Joint Power and Resource Allocation for Block-Fading Relay-Assisted Broadcast Channels

We provide the solution for optimizing the power and resource allocation over block-fading relay-assisted broadcast channels in order to maximize the long term average achievable rates region of the users. The problem formulation assumes regenerative (repetition coding) decode-and-forward (DF) relaying strategy, long-term average total transmitted power constraint, orthogonal multiplexing of the users messages within the channel blocks, possibility to use a direct transmission (DT) mode from the base station to the user terminal directly or a relaying (DF) transmission mode, and partial channel state information. We show that our optimization problem can be transformed into an equivalent "no-relaying" broadcast channel optimization problem with each actual user substituted by two virtual users having different channel qualities and multiplexing weights. The proposed power and resource allocation strategies are expressed in closed-form that can be applied practically in centralized relay-assisted wireless networks. Furthermore, we show by numerical examples that our scheme enlarges the achievable rates region significantly.Comment: IEEE Transactions on Wireless Communications, June 201

Outage Probability of Dual-Hop Multiple Antenna AF Relaying Systems with Interference

This paper presents an analytical investigation on the outage performance of dual-hop multiple antenna amplify-and-forward relaying systems in the presence of interference. For both the fixed-gain and variable-gain relaying schemes, exact analytical expressions for the outage probability of the systems are derived. Moreover, simple outage probability approximations at the high signal to noise ratio regime are provided, and the diversity order achieved by the systems are characterized. Our results suggest that variable-gain relaying systems always outperform the corresponding fixed-gain relaying systems. In addition, the fixed-gain relaying schemes only achieve diversity order of one, while the achievable diversity order of the variable-gain relaying scheme depends on the location of the multiple antennas.Comment: Accepted to appear in IEEE Transactions on Communication

Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey

This paper provides a comprehensive review of the domain of physical layer security in multiuser wireless networks. The essential premise of physical-layer security is to enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers without relying on higher-layer encryption. This can be achieved primarily in two ways: without the need for a secret key by intelligently designing transmit coding strategies, or by exploiting the wireless communication medium to develop secret keys over public channels. The survey begins with an overview of the foundations dating back to the pioneering work of Shannon and Wyner on information-theoretic security. We then describe the evolution of secure transmission strategies from point-to-point channels to multiple-antenna systems, followed by generalizations to multiuser broadcast, multiple-access, interference, and relay networks. Secret-key generation and establishment protocols based on physical layer mechanisms are subsequently covered. Approaches for secrecy based on channel coding design are then examined, along with a description of inter-disciplinary approaches based on game theory and stochastic geometry. The associated problem of physical-layer message authentication is also introduced briefly. The survey concludes with observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials, 201

Finite Random Matrix Theory Analysis of Multiple Antenna Communication Systems

Multiple-antenna systems are capable of providing substantial improvement to wireless communication networks, in terms of data rate and reliability. Without utilizing extra spectrum or power resources, multiple-antenna technology has already been supported in several wireless communication standards, such as LTE, WiFi and WiMax. The surging popularity and enormous prospect of multiple-antenna technology require a better understanding to its fundamental performance over practical environments. Motivated by this, this thesis provides analytical characterizations of several seminal performance measures in advanced multiple-antenna systems. The analytical derivations are mainly based on finite dimension random matrix theory and a collection of novel random matrix theory results are derived. The closed-form probability density function of the output of multiple-input multiple-output (MIMO) block-fading channels is studied. In contrast to the existing results, the proposed expressions are very general, applying for arbitrary number of antennas, arbitrary signal-to-noise ratio and multiple classical fading models. Results are presented assuming two input structures in the system: the independent identical distributed (i.i.d.) Gaussian input and a product form input. When the channel is fed by the i.i.d. Gaussian input, analysis is focused on the channel matrices whose Gramian is unitarily invariant. When the channel is fed by a product form input, analysis is conducted with respect to two capacity-achieving input structures that are dependent upon the relationship between the coherence length and the number of antennas. The mutual information of the systems can be computed numerically from the pdf expression of the output. The computation is relatively easy to handle, avoiding the need of the straight Monte-Carlo computation which is not feasible in large-dimensional networks. The analytical characterization of the output pdf of a single-user MIMO block-fading channels with imperfect channel state information at the receiver is provided. The analysis is carried out under the assumption of a product structure for the input. The model can be thought of as a perturbation of the case where the statistics of the channel are perfectly known. Specifically, the average singular values of the channel are given, while the channel singular vectors are assumed to be isotropically distributed on the unitary groups of dimensions given by the number of transmit and receive antennas. The channel estimate is affected by a Gaussian distributed error, which is modeled as a matrix with i.i.d. Gaussian entries of known covariance. The ergodic capacity of an amplify-and-forward (AF) MIMO relay network over asymmetric channels is investigated. In particular, the source-relay and relay-destination channels undergo Rayleigh and Rician fading, respectively. Considering arbitrary-rank means for the relay-destination channel, the marginal distribution of an unordered eigenvalue of the cascaded AF channel is presented, thus the analytical expression of the ergodic capacity of the system is obtained. The results indicate the impact of the signal-to-noise ratio and of the Line-of-Sight component on such asymmetric relay network

