General Rank Multiuser Downlink Beamforming With Shaping Constraints Using Real-valued OSTBC

In this paper we consider optimal multiuser downlink beamforming in the presence of a massive number of arbitrary quadratic shaping constraints. We combine beamforming with full-rate high dimensional real-valued orthogonal space time block coding (OSTBC) to increase the number of beamforming weight vectors and associated degrees of freedom in the beamformer design. The original multi-constraint beamforming problem is converted into a convex optimization problem using semidefinite relaxation (SDR) which can be solved efficiently. In contrast to conventional (rank-one) beamforming approaches in which an optimal beamforming solution can be obtained only when the SDR solution (after rank reduction) exhibits the rank-one property, in our approach optimality is guaranteed when a rank of eight is not exceeded. We show that our approach can incorporate up to 79 additional shaping constraints for which an optimal beamforming solution is guaranteed as compared to a maximum of two additional constraints that bound the conventional rank-one downlink beamforming designs. Simulation results demonstrate the flexibility of our proposed beamformer design

High Data Rate Wireless Communication Using MIMO

Wireless communication is the most popular and rapidly growing sector of the commu-nication industry. The permitted bandwidth for every service is very limited and the demand of data transferring is increasing day by day. Moreover, the channels are further limited by multipath and fading. Hence, it is a big challenge to provide excellent quality of service and meet the growing demand with the existing bandwidth limitation. MIMO is one very promising technique to enhance the data rate. Fading has been considered as problem for high quality with low outage wireless com-munication. However, multiple-input multiple-output (MIMO) antenna has used this fading phenomenon not only to mitigate the fading but also to exploit this fading to obtain high data rate through spatial multiplexing. In this thesis, MIMO spatial multiplexing has been studied in details. Different MIMO channel models, space time coding, and channel capacity constraints as well as the fac-tors those limits the capacity are studied. One major aim of this study is to find a com-bined optimal solution for MIMO system so that it could provide high rate data transfer.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

The Multi-Input Multi-Output (MIMO) Channel Modeling, Simulation and Applications

This thesis mainly focus on the Multi-Input Multi-Output (MIMO) channel modeling, simulation and applications. There are several ways to design a MIMO channel. Most of the examples are given in Chapter 2, where we can design channels based on the environments and also based on other conditions. One of the new MIMO channel designs based on physical and virtual channel design is discussed in Unitary-Independent- Unitary (UIU) channel modeling. For completeness, the different types of capacity are discussed in details. The capacity is very important in wireless communication. By understanding the details behind different capacity, we can improve our transmission efficiently and effectively. The level crossing rate and average duration are discussed.One of the most important topics in MIMO wireless communication is estimation. Without having the right estimation in channel prediction, the performance will not be correct. The channel estimation error on the performance of the Alamouti code was discussed. The design of the transmitter, the channel and the receiver for this system model is shown. The two different types of decoding scheme were shown - the linear combining scheme and the Maximum likelihood (ML) decoder. Once the reader understands the estimation of the MIMO channel, the estimation based on different antenna correlation is discussed. Next, the model for Mobile-to-Mobile (M2M) MIMO communication link is proposed. The old M2M Sum-of-Sinusoids simulation model and the new two ring models are discussed. As the last step, the fading channel modeling using AR model is derived and the effect of ill-conditioning of the Yule-Walker equation is also shown. A number of applications is presented to show how the performance can be evaluated using the proposed model and techniques

Multiple-Input Multiple-Output Communications Systems Using Reconfigurable Antennas

