Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2016-04-18T18:05:24Z No. of bitstreams: 1 ANA LÚCIA ROTH_.pdf: 1643482 bytes, checksum: 4e4cda2780cc7255c2502065566263c6 (MD5) / Made available in DSpace on 2016-04-18T18:05:24Z (GMT). No. of bitstreams: 1 ANA LÚCIA ROTH_.pdf: 1643482 bytes, checksum: 4e4cda2780cc7255c2502065566263c6 (MD5) Previous issue date: 2011-08-30 / Nenhuma / O presente trabalho versa sobre a governança de Redes de Cooperação Federadas, uma tipologia específica das Relações Interorganizacionais. O estudo buscou, motivado pelas lacunas teóricas observadas na literatura, identificar os elementos que compõem o sistema de governança das Redes de Cooperação Federadas e como eles podem ser projetados para reduzir os conflitos e os custos de agência nas Federações. Percebeu-se que os estudos que descrevem e analisam os elementos internos da Governança das RIs não chegam a abordar a separação da propriedade e do controle, característico das Redes de Cooperação Federadas. Autores que versam sobre a separação da propriedade e do controle não apresentam os elementos internos da Governança das RIs. Da mesma forma, os estudos não chegam a tratar como os elementos internos da governança (estrutura e mecanismos de governança) podem ser combinados para minimizar os conflitos e custos de agência. Sob a luz da Teoria da Agência, da Teoria da Representação e da Teoria Organizacional usada no contexto das RIs, chegou-se à proposição de três elementos do sistema de governança das Redes de Cooperação Federadas: (a) a estrutura de governança; (b) os mecanismos de governança instituídos para incentivar e controlar o comportamento dos agentes; (c) os mecanismos de governança instituídos para incentivar e controlar o comportamento dos principais. Para a validação empírica do modelo proposto, optou-se pela realização de um estudo qualitativo, de natureza exploratória, por meio do método de estudo de caso múltiplo. O estudo foi operacionalizado por meio de dois estudos de caso: um na Rede Âncora Brasil e o outro na Rede Construir. Os resultados permitem afirmar que, embora presentes, os elementos estruturais e mecanismos de governança sobre os principais e sobre os agentes apresentam características distintas. Há, em um extremo, uma Federação com um maior nível de instâncias de decisão, maior número de atividades desenvolvidas pela Federação, o que tende a levar a uma maior centralização, formalização, padronização, coordenação e controle. No outro extremo, encontra-se uma Federação com poucas instâncias de decisão, menor número de atividades desenvolvidas pela Federação, o que tende a levar a uma descentralização, menor formalização, padronização, coordenação e controle. O estudo empírico levou à adição do elemento representação e participação na estrutura de governança das Redes de Cooperação Federadas. Os mecanismos internos e externos de governança, amplamente utilizados nas corporações também foram identificados no contexto das Redes de Cooperação Federadas. Constatou-se, entretanto, que o Conselho de Administração ou órgão correspondente é o mecanismo mais efetivo para redução dos custos e conflitos de agência. Entre as contribuições teóricas do trabalho, destaca-se a adoção de uma nova perspectiva do conceito de governança das Redes de Cooperação Federadas sob a luz da Teoria da Agência. / This study concerns Federated Cooperative Networks governance, a specific Interorganizational Relationship (IOR) typology. Motivated by a theoretical gap in this subject, we sought to identify the elements forming the Federated Cooperative Networks governance system and how they can be designed to reduce conflicts and agency costs in Federations. It was noticed that studies describing and analyzing internal IORs governance elements do not approach separation of ownership from control, characteristic of Federated Cooperative Networks. Authors who discuss separation of ownership from control don’t show the internal elements of IOR governance. And the studies don’t discuss how the internal governance elements (governance structure and mechanisms) might be combined to minimize conflicts and agency costs either. Based on the Agency Theory, Representation Theory and Organizational Theory employed in IORs context, we have proposed three elements for the Federated Cooperative Networks governance system: (a) a governance structure; (b) governance mechanisms instituted to encourage and control the behavior of agents; (c) governance mechanisms instituted to encourage and control the behavior of principals. For the empirical validation of these elements, we have chosen to perform a qualitative study, of exploratory nature, through the multiple case study method. The study was operated through two case studies: one at Rede Âncora Brasil and the other at Rede Construir. The results allow us to assert that, although present, structural elements and governance mechanisms over principals and agents show distinct features. On one extreme, there is a Federation with a higher level of decision instances, a higher number of activities developed by the Federation, which tend to lead to more centralization, formalization, standardization, coordination and control. On the other extreme, a Federation with little decision instances, and a lower number of activities developed by the Federation, which tend to lead to decentralization, less formalization, standardization, coordination and control. The empirical study added the element representation and participation in the Federated Cooperative Networks governance structure. The internal and external governance mechanisms, widely employed in corporations, were also identified in the Federated Cooperative Networks context. However, we have found that the Administrative Council, or corresponding agency, is the most effective mechanism in reducing agency costs and conflicts. Among the theoretical contributions of the study, adopting a new perspective in the concept of Federated Cooperative Networks governance under the light of the Agency theory can be stressed.

