Dissertations / Theses on the topic 'MIMO multi users'

Avec la progression de l'utilisation des smartphones, les modèles de systèmes ont rapidement évolué pour répondre aux besoins croissants en terme de capacité dans les réseaux sans fil. En effet, les progrès technologiques ont été considérables, depuis les communications point à point mono-utilisateur et mono-antenne jusqu'aux réseaux cellulaires multi-cellules et multi-antennes. Depuis la 3G, la technologie MIMO (multiple-input multiple-output) pour les communications sans fil est désormais intégrée aux normes de la large bande sans fil. L'ajout de plusieurs antennes, tant du côté de l'émetteur que du côté du récepteur, permet le multiplexage spatial (c'est-à-dire l'envoi simultané de plusieurs flux de données), qui permet d'augmenter les débits de données, et l'exploitation de la diversité spatiale, améliorant considérablement la qualité des liaisons. MIMO Multi-Utilisateurs (MU) a été un sujet bien étudié dans le domaine des communications sans fil en raison du grand potentiel qu'il offre pour améliorer le débit du système. Par conséquent, différents critères de conception pour les communications MIMO MU ont été étudiés dans la littérature. La plupart des conceptions de liaisons descendantes prennent en compte les problèmes d'optimisation de la capacité totale de tous les utilisateurs. D'autre part, la principale limitation des communications sans fil modernes est l'interférence (intracellulaire et intercellulaire) due à la réutilisation des fréquences. Ainsi, dans un scénario MIMO MU, lors de l'optimisation de l'efficacité globale, l'allocation de puissance se concentre sur les bons canaux, c'est-à-dire que les utilisateurs soumis à une forte interférence (e.g., les utilisateurs en bordure de cellule) sont délaissés. Il en résulte une répartition inéquitable de puissance entre les utilisateurs. Pour pallier ce problème, différentes notions d'équité sont introduites, comme l'équité max-min, l'équité pondérée ou l'équité proportionnelle. Dans cette thèse, nous nous concentrons sur l'équité max-min pondérée. En particulier, nous étudions le problème de l'équilibrage du débit pondéré par utilisateur dans un système MIMO multi-cellules MU. Nous abordons ce dernier dans le cadre d'une formulation conjointe du problème de beamforming et d'allocation de puissance, visant à satisfaire l'exigence d'équité. Dans la première partie, nous considérons la connaissance parfaite du canal pour résoudre le problème. Dans ce cas, nous maximisons le débit minimum pondéré via i) la dualité liaison montante/descendante et ii) la dualité Lagrangienne. Dans la deuxième partie, nous considérons la connaissance partielle du canal. Nous optimisons le problème d'équilibrage de débit ergodique via i) l'erreur quadratique moyenne pondérée (EQM) en exploitant la relation débit - EQM, et ii) deux approximations du débit estimé comme le débit de signal et de puissance d'interférence estimés (ESIP) au niveau du flux et du signal reçu. Par ailleurs, nous proposons une stratégie d'efficacité énergétique au moyen des approches d'équilibrage des débits proposées
With the rise in smartphone usage, the system models have rapidly evolved to meet ever-growing needs for capacity in wireless networks. Indeed, there have been large advances in technology, from single-user single-antenna point-to-point communications to multi-cell multi-antenna cellular networks. In fact, multiple-input multiple-output (MIMO) technology for wireless communications is now incorporated into wireless broadband standards since 3G. Adding multiple antennas at both the transmitter and the receiver sides enables spatial multiplexing (i.e. sending multiple data streams simultaneously), which allows to increase data rates, and spatial diversity exploitation, which allows to greatly improve link quality. The multi-user MIMO downlink (so-called Broadcast Channel (BC)) has been a well investigated subject in wireless communications because of the high potential it offers in improving the system throughput. Therefore, different design criteria for multi-user MIMO communication have been investigated in the literature. Most of the downlink designs consider optimization problems w.r.t. the sum-capacity of all users. On the other hand, the major bottleneck of modern wireless communication is the interference (intracell and intercell) due to frequency reuse. Thus, in a multi-user MIMO scenario, when optimizing the overall efficiency, the power allocation is focused on the good channels, i.e., users that are subject to strong interference (e.g. cell-edge users) are neglected. The result is an unfair distribution of rate among users. In order to avoid this effect, different fairness notions have been introduced, like max-min fairness, weighted fairness, or proportional fairness. In this thesis, we focus on the weighted max-min fairness. In particular, we study the (weighted) user rate balancing problem in a multi-cell multi-user MIMO system. We address this problem by joint beamforming and power allocation optimization, aiming to satisfy the fairness requirements. In the first part, we consider perfect knowledge of the channel to solve the problem. Therein, we maximize the minimum (weighted) rate via i) weighted user Mean Square Error (MSE) uplink/downlink duality and ii) Lagrangian duality. In the second part, we consider partial knowledge of the channel. We optimize the ergodic rate balancing problem via i) weighted expected MSE by exploiting the rate – MSE relation, and ii) two approximations of the expected rate as the Expected Signal and Interference Power (ESIP) rate at the stream level and the received signal level. Furthermore, we study the transmit power minimization problem with fixed user-rate targets and provide a strategy exploiting the proposed rate balancing approaches

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003.
Includes bibliographical references (leaves 167-170). Also available in electronic version. Access restricted to campus users.