RÉSUMÉ Depuis les années 1990, l'utilisation des systèmes de communications sans-fil à entrées multiples-sorties multiples (MIMO) a été introduit pour fournir des transmissions fiables à grande vitesse. Cette thèse porte sur l'application et l’étude des systèmes MIMO avec des antennes reconfigurables, qui sont ajustable électroniquement pour produire différents diagrammes de rayonnement d'un seul élément d'antenne et ainsi offrir une diversité de diagrammes de rayonnement. En particulier, nous étudions le comportement de la capacité de canal des systèmes MIMO à sélection de diagrammes de rayonnement (PS-MIMO), et nous proposons aussi des algorithmes de sélection du diagramme de rayonnement atteignant la capacité maximale. Tout d'abord, nous étudions l'application des antennes reconfigurables dans l'estimation des statistiques spatiales à long terme de canaux spatiaux avec grappes de multi-trajets (cluster). Nous proposons un estimateur de spectre de type Capon et une technique d'adaptation de la covariance (COMET) pour estimer conjointement l'angle moyen et l’étalement angulaire de la grappe spatiale avec des antennes reconfigurables. En second lieu, sur la base des statistiques à long terme du canal MIMO, nous proposons des algorithmes de sélection de diagramme de rayonnement MIMO (SPS-MIMO) pour atteindre la capacité maximale de canal ergodique. L'analyse de la maximisation de la capacité ergodique du système SPS-MIMO indique que le modèle statistique de sélection fournit des gains supplémentaires en améliorant la puissance du signal reçu et en décorrélant les signaux reçus avec différents diagrammes de rayonnement directionnels. Troisièmement, nous nous concentrons sur le modèle de sélection instantanée des diagrammes de rayonnement MIMO (IPS-MIMO) basé sur des informations instantanées d'état de canal (CSI) afin de maximiser la capacité instantanée pour chaque réalisation de canal. Nous démontrons que l’ordre de diversité des systèmes MIMO peut être multipliée par le nombre de diagrammes de rayonnement avec sélection de diagramme instantanée. Afin d'évaluer la capacité moyenne de l'IPS-MIMO, nous proposons un nouvel algorithme qui permet d’approximer étroitement la moyenne de la valeur maximale de la capacité du canal MIMO avec des trajets arbitrairement corrélés. Nous proposons également un algorithme pour sélectionner instantanément les diagrammes de rayonnement pour atteindre la capacité moyenne. En outre, sur la base d'une simple expression en forme fermée de la capacité coefficient de corrélation, nous sommes en mesure de proposer un algorithme de sélection de sous-ensemble de diagrammes qui offre un compromis entre performances et la complexité de l’algorithme de sélection. En conclusion, des gains de performance importants peuvent être obtenus grâce à la combinaison de l'utilisation d’antennes reconfigurables et de systèmes MIMO avec soit des algorithmes de sélection de diagramme de rayonnement statistique ou instantanée. La capacité des systèmes PS-MIMO à améliorer les performances du système, y compris la capacité et de l'ordre de la diversité, est démontrée par l'analyse théorique et des simulations numériques.----------ABSTRACT Since the 1990s, the use of multiple-input multiple-output (MIMO) systems has been introduced to modern wireless communications to provide reliable transmission at high data rates. This thesis focuses on the application of MIMO systems with reconfigurable antennas, which are electronically tunable to produce a number of radiation patterns at a single antenna element and provide pattern diversity. In particular, we investigate the capacity performance of the pattern selection MIMO (PS-MIMO) systems, and we also present maximum capacity achieving algorithms for radiation pattern selection. First, we investigate the application of reconfigurable antennas in estimating long term spatial statistics of spatial clustered channels. We propose a Capon-like spectrum estimator and a covariance matching technique (COMET) to jointly estimate the mean angle and the angular spread of the spatial cluster with reconfigurable antennas. Second, based on the long term statistics of the MIMO channel, we propose statistical pattern selection MIMO (SPS-MIMO) algorithms to achieve maximum ergodic channel capacity. Analysis of the ergodic capacity maximization of the SPS-MIMO indicates that the statistical pattern selection provides additional gains by enhancing received signal power and decorrelating received signals with different directional radiation patterns. Third, we focus on the instantaneous pattern selection MIMO (IPS-MIMO) based on instantaneous channel state information (CSI) in order to maximize the instantaneous capacity for every channel realization. We prove that the diversity order of MIMO systems can be multiplied by the number of radiation patterns with instantaneous pattern selection. In order to evaluate the mean capacity of the IPS-MIMO, we propose a novel algorithm which closely approximates the mean of the maximum of the channel capacity of arbitrarily correlated MIMO channels. We also propose an algorithm for instantaneously selecting radiation patterns to achieve the mean capacity. In addition, based on a simple closed-form approximation to the capacity correlation coefficient, we are able to propose a subset pattern selection algorithm which enables the trade-off between performances and complexity. In conclusion, important extra gains can be obtained as a result of combining the use of reconfigurable antennas and MIMO systems with either statistical or instantaneous radiation pattern selection. The capability of the PS-MIMO to improve system performances, including capacity and diversity order, is demonstrated through theoretical analysis and numerical simulations