Spectrum sharing is known as a key solution to accommodate the increasing number of users and the growing demand for throughput in wireless networks. While spectrum sharing improves the data rate in sparse networks, it suffers from interference of concurrent links in dense networks. In fact, interference is the primary barrier to enhance the overall throughput of the network, especially in the medium and high signal-to-noise ratios (SNR’s). Managing interference to overcome this barrier has emerged as a crucial step in developing efficient wireless networks. This thesis deals with optimum and sub-optimum interference management-cancelation in non-cooperative networks. Several techniques for interference management including novel strategies such as interference alignment and structural coding are investigated. These methods are applied to obtain optimum and sub-optimum coding strategies in such networks. It is shown that a single strategy is not able to achieve the maximum throughput in all possible scenarios and in fact a careful design is required to fully exploit all available resources in each realization of the system. This thesis begins with a complete investigation of the capacity region of the two-user Gaussian interference channel. This channel models the basic interaction between two users sharing the same spectrum for data communication. New outer bounds outperforming known bounds are derived using Genie-aided techniques. It is proved that these outer bounds meet the known inner bounds in some special cases, revealing the sum capacity of this channel over a certain range of parameters which has not been known in the past. A novel coding scheme applicable in networks with single antenna nodes is proposed next. This scheme converts a single antenna system to an equivalent Multiple Input Multiple Output (MIMO) system with fractional dimensions. Interference can be aligned along these dimensions and higher multiplexing gains can be achieved. Tools from the field of Diophantine approximation in number theory are used to show that the proposed coding scheme in fact mimics the traditional schemes used in MIMO systems where each data stream is sent along a direction and alignment happens when several streams are received along the same direction. Two types of constellation are proposed for the encoding part, namely the single layer constellation and the multi-layer constellation. Using single layer constellations, the coding scheme is applied to the two-user $X$ channel. It is proved that the total Degrees-of-Freedom (DOF), i.e. $\frac{4}{3}$, of the channel is achievable almost surely. This is the first example in which it is shown that a time invariant single antenna system does not fall short of achieving this known upper bound on the DOF. Using multi-layer constellations, the coding scheme is applied to the symmetric three-user GIC. Achievable DOFs are derived for all channel gains. It is observed that the DOF is everywhere discontinuous (as a function of the channel gain). In particular, it is proved that for the irrational channel gains the achievable DOF meets the upper bound of $\frac{3}{2}$. For the rational gains, the achievable DOF has a gap to the known upper bounds. By allowing carry over from multiple layers, however, it is shown that higher DOFs can be achieved for the latter. The $K$-user single-antenna Gaussian Interference Channel (GIC) is considered, where the channel coefficients are NOT necessarily time-variant or frequency selective. It is proved that the total DOF of this channel is $\frac{K}{2}$ almost surely, i.e. each user enjoys half of its maximum DOF. Indeed, we prove that the static time-invariant interference channels are rich enough to allow simultaneous interference alignment at all receivers. To derive this result, we show that single-antenna interference channels can be treated as \emph{pseudo multiple-antenna systems} with infinitely-many antennas. Such machinery enables us to prove that the real or complex $M \times M$ MIMO GIC achieves its total DOF, i.e., $\frac{MK}{2}$, $M \geq 1$. The pseudo multiple-antenna systems are developed based on a recent result in the field of Diophantine approximation which states that the convergence part of the Khintchine-Groshev theorem holds for points on non-degenerate manifolds. As a byproduct of the scheme, the total DOFs of the $K\times M$ $X$ channel and the uplink of cellular systems are derived. Interference alignment requires perfect knowledge of channel state information at all nodes. This requirement is sometimes infeasible and users invoke random coding to communicate with their corresponding receivers. Alternative interference management needs to be implemented and this problem is addressed in the last part of the thesis. A coding scheme for a single user communicating in a shared medium is proposed. Moreover, polynomial time algorithms are proposed to obtain best achievable rates in the system. Successive rate allocation for a $K$-user interference channel is performed using polynomial time algorithms.