In this treatise, we explore diverse multi-user transmission techniques and joint detection-decoding schemes designed for downlink multi-user transmissions, while maintaining a low complexity, a high throughput and a high integrity. More specifically, in Chapter 2 we will introduce various Multi-User Transmission (MUT) techniques for the Space Division Multiple Access Down-Link (DL-SDMA) employing the sophisticated linear SpatioTemporal Pre-processing (STP) schemes, which are capable of eliminating the multi-user interference at the Base Station (BS) and increase the transmission integrity at the Mobile Sta,ions (MS). Additionally, we will design signal detection techniques for the DL-SDMA system, which achieves a near-Maximum Likelihood (ML) performance at a fraction of the ML detector's complexity. In Chapter 3 we extend our research to a joint iterative detection and decoding based DL-SDMA system. We will introduce a precoder aided iterative DL-SDMA system, which is designed with the aid of Extrinsic Information Transfer (EXIT) charts and has an improved iterative decoding gain. Finally, we will characterize the impact of imperfect Channel State Information (CSI) on the proposed iterative DL-SDMA and introduce sophisticated IrRegular Convolutional Codes (IRCC) for improving the integrity of the iterative DL-SDMA system. In order to reduce the complexity of the iterative receivers, in Chapter 4 we will introduce a novel detection algorithm, which is referred to as the Irregular Generic Detection (IrGD) algorithm. The IrGD has a tunable • complexity and it was particularly designed for redUcing the complexity of the iterative decoding aided system. Furthermore, we will demonstrate the impact of imperfect CSI with the aid of EXIT charts. In addition, we will introduce an EXIT-Chart Optimized CSI Quantizer (ECO-CQ) for the iterative DL-SDMA system, which is capable of reducing CSI-related feedback overhead. In Chapter 5 we will introduce an advanced space-time signaling technique aided MUT designed for the DL-SDMA system, which results in an improved capacity. Furthermore, we will propose a low-complexity Irregular Sphere Detection (IrSD) scheme designed for approaching the capacity DL-SDMA systems, which is capable of maintaining a near-ML performance. Additionally, we will characterize our pilot assisted channel prediction aided DL-SDMA system using limited CSI feedback.

Thesis (Ph. D.)--University of California, San Diego, 2008.
Title from first page of PDF file (viewed December 16, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 144-151).

In this thesis, linear precoding designs and scheduling algorithms are studied based on the maximum Signal-to-Leakage-plus-Noise Ratio (SLNR) criteria in single-cell Multi-user MIMO (MU-MIMO) systems as well as in multi-cell MIMO cooperative networks. The conventional SLNR precoding scheme is firstly investigated. Analytic expressions of the conventional SLNR-based solution are derived and are shown to be a generalised form of regularised channel inversion techniques. Consequently, equivalence between the SLNR and other regularised channel inversion schemes for the case of single-antenna and multi-antenna receivers can be established. This provides an alternative view of the conventional SLNR precoding design and leads to several useful implications in terms of possible exchange of relevant algorithms and performance analysis among these linear precoding schemes. One of the main issues of the conventional SLNR precoding design for the case that all available eignmodes are not fully transmitted is then addressed. Enhanced leakage-based precoding designs are proposed and are thoroughly studied in single-cell MU-MIMO based on two main approaches, i.e. the receive antenna selection and the enhanced receive subspace estimation. The latter is seen to be superior to the former and, as a result, serves as an underlying technique for subsequent studies. The proposed leakage-based precoding designs with receive subspace estimation techniques are further applied to the transceiver design for achieving the maximum Weighted Sum Rate (WSR) in single-cell MU-MIMO systems. Based on the proposed trallsceiver structure, the problem call be simplified into two different problems, i.e. the power allocation and the data stream selection problems, to which the solutions are separately proposed. The resulting precoding designs are shown to have comparable performance to existing joint Transmit (TX)-Receive (RX) filter designs despite requiring simpler receiver structures. The enhanced leakage-based transceiver designs are also extended from the single-cell MU-MIMO systems to multi-cell coordinated beamforming scenarios. Further, the resulting transceiver designs are applied to the WSR maximisation problem in the multi-cell case by extending the power allocation and the data stream selection approaches as previously studied in the single-cell case to the multi-cell coordinated beamforming systems.

In a cellular network with small cells, where all the communication resources are shared, the inter-cell interference becomes a limiting factor of performance. The strategies for mitigating the inter-cell interference has been quite extensively studied lately. One of the promising candidates is coordinated beamforming/scheduling, where a certain number of cells is allowed to cooperate such that the transmission from each cell takes into account the interference it would cause to the users of other cells. In this thesis, the performances of different signaling strategies which perform the weighted sum rate maximization in time division duplex multi-cell multi-user MIMO downlink system are studied. The strategies consist of iterative decentralized algorithms, aiming at reduced pilot signaling overhead and faster convergence. The required control information between the cells is provided via uplink reference signals and a backhaul. Uplink reference signals include sounding reference signals and busy bursts. Based on the earlier work, the strategies have now been extended to a larger cellular system in which the frequency selectivity and the uncertainty of the channel information are also taken into account. The ability of the strategies to handle the large network can be seen from the simulation results. It is shown that even when there is strong inter-cell interference, the strategies utilizing parallel cell-specific iterations offer practical convergence speed. It is also noticed that the joint optimization over many frequency blocks brings a minor improvement on the sum rate performance, meaning that it could also be utilized with the same order of computational complexity compared to the frequency flat case. Finally, the robustness of the centralized strategy to the imperfect channel state information is shown and the trade-off between the CSI uncertainty and multi-user diversity is stated
Solukkoverkossa, jossa solujen koot ovat pieniä ja kaikki käyttävät samoja taajuuksia, solujen välinen häiriö rajoittaa verkon suorituskykyä. Viime aikoina on laajasti tutkittu strategioita, joilla häiriötä saataisiin vähennettyä. Yksi lupaavista menetelmistä tähän tarkoitukseen on koordinoitu keilanmuodostus/skedulointi, jossa tietty ryhmä soluja voi koordinoida keskenään ja näin ottaa huomioon lähetyksestä aiheutuvan häiriön toisia soluja kohtaan. Tässä diplomityössä tutkitaan erilaisten painotetun summadatanopeuden maksimoivien signalointistrategioiden suorituskykyä aikajakodupleksoidussa usean solun ja käyttäjän moniantenniverkossa, jossa dataa lähetetään tukiasemasta käyttäjille. Strategiat perustuvat iteratiivisiin hajautettuihin algoritmeihin, joiden tarkoituksena on vähentää opetussignaloinnista aiheutuvaa kuormitusta ja nopeuttaa suppenemista. Kontrolli-informaation signaloimiseen verkossa käytetään käyttäjiltä tukiasemille lähetettäviä opetussignaaleja ja taustayhteyttä tukiasemien välillä. Työ perustuu aiemmin tehtyyn tutkimukseen, josta strategiat on nyt laajenettu suurempaan solukkojärjestelmään, ottaen huomioon myös taajuusselektiivisyyden ja kanavainformaation epävarmuuden vaikutukset. Simulointitulosten perusteella voidaan sanoa, että strategiat toimivat usean käyttäjän ja solun verkossa. Tuloksista nähdään, että rinnakaisia solukohtaisia iteraatioita hyödyntävillä strategioilla voidaan saavuttaa käytännöllinen suppenemisnopeus, vaikka solujen välinen häiriö on voimakasta. Taajuusselektiivisen kanavan tuloksista huomataan, että yhteisoptimointi usean taajuuslohkon yli parantaa vähän suorituskykyä verrattuna yhden taajuuden tapaukseen. Yhteisoptimointia voitaisiin siis myös hyödyntää, koska laskennallinen monimutkaisuus on samaa suuruusluokkaa verrattuna yhden taajuuden tilanteeseen. Epävarman kanavatiedon vaikutusta tutkitaan keskitetyllä optimointimenetelmällä, joka selvästi laskee suorituskykyä verrattuna täydellisen kanavan tapaukseen, mutta antaa kuitenkin selkeän parannuksen alkuperäiseen algoritmiin verrattuna. Koska opetussignaalien teho jaetaan käyttäjien kesken, tulokset näyttävät kompromissin kanavatiedon epävarmuuden ja monikäyttäjädiversiteetin välillä

