Performance analysis of channel codes in multiple antenna OFDM systems

Multiple antenna techniques are used to increase the robustness and performance of wireless networks. Multiple antenna techniques can achieve diversity and increase bandwidth efficiency when specially designed channel codes are used at the scheme’s transmitter. These channel codes can be designed in the space, time and frequency domain. These specially designed channel codes in the space and time domain are actually designed for flat fading channels and in frequency selective fading channel, their performance may be degraded. To counteract this possible performance degradation in frequency selective fading channel, two main approaches can be applied to mitigate the effect of the symbol interference due to the frequency selective fading channel. These approaches are multichannel equalisation and orthogonal frequency division multiplexing (OFDM). In this thesis, a multichannel equalisation technique and OFDM were applied to channel codes specially designed for multiple antenna systems. An optimum receiver was proposed for super-orthogonal space-time trellis codes in a multichannel equalised frequency selective environment. Although the proposed receiver had increased complexity, the diversity order is still the same as compared to the code in a flat fading channel. To take advantage of the multipath diversity possible in a frequency selective fading channel, super-orthogonal block codes were employed in an OFDM environment. A new kind of super-orthogonal block code was proposed in this thesis. Super-orthogonal space-frequency trellis-coded OFDM was proposed to take advantage of not only the possible multipath diversity but also the spatial diversity for coded OFDM schemes. Based on simulation results in this thesis, the proposed coded OFDM scheme performs better than all other coded OFDM schemes (i.e. space time trellis-coded OFDM, space-time block coded OFDM, space-frequency block coded OFDM and super-orthogonal space-time trellis-coded OFDM). A simplified channel estimation algorithm was proposed for two of the coded OFDM schemes, which form a broad-based classification of coded OFDM schemes, i.e. trelliscoded schemes and block-coded schemes. Finally in this thesis performance analysis using the Gauss Chebychev quadrature technique as a way of validating simulation results was done for super-orthogonal block coded OFDM schemes when channel state information is known and when it is estimated. The results obtained show that results obtained via simulation and analysis are asymptotic and therefore the proposed analysis technique can be use to obtain error rate values for different SNR region instead of time consuming simulation.Thesis (PhD)--University of Pretoria, 2012.Electrical, Electronic and Computer Engineeringunrestricte

Performance of high rate space-time trellis coded modulation in fading channels.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.Future wireless communication systems promise to offer a variety of multimedia services which require reliable transmission at high data rates over wireless links. Multiple input multiple output (MIMO) systems have received a great deal of attention because they provide very high data rates for such links. Theoretical studies have shown that the quality provided by MIMO systems can be increased by using space-time codes. Space-time codes combine both space (antenna) and time diversity in the transmitter to increase the efficiency of MIMO system. The three primary approaches, layered spacetime architecture, space-time trellis coding (STTC) and space-time block coding (STBC) represent a way to investigate transmitter-based signal processing for diversity exploitation and interference suppression. The advantages of STBC (i.e. low decoding complexity) and STTC (i.e. TCM encoder structure) can be used to design a high rate space-time trellis coded modulation (HR-STTCM). Most space-time codes designs are based on the assumption of perfect channel state information at the receiver so as to make coherent decoding possible. However, accurate channel estimation requires a long training sequence that lowers spectral efficiency. Part of this dissertation focuses on the performance of HR-STTCM under non-coherent detection where there is imperfect channel state information and also in environment where the channel experiences rapid fading. Prior work on space-time codes with particular reference to STBC systems in multiuser environment has not adequately addressed the performance of the decoupled user signalto-noise ratio. Part of this thesis enumerates from a signal-to-noise ratio point of view the performance of the STBC systems in multiuser environment and also the performance of the HR-STTCM in such environment. The bit/frame error performance of space-time codes in fading channels can be evaluated using different approaches. The Chemoff upper-bound combined with the pair state generalized transfer function bound approach or the modified state transition diagram transfer function bound approach has been widely used in literature. However, although readily detennined, this bound can be too loose over nonnal signal-to-noise ranges of interest. Other approaches, based on the exact calculation of the pairwise error probabilities, are often too cumbersome. A simple exact numerical technique, for calculating, within any desired degree of accuracy, of the pairwise error probability of the HR-STTCM scheme over Rayleigh fading channel is proposed in this dissertation