Distributed Quasi-Orthogonal Space-Time coding in wireless cooperative relay networks

Cooperative diversity provides a new paradigm in robust wireless re- lay networks that leverages Space-Time (ST) processing techniques to combat the effects of fading. Distributing the encoding over multiple relays that potentially observe uncorrelated channels to a destination terminal has demonstrated promising results in extending range, data- rates and transmit power utilization. Specifically, Space Time Block Codes (STBCs) based on orthogonal designs have proven extremely popular at exploiting spatial diversity through simple distributed pro- cessing without channel knowledge at the relaying terminals. This thesis aims at extending further the extensive design and analysis in relay networks based on orthogonal designs in the context of Quasi- Orthogonal Space Time Block Codes (QOSTBCs). The characterization of Quasi-Orthogonal MIMO channels for cooper- ative networks is performed under Ergodic and Non-Ergodic channel conditions. Specific to cooperative diversity, the sub-channels are as- sumed to observe different shadowing conditions as opposed to the traditional co-located communication system. Under Ergodic chan- nel assumptions novel closed-form solutions for cooperative channel capacity under the constraint of distributed-QOSTBC processing are presented. This analysis is extended to yield closed-form approx- imate expressions and their utility is verified through simulations. The effective use of partial feedback to orthogonalize the QOSTBC is examined and significant gains under specific channel conditions are demonstrated. Distributed systems cooperating over the network introduce chal- lenges in synchronization. Without extensive network management it is difficult to synchronize all the nodes participating in the relaying between source and destination terminals. Based on QOSTBC tech- niques simple encoding strategies are introduced that provide compa- rable throughput to schemes under synchronous conditions with neg- ligible overhead in processing throughout the protocol. Both mutli- carrier and single-carrier schemes are developed to enable the flexi- bility to limit Peak-to-Average-Power-Ratio (PAPR) and reduce the Radio Frequency (RF) requirements of the relaying terminals. The insights gained in asynchronous design in flat-fading cooperative channels are then extended to broadband networks over frequency- selective channels where the novel application of QOSTBCs are used in distributed-Space-Time-Frequency (STF) coding. Specifically, cod- ing schemes are presented that extract both spatial and mutli-path diversity offered by the cooperative Multiple-Input Multiple-Output (MIMO) channel. To provide maximum flexibility the proposed schemes are adapted to facilitate both Decode-and-Forward (DF) and Amplify- and-Forward (AF) relaying. In-depth Pairwise-Error-Probability (PEP) analysis provides distinct design specifications which tailor the distributed- STF code to maximize the diversity and coding gain offered under the DF and AF protocols. Numerical simulation are used extensively to confirm the validity of the proposed cooperative schemes. The analytical and numerical re- sults demonstrate the effective use of QOSTBC over orthogonal tech- niques in a wide range of channel conditions

The optimization of multiple antenna broadband wireless communications. A study of propagation, space-time coding and spatial envelope correlation in Multiple Input, Multiple Output radio systems

