On the Error Probability of Cognitive RF-FSO Relay Networks over Rayleigh/EW Fading Channels with Primary-Secondary Interference

Free space optical (FSO) communication has emerged to provide line of sight connectivity and higher throughput over unlicensed optical spectrums. Cognitive radio (CR), on the other hand, can utilize the radio frequency (RF) spectrum and allow a secondary user (SU) to share the same spectrum with the primary user (PU) as long as the SU does not impose interference on the PU. Owing to the potential of these emerging technologies, to provide full spectrum efficiency, this paper focuses on the mixed CR RF-FSO transmission scheme, where RF communication is employed at one hop followed by the FSO transmission on the other hop in a dual-hop decode-and-forward (DF) configuration. To quantify the performance of the propose

A Hop-by-Hop Relay Selection Strategy in Multi-Hop Cognitive Relay Networks

In this paper, a hop-by-hop relay selection strategy for multi-hop underlay cognitive relay networks (CRNs) is proposed. In each stage, relays that successfully decode the message from previous hop form a decoding set. Taking both maximum transmit power and maximum interference constraints into consideration, the relay in the decoding set which has the largest number of channels with an acceptable signal-to-noise ratio (SNR) level to the relays in the next stage is selected for retransmission. Therefore, relay selection in each stage only relies on channel state information (CSI) of the channels in that stage and does not require the CSI of any other stage. We analyze the performance of the proposed strategy in terms of endto-end outage probability and throughput, and show that the results match those obtained from simulation closely. Moreover, we derive the asymptotic end-to-end outage probability of the proposed strategy when there is no upper bound on transmitters’ power. We compare this strategy to other hop-by-hop strategies that have appeared recently in the literature and show that this strategy has the best performance in terms of outage probability and throughput. Finally it is shown that the outage probability and throughput of the proposed strategy are very close to that of exhaustive strategy which provides a lower bound for outage probability and an upper bound for throughput of all path selection strategies

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

Channel assembling and resource allocation in multichannel spectrum sharing wireless networks

Submitted in fulfilment of the academic requirements for the degree of Doctor of Philosophy (Ph.D.) in Engineering, in the School of Electrical and Information Engineering, Faculty of Engineering and the Built Environment, at the University of the Witwatersrand, Johannesburg, South Africa, 2017The continuous evolution of wireless communications technologies has increasingly imposed a burden on the use of radio spectrum. Due to the proliferation of new wireless networks applications and services, the radio spectrum is getting saturated and becoming a limited resource. To a large extent, spectrum scarcity may be a result of deficient spectrum allocation and management policies, rather than of the physical shortage of radio frequencies. The conventional static spectrum allocation has been found to be ineffective, leading to overcrowding and inefficient use. Cognitive radio (CR) has therefore emerged as an enabling technology that facilitates dynamic spectrum access (DSA), with a great potential to address the issue of spectrum scarcity and inefficient use. However, provisioning of reliable and robust communication with seamless operation in cognitive radio networks (CRNs) is a challenging task. The underlying challenges include development of non-intrusive dynamic resource allocation (DRA) and optimization techniques. The main focus of this thesis is development of adaptive channel assembling (ChA) and DRA schemes, with the aim to maximize performance of secondary user (SU) nodes in CRNs, without degrading performance of primary user (PU) nodes in a primary network (PN). The key objectives are therefore four-fold. Firstly, to optimize ChA and DRA schemes in overlay CRNs. Secondly, to develop analytical models for quantifying performance of ChA schemes over fading channels in overlay CRNs. Thirdly, to extend the overlay ChA schemes into hybrid overlay and underlay architectures, subject to power control and interference mitigation; and finally, to extend the adaptive ChA and DRA schemes for multiuser multichannel access CRNs. Performance analysis and evaluation of the developed ChA and DRA is presented, mainly through extensive simulations and analytical models. Further, the cross validation has been performed between simulations and analytical results to confirm the accuracy and preciseness of the novel analytical models developed in this thesis. In general, the presented results demonstrate improved performance of SU nodes in terms of capacity, collision probability, outage probability and forced termination probability when employing the adaptive ChA and DRA in CRNs.CK201