동일채널간섭이 존재하는 페이딩채널에서 무선 중계 네트워크의 성능 분석

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 8. 이재홍.무선 중계 기술은 차세대 통신 시스템에서 요구되는 높은 서비스 품질/데이터 전송률 달성을 위한 가장 중요한 기술 중 하나이다. 중계 기술이 갖고 있는 다양한 장점으로 인해 중계 기술은 지금까지 IEEE 802.16j 및 3GPP LTE-Advanced 등의 무선통신 시스템 표준에 반영되기도 하였다. 그러나 실질적인 무선 중계 네트워크의 프로토콜 개발을 위해서는 여전히 해결해야하는 많은 문제들이 있다. 특히 대형셀과 소형셀이 동시에 존재하는 중첩셀 네트워크에서 이웃한 대형셀 및 소형셀로부터 받게되는 동일채널간섭은 차세대 무선통신 시스템의 성능을 저하시키는 주요 제한 요소인데 아직 연구가 미흡한 실정이다. 또한 전이중 중계 네트워크에서 단말기의 송신안테나에서 수신안테나로 들어오는 동일채널 루프간섭은 전이중 중계 네트워크의 성능을 결정하는 중요한 요소로 추가적인 연구가 필요한 실정이다. 본 논문에서는 동일채널간섭을 포함한 양방향 중계 네트워크, 동일채널 루프간섭을 포함한 양방향 전이중 중계 네트워크 및 무선 인지 다중 홉 네트워크의 성능을 분석하며, 주요한 연구결과는 다음과 같다. 첫째, 셀룰러 환경에서 높은 주파수 재사용율로 인해 발생한 동일채널간섭이 존재하는 양방향 중계 네트워크의 성능을 분석한다. 이때 임의의 한 사용자가 불능 사건이 발생하는 시나리오(개별 사용자 불능), 전체 사용자가 동시에 불능 사건이 발생한 시나리오(전체 사용자 불능)의 두 가지에 대해 성능을 분석한다. 여기에서 각 시나리오에 대하여 개별 사용자 불능 확률 및 전체 사용자 불능 확률을 폐형으로 유도한다. 모의실험을 통해 얻어진 불능 확률이 유도한 불능 확률 값과 일치함을 확인한다. 또한 동일채널간섭을 발생하는 인접 셀의 사용자가 늘어날수록 개별 사용자 불능 확률 및 전체 사용자 불능 확률이 증가함을 확인한다. 둘째, 동일채널 루프간섭이 존재하는 전이중 양방향 중계 네트워크를 연구한다. 여기에서 두 전이중 방식의 사용자들이 전이중 방식의 중계기를 이용하여 서로 신호를 교환한다. 이때 각 단말기들은 자신의 수신 신호에서 루프간섭 신호의 추정치를 제거한다. 단말기들이 채널 상태 정보를 정확하게 혹은 부정확하게 알고 있는 경우에 전이중 양방향 중계 네트워크의 불능 확률을 정확한 적분 표현 및 근사적 폐형 표현으로 유도한다. 모의실험을 통해 얻어지 결과가 유도한 수식과 일치함을 확인한다. 셋째, 대형셀과 소형셀이 동시에 존재하는 중첩셀 네트워크를 연구한다. 특히 인접 대형셀 및 소형셀에서 발생한 동일채널간섭이 존재하는 무선 인지 기반 다중 홉 소형셀 네트워크의 불능 확률을 분석한다. 모의실험을 통해 얻어진 불능 확률을 통해 유도한 불능 확률을 검증한다. 유도한 불능 확률 값과 모의실험을 통해 얻어진 불능 확률 값이 일치함을 확인한다. 대형셀의 수가 증가할수록 불능 확률이 증가함을 확인한다.Wireless relay technology is one of the most promising technologies for the future communication systems which provide higher data rate and better quality of service (QoS). Thanks to its advantages, it has been adopted in wireless standards such as IEEE 802.16j and 3GPP LTE-Advanced. However, there are still many challenges to be addressed for developing protocols of wireless relay networks. Especially, in multitier cellular networks (e.g. small cell underlaid macro cell), cochannel interference from multiple interferers in other macro cells and neighboring small cells is one of the major limiting factors due to frequency reuse for high spectrum utilization. In the full-duplex relay networks, cochannel loop interference from a transmit antenna to a receive antenna of a terminal is an important limiting factor to determine the performance of full-duplex relay networks. The dissertation consists of three main results. First, we analyze the performance of a two-way relay network experiencing cochannel interference from multiple interferers due to frequency reuse in cellular networks. In the two-way relay network, two users exchange their information with the help of an amplify-and-forward (AF) relay. We discuss two different scenarios: Outages are declared individually for each user (individual outage) and an outage is declared simultaneously for all users (common outage). We derive the closed-form expression for the individual outage probability and the exact integral expression for the common outage probability of the two-way relay network with multiple interferers. The validity of our analytical results is verified by a comparison with simulation results. It is shown that the analytical results perfectly match the simulation results of the individual and common outage probabilities. Also, it is shown that the individual and common outage probabilities increase as the number of interferers increases. Second, we investigate two-way full-duplex relaying with cochannel loop interference. In the two-way full-duplex relaying, two full-duplex users exchange data with each other via a full-duplex relay and each node attempts to subtract the estimate of the cochannel loop interference from its received signal. We derive the exact integral and approximate closed-form expressions for the outage probability of the two-way full-duplex relaying in case of perfect and imperfect channel state information. Monte Carlo simulation verifies the validity of analytical results. Third, we investigate a cognitive small cell network which is overlaid with a cellular network. We analyze the performance of the cognitive small cell network in the presence of cochannel interference from the cellular network. Analytical results are verified by Monte Carlo simulations. It is shown that the analytical results are in complete agreement with simulation results. It is shown that the outage probability increases as the number of cells increases.Abstract 1 Introduction 1.1 Background and Related Works 1.1.1 Relay Technology 1.1.2 Cognitive Radio 1.2 Outline of Dissertation 1.3 Notations 2 Two-Way Relay Network with Cochannel Interference 2.1 System Model 2.2 Outage Probability Derivation 2.2.1 Moment Generating Functions 2.2.2 Individual Outage Probability 2.2.3 Common Outage Probability 2.3 Numerical Results 2.4 Summary 3 Two-Way Full-Duplex Relaying with Cochannel Loop Interference 3.1 System Model 3.2 Outage Probability Derivation 3.2.1 Signal-to-Interference-plus-Noise Ratio 3.2.2 Cumulative Density Function 3.2.3 Outage Probability 3.3 Numerical Results 3.4 Summary 4 Multi-hop Cognitive Radio Network with Cochannel Interference 4.1 System Model 4.2 Outage Probability Derivation 4.2.1 Signal-to-Interference-plus-Noise Ratio 4.2.2 Cumulative Density Function 4.2.3 Outage Probability 4.3 Numerical Results 4.4 Summary 5 Conclusions 5.1 Summary 5.2 Future Works Bibliography Korean Abstract AcknowledgmentsDocto

Joint transceiver design and power optimization for wireless sensor networks in underground mines

Avec les grands développements des technologies de communication sans fil, les réseaux de capteurs sans fil (WSN) ont attiré beaucoup d’attention dans le monde entier au cours de la dernière décennie. Les réseaux de capteurs sans fil sont maintenant utilisés pour a surveillance sanitaire, la gestion des catastrophes, la défense, les télécommunications, etc. De tels réseaux sont utilisés dans de nombreuses applications industrielles et commerciales comme la surveillance des processus industriels et de l’environnement, etc. Un réseau WSN est une collection de transducteurs spécialisés connus sous le nom de noeuds de capteurs avec une liaison de communication distribuée de manière aléatoire dans tous les emplacements pour surveiller les paramètres. Chaque noeud de capteur est équipé d’un transducteur, d’un processeur de signal, d’une unité d’alimentation et d’un émetteur-récepteur. Les WSN sont maintenant largement utilisés dans l’industrie minière souterraine pour surveiller certains paramètres environnementaux, comme la quantité de gaz, d’eau, la température, l’humidité, le niveau d’oxygène, de poussière, etc. Dans le cas de la surveillance de l’environnement, un WSN peut être remplacé de manière équivalente par un réseau à relais à entrées et sorties multiples (MIMO). Les réseaux de relais multisauts ont attiré un intérêt de recherche important ces derniers temps grâce à leur capacité à augmenter la portée de la couverture. La liaison de communication réseau d’une source vers une destination est mise en oeuvre en utilisant un schéma d’amplification/transmission (AF) ou de décodage/transfert (DF). Le relais AF reçoit des informations du relais précédent et amplifie simplement le signal reçu, puis il le transmet au relais suivant. D’autre part, le relais DF décode d’abord le signal reçu, puis il le transmet au relais suivant au deuxième étage s’il peut parfaitement décoder le signal entrant. En raison de la simplicité analytique, dans cette thèse, nous considérons le schéma de relais AF et les résultats de ce travail peuvent également être développés pour le relais DF. La conception d’un émetteur/récepteur pour le relais MIMO multisauts est très difficile. Car à l’étape de relais L, il y a 2L canaux possibles. Donc, pour un réseau à grande échelle, il n’est pas économique d’envoyer un signal par tous les liens possibles. Au lieu de cela, nous pouvons trouver le meilleur chemin de la source à la destination qui donne le rapport signal sur bruit (SNR) de bout en bout le plus élevé. Nous pouvons minimiser la fonction objectif d’erreur quadratique moyenne (MSE) ou de taux d’erreur binaire (BER) en envoyant le signal utilisant le chemin sélectionné. L’ensemble de relais dans le chemin reste actif et le reste des relais s’éteint, ce qui permet d’économiser de l’énergie afin d’améliorer la durée de vie du réseau. Le meilleur chemin de transmission de signal a été étudié dans la littérature pour un relais MIMO à deux bonds mais est plus complexe pour un ...With the great developments in wireless communication technologies, Wireless Sensor Networks (WSNs) have gained attention worldwide in the past decade and are now being used in health monitoring, disaster management, defense, telecommunications, etc. Such networks are used in many industrial and consumer applications such as industrial process and environment monitoring, among others. A WSN network is a collection of specialized transducers known as sensor nodes with a communication link distributed randomly in any locations to monitor environmental parameters such as water level, and temperature. Each sensor node is equipped with a transducer, a signal processor, a power unit, and a transceiver. WSNs are now being widely used in the underground mining industry to monitor environmental parameters, including the amount of gas, water, temperature, humidity, oxygen level, dust, etc. The WSN for environment monitoring can be equivalently replaced by a multiple-input multiple-output (MIMO) relay network. Multi-hop relay networks have attracted significant research interest in recent years for their capability in increasing the coverage range. The network communication link from a source to a destination is implemented using the amplify-and-forward (AF) or decode-and-forward (DF) schemes. The AF relay receives information from the previous relay and simply amplifies the received signal and then forwards it to the next relay. On the other hand, the DF relay first decodes the received signal and then forwards it to the next relay in the second stage if it can perfectly decode the incoming signal. For analytical simplicity, in this thesis, we consider the AF relaying scheme and the results of this work can also be developed for the DF relay. The transceiver design for multi-hop MIMO relay is very challenging. This is because at the L-th relay stage, there are 2L possible channels. So, for a large scale network, it is not economical to send the signal through all possible links. Instead, we can find the best path from source-to-destination that gives the highest end-to-end signal-to-noise ratio (SNR). We can minimize the mean square error (MSE) or bit error rate (BER) objective function by sending the signal using the selected path. The set of relay in the path remains active and the rest of the relays are turned off which can save power to enhance network life-time. The best path signal transmission has been carried out in the literature for 2-hop MIMO relay and for multiple relaying it becomes very complex. In the first part of this thesis, we propose an optimal best path finding algorithm at perfect channel state information (CSI). We consider a parallel multi-hop multiple-input multiple-output (MIMO) AF relay system where a linear minimum mean-squared error (MMSE) receiver is used at the destination. We simplify the parallel network into equivalent series multi-hop MIMO relay link using best relaying, where the best relay ..

