The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Xiang-gen Xia - One of the best experts on this subject based on the ideXlab platform.
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IRCI free colocated mimo radar based on sufficient Cyclic Prefix OFDM waveforms
IEEE Transactions on Aerospace and Electronic Systems, 2015Co-Authors: Yunhe Cao, Xiang-gen Xia, Shenghua WangAbstract:In this paper, we propose a Cyclic Prefix (CP)-based multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) range reconstruction method and its corresponding MIMO-OFDM waveform design for colocated MIMO radar systems. Our proposed MIMO-OFDM waveform design achieves the maximum signal-to-noise ratio gain after the range reconstruction, and its peak-to-average power ratio in the discrete time domain is also optimal, i.e., 0 dB, when Zadoff-Chu sequences are used in the discrete frequency domain as the weighting coefficients for the subcarriers. We also investigate the performance when there are transmit and receive digital beamforming (DBF) pointing errors. It is shown that our proposed CP-based MIMO-OFDM range reconstruction is interrange cell interference free no matter whether there are transmit and receive DBF pointing errors or not. Simulation results are presented to verify the theory and compare it with the conventional OFDM and linear frequency modulation colocated MIMO radars.
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MIMO OFDM radar IRCI free range reconstruction with sufficient Cyclic Prefix
IEEE Transactions on Aerospace and Electronic Systems, 2015Co-Authors: Xiang-gen Xia, Tianxian Zhang, Lingjiang KongAbstract:In this paper, we propose multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) radar with sufficient Cyclic Prefix (CP), where all OFDM pulses transmitted from different transmitters share the same frequency band and are orthogonal to each other for every subcarrier in the discrete frequency domain. The orthogonality is not affected by time delays from transmitters. Thus, our proposed MIMO OFDM radar has the same range resolution as single transmitter radar and achieves full spatial diversity. Orthogonal designs are used to achieve this orthogonality across the transmitters, with which it is only needed to design OFDM pulses for the first transmitter. We also propose a joint pulse compression and pulse coherent integration for range reconstruction. In order to achieve the optimal signal-to-noise ratio (SNR) for the range reconstruction, we apply the paraunitary filterbank theory to design the OFDM pulses. We then propose a modified iterative clipping and filtering (MICF) algorithm for the designs of OFDM pulses jointly, when other important factors, such as peak-to-average power ratio (PAPR) in time domain, are also considered.With our proposed MIMO OFDM radar, there is no interference for the range reconstruction not only across the transmitters but also across the range cells in a swath called inter-range-cell interference (IRCI) free that is similar to our previously proposed CP-based OFDM radar for single transmitter. Simulations are presented to illustrate our proposed theory and show that the CP-based MIMO OFDM radar outperforms the existing frequency-band shared MIMO radar with polyphase codes and also frequency division MIMO radar.
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ofdm synthetic aperture radar imaging with sufficient Cyclic Prefix
IEEE Transactions on Geoscience and Remote Sensing, 2015Co-Authors: Tianxian Zhang, Xiang-gen XiaAbstract:The existing linear-frequency-modulated (or step frequency) and random noise synthetic aperture radar (SAR) