol (CLSP), and obtain the optimum threshold of CLSP.