Beacon-Assisted Spectrum Access with Cooperative Cognitive Transmitter and Receiver

Spectrum access is an important function of cognitive radios for detecting and utilizing spectrum holes without interfering with the legacy systems. In this paper we propose novel cooperative communication models and show how deploying such cooperations between a pair of secondary transmitter and receiver assists them in identifying spectrum opportunities more reliably. These cooperations are facilitated by dynamically and opportunistically assigning one of the secondary users as a relay to assist the other one which results in more efficient spectrum hole detection. Also, we investigate the impact of erroneous detection of spectrum holes and thereof missing communication opportunities on the capacity of the secondary channel. The capacity of the secondary users with interference-avoiding spectrum access is affected by 1) how effectively the availability of vacant spectrum is sensed by the secondary transmitter-receiver pair, and 2) how correlated are the perceptions of the secondary transmitter-receiver pair about network spectral activity. We show that both factors are improved by using the proposed cooperative protocols. One of the proposed protocols requires explicit information exchange in the network. Such information exchange in practice is prone to wireless channel errors (i.e., is imperfect) and costs bandwidth loss. We analyze the effects of such imperfect information exchange on the capacity as well as the effect of bandwidth cost on the achievable throughput. The protocols are also extended to multiuser secondary networks.Comment: 36 pages, 6 figures, To appear in IEEE Transaction on Mobile Computin

