125 research outputs found

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

    Get PDF
    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

    Relay Selection Strategies for Multi-hop Cooperative Networks

    Get PDF
    In this dissertation we consider several relay selection strategies for multi-hop cooperative networks. The relay selection strategies we propose do not require a central controller (CC). Instead, the relay selection is on a hop-by-hop basis. As such, these strategies can be implemented in a distributed manner. Therefore, increasing the number of hops in the network would not increase the complexity or time consumed for the relay selection procedure of each hop. We first investigate the performance of a hop-by-hop relay selection strategy for multi-hop decode-and-forward (DF) cooperative networks. In each relay cluster, relays that successfully receive and decode the message from the previous hop form a decoding set for relaying, and the relay which has the highest signal-to-noise ratio (SNR) link to the next hop is then selected for retransmission. We analyze the performance of this method in terms of end-to-end outage probability, and we derive approximations for the ergodic capacity and the effective ergodic capacity of this strategy. Next we propose a novel hop-by-hop relay selection strategy where the relay in the decoding set with the largest number of ``good\u27\u27 channels to the next stage is selected for retransmission. We analyze the performance of this method in terms of end-to-end outage probability in the case of perfect and imperfect channel state information (CSI). We also investigate relay selection strategies in underlay spectrum sharing cognitive relay networks. We consider a two-hop DF cognitive relay network with a constraint on the interference to the primary user. The outage probability of the secondary user and the interference probability at the primary user are analyzed under imperfect CSI scenario. Finally we introduce a hop-by-hop relay selection strategy for underlay spectrum sharing multi-hop relay networks. Relay selection in each stage is only based on the CSI in that hop. It is shown that in terms of outage probability, the performance of this method is nearly optimal

    Performance Comparison between Adaptive and Fixed Transmit Power in Underlay Cognitive Radio Networks

    Get PDF
    In this paper, we compare the performance in terms of symbol error probability, data rate and power consumption of the use of fixed transmit power (FTP) and adaptive transmit power (ATP) in underlay cognitive radio networks. The use of FTP alleviates the signaling requirements of underlay cognitive radio networks compared to the ATP. Nevertheless, the use of FTP influences the performances of the underlay cognitive radio networks. To study this influence, we consider three relay selection schemes using FTP: opportunistic decode and forward with FTP (O-DF with FTP), opportunistic amplify and forward with FTP (O-AF with FTP) and partial relay selection with FTP (PR with FTP). We compare the performances of these schemes in terms of symbol error probability, data rate and power consumption with three relay selection schemes using ATP: opportunistic decode and forward with ATP (O-DF with ATP), opportunistic amplify and forward with ATP (O-AF with ATP) and partial relay selection with ATP (PR with ATP). We provide exact and/or lower bound expressions of the symbol error probabilities of O-DF, O-AF and PR with FTP. The analytical study for the data rate and the power consumption is also provided. Our comparison study shows that FTP has a positive impact on the data rate and power consumption performance while it deteriorates the symbol error probability performance