One major limiting factor for wireless communication systems is the limited available bandwidth for cellular networks. Current technologies like Long Term Evolution (LTE) and LTE-Advanced (LTE-A) have standardised a frequency reuse factor of 1 to enable more channel resources in each cell. Also multi-layer networks that consist of overlapping macro cells and small cells like pico cells, micro cells and femto cells have also been used to improve the capacity of the cellular network system. These multi-layer networks are known as heterogeneous networks or HetNets while the single layer, traditional cellular systems are referred to as homogeneous networks or HomoNets. Several interference management systems and techniques have been proposed in the past to deal with the effect of inter-cell interference (ICI) (i.e., the interference from a macro cell base station (BS) to a macro cell user in another macro cell) and inter-user interference (IUI) (i.e., the interference of another user's data signal to a given user within the same cell on the same time and frequency slot). Interference cancellation techniques such as beamforming, uses transmit pre-coders and receive beam-formers to limit the effect of interference. The interference alignment strategy ensures that the interference is aligned into a given subspace and leaves a residual subspace free for the desired signal. Coordinated scheduling/beam-forming and coordinated multi-point transmission (CoMP) have also been used to limit the interference within the cellular network. For HetNets, interference avoidance techniques based on radio resource management (RRM) have been used to limit the effect of interference within the network and improve the attainable system capacity. This thesis investigates the challenges of two main interference management techniques and proposes methods to alleviate these issues without impeding the expected performance already attained. The main techniques considered for HomoNets and HetNets are: CoMP transmission under the interference cancellation technique and resource block allocation (RBA) under the interference avoidance technique. The setbacks for the well known CoMP transmission strategy are high data overhead, energy consumption and other associated costs to the network provider. Further investigations were carried out and a joint selection of transmit antennas for the users was proposed with the main aim of preserving or exceeding the already achieved gains but obtaining a further reduction in the data overhead. Fully distributed RBA solutions are required, especially since future networks tend to become self-organising networks (SON). Another major consideration in choosing the resource blocks (RBs) for the users in each cell is the RBA metric. Since the capacity of the cell is dependent on the sum-rate of the users, it is important to consider the maximisation of the sum-rate or sum-SINR (i.e the sum signal to interference and noise ratio) when assigning RBs to users. The RBA technique aims to choose the RBs such that the interference within the cell is avoided. To achieve this, a RBA metric is required to obtain the qualification matrix before allocating RBs to the users. Many authors in the past have proposed several metrics for RBA but avoided any RBA metric that required a direct estimation of the interference power on each RB for each user's allocation. This is because the SINR or interference power on each RB for any user can only be obtained with pre-knowledge of already occupied RBs in neighbouring cells. In this thesis, two distributed RBA solutions based on a direct interference estimation was proposed to obtain the required qualification matrix for the RBA under the HomoNet and HetNet system models. The gains and advantages obtained are shown and analysed using the obtained simulation results. The issue of interference coupled with limited available channels remains a major limiting factor for HetNets. Therefore, it is very important to develop techniques that maximise the utilisation of available bandwidth for each cell while minimising possible interference from neighbouring cells. Finally, this thesis considers and investigates a possible joint solution using both interference avoidance and interference mitigation techniques. Hence two solutions are proposed: joint RBA plus beam-forming and joint RBA plus CoMP transmission, to further mitigate the high interference in HetNets. The simulation results have shown significantly improved system performance especially for a highly dense HetNet.

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.

Channel estimation problem is a crucial state of the art research topic that has been addressed in the literature for the past decade. The importance of such research area emerged from the fact that telecommunication scholars are searching for a wireless telecommunication system that provides a minimum error performance yet can utilize the used spectrum efficiently. Channel estimation is a common practice in most of the wireless communication systems to give the receiver an indication about the channel conditions and hence will affect his decision in detecting the transmitted information This thesis will Compare Four methods for Channel estimation problems based in semi-blind approach for MU-MIMO systems; the Rank Revealing QR factorization RRQR, Least square method LS, CAPON method and the Eigenvector method. Performance comparison is based on the Minimum mean square error (MMSE). The introduced method in this thesis is the Eigenvector method, and it's presented in comparison to the first three methods. Compared to the RRQR the Eigenvector is based on a searching function similar to the MUSIC function with the addition of the Eigen values of the null space in the search function.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Electrical Engineering and Computer Science

