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

Modelação comportamental da camada física de NB-IoT em downlink

Mestrado em Engenharia Eletrónica e TelecomunicaçõesThe Internet of Things (IoT) paradigm de nes a fully connected network of devices enabling new forms of interaction between users and devices. The constant growth of these networks, as well as an increasing demand for more reliable, low bit rate and massive communication data ows lead to the emergence of new technologies and set of standards, such as, the Low Power Wide Area Networks (LPWAN). In June 2016, 3GPP, the consortium responsible for LTE development and standardization, released a new licensed band based standard, named Narrow Band (NB) IoT. NB-IoT was designed based on the same principles of other LPWAN standards, providing better coverage and additionally an easier integration on existing cellular systems. In this dissertation a study on the NB-IoT Physical Layer is presented along with an open source behavioral implementation in MATLAB of the downlink transmission and reception chains. The system generates and recovers one radio frame successfully performings procedures such as MIB and SIB1-N extracting along with scheduling and recovering data scheduled through control channels by higher layer paramenters. The project models and executes the downlink transmission (eNodeB) and reception (terminal) PHYs either in a pure simulation environment using di erent channel models, as well as integrated with an USRP software de ned radio device for co-simulation. The simulation and co-simulation results are presented evaluating the transmission's quality and performance of the implemented Zero Forcing equalizer.O paradigma da Internet of Things (IoT) define uma rede interligada de dispositivos que permite o surgimento de novas formas de interacção entre utilizadores e dispositivos. O constante crescimento destas redes assim como a crescente demanda por uma fiabilidade maior, bit rates mais baixos e circulação massiva de informação insurgiu o aparecimento de novas tecnologias tais como as Low Power Wide Area Networks (LPWAN). Em Junho de 2016 a 3GPP, o órgão responsável pelo LTE, lançou um novo standard para bandas licenciadas o Narrowband (NB) -IoT. O NB-IoT foi desenhado com base nos mesmos princípios que as outras LPWAN com o acréscimo de uma maior cobertura assim como uma mais fácil integração em sistemas celulares existentes. Nesta dissertação aborda-se um estudo da sua camada física (PHY Layer) juntamente com uma implementação comportamental open source em Matlab das cadeias de transmissão e recepção em downlink. O projecto modela e executa transmissões em downlink (eNodeB) e sua recepcção (terminal) tanto em ambiente simulado como integrado com um dispositivo de software defined radio, USRP, para validação laboratorial. Os resultados obtidos tanto de simulação como co-simulação são apresentados avaliando a qualidade de transmissão assim como o comportamento do equalizador Zero Forcing implementado

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

Polynomial matrix decomposition techniques for frequency selective MIMO channels

For a narrowband, instantaneous mixing multi-input, multi-output (MIMO) communications system, the channel is represented as a scalar matrix. In this scenario, singular value decomposition (SVD) provides a number of independent spatial subchannels which can be used to enhance data rates or to increase diversity. Alternatively, a QR decomposition can be used to reduce the MIMO channel equalization problem to a set of single channel equalization problems. In the case of a frequency selective MIMO system, the multipath channel is represented as a polynomial matrix. Thus conventional matrix decomposition techniques can no longer be applied. The traditional solution to this broadband problem is to reduce it to narrowband form by using a discrete Fourier transform (DFT) to split the broadband channel into N narrow uniformly spaced frequency bands and applying scalar decomposition techniques within each band. This describes an orthogonal frequency division multiplexing (OFDM) based system. However, a novel algorithm has been developed for calculating the eigenvalue decomposition of a para-Hermitian polynomial matrix, known as the sequential best rotation (SBR2) algorithm. SBR2 and its QR based derivatives allow a true polynomial singular value and QR decomposition to be formulated. The application of these algorithms within frequency selective MIMO systems results in a fundamentally new approach to exploiting spatial diversity. Polynomial matrix decomposition and OFDM based solutions are compared for a wide variety of broadband MIMO communication systems. SVD is used to create a robust, high gain communications channel for ultra low signal-to-noise ratio (SNR) environments. Due to the frequency selective nature of the channels produced by polynomial matrix decomposition, additional processing is required at the receiver resulting in two distinct equalization techniques based around turbo and Viterbi equalization. The proposed approach is found to provide identical performance to that of an existing OFDM scheme while supporting a wider range of access schemes. This work is then extended to QR decomposition based communications systems, where the proposed polynomial approach is found to not only provide superior bit-error-rate (BER) performance but significantly reduce the complexity of transmitter design. Finally both techniques are combined to create a nulti-user MIMO system that provides superior BER performance over an OFDM based scheme. Throughout the work the robustness of the proposed scheme to channel state information (CSI) error is considered, resulting in a rigorous demonstration of the capabilities of the polynomial approach

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

Low complexity channel estimation for OFDM based satellite systems

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Rapid Industrial Prototyping and SoC Design of 3G/4G Wireless Systems Using an HLS Methodology