Space-time coding for mimo rayleigh fading systems

Ph.DDOCTOR OF PHILOSOPH

Space-Time Codes for MIMO systems : Quasi-Orthogonal design and concatenation

Der Nachfrage an Mobilfunksystemen mit hoher Datenrate und Übertragungsqualität für eine Vielfalt von Anwendungen ist in den letzten Jahren dramatisch gestiegen. Zur Deckung des hohen Bedarfs werden jedoch neue Konzepte und Technologien benötigt, die den Beeinträchtigungen des Mobilfunkkanals entgegenwirken oder sich diese zu Nutze machen und die knappen Ressourcen wie Bandbreite und Leistung optimal ausnutzen. Eine effiziente Maßnahme zur Erhöhung der Performanz stellen Mehrantennensysteme dar. Um das große Potenzial von solchen Mehrantennensystemen auszunutzen, wurden neue Sendestrategien, so genannte Raum-Zeit Codes entworfen und analysiert, die neben der zeitlichen und spektralen auch die räumliche Komponente ausnutzen sollen. In dieser Arbeit wird die Leistungsfähigkeit solcher Raum-Zeit Codes zunächst isoliert und später, im zweiten Teil der Arbeit, in Kombination mit herkömmlichen Kanalcodierungsverfahren untersucht. Im ersten Abschnitt, d.h. im Fall ohne herkömmliche Kanalcodierung liegt der Fokus auf diversitäts-orientierten Raum-Zeit Codes. Zunächst werden basierend auf den Raum-Zeit Codes mit orthogonaler Struktur (OSTBC) Raum-Zeit Codes mit quasi-orthogonaler Struktur für eine beliebige Anzahl von Sende-und Empfangsantennen entworfen. Aus der Konstruktion resultieren dann zwei Gruppen von Codes. Die wesentliche Charakteristik der ersten Gruppe ist es, dass sie Verbindungen mit hoher Qualität gewährleistet. Dies wird erreicht, indem räumliche und zeitliche Redundanz eingebracht wird und daraus die volle Diversität (entspricht dem maximalen Abfall der Bitfehlerratenkurve) resultiert. Volle Diversität wird auch von den OSTBC erreicht, die aufgrund ihrer Struktur den matrix-wertigen Kanal für Mehrantennensysteme, so genannte Multiple-Input-Multiple-Output (MIMO)-Kanäle in parallele skalare Ersatzkanäle, so genannte Single-Input-Single-Output (SISO)-Kanäle, transformieren. Die Anzahl der parallelen Ersatzkanäle entspricht dabei der Anzahl der Sendeantennen. Diese Erkenntnis und die Einsicht in die Eigenschaften dieser Ersatzkanäle waren ein wichtiger Meilenstein und ermöglichten es, die Leistungsfähigkeit der OSTBC zu analysieren. Die Bestimmung der Ersatzkanalstuktur ist daher auch hier von zentraler Bedeutung. Im Falle von Raum-Zeit Codes mit quasi-orthogonaler Struktur wird in dieser Arbeit gezeigt, dass der MIMO-Kanal in einen block-diagonalen MIMO-Kanal zerlegt wird, dessen Eigenvektoren konstant und Blöcke identisch sind. Weiterhin konnte gezeigt werden, dass die Eigenwerte von jedem Block voneinander unabhängig sind und einer nichtzentralen Chi-Quadrat-Verteilung mit einer Anzahl von Freiheitsgraden, die dem Vierfachen der Anzahl der Empfangsantennen entspricht, folgen. Durch Lockerung der Anforderung von voller Diversität an die zu entwerfenden Codes gelangt man zu der zweiten Gruppe der Raum-Zeit Codes mit quasi-orthogonaler Stuktur, welche eine Verallgemeinerung der OSTBC darstellen. Insbesondere wird in dieser Arbeit gezeigt, dass nicht nur das Alamouti-Schema, ein OSTBC für zwei Sendeantennen, sondern auch eine verallgemeinerte Version dieses Alamouti-Schemas, die Kapazität im Falle einer Empfangsantenne erreicht. Die in dieser Arbeit entworfenen Raum-Zeit Codes werden schließlich hinsichtlich ihrer Fehlerraten-Performanz und ihrer spektralen Effizienz mit optimalen als auch mit suboptimalen Empfängerstrukturen analysiert. Im zweiten Teil dieser Arbeit werden verschiedene Raum-Zeit Codes mit herkömmlichen Kanalcodierungsverfahren kombiniert. Dabei werden neue Empfängerstrukturen vorgestellt und die Leistungsfähigkeit der Raum-Zeit Codes mit iterativen Algorithmen zur so genannten Soft-Input-Soft-Output-Decodierung mit Hilfe von neuen Analysetechniken, den so genannten EXIT-Charts, untersucht und optimiert. Im Falle von OSTBC werden zusätzlich Kriterien für die optimale Abbildung von Bitsequenzen auf Sendesymbole hergeleitet.The demand for mobile communication systems with high data rates and improved link quality for a variety of applications has dramatically increased in recent years. New concepts and methods are necessary in order to cover this huge demand, which counteract or take advantage of the impairments of the mobile communication channel and optimally exploit the limited resources such as bandwidth and power. Multiple antenna systems are an efficient means for increasing the performance. In order to utilize the huge potential of multiple antenna concepts, it is necessary to resort to new transmit strategies, referred to as Space-Time Codes, which, in addition to the time and spectral domain, also use the spatial domain. The performance of such Space-Time Codes is analyzed in this thesis with and without conventional channel coding strategies. In case without conventional channel codes, the focus is on diversity-oriented Space-Time Codes. Based on Space-Time Block Codes from orthogonal designs (OSTBC), the Space-Time Block Codes from quasi-orthogonal designs are developed for any number of transmit and receive antennas. The outcome of this construction are two groups of codes. The main property of the first group is the support of links with high quality. This is achieved by incorporating spatial and temporal redundancy, which results in full diversity or in other words, in the maximum decay of the bit error rate curves. Full diversity is also achieved by OSTBC, which due to their structure transform the matrix-valued channel for multi-antenna systems, so called multiple-input-multiple-output (MIMO)-channels, into several parallel, scalar single-input-single-output (SISO)-channels. This insight and the understanding of the properties of the equivalent SISO-channels were the key results in order to analyze the performance of the OSTBC. The determination of the structure of the equivalent channel is also a matter of vital importance in this work. To this end, we show that the MIMO-channel in the case of Space-Time Codes from quasi-orthogonal designs is transformed into an equivalent block-diagonal MIMO-channel with identical blocks having constant eigenvectors, independent of the channel realization. Furthermore, we show that the eigenvalues of each block are pairwise independent and follow a non-central chi-square distribution, where the number of degrees of freedom equals four times the number of receive antennas. By relaxing the requirement of full diversity one arrives at the second group of Space-Time Codes from quasi-orthogonal designs. These codes represent a generalization of Space-Time Codes from orthogonal designs. Particularly, we show in this work, that not only the Alamouti-scheme, a OSTBC for two transmit antennas, but also its generalized version achieves capacity in the case of one receive antenna. The drafted codes are then analyzed with respect to the error rate performance and the spectral efficiency with optimal as well as suboptimal receiver structures. In the second part of this work the combination of Space-Time Codes with conventional channel coding techniques is considered. New receiver structures are presented and the performance of Space-Time Codes with iterative algorithms for soft-input-soft-output-decoding is analyzed and optimized with the help of new analytical tools, the so called EXIT-charts. Furthermore, some criteria for the optimal mapping strategy are derived in the case of OSTBC

