Storskaliga fleranvändar-MIMO-system, med hundratals basstationsantenner, studeras med allt större intresse både inom akademin och industrin. En anledning är att sådana system kan betjäna flera enantennsanvändare samtidigt över samma tids-frekvens-resurs med fleranvändarförkodning. Det innebär högre datahastigheter och bättre spektral effektivitet. En annan anledning är att basstationens energiförbrukning förväntas avta linjärt med antalet antenner tack vare den ökade antennförstärkningen. För att möjliggöra den stora ökningen av antalet antenner, måste priset per antenn, med dess sändtagarkedja, vara lågt. Vore det möjligt att tillverka basstationsantenner av billiga, massproducerade mobiltelefonskomponenter, som effektförstärkare utan avancerad linearisering, då skulle storskalig fleranvändar-MIMO kunna bli verklighet. Effektförstärkare i mobiltelefoner är generellt anpassade att ha hög verkningsgrad och har, i och med detta, kraftigt olinjära överföringsegenskaper. Det är fördelaktigt att sända signaler med lågt toppvärde genom sådana effektförstärkare, för att undvika svår distortion och för att maximera verkningsgraden genom att endast använda en liten avbackning från arbetspunkten. Konventionellt förkodade signaler har tyvärr högt toppvärde (ca. 10 dB). Detta arbete har undersökt en av Mohammed m.fl. (2013a) föreslagen förkodning för storskalig MIMO som resulterar i sändarsignaler med lågt toppvärde. Det visas att denna förkodning ger signaler med ett toppvärde på 4 dB, och att toppvärdet kan göras godtyckligt litet genom att dessutom begränsa fasvariationen. Ju mer fasen begränsas, desto lägre blir emellertid antennförstärkning. Till exempel om fasvariationen begränsas till π/2, sänks toppvärdet till 2,6 dB, men 2-3 dB högre sändareffekt behövs för att bibehålla samma prestanda eller, likvärdigt, så måste basstationen utrustas med 1,6-2,0 gånger fler antenner. Kontinuerlig fasmodulering som ett sätt att få sändarsignaler med konstant envelopp har studerats kort. Lågtoppvärdesförkodning, där sändarsignalerna ligger innanför en cirkel, föreslås som ett sätt att minska den erfodrade sändareffekten utan att öka toppvärdet märkvärt (<4,5 dB) relativt Mohammeds m.fl. förkodning. Förkodningsalgoritmen som utvecklades för detta fastnade dock i lokala minima, vilket försämrade dess prestanda. Sändareffekten kunde därför endast minskas lite grand (<1 dB) vid höga datahastigheter. En preliminär länkbudget baserad på en enkel effektförstärkarmodell har visat att, med fullständig kanalkännedom och i frekvensplatt fädning, skulle lågtoppvärdesförkodning kunna minska energiförbrukningen med 33 % jämfört med konventionell, linjär förkodning i en basstation med 100 antenner. Analysen antyder att olineariserade klass AB mobiltelefonseffektförstärkare kan vara ett alternativ för storskalig fleranvändar-MIMO-basstationer. / Very-large multi-user MIMO systems, with hundreds of base station antennae, are increasingly attracting attention from both academia and industry. One reason is that such systems can use multi-user precoding to simultaneously serve multiple single-antenna users over the same time-frequency resource. This implies increased data rates and improved spectral efficiency. Another reason is that