車車間通信のための分散協調ダイバーシチの研究

In recent years, intelligent transportation system (ITS) is well known as an effective way to provide road safety and comfortable driving. In vehicular communications, the current standards can be applied for safety related message exchange but in the future world, other new applications like autonomous controlled vehicles require more reliability and capacity with small delay. Moreover, multi-hop data delivery for emergency situations on road is not explicitly supported. Vehicular communications have some attractive characteristics such as constrained mobility along a predetermined road and predictability of vehicle\u27s position, etc. However, network topology changes frequently and very fast due to vehicle mobility. As a result, inter-vehicle connectivity can be impacted significantly. Moreover, the line-of-sight signal components are often blocked by obstacles as buildings at intersections or trucks on highway. Consequently, signal attenuation is large. Therefore, multi-hop data delivery in vehicle-to-vehicle communications with high reliability and small delay should be investigated. In wireless communications, cooperative communications are widely known as a technique allowing single-antenna nodes to reap the benefits of the conventional MIMO systems. By using distributed intermediate nodes, cooperative communications can obtain the same diversity gain benefits as conventional MIMO systems without requiring multiple antennas on the same node, which is also known as distributed cooperative diversity technique. In the cooperative diversity, space-time block code (STBC) is often applied because the diversity gain can be obtained without channel state information (CSI) at the transmitter. In addition, this encoding scheme can achieve both full diversity order and full data transmission rate with simple decoding algorithm at the receiver. However, in multi-hop relay communications, it is di cult to establish the path route from the source node to the destination node with selecting the efficient cooperative relays. The existing routing protocols in MANETs are not suitable for most applications in multi-hop vehicular communications due to the distinctive characteristics of V2V communications. This is because in these routing protocols, one or multiple routes from a source node to a particular destination node should be discovered before transmitting data packet. Consequently, these protocols are not suitable for the scenarios with more than one destination node. Furthermore, problems of redundant broadcast messages and the broadcast storm can make the design of routing protocols further complicated. However, in order to achieve high reliability for wireless multi-hop communications, the efficient cooperative relays must be selected to forward the packet in each hop. Distributed STBC encoding should be also applied to obtain higher cooperative diversity gain. In addition, the number of transmitted packet and the power consumption in network must be reduced while still maintaining the performance improvement of system, which can reduce the mutual interference in the shared radio channel. Therefore, in order to meet the requirements, transmission methods are proposed in this thesis as follows. In proposal 1, a method of cooperative diversity transmission is proposed to reduce the power consumption normalized by one data packet transmission power consumption with keeping the performance improvement for wireless multi-hop ad-hoc networks. The normalized power consumption is reduced by limiting the number of transmitting relay nodes in each hop and the number of repetition of the same data packet transmission at each node, which in turn makes the reduction of the number of transmitted packets in network. As a result, this can also lead to the reduction of interferences and better efficiency frequency utilization in network. More specifically, a relay selection procedure is proposed to select the two relays with high contribution according to the transmission direction in each hop by installing a new timer at each node and using control packets. The timer is also used to assign the STBC encoding pattern to the two selected relays in order to obtain higher cooperative diversity gain. In proposal 2, a cooperative diversity transmission method for wireless multi-hop relay V2V communications is proposed to disseminate emergency messages in the emergency situations. In this method, we consider to exploit the attractive characteristics of the constrained mobility and predictability in vehicular communications. In order to obtain higher cooperative diversity gain, a group of distributed vehicle stations which have high contribution according to the transmission direction is selected to forward the same data packet simultaneously to the further vehicle stations. This relay selection algorithm is based-on position, speed and movement direction, combining with the digital road map equipped on the vehicles. The STBC encoding is also used at the selected group of distributed vehicle relays. Moreover, in order to manage the transmission of whole network in each hop, a master vehicle station is selected by installing another new timer at each vehicle station and using control packets in each hop. From the simulation results, we can confirm that the proposed methods can reduce the power consumption normalized by one data packet transmission power consumption and the redundant broadcast packets significantly with keeping the improvement of packet loss probability by limiting the number of repetition of packet transmission at each node and selecting the only distributed relays with high contribution according to the transmission direction. As a result, these methods can achieve high reliability and partly meet the requirements of ITS system in the future.電気通信大学201

Energy Efficiency in Communications and Networks

The topic of "Energy Efficiency in Communications and Networks" attracts growing attention due to economical and environmental reasons. The amount of power consumed by information and communication technologies (ICT) is rapidly increasing, as well as the energy bill of service providers. According to a number of studies, ICT alone is responsible for a percentage which varies from 2% to 10% of the world power consumption. Thus, driving rising cost and sustainability concerns about the energy footprint of the IT infrastructure. Energy-efficiency is an aspect that until recently was only considered for battery driven devices. Today we see energy-efficiency becoming a pervasive issue that will need to be considered in all technology areas from device technology to systems management. This book is seeking to provide a compilation of novel research contributions on hardware design, architectures, protocols and algorithms that will improve the energy efficiency of communication devices and networks and lead to a more energy proportional technology infrastructure

Radio Communications

In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks

Cross-layer analysis for video transmission over COFDM-based wireless local area networks

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Program of the 3rd International Conference on Signal Processing and Communication Systems, Omaha, Nebraska, 28-30 September 2009

10 sessions; 2 poster sessions. Schedule and Table of Contents

A universal space-time architecture for multiple-antenna aided systems

In this tutorial, we first review the family of conventional multiple-antenna techniques, and then we provide a general overview of the recent concept of the powerful Multiple-Input Multiple-Output (MIMO) family based on a universal Space-Time Shift Keying (STSK) philosophy. When appropriately configured, the proposed STSK scheme has the potential of outperforming conventional MIMO arrangements