Spatial diversity in MIMO communication systems with distributed or co-located antennas

The use of multiple antennas in wireless communication systems has gained much attention during the last decade. It was shown that such multiple-input multiple-output (MIMO) systems offer huge advantages over single-antenna systems. Typically, quite restrictive assumptions are made concerning the spacing of the individual antenna elements. On the one hand, it is typically assumed that the antenna elements at transmitter and receiver are co-located, i.e., they belong to some sort of antenna array. On the other hand, it is often assumed that the antenna spacings are sufficiently large, so as to justify the assumption of independent fading. In this thesis, the above assumptions are relaxed. In the first part, it is shown that MIMO systems with distributed antennas and MIMO systems with co-located antennas can be treated in a single, unifying framework. In the second part this fact is utilized, in order to develop appropriate transmit power allocation strategies for co-located and distributed MIMO systems. Finally, the third part focuses on specific synchronization problems that are of interest for distributed MIMO systems

On multiple-antenna communications: signal detection, error exponent and and quality of service

Motivated by the demand of increasing data rate in wireless communication, multiple-antenna communication is becoming a key technology in the next generation wireless system. This dissertation considers three different aspects of multipleantenna communication. The first part is signal detection in the multiple-input multiple-output (MIMO) communication. Some low complexity near optimal detectors are designed based on an improved version of Bell Laboratories Layered Space-Time (BLAST) architecture detection and an iterative space alternating generalized expectation-maximization (SAGE) algorithm. The proposed algorithms can almost achieve the performance of optimal maximum likelihood detection. Signal detections without channel knowledge (noncoherent) and with co-channel interference are also investigated. Novel solutions are proposed with near optimal performance. Secondly, the error exponent of the distributed multiple-antenna communication (relay) in the windband regime is computed. Optimal power allocation between the source and relay node, and geometrical relay node placement are investigated based on the error exponent analysis. Lastly, the quality of service (QoS) of MIMO/single-input single- output(SISO) communication is studied. The tradeoff of the end-to-end distortion and transmission buffer delay is derived. Also, the SNR exponent of the distortion is computed for MIMO communication, which can provide some insights of the interplay among time diversity, space diversity and the spatial multiplex gain