the energy consumed by the base station is expected to decrease linearly with the number of antennae because of the increasing array gain. To enable the massive increase in the number of antennae, each antenna, together with its tranceiver chain, has to be cheap. If one could manufacture base station antennae using low-cost, mass-produced handset technology, including power amplifiers without advanced linearisation techniques, then very-large multi-user MIMO could become reality. Handset power amplifiers generally aim to be power-efficient, and in doing so often have highly non-linear transfer characteristics. It is of benefit to transmit signals with low peak-to-average ratio (PAR) through such power amplifiers, to avoid excessive distortion and to maximise the power efficiency by only having small operating back-offs. Conventionally precoded signals unfortunately have high PAR (approx. 10 dB). This work has investigated the low-PAR precoding scheme for very-large MIMO proposed by Mohammed et al. (2013a). It is shown that, the transmit signals of this precoding scheme have 4 dB PAR, and that by further limiting the phase variation, the PAR can be made arbitrarily small. However, the more the phase is constrained, the smaller the array gain will be. For example, if the phase variation is limited to π/2, the PAR is lowered to 2.6 dB, but 2-3 dB more transmit power is needed to maintain the same performance or, equivalently, 1.6-2.0 times more antennae are needed at the base station. Continuous phase modulation has briefly been studied as a means of producing constant-envelope transmit signals. Low-PAR precoding, where the transmit signals lie inside a circle, is suggested as a way to decrease the required transmit power without increasing PAR noticeably (<4.5 dB) relative to scheme of Mohammed et al. The algorithm that was developed for this purpose, however got stuck in local minima, which degraded its performance. The transmit power could therefore only be slightly (<1 dB) lowered in the regime of high data rates. A preliminary link budget analysis based on a simplistic model of the power amplifier has shown that, assuming perfect channel state information and frequency-flat fading, low-PAR precoding can reduce energy consumption by 33 % compared to conventional linear precoding in a base station with 100 antennae. The analysis suggests that using unlinearised class AB handset power amplifiers might be a viable option for very-large multi-user MIMO base stations. / 大規模多用戶多輸入多輸出通信系統，即配備上百基站天線的系統，正吸引著學術界及工業界越來越多的關注。其中一個原因是通過多用戶預編碼，該系統可以在同一時頻資源上同時服務多個單天線用戶，有效地增加數據速率及頻譜效率。另一個原因是，跟著陣增益的增加，基站功耗將隨天線數線性遞減。爲了使天線數的極大化可行，每根天線與其收發機的成本必須非常廉價。只有在多天線基站的生產中使用低成本的手機配件，比如不包含複雜線性化技術的功率放大器，大規模多用戶多入多出系統才有可能真正實現。 手機功放通常爲了降低功耗而有著高度非線性傳輸特性。因此，通過這樣的功放更適合傳輸低峯均比的信號以避免過度失真，同時可以在小的運作功率回退下提高功耗效率。傳統預編碼的信號峯均比不巧很高（約10分貝）。本論文研究了由Mohammed等人（2013a）提出的低峯均比預編碼。表明該預編碼的信號有4分貝的峯均比，另外加上相位變化約束信號峯均比可以降到任意小。但相位約束越緊陣增益會隨之減小。譬如約束相位變化小於π/2，峯均比降低到2.6分貝，但需要增加2至3分貝的發射功率保持相同的性能，或增加天線數於1.6至2倍。本文也簡要地描述了恆定包絡信號的連續相位調制，並提出一個預編碼讓傳播信號在一個圓內，以便減少所需要的發射功率，而峯均比也不明顯比Mohammed等人的預編碼大（＜4.5分貝）。爲此設計的算法會陷入局部最優點，從而降低其性能。因此傳輸功率只有在高數據速率場景觀察到稍微減小（＜1分貝）。 一個初步的基於簡單的功放模型的鏈路預算分析表明，假設收發端具有全部的信道狀態信息，並假設頻率平坦衰落，在一台以一百根天線的基站，低峯均比預編碼可以比普通的線性預編碼進一步降低33％功耗。也表示在大規模多用戶多入多出基站中使用非線性的手機功放應該是可行的。 / Mehrbenutzer-MIMO-Systeme mit hunderten von Antennen auf Seite der Basisstation werden mit zunehmendem Interesse sowohl von Universitäten als auch in der Telekommunikationsindustrie erforscht. Ein Vorteil Systeme dieser Art ist die gleichzeitige Versorgung mehreren Benutzer mittels Mehrbenutzervorkodierung über dieselbe Zeit-Frequenz-Ressourcen. Dieses führt zu höheren Datenraten und besserer spektraler Effizienz. Ein weiterer Vorteil, wegen des zunehmenden Antennengewinn, ist der mit der Antennenanzahl erwartete linear abnehmende Energieverbrauch der Basisstation. Um eine große Anzahl von Antennen sinnvoll zu ermöglichen, muss jede individuelle Antenne, mit ihrer zugehörigen Sendeempfängerkette, kostengünstig sein. Wäre es möglich, Antennen einer Basisstation auf kostengünstigen serienmäßig hergestellten Mobiltelefonkomponenten, z.B. Leistungsverstärkern ohne komplexe Linearisierung, aufzubauen, könnten Mehrbenutzer-MIMO-Systeme mit hunderten Antennen wirklich realisiert werden. Mobiltelefonleistungsverstärker sind gewöhnlich eher auf hohen Wirkungsgrade angepasst, deren Übertrangungseigenschaften sind daher stark nichtlinear. Es ist von Vorteil, Signale mit niedrigem Scheitelfaktor durch solche Leistungsverstärker zu übertragen, um übermäßige Verzerrung zu vermeiden und die Wirkungsgrad durch kleineren Backoff vom Arbeitspunkt zu maximieren. Leider haben herkömmlich vorkodierte Signale hohen Scheitelfaktor (ca. 10 dB). Diese Arbeit untersucht die Vorkodierungsmethode von Mohammed u.a. (2013a) zur Verringerung des Scheitelfaktors. Es wird gezeigt, dass die Signale dieser Vorkodierungsmethode haben einen Scheitelfaktor von 4 dB und dass der Scheitelfaktor durch eine zusätzliche Begrenzung der Phasenvariation beliebig klein gemacht werden kann. Je mehr die Phasen begrenzt werden, desto kleiner wird jedoch die Antennenverstärkung. Z.B, wenn die Phasenvariation auf π/2 begrenzt wird, wird der Scheitelfaktor auf 2,6 dB reduziert, aber 2-3 dB höhere Sendeleistung ist benötigt, um die gleiche Datenraten zu behalten, oder, entsprechend, muss die Antennenanzahl um einen Faktor 1,6-2 erhöht werden. Modulation mit stetiger Phase, als eine Methode um Sendesignale mit konstanten Einhüllenden zu bekommen, wird kurz untersucht. Eine Vorkodierungsmethode, wo die Signale innerhalb eines Kreises liegen, wird vorgeschlagen, zur Verringerung der erforderlichen Sendeleistung, ohne den Scheitelfaktor (<4,5 dB), im Vergleich zur Vorkodierung von Mohammed u.a, erkennbar zu erhöhern. Der Algorithmus, der für diesen Zweck entwickelt wurde, fährt aber in lokale Mimima fest, was dessen Leistung vermindern. Die Sendeleistung kann deshalb nur im Bereich hohen Datenraten etwas (<1 dB) gesenkt werden. Eine Kanalgewinnanalyse, die auf einem einfachen Leistungsverstärkermodell beruht, zeigt ansatzweise im Fall perfekter Kanalzustandsinformation und Flachschwunds, dass geeignete Scheitelfaktorvorkodierung in einem Basisstation mit 100 Antennen den Stromverbrauch im Vergleich zu herkömmlicher linearer Vorkodierung um 33 % verringern kann. Die Analyse deutet an, dass die Anwendung unlinearisierter Mobiltelefonleistungsverstärker Klasse AB eine Möglichkeit in Mehrbenutzer-MIMO-Basisstationen mit hunderten von Antennen ist.

