The Experts below are selected from a list of 5715 Experts worldwide ranked by ideXlab platform
Peter Willett - One of the best experts on this subject based on the ideXlab platform.
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multicarrier communication over underwater acoustic channels with nonuniform doppler shifts
IEEE Journal of Oceanic Engineering, 2008Co-Authors: Baosheng Li, Shengli Zhou, Milica Stojanovic, Lee Freitag, Peter WillettAbstract:Underwater acoustic (UWA) channels are wideband in nature due to the small ratio of the carrier frequency to the signal bandwidth, which introduces frequency-dependent Doppler shifts. In this paper, we treat the channel as having a common Doppler scaling factor on all propagation paths, and propose a two-step approach to mitigating the Doppler effect: 1) nonuniform Doppler compensation via resampling that converts a "wideband" problem into a "narrowband" problem and 2) high-resolution uniform compensation of the residual Doppler. We focus on zero-padded orthogonal frequency-division multiplexing (Ofdm) to minimize the transmission power. Null Subcarriers are used to facilitate Doppler compensation, and pilot Subcarriers are used for channel estimation. The receiver is based on block-by-block processing, and does not rely on channel dependence across Ofdm blocks; thus, it is suitable for fast-varying UWA channels. The data from two shallow-water experiments near Woods Hole, MA, are used to demonstrate the receiver performance. Excellent performance results are obtained even when the transmitter and the receiver are moving at a relative speed of up to 10 kn, at which the Doppler shifts are greater than the Ofdm Subcarrier spacing. These results suggest that Ofdm is a viable option for high-rate communications over wideband UWA channels with nonuniform Doppler shifts.
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non uniform doppler compensation for zero padded Ofdm over fast varying underwater acoustic channels
OCEANS 2007 - Europe, 2007Co-Authors: Baosheng Li, Shengli Zhou, Milica Stojanovic, Lee Freitag, Peter WillettAbstract:Underwater acoustic channels are wideband in nature due to the fact that the signal bandwidth is not negligible with respect to the center frequency. Ofdm transmissions over UWA channels encounter frequency-dependent Doppler drifts that destroy the orthogonality among Ofdm Subcarriers. In this paper, we propose a two-step approach to mitigating the frequency-dependent Doppler drifts in zero-padded Ofdm transmissions over fast-varying channels: (1) non-uniform Doppler compensation via resampling that converts a "wideband" problem into a "narrowband" problem; and (2) high-resolution uniform compensation on the residual Doppler. Based on block-by-block processing, our receiver does not rely on channel dependence across Ofdm blocks, and is thus desirable for fast-varying UWA channels. We test our receiver with data from a shallow water experiment at Buzzards Bay, Massachusetts. Our receiver achieves excellent performance even when the transmitter and the receivers have a relative speed up to 10 knots, where the Doppler drifts are several times larger than the Ofdm Subcarrier spacing.
