vii

pour toute la sympathie qu'ils ont offert pendant mes séjours en Bretagne. Je remercie tous lescolì egues et amis du département COMELEC de l'ENST :Danì ele, Marc Fossorier de l'Université d'Hawaii, Emanuele Viterbo du Politecnico di Torino pour toutes les discussions techniques fructueuses et motivantes, et pour leur soutien inconditionnel. Bien ´ evidemment, je remercie toute l'´ equipe des thésards et stagiaires de différents horizons qui ont réussì a me supporter pendant trois ans et ont partagé leur richesse culturelle. Un grand mercì a (aléatoirement, comme on en a l'habitude dans le domaine) A mes parents età Christelle. v Thesis abstract This thesis report describes new designs for transmitters and receivers of bit-interleaved coded modulations over multiple antenna channels. The objective is to achieve near Shannon capacity performance over ergodic channels and near outage probability performance over block fading channels. Iterative joint detection and decoding are applied in the aim of achieving near maximum likelihood performance. Design criteria are derived for each block optimization from the error performance expressions under the ideal interleaving assumption. First, we describe the binary mapping optimization for ergodic channels by introducing the new concept of mul-tidimensional mapping that provides large amount of coding gain. We achieve near capacity performance either with turbo-codes or with multi-dimensional mappings associated with a simple code. Then, we present the bit-interleaved coded modulation with linear precoding as a Space-Time code for multiple antenna block fading channels. We show that the channel inter-leaver is the fundamental part of the bit-interleaved coded modulation calling the shots about the achieved diversity. We describe the linear precoding optimality condition and a class of quasi-optimal linear precoders. The minimal linear precoder size providing full diversity is deduced from a modified Singleton bound applied to the global Euclidean code. We show that full diversity and quasi-optimal coding gains are observed for a given error correcting code. Finally, we achieve near outage capacity performance thanks to turbo-codes. Next, iterative joint detection and decoding techniques are considered, we describe a near optimum soft-input soft-output list sphere decoder which allows the computation of a posteriori probabilities for very high spectral efficiency transmitter schemes with reduced complexity.

iii OZ v ACKNOWLEDGMENTS viii LIST OF TABLES xii LIST OF FIGURES xiii LIST OF SYMBOLS AND ABBREVIATIONS xv

ii I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. Abstract The revolutionary concept of space-time coding introduced in the last decade has demonstrated that the deployment of multiple antennas at the transmitter allows for simultaneous increase in throughput and reliability because of the additional degrees of freedom offered by the spatial dimension of the wireless channel. However, the use of antenna arrays is not practical for deployment in some practical scenarios, e.g., sensor networks, due to space and power limitations. A new form of realizing transmit diversity has been recently introduced under the name of user cooperation or cooperative diversity. The basic idea behind cooperative diversity rests on the observation that in a wireless environment, the signal transmitted by the source node is overheard by other nodes, which can be defined as " partners " or " relays ". The source and its partners can jointly process and transmit their information, creating a " virtual antenna array " and therefore emulating transmit diversity. Most of the ongoing research efforts in cooperative diversity assume frequency flat channels with perfect channel knowledge. However, in practical scenarios, e.g. broadband wireless networks, these assumptions do not apply. Frequency-selective fading and imperfect channel knowledge should be considered as a more realistic channel model. The development of equalization and channel estimation algorithms play a crucial element in the design of digital receivers as their accuracy determine the overall performance. This dissertation creates a framework for designing and analyzing various time and frequency domain equalization schemes, i.e. distributed time reversal (D-TR) STBC, distributed single carrier frequency domain (D-SC-FDE) STBC, and distributed orthogonal frequency division multiplexing (D-OFDM) STBC schemes, for broadband cooperative communication systems. Exploiting the orthogonally embedded in D-STBCs, we were able iv to maintain low-decoding complexity for all underlying schemes, thus, making them excellent candidates for practical scenarios, such as multi-media broadband communication systems. Furthermore, we propose and analyze various non-coherent and channel estimation algorithms to improve the quality and reliability of wireless communication networks. Specifically, we derive a non-coherent decoding rule which can be implemented in practice by a Viterbi-type algorithm. We demonstrate through the derivation of a pairwise error probability expression that the proposed non-coherent detector guarantees full diversity. …

