This dissertation studies several problems centered around developing a better understanding of the energy efficiency of cooperative wireless communication systems. Cooperative communication is a technique where two or more nodes in a wireless network pool their antenna resources to form a "virtual antenna array". Over the last decade, researchers have shown that many of the benefits of real antenna arrays, e.g. spatial diversity, increased range, and/or decreased transmission energy, can be achieved by nodes using cooperative transmission. This dissertation extends the current body of knowledge by providing a comprehensive study of the energy efficiency of two-source cooperative transmission under differing assumptions about channel state knowledge, cooperative protocol, and node selfishness. The first part of this dissertation analyzes the effect of channel state information on the optimum energy allocation and energy efficiency of a simple cooperative transmission protocol called "orthogonal amplify-and-forward" (OAF). The source nodes are required to achieve a quality-of service (QoS) constraint, e.g. signal to noise ratio or outage probability, at the destination. Since a QoS constraint does not specify a unique transmit energy allocation when the nodes use OAF cooperative transmission, minimum total energy strategies are provided for both short-term and long-term QoS constraints. For independent Rayleigh fading channels, full knowledge of the channel state at both of the sources and at the destination is shown to significantly improve the energy efficiency of OAF cooperative transmission as well as direct (non-cooperative) transmission. The results also demonstrate how channel state knowledge affects the minimum total energy allocation strategy. Under identical channel state knowledge assumptions, the results demonstrate that OAF cooperative transmission tends to have better energy efficiency than direct transmission over a wide range of channel conditions. The second part of this dissertation focuses on the development of an opportunistic hybrid cooperative transmission protocol that achieves increased energy efficiency by not only optimizing the resource allocation but also by selecting the most energy efficient cooperative transmission protocol from a set of available protocols according to the current channel state. The protocols considered in the development of the hybrid cooperative transmission protocol include compress-and-forward (CF), estimate-and-forward (EF), non-orthogonal amplify-and-forward (NAF), and decode-and-forward (DF). Instantaneous capacity results are analyzed under the assumption of full channel state knowledge at both of the sources and the destination node. Numerical results are presented showing that the delay limited capacity and outage probability of the hybrid cooperative transmission protocol are superior to that of any single protocol and are also close to the cut-set bound over a wide range of channel conditions. The final part of this dissertation focuses on the issue of node selfishness in cooperative transmission. It is common to assume in networks with a central authority, e.g. military networks, that nodes will always be willing to offer help to other nodes when requested to do so. This assumption may not be valid in ad hoc networks operating without a central authority. This section of the dissertation considers the effect selfish behavior on the energy efficiency of cooperative communication systems. Using tools from non-cooperative game theory, a two-player relaying game is formulated and analyzed in non-fading and fading channel scenarios. In non-fading channels, it is shown that a cooperative equilibrium can exist between two self-interested sources given that the end of the cooperative interaction is uncertain, that the sources can achieve mutual benefit through cooperation, and that the sources are sufficiently patient in the sense that they value future payoffs. In fading channels, a cooperative conditional trigger strategy is proposed and shown to be an equilibrium of the two-player game. Sources following this strategy are shown to achieve an energy efficiency very close to that of a centrally-controlled system when they are sufficiently patient. The results in this section show that cooperation can often be established between two purely self-interested sources without the development of extrinsic incentive mechanisms like virtual currency.

This thesis describes a real-time software-defined-radio implementation of a two source distributed beamformer. The technique in this thesis can be used to synchronize the carriers of two single antenna wireless transmitters (i.e. ``sources") with independent local clocks so that their bandpass transmissions arrive in-phase at an intended receiver (i.e. ``destination"). Synchronization is achieved via: (i) an unmodulated beacon transmitted by the destination to the sources and (ii) a pair of secondary unmodulated beacons between the sources. No explicit channel state information is exchanged between the sources and/or the destination. Using this method, it is possible to realize a two-source distributed beamformer that provides a reduction in overall transmit energy and increased security due to the directionality of the transmitted signal. System characterization results are provided along with experimental results for both time-invariant and time-varying channels. The experimental results in this thesis confirm the theoretical predictions and also provide explicit guidelines for a real-time implementation of a two-source distributed beamforming system.

