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

MIMO Systems

In recent years, it was realized that the MIMO communication systems seems to be inevitable in accelerated evolution of high data rates applications due to their potential to dramatically increase the spectral efficiency and simultaneously sending individual information to the corresponding users in wireless systems. This book, intends to provide highlights of the current research topics in the field of MIMO system, to offer a snapshot of the recent advances and major issues faced today by the researchers in the MIMO related areas. The book is written by specialists working in universities and research centers all over the world to cover the fundamental principles and main advanced topics on high data rates wireless communications systems over MIMO channels. Moreover, the book has the advantage of providing a collection of applications that are completely independent and self-contained; thus, the interested reader can choose any chapter and skip to another without losing continuity

Multipacket reception in the presence of in-band full-duplex communication

In-Band Full-DupleX (IB-FDX) is defined as the ability for nodes to transmit and receive signals simultaneously on the same channel. Conventional digital wireless networks do not implement it, since a node’s own transmission signal causes interference to the signal it is trying to receive. However, recent studies attempt to overcome this obstacle, since it can potentially double the spectral efficiency of current wireless networks. Different mechanisms exist today that are able to reduce a significant part of the Self- Interference (SI), although specially tuned Medium Access Control (MAC) protocols are required to optimize its use. One of IB-FDX’s biggest problems is that the nodes’ interference range is extended, meaning the unusable space for other transmissions and receptions is broader. This dissertation proposes using MultiPacket Reception (MPR) to address this issue and adapts an already existing Single-Carrier with Frequency-Domain Equalization (SC-FDE) receiver to IB-FDX. The performance analysis suggests that MPR and IB-FDX have a strong synergy and are able to achieve higher data rates, when used together. Using analytical models, the optimal transmission patterns and transmission power were identified, which maximize the channel capacity with the minimal energy consumption. This was used to define a new MAC protocol, named Full-duplex Multipacket reception Medium Access Control (FM-MAC). FM-MAC was designed for a single-hop cellular infrastructure, where the Access Point (AP) and the terminals implement both IB-FDX and MPR. It divides the coverage range of the AP into a closer Full-DupleX (FDX) zone and a farther Half-DupleX (HDX) zone and adds a tunable fairness mechanism to avoid terminal starvation. Simulation results show that this protocol provides efficient support for both HDX and FDX terminals, maximizing its capacity when more FDX terminals are used

Error models for digital channels and applications to wireless communication systems

Digital wireless channels are extremely prone to errors that appear in bursts or clusters. Error models characterise the statistical behaviour of bursty profiles derived from digital wireless channels. Generative error models also utilise those bursty profiles in order to create alternatives, which are more efficient for experimental purposes. Error models have a tremendous value for wireless systems. They are useful for the design and performance evaluation of error control schemes, in addition to higher layer protocols in which the statistical properties of the bursty profiles are greatly functional. Furthermore, underlying wireless digital channels can be substituted by generated error profiles. Consequently, computational load and simulation time can be significantly reduced when executing experiments and performing evaluation simulations for higher layer communications protocols and error control strategies. The burst error statistics are the characterisation metrics of error models. These statistics include: error-free run distribution; error-free burst distribution; error burst distribution; error cluster distribution; gap distribution; block error probability distribution; block burst probability distribution; bit error correlation function; normalised covariance function; gap correlation function; and multigap distribution. These burst error statistics scrutinise the error models and differentiate between them, with regards to accuracy. Moreover, some of them are advantageous for the design of digital components in wireless communication systems. This PhD thesis aims to develop accurate and efficient error models and to find applications for them. A thorough investigation has been conducted on the burst error statistics. A breakdown of this thesis is presented as follows. Firstly, an understanding of the different types of generative error models, namely, Markovian based generative models, context-free grammars based generative models, chaotic models, and deterministic process based generative models, has been presented. The most widely used models amongst the generative models have been compared with each other consulting the majority of burst error statistics. In order to study generative error models, error burst profiles were obtained mainly from the Enhanced General Packet Radio Service (EGPRS) system and also the Long Term Evolution (LTE) system. Secondly, more accurate and efficient generative error models have been proposed. Double embedded processes based hidden Markov model and three-layered processes based hidden Markov model have been developed. The two types of error profiles, particularly the bit-level and packet-level error profiles were considered. Thirdly, the deterministic process based generative models’ parameters have been tuned or modified in order to generate packet error sequences rather than only bit error sequences. Moreover, a modification procedure has been introduced to the same models to enhance their generation process and to make them more desirable. Fourthly, adaptive generative error models have been built in order to accommodate widely used generative error models to different digital wireless channels with different channel conditions. Only a few reference error profiles have been required in order to produce additional error profiles in various conditions that are beneficial for the design and performance evaluation of error control schemes and higher layer protocols. Finally, the impact of the Hybrid Automatic Repeat reQuest (HARQ) on the burst error statistics of physical layer error profiles has been studied. Moreover, a model that can generate predicted error sequences with burst error statistics similar to those of error profiles when HARQ is included has been proposed. This model is constructive in predicting the behaviour of the HARQ in terms of a set of higher order statistics rather than only predicting a first order statistic. Moreover, the whole physical layer is replaced by adaptively generated error profiles in order to check the performance of the HARQ protocol. The developed generative error models as well as the developed adaptive generative error models are expected to benefit future research towards the testing of many digital components in the physical layer as well as the wireless protocols of the link and transport layers for many existing and emerging systems in the field of wireless communications