Spectrum sharing is known as a key solution to accommodate the increasing number of users and the growing demand for throughput in wireless networks. While spectrum sharing improves the data rate in sparse networks, it suffers from interference of concurrent links in dense networks. In fact, interference is the primary barrier to enhance the overall throughput of the network, especially in the medium and high signal-to-noise ratios (SNR’s). Managing interference to overcome this barrier has emerged as a crucial step in developing efficient wireless networks. This thesis deals with optimum and sub-optimum interference management-cancelation in non-cooperative networks. Several techniques for interference management including novel strategies such as interference alignment and structural coding are investigated. These methods are applied to obtain optimum and sub-optimum coding strategies in such networks. It is shown that a single strategy is not able to achieve the maximum throughput in all possible scenarios and in fact a careful design is required to fully exploit all available resources in each realization of the system. This thesis begins with a complete investigation of the capacity region of the two-user Gaussian interference channel. This channel models the basic interaction between two users sharing the same spectrum for data communication. New outer bounds outperforming known bounds are derived using Genie-aided techniques. It is proved that these outer bounds meet the known inner bounds in some special cases, revealing the sum capacity of this channel over a certain range of parameters which has not been known in the past. A novel coding scheme applicable in networks with single antenna nodes is proposed next. This scheme converts a single antenna system to an equivalent Multiple Input Multiple Output (MIMO) system with fractional dimensions. Interference can be aligned along these dimensions and higher multiplexing gains can be achieved. Tools from the field of Diophantine approximation in number theory are used to show that the proposed coding scheme in fact mimics the traditional schemes used in MIMO systems where each data stream is sent along a direction and alignment happens when several streams are received along the same direction. Two types of constellation are proposed for the encoding part, namely the single layer constellation and the multi-layer constellation. Using single layer constellations, the coding scheme is applied to the two-user $X$ channel. It is proved that the total Degrees-of-Freedom (DOF), i.e. $\frac{4}{3}$, of the channel is achievable almost surely. This is the first example in which it is shown that a time invariant single antenna system does not fall short of achieving this known upper bound on the DOF. Using multi-layer constellations, the coding scheme is applied to the symmetric three-user GIC. Achievable DOFs are derived for all channel gains. It is observed that the DOF is everywhere discontinuous (as a function of the channel gain). In particular, it is proved that for the irrational channel gains the achievable DOF meets the upper bound of $\frac{3}{2}$. For the rational gains, the achievable DOF has a gap to the known upper bounds. By allowing carry over from multiple layers, however, it is shown that higher DOFs can be achieved for the latter. The $K$-user single-antenna Gaussian Interference Channel (GIC) is considered, where the channel coefficients are NOT necessarily time-variant or frequency selective. It is proved that the total DOF of this channel is $\frac{K}{2}$ almost surely, i.e. each user enjoys half of its maximum DOF. Indeed, we prove that the static time-invariant interference channels are rich enough to allow simultaneous interference alignment at all receivers. To derive this result, we show that single-antenna interference channels can be treated as \emph{pseudo multiple-antenna systems} with infinitely-many antennas. Such machinery enables us to prove that the real or complex $M \times M$ MIMO GIC achieves its total DOF, i.e., $\frac{MK}{2}$, $M \geq 1$. The pseudo multiple-antenna systems are developed based on a recent result in the field of Diophantine approximation which states that the convergence part of the Khintchine-Groshev theorem holds for points on non-degenerate manifolds. As a byproduct of the scheme, the total DOFs of the $K\times M$ $X$ channel and the uplink of cellular systems are derived. Interference alignment requires perfect knowledge of channel state information at all nodes. This requirement is sometimes infeasible and users invoke random coding to communicate with their corresponding receivers. Alternative interference management needs to be implemented and this problem is addressed in the last part of the thesis. A coding scheme for a single user communicating in a shared medium is proposed. Moreover, polynomial time algorithms are proposed to obtain best achievable rates in the system. Successive rate allocation for a $K$-user interference channel is performed using polynomial time algorithms.

In this thesis, we investigate cooperation by applying OFDM signals to cooperative relay networks. We consider the single path relay network and the multiple path relay network. Using the amplify-and-forward relay algorithm, we derive the input-output relations and mutual informations of both networks. Using a power constraint at each relay, we consider two relay power allocation schemes. The first is constant gain allocation, where the amplifying gain used in the amplify-and-forward algorithm is constant for all subcarriers. The second is equal power allocation, where each subcarrier transmits the same power. The former scheme does not require CSI (channel state information), while the latter one does. We simulate the mutual informations using the two relay power allocation schemes. Results indicate that equal power allocation gives a slightly higher mutual information for the single path relay network. For the multiple path network, the mutual information is practically the same for both schemes. Using the decode-and-forward relay algorithm, we derive the input-output relations for both networks. The transmitter and each relay are assumed to have uniform power distributions in this case. We simulate the BER (bit error rate) and WER (word error rate) performance for the two networks using both the amplify-and-forward and decode-and-forward relay algorithms. For the single path relay network, amplify-and-forward gives very poor performance, because as we increase the distance between the transmitter and receiver (and thus, add more relays), more noise and channel distortion enter the system. Decode-and-forward gives significantly better performance because noise and channel distortion are eliminated at each relay. For the multiple path relay network, decode-and-forward again gives better performance than amplify-and-forward. However, the performance gains are small compared to the single path relay network case. Therefore, amplify-and-forward may be a more attractive choice due to its lower complexity.