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recursive and trellis based feedback reduction for mimo Ofdm with rate limited feedback
IEEE Transactions on Wireless Communications, 2006Co-Authors: Shengli Zhou, Baosheng Li, Peter WillettAbstract:We investigate an adaptive MIMO-Ofdm system with a feedback link that can only convey a finite number of bits. We consider three different transmitter configurations: i) beamforming applied per Ofdm Subcarrier, ii) precoded spatial multiplexing applied per Subcarrier, and iii) precoded orthogonal space time block coding applied per Subcarrier. Depending on the channel realization, the receiver selects the optimal beamforming vector or precoding matrix from a finite-size codebook on each Subcarrier, and informs the transmitter through finite-rate feedback. Exploiting the fact that the channel responses across Ofdm Subcarriers are correlated, we propose two methods to reduce the amount of feedback. One is recursive feedback encoding that selects the optimal beamforming/precoding choices sequentially across the Subcarriers, and adopts a smaller-size time-varying codebook per Subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal decisions for all Subcarriers at once along a trellis structure via the Viterbi algorithm. Our methods are applicable to different transmitter configurations in a unified fashion. Simulation results demonstrate that the trellis-based approach outperforms the recursive method as well as an existing interpolation-based alternative at high signal-to-noise-ratio, as the latter suffers from "diversity loss"
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GLOBECOM - Recursive and trellis-based feedback reduction for MIMO-Ofdm with transmit beamforming
GLOBECOM '05. IEEE Global Telecommunications Conference 2005., 2005Co-Authors: Shengli Zhou, Peter WillettAbstract:We consider a MIMO-Ofdm system with transmit beamforming applied on each Ofdm Subcarrier, where each beamforming vector is drawn from a codebook with finite size. Depending on the channel realization, the receiver decides the optimal beamforming vector on each Subcarrier, and informs the transmitter through a rate-limited feedback link. Exploiting the fact that the channel responses across Ofdm Subcarriers are correlated, we propose two methods to reduce the amount of needed feedback. One is recursive feedback encoding that selects the optimal beamforming vectors sequentially across the Subcarriers, and adopts a smaller-size time-varying codebook per Subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal beamforming vectors for all Subcarriers at once along a trellis structure via the A. The trellis-based feedback encoding outperforms the recursive feedback encoding at the expense of encoding complexity at the receiver. Simulation results demonstrate that our trellis-based approach outperforms an existing interpolation-based alternative, as the latter incurs diversity loss at high SNR
Shengli Zhou - One of the best experts on this subject based on the ideXlab platform.
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multicarrier communication over underwater acoustic channels with nonuniform doppler shifts
IEEE Journal of Oceanic Engineering, 2008Co-Authors: Baosheng Li, Shengli Zhou, Milica Stojanovic, Lee Freitag, Peter WillettAbstract:Underwater acoustic (UWA) channels are wideband in nature due to the small ratio of the carrier frequency to the signal bandwidth, which introduces frequency-dependent Doppler shifts. In this paper, we treat the channel as having a common Doppler scaling factor on all propagation paths, and propose a two-step approach to mitigating the Doppler effect: 1) nonuniform Doppler compensation via resampling that converts a "wideband" problem into a "narrowband" problem and 2) high-resolution uniform compensation of the residual Doppler. We focus on zero-padded orthogonal frequency-division multiplexing (Ofdm) to minimize the transmission power. Null Subcarriers are used to facilitate Doppler compensation, and pilot Subcarriers are used for channel estimation. The receiver is based on block-by-block processing, and does not rely on channel dependence across Ofdm blocks; thus, it is suitable for fast-varying UWA channels. The data from two shallow-water experiments near Woods Hole, MA, are used to demonstrate the receiver performance. Excellent performance results are obtained even when the transmitter and the receiver are moving at a relative speed of up to 10 kn, at which the Doppler shifts are greater than the Ofdm Subcarrier spacing. These results suggest that Ofdm is a viable option for high-rate communications over wideband UWA channels with nonuniform Doppler shifts.
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non uniform doppler compensation for zero padded Ofdm over fast varying underwater acoustic channels
OCEANS 2007 - Europe, 2007Co-Authors: Baosheng Li, Shengli Zhou, Milica Stojanovic, Lee Freitag, Peter WillettAbstract:Underwater acoustic channels are wideband in nature due to the fact that the signal bandwidth is not negligible with respect to the center frequency. Ofdm transmissions over UWA channels encounter frequency-dependent Doppler drifts that destroy the orthogonality among Ofdm Subcarriers. In this paper, we propose a two-step approach to mitigating the frequency-dependent Doppler drifts in zero-padded Ofdm transmissions over fast-varying channels: (1) non-uniform Doppler compensation via resampling that converts a "wideband" problem into a "narrowband" problem; and (2) high-resolution uniform compensation on the residual Doppler. Based on block-by-block processing, our receiver does not rely on channel dependence across Ofdm blocks, and is thus desirable for fast-varying UWA channels. We test our receiver with data from a shallow water experiment at Buzzards Bay, Massachusetts. Our receiver achieves excellent performance even when the transmitter and the receivers have a relative speed up to 10 knots, where the Doppler drifts are several times larger than the Ofdm Subcarrier spacing.