Wireless networks have become an increasingly important part of our daily lives. The rise in number of mobile clients and the subsequent services being offered on them has led to not just an increase in demand for wireless data but also change in network traffic characteristics. The proliferation of mobile devices also causes change in wireless topologies over time. However, the available bandwidth remains scarce. Thus, the need for wireless networks to be more spectral efficient is critical. This dissertation investigates a suite of solutions to address this trend in changing wireless networks. We first investigate physical layer solutions at the node level to enhance wireless networks and then look at collaborative techniques across distributed nodes to improve wireless networks. First, collaborative communication techniques such as interference alignment, distributed MIMO have been theoretically explored to enhance the spectral efficiency of wireless networks. However, implementing such solutions in practice require tight synchronization requirements either in time, frequency or both. We present Vidyut, which uses the power lines to provide time and frequency synchronization across distributed nodes to implement such techniques in practice. The advantage of using an orthogonal medium (the power lines) for synchronization purposes alleviates the MAC overhead required to simply synchonize nodes distributed in space. We demonstrate

We study space-time precoding techniques for asymmetric multiple-input multiple-output (MIMO) channels with more transmit than receive antennas which is a typical downlink setup. Under the condition that channel state information (CSI) is perfectly known at the receiver, but not known at the transmitter, we consider groupwise space-time block coding (GSTBC), quasi-orthogonal space-time block coding (QSTBC), linear dispersion coding (LDC), and spatial spreading (SS). We show that for narrow-band i.i.d. circularly symmetric complex Gaussian (CSCG) MIMO channels, SS has the lowest ergodic capacity, while GSTBC, QSTBC and LDC have almost the same ergodic capacity. We then compare their input-output mutual information when fixed-order modulation is deployed and show that the same performance order maintains. Finally we look into their bit error rate (BER) performance for uncoded systems, and show that LDC slightly outperforms GSTBC and QSTBC in high SNR regions and below BER of 10-2, and SS has the worst performance. Due to the good flexibility for various asymmetric channels and its simple implementation, we therefore recommend GSTBC as the asymmetric MIMO precoding scheme

We study motion compensated fine granular scalable (MC-FGS) video transmission over multiinput multioutput (MIMO) wireless channels applicable to video streaming, where leaky and partial prediction schemes are applied in the enhancement layer of MC-FGS to exploit the tradeoff between error propagation and coding efficiency. For reliable transmission, we propose unequal error protection (UEP) by considering a tradeoff between reliability and data rates, which are controlled by forward error correction and MIMO mode selection to minimize the average distortion. In a high Doppler environment, where it is hard to get an accurate channel estimate, we investigate the performance of the proposed MC-FGS video transmission scheme with joint control of both the leaky and partial prediction parameters, and the UEP. In a slow fading channel, where the channel throughput can be estimated at the transmitter, adaptive control of prediction parameters is considered.

We report a simple differential modulation scheme for quasi-orthogonal space-time block codes. A new class of quasi-orthogonal coding structures that can provide partial transmit diversity is presented for various numbers of transmit antennas. Differential encoding and decoding can be simplified for differential Alamouti-like codes by grouping the signals in the transmitted matrix and decoupling the detection of data symbols, respectively. The new scheme can achieve constant amplitude of transmitted signals, and avoid signal constellation expansion; in addition it has a linear signal detector with very low complexity. Simulation results show that these partial-diversity codes can provide very useful results at low SNR for current communication systems. Extension to more than four transmit antennas is also considered.

We propose the use of multistratum space-time codes (MSSTC) for the asynchronous uplink of broadband MIMO-CDMA systems. This transmission scheme, originally proposed for single-user systems and flat fading channels, combines the benefits of both space-time block codes and multilayer transmission, i.e. it exploits transmit diversity and simultaneously enables high data rates with reasonable decoding complexity. Though the full potential of multistratum codes can only be achieved by using adaptive channel coding, we show by simulation results that they are a promising approach even in the uncoded case.