O presente estudo foi motivado por lacunas teóricas sobre a governança e gestão de redes horizontais de empresas e suas relações com o capital social dos empresários e o desempenho das empresas participantes. Argumenta-se que, apesar do interesse acadêmico na cooperação interorganizacional, os estudos enfatizam excessivamente os motivos e benefícios das estratégias cooperativas, mas pouco os aspectos internos de organização das redes horizontais. Além disso, estima-se que no Brasil tenham sido constituídas até o presente aproximadamente 1.000 redes horizontais, formadas principalmente por micro e pequenas empresas que mantêm sua individualidade legal, mas usufruem dos benefícios que o trabalho em rede proporciona. Através de uma pesquisa com 218 empresas associadas a 34 redes horizontais no Brasil, analisou-se como a governança da rede, as práticas de gestão da rede e o capital social dos empresários estão relacionados ao desempenho empresarial. Os resultados mostram que a governança se modifica de acordo com as características da rede em termos de tempo de existência, número de associados e abrangência geográfica. Além disso, verificou-se a relação negativa da centralização das decisões nas redes tanto para o desempenho das empresas associadas quanto para o capital social dos empresários. Esse resultado aponta para um dilema que as redes brasileiras devem enfrentar à medida que crescem: desenvolver sistemas de governança que sejam suficientemente ágeis e eficientes em mercados altamente competitivos e que, ao mesmo tempo, garantam a participação dos empresários e o alinhamento das decisões com os interesses dos associados. As análises também confirmaram o papel do capital social do empresário como fonte de informações e recursos positivamente relacionados aos resultados da sua empresa, assim como o papel das práticas de gestão da rede para potencializar esse desempenho. Entre as contribuições teóricas do trabalho está a adoção de uma nova perspectiva do conceito de governança em redes horizontais de empresas, entendido aqui como as ‘regras do jogo’ da cooperação. O estudo também confirma a importância do número e diversidade dos contatos dos empresários dentro da rede, a qualidade dos relacionamentos e a semelhança cognitiva para o desempenho empresarial. Verificou-se ainda que o nível de acesso a informações atua como variável mediadora da influência do capital social sobre o desempenho empresarial. / This study was motivated by the theoretical gaps that exist in the network governance, network management and social capital of entrepreneurs and their relations with the performance of network firms. It is argued that despite the academic interest in interorganizational cooperation, studies overemphasize the reasons and benefits of cooperative strategies and give little attention to the internal aspects of the network organization. Besides that, it is currently estimated that in Brazil approximately 1,000 horizontal networks have been created. Such networks consist mainly of micro and small firms, which maintain their individuality, but enjoy the benefits that networking brings. Through a survey of 218 firms associated to 34 horizontal business networks in Brazil, the study analyzed how the governance and management practices adopted by the network and social capital of entrepreneurs are related to business performance. The study highlights that the network governance changes according to the characteristics of the network on duration, number of members and geographic coverage. In addition, there was a negative influence of centralized decision-making in networks, both for the performance of member firms and for the social capital of entrepreneurs. This result points to a dilemma that the Brazilian networks must face as they grow: develop governance systems that ensure the participation and alignment of decisions with the interests of members, while being sufficiently agile and efficient in highly competitive markets. The analysis also confirmed the role of the entrepreneurs’ social capital as a source of information and resources positively related to the performance of the firm, as well as the role of network management practices to enhance this performance. One of the theoretical contributions of the study is to adopt a new perspective on the concept of governance in horizontal business networks, understood here as the 'rules of the game' of the cooperation. The study also confirms the importance of the number and diversity of contacts, the quality of relationships and cognitive similarity that entrepreneurs have with their contacts for business performance. It was also found that the level of access to information acts as a mediating variable of the influence of social capital on corporate performance.

O presente estudo foi motivado por lacunas teóricas sobre a governança e gestão de redes horizontais de empresas e suas relações com o capital social dos empresários e o desempenho das empresas participantes. Argumenta-se que, apesar do interesse acadêmico na cooperação interorganizacional, os estudos enfatizam excessivamente os motivos e benefícios das estratégias cooperativas, mas pouco os aspectos internos de organização das redes horizontais. Além disso, estima-se que no Brasil tenham sido constituídas até o presente aproximadamente 1.000 redes horizontais, formadas principalmente por micro e pequenas empresas que mantêm sua individualidade legal, mas usufruem dos benefícios que o trabalho em rede proporciona. Através de uma pesquisa com 218 empresas associadas a 34 redes horizontais no Brasil, analisou-se como a governança da rede, as práticas de gestão da rede e o capital social dos empresários estão relacionados ao desempenho empresarial. Os resultados mostram que a governança se modifica de acordo com as características da rede em termos de tempo de existência, número de associados e abrangência geográfica. Além disso, verificou-se a relação negativa da centralização das decisões nas redes tanto para o desempenho das empresas associadas quanto para o capital social dos empresários. Esse resultado aponta para um dilema que as redes brasileiras devem enfrentar à medida que crescem: desenvolver sistemas de governança que sejam suficientemente ágeis e eficientes em mercados altamente competitivos e que, ao mesmo tempo, garantam a participação dos empresários e o alinhamento das decisões com os interesses dos associados. As análises também confirmaram o papel do capital social do empresário como fonte de informações e recursos positivamente relacionados aos resultados da sua empresa, assim como o papel das práticas de gestão da rede para potencializar esse desempenho. Entre as contribuições teóricas do trabalho está a adoção de uma nova perspectiva do conceito de governança em redes horizontais de empresas, entendido aqui como as ‘regras do jogo’ da cooperação. O estudo também confirma a importância do número e diversidade dos contatos dos empresários dentro da rede, a qualidade dos relacionamentos e a semelhança cognitiva para o desempenho empresarial. Verificou-se ainda que o nível de acesso a informações atua como variável mediadora da influência do