    Analysis and Ad-hoc Networking Solutions for Cooperative Relaying Systems

    Get PDF
    Users of mobile networks are increasingly demanding higher data rates from their service providers. To cater to this demand, various signal processing and networking algorithms have been proposed. Amongst them the multiple input multiple output (MIMO) scheme of wireless communications is one of the most promising options. However, due to certain physical restrictions, e.g., size, it is not possible for many devices to have multiple antennas on them. Also, most of the devices currently in use are single-antenna devices. Such devices can make use of the MIMO scheme by employing cooperative MIMO methods. This involves nearby nodes utilizing the antennas of each other to form virtual antenna arrays (VAAs). Nodes with limited communication ranges can further employ multi-hopping to be able to communicate with far away nodes. However, an ad-hoc communications scheme with cooperative MIMO multi-hopping can be challenging to implement because of its de-centralized nature and lack of a centralized controling entity such as a base-station. This thesis looks at methods to alleviate the problems faced by such networks.In the first part of this thesis, we look, analytically, at the relaying scheme under consideration and derive closed form expressions for certain performance measures (signal to noise ratio (SNR), symbol error rate (SER), bit error rate (BER), and capacity) for the co-located and cooperative multiple antenna schemes in different relaying configurations (amplify-and-forward and decode-and-forward) and different antenna configurations (single input single output (SISO), single input multiple output (SIMO) and MIMO). These expressions show the importance of reducing the number of hops in multi-hop communications to achieve a better performance. We can also see the impact of different antenna configurations and different transmit powers on the number of hops through these simplified expressions.We also look at the impact of synchronization errors on the cooperative MIMO communications scheme and derive a lower bound of the SINR and an expression for the BER in the high SNR regime. These expressions can help the network designers to ensure that the quality of service (QoS) is satisfied even in the worst-case scenarios. In the second part of the thesis we present some algorithms developed by us to help the set-up and functioning of cluster-based ad-hoc networks that employ cooperative relaying. We present a clustering algorithm that takes into account the battery status of nodes in order to ensure a longer network life-time. We also present a routing mechanism that is tailored for use in cooperative MIMO multi-hop relaying. The benefits of both schemes are shown through simulations.A method to handle data in ad-hoc networks using distributed hash tables (DHTs) is also presented. Moreover, we also present a physical layer security mechanism for multi-hop relaying. We also analyze the physical layer security mechanism for the cooperative MIMO scheme. This analysis shows that the cooperative MIMO scheme is more beneficial than co-located MIMO in terms of the information theoretic limits of the physical layer security.Nutzer mobiler Netzwerke fordern zunehmend höhere Datenraten von ihren Dienstleistern. Um diesem Bedarf gerecht zu werden, wurden verschiedene Signalverarbeitungsalgorithmen entwickelt. Dabei ist das "Multiple input multiple output" (MIMO)-Verfahren für die drahtlose Kommunikation eine der vielversprechendsten Techniken. Jedoch ist aufgrund bestimmter physikalischer Beschränkungen, wie zum Beispiel die Baugröße, die Verwendung von mehreren Antennen für viele Endgeräte nicht möglich. Dennoch können solche Ein-Antennen-Geräte durch den Einsatz kooperativer MIMO-Verfahren von den Vorteilen des MIMO-Prinzips profitieren. Dabei schließen sich naheliegende Knoten zusammen um ein sogenanntes virtuelles Antennen-Array zu bilden. Weiterhin können Knoten mit beschränktem Kommunikationsbereich durch mehrere Hops mit weiter entfernten Knoten kommunizieren. Allerdings stellt der Aufbau eines solchen Ad-hoc-Netzwerks mit kooperativen MIMO-Fähigkeiten aufgrund der dezentralen Natur und das Fehlen einer zentral-steuernden Einheit, wie einer Basisstation, eine große Herausforderung dar. Diese Arbeit befasst sich mit den Problemstellungen dieser Netzwerke und bietet verschiedene Lösungsansätze.Im ersten Teil dieser Arbeit werden analytisch in sich geschlossene Ausdrücke für ein kooperatives Relaying-System bezüglicher verschiedener Metriken, wie das Signal-Rausch-Verhältnis, die Symbolfehlerrate, die Bitfehlerrate und die Kapazität, hergeleitet. Dabei werden die "Amplify-and forward" und "Decode-and-forward" Relaying-Protokolle, sowie unterschiedliche Mehrantennen-Konfigurationen, wie "Single input single output" (SISO), "Single input multiple output" (SIMO) und MIMO betrachtet. Diese Ausdrücke zeigen die Bedeutung der Reduzierung der Hop-Anzahl in Mehr-Hop-Systemen, um eine höhere Leistung zu erzielen. Zudem werden die Auswirkungen verschiedener Antennen-Konfigurationen und Sendeleistungen auf die Anzahl der Hops analysiert.  Weiterhin wird der Einfluss von Synchronisationsfehlern auf das kooperative MIMO-Verfahren herausgestellt und daraus eine untere Grenze für das Signal-zu-Interferenz-und-Rausch-Verhältnis, sowie ein Ausdruck für die Bitfehlerrate bei hohem Signal-Rausch-Verhältnis entwickelt. Diese Zusammenhänge sollen Netzwerk-Designern helfen die Qualität des Services auch in den Worst-Case-Szenarien sicherzustellen. Im zweiten Teil der Arbeit werden einige innovative Algorithmen vorgestellt, die die Einrichtung und die Funktionsweise von Cluster-basierten Ad-hoc-Netzwerken, die kooperative Relays verwenden, erleichtern und verbessern. Darunter befinden sich ein Clustering-Algorithmus, der den Batteriestatus der Knoten berücksichtigt, um eine längere Lebensdauer des Netzwerks zu gewährleisten und ein Routing-Mechanismus, der auf den Einsatz in kooperativen MIMO Mehr-Hop-Systemen zugeschnitten ist. Die Vorteile beider Algorithmen werden durch Simulationen veranschaulicht. Eine Methode, die Daten in Ad-hoc-Netzwerken mit verteilten Hash-Tabellen behandelt wird ebenfalls vorgestellt. Darüber hinaus wird auch ein Sicherheitsmechanismus für die physikalische Schicht in Multi-Hop-Systemen und kooperativen MIMO-Systemen präsentiert. Eine Analyse zeigt, dass das kooperative MIMO-Verfahren deutliche Vorteile gegenüber dem konventionellen MIMO-Verfahren hinsichtlich der informationstheoretischen Grenzen der Sicherheit auf der physikalischen Schicht aufweist