This thesis describes a real-time software-defined-radio implementation of the time-slotted round-trip carrier synchronization protocol in two-source and three-source communication systems. The techniques developed in this thesis can be used to synchronize the carriers of two or three single-antenna wireless transmitters with independent local oscillators so that their band-pass transmissions combine constructively at an intended receiver. Synchronization is achieved via the time-slotted transmission of (i) an unmodulated primary beacon from the destination to the sources and (ii) a series of secondary unmodulated beacons between the sources. Explicit channel state information is not exchanged between the sources and/or the destination. When synchronized, the single-antenna sources are able to cooperatively transmit as a distributed beamformer and achieve increased transmission range, reduced transmission energy, and/or increased security. The experimental results in this thesis confirm the theoretical predictions and also provide explicit guidelines for the real-time implementation of a carrier synchronization technique suitable for distributed transmit beamforming.

Une des problématiques qui est souvent associée aux réseaux large bande est l’apparition des lobes de réseaux, liée à la périodicité de l’espacement entre les éléments du réseau. Un autre problème dans les réseaux large bande est la fréquence de fonctionnement de l’élément du réseau. La plus basse fréquence d’opération est généralement liée à la taille de l’élément. Dans cette thèse un réseau d’anneaux concentriques a été développé. Les connections entre les spirales de polarisation opposée diminuent le coefficient de réflexion dans les fréquences basses. La topologie des anneaux concentriques a été optimisée avec des Algorithmes Génétiques pour minimiser le niveau des lobes secondaires relatifs dans les hautes fréquences. L’addition d’une contrainte de taille dans la procédure d’optimisation a assuré que le réseau soit compact. Le réseau optimisé opère entre 1 et 6.9 GHz. Le design a été d’avantage développé avec la technique WAVES avec l’inclusion d’une copie réduite en son centre, ce qu’a permis l’extension de la bande passante jusque 13 GHz. De plus, nous avons proposé un nouveau design pour le réseau de spirales connectés qui consiste en des antennes spirales disposées dans un réseau uniforme avec les bras connectés aux bras des antennes voisines. Les simulations indiquent que le réseau peut avoir une bande passante arbitrairement large selon la finitude du réseau. Un prototype a été construit et mesuré pour valider le concept. / One of the usual problems associated with wideband arrays is having the highest frequency of operation limited by the appearance of grating lobes, associated with the periodicity in the spacing between elements of the array. Another issue is the working frequency of the element of the array. The lowest frequency of operation is in general related to the size of the element. In this thesis a Concentric Ring Array of Connecting Spirals has been developed. The connections between spirals of opposite polarizations reduces the reflection coefficient at lower frequencies. The concentric rings topology had the radius and relative rotations of each ring optimized using Genetic Algorithms to minimize the RSLL at higher frequencies. The addition of a size constraint in the optimization procedure kept the array compact. The optimized array operates from 1 to 6.9 GHz. The design was then updated using the WAVES technique to include a scaled down copy in its center, extending the bandwidth of the array up to 13 GHz. Moreover, we proposed a new design for the array of connected spirals which consists of arranging spirals in a uniform array and connecting the arms of the neighboring spirals. Simulations indicate that the design can have an arbitrarily large bandwidth depending on the finiteness of the array. A prototype has been built and measured to validate the concept.

MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1980. / Includes bibliographical references. / by Jeffrey Hastings Lang. / Ph.D.

This thesis is about the researching for 5th generation (5G) communication system, which focus on the improvement of 3D beamforming technology in the antenna array using in the Full Dimension Multiple-Input Multiple-Output (FD-MIMO) system and Millimeter-wave (mm-wave) system. When the 3D beamforming technology has been used in 5G communication system, the beam needs a weighting matrix to direct the beam to cover the UEs, but some compromises should be considered. If the narrow beams are used to transmit signals, then more energy is focused in the desired direction, but this has a restricted coverage area to a single or few User Equipments (UEs). If the BS covers multiple UEs, then multiple beams need to be steered towards more groups of UEs, but there is more interference between these beams from their side lobes when they are transmitted at same time. These challenges are waiting to be solved, which are about interference between each beam when the 3D beamforming technology is used. Therefore, there needs to be one method to decrease the generated interference between each beam through directing the side lobe beams and nulls to minimize interference in the 3D beamforming system. Simultaneously, energy needs to be directed towards the desired direction. If it has been decided that one beam should covera cluster of UEs, then there will be a range of received Signal to Interference plus Noise Ratio (SINR) depending on the location of the UEs relative to the direction of the main beam. If the beam is directed towards a group of UEs then there needs be a clustering method to cluster the UEs. In order to cover multiple UEs, an improved K-means clustering algorithm is used to cluster the multiple UEs into different groups, which is based on the cosine distance. Itcan decrease the number of beams when multiple UEs need be covered by multiple beams at same time. Moreover, a new method has been developed to calculate the weighting matrix for beamforming. It can adjust the values of weighting matrix according to the UEs' location and direct the main beam in a desired direction whilst minimizing its side lobes in other undesired directions. Then the minimum side lobe beamforming system only needs to know the UEs' location and can be used to estimate the Channel State Information (CSI) of UEs. Therefore, the scheme also shows lower complexity when compared to the beamforming methods with pre-coding. In order to test the improved K-means clustering algorithm and the new weighting method that can enhance the performance for 3D beamforming system, the two simulation systems are simulated to show the results such as 3D beamforming LTE system and mm-wave system.