Thesis (Ph.D.)--Ohio University, March, 2010. / Title from PDF t.p. Includes bibliographical references.

Teams of design engineers are increasingly working as members of virtual teams, or teams whose members are distributed geographically and communicate mostly through electronic means. In addition, emerging multi-user (MU) applications engage complementary teams in synchronous design activities. These new MU tools are changing the way engineers work together. Together, these factors have created a new and interesting environment in which engineering design teams must function. The work presented here lays out two major themes that teams and their managers can effectively apply to organizing and managing MU teams: 1) teams can maximize their potential productivity by determining the optimal number of teammates for a given modeling effort and by implementing a profile and team formation system based on the principle of optimizing complementary team member characteristics; and 2) to minimize process losses, teams can implement effective strategies for working in a MU and/or virtual setting and they can use novel new MU tools that address portions of the product development process that have previously not been addressed with such tools. It is my hope that these contributions can enable greater effectiveness and productivity among virtual engineering design teams as they strive to remedy many of the most pressing and dire issues facing humanity. By improving the way we work together, we can increase our ability to bless all of God's children.

Efficient implementation of resource sharing strategies in a multi-user wireless environment can improve the performance of a network significantly. In this thesis we study various scheduling strategies for wireless networks and handle the problem of opportunistically scheduling transmissions using channel aware schemes. First we propose a scheme that can handle users with asymmetric channel conditions and is opportunistic in the sense that it exploits the multi-user diversity of the network. The scheme requires the users to have a priori knowledge of their channel distributions. The associated overhead is limited meaning it offers reduced feedback load, that does not scale with the increasing number of users. The main technique used to shrink the feedback load is the contention based distributed implementation of a splitting algorithm that does not require explicit feedback to the scheduler from every user. The users find the best among themselves, in a distributed manner, while requiring just a ternary broadcast feedback from the scheduler at the end of each mini-slot. In addition, it can also handle fairness constraints in time and throughput to various degrees. Next we propose another opportunistic scheduler that offers most of the benefits of the previously proposed scheme but is more practical because it can also handle heterogenous users whose channel distributions are unknown. This new scheme actually reduces the complexity and is also more robust for changing traffic patterns. Finally we extend both these schemes to the scenario where there are fixed thresholds, this enables us to handle opportunistic scheduling in practical systems that can only transmit over finite number of discrete rates with the additional benefit that full feedback session, even from the selected user, is never required.

In underlay cognitive radio networks, secondary users can share the spectrum with primary users as long as the interference caused by the secondary users to primary users is below a certain predetermined threshold. It is reasonable to assume that there is always a large pool of secondary users trying to access the channel, which can be occupied by only one secondary user at a given time. As a result, a multi-user scheduling problem arises among the secondary users. In this thesis, by manipulating basic schemes based on selective multi-user diversity, normalized thresholding, transmission power control, and opportunistic round robin, we propose and analyze eight scheduling schemes of secondary users in an underlay cognitive radio set-up. The system performance of these schemes is quantified by using various performance metrics such as the average system capacity, normalized average feedback load, scheduling outage probability, and system fairness of access. In our proposed schemes, the best user out of all the secondary users in the system is picked to transmit at each given time slot in order to maximize the average system capacity. Two thresholds are used in the two rounds of the selection process to determine the best user. The first threshold is raised by the power constraint from the primary user. The second threshold, which can be adjusted by us, is introduced to reduce the feedback load. The overall system performance is therefore dependent on the choice of these two thresholds and the number of users in the system given the channel conditions for all the users. In this thesis, by deriving analytical formulas and presenting numerical examples, we try to provide insights of the relationship between the performance metrics and the involved parameters including two selection thresholds and the number of active users in the system, in an effort to maximize the average system capacity as well as satisfy the requirements of scheduling outage probability and feedback load.

The development of a polyimide and metals multi-user surface micro-machining process for Micro-electro-mechanical Systems (MEMS) is presented. The process was designed to be as general as possible, and designed to be capable to fabricate different designs on a single silicon wafer. The process was not optimized with the purpose of fabricating any one specific device but can be tweaked to satisfy individual needs depending on the application. The fabrication process uses Polyimide as the structural material and three separated metallization layers that can be interconnected depending on the desired application. The technology allows the development of out-of-plane compliant mechanisms, which can be combined with six variations of different physical principles for actuation and sensing on a single processed silicon wafer. These variations are: electrostatic motion, thermal bimorph actuation, capacitive sensing, magnetic sensing, thermocouple-based sensing and radio frequency transmission and reception.

This thesis investigates the performance of a multi-user multiple-input single- output (MISO) system considering maximum ratio transmission (MRT) downlink precoding. The transmitted signal from the base station (BS) to each user is as- sumed to experience the double scattering channel. We adopt the minimum-mean- square-error (MMSE) channel estimator for the proposed model. Within this setting, we are interested in deriving tight approximations of the ergodic rate assuming the number of BS antennas, users, and scatterers grow large with the same pace. Under the special multi-keyhole channels, these deterministic equivalents are expressed in more simplified closed-form expressions. The simplified expressions reveal that unlike the standard Rayleigh channel in which the SINR grows as as O(N/k), the SINR associated with a multi-keyhole channel scales as O(S/N). This particularly shows that the K reaped gains of the large-scale MIMO over double scattering channels do not linearly increase with the number of antennas and are limited by the number of scatterers. We further show that the derived asymptotic results match the simulation results closely under moderate system dimensions and provide some useful insights into the interplay between N, K and S.