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recursive and trellis based feedback reduction for mimo Ofdm with rate limited feedback
IEEE Transactions on Wireless Communications, 2006Co-Authors: Shengli Zhou, Baosheng Li, Peter WillettAbstract:We investigate an adaptive MIMO-Ofdm system with a feedback link that can only convey a finite number of bits. We consider three different transmitter configurations: i) beamforming applied per Ofdm Subcarrier, ii) precoded spatial multiplexing applied per Subcarrier, and iii) precoded orthogonal space time block coding applied per Subcarrier. Depending on the channel realization, the receiver selects the optimal beamforming vector or precoding matrix from a finite-size codebook on each Subcarrier, and informs the transmitter through finite-rate feedback. Exploiting the fact that the channel responses across Ofdm Subcarriers are correlated, we propose two methods to reduce the amount of feedback. One is recursive feedback encoding that selects the optimal beamforming/precoding choices sequentially across the Subcarriers, and adopts a smaller-size time-varying codebook per Subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal decisions for all Subcarriers at once along a trellis structure via the Viterbi algorithm. Our methods are applicable to different transmitter configurations in a unified fashion. Simulation results demonstrate that the trellis-based approach outperforms the recursive method as well as an existing interpolation-based alternative at high signal-to-noise-ratio, as the latter suffers from "diversity loss"
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GLOBECOM - Recursive and trellis-based feedback reduction for MIMO-Ofdm with transmit beamforming
GLOBECOM '05. IEEE Global Telecommunications Conference 2005., 2005Co-Authors: Shengli Zhou, Peter WillettAbstract:We consider a MIMO-Ofdm system with transmit beamforming applied on each Ofdm Subcarrier, where each beamforming vector is drawn from a codebook with finite size. Depending on the channel realization, the receiver decides the optimal beamforming vector on each Subcarrier, and informs the transmitter through a rate-limited feedback link. Exploiting the fact that the channel responses across Ofdm Subcarriers are correlated, we propose two methods to reduce the amount of needed feedback. One is recursive feedback encoding that selects the optimal beamforming vectors sequentially across the Subcarriers, and adopts a smaller-size time-varying codebook per Subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal beamforming vectors for all Subcarriers at once along a trellis structure via the A. The trellis-based feedback encoding outperforms the recursive feedback encoding at the expense of encoding complexity at the receiver. Simulation results demonstrate that our trellis-based approach outperforms an existing interpolation-based alternative, as the latter incurs diversity loss at high SNR
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Adaptive MIMO-Ofdm based on partial channel state information
IEEE Transactions on Signal Processing, 2004Co-Authors: Pengfei Xia, Shengli Zhou, Georgios B GiannakisAbstract:Relative to designs assuming no channel knowledge at the transmitter, considerably improved communications become possible when adapting the transmitter to the intended propagation channel. As perfect knowledge is rarely available, transmitter designs based on partial (statistical) channel state information (CSI) are of paramount importance not only because they are more practical but also because they encompass the perfect- and no-knowledge paradigms. In this paper, we first provide a partial CSI model for orthogonal frequency division multiplexed (Ofdm) transmissions over multi-input multi-output (MIMO) frequency-selective fading channels. We then develop an adaptive MIMO-Ofdm transmitter by applying an adaptive two-dimensional (2-D) coder-beamformer we derived recently on each Ofdm Subcarrier, along with an adaptive power and bit loading scheme across Ofdm Subcarriers. Relying on the available partial CSI at the transmitter, our objective is to maximize the transmission rate, while guaranteeing a prescribed error performance, under the constraint of fixed transmit-power. Numerical results confirm that the adaptive 2-D space-time coder-beamformer (with two basis beams as the two "strongest" eigenvectors of the channel's correlation matrix perceived at the transmitter) combined with adaptive Ofdm (power and bit loaded with M-ary quadrature amplitude modulated (QAM) constellations) improves the transmission rate considerably.