This work concentrates on the application of diversity techniques and space time block coding for future mobile wireless communications. The initial system analysis employs a space-time coded OFDM transmitter over a multipath Rayleigh channel, and a receiver which uses a selection combining diversity technique. The performance of this combined scenario is characterised in terms of the bit error rate and throughput. A novel four element QOSTBC scheme is introduced, it is created by reforming the detection matrix of the original QOSTBC scheme, for which an orthogonal channel matrix is derived. This results in a computationally less complex linear decoding scheme as compared with the original QOSTBC. Space time coding schemes for three, four and eight transmitters were also derived using a Hadamard matrix. The practical optimization of multi-antenna networks is studied for realistic indoor and mixed propagation scenarios. The starting point is a detailed analysis of the throughput and field strength distributions for a commercial dual band 802.11n MIMO radio operating indoors in a variety of line of sight and non-line of sight scenarios. The physical model of the space is based on architectural schematics, and realistic propagation data for the construction materials. The modelling is then extended and generalized to a multi-storey indoor environment, and a large mixed site for indoor and outdoor channels based on the Bradford University campus. The implications for the physical layer are also explored through the specification of antenna envelope correlation coefficients. Initially this is for an antenna module configuration with two independent antennas in close proximity. An operational method is proposed using the scattering parameters of the system and which incorporates the intrinsic power losses of the radiating elements. The method is extended to estimate the envelope correlation coefficient for any two elements in a general (N,N) MIMO antenna array. Three examples are presented to validate this technique, and very close agreement is shown to exist between this method and the full electromagnetic analysis using the far field antenna radiation patterns

Signal processing techniques for mobile multimedia systems

Recent trends in wireless communication systems show a significant demand for the delivery of multimedia services and applications over mobile networks - mobile multimedia - like video telephony, multimedia messaging, mobile gaming, interactive and streaming video, etc. However, despite the ongoing development of key communication technologies that support these applications, the communication resources and bandwidth available to wireless/mobile radio systems are often severely limited. It is well known, that these bottlenecks are inherently due to the processing capabilities of mobile transmission systems, and the time-varying nature of wireless channel conditions and propagation environments. Therefore, new ways of processing and transmitting multimedia data over mobile radio channels have become essential which is the principal focus of this thesis. In this work, the performance and suitability of various signal processing techniques and transmission strategies in the application of multimedia data over wireless/mobile radio links are investigated. The proposed transmission systems for multimedia communication employ different data encoding schemes which include source coding in the wavelet domain, transmit diversity coding (space-time coding), and adaptive antenna beamforming (eigenbeamforming). By integrating these techniques into a robust communication system, the quality (SNR, etc) of multimedia signals received on mobile devices is maximised while mitigating the fast fading and multi-path effects of mobile channels. To support the transmission of high data-rate multimedia applications, a well known multi-carrier transmission technology known as Orthogonal Frequency Division Multiplexing (OFDM) has been implemented. As shown in this study, this results in significant performance gains when combined with other signal-processing techniques such as spa ce-time block coding (STBC). To optimise signal transmission, a novel unequal adaptive modulation scheme for the communication of multimedia data over MIMO-OFDM systems has been proposed. In this system, discrete wavelet transform/subband coding is used to compress data into their respective low-frequency and high-frequency components. Unlike traditional methods, however, data representing the low-frequency data are processed and modulated separately as they are more sensitive to the distortion effects of mobile radio channels. To make use of a desirable subchannel state, such that the quality (SNR) of the multimedia data recovered at the receiver is optimized, we employ a lookup matrix-adaptive bit and power allocation (LM-ABPA) algorithm. Apart from improving the spectral efficiency of OFDM, the modified LM-ABPA scheme, sorts and allocates subcarriers with the highest SNR to low-frequency data and the remaining to the least important data. To maintain a target system SNR, the LM-ABPA loading scheme assigns appropriate signal constella tion sizes and transmit power levels (modulation type) across all subcarriers and is adapted to the varying channel conditions such that the average system error-rate (SER/BER) is minimised. When configured for a constant data-rate load, simulation results show significant performance gains over non-adaptive systems. In addition to the above studies, the simulation framework developed in this work is applied to investigate the performance of other signal processing techniques for multimedia communication such as blind channel equalization, and to examine the effectiveness of a secure communication system based on a logistic chaotic generator (LCG) for chaos shift-keying (CSK)