The fundamental detection problem in fading channels involves the correct estimation of transmitted symbols at the receiver in the presence of Additive White Gaussian Noise (AWGN). Detection can be considered when the receiver is assumed not to know the channel (non-coherent detection), or alternatively, when the random channel is tracked at the receiver (coherent detection). It can be shown that for a given error probability, coherent detection schemes require a Signal to Noise Ratio (SNR) that is 3dB less than the SNR required for non-coherent detection schemes. It is also known that the performance of coherent detection schemes can be further improved using space-frequency diversity techniques, for example, when multiple-input multiple-output (MIMO) antenna technologies are employed in conjunction with Orthogonal Frequency Division Multiplexing (OFDM). However, the superior performance promised by the MIMO-OFDM technology relies on the availability of accurate Channel State Information (CSI) at the receiver. In the literature, the Mean Square Error (MSE) performance of MIMO-OFDM CSI estimators is known to be limited by the SNR. This thesis adopts a di®erent view to estimator performance, by evaluating the accuracy of CSI estimates as limited by the maximum delay spread of the multipath channel. These considerations are particularly warranted for high data rate multi-user MIMO-OFDM systems which deploy large numbers of transmit antennas at either end of the wireless link. In fact, overloaded multi-user CSI estimation can be e®ectively studied by considering the grouping together of the user antennas for the uplink while conversely, considering a small number of antennas due to size constraints for the downlink. Therefore, most of the work developed in this thesis is concerned with improving existing single-user MIMO-OFDM CSI estimators but the results can be extended to multi-user system.

This research has analysed both reciprocity and feedback mechanisms in multi-antenna wireless systems. It has presented the basis of an effective CSI feedback mechanism that efficiently provides the transmitter with the minimum information to allow the accurate knowledge of a rapidly changing channel. The simulations have been conducted using MATLAB to measure the improvement when the channel is estimated at the receiver in a 2 X 2 multi-antenna system and compared to the case of perfect channel knowledge at the receiver.

Thesis (M.S.)--Wichita State University,College of Engineering. Dept. of Electrical and Computer Engineering.
"May 2007." Title from PDF title page (viewed on Dec. 27, 2007). Thesis adviser: Hyuck M. Kwon. Includes bibliographic references (leaves 29-33).

The past decade has seen an enormous increase in the number of connected wireless devices, and currently there are billions of devices that are connected and managed by wireless networks. At the same time, the applications that are running on these devices have also developed significantly and became more data rate insatiable. As the number of wireless devices and the demand for a high data rate will always increase, in addition to the growing concern about the energy consumption of wireless communication systems, the future wireless communication systems will have to meet three main requirements. These three requirements are: i) being able to achieve high throughput; ii) serving a large number of users simultaneously; and iii) being energy efficient (less energy consumption). Massive multiple-input multiple-output (MIMO) technology can satisfy the aforementioned requirements; and thus, it is a promising candidate technology for the next generations of wireless communication systems. Massive MIMO technology simply refers to the idea of utilizing a large number of antennas at the base station (BS) to serve a large number of users simultaneously using the same time-frequency resources. The hypothesis behind using a massive number of antennas at the BS is that as the number of antennas increases, the channels become favourable. In other words, the channel vectors between the users and their serving BS become (nearly) pairwisely orthogonal as the number of BS antennas increases. This in turn enables the use of linear processing at the BS to achieve near optimal performance. Moreover, a huge throughput and energy efficiency can be attained due to users multiplexing and array gain. In this thesis, we investigate the performance of massive MIMO systems under different scenarios. Firstly, we investigate the performance of a single-cell multi-user massive MIMO system, in which the channel vectors for the different users are assumed to be correlated. In this aspect, we propose two algorithms for users grouping that aim to improve the system performance. Afterwards, the problem of pilot contamination in multi-cell massive MIMO systems is discussed. Based on this discussion, we propose a pilot allocation algorithm that maximizes the minimum achievable rate in a target cell. Following that, we consider two different scenarios for pilot sequences allocation in multi-cell massive MIMO systems. Lower bounds on the achievable rates are derived for two linear detectors, and the performance under different system settings is analysed and discussed for both scenarios. Finally, two algorithms for pilot sequences allocation are proposed. The first algorithm takes advantage of the multiplicity of pilot sequences over the number of users to improve the achievable rate of edge cell users. While the second algorithm aims to mitigate the negative impact of pilot contamination by utilizing more system resources for the channel estimation process to reduce the inter-cell interference.

We consider the multi-user MIMO broadcast channel with M single-antenna users and N transmit antennas under the constraint that each antenna emits signals having constant envelope (CE). The motivation for this is that CE signals facilitate the use of power-efficient RF power amplifiers. Analytical and numerical results show that, under certain mild conditions on the channel gains, for a fixed M, an array gain is achievable even under the stringent per-antenna CE constraint. Essentially, for a fixed M, at sufficiently large N the total transmitted power can be reduced with increasing N while maintaining a fixed information rate to each user. Simulations for the i.i.d. Rayleigh fading channel show that the total transmit power can be reduced linearly with increasing N (i.e., an O(N) array gain). We also propose a precoding scheme which finds near-optimal CE signals to be transmitted, and has O(MN) complexity. Also, in terms of the total transmit power required to achieve a fixed desired information sum-rate, despite the stringent per-antenna CE constraint, the proposed CE precoding scheme performs close to the sum-capacity achieving scheme for an average-only total transmit power constrained channel.

Funding Agencies|Swedish Foundation for Strategic Research (SSF)||ELLIIT||Knut and Alice Wallenberg Foundation||Center for Industrial Information Technology at ISY, Linkoping University (CENIIT)||

Capacity of current and future high data rate wireless communications depend significantly on how well changes in the wireless channel are predicted and tracked. Generally, this can be estimated by transmitting known symbols. However, this increases overheads if the channel varies over time. Given today’s bandwidth demand and the increased necessity for mobile wireless devices, the contributions of this research are very significant. This study has developed a novel and efficient channel tracking algorithm that can recursively update the channel estimation for wireless broadband communications reducing overheads, therefore increasing the speed of wireless communication systems.