Pattern and Decoration: An Ideal Vision in American Art, 1975-1985

This illustrated catalogue accompanied an exhibition at the Hudson River Museum, Yonkers, New York (October 27, 2007-January 20, 2008). It is the first extended discussion of the Pattern and Decoration movement. This exhibition catalogue was edited by Anne Swartz with an introduction by Michael Botwinick, with essays by Temma Balducci, Arthur C. Danto, John Perrault, and Anne Swartz

Récepteur itératif pour les systèmes MIMO-OFDM basé sur le décodage sphérique : convergence, performance et complexité

Recently, iterative processing has been widely considered to achieve near-capacity performance and reliable high data rate transmission, for future wireless communication systems. However, such an iterative processing poses significant challenges for efficient receiver design. In this thesis, iterative receiver combining multiple-input multiple-output (MIMO) detection with channel decoding is investigated for high data rate transmission. The convergence, the performance and the computational complexity of the iterative receiver for MIMO-OFDM system are considered. First, we review the most relevant hard-output and soft-output MIMO detection algorithms based on sphere decoding, K-Best decoding, and interference cancellation. Consequently, a low-complexity K-best (LCK- Best) based decoder is proposed in order to substantially reduce the computational complexity without significant performance degradation. We then analyze the convergence behaviors of combining these detection algorithms with various forward error correction codes, namely LTE turbo decoder and LDPC decoder with the help of Extrinsic Information Transfer (EXIT) charts. Based on this analysis, a new scheduling order of the required inner and outer iterations is suggested. The performance of the proposed receiver is evaluated in various LTE channel environments, and compared with other MIMO detection schemes. Secondly, the computational complexity of the iterative receiver with different channel coding techniques is evaluated and compared for different modulation orders and coding rates. Simulation results show that our proposed approaches achieve near optimal performance but more importantly it can substantially reduce the computational complexity of the system. From a practical point of view, fixed-point representation is usually used in order to reduce the hardware costs in terms of area, power consumption and execution time. Therefore, we present efficient fixed point arithmetic of the proposed iterative receiver based on LC-KBest decoder. Additionally, the impact of the channel estimation on the system performance is studied. The proposed iterative receiver is tested in a real-time environment using the MIMO WARP platform.Pour permettre l’accroissement de débit et de robustesse dans les futurs systèmes de communication sans fil, les processus itératifs sont de plus considérés dans les récepteurs. Cependant, l’adoption d’un traitement itératif pose des défis importants dans la conception du récepteur. Dans cette thèse, un récepteur itératif combinant les techniques de détection multi-antennes avec le décodage de canal est étudié. Trois aspects sont considérés dans un contexte MIMOOFDM: la convergence, la performance et la complexité du récepteur. Dans un premier temps, nous étudions les différents algorithmes de détection MIMO à décision dure et souple basés sur l’égalisation, le décodage sphérique, le décodage K-Best et l’annulation d’interférence. Un décodeur K-best de faible complexité (LC-K-Best) est proposé pour réduire la complexité sans dégradation significative des performances. Nous analysons ensuite la convergence de la combinaison de ces algorithmes de détection avec différentes techniques de codage de canal, notamment le décodeur turbo et le décodeur LDPC en utilisant le diagramme EXIT. En se basant sur cette analyse, un nouvel ordonnancement des itérations internes et externes nécessaires est proposé. Les performances du récepteur ainsi proposé sont évaluées dans différents modèles de canal LTE, et comparées avec différentes techniques de détection MIMO. Ensuite, la complexité des récepteurs itératifs avec différentes techniques de codage de canal est étudiée et comparée pour différents modulations et rendement de code. Les résultats de simulation montrent que les approches proposées offrent un bon compromis entre performance et complexité. D’un point de vue implémentation, la représentation en virgule fixe est généralement utilisée afin de réduire les coûts en termes de surface, de consommation d’énergie et de temps d’exécution. Nous présentons ainsi une représentation en virgule fixe du récepteur itératif proposé basé sur le décodeur LC K-Best. En outre, nous étudions l’impact de l’estimation de canal sur la performance du système. Finalement, le récepteur MIMOOFDM itératif est testé sur la plateforme matérielle WARP, validant le schéma proposé