Throughput analysis of non-orthogonal multiple access and orthogonal multiple access assisted wireless energy harvesting K-hop relaying networks

This study introduces the non-orthogonal multiple access (NOMA) technique into the wireless energy harvesting K-hop relay network to increase throughput. The relays have no dedicated energy source and thus depend on energy harvested by wireless from a power beacon (PB). Recently, NOMA has been promoted as a technology with the potential to enhance connectivity, reduce latency, increase fairness amongst users, and raise spectral effectiveness compared to orthogonal multiple access (OMA) technology. For performance considerations, we derive exact throughput expressions for NOMA and OMA-assisted multi-hop relaying and compare the performance between the two. The obtained results are validated via Monte Carlo simulations

A review of relay network on UAVS for enhanced connectivity

One of the best evolution in technology breakthroughs is the Unmanned Aerial Vehicle (UAV). This aerial system is able to perform the mission in an agile environment and can reach the hard areas to perform the tasks autonomously. UAVs can be used in post-disaster situations to estimate damages, to monitor and to respond to the victims. The Ground Control Station can also provide emergency messages and ad-hoc communication to the Mobile Users of the disaster-stricken community using this network. A wireless network can also extend its communication range using UAV as a relay. Major requirements from such networks are robustness, scalability, energy efficiency and reliability. In general, UAVs are easy to deploy, have Line of Sight options and are flexible in nature. However, their 3D mobility, energy constraints, and deployment environment introduce many challenges. This paper provides a discussion of basic UAV based multi-hop relay network architecture and analyses their benefits, applications, and tradeoffs. Key design considerations and challenges are investigated finding fundamental issues and potential research directions to exploit them. Finally, analytical tools and frameworks for performance optimizations are presented

Security–Reliability Tradeoff Analysis for SWIPT- and AF-Based IoT Networks With Friendly Jammers

Radio-frequency (RF) energy harvesting (EH) in wireless relaying networks has attracted considerable recent interest, especially for supplying energy to relay nodes in the Internet of Things (IoT) systems to assist the information exchange between a source and a destination. Moreover, limited hardware, computational resources, and energy availability of IoT devices have raised various security challenges. To this end, physical-layer security (PLS) has been proposed as an effective alternative to cryptographic methods for providing information security. In this study, we propose a PLS approach for simultaneous wireless information and power transfer (SWIPT)-based half-duplex (HD) amplify-and-forward (AF) relaying systems in the presence of an eavesdropper. Furthermore, we take into account both static power splitting relaying (SPSR) and dynamic power splitting relaying (DPSR) to thoroughly investigate the benefits of each one. To further enhance secure communication, we consider multiple friendly jammers to help prevent wiretapping attacks from the eavesdropper. More specifically, we provide a reliability and security analysis by deriving closed-form expressions of outage probability (OP) and intercept probability (IP), respectively, for both the SPSR and DPSR schemes. Then, simulations are also performed to validate our analysis and the effectiveness of the proposed schemes. Specifically, numerical results illustrate the nontrivial tradeoff between reliability and security of the proposed system. In addition, we conclude from the simulation results that the proposed DPSR scheme outperforms the SPSR-based scheme in terms of OP and IP under the influences of different parameters on system performance

Improving Physical Layer Security of Cellular Networks Using Full-Duplex Jamming Relay-Aided D2D Communications