capital social sobre o desempenho empresarial. / This study was motivated by the theoretical gaps that exist in the network governance, network management and social capital of entrepreneurs and their relations with the performance of network firms. It is argued that despite the academic interest in interorganizational cooperation, studies overemphasize the reasons and benefits of cooperative strategies and give little attention to the internal aspects of the network organization. Besides that, it is currently estimated that in Brazil approximately 1,000 horizontal networks have been created. Such networks consist mainly of micro and small firms, which maintain their individuality, but enjoy the benefits that networking brings. Through a survey of 218 firms associated to 34 horizontal business networks in Brazil, the study analyzed how the governance and management practices adopted by the network and social capital of entrepreneurs are related to business performance. The study highlights that the network governance changes according to the characteristics of the network on duration, number of members and geographic coverage. In addition, there was a negative influence of centralized decision-making in networks, both for the performance of member firms and for the social capital of entrepreneurs. This result points to a dilemma that the Brazilian networks must face as they grow: develop governance systems that ensure the participation and alignment of decisions with the interests of members, while being sufficiently agile and efficient in highly competitive markets. The analysis also confirmed the role of the entrepreneurs’ social capital as a source of information and resources positively related to the performance of the firm, as well as the role of network management practices to enhance this performance. One of the theoretical contributions of the study is to adopt a new perspective on the concept of governance in horizontal business networks, understood here as the 'rules of the game' of the cooperation. The study also confirms the importance of the number and diversity of contacts, the quality of relationships and cognitive similarity that entrepreneurs have with their contacts for business performance. It was also found that the level of access to information acts as a mediating variable of the influence of social capital on corporate performance.

O presente estudo foi motivado por lacunas teóricas sobre a governança e gestão de redes horizontais de empresas e suas relações com o capital social dos empresários e o desempenho das empresas participantes. Argumenta-se que, apesar do interesse acadêmico na cooperação interorganizacional, os estudos enfatizam excessivamente os motivos e benefícios das estratégias cooperativas, mas pouco os aspectos internos de organização das redes horizontais. Além disso, estima-se que no Brasil tenham sido constituídas até o presente aproximadamente 1.000 redes horizontais, formadas principalmente por micro e pequenas empresas que mantêm sua individualidade legal, mas usufruem dos benefícios que o trabalho em rede proporciona. Através de uma pesquisa com 218 empresas associadas a 34 redes horizontais no Brasil, analisou-se como a governança da rede, as práticas de gestão da rede e o capital social dos empresários estão relacionados ao desempenho empresarial. Os resultados mostram que a governança se modifica de acordo com as características da rede em termos de tempo de existência, número de associados e abrangência geográfica. Além disso, verificou-se a relação negativa da centralização das decisões nas redes tanto para o desempenho das empresas associadas quanto para o capital social dos empresários. Esse resultado aponta para um dilema que as redes brasileiras devem enfrentar à medida que crescem: desenvolver sistemas de governança que sejam suficientemente ágeis e eficientes em mercados altamente competitivos e que, ao mesmo tempo, garantam a participação dos empresários e o alinhamento das decisões com os interesses dos associados. As análises também confirmaram o papel do capital social do empresário como fonte de informações e recursos positivamente relacionados aos resultados da sua empresa, assim como o papel das práticas de gestão da rede para potencializar esse desempenho. Entre as contribuições teóricas do trabalho está a adoção de uma nova perspectiva do conceito de governança em redes horizontais de empresas, entendido aqui como as ‘regras do jogo’ da cooperação. O estudo também confirma a importância do número e diversidade dos contatos dos empresários dentro da rede, a qualidade dos relacionamentos e a semelhança cognitiva para o desempenho empresarial. Verificou-se ainda que o nível de acesso a informações atua como variável mediadora da influência do capital social sobre o desempenho empresarial. / This study was motivated by the theoretical gaps that exist in the network governance, network management and social capital of entrepreneurs and their relations with the performance of network firms. It is argued that despite the academic interest in interorganizational cooperation, studies overemphasize the reasons and benefits of cooperative strategies and give little attention to the internal aspects of the network organization. Besides that, it is currently estimated that in Brazil approximately 1,000 horizontal networks have been created. Such networks consist mainly of micro and small firms, which maintain their individuality, but enjoy the benefits that networking brings. Through a survey of 218 firms associated to 34 horizontal business networks in Brazil, the study analyzed how the governance and management practices adopted by the network and social capital of entrepreneurs are related to business performance. The study highlights that the network governance changes according to the characteristics of the network on duration, number of members and geographic coverage. In addition, there was a negative influence of centralized decision-making in networks, both for the performance of member firms and for the social capital of entrepreneurs. This result points to a dilemma that the Brazilian networks must face as they grow: develop governance systems that ensure the participation and alignment of decisions with the interests of members, while being sufficiently agile and efficient in highly competitive markets. The analysis also confirmed the role of the entrepreneurs’ social capital as a source of information and resources positively related to the performance of the firm, as well as the role of network management practices to enhance this performance. One of the theoretical contributions of the study is to adopt a new perspective on the concept of governance in horizontal business networks, understood here as the 'rules of the game' of the cooperation. The study also confirms the importance of the number and diversity of contacts, the quality of relationships and cognitive similarity that entrepreneurs have with their contacts for business performance. It was also found that the level of access to information acts as a mediating variable of the influence of social capital on corporate performance.