先進ITSのための中継アシスト車車間通信技術の研究

Wireless vehicular communications for advanced Intelligent Transport Systems (ITS) have the potential to support safety driving, enhance the efficiency of transportation and play an important role in the future automated driving system. The vehicle-to-vehicle(V2V), vehicle-to-infrastructure (V2I) and vehicle-to-pedestrian (V2P) communications in the advanced ITS enable safety support applications that can predict potential traffic accidents, warn drivers and, in some cases, directly control vehicles to prevent collisions. Such applications require highly reliable broadcast communications. However, the reliability of wireless communication in vehicular environments suffers from fast fading due to multipath propagation, shadowing , and distance-dependent path loss. In addition, hidden terminal (HT) problem is a great concern in CSMA/CA based wireless networks due to its distributed access nature. The packet delivery rate (PDR) of V2V communications rapidly decreases especially under non-line-of-sight (NLOS) environments such as intersections. A vehicle-roadside-vehicle relay-assisted V2V communication scheme has been proposed to improve the reliability of V2V communications. In the scheme, packets sent from a vehicle can be directly received by other vehicles or relayed by a relay station (RS) to the other vehicles. Then path diversity effect can be obtained that improves PDR of V2V communications. However, when the V2V traffic becomes higher, the number of packets that RS has to retransmit becomes larger. This leads to a large number of packets waiting in the transmit queue of RS and packet congestion happens. If the normal relay scheme is employed, thepackets may be dropped due to the limited queue size. Then the gain obtained by relay-assist may be decreased. A packet payload combining relay (PCRL) scheme is proposed to deal with the congestion issue. In the scheme, multiple V2V packet payloads are combined into a single packet and the resultant packet is rebroadcasted once the channel becomes idle. Analytical and simulated results show that the proposed PCRL scheme can remarkably alleviate the congestion issue and improve the relaying performance.The PCRL scheme, however, still suffers from HT problem. In the intersection environments where LOS propagation between VSs is often unavailable, the packet collision frequently happens due to HTs when RS receives V2V packets. If RS cannot receive V2V packets, the advantage of relay-assist becomes smaller. Therefore an improved PCRL scheme with sectorized receiving RS (SR-V2VC/PCRL) is proposed to mitigate the effect of HT problem as well as alleviating the congestion issue. An analytical model is then developed to analyze the performance of SR-V2VC/PCRL scheme considering a single intersection scenario. Numerical results show that the reliability of V2V communications is significantly improved by the proposed scheme. Furthermore, performance of the SR-V2VC/PCRL scheme is discussed for an urban environment with multiple intersections. In such environment, RSs at intersections should cooperate with each other to obtain the largest diversity gain. After theoretically analyzing the performance of the sectorized receiving scheme under multiple interference sources, large-scale simulations are conducted to evaluate the performance of SR-V2VC/PCRL scheme. It is shown that the SR-V2VC/PCRL remarkably improves the reliability of V2V communications. SR-V2VC/PCRL scheme even performs better when employing higher data rate modulation for V2V and relay transmissions.The aforementioned proposals can remarkably improve the reliability of V2V communications. In order to improve the performance of relay-assist ed scheme when traffic load becomes even higher, a network coding(NC)based PCRL scheme (PCRL-NC) with a payload sorting and selection algorithm is proposed to adapt multiple node environment in an intersection. It is shown that the scheme can benefit from NC in alleviating the congestion issue while effectively mitigating the disadvantage of NC. As a result, the introduction of PCRL-NC to the proposed SR-V2VC/PCRL scheme can remarkably improve the reliability of V2V communications under various traffic environments.　近年，先進的なITS (Intelligent Transport Systems: 高度道路交通システム)のための通信技術への期待が高まっている．これには，車両がその位置や速度などの情報を交換する車車間通信，路側機が車両へ信号状態や道路規制などの情報を提供する路車間通信，車両と歩行者の間で情報の交換を行う歩車間通信などがある．これらにブロードキャスト通信を活用することで，各車両では潜在的な交通事故を予測して運転手に警告し，さらには制動を行うことにより事故を未然に回避できる．さらにこの情報を利用して車両を自動制御することで，交通流を意識した協調型自動走行を実現することが可能になるものと期待されている． 車車間通信を用いて安全運転支援およびより高度な自動走行システムを実現するためには，高信頼，かつ低遅延の無線通信技術が要求される．しかしながら道路上の移動通信では，多重波伝搬によるフェージングや建物によるシャドウイング，さらに自律分散通信システム特有の問題である隠れ端末問題による干渉などの影響で，通信の信頼度が低下する．特に事故発生確率の高い交差点ではその影響が顕著である．　本論文では車車間通信の品質を改善することを目的として，交差点等に中継局(Relay Station; RS)を設置し，車車間通信パケットを転送中継する中継アシスト車車間通信に関する諸技術が提案されている．中継局は交差点付近の信号機などに併設され，高いアンテナ高を有することと，他の車載局に対して見通し内(Line-of-Sight; LOS)伝搬環境にあるため，中継アシストシステムはシャドウイングやフェージングの問題の軽減に有効であることが既に示されている．しかしながら，トラヒックが増加するにつれて中継局での輻輳問題が発生し，中継効果が低下するという課題があった．そこで本論文では中継によるエアトラヒックの増加を抑える方法として，中継送信時に複数のパケットペイロードをまとめて１つのパケットに再構成して送信するペイロード合成中継法を提案する．本提案法により中継局での輻輳問題が解決でき，中継効果が向上することを解析結果から明らかにした．　交差点における中継アシスト車車間通信のもう1つの課題として，中継局受信時に隠れ端末問題の影響で受信成功率が低下することがある．この課題に対しては中継局受信時にセクタアンテナを用いることが有効であることが示されているが，本研究ではペイロード合成中継法にセクタ化受信を組合せたセクタ化受信ペイロード合成中継法を提案し，その効果を理論解析およびシミュレーションにより示した．セクタ化受信によって中継局での受信成功率を改善すると中継すべきパケット数が増加するが，提案法ではペイロード合成によって中継パケットの送信効率を高めることができるので，結果として中継効果を高めて平均パケット伝送成功率を大幅に向上できることを明らかにした．　さらに，複数交差点からなる市街地環境におけるセクタ化受信ペイロード合成中継法の効果を，大規模ネットワークシミュレーションを用いてブロードキャスト配信成功率として総合的に評価した．他の車両および離れた中継局など干渉源が複数存在する市街地環境においても，提案法を用いることによって隠れ端末問題の影響が有効に回避できること，隣接する中継局間で互いに棲分け中継をすることで非常に高い中継効果が得られることを明らかにした．　以上のように提案法は中継アシスト車車間通信の特性を大幅に改善できるが，通信トラヒックがさらに高い環境に対処するため，中継パケットのエアトラヒックをさらに圧縮できる方法として，複数ノード環境に適したネットワークコーディング法を用いたペイロード合成中継法を提案する．本提案法では，車車間ペイロードのソーティングと合成対象パケットの選択アルゴリズムによって複数ノード環境でのネットワークコーディングの弱点を抑えつつ，輻輳問題に有効に対処できることを示した．結果として本提案法をセクタ化受信と組合せることで，幅広い通信トラヒック条件においてブロードキャスト配信成功率が大きく向上することを明らかにした．電気通信大学201