This paper investigates the physical layer security and data transmission in cellular networks with inband underlay Device-to-Device (D2D) communications, where there is no direct link between D2D users. We propose to apply full-duplex (FD) transmission and dual antenna selection at the D2D relay node. The relay node can simultaneously act as a friendly jammer to improve the secrecy performance of the cellular network while enhancing the D2D communication data transmission. This is an appealing and practical scheme where spectrum sharing is beneficial for the D2D and cellular networks in terms of reliability enhancement and security provisioning, respectively. The practical scenario, where the eavesdropper is passive, is considered. The eavesdropper uses either selection combining or maximal ratio combining to combine the wiretapped signals of the cellular network. The secrecy performance of the cellular network is analyzed, and closed-form expressions for the secrecy outage probability and the probability of non-zero secrecy capacity are derived. We show that increasing the number of FD jamming antennas enhances the secrecy performance of the cellular network. A closed-form expression of the D2D outage probability is also provided. Simulation and numerical results are provided to verify the efficiency of the proposed scheme and to validate the accuracy of the derived expressions

Performance study of an underlay cognitive radio network in the presence of co-channel interference

PhD ThesisMassive innovation in all aspects of the wireless communication network has been witnessed over the last few decades. The demand for data throughput is continuously growing, as such, the current regulations for allocating frequency spectrum are not able to respond to this exponential growth. Cognitive radio (CR), has been proposed as a solution to this problem. One of the possible scenarios of the implementation of CR is underlay cognitive radio. In this thesis the performance of an underlay cognitive radio network (UCRN) in the presence of the co-channel interference (CCI) is assessed. Firstly, the impact of CCI on the dual-hop cooperative UCRN is investigated over Rayleigh fading channels. In order to do this, the exact outage probability (OP), average error probability (AEP) and the ergodic capacity (EC) are studied. In addition, simple and asymptotic expressions for the OP and AEP are derived. Furthermore, the optimal power allocation is investigated to enhance the network performance. Moreover, the performance of a multi-user scenario is studied by considering the opportunistic SNR-based selection technique. Secondly, the effect of both primary network interference and CCI on the dual-hop UCRN over Rayleigh fading channels are studied. The equivalent signal-to-interference-plus-noise ratio (SINR) for this network scenario is obtained by considering multi-antenna schemes at all receiver nodes. The different signal combinations at the receiver nodes are investigated and compared, such as selection combining (SC) and maximum ratio combining (MRC) techniques. Then, the equivalent probability density function (PDF) and cumulative distribution function (CDF) of the network’s equivalent SINR are derived and discussed. Furthermore, expressions for the exact OP, AEP, and EC are derived and reviewed. In addition, asymptotic OP expressions are obtained for different case scenarios to gain an insight into the network parameters. Thirdly, multiple-input multiple-output (MIMO) UCRN is investigated under the influence of primary transmitter interference and CCI over Rayleigh fading channels. The transmit antenna selection and maximum ratio combining (TAS/MRC) techniques are considered for examining the performance of the secondary network. At first the equivalent SINR for the system is derived, then the exact and approximate expressions for the OP are derived and discussed. Fourthly, considering Nakagami-m fading channels, the performance of the UCRN is thoroughly studied with the consideration of the impact of primary network interference and CCI. The equivalent SINR for the secondary system is derived. Then, the system equivalent PDF and CDF are derived and discussed. Furthermore, the OP and AEP performances are investigated. Finally, for the cases mentioned above, numerical examples in conjunction with MatLab Monte Carlo simulations are provided to validate the derived results. The results show that CCI is one of the factors that severely reduces the UCRN performance. This can be more observable when the CCI power increases linearly with the transmission power of the secondary transmitter nodes. Furthermore, it was found that in a multi-user scenario the opportunistic SNR-based selection technique consideration can improve the performance of the network. Moreover, adaptive power allocation is found to give better results than equal power allocation. In addition, cooperative communication can be considered to be an effective way to combat the impact of transmission power limitation of the secondary network and interference power constraint. The multi-antenna schemes are another important consideration for enhancing the overall performance. In fact, despite the interference from the CCI and primary user sources, the multi-antennas scheme does not lose its advantage in the UCRN performance improvementHigher Committee for Education Development in Iraq (HCED). I am also grateful to the Ministry of Transportation and Communication, Kurdistan Regional Government-Iraq