Les réseaux radio actuelles utilisent le spectre inefficacement, car une bande de fréquence est allouée de façon permanente à une technologie spécifique. Vu que le spectre est une ressource limitée, cette attribution statique ne pourra bientôt plus combler les besoins des systèmes de transmission qui ne cessent de croître. On peut toutefois optimiser l'utilisation du spectre en permettant des transmissions secondaires (SU) dans les espaces libres du primaire (PU). Cette vision constitue l'objectif principal de la radio cognitive. Nous proposons d'évaluer les stratégies de transmission pour la coexistence des systèmes primaires (PU) et SU dans les mêmes réseaux. Plus concrètement, nous nous focalisons sur un scénario spatial interweave en émettant les signaux SU dans les espaces vides du PU à l'aide d'un précodeur linéaire. Néanmoins, ce précodage nécessite une connaissance a priori des canaux interférents. L'échange d'informations entre le PU et le SU étant proscrit, nous exploitons l'hypothèse de la réciprocité du canal. Cette hypothèse compense l'absence de coopération, mais elle n'est pas si évidente à exploiter en pratique à cause des perturbations des circuits radio fréquence. Nous suggérons de compenser ces perturbations par des méthodes de calibration relative. Nous proposons ensuite une implémentation temps-réel des solutions sur une plateforme LTE. Pour finir, nous généralisons l'approche RC à un système de transmission multi-utilisateurs, à travers une combinaison des techniques RC et massive MIMO, cette approche constitue s'établit comme une solution à la progression exponentielle du trafic.

The global shortage of microwave bandwidth has become a critical issue that may inhibit the growth of mobile networks needing to support content-rich applications. For this reason, the underutilized millimeter wave (mmWave) spectrum has attracted significant attention as a medium to support next-generation mobile. Although this spectrum has an abundance of available bandwidth, mmWave wave frequencies also have propagation characteristics that make digital communication very challenging. Due to the signals atmospheric, reflection, and penetration losses, this spectrum suffers from much greater attenuation compared to microwave signals. To overcome these losses, mmWave systems will need to be equipped with large antenna arrays to enable directionality gains through beamforming. Due to the reduced wavelength of mmWave signals, large arrays can be packed into a small area and are therefore suitable for consumer electronics. However, by simply adopting conventional multiple-input multiple-output (MIMO) electronics with high-rate digital components tied to each antenna, the resulting power drain becomes unpractical for portable devices. To reduce hardware cost, complexity, and power consumption, constrained hardware architectures have been proposed for use in mmWave mobile systems. These consist of a small number of RF chains that are tied to the array of antennas through a network of phase shifters. In these architectures the role of beamforming is split across both the analog and the digital domains, which can make the task of channel estimation difficult and time-consuming. Furthermore, due to heavy signal losses, pilot signals will also need to be beamformed in order to get a clear estimate of the channel. In this thesis, we consider this problem of mmWave channel estimation for a wide range of deployment topologies including; point-to-point, multi-user, and multi-cellular. .

Les futurs systèmes de communication sans fil devront utiliser des architectures cellulaires hétérogènes composées de grandes cellules (macro) plus performantes et de petites cellules (femto, micro, ou pico) très denses, afin de soutenir la demande de débit en augmentation exponentielle au niveau de la couche physique. Ces structures provoquent un niveau d'interférence sans précèdent à l'intérieur, comme à l'extérieur des cellules, qui doit être atténué ou, idéalement, exploité afin d'améliorer l'efficacité spectrale globale du réseau. Des techniques comme le MIMO à grande échelle (dit massive MIMO), la coopération, etc., qui contribuent aussi à la gestion des interférences, vont encore augmenter la taille des grandes architectures hétérogènes, qui échappent ainsi à toute possibilité d'analyse théorique par des techniques statistiques traditionnelles.Par conséquent, dans cette thèse, nous allons appliquer et améliorer des résultats connus de la théorie des matrices aléatoires à grande échelle (RMT) afin d'analyser le problème d'interférence et de proposer de nouveaux systèmes de précodage qui s'appuient sur les résultats acquis par l'analyse du système à grande échelle. Nous allons d'abord proposer et analyser une nouvelle famille de précodeurs qui réduit la complexité de calcul de précodage pour les stations de base équipées d'un grand nombre d'antennes, tout en conservant la plupart des capacités d'atténuation d'interférence de l'approche classique et le caractère quasi-optimal du précodeur regularised zero forcing. Dans un deuxième temps, nous allons proposer une variation de la structure de précodage linéaire optimal (obtenue pour de nombreuses mesures de performance) qui permet de réduire le niveau d'interférence induit aux autres cellules. Ceci permet aux petites cellules d'atténuer efficacement les interférences induites et reçues au moyen d'une coopération minimale. Afin de faciliter l'utilisation de l'approche analytique RMT pour les futures générations de chercheurs, nous fournissons également un tutoriel exhaustif sur l'application pratique de la RMT pour les problèmes de communication en début du manuscrit
Future wireless communication systems will need to feature multi cellular heterogeneous architectures consisting of improved macro cells and very dense small cells, in order to support the exponentially rising demand for physical layer throughput. Such structures cause unprecedented levels of inter and intra cell interference, which needs to be mitigated or, ideally, exploited in order to improve overall spectral efficiency of the communication network. Techniques like massive multiple input multiple output (MIMO), cooperation, etc., that also help with interference management, will increase the size of the already large heterogeneous architectures to truly enormous networks, that defy theoretical analysis via traditional statistical methods.Accordingly, in this thesis we will apply and improve the already known framework of large random matrix theory (RMT) to analyse the interference problem and propose solutions centred around new precoding schemes, which rely on large system analysis based insights. First, we will propose and analyse a new family of precoding schemes that reduce the computational precoding complexity of base stations equipped with a large number of antennas, while maintaining most of the interference mitigation capabilities of conventional close-to-optimal regularized zero forcing. Second, we will propose an interference aware linear precoder, based on an intuitive trade-off and recent results on multi cell regularized zero forcing, that allows small cells to effectively mitigate induced interference with minimal cooperation. In order to facilitate utilization of the analytic RMT approach for future generations of interested researchers, we will also provide a comprehensive tutorial on the practical application of RMT in communication problems

Multi-user MIMO (MIMO-MU) communication techniques make use of available channel state information at the transmitter to mitigate the inter-user interference. The goal of these techniques is to provide the least interference at the mobile stations by applying a precoding operation. In this thesis a comparison of available techniques in the literature such as Channel Decomposition, SINR Balancing, Joint-MMSE optimization is presented. Novel techniques for the MIMO multi-user downlink communication systems, where a single stream is transmitted to each user are proposed. The proposed methods, different from the other methods in the literature, use a simple receiver to combat the interference. It has been shown that MRC based receivers are as good as more complicated joint MMSE receivers.

