Successive interference cancellation schemes for time-reversal space-time block codes

In this paper, we propose two simple signal detectors that are based on successive interference cancellation (SIC) for time-reversal space-time block codes to combat intersymbol interference in frequency-selective fading environments. The main idea is to treat undetected symbols and noise together as Gaussian noise with matching mean and variance and use the already-detected symbols to help current signal recovery. The first scheme is a simple SIC signal detector whose ordering is based on the channel powers. The second proposed SIC scheme, which is denoted parallel arbitrated SIC (PA-SIC), is a structure that concatenates in parallel a certain number of SIC detectors with different ordering sequences and then combines the soft output of each individual SIC to achieve performance gains. For the proposed PA-SIC, we describe the optimal ordering algorithm as a combinatorial problem and present a low-complexity ordering technique for signal decoding. Simulations show that the new schemes can provide a performance that is very close to maximum-likelihood sequence estimation (MLSE) decoding under time-invariant conditions. Results for frequency-selective and doubly selective fading channels show that the proposed schemes significantly outperform the conventional minimum mean square error-(MMSE) like receiver and that the new PA-SIC performs much better than the proposed conventional SIC and is not far in performance from the MLSE. The computational complexity of the SIC algorithms is only linear with the number of transmit antennas and transmission rates, which is very close to the MMSE and much lower than the MLSE. The PA-SIC also has a complexity that is linear with the number of SIC components that are in parallel, and the optimum tradeoff between performance and complexity can be easily determined according to the number of SIC detectors

Robust frequency-domain turbo equalization for multiple-input multiple-output (MIMO) wireless communications

This dissertation investigates single carrier frequency-domain equalization (SC-FDE) with multiple-input multiple-output (MIMO) channels for radio frequency (RF) and underwater acoustic (UWA) wireless communications. It consists of five papers, selected from a total of 13 publications. Each paper focuses on a specific technical challenge of the SC-FDE MIMO system. The first paper proposes an improved frequency-domain channel estimation method based on interpolation to track fast time-varying fading channels using a small amount of training symbols in a large data block. The second paper addresses the carrier frequency offset (CFO) problem using a new group-wise phase estimation and compensation algorithm to combat phase distortion caused by CFOs, rather than to explicitly estimate the CFOs. The third paper incorporates layered frequency-domain equalization with the phase correction algorithm to combat the fast phase rotation in coherent communications. In the fourth paper, the frequency-domain equalization combined with the turbo principle and soft successive interference cancelation (SSIC) is proposed to further improve the bit error rate (BER) performance of UWA communications. In the fifth paper, a bandwidth-efficient SC-FDE scheme incorporating decision-directed channel estimation is proposed for UWA MIMO communication systems. The proposed algorithms are tested by extensive computer simulations and real ocean experiment data. The results demonstrate significant performance improvements in four aspects: improved channel tracking, reduced BER, reduced computational complexity, and enhanced data efficiency --Abstract, page iv

Frequency-domain equalization for space-time block-coded transmissions over frequency-selective fading channels

