722 research outputs found
Dispensing with channel estimation: differentially modulated cooperative wireless communications
As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective
Implementation of relay-based systems in wireless cellular networks
Thesis (Master)--Izmir Institute of Technology, Electronics and Communication Engineering, Izmir, 2010Includes bibliographical references (leaves: 69-72)Text in English; Abstract: Turkish and Englishxiii, 72 leavesThe wireless cellular networks are limited by interference and coverage issues where the users at the edge of the cell usually do not receive enough signal energy. To combat these problems and provide higher signal to interference noise ratio and capacity without increasing the transmit power, the idea of using relays in cellular networks was explored and evaluated in the literature. On the other hand, multiple input multiple output (MIMO) antenna systems have great potential to increase capacity and reliability of a wireless cellular network compared to single input single output systems. Hence, the integration of MIMO systems in the relay-based cellular networks has great potential to meet the growing demands of future communication. In this thesis, we explore the performances in conventional and relay-based wireless systems with single and multiple antennas by ad justing the frequency reuse factor as one and four. We consider wireless cellular based networks where six fixed relays are placed evenly in each cell in a hexagonal layout. A user chooses to receive the transmitted signal either directly from the base station or via one of the relays by employing selection algorithms. Throughout this thesis, we first determine the optimum relay locations considering different relay powers. Then, we investigate the system capacity for the cell with and without relays. Next, we examine the capacity performances by changing the cell diameter and the relay power. Finally, we explore the performances of relay based networks with multiple antennas
Joint transceiver design and power optimization for wireless sensor networks in underground mines
Avec les grands dĂ©veloppements des technologies de communication sans fil, les rĂ©seaux de capteurs sans fil (WSN) ont attirĂ© beaucoup dâattention dans le monde entier au cours de la derniĂšre dĂ©cennie. Les rĂ©seaux de capteurs sans fil sont maintenant utilisĂ©s pour a surveillance sanitaire, la gestion des catastrophes, la dĂ©fense, les tĂ©lĂ©communications, etc. De tels rĂ©seaux sont utilisĂ©s dans de nombreuses applications industrielles et commerciales comme la surveillance des processus industriels et de lâenvironnement, etc. Un rĂ©seau WSN est une collection de transducteurs spĂ©cialisĂ©s connus sous le nom de noeuds de capteurs avec une liaison de communication distribuĂ©e de maniĂšre alĂ©atoire dans tous les emplacements pour surveiller les paramĂštres. Chaque noeud de capteur est Ă©quipĂ© dâun transducteur, dâun processeur de signal, dâune unitĂ© dâalimentation et dâun Ă©metteur-rĂ©cepteur. Les WSN sont maintenant largement utilisĂ©s dans lâindustrie miniĂšre souterraine pour surveiller certains paramĂštres environnementaux, comme la quantitĂ© de gaz, dâeau, la tempĂ©rature, lâhumiditĂ©, le niveau dâoxygĂšne, de poussiĂšre, etc. Dans le cas de la surveillance de lâenvironnement, un WSN peut ĂȘtre remplacĂ© de maniĂšre Ă©quivalente par un rĂ©seau Ă relais Ă entrĂ©es et sorties multiples (MIMO). Les rĂ©seaux de relais multisauts ont attirĂ© un intĂ©rĂȘt de recherche important ces derniers temps grĂące Ă leur capacitĂ© Ă augmenter la portĂ©e de la couverture. La liaison de communication rĂ©seau dâune source vers une destination est mise en oeuvre en utilisant un schĂ©ma dâamplification/transmission (AF) ou de dĂ©codage/transfert (DF). Le relais AF reçoit des informations du relais prĂ©cĂ©dent et amplifie simplement le signal reçu, puis il le transmet au relais suivant. Dâautre part, le relais DF dĂ©code dâabord le signal reçu, puis il le transmet au relais suivant au deuxiĂšme Ă©tage sâil peut parfaitement dĂ©coder le signal entrant. En raison de la simplicitĂ© analytique, dans cette thĂšse, nous considĂ©rons le schĂ©ma de relais AF et les rĂ©sultats de ce travail peuvent Ă©galement ĂȘtre dĂ©veloppĂ©s pour le relais DF. La conception dâun Ă©metteur/rĂ©cepteur pour le relais MIMO multisauts est trĂšs difficile. Car Ă lâĂ©tape de relais L, il y a 2L canaux possibles. Donc, pour un rĂ©seau Ă grande Ă©chelle, il nâest pas Ă©conomique dâenvoyer un signal par tous les liens possibles. Au lieu de cela, nous pouvons trouver le meilleur chemin de la source Ă la destination qui donne le rapport signal sur bruit (SNR) de bout en bout le plus Ă©levĂ©. Nous