Multiple-input multiple-output (MIMO) networks are known to be able to achieve throughput performance superior to that available from single-input single-output (SISO) systems. However, when applying MIMO in multi-user networks, achieving this throughput advantage requires efficient precoding and optimal network scheduling. Furthermore, MIMO radios can help ensure security in a multi-user network. Previous work has proposed various precoding techniques for the MIMO broadcast channel, based either on channel state information (CSI) or channel distribution information (CDI), which achieve optimal or near- optimal MIMO channel throughput. The performance of these techniques largely depends on the availability of the channel information at the transmitter that must be fed back from the receiver. However, the past work has not examined the impact of latency caused by feedback of channel information and computation. This research proposes a performance metric to measure the throughput degradation caused by compression and feedback of channel information. We further propose an effective data compression technique based on the Karhunen-Lo`eve (KL) Transform and show that linear precoding (beamforming) based on CDI can achieve superior performance by providing stable channel throughput in both time- varying and frequency-selective channels. Very little prior work exists on optimal scheduling for multi-user MIMO networks, particularly in time-varying channels. One reason for this is that hybrid MIMO channels permit much more complex channel structures, such as broadcast channel (BC) and multiple access channel (MAC), whose capacity is limited not only by random channel noise but also by the multi-user interference. Furthermore, the achieved MIMO channel throughput depends on the spatial characteristics of the multi-user channels, a feature not captured by traditional network models based on signal-to-noise ratio and Doppler. Therefore, achieving near optimal performance requires development of scheduling techniques that depend on detailed channel characteristics. This dissertation proposes a novel parametric representation of the channel that simply describes the complex multi-user MIMO channels and allows for efficient scheduling. Because of the computational and feedback efficiency enabled by this parametric approach, it achieves low latency and therefore excellent performance.Finally, in any network setting, security is an important consideration. Specifically authentication ensures that unauthorized users do not gain network access. Unfortunately, user identity can be relatively easy to forge. This work therefore explores the user of radio- metric fingerprinting that uniquely identifies a device by unique imperfections in its transmitted waveform. This work shows that by applying this fingerprinting technique to MIMO devices, authentication reliability can be dramatically improved. The work also develops an information-theoretic approach to identify the optimal set of radiometric features to use for authentication and further considers the impact of drift in radiometric features on authentication performance.

Thesis (Ph. D.) -- University of Maryland, College Park, 2008.
Thesis research directed by: Dept. of Electrical and Computer Engineering . Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

To meet the very high data rate requirements for wireless Internet and multimedia services, cooperative systems with multiple antennas have been proposed for future generation wireless systems. In this thesis, we focus on multiple antennas at the source, relay and destination. We study both downlink and uplink cooperative systems with single antenna relays. For downlink systems, the optimal precoder to minimize the sum transmit power subject to quality of service (QoS) constraints with fixed relay weights is derived. We also study the optimization of relay weights with a fixed precoder. An iterative algorithm is developed to jointly optimize the precoder and relay weights. The performance of the downlink system with imperfect CSI as well as multiple receive antennas is also studied. For the uplink system, we similarly derive the optimum receiver as in the downlink with fixed relay weights. The optimization of relay weights for a fixed receiver is then studied. An iterative algorithm is developed to jointly optimize the receiver and relay weights in the uplink. Systems with imperfect channel estimation are also considered. The study of cooperative MIMO systems is then extended to a multi-cell scenario. In particular, two scenarios are studied. In the first, the cells coordinate their beamformers to find the most suitable cell to serve a specific user. In the second, each base station selectively transmits to a fixed group of users, and the cells coordinate to suppress mutual interference. Finally, our investigation culminates with a study of an uplink cooperative system equipped with multi-antenna relays under a capacity maximization criterion. The specific scheme that users access the base station through a single multi-antenna relay are studied. Iterative capacity maximization algorithm are proposed and shown to converge to local maxima. Numerical results are presented to highlight that the algorithms are able to come close to these bounds after only a few iterations.
Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2013-06-25 15:43:23.343

碩士
國立中正大學
通訊工程研究所
106
With the rapid development of communication technologies, the 4th generation (4G) system has been widely deployed. Due to the increase of networking devices, 4G networks will become more and more difficult to offer such a heavy data traffic from massive devices. The future 5th generation (5G) system will be able to improve system capacity in the same cell. In a small area with a large number of networked devices, the base station can not serve all of the devices at the same time due to large interference between signals of different users. To solve this problem, these devices must be properly grouped, and only users in the same group can be transmitted simultaneously. The users in different groups are transmit in different time slots to avoid interference. In this way, the mutual influence between the devices can be well controlled. In this paper, the problem of mutual interference is transformed to a graph coloring problem. Base on graph coloring, two algorithms are proposed. Simulation results show that the new methods have much better performance levels than that of the conventional method.

碩士
國立交通大學
電信工程研究所
100
In multi-user MIMO channel downlink transmission, the base station sums the data for each user and then transmits. Although transmitting data simultaneously to multiple users can increase channel capacity, every user would receive the data for him as well as data for others, which is co-channel interference. In order to cancel the co-channel interference previously, the base station precodes the data before transmitting. As a result, every user can receive data intended for him correctly with interference as little as possible. Besides, when total receiving antennas are more than the transmitting antennas, the base station can use the precoder to select a group of users that maximizes the channel capacity. In recent years, a number of precoder designing solutions have been proposed. For MU-MISO channel, we introduce some existing precoder designing solutions and discuss the concept of the process, computation complexity and so on. Since PU2RC and JTRUS have worse performance at channel capacity, we improve the two solutions by performing second time user scheduling. We make the tradeoff between interference and capacity to find a threshold value for base station to decide whether or not to add additional receiver. For MU-MIMO channel, we introduce some existing precoder designing solution and compare their computation complexity, form of precoder, achievable capacity and so on.