Recent Advances in Cellular D2D Communications

Device-to-device (D2D) communications have attracted a great deal of attention from researchers in recent years. It is a promising technique for offloading local traffic from cellular base stations by allowing local devices, in physical proximity, to communicate directly with each other. Furthermore, through relaying, D2D is also a promising approach to enhancing service coverage at cell edges or in black spots. However, there are many challenges to realizing the full benefits of D2D. For one, minimizing the interference between legacy cellular and D2D users operating in underlay mode is still an active research issue. With the 5th generation (5G) communication systems expected to be the main data carrier for the Internet-of-Things (IoT) paradigm, the potential role of D2D and its scalability to support massive IoT devices and their machine-centric (as opposed to human-centric) communications need to be investigated. New challenges have also arisen from new enabling technologies for D2D communications, such as non-orthogonal multiple access (NOMA) and blockchain technologies, which call for new solutions to be proposed. This edited book presents a collection of ten chapters, including one review and nine original research works on addressing many of the aforementioned challenges and beyond

NOMA Assisted Wireless Caching: Strategies and Performance Analysis

Conventional wireless caching assumes that content can be pushed to local caching infrastructure during off-peak hours in an error-free manner; however, this assumption is not applicable if local caches need to be frequently updated via wireless transmission. This paper investigates a new approach to wireless caching for the case when cache content has to be updated during on-peak hours. Two non-orthogonal multiple access (NOMA) assisted caching strategies are developed, namely the push-then-deliver strategy and the push-and-deliver strategy. In the push-then-deliver strategy, the NOMA principle is applied to push more content files to the content servers during a short time interval reserved for content pushing in on-peak hours and to provide more connectivity for content delivery, compared to the conventional orthogonal multiple access (OMA) strategy. The push-and-deliver strategy is motivated by the fact that some users' requests cannot be accommodated locally and the base station has to serve them directly. These events during the content delivery phase are exploited as opportunities for content pushing, which further facilitates the frequent update of the files cached at the content servers. It is also shown that this strategy can be straightforwardly extended to device-to-device caching, and various analytical results are developed to illustrate the superiority of the proposed caching strategies compared to OMA based schemes

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

A Study Of Cooperative Spectrum Sharing Schemes For Internet Of Things Systems

The Internet of Things (IoT) has gained much attention in recent years with the massive increase in the number of connected devices. Cognitive Machine-to-Machine (CM2M) communications is a hot research topic in which a cognitive dimension allows M2M networks to overcome the challenges of spectrum scarcity, interference, and green requirements. In this paper, we propose a Generalized Cooperative Spectrum Sharing (GCSS) scheme for M2M communication. Cooperation extends the coverage of wireless networks as well as increasing their throughput while reducing the energy consumption of the connected low power devices. We study the outage performance of the proposed GCSS scheme for M2M system and derive exact expressions for the outage probability. We also analyze the effect of varying transmission powers on the performance of the system

Enabling Technologies for Ultra-Reliable and Low Latency Communications: From PHY and MAC Layer Perspectives

© 1998-2012 IEEE. Future 5th generation networks are expected to enable three key services-enhanced mobile broadband, massive machine type communications and ultra-reliable and low latency communications (URLLC). As per the 3rd generation partnership project URLLC requirements, it is expected that the reliability of one transmission of a 32 byte packet will be at least 99.999% and the latency will be at most 1 ms. This unprecedented level of reliability and latency will yield various new applications, such as smart grids, industrial automation and intelligent transport systems. In this survey we present potential future URLLC applications, and summarize the corresponding reliability and latency requirements. We provide a comprehensive discussion on physical (PHY) and medium access control (MAC) layer techniques that enable URLLC, addressing both licensed and unlicensed bands. This paper evaluates the relevant PHY and MAC techniques for their ability to improve the reliability and reduce the latency. We identify that enabling long-term evolution to coexist in the unlicensed spectrum is also a potential enabler of URLLC in the unlicensed band, and provide numerical evaluations. Lastly, this paper discusses the potential future research directions and challenges in achieving the URLLC requirements