Many very-high-complexity signal processing algorithms are required in future wireless systems, giving tremendous challenges to real-time implementations. In this paper, we present our industrial rapid prototyping experiences on 3G/4G wireless systems using advanced signal processing algorithms in MIMO-CDMA and MIMO-OFDM systems. Core system design issues are studied and advanced receiver algorithms suitable for implementation are proposed for synchronization, MIMO equalization, and detection. We then present VLSI-oriented complexity reduction schemes and demonstrate how to interact these high-complexity algorithms with an HLS-based methodology for extensive design space exploration. This is achieved by abstracting the main effort from hardware iterations to the algorithmic C/C++ fixed-point design. We also analyze the advantages and limitations of the methodology. Our industrial design experience demonstrates that it is possible to enable an extensive architectural analysis in a short-time frame using HLS methodology, which significantly shortens the time to market for wireless systems.National Science Foundatio

Peak to average power ratio reduction and error control in MIMO-OFDM HARQ System

Currently, multiple-input multiple-output orthogonal frequency division multiplexing (MIMOOFDM) systems underlie crucial wireless communication systems such as commercial 4G and 5G networks, tactical communication, and interoperable Public Safety communications. However, one drawback arising from OFDM modulation is its resulting high peak-to-average power ratio (PAPR). This problem increases with an increase in the number of transmit antennas. In this work, a new hybrid PAPR reduction technique is proposed for space-time block coding (STBC) MIMO-OFDM systems that combine the coding capabilities to PAPR reduction methods, while leveraging the new degree of freedom provided by the presence of multiple transmit chairs (MIMO). In the first part, we presented an extensive literature review of PAPR reduction techniques for OFDM and MIMO-OFDM systems. The work developed a PAPR reduction technique taxonomy, and analyzed the motivations for reducing the PAPR in current communication systems, emphasizing two important motivations such as power savings and coverage gain. In the tax onomy presented here, we include a new category, namely, hybrid techniques. Additionally, we drew a conclusion regarding the importance of hybrid PAPR reduction techniques. In the second part, we studied the effect of forward error correction (FEC) codes on the PAPR for the coded OFDM (COFDM) system. We simulated and compared the CCDF of the PAPR and its relationship with the autocorrelation of the COFDM signal before the inverse fast Fourier transform (IFFT) block. This allows to conclude on the main characteristics of the codes that generate high peaks in the COFDM signal, and therefore, the optimal parameters in order to reduce PAPR. We emphasize our study in FEC codes as linear block codes, and convolutional codes. Finally, we proposed a new hybrid PAPR reduction technique for an STBC MIMO-OFDM system, in which the convolutional code is optimized to avoid PAPR degradation, which also combines successive suboptimal cross-antenna rotation and inversion (SS-CARI) and iterative modified companding and filtering schemes. The new method permits to obtain a significant net gain for the system, i.e., considerable PAPR reduction, bit error rate (BER) gain as compared to the basic MIMO-OFDM system, low complexity, and reduced spectral splatter. The new hybrid technique was extensively evaluated by simulation, and the complementary cumulative distribution function (CCDF), the BER, and the power spectral density (PSD) were compared to the original STBC MIMO-OFDM signal

LTE Multicodeword-MIMO; Hybrid-ARQ performance studies

Langattomassa tiedonsiirrossa on tällä hetkellä meneillään suuria muutoksia, sitten ensimmäisen matkapuhelinsukupolven käyttöönoton. Uusia datapuhelimia, kuten myös kämmentietokoneita käytetään internetin selaamiseen, videoiden katselemiseen ja pelaamiseen matkapuhelinverkon kautta. Voidaakseen tyydyttämään kuluttajien vaatimukset, tarve uusien langattoman tiedonsiirron normien luomiseen on merkittävä. Long Term Evolution (LTE) on, Third Generation Partership Project:in (3GPP) johtama, ehdokas seuraavaksi matkapuhelinsukupolven standardiksi. LTE:n ominaisuuksiin kuuluvat mm. korkea suoritusteho, matala latenssi, yksinkertaisuus ja alhaiset kustannukset. Tulevassa standardissa on aihealueita, joita ei ole varsinaisesti tutkittu akateemisessa maailmassa kuten Hybrid Automatic Repeat Request:in (HARQ) suorituskykyä. Koska langaton tiedonsiirto on epälineaarinen prosessi, sitä mallinnetaan simulaattorin avulla. Simulaattori on tehty MATLAB ympäristössä LTE:n standardien mukaisesti. Kolme eri Multiple Input Multiple Output (MIMO) downlink HARQ skenaariota luotiin ja niiden suorituskykyä arvioitiin. Pääpaino työn tutkimukselle kohdistuu kolmen HARQ:n suorituskykyyn, tosin simulaattorimallin todistaminen on myös keskeinen osa tätä työtä.Mobile communication is going through major changes since the introduction of first generation mobile phones. Not only phones, but various handheld devices are starting to use the mobile communication network for internet browsing, multimedia or even online gaming. There is a high need for fast mobile connection and therefore new standards and specifications need to be created to satisfy the consumer requirements. Long Term Evolution (LTE) is the latest candidate for the next mobile communication standard led by Third Generation Partnership Project (3GPP). LTEs main features are high throughput, low latency, simple architecture and low operating costs. Since mobile data transmission is a non linear process, a simulator is built to model the procedure. Simulator made for this thesis was written in MATLAB meeting the 3GPPs set standards for LTE. Three different Multiple Input Multiple Output (MIMO) downlink HARQ scenarios were created and their performance was evaluated. The main focus of this thesis is the performance comparison of the three downlink scenarios; however the verification of the simulator model plays also a significant role in this work