Sistemas modernos de comunicação móvel sem fio, como os de quarta geração (4G), têm como principais metas prover elevada capacidade e alta qualidade de serviço (QoS) para os usuários. Para prover tal aumento de capacidade e QoS, sistemas 4G empregam diversas técnicas avançadas de transmissão e maior largura de banda, combinados com algoritmos de alocação de recursos que possam explorar de maneira eficiente tais técnicas, como por exemplo aproveitando as dimensões de diversidade do sistema. Em geral, porém, é necessário também aumentar a potência de transmissão para se atingir o ganho de capacidade desejado, o que implica maior custo para os provedores de serviço, menor tempo de vida para os dispositivos móveis e impacto ambiental cada vez mais pronunciado. Dado que a expectativa é que o número de usuários e a necessidade de dados continuem crescendo rapidamente, torna-se evidente a importância de analisar a relação entre capacidade e potência dispendida pelo sistema. Essa relação pode ser vista através da métrica de eficiência energética (EE), que é dada pela razão entre o número de bits efetivamente recebidos e a energia consumida no processo, revelando quão eficientemente o sistema transforma a energia consumida em informação efetivamente recuperada no receptor. Um sistema otimizado em relação à EE é capaz de transmitir mais informação por unidade de energia consumida, resultando em utilização mais racional e eficiente dos escassos recursos energéticos. Uma segunda questão acerca das metas é em relação à distribuição dos ganhos de capacidade/ QoS pela célula, i.e., quais usuários serão capazes de usufruir da maior capacidade e QoS. Em ambientes macrocelulares urbanos, a perda de percurso pode chegar a várias dezenas de decibéis em distâncias relativamente pequenas, além dos obstáculos naturais, como relevo, e artificiais, como prédios, o que limita ainda mais o desenvolvimento de sistemas energeticamente eficientes. Em abordagens tradicionais, tais problemas exigem a utilização de potências elevadas, em geral superiores à potência que os dispositivos podem utilizar, ou então requerem o aumento da densidade de estações rádio-base (BSs), o que geralmente resulta em custos inviáveis do ponto de vista dos operadores. Assim, busca-se em sistemas 4G emular o aumento da densidade de BSs através do conceito de redes heterogêneas, que são células com menor área de cobertura instaladas em pontos críticos de cobertura da célula original, como por exemplo a região de borda de célula, atendendo de maneira eficiente os usuários. No cenário de redes heterogêneas, um dos principais paradigmas é o conceito de redes cooperativas, no qual estações retransmissoras (RSs) reenviam o sinal recebido da estação fonte para estação destino, reduzindo a potência consumida com o canal móvel sem fio. Como utilizam conexão sem fio com a BS, as RSs podem ser instaladas em regiões com pouca infraestrutura sem a necessidade de grandes modificações, resultando em implantações bastante flexíveis. Assim, este trabalho de doutorado visa investigar estratégias de alocação de recursos baseadas no incremento da eficiência energética para sistemas celulares de quarta e quinta gerações utilizando o paradigma de redes cooperativas, determinando potencialidades e também itens que necessitam ser modificados, otimizados ou mesmo redefinidos, tendo em vista um aumento substancial da eficiência energética global da rede de comunicação sem fio. Busca-se durante o desenvolvimento do modelo de sistema capturar e quantificar as principais características de importantes sistemas celulares em uso atualmente, i.e., LTE-A e WiMAX, de modo que as decisões de design considerem os esforços de padronização, porém não se limitem a eles. Como a abordagem de alocação de recursos baseada em EE pode impactar nas métricas de desempenho do sistema, investiga-se também o compromisso entre as eficiências energética e espectral (SE), de modo que o aumento da EE não seja causado apenas pela degradação da SE e que seja possível obter maior EE para uma mesma SE e QoS. / Modern wireless communication systems, such as the fourth generation (4G) ones, have as main objectives to provide high capacity and quality of service (QoS) for the users. In order to provide such capacity and QoS gain, 4G systems use several advanced transmission techniques and higher bandwidth, combined with resource allocation algorithms that are able to efficiently exploit such techniques, as for example taking advantage of the diversity dimensions of the system. Generally, however, it is also necessary to increase the transmission power to achieve the desired capacity gain, which implies increased costs for service providers, shorter lifetime for the mobile devices and increasingly pronounced environmental impact. Since the expectation is that the number of users and data necessity will continue growing rapidly, it is evident the importance of analyzing the relation between capacity and power expended by the system. This relation can be seen through the energy efficiency (EE) metric, which is given by the ratio between the number of effectively received information bits and the energy consumed in the transmission process, revealing how efficiently the system transform consumed energy into effectively recovered information at the receiver. A system optimized regarding EE is able to transmit more information per unit of energy consumed, resulting in a more rational and efficient utilization of the scarce energetic resources. A second issue is relative to the distribution of the capacity/QoS gains over the whole cell, i.e, which users will be able to take advantage of the higher capacity and QoS. In urban macrocellular environments, the path-loss can reach several tens of decibels in relatively short distances, in addition to natural obstacles, such as land relief, or artificial, such as buildings, which further limits the development of energetically efficient systems. In traditional approaches, such problems require the use of high transmission power, generally greater than the power that the devices can use, or else require increased density of base-stations (BSs), which generally results in unviable costs from the