We propose single-carrier transmission systems for STBC coded and concatenation of a FEC code with a STBC over ISI fading channels. The proposed receivers rely on iterative successive interference cancellation technique, which avoids the disadvantages of multicarrier systems. Simulation results show that for the STBC only system, the proposed receiver outperforms the OFDM receiver under the power constraint scenario. For the concatenated coding system, the proposed receiver outperforms the OFDM receiver when there is more than one receive antenna.

We propose several differential decoding schemes for asynchronous multi-user MIMO systems based on orthogonal space-time block codes (OSTBCs), where neither the transmitters nor the receiver has knowledge of the channel. First, we derive novel low complexity differential decoders by performing interference cancellation in time and employing different decoding methods. The decoding complexity of these schemes grows linearly with the number of users. We then present additional differential decoding schemes that perform significantly better than our low complexity decoders and outperform the existing synchronous differential schemes but require higher decoding complexity compared to our low complexity decoders. The proposed schemes work for any square OSTBC, any constant amplitude constellation, any number of users, and any number of receive antennas. Furthermore, we analyze the diversity of the proposed schemes and derive conditions under which our schemes provide full diversity. For the cases of two and four transmit antennas, we provide examples of PSK constellations to achieve full diversity. Simulation results show that our differential schemes provide good performance. To the best of our knowledge, the proposed differential detection schemes are the first differential schemes for asynchronous multi-user systems.

We propose a very simple and efficient soft linear multi-input multi-output (MIMO) detection scheme. The detection process is divided into two separate problems. The proposed scheme first detects MIMO symbols using conventional linear detection methods and produces soft bit information using a simple soft demapping method. Next, we refine the soft information by accounting for uneven post-detection noise variance across MIMO layers. From the simulation result investigated in this paper, we first emphasize that powerful channel coding may suppress the differences of diversity gains among various MIMO detection schemes. This implies that the channel decoding operation may not be transparent to performance gain that resulted from MIMO detection process. The proposed scheme concentrates on accurate estimation of soft post-MIMO detected information in a very simple manner, rather than concentrating on a complex MIMO detection scheme prior to decoding process. In combination with turbo codes, the proposed scheme produces comparable performance to maximum likelihood detection, even with the simplest scheme such as zero forcing detection, with drastically reduced complexity. Copyright © 2011 John Wiley & Sons, Ltd.

We propose a space-time coding strategy based on the use of families of matrices orthogonal in the trace of their product. The advantages of the proposed method are: i) possibility for symbol-by-symbol detection; ii) full diversity gain with respect to the noise; iii) full transmission rate, provided that the number of receive antennas is sufficiently higher than the number of transmit antennas; iv) direct extension to multiuser systems. The price paid for these advantages is the presence of ISI or multiuser interference (MUI). The method offers great flexibility in designing codes that provide the desired trade-off between BER, transmission rate and receiver complexity. We provide a theoretical analysis, supported by simulation results, showing how to balance transmission rate with BER, in the presence of (controllable) ISI. Finally, we generalize the method to the multiuser case.

We propose a novel rate-one (i.e., one symbol per transmission), space-frequency block code (SFBC) for an orthogonal frequency division multiplexing (OFDM) system with transmit (M), and receive (N) antennas that achieves the maximum diversity attainable over frequency-selective channels. Moreover, the space-frequency (SF) code design is shown to be robust to overestimation of the (true) channel order L at the price of increasing decoding complexity. Further, even if the channel order is underestimated (K<L), diversity order of MNK is achieved with commensurately reduced decoding complexity; this allows a natural mechanism for trading diversity for decoding complexity as desired. In addition, since the SF code symbol is transmitted in one OFDM block duration, it has a smaller processing delay than comparable space-time-frequency block codes (STFBC).