    Esquemas de retransmissão baseados no protocolo decodifica-e-encaminha em redes cognitivas do tipo underlay

    Get PDF
    Orientador: José Cândido Silveira Santos FilhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: O conceito de compartilhamento de espectro do tipo underlay tem sido proposto como uma técnica promissora para contornar o problema da escassez e da subutilização do espectro, permitindo que usuários não licenciados, chamados de usuários secundários, possam acessar simultaneamente uma banda licenciada, alocada aos usuários primários, desde que o nível de interferência sobre os mesmos seja mantido abaixo de um dado limiar aceitável. Entretanto, isso implica que a potência de transmissão na rede secundária deve ser restringida, comprometendo assim a confiabilidade e a cobertura da comunicação. A fim de contornar esse problema, técnicas de retransmissão cooperativa, as quais proveem um novo tipo de diversidade espacial, podem ser exploradas como um meio eficaz para melhorar o desempenho da rede secundária. De fato, a utilização conjunta de ambas as técnicas ¿ compartilhamento de espectro do tipo underlay e retransmissão cooperativa ¿ em redes cooperativas e cognitivas tem recebido especial atenção, já que a eficiência espectral do sistema e o desempenho da rede secundária podem ser melhorados significativamente. Esta tese apresenta quatro contribuições principais na referida área. Em particular, estuda-se o efeito conjunto de duas restrições de potência importantes sobre o desempenho de outage de redes cooperativas e cognitivas, especificamente, o nível máximo de potência interferente tolerada pelo receptor primário e o valor máximo de potência transmitida nos usuários secundários. Foca-se em esquemas de retransmissão baseados no protocolo decodifica-e-encaminha, abordando cenários em que o enlace direto entre fonte e destino está disponível para transmitir informação útil. Como uma primeira contribuição, analisa-se o desempenho de dois esquemas baseados no protocolo de retransmissão half-duplex incremental, os quais exploram a diversidade espacial dos enlaces diretos em redes cooperativas e cognitivas multiusuário. A segunda contribuição investiga o impacto de estimativas desatualizadas do canal sobre o mecanismo de seleção de destino para um desses esquemas anteriores, focando-se apenas no aspecto cooperativo da rede, ou seja, desconsiderando-se o uso de compartilhamento espectral. A terceira contribuição estuda o desempenho de redes cooperativas e cognitivas baseadas no modo full-duplex. Para esse cenário, avalia-se o impacto tanto da autointerferência residual, que é inerente ao modo full-duplex, bem como das restrições de potência que caracterizam o compartilhamento de espectro do tipo underlay. Como contribuição final, motivada pelo compromisso entre a perda de eficiência espectral e o problema da autointerferência residual, próprios dos modos half-duplex e full-duplex, respectivamente, propõe-se e analisa-se um esquema de transmissão adaptativo para redes cooperativas e cognitivas, através do qual, antes de cada processo de comunicação, um dos seguintes modos de transmissão é selecionado: retransmissão half-duplex, retransmissão full-duplex ou transmissão direta. Para todos os cenários considerados, expressões analíticas exatas para a probabilidade de outage são obtidas. Adicionalmente, uma análise assintótica é realizada a fim de caracterizar a ordem de diversidade e o comportamento de outage da rede secundária no regime assintótico de alta relação sinal-ruído. Simulações de Monte Carlo validam os resultados analíticos apresentadosAbstract: Underlay spectrum sharing has been proposed as a promising technique to alleviate the problem of spectrum scarcity and underutilization, by enabling secondary (unlicensed) users to concurrently access a licensed band, provided that the resulting interference on the primary (licensed) users remains below a given acceptable level. However, such a technique implies that the transmit power at the secondary network must be constrained, thereby compromising the communication reliability and coverage. To counteract this, cooperative relaying techniques, which provide a new form of spatial diversity, can be exploited as an effective means to boost the performance of the secondary network. Indeed, the joint use of both techniques¿underlay spectrum sharing and cooperative relaying¿in cognitive relaying networks has drawn special attention, since the overall spectral efficiency and the secondary-network performance can be significantly improved. This dissertation comprises four main contributions in this field. In particular, we examine the combined effect of two crucial power constraints on the outage performance of cognitive relaying networks, namely, the maximum tolerable interference power at the primary receiver and the maximum transmit power at the secondary users. We focus on relaying schemes operating under the decode-and-forward protocol, for scenarios in which the direct link between source and destination is available to convey useful information. As a first contribution, we analyze the performance of two incremental half-duplex relaying schemes, which exploit the spatial diversity of the direct links in a multiuser scenario. Our second contribution investigates the impact of outdated channel estimates on the destination-scheduling mechanism of one of those incremental schemes, from the perspective of a cooperative network only, that is, in the absence of spectrum sharing. The third contribution addresses cognitive full-duplex relaying networks. More specifically, we assess the system performance as a function of both the residual self-interference, which is inherent to the full-duplex relaying mode, and the underlay spectrum-sharing power constraints. As a final contribution, driven by the tradeoff between the spectral-efficiency loss and the residual self-interference problem, intrinsic to the half- and full-duplex relaying modes, respectively, we propose and analyze an adaptive transmission scheme whereby, before each communication process, one out of the following transmission modes is selected: half-duplex relaying, full-duplex relaying, or direct transmission. For all the considered scenarios, exact analytical expressions for the outage probability are derived. In addition, an asymptotic analysis is performed to obtain further insights on the diversity order and outage behavior of the secondary network at the high signal-to-noise ratio regime. Monte Carlo simulations corroborate the accuracy of the presented mathematical analysisDoutoradoTelecomunicações e TelemáticaDoutor em Engenharia ElétricaCAPE