operators point of view. Thus, in 4G systems it is sought to emulate the increase in the density of BSs through the concept of heterogeneous networks, which are cells with smaller coverage area installed in critical points of the original macrocell coverage, as for example the cell-edge area, serving efficiently the users. In the heterogeneous networks scenario, one of the main paradigms is the concept of cooperative networks, in which relay stations (RSs) retransmit the signal received from the source station to the destination station, reducing the power consumed with the mobile wireless channel. As the RSs use a wireless connection to the BS, they can be installed in places with poor infrastructure without requiring major modifications, resulting in very flexible deployments. Thus, this PhD work aims to investigate resource allocation strategies based on the improvement of the energy efficiency for fourth and fifty generation cellular systems using the cooperative networks paradigm, determining potentialities and also items that need to be modified, optimized or even redefined, aiming to a substantial increase in the overall energy efficiency of the wireless communication network. It is sought during the development of the system model to capture and quantify the main features of important cellular systems currently in use, i.e., LTE-A and WiMAX, so that the design decisions consider the standardization efforts, but do not be limited by them. Since the EE-based resource allocation approach can impact the performance metrics of the system, it will be investigated also the tradeoff between energy and spectral (SE) efficiencies, so that the increase in energy efficiency is not caused by degradation of the SE and also to be possible to obtain a higher EE for a same SE and QoS.

Sistemas modernos de comunicação móvel sem fio, como os de quarta geração (4G), têm como principais metas prover elevada capacidade e alta qualidade de serviço (QoS) para os usuários. Para prover tal aumento de capacidade e QoS, sistemas 4G empregam diversas técnicas avançadas de transmissão e maior largura de banda, combinados com algoritmos de alocação de recursos que possam explorar de maneira eficiente tais técnicas, como por exemplo aproveitando as dimensões de diversidade do sistema. Em geral, porém, é necessário também aumentar a potência de transmissão para se atingir o ganho de capacidade desejado, o que implica maior custo para os provedores de serviço, menor tempo de vida para os dispositivos móveis e impacto ambiental cada vez mais pronunciado. Dado que a expectativa é que o número de usuários e a necessidade de dados continuem crescendo rapidamente, torna-se evidente a importância de analisar a relação entre capacidade e potência dispendida pelo sistema. Essa relação pode ser vista através da métrica de eficiência energética (EE), que é dada pela razão entre o número de bits efetivamente recebidos e a energia consumida no processo, revelando quão eficientemente o sistema transforma a energia consumida em informação efetivamente recuperada no receptor. Um sistema otimizado em relação à EE é capaz de transmitir mais informação por unidade de energia consumida, resultando em utilização mais racional e eficiente dos escassos recursos energéticos. Uma segunda questão acerca das metas é em relação à distribuição dos ganhos de capacidade/ QoS pela célula, i.e., quais usuários serão capazes de usufruir da maior capacidade e QoS. Em ambientes macrocelulares urbanos, a perda de percurso pode chegar a várias dezenas de decibéis em distâncias relativamente pequenas, além dos obstáculos naturais, como relevo, e artificiais, como prédios, o que limita ainda mais o desenvolvimento de sistemas energeticamente eficientes. Em abordagens tradicionais, tais problemas exigem a utilização de potências elevadas, em geral superiores à potência que os dispositivos podem utilizar, ou então requerem o aumento da densidade de estações rádio-base (BSs), o que geralmente resulta em custos inviáveis do ponto de vista dos operadores. Assim, busca-se em sistemas 4G emular o aumento da densidade de BSs através do conceito de redes heterogêneas, que são células com menor área de cobertura instaladas em pontos críticos de cobertura da célula original, como por exemplo a região de borda de célula, atendendo de maneira eficiente os usuários. No cenário de redes heterogêneas, um dos principais paradigmas é o conceito de redes cooperativas, no qual estações retransmissoras (RSs) reenviam o sinal recebido da estação fonte para estação destino, reduzindo a potência consumida com o canal móvel sem fio. Como utilizam conexão sem fio com a BS, as RSs podem ser instaladas em regiões com pouca infraestrutura sem a necessidade de grandes modificações, resultando em implantações bastante flexíveis. Assim, este trabalho de doutorado visa investigar estratégias de alocação de recursos baseadas no incremento da eficiência energética para sistemas celulares de quarta e quinta gerações utilizando o paradigma de redes cooperativas, determinando potencialidades e também itens que necessitam ser modificados, otimizados ou mesmo redefinidos, tendo em vista um aumento substancial da eficiência energética global da rede de comunicação sem fio. Busca-se durante o desenvolvimento do modelo de sistema capturar e quantificar as principais características de importantes sistemas celulares em uso atualmente, i.e., LTE-A e WiMAX, de modo que as decisões de design considerem os esforços de padronização, porém não se limitem a eles. Como a abordagem de alocação de recursos baseada em EE pode impactar nas métricas de desempenho do sistema, investiga-se também o compromisso entre as eficiências energética e espectral (SE), de modo que o aumento da EE não seja causado apenas pela degradação da SE e que seja possível obter maior EE para uma mesma SE e QoS. / Modern wireless communication systems, such as the fourth generation (4G) ones, have as main objectives to provide high capacity and quality of service (QoS) for the users. In order to provide such capacity and QoS gain, 4G systems use several advanced transmission techniques and higher bandwidth, combined with resource allocation algorithms that are able