476 research outputs found

    Impact of channel statistics and correlation on underwater acoustic communication systems

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    Several statistical properties of underwater acoustic channels gathered from experiment data are analyzed. The baseband channel impulse response (CIR) is estimated using a time domain least squares technique with a sliding window applied to the probing sequences. From the CIR estimation, the probability distribution functions (PDFs) of the magnitude, real part, imaginary part, and phase of the CIR are calculated. Gamma, Rayleigh, and compound k distributions are fitted to the magnitude PDF and the fitness of the distributions are calculated with a two-sample Kolmogorov-Smirnov test. Other statistics such as the autocorrelation function, coherence time, and scattering function are evaluated. The results show that the underwater acoustics channels are worse than the Rayleigh fading commonly seen as the worst case radio channel. Furthermore, the spatial and intertap correlation matrices of multiple input multiple output (MIMO) systems are estimated using experimental data. It is shown that underwater acoustic MIMO channels exhibit high spatial and temporal correlation. The bit error rate (BER) of the receiver using Frequency-domain turbo equalization is also evaluated in different channel correlation setups, demonstrating strong effects of the spatial-temporal correlation function on the performance --Abstract, page iv

    Hardware emulation of wireless communication fading channels

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    This dissertation investigates several main challenges to implementing hardware-based wireless fading channel emulators with emphasis on incorporating accurate correlation properties. Multiple-input multiple-output (MIMO) fading channels are usually triply-selective with three types of correlation: temporal correlation, inter-tap correlation, and spatial correlation. The proposed emulators implement the triply-selective fading Channel Impulse Response (CIR) by incorporating the three types of correlation into multiple uncorrelated frequency-flat Rayleigh fading waveforms while meeting real-time requirements for high data-rate, large-sized MIMO, and/or long CIR channels. Specifically, mixed parallel-serial computational structures are implemented for Kronecker products of the correlation matrices, which makes the best tradeoff between computational speed and hardware usage. Five practical fading channel examples are implemented for RF or underwater acoustic MIMO applications. The performance of the hardware emulators are verified with an Altera Field-Programmable Gate Array (FPGA) platform and the results match the software simulators in terms of statistical and correlation properties. The dissertation also contributes to the development of a 2-by-2 MIMO transceiver testbench that is used to measure real-world fading channels. Intensive channel measurements are performed for indoor fixed mobile-to-mobile channels and the estimated CIRs demonstrate the triply-selective correlation properties --Abstract, page iv

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

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    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

    Eigenvalue Dynamics of a Central Wishart Matrix with Application to MIMO Systems

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    We investigate the dynamic behavior of the stationary random process defined by a central complex Wishart (CW) matrix W(t){\bf{W}}(t) as it varies along a certain dimension tt. We characterize the second-order joint cdf of the largest eigenvalue, and the second-order joint cdf of the smallest eigenvalue of this matrix. We show that both cdfs can be expressed in exact closed-form in terms of a finite number of well-known special functions in the context of communication theory. As a direct application, we investigate the dynamic behavior of the parallel channels associated with multiple-input multiple-output (MIMO) systems in the presence of Rayleigh fading. Studying the complex random matrix that defines the MIMO channel, we characterize the second-order joint cdf of the signal-to-noise ratio (SNR) for the best and worst channels. We use these results to study the rate of change of MIMO parallel channels, using different performance metrics. For a given value of the MIMO channel correlation coefficient, we observe how the SNR associated with the best parallel channel changes slower than the SNR of the worst channel. This different dynamic behavior is much more appreciable when the number of transmit (NTN_T) and receive (NRN_R) antennas is similar. However, as NTN_T is increased while keeping NRN_R fixed, we see how the best and worst channels tend to have a similar rate of change.Comment: 15 pages, 9 figures and 1 table. This work has been accepted for publication at IEEE Trans. Inf. Theory. Copyright (c) 2014 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending a request to [email protected]

    Designing the Undersea Internet of Things (IoT) and Machine-to-Machine (M2M) Communications Using UnderWater Acoustic MIMO Networks