Jinho Choi - One of the best experts on this subject based on the ideXlab platform.
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WCNC - Short-Range Ambient Backscatter Communication Using Reconfigurable Intelligent Surfaces
2020 IEEE Wireless Communications and Networking Conference (WCNC), 2020Co-Authors: Mahyar Nemati, Jie Ding, Jinho ChoiAbstract:Ambient backscatter communication (AmBC) has been introduced to address communication and power efficiency issues for short-range and low-power Internet-of-Things (IoT) applications. On the other hand, reconfigurable intelligent surface (RIS) has been recently proposed as a promising approach that can control the propagation environment especially in indoor communication environments. In this paper, we propose a new AmBC model over ambient orthogonal-frequency-division-multiplexing (Ofdm) Subcarriers in the frequency domain in conjunction with RIS for short-range communication scenarios. A tag transmits one bit per each Ofdm Subcarrier broadcasted from a WiFi access point. Then, RIS augments the signal quality at a reader by compensating the phase distortion effect of multipath channel on the incident signal. We also exploit the special spectrum structure of Ofdm to transmit more data over its squeezed orthogonal Subcarriers in the frequency domain. Consequently, the proposed method improves the bit-error-rate (BER) performance and provides a higher data rate compared to existing AmBC methods. Analytical and numerical evaluations show the superior performance of the proposed approach in terms of BER and data rate.
Xingwen Yi - One of the best experts on this subject based on the ideXlab platform.
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Theoretical calculation on ICI reduction using digital coherent superposition of optical Ofdm Subcarrier pairs in the presence of laser phase noise
Optics Express, 2014Co-Authors: Xingwen Yi, Bo Xu, Jing ZhangAbstract:Digital coherent superposition (DCS) of optical Ofdm Subcarrier pairs with Hermitian symmetry can reduce the inter-carrier-interference (ICI) noise resulted from phase noise. In this paper, we show two different implementations of DCS-Ofdm that have the same performance in the presence of laser phase noise. We complete the theoretical calculation on ICI reduction by using the model of pure Wiener phase noise. By Taylor expansion of the ICI, we show that the ICI power is cancelled to the second order by DCS. The fourth order term is further derived out and only decided by the ratio of laser linewidth to Ofdm Subcarrier symbol rate, which can greatly simplify the system design. Finally, we verify our theoretical calculations in simulations and use the analytical results to predict the system performance. DCS-Ofdm is expected to be beneficial to certain optical fiber transmissions.
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Enhanced phase noise tolerance of coherent optical Ofdm using digital coherent superposition
2014Co-Authors: Xingwen Yi, Xuemei Chen, Dinesh Sharma, Jing Zhang, Qi YangAbstract:We experimentally demonstrate that the digital coherent superposition of optical Ofdm Subcarrier pairs with Hermitian symmetry can mitigate phase noise, including laser phase noise and self-phase modulation in a nonlinear optical fiber transmission.