to efficiently exploit such techniques, as for example taking advantage of the diversity dimensions of the system. Generally, however, it is also necessary to increase the transmission power to achieve the desired capacity gain, which implies increased costs for service providers, shorter lifetime for the mobile devices and increasingly pronounced environmental impact. Since the expectation is that the number of users and data necessity will continue growing rapidly, it is evident the importance of analyzing the relation between capacity and power expended by the system. This relation can be seen through the energy efficiency (EE) metric, which is given by the ratio between the number of effectively received information bits and the energy consumed in the transmission process, revealing how efficiently the system transform consumed energy into effectively recovered information at the receiver. A system optimized regarding EE is able to transmit more information per unit of energy consumed, resulting in a more rational and efficient utilization of the scarce energetic resources. A second issue is relative to the distribution of the capacity/QoS gains over the whole cell, i.e, which users will be able to take advantage of the higher capacity and QoS. In urban macrocellular environments, the path-loss can reach several tens of decibels in relatively short distances, in addition to natural obstacles, such as land relief, or artificial, such as buildings, which further limits the development of energetically efficient systems. In traditional approaches, such problems require the use of high transmission power, generally greater than the power that the devices can use, or else require increased density of base-stations (BSs), which generally results in unviable costs from the operators point of view. Thus, in 4G systems it is sought to emulate the increase in the density of BSs through the concept of heterogeneous networks, which are cells with smaller coverage area installed in critical points of the original macrocell coverage, as for example the cell-edge area, serving efficiently the users. In the heterogeneous networks scenario, one of the main paradigms is the concept of cooperative networks, in which relay stations (RSs) retransmit the signal received from the source station to the destination station, reducing the power consumed with the mobile wireless channel. As the RSs use a wireless connection to the BS, they can be installed in places with poor infrastructure without requiring major modifications, resulting in very flexible deployments. Thus, this PhD work aims to investigate resource allocation strategies based on the improvement of the energy efficiency for fourth and fifty generation cellular systems using the cooperative networks paradigm, determining potentialities and also items that need to be modified, optimized or even redefined, aiming to a substantial increase in the overall energy efficiency of the wireless communication network. It is sought during the development of the system model to capture and quantify the main features of important cellular systems currently in use, i.e., LTE-A and WiMAX, so that the design decisions consider the standardization efforts, but do not be limited by them. Since the EE-based resource allocation approach can impact the performance metrics of the system, it will be investigated also the tradeoff between energy and spectral (SE) efficiencies, so that the increase in energy efficiency is not caused by degradation of the SE and also to be possible to obtain a higher EE for a same SE and QoS.

Relay-based cooperation promises significant gains in a wireless network as it provides an inde-pendent path between a source and a destination. Using simple single antenna nodes, it exploits the spatial diversity provided by the geographically separated nodes in a network to improve the robustness of the communication system against fading. Among the cooperative commu¬nication schemes, the amplify-and-forward (AF) relaying scheme is considered to be easy to implement since the relay does not need to decode its received signal. Instead, it just forwards to the destination the signal it receives from the source. We analyze the performance of fixed-gain AF relaying with imperfect channel knowledge that is acquired through an AF relay-specific training protocol. The analysis is challenging because the received signal at the destination contains the product (or cascade) of source-relay (SR) and relay-destination (RD) complex baseband channel gains, and additional products terms that arise due to imperfect estimation related errors. We focus on the time-efficient cascaded channel estimation (CCE) protocol to acquire the channel estimates at the destination. Using it, the destination can only estimate the product of SR and RD complex baseband channel gains, but not the two separately. Our analysis encompasses a single AF relay system and an opportunistic system with mul¬tiple AF relays, among which one is selected to forward its received signal to the destination, based on its SR and RD complex baseband channel gains. For a single relay system, we first de¬velop a novel SEP expression and a tight SEP upper bound. We then analyze the opportunistic multi-relay system, in which both selection and coherent demodulation use imperfect channel estimates. A distinctive aspect of our approach is the use of as few simplifying approximations as possible. It results in a new analysis that is accurate at signal-to-noise-ratios as low as 1 dB for single and multi-relay systems. Further, the training protocol is an integral part of the model and analysis. Using an insightful asymptotic analysis, we then present a simple, closed-form, nearly-optimal solution for allocation of energy between pilot and data symbols at the source and relay(s). Further, the optimal energy allocation between a source and a relay is characterized when both together operate under a sum energy constraint, as has often been assumed in the literature. In summary, the sum total of the results in this work provides a rigorous and accurate performance characterization and optimization of cascaded channel estimation for AF relaying.