O presente trabalho trata do estudo, projeto, desenvolvimento, construção e medida de lentes discretas planares (DLAs). Estes dispositivos atuam como sistemas irradiantes, especialmente com características multi-feixes. A construção destas lentes utiliza tecnologias compatíveis com a fabricação de circuitos impressos, com alguns detalhes que são característicos da área de antenas e circuitos planares. O estudo aborda as equações de projeto e considerações gerais relativas ao atendimento de especificações técnicas preliminares. Foram desenvolvidas duas lentes discretas, uma na frequência de 8GHz (banda X) e outra na frequência de 40GHz (banda Ka- faixa de ondas milimétricas). São apresentados os resultados de medidas destas duas lentes, que comprovam a possibilidade de uso em aplicações multi-feixes, bem como seu efeito de foco, análogo ao observado em lentes óticas comuns. / The object of this work is the study, design, development, fabrication and measurement of discrete lens arrays (DLAs). These devices act as radiant systems, especially with multi-beam characteristics. Their construction follows the same procedures and techniques normally found in printed circuit fabrication, with some further details that are pertinent to the antenna and planar circuit field. This study contains the design equations and general remarks as to fulfill preliminary technical specifications. Two real designs were developed, one in the X-band (8GHz) and another in the millimeter range, Ka band (40GHz). Their respective measurement results are presented, which proved their possible application in multi-beam systems, as well as their focusing effect, which is analogous to that observed in common optical lenses.

We describe a set of fundamental contributions to the design, analysis and implementation of distributed MIMO techniques in wireless networks. The main idea behind distributed MIMO is to organize groups of wireless transmitters and receivers into distributed antenna arrays to cooperatively achieve beamforming and spatial multiplexing gains in ad-hoc wireless networks. This technique promises orders-of-magnitude increases in wireless data rates, however it presupposes very stringent timing, carrier frequency and phase synchronization of the RF signals between the cooperating nodes in the array. Specifically in this dissertation, we consider a sub-class of distributed MIMO systems called distributed MISO systems. In other words, we focus on distributed transmit arrays, wherein a group of N transmitters organize themselves into a virtual antenna array (VAA) to talk to a single-antenna receiver. While distributed MIMO involves virtual arrays on both transmit and receive ends, transmit arrays require real-time coordination, and therefore present unique challenges as compared to receive arrays. We explore two specific MISO techniques: i) distributed beamforming and ii) distributed nullforming in this work. Beamforming involves focusing transmitted energy selectively in the direction of an intended receiver, and nullforming involves forming a "null" i.e. having the transmissions of the different array nodes cancel each other completely at a desired location. Beamforming has the potential of substantially increasing the energy efficiency of wireless communications, while nullforming allows multiple nodes to communicate simultaneously over the same frequency band by carefully canceling the resulting interference. Beamforming and nullforming can also be thought of as basic building blocks for more sophisticated MIMO techniques. In this work, we present a set of frequency synchronization and phase control algorithms to establish and maintain a VAA for distributed beamforming and nullforming. For frequency-locking, we propose a novel distributed consensus-based algorithm. For a VAA with two nodes, we show that our algorithm achieves frequency lock globally and exponentially with a residual phase disparity that is either 0 or pi. This is in contrast to PLL-like algorithms that only achieve lock locally. Next, we describe in detail the key ideas behind an implementation of distributed beamforming on a GNU-radio/USRP based software-defined radio (SDR) platform. We introduce a novel DSP-centric Master-Slave (MS) architecture that enables the use of low-rate DSP algorithms for synchronization of high frequency RF signals. We describe the evolution of our implementation from initially using analog signaling with Costas loops/PLLs for frequency offset estimation and compensation, to a digital signaling scheme that uses extended Kalman filters (EKF) to track and compensate for frequency offsets. The EKF-based frequency locking scheme is well-suited for packet wireless networks, e.g., WiFi, ZigBee. We next consider phase control algorithms for forming beams and nulls with a VAA. In our experimental implementation, we have used several variants of classical 1-bit feedback control algorithm during different stages of our work. 1-bit feedback algorithm is an iterative gradient-ascent algorithm which causes the VAA nodes' signals to add constructively at a designated receiver. We present results to demonstrate the gains in the RSS at the receiver due to beamforming in the real-time settings. We also describe a distributed gradient-descent based algorithm that causes VAA nodes to achieve a null at a designated null target. We provide detailed convergence analysis for the proposed null-steering algorithm. This analysis shows that the algorithm always achieves practical null at null-target; moreover, all the spurious stationary points are locally unstable. Finally, we conclude by providing suggestions for future work.