pouvons minimiser la fonction objectif dâerreur quadratique moyenne (MSE) ou de taux dâerreur binaire (BER) en envoyant le signal utilisant le chemin sĂ©lectionnĂ©. Lâensemble de relais dans le chemin reste actif et le reste des relais sâĂ©teint, ce qui permet dâĂ©conomiser de lâĂ©nergie afin dâamĂ©liorer la durĂ©e de vie du rĂ©seau. Le meilleur chemin de transmission de signal a Ă©tĂ© Ă©tudiĂ© dans la littĂ©rature pour un relais MIMO Ă deux bonds mais est plus complexe pour un ...With the great developments in wireless communication technologies, Wireless Sensor Networks (WSNs) have gained attention worldwide in the past decade and are now being used in health monitoring, disaster management, defense, telecommunications, etc. Such networks are used in many industrial and consumer applications such as industrial process and environment monitoring, among others. A WSN network is a collection of specialized transducers known as sensor nodes with a communication link distributed randomly in any locations to monitor environmental parameters such as water level, and temperature. Each sensor node is equipped with a transducer, a signal processor, a power unit, and a transceiver. WSNs are now being widely used in the underground mining industry to monitor environmental parameters, including the amount of gas, water, temperature, humidity, oxygen level, dust, etc. The WSN for environment monitoring can be equivalently replaced by a multiple-input multiple-output (MIMO) relay network. Multi-hop relay networks have attracted significant research interest in recent years for their capability in increasing the coverage range. The network communication link from a source to a destination is implemented using the amplify-and-forward (AF) or decode-and-forward (DF) schemes. The AF relay receives information from the previous relay and simply amplifies the received signal and then forwards it to the next relay. On the other hand, the DF relay first decodes the received signal and then forwards it to the next relay in the second stage if it can perfectly decode the incoming signal. For analytical simplicity, in this thesis, we consider the AF relaying scheme and the results of this work can also be developed for the DF relay. The transceiver design for multi-hop MIMO relay is very challenging. This is because at the L-th relay stage, there are 2L possible channels. So, for a large scale network, it is not economical to send the signal through all possible links. Instead, we can find the best path from source-to-destination that gives the highest end-to-end signal-to-noise ratio (SNR). We can minimize the mean square error (MSE) or bit error rate (BER) objective function by sending the signal using the selected path. The set of relay in the path remains active and the rest of the relays are turned off which can save power to enhance network life-time. The best path signal transmission has been carried out in the literature for 2-hop MIMO relay and for multiple relaying it becomes very complex. In the first part of this thesis, we propose an optimal best path finding algorithm at perfect channel state information (CSI). We consider a parallel multi-hop multiple-input multiple-output (MIMO) AF relay system where a linear minimum mean-squared error (MMSE) receiver is used at the destination. We simplify the parallel network into equivalent series multi-hop MIMO relay link using best relaying, where the best relay ..
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LTE-Advanced radio access enhancements: A survey
Long Term Evolution Advanced (LTE-Advanced) is the next step in LTE evolution and allows operators to improve network performance and service capabilities through smooth deployment of new techniques and technologies. LTE-Advanced uses some new features on top of the existing LTE standards to provide better user experience and higher throughputs. Some of the most significant features introduced in LTE-Advanced are carrier aggregation, enhancements in heterogeneous networks, coordinated multipoint transmission and reception, enhanced multiple input multiple output usage and deployment of relay nodes in the radio network. Mentioned features are mainly aimed to enhance the radio access part of the cellular networks. This survey article presents an overview of the key radio access features and functionalities of the LTE-Advanced radio access network, supported by the simulation results. We also provide a detailed review of the literature together with a very rich list of the references for each of the features. An LTE-Advanced roadmap and the latest updates and trends in LTE markets are also presented
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