碩士
國立中正大學
通訊工程研究所
104
Since the radio spectrum is a finite and precious resource, the spectrum arrangement for multi-user MIMO (MU-MIMO) wireless networks is an important problem. In this paper, we propose two complexity user pairing strategies for MU-MIMO downlink scenario. The goal of sum rate user selection strategy is to select users which have the maximum sum of data rate in certain frequency resources to enhance system throughput. This problem has been shown to be an NP-hard problem, since for any given users, to find the optimum precoding matrices with maximal throughput is essentially an NP-hard problem. 　　Therefore, we attempt to design a low-complexity algorithm to find an appropriate of users under multi-channel scenario. The user selection problem and the design of precoding matrix are treated separately, which makes the problem easier. Simulation results show that the proposed algorithm achieves slightly inferior performance than conventional one but with lower complexity.

Submitted in fulfilment of the academic requirements for the degree of Master of Science (Msc) in Engineering, in the School of Electrical and Information Engineering (EIE), Faculty of Engineering and the Built Environment, at the University of the Witwatersrand, Johannesburg, South Africa, 2017
The benefits of massive Multiple-Input Multiple-Output (MIMO) systems have made it a solution for future wireless networking demands. The increase in the number of base station antennas in massive MIMO systems results in an increase in capacity. The throughput increases linearly with an increase in number of antennas. To reap all the benefits of massive MIMO, resources should be allocated optimally amongst users. A lot of factors have to be taken into consideration in resource allocation in multi-cell massive MIMO systems (e.g. intra-cell, inter-cell interference, large scale fading etc.) This dissertation investigates user selection and power allocation algorithms in multi-cell massive MIMO systems. The focus is on designing algorithms that maximizes a particular cell of interest’s sum rate capacity taking into consideration the interference from other cells. To maximize the sum-rate capacity there is need to optimally allocate power and select the optimal number of users who should be scheduled. Global interference coordination has very high complexity and is infeasible in large networks. This dissertation extends previous work and proposes suboptimal per cell resource allocation models that are feasible in practice. The interference is introduced when non-orthogonal pilots are used for channel estimation, resulting in pilot contamination. Resource allocation values from interfering cells are unknown in per cell resource allocation models, hence the inter-cell interference has to be modelled. To tackle the problem sum-rate expressions are derived to enable power allocation and user selection algorithm analysis. The dissertation proposes three different approaches for solving resource allocation problems in multi-cell multi-user massive MIMO systems for a particular cell of interest. The first approach proposes a branch and bound algorithm (BnB algorithm) which models the inter-cell interference in terms of the intra-cell interference by assuming that the statistical properties of the intra-cell interference in the cell of interest are the same as in the other interfering cells. The inter-cell interference is therefore expressed in terms of the intra-cell interference multiplied by a correction factor. The correction factor takes into consideration pilot sequences used in the interfering cells in relation to pilot sequences used in the cell of interest and large scale fading between the users in the interfering cells and the users in the cell of interest. The resource allocation problem is modelled as a mixed integer programming problem. The problem is NP-hard and cannot be solved in polynomial time. To solve the problem it is converted into a convex optimization problem by relaxing the user selection constraint. Dual decomposition is used to solve the problem. In the second approach (two stage algorithm) a mathematical model is proposed for maximum user scheduling in each cell. The scheduled users are then optimally allocated power using the multilevel water filling approach. Finally a hybrid algorithm is proposed which combines the two approaches described above. Generally in the hybrid algorithm the cell of interest allocates resources in the interfering cells using the two stage algorithm to obtain near optimal resource allocation values. The cell of interest then uses these near optimal values to perform its own resource allocation using the BnB algorithm. The two stage algorithm is chosen for resource allocation in the interfering cells because it has a much lower complexity compared to the BnB algorithm. The BnB algorithm is chosen for resource allocation in the cell of interest because it gives higher sum rate in a sum rate maximization problem than the two stage algorithm. Performance analysis and evaluation of the developed algorithms have been presented mainly through extensive simulations. The designed algorithms have also been compared to existing solutions. In general the presented results demonstrate that the proposed algorithms perform better than the existing solutions.
XL2018

碩士
國立交通大學
電信工程研究所
107
Successive zero-forcing DPC (SZFDPC) combines DPC and zero-forcing technologies. However, the null space constraint limits on the number of users that can be supported simultaneously. In the past researches, the way of user selection made sum rate capacity restricted. In this correspondence, we consider the problem of user and antenna selection of SZFDPC for multiuser MIMO (MU-MIMO) broadcast channel (BC). Make choices for the users and antennas simultaneously, no longer treat all antennas in a user as one unit. We develop three antenna and user scheduling algorithms to maximize the sum rate capacity of MU-MIMO systems. At each iteration of the scheduling process, one antenna is selected based on a selection criterion. The first algorithm selects the selection set with the maximum sum rate of ZFDPC. If they can cooperate, the corresponding sum rate will be recalculated. The second algorithm selects the selection set with the maximum sum rate of SZFDPC. The final algorithm uses Householder transform instead of QR decomposition and select the antennas and users. Simulation results demonstrate that the second algorithm achieves a better performance at a low signal-to-noise (SNR) or small number of users, and the capacity-based algorithm achieves performance very close at a high SNR or large number of users. However, at SNR$=10 \:\mathrm{dB}$ the difference in performance between capacity-based algorithm and the algorithm which treats each antenna as a independent user is less than 0.6 bps/Hz. For this reason, considering the amount of computation, at a large number of users, it is recommended to treat each antenna as a different user.

碩士
國立交通大學
電子工程學系 電子研究所
104
For the past twenty years, multiple-input multiple-output (MIMO) had been widely researched. From point to point (P2P) to multi-user MIMO (MU-MIMO), the user terminals (UTs) can share the same resource block, but cause inter-antenna interference (IAI) and multi-user interference (MUI). In order to resolve influence of interference in multi-user communication systems, the base station and users have to design precoding and decoding scheme. Block Diagonalization (BD) is a well-known algorithm in past research which has two structure precoding process. In the first stage precoding design, it guarantees zero MUI. In the second stage, it separates the desired signal of target users into sub-channels, and designs demodulation matrix to users. Although this structure can get some of benefits in transmit scheme, but problems resist. First, design process does not consider noise, so the performance will poor in low SNR region. Second, high computational complexity causes hardware burden. Third, base station has to use extra bandwidth to transmit demodulation matrix or users joint design. Both methods cause communication overhead. Focus on the drawbacks of BD, we combine the square root algorithm into design process which can consider noise into design process to improve performance in low SNR region and use the LQ decomposition replace SVD operation to reduce computational complexity. Finally, we modify second stage precoding design of BD which can retard communication overhead in original BD algorithm.