    Performance of a Cognitive Relay Network under AF Relay Selection Scheme with Imperfect Channel Estimation

    Get PDF
    In this paper outage performance of a secondary user (SU) is evaluated under amplify and forward (AF) relay selection scheme with an imperfect channel state information (CSI)while sharing spectrum in an underlay cognitive radio network (CRN). In underlay, the SU coexists with primary user (PU) in the same band provided the interference produced by SU at the PU receiver is below the interference threshold of PU which limits the transmission power of SU and coverage area. Relays help to improve the performance of SU in underlay. However relays are also constrained in transmit power due to interference constraint imposed by PU. Closed form expression of the outage probability of SU with maximum transmit power constraint of relay under imperfect CSI is derived. A scaling factor based power control is used for the SU transmitter and the relay in order to maintain the interference constraint at PU receiver due to imperfect CSI. The impact of different parameters viz. correlation coefficient, channel estimation error, tolerable interference threshold, number of relays and the maximum transmit power constraint of relay on SU performance is investigated. A MATLAB based test bed has also been developed to carry out simulation in order to validate the theoretical result

    Proactive and Reactive DF Relaying for Cognitive Network with Multiple Primary Users

    Get PDF
    In this paper, the outage performance of a cognitive radio network with a pair of secondary transmitter and receiver is investigated in the presence multiple primary users over a number of licensed frequency band and multiple secondary relays (SRs). Two decode and forward (DF) schemes are considered for the relays, namely proactive and reactive DF schemes. An adaptive power allocation scheme for secondary transmitter and secondary relays is formulated under the joint constraints of the primary user outage and peak transmit power of the secondary users. Based on these strategies, analytical expressions for the outage probability of proactive and reactive DF schemes are derived. More precisely, our results demonstrate the impact of number of the active primary users (PUs) over a number of available licensed frequency bands on the outage performance of secondary network. Further, it is observed that the performance of the secondary network can be improved by extending the bandwidth of the primary users
    corecore