Collaboration has always been critical to the success of new product development teams, and the advent of geographically dispersed teams has significantly altered the way that team members interact. Multi-user computer-aided design (MUCAD) and crowdsourcing are two results of efforts to enable collaboration between geographically dispersed individuals. In this research, a study was done to investigate the differences in performance between MUCAD and single-user CAD teams, in which teams competed to create the best model of a hand drill. This was done across a three-day period to recreate the scenario found in industry. It was found that MUCAD increases awareness of teammates' activities and increases communication between team members. Different sources of frustration for single-user and multi-user teams were identified, as well as differing patterns of modeling style. These findings demonstrate that MUCAD software has significant potential to improve team collaboration and performance. A second study explored a number of potentially significant factors in MUCAD team performance, including leadership, design style, unfamiliar parts, knowledge transfer, individual experience, and team composition. In this study, teams of undergraduate mechanical engineering students worked together to complete tasks using NXConnect, a MUCAD plugin for NX developed at Brigham Young University. A primary finding was that having an appointed leader for a MUCAD team improves performance, in particular when that leader works with the team in creating the CAD model. It was also found that creating a framework to aid in organizing and coordinating the creation of the CAD model may decrease the time required for completion. In the final study, the possibility of using crowdsourcing to complete complex product design tasks was explored. In this study, a process for crowdsourcing complex product design tasks was developed, as well as a website to act as the platform for testing this process. A crowd consisting of engineering and technology students then worked together on the website to design a frisbee tracking device. The crowd was able to collaborate to accomplish some detailed product design tasks, but was not able to develop a complete product. Major findings include the need for more formal leadership and crowd organization, the need for better decision making mechanisms, and the need for a better model for engaging crowd members on a consistent basis. It was also found that crowd members had a greater willingness to pay for the product they developed than individuals who had not worked on the project. Results also show that although crowd members were often frustrated with the collaboration process, they enjoyed being able to work with a large group of people on a complex project.

Collaboration has always been critical to the success of new product development teams, and the advent of geographically dispersed teams has significantly altered the way that team members interact. Multi-user computer-aided design (MUCAD) and crowdsourcing are two results of efforts to enable collaboration between geographically dispersed individuals. In this research, a study was done to investigate the differences in performance between MUCAD and single-user CAD teams, in which teams competed to create the best model of a hand drill. This was done across a three-day period to recreate the scenario found in industry. It was found that MUCAD increases awareness of teammates' activities and increases communication between team members. Different sources of frustration for single-user and multi-user teams were identified, as well as differing patterns of modeling style. These findings demonstrate that MUCAD software has significant potential to improve team collaboration and performance. A second study explored a number of potentially significant factors in MUCAD team performance, including leadership, design style, unfamiliar parts, knowledge transfer, individual experience, and team composition. In this study, teams of undergraduate mechanical engineering students worked together to complete tasks using NXConnect, a MUCAD plugin for NX developed at Brigham Young University. A primary finding was that having an appointed leader for a MUCAD team improves performance, in particular when that leader works with the team in creating the CAD model. It was also found that creating a framework to aid in organizing and coordinating the creation of the CAD model may decrease the time required for completion. In the final study, the possibility of using crowdsourcing to complete complex product design tasks was explored. In this study, a process for crowdsourcing complex product design tasks was developed, as well as a website to act as the platform for testing this process. A crowd consisting of engineering and technology students then worked together on the website to design a frisbee tracking device. The crowd was able to collaborate to accomplish some detailed product design tasks, but was not able to develop a complete product. Major findings include the need for more formal leadership and crowd organization, the need for better decision making mechanisms, and the need for a better model for engaging crowd members on a consistent basis. It was also found that crowd members had a greater willingness to pay for the product they developed than individuals who had not worked on the project. Results also show that although crowd members were often frustrated with the collaboration process, they enjoyed being able to work with a large group of people on a complex project.

No description available.