Master'sMASTER OF ENGINEERIN

Channel estimation and equalization in multiGigabit systems

In actual mobile radio systems, multipath conditions pose a problem, as the channel becomes frequency dependent. This point is especially critical in case of high frequency transmissions with very high data rate and high error performance, such as defined in the IEEE 802.15.3c which is an emerging 60-GHz standard supporting data rates of multi-giga bits per second (multi-Gbps) for short-range indoor applications. The deployment of such high speed wireless transmission has been very difficult throughout history mainly by two critical factors: the first one was the lack of wide enough spectrum and the second one is the high cost of high frequency circuits and devices. However, this trend is changing to the point that not too long ago, the substantial unlicensed spectrum became available at the millimeter-wave band of 60-GHz. Also, the advancement in technology drives the cost of 60-GHz circuits and devices much lower than in the past making possible its use for high definition audio and video wireless transmissions. In order to overcome the transmission channel issues, it is necessary to include a channel equalizer in the receiver, which must estimate the channel impulse response and make some operations to transform the frequency dependent channel to a flat channel. Nevertheless, the equalizer technology will depend on three different factors: first one the physical layer (PHY) technique under consideration for multi-Gbps Wireless Personal Area Network (WPAN) which basically could be orthogonal frequency division multiplexing (OFDM) or single-carrier frequency domain equalization (SC-FDE); second, the channel impulse response estimation carried out in order to determine the channel transfer function H(f), existing several methods to obtain an estimation; and third, the used equalization method and structure in order to reverse all distortions produced by the channel. This Master thesis has been carry out during an Erasmus program in the Technische Universitat of Braunchweig, Germany, and it is the first part of a whole European project for the study, analysis and deployment of the IEEE 802.15.3c standard for wireless communications with very high data rate and high error performance in the 60-GHz band. According to the instructions and requirements defined by professor Thomas Kürner which was in charge of this project, this thesis include: first, a theoretical study of all the different propagation effects which could affect a wireless communication channel in order to run not only the simulations presented in this thesis but also the future simulations; second, the development of a model in Matlab/Simulink that will be useful to carry out all the project simulations (taken into account the specifications collected in IEEE 802.15.3c standard); third, the results of the carried simulations for Single Carrier Channel estimation and equalization by using two different equalization methods in the frequency domain: Zero Forcing and Minimum Mean Square Error equalization. Taking this into account, the thesis is organized as follows. Section I is dedicated to the study of all the different propagation effects and problems which affects a wireless communication transmissions; In Section II, technologies and Physical Layer Modes are described attending the IEEE 802.15.3c in order to learn its different characteristics for the subsequent channel estimation; Section III is devoted to channel estimation and equalization methods description; estimation and equalization methods are selected in order to carry out the simulations in Section IV; finally, in Section V the developed system simulator as well as the obtained simulation results are presented after implementation of Zero Forcing and Minimum Mean Square Error equalization methods in Matlab/Simulink

Simulation framework for multigigabit applications at 60 GHz

This dissertation describes the implementation of a OFDM-based simulation framework for multigigabit applications at 60 GHz band over indoor multipath fading channels. The main goal of the framework is to provide a modular simulation tool designed for high data rate application in order to be easily adapted to a speci c standard or technology, such as 5G. The performance of OFDM using mmWave signals is severely a ected by non-linearities of the RF front-ends. This work analyses the impact of RF impairments in an OFDM system over multipath fading channels at 60 GHz using the proposed simulation framework. The impact of those impairments is evaluated through the metrics of BER, CFR, operation range and PSNR for residential and kiosk scenarios, suggested by the standard for LOS and NLOS. The presented framework allows the employment of 16 QAM or 64 QAM modulation scheme, and the length of the cyclic pre x extension is also con gurable. In order to simulate a realistic multipath fading channel, the proposed framework allows the insertion of a channel impulse response de ned by the user. The channel estimation can be performed either using pilot subcarriers or Golay sequence as channel estimation sequences. Independently of the channel estimation technique selected, frequency domain equalization is available through ZF approach or MMSE. The simulation framework also allows channel coding techniques in order to provide a more robustness transmission and to improve the link budget

Mobile and Wireless Communications

Mobile and Wireless Communications have been one of the major revolutions of the late twentieth century. We are witnessing a very fast growth in these technologies where mobile and wireless communications have become so ubiquitous in our society and indispensable for our daily lives. The relentless demand for higher data rates with better quality of services to comply with state-of-the art applications has revolutionized the wireless communication field and led to the emergence of new technologies such as Bluetooth, WiFi, Wimax, Ultra wideband, OFDMA. Moreover, the market tendency confirms that this revolution is not ready to stop in the foreseen future. Mobile and wireless communications applications cover diverse areas including entertainment, industrialist, biomedical, medicine, safety and security, and others, which definitely are improving our daily life. Wireless communication network is a multidisciplinary field addressing different aspects raging from theoretical analysis, system architecture design, and hardware and software implementations. While different new applications are requiring higher data rates and better quality of service and prolonging the mobile battery life, new development and advanced research studies and systems and circuits designs are necessary to keep pace with the market requirements. This book covers the most advanced research and development topics in mobile and wireless communication networks. It is divided into two parts with a total of thirty-four stand-alone chapters covering various areas of wireless communications of special topics including: physical layer and network layer, access methods and scheduling, techniques and technologies, antenna and amplifier design, integrated circuit design, applications and systems. These chapters present advanced novel and cutting-edge results and development related to wireless communication offering the readers the opportunity to enrich their knowledge in specific topics as well as to explore the whole field of rapidly emerging mobile and wireless networks. We hope that this book will be useful for students, researchers and practitioners in their research studies