A Distributed Multi-Input Multi-Output (DMIMO) system consists of many transceivers coordinating themselves into a "virtual antenna array" in order to emulate MIMO capabilities. In recent years, the field of research investigating DMIMO Communications has grown substantially. DMIMO systems offer all of the same benefits of standard MIMO systems on a larger scale because arrays are not limited by the physical constraint of placing many antennas on a single transceiver. This additional benefit does come at a cost, however. Since nodes are distributed and run from independent clock signals and with unknown geometry, each one must its own obtain channel state information (CSI) to the target nodes. In existing DMIMO architectures, array nodes depend on feedback from target nodes to properly synchronize. This means that target nodes must be cooperative and are responsible for the overhead calculating and transmitting CSI feedback to each node in the array. Within this work, we develop a set of techniques for Retrodirective Distributed Antenna Arrays. Retrodirective arrays have traditionally been used to direct a beam towards a target node, but the work in this thesis seeks to develop a more generalized definition of retrodirectivity. By our definition, a retrodirective array is one that acquires CSI to one or more intended targets simply by listening to the incoming transmissions of those targets; the array may subsequently use this information to do any number of typical MIMO tasks (i.e., beamforming, nullforming, spatial multiplexing, etc.). We explore two primary techniques: i) distributed beamforming and ii) distributed nullforming. Beamforming involves focusing transmitted power towards a specific target node and nullforming involves directing transmissions of array nodes to cancel one another at a specific target node. We focus on these techniques because they can be thought of as basic building blocks for more sophisticated DMIMO techniques. We first develop the theory for retrodirective arrays. Then, we present an architecture for the implementation of this theory. Specifically, we focus on the pre-synchronization of the array, which involves use of a master/slave architecture and a timeslotted message exchange among the array nodes. Finally, developing algorithms to make these arrays both robust and scalable is the focus of this thesis.

<p>Adaptive antenna arrays have a great importance in reduction of the effect of interference and increase the capacity for the mobile satellite communication. Interference and multipath fading remain a main problem for reception of signals. These two problems obviously affect the overall capacity.  Adaptive antenna arrays in the handheld mobile apparatus will be the solution for the above two problems.</p><p> </p><p>Satellite mobile communication is one of the growing fields in the communication area where terrestrial infrastructures are unable or ineffective to supply. Maritime, aeronautical and land mobile are some of the applications. During natural disasters where ground services are stopped, mobile satellite communications has great importance. Following the hurricane season, the Asian Tsunami and the devastating Haiti earthquake, mobile satellite communications had played a great role to fill the communication gaps.  The satellites can be tracked automatically by adaptive antenna array when it moves in its orbital plane.</p><p> </p><p>In this thesis the methods that how the adaptive antenna array combats interferers is presented and simulated using MATLAB software. The performance of the adaptive antenna array is evaluated by simulating the directivity pattern of the antenna and Mean Square Error (MSE) graph for different scenario like Signal to Interference Noise ratio (SINR), number of iterations, antenna array elements and convergence factor (μ), assuming the signals are coming from different Direction of Arrival (DOA).</p><p> </p><p> </p>