Efficient Signal, Code, and Receiver Designs for MIMO Communication Systems

Thesis Supervisor: Gregory W. Wornell Title: ProfessorThe so-called diversity-multiplexing tradeoff characterizes the fundamental interaction between the robustness and capacity gains obtainable from multiple-input and multiple-output (MIMO) systems in fading environments. This thesis develops practical schemes for approaching the optimal tradeoff in various delay and complexity regimes. We focus on a two-transmit and two-receive antenna system, in which the receiver has channel knowledge, but the transmitter does not. We first investigate uncoded transmission. We propose a class of lattice-reduction- aided low-complexity detectors that can achieve near maximum likelihood performance and the best diversity-multiplexing tradeoff achievable by any length-one code. We also design a family of structured space-time block codes that we call tilted- QAM codes. It achieves the optimal infinite-delay tradeoff with the necessary minimum delay of two, answering a previously open question. It uses constellation rotation ideas to effectively spread information across space and time. We identify rotation angles that are universally optimal at all rates in terms of a determinant criterion. We further develop efficient coding schemes using long error correction codes. In particular, we combine them with tilted-QAM codes using hard and soft decision decoding to obtain good performance at moderate SNR. These new systems are compared to orthogonal space-time coded systems, which we show to achieve near optimal performance at low SNR. We also examine traditional sequential versions and develop new block versions of the Bell Labs layered architecture (BLAST). While some of these can in principle reach the performance limit at all SNRs, we show they also have various practical problems. Finally, for the case where no channel knowledge is available, we present a geometric view of the signal design problem. This view reveals how training based approaches can achieve the optimal (non-coherent) diversity-multiplexing tradeNational Science Foundation Graduate Research Fellowship Program, the AT&T Labs Fellowship Program, HP through the HP/MIT Alliance, TI through the Leadership Universities Program, NSF, Army Research Laboratory under Collaborative Technology Alliance and MARCO/DARPA

Diversity Combining under Interference Correlation in Wireless Networks

A theoretical framework is developed for analyzing the performance of diversity combining under interference correlation. Stochastic models for different types of diversity combining and networks are presented and used for analysis. These models consider relevant system aspects such as network density, path loss, channel fading, number of antennas, and transmitter/receiver processing. Theoretical results are derived, performance comparisons are presented, and design insights are obtained

MIMO techniques for higher data rate wireless communications

The demand for higher data rate, higher spectral efficiency and better quality of service in wireless communications is growing fast in the past few years. However, obtaining these requirements become challenging for wireless communication systems due to the problems of channel multi-path fading, higher power loss and power bandwidth limitations. A lot of research interest has been directed towards implementing new techniques in wireless communication systems, such as MIMO an OFDM, to overcome the above mentioned problems. Methods of achieving higher data rate and better spectral efficiency have been dealt with in the thesis. The work comprised three parts; the first part focuses on channel modelling, the second looks at fading mitigation techniques, and the third part deals with adaptive transmission schemes for different diversity techniques. In the first part, we present multiple-input multiple-output (MIMO) space-time geometrical channel model with hyperbolically distributed scatterers (GBHDS) for a macro-cell mobile environment. The model is based on one-ring scattering assumption. This MIMO model provides statistics of the time of arrival (TOA) and direction of arrival (DOA). Our analytical results are validated with measurement data and compared to different geometrical based signal bounce macro-cell (GBSSBM) channel models including Gaussian scatterer density (GSD) channel model, the geometrical based exponential (GBE) channel model. On the other hand, for the same channel model we investigate the analytical methods which capture physical wave and antenna configuration at both ends representing in a matrix form. In the second part, we investigate the proposed channel model using joint frequency and spatial diversity system. . We combine STBC with OFDM to improve the error performance in the fading channels. We consider two different fading scenarios namely frequency selective and time selective fading channels. For the first scenario we propose a new technique to suppress the frequency error offset caused by the motion of mobile (Doppler shift). On the other hand, we examine the performance of STBC-OFDM in time selective macro-cell channel environment. In the last part, we evaluate the spectral efficiency for different receiver diversity namely maximal ratio combiner (MRC), selection combiner (SC), and Hybrid (MRC/SC). We derive closed form expressions for the single user capacity, taking into account the effect of imperfect channel estimation at the receiver. The channel considered is a slowly varying spatially independent flat Rayleigh fading channel. Three adaptive transmission schemes are analysed: 1) optimal power rate and rate adaptation (opra), constant power with optimal rate adaptation (ora), and 3) channel inversion with fixed rate (cifr). Furthermore, we derive analytical results for capacity statistics including moment generating function (MGF), complementary cumulative distribution function (CDF) and probability density function (pdf)