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    This review paper tries to assess the spectral-efficient (SE) and energy-efficient (EE) performance of underwater acoustic multiple-input multiple-output (UWA/MIMO) networks. Since UWA/MIMO networks define the cutting-edge communications platform of the future’s undersea IoT and M2M networks, the factors that influence their SE and EE performance are thoroughly examined in this paper.The contribution of this paper is three-fold. First, the performance of UWA/MIMO networks is studied with regard to appropriate transmission, SE and EE metrics. The SE and EE performance of these networks drastically depends on the used frequency band, the transmitted power, the MIMO scheme properties, the power consumption profile of the deployed UWA system equipment and the topological characteristics of MIMO configurations. In order to achieve the transition from traditional UWA single-input single-output (UWA/SISO) networks to UWA/MIMO networks, a new singular value decomposition MIMO (SVD/MIMO) module, which also permits the theoretical computation of the aforementioned transmission, SE and EE metrics in UWA networks, is first presented. Second, based on the aforementioned transmission, SE and EE metrics, a SE/EE trade-off relation is proposed in order to investigate the combined SE and EE performance of UWA/MIMO networks. On the basis of this SE/EE trade-off relation, it is first revealed that today’s UWA system equipment cannot support the further IoT broadband exploitation with satisfactory EE performance. Third, the concepts of multi-hop UWA communications and standard UWA topologies are outlined and promoted so that further SE and EE improvement can concurrently occur. These concepts are quantitatively validated by the SE and EE metrics as well as the SE/EE trade-off curves.Based on the findings of this paper, suitable transmitted power levels and better design of UWA/MIMO configurations are promoted so that: (i) SE and EE requirements can be satisfied at will; and (ii) EE-oriented high-bitrate M2M communications network design can be established.Citation: Lazaropoulos, A. G. (2016). "Designing the Undersea Internet of Things (IoT) and Machine-to-Machine (M2M) Communications Using UnderWater Acoustic MIMO Networks." Trends in Renewable Energy, 2(1), 13-50. DOI: 10.17737/tre.2016.2.1.001

    Investigation of VBLAST Equalization Technique for Underwater Acoustic Communications

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    Underwater Acoustic Communications (UWAC) is an emerging technology in the field of underwater communications, and it is challenging because of the signal attenuation of the sound waves. Multiple Input and Multiple-Output (MIMO) is introduced in UWAC because of its support in enhancing the data throughput even under the conditions of interference, signal fading, and multipath. The paper presents the concept and analysis of 2× 2 MIMO UWAC systems that uses a 4- QAM spatial modulation scheme thus minimizing the decoding complexity and overcoming the Inter Channel Interference (IChI). Bit Error Rate (BER) investigation is carried out over different link distances under acoustic Line of Sight (LOS). The utilization of Zero Forcing (ZF) and Vertical-Bell Laboratories Layered Space-Time (VBLAST) equalizers, which estimates the transmitted data proves a success of removing Inter Symbol Interference (ISI).  The ISI caused due to multipath effect and scattering in UWAC can be reduced by iterative process considered in VBLAST.  A study is made on how the distance between the transmitter and the receiver and the Doppler Effect has its impact on the performance of the system

    Doctor of Philosophy

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    dissertationThis dissertation addresses several key challenges in multiple-antenna communications, including information-theoretical analysis of channel capacity, capacity-achieving signaling design, and practical statistical detection algorithms. The first part of the thesis studies the capacity limits of multiple-input multiple-output (MIMO) multiple access channel (MAC) via virtual representation (VR) model. The VR model captures the physical scattering environment via channel gains in the angular domain, and hence is a realistic MIMO channel model that includes many existing channel models as special cases. This study provides analytical characterization of the optimal input distribution that achieves the sum-capacity of MAC-VR. It also investigates the optimality of beamforming, which is a simple scalar coding strategy desirable in practice. For temporally correlated channels, beamforming codebook designs are proposed that can efficiently exploit channel correlation. The second part of the thesis focuses on statistical detection for time-varying frequency-selective channels. The proposed statistical detectors are developed based on Markov Chain Monte Carlo (MCMC) techniques. The complexity of such detectors grows linearly in system dimensions, which renders them applicable to inter-symbol-interference (ISI) channels with long delay spread, for which the traditional trellis-based detectors fail due to prohibitive complexity. The proposed MCMC detectors provide substantial gain over the de facto turbo minimum-mean square-error (MMSE) detector for both synthetic channel and underwater acoustic (UWA) channels. The effectiveness of the proposed MCMC detectors is successfully validated through experimental data collected from naval at-sea experiments
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