Frequency-domain receiver design for doubly-selective channels

This work is devoted to the broadband wireless transmission techniques, which are serious candidates to be implemented in future broadband wireless and cellular systems, aiming at providing high and reliable data transmission and concomitantly high mobility. In order to cope with doubly-selective channels, receiver structures based on OFDM and SC-FDE block transmission techniques, are proposed, which allow cost-effective implementations, using FFT-based signal processing. The first subject to be addressed is the impact of the number of multipath components, and the diversity order, on the asymptotic performance of OFDM and SC-FDE, in uncoded and for different channel coding schemes. The obtained results show that the number of relevant separable multipath components is a key element that influences the performance of OFDM and SC-FDE schemes. Then, the improved estimation and detection performance of OFDM-based broadcasting systems, is introduced employing SFN (Single Frequency Network) operation. An initial coarse channel is obtained with resort to low-power training sequences estimation, and an iterative receiver with joint detection and channel estimation is presented. The achieved results have shown very good performance, close to that with perfect channel estimation. The next topic is related to SFN systems, devoting special attention to time-distortion effects inherent to these networks. Typically, the SFN broadcast wireless systems employ OFDM schemes to cope with severely time-dispersive channels. However, frequency errors, due to CFO, compromises the orthogonality between subcarriers. As an alternative approach, the possibility of using SC-FDE schemes (characterized by reduced envelope fluctuations and higher robustness to carrier frequency errors) is evaluated, and a technique, employing joint CFO estimation and compensation over the severe time-distortion effects, is proposed. Finally, broadband mobile wireless systems, in which the relative motion between the transmitter and receiver induces Doppler shift which is different or each propagation path, is considered, depending on the angle of incidence of that path in relation to the direction of travel. This represents a severe impairment in wireless digital communications systems, since that multipath propagation combined with the Doppler effects, lead to drastic and unpredictable fluctuations of the envelope of the received signal, severely affecting the detection performance. The channel variations due this effect are very difficult to estimate and compensate. In this work we propose a set of SC-FDE iterative receivers implementing efficient estimation and tracking techniques. The performance results show that the proposed receivers have very good performance, even in the presence of significant Doppler spread between the different groups of multipath components

Datacenter Design for Future Cloud Radio Access Network.

Cloud radio access network (C-RAN), an emerging cloud service that combines the traditional radio access network (RAN) with cloud computing technology, has been proposed as a solution to handle the growing energy consumption and cost of the traditional RAN. Through aggregating baseband units (BBUs) in a centralized cloud datacenter, C-RAN reduces energy and cost, and improves wireless throughput and quality of service. However, designing a datacenter for C-RAN has not yet been studied. In this dissertation, I investigate how a datacenter for C-RAN BBUs should be built on commodity servers. I first design WiBench, an open-source benchmark suite containing the key signal processing kernels of many mainstream wireless protocols, and study its characteristics. The characterization study shows that there is abundant data level parallelism (DLP) and thread level parallelism (TLP). Based on this result, I then develop high performance software implementations of C-RAN BBU kernels in C++ and CUDA for both CPUs and GPUs. In addition, I generalize the GPU parallelization techniques of the Turbo decoder to the trellis algorithms, an important family of algorithms that are widely used in data compression and channel coding. Then I evaluate the performance of commodity CPU servers and GPU servers. The study shows that the datacenter with GPU servers can meet the LTE standard throughput with 4× to 16× fewer machines than with CPU servers. A further energy and cost analysis show that GPU servers can save on average 13× more energy and 6× more cost. Thus, I propose the C-RAN datacenter be built using GPUs as a server platform. Next I study resource management techniques to handle the temporal and spatial traffic imbalance in a C-RAN datacenter. I propose a “hill-climbing” power management that combines powering-off GPUs and DVFS to match the temporal C-RAN traffic pattern. Under a practical traffic model, this technique saves 40% of the BBU energy in a GPU-based C-RAN datacenter. For spatial traffic imbalance, I propose three workload distribution techniques to improve load balance and throughput. Among all three techniques, pipelining packets has the most throughput improvement at 10% and 16% for balanced and unbalanced loads, respectively.PhDComputer Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120825/1/qizheng_1.pd