The idea of utilizing multiple antennas (MIMO) has emerged as one of the significant breakthroughs in modern wireless communications. MIMO techniques can improve the spectral efficiency of wireless systems and provide significant throughput gains. As such, MIMO will be increasingly deployed in future wireless systems. On the other hand, in order to meet the increasing demand for high data rate multimedia wireless services, future wireless systems are evolving towards universal frequency reuse, where neighboring cells may utilize the same radio spectrum. As such, the performance of future wireless systems will be mainly limited by inter-cell interference (ICI). It has been shown that the throughput gains promised by conventional MIMO techniques degrade severely in multi-cell systems. This definitely attributes to the existence of the ICI. A lot of related work has been performed on the ICI mitigation or cancellation strategies, in multi-cell MIMO systems. Most of them assume that the channel and even data information is available at the collaborating base stations (BSs). Different from the previous work, we are looking into certain low-complexity codebook-based multi-cell multi-user MIMO strategies. For most of our work, we derive the statistics of the selected user's signal-to-interference-and-noise-ratio (SINR), which enable us to calculate the achieved sum-rate accurately and e ciently. With the derived sum-rate expressions, we evaluate and compare the sum-rate performance for several proposed low-complexity ICI-mitigation systems with various system parameters for single-user per-cell scheduling case. Furthermore, in order to fully exploit spatial multiplexing gain, we are considering multi-user per-cell scheduling case. Based on the assumption that all CSI including intra-cell and inter-cell channels are available at each BS, we rstly look into the centralized optimization approach. Typically, since the sum-rate maximization problem is mostly non-convex, it is generally di cult to obtain the globally optimum solution. Through certain approximation and relaxations, we successfully investigate an iterative optimization algorithm which exploits the second-order cone programming (SOCP) approach. From the simulation results, we will observe that the iterative option can provide near-optimum sum capacity, although only locally optimized. Afterwards, inspired by the successful application of Per-User Unitary Rate Control (PU2RC) scheme, we manage to extend it into dual-cell environment, with limited coordination between two cells.
Graduate

碩士
國立中正大學
通訊工程研究所
99
Since the radio spectrum is a finite and precious resource, the spectrum arrangement for multi-user MIMO (MU-MIMO) wireless networks is a well discussed problem. User pairing can be considered as a kind of spectrum arrangement. Employing the pairing schemes appropriately can improve the system throughput significantly and facilitate effective use of radio spectrum. In this paper, we propose two complexity user pairing strategies for MU-MIMO downlink scenario. The goal of sum rate pairing strategy is selecting two users which have the maximum sum of data rate in certain frequency resources to enhance system throughput. However, this pairing strategy needs to calculate the precoding matrices before pairing, regardless of the level of the complexity of calculating the precoding matrices. We propose a low-complexity eigenvalue pairing strategy based on eigenvalues of function of channel state information (CSI) without regard of precoding matrices. Simulation results show that the algorithm has significantly low complexity and provides performance that is very close to the sum rate pairing strategy.We propose a new linear precoding scheme, Gradient precoding. It iteratively takes the partial derivative of sum-rate with respect of precoding matrix until obtaining a convergent solution. It performs better than other linear precoding schemes, in spite of the higher complexity.

碩士
國立中央大學
通訊工程學系
102
With the development of multimedia applications and mobile broadband technology network, bandwidth demand is much more higher than before, it causes frequency efficiency higher and higher. Actually, high-speed downlink/uplink transmission in 4G wireless system has been one of basic requirement. Spatial-Division Multiple Access(SDMA) is one of the solutions to improve frequency efficiency; Multi-User Multi-Input Multi-Output(MU-MIMO) is one the application of SDMA. In the paper, we proposed a single-cell scheduling considering both channel quality and fairness that improve the performance and fairness when scheduler selects UE pair. Existing paper which discuss about proportional fair MU-MIMO is only about two UE pair. For proposed algorithm in this paper, there is no limitation of the UE number in pair, besides we further discuss about LTE codebook and ZF precoding and give some comparison in simulation result.

Employment of the multiple-antenna transmitters/receivers in communication systems is known as a promising solution to provide high-data-rate wireless links. In the multi-user environments, the problems of signaling and fairness for multi-antenna systems have emerged as challenging problems. This dissertation deals with these problems in several multi-antenna multi-user scenarios. In part one, a simple signaling method for the multi-antenna broadcast channels is proposed. This method reduces the MIMO broadcast system to a set of parallel channels. The proposed scheme has several desirable features in terms of: (i) accommodating users with different number of receive antennas, (ii) exploiting multi-user diversity, and (iii) requiring low feedback rate. The simulation results and analytical evaluations indicate that the achieved sum-rate is close to the sum-capacity of the underlying broadcast channel. In part two, for multiple-antenna systems with two transmitters and two receivers, a new non-cooperative scenario of data communication is studied in which each receiver receives data from both transmitters. For such a scenario, a signaling scheme is proposed which decomposes the system into two broadcast or two multi-access sub-channels. Using the decomposition scheme, it is shown that this signaling scenario outperforms the other known non-cooperative schemes in terms of the achievable multiplexing gain. In particular for some special cases, the achieved multiplexing gain is the same as the multiplexing gain of the system, where the full cooperation is provided between the transmitters and/or between the receivers. Part three investigates the problem of fairness for a class of systems for which a subset of the capacity region, which includes the sum-capacity facets, forms a polymatroid structure. The main purpose is to find a point on the sum-capacity facet which satisfies a notion of fairness among active users. This problem is addressed in the cases where the complexity of achieving interior points is not feasible, and where the complexity of achieving interior points is feasible. In part four, $K$-user memoryless interference channels are considered; where each receiver sequentially decodes the data of a subset of transmitters before it decodes the data of the designated transmitter. A greedy algorithm is developed to find the users which are decoded at each receiver and the corresponding decoding order such that the minimum rate of the users is maximized. It is proven that the proposed algorithm is optimal. The results of the parts three and four are presented for general channels which include the multiple-antenna systems as special cases.