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Digital coherent superposition of optical Ofdm Subcarrier pairs with Hermitian symmetry for phase noise mitigation
Optics Express, 2014Co-Authors: Xingwen Yi, Xuemei Chen, Dinesh Sharma, Qi Yang, Chao Li, Zhaohui LiAbstract:Digital coherent superposition (DCS) provides an approach to combat fiber nonlinearities by trading off the spectrum efficiency. In analogy, we extend the concept of DCS to the optical Ofdm Subcarrier pairs with Hermitian symmetry to combat the linear and nonlinear phase noise. At the transmitter, we simply use a real-valued Ofdm signal to drive a Mach-Zehnder (MZ) intensity modulator biased at the null point and the so-generated Ofdm signal is Hermitian in the frequency domain. At receiver, after the conventional Ofdm signal processing, we conduct DCS of the optical Ofdm Subcarrier pairs, which requires only conjugation and summation. We show that the inter-carrier-interference (ICI) due to phase noise can be reduced because of the Hermitain symmetry. In a simulation, this method improves the tolerance to the laser phase noise. In a nonlinear WDM transmission experiment, this method also achieves better performance under the influence of cross phase modulation (XPM).
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Experimental Demonstration of Digital Coherent Superposition of Optical Ofdm Subcarrier Pairs for Mitigation of Linear and Nonlinear Phase Noise
Optical Fiber Communication Conference, 2014Co-Authors: Xingwen Yi, Xuemei Chen, Qi Yang, Chao Li, Zhaohui LiAbstract:We experimentally demonstrate digital coherent superposition of optical Ofdm Subcarrier pairs with Hermitian symmetry to mitigate phase noise, including laser phase noise and cross-phase modulation in a WDM transmission.
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Proposal of Digital Coherent Superposition of Optical Ofdm Subcarrier Pairs in the Presence of Phase Noise
Asia Communications and Photonics Conference 2013, 2013Co-Authors: Xingwen Yi, Qi YangAbstract:We propose digital coherent superposition of optical Ofdm Subcarrier pairs with Hermitian symmetry to mitigate phase noise. Both in theory and simulation, we show that the inter-carrier-interference resulted from phase noise can be reduced.
Robert W. Heath - One of the best experts on this subject based on the ideXlab platform.
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interpolation based unitary precoding for spatial multiplexing mimo Ofdm with limited feedback
IEEE Transactions on Signal Processing, 2006Co-Authors: Jihoon Choi, Bishwarup Mondal, Robert W. HeathAbstract:Spatial multiplexing with linear precoding is a simple technique for achieving high spectral efficiency in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-Ofdm) systems. Linear precoding requires channel state information for each Ofdm Subcarrier, which can be achieved using feedback. To reduce the amount of feedback, this paper proposes a limited feedback architecture that combines precoder quantization with a special matrix interpolator. In the proposed system, the receiver sends information about a fraction of the precoding matrices to the transmitter and the transmitter reconstructs the precoding matrices for all the Subcarriers. A new interpolator is proposed inspired by spherical interpolation that respects the orthogonal columns of the precoding matrices and the performance invariance to right multiplication by a unitary matrix. The interpolator is parameterized by a set of unitary matrices; a construction of a suitable set is briefly described. Simulations illustrate the performance of limited feedback precoding with coding, estimation or prediction error, and time variation for bit error rate (BER), mutual information, and mean squared error (MSE)
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interpolation based transmit beamforming for mimo Ofdm with limited feedback
IEEE Transactions on Signal Processing, 2005Co-Authors: Jihoon Choi, Robert W. HeathAbstract:Transmit beamforming and receive combining are simple methods for exploiting spatial diversity in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-Ofdm) system. Optimal beamforming requires channel state information in the form of the beamforming vectors for each Ofdm Subcarrier. This paper proposes a limited feedback architecture that combines beamforming vector quantization and smart vector interpolation. In the proposed system, the receiver sends a fraction of information about the optimal beamforming vectors to the transmitter and the transmitter computes the beamforming vectors for all Subcarriers through interpolation. A new spherical interpolator is developed that exploits parameters for phase rotation to satisfy the phase invariance and unit norm properties of the transmitted beamforming vectors. The beamforming vectors and phase parameters are quantized at the receiver and the quantized information is provided to the transmitter. The proposed quantization system provides only a moderate increase in complexity versus over comparable approaches. Numerical simulations show that the proposed scheme performs better than existing diversity techniques with the same feedback data rate.