A Stochastic Geometric Analysis of Device-to-Device Communications Operating over Generalized Fading Channels

Device-to-device (D2D) communications are now considered as an integral part of future 5G networks which will enable direct communication between user equipment (UE) without unnecessary routing via the network infrastructure. This architecture will result in higher throughputs than conventional cellular networks, but with the increased potential for co-channel interference induced by randomly located cellular and D2D UEs. The physical channels which constitute D2D communications can be expected to be complex in nature, experiencing both line-of-sight (LOS) and non-LOS (NLOS) conditions across closely located D2D pairs. As well as this, given the diverse range of operating environments, they may also be subject to clustering of the scattered multipath contribution, i.e., propagation characteristics which are quite dissimilar to conventional Rayeligh fading environments. To address these challenges, we consider two recently proposed generalized fading models, namely $\kappa-\mu$ and $\eta-\mu$, to characterize the fading behavior in D2D communications. Together, these models encompass many of the most widely encountered and utilized fading models in the literature such as Rayleigh, Rice (Nakagami-$n$), Nakagami-$m$, Hoyt (Nakagami-$q$) and One-Sided Gaussian. Using stochastic geometry we evaluate the rate and bit error probability of D2D networks under generalized fading conditions. Based on the analytical results, we present new insights into the trade-offs between the reliability, rate, and mode selection under realistic operating conditions. Our results suggest that D2D mode achieves higher rates over cellular link at the expense of a higher bit error probability. Through numerical evaluations, we also investigate the performance gains of D2D networks and demonstrate their superiority over traditional cellular networks.Comment: Submitted to IEEE Transactions on Wireless Communication

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

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

Data-precoded algorithm for multiple-relay-assisted systems

A data-precoded relay-assisted (RA) scheme is proposed for a system cooperating with multiple relay nodes (RNs), each equipped with either a single-antenna or a two-antenna array. The classical RA systems using distributed space-time/frequency coding algorithms, because of the half-duplex constraint at the relays, require the use of a higher order constellation than in the case of a continuous link transmission from the base station to the user terminal. This implies a penalty in the power efficiency. The proposed precoding algorithm exploits the relation between QPSK and 4 L -QAM, by alternately transmitting through L relays, achieving full diversity, while significantly reducing power penalty. This algorithm explores the situations where a direct path (DP) is not available or has poor quality, and it is a promising solution to extend coverage or increase system capacity. We present the analytical derivation of the gain obtained with the data-precoded algorithm in comparison with distributed space-frequency block code (SFBC) ones. Furthermore, analysis of the pairwise error probability of the proposed algorithm is derived and confirmed with numerical results. We evaluate the performance of the proposed scheme and compare it relatively to the equivalent distributed SFBC scheme employing 16-QAM and non-cooperative schemes, for several link quality scenarios and scheme configurations, highlighting the advantages of the proposed scheme