Design and Analysis of Forward Error Control Coding and Signaling for Guaranteeing QoS in Wireless Broadcast Systems

Broadcasting systems are networks where the transmission is received by several terminals. Generally broadcast receivers are passive devices in the network, meaning that they do not interact with the transmitter. Providing a certain Quality of Service (QoS) for the receivers in heterogeneous reception environment with no feedback is not an easy task. Forward error control coding can be used for protection against transmission errors to enhance the QoS for broadcast services. For good performance in terrestrial wireless networks, diversity should be utilized. The diversity is utilized by application of interleaving together with the forward error correction codes. In this dissertation the design and analysis of forward error control and control signalling for providing QoS in wireless broadcasting systems are studied. Control signaling is used in broadcasting networks to give the receiver necessary information on how to connect to the network itself and how to receive the services that are being transmitted. Usually control signalling is considered to be transmitted through a dedicated path in the systems. Therefore, the relationship of the signaling and service data paths should be considered early in the design phase. Modeling and simulations are used in the case studies of this dissertation to study this relationship. This dissertation begins with a survey on the broadcasting environment and mechanisms for providing QoS therein. Then case studies present analysis and design of such mechanisms in real systems. The mechanisms for providing QoS considering signaling and service data paths and their relationship at the DVB-H link layer are analyzed as the first case study. In particular the performance of different service data decoding mechanisms and optimal signaling transmission parameter selection are presented. The second case study investigates the design of signaling and service data paths for the more modern DVB-T2 physical layer. Furthermore, by comparing the performances of the signaling and service data paths by simulations, configuration guidelines for the DVB-T2 physical layer signaling are given. The presented guidelines can prove useful when configuring DVB-T2 transmission networks. Finally, recommendations for the design of data and signalling paths are given based on findings from the case studies. The requirements for the signaling design should be derived from the requirements for the main services. Generally, these requirements for signaling should be more demanding as the signaling is the enabler for service reception.Siirretty Doriast

Transmit and receive techniques for MIMO-OFDM systems

Ph.DDOCTOR OF PHILOSOPH

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

Enabling Technologies for Internet of Things: Licensed and Unlicensed Techniques

The Internet of Things (IoT) is a novel paradigm which is shaping the evolution of the future Internet. According to the vision underlying the IoT, the next step in increasing the ubiquity of the Internet, after connecting people anytime and everywhere, is to connect inanimate objects. By providing objects with embedded communication capabilities and a common addressing scheme, a highly distributed and ubiquitous network of seamlessly connected heterogeneous devices is formed, which can be fully integrated into the current Internet and mobile networks, thus allowing for the development of new intelligent services available anytime, anywhere, by anyone and anything. Such a vision is also becoming known under the name of Machine-to-Machine (M2M), where the absence of human interaction in the system dynamics is further emphasized. A massive number of wireless devices will have the ability to connect to the Internat through the IoT framework. With the accelerating pace of marketing such framework, the new wireless communications standards are studying/proposing solutions to incorporate the services needed for the IoT. However, with an estimate of 30 billion connected devices, a lot of challenges are facing the current wireless technology. In our research, we address a variety of technology candidates for enabling such a massive framework. Mainly, we focus on the nderlay cognitive radio networks as the unlicensed candidate for IoT. On the other hand, we look into the current efforts done by the standardization bodies to accommodate the requirements of the IoT into the current cellular networks. Specifically, we survey the new features and the new user equipment categories added to the physical layer of the LTE-A. In particular, we study the performance of a dual-hop cognitive radio network sharing the spectrum of a primary network in an underlay fashion. In particular, the cognitive network consists of a source, a destination, and multiple nodes employed as amplify-and-forward relays. To improve the spectral efficiency, all relays are allowed to instantaneously transmit to the destination over the same frequency band. We present the optimal power allocation that maximizes the received signal-to-noise ratio (SNR) at the destination while satisfying the interference constrains of the primary network. The optimal power allocation is obtained through an eigen-solution of a channel-dependent matrix, and is shown to transform the transmission over the non-orthogonal relays into parallel channels. Furthermore, while the secondary destination is equipped with multiple antennas, we propose an antenna selection scheme to select the antenna with the highest SNR. To this end, we propose a clustering scheme to subgroup the available relays and use antenna selection at the receiver to extract the same diversity order. We show that random clustering causes the system to lose some of the available degrees of freedom. We provide analytical expression of the outage probability of the system for the random clustering and the proposed maximum-SNR clustering scheme with antenna selection. In addition, we adapt our design to increase the energy-efficiency of the overall network without significant loss in the data rate. In the second part of this thesis, we will look into the current efforts done by the standardization bodies to accommodate the equirements of the IoT into the current cellular networks. Specifically, we present the new features and the new user equipment categories added to the physical layer of the LTE-A. We study some of the challenges facing the LTE-A when dealing with Machine Type communications (MTC). Specifically, the MTC Physical Downlink control channel (MPDCCH) is among the newly introduced features in the LTE-A that carries the downlink control information (DCI) for MTC devices. Correctly decoding the PDCCH, mainly depends on the channel estimation used to compensate for the channel errors during transmission, and the choice of such technique will affect both the complexity and the performance of the user equipment. We propose and assess the performance of a simple channel estimation technique depends in essence on the Least Squares (LS) estimates of the pilots signal and linear interpolations for low-Doppler channels associated with the MTC application