We propose a new full rate space-time block code for a three transmit antenna system that is orthogonal when using a special modulation scheme, called "triple QPSK". This space-time block code achieves full diversity gain when used with "triple QPSK" modulation. The performance of this new space-time block code is evaluated by using Monte Carlo simulation and union bounding techniques. Simulation results match the results obtained from the union bound analysis very well at reasonable signal to noise ratios. We conclude that the new space-time block code achieves better performance when compared with conventional space-time block codes.

We propose a full-rate iterative space-time code construction, which uses an algebraic space-time code in order to design a new space-time code of double the code rank. We give a condition for determining whether the resulting codes satisfy the full diversity property, and study their maximum likelihood decoding complexity with respect to sphere decoding. Particular emphasis is given to the asymmetric multiple input double output codes. In the process, we derive an interesting way of obtaining division algebras, and study their centers and maximal subfields.

We present an overview of multiple-input multiple-output (MIMO) wireless communication systems followed by some of the new techniques proposed by us to enhance performance. Firstly, some of the popular transmit and receive diversity schemes available in the literature are discussed and issues like diversity, rate, power distribution, decoding complexity, decoding delay, amount of feedback and feedback delay and their tradeoffs to achieve reliable and cost effective communications are described. We then analyze the merits and demerits of some of the open-loop (no feedback) and closed-loop (with feedback) schemes, and discuss various methods proposed by us recently to improve the performance of such schemes. The symbol error rate (SER) performance of the various schemes are compared through computer simulations.

We present a unified approach to designing space-time (ST) block codes using linear constellation precoding (LCP). Our designs are based either on parameterizations of unitary matrices, or on algebraic number-theoretic constructions. With an arbitrary number of N/sub t/ transmit- and N/sub r/ receive-antennas, ST-LCP achieves rate 1 symbol/s/Hz and enjoys diversity gain as high as N/sub t/N/sub r/ over (possibly correlated) quasi-static and fast fading channels. As figures of merit, we use diversity and coding gains, as well as mutual information of the underlying multiple-input-multiple-output system. We show that over quadrature-amplitude modulation and pulse-amplitude modulation, our LCP achieves the upper bound on the coding gain of all linear precoders for certain values of N/sub t/ and comes close to this upper bound for other values of N/sub t/, in both correlated and independent fading channels. Compared with existing ST block codes adhering to an orthogonal design (ST-OD), ST-LCP offers not only better performance, but also higher mutual information for N/sub t/>2. For decoding ST-LCP, we adopt the near-optimum sphere-decoding algorithm, as well as reduced-complexity suboptimum alternatives. Although ST-OD codes afford simpler decoding, the tradeoff between performance and rate versus complexity favors the ST-LCP codes when N/sub t/, N/sub r/, or the spectral efficiency of the system increase. Simulations corroborate our theoretical findings.

We present a phase-aligned space-time coding scheme that expands the original Alamouti codeword to three or four transmit antennas ($N_t = 3$ or 4) with phase alignment. With $1 \sim 2$ bits feedback for the phase information, the fundamental performance penalty of $10log_{10}(N_t)$ dB of orthogonal space-time coding compared to the optimum beamforming is reduced by 1 dB (for $N_t=3$) or 2 dB (for $N_t = 4$) on average. With the proposed scheme, the full diversity order of $N_t$ is achievable, whereas the receiver architecture remains the same as the legacy Alamouti decoding with codeword size of two, since the spatial expansion is transparent to the receiver. Our results show the proposed scheme outperforms open-loop space-time coding for three or four transmit antennas by more than 3 dB.

We present a new class of space-time-frequency block codes (STFBC) for multiantenna orthogonal frequency division multiplexing (MIMO-OFDM) transmissions over frequency selective Rayleigh fading channels. We show that these codes admit symbol-by-symbol decoding (decoupled decoding) when the number of nonzero taps of the channel impulse response is equal to two and they admit reduced complexity (1/2 of that of known schemes) for more than two channel taps. We also present simulation results to show that our codes perform better than the known codes.