Performance Analysis, Resource Allocation and Optimization of Cooperative Communication Systems under Generalized Fading Channels

The increasing demands for high-speed data transmission, efficient wireless access, high quality of service (QoS) and reliable network coverage with reduced power consumption impose demanding intensive research efforts on the design of novel wireless communication system architectures. A notable development in the area of communication theory is the introduction of cooperative communication systems. These technologies become promising solution for the next-generation wireless transmission systems due to their applicability in size, power, hardware and price constrained devices, such as cellular mobile devices, wireless sensors, ad-hoc networks and military communications, being able to provide, e.g., diversity gain against fading channels without the need for installing multiple antennas in a single terminal. The performance of the cooperative systems can in general be significantly increased by allocating the limited power efficiently. In this thesis, we address in detail the performance analysis, resource allocation and optimization of such cooperative communication systems under generalized fading channels. We focus first on energy-efficiency (EE) optimization and optimal power allocation (OPA) of regenerative cooperative network with spatial correlation effects under given power constraint and QoS requirement. The thesis also investigates the end-to-end performance and power allocation of a regenerative multi-relay cooperative network over non-homogeneous scattering environment, which is realistic case in practical wireless communication scenarios. Furthermore, the study investigates the end-to-end performance, OPA and energy optimization analysis under total power constraint and performance requirement of full-duplex (FD) relaying transmission scheme over asymmetric generalized fading models with relay self-interference (SI) effects.The study first focuses on exact error analysis and EE optimization of regenerative relay systems under spatial correlation effects. It first derives novel exact and asymptotic expressions for the symbol-error-rates (SERs) of M -ary quadrature amplitude and M -ary phase-shift keying (M -QAM) and (M -PSK) modulations, respectively, assuming a dual-hop decode-and-forward relay system, spatial correlation, path-loss effects and maximum-ratio-combing (MRC) at the destination. Based on this, EEoptimization and OPA are carried out under certain QoS requirement and transmit power constraints.Furthermore, the second part of the study investigates the end-to-end performance and power allocation of MRC based regenerative multi-relay cooperative system over non-homogeneous scattering environment. Novel exact and asymptotic expressions are derived for the end-to-end average SER for M -QAM and M -PSK modulations.The offered results are employed in performance investigations and power allocation formulations under total transmit power constraints.Finally, the thesis investigates outage performance, OPA and energy optimization analysis under certain system constraints for the FD and half-duplex (HD) relaying systems. Unlike the previous studies that considered the scenario of information transmission over symmetric fading conditions, in this study we considered the scenario of information transmission over the most generalized asymmetric fading environments.The obtained results indicate that depending on the severity of multipath fading, the spatial correlation between the direct and relayed paths and the relay location, the direct transmission is more energy-efficient only for rather short transmission distances and until a certain threshold. Beyond this, the system benefits substantially from the cooperative transmission approach where the cooperation gain increases as the transmission distance increases. Furthermore, the investigations on the power allocation for the multi-relay system over the generalized small-scale fading model show that substantial performance gain can be achieved by the proposed power allocation scheme over the conventional equal power allocation (EPA) scheme when the source-relay and relay-destination paths are highly unbalanced. Extensive studies on the FD relay system also show that OPA provides significant performance gain over the EPA scheme when the relay SI level is relatively strong. In addition, it is shown that the FD relaying scheme is more energy-efficient than the reference HD relaying scheme at long transmission distances and for moderate relay SI levels.In general, the investigations in this thesis provide tools, results and useful insights for implementing space-efficient, low-cost and energy-efficient cooperative networks, specifically, towards the future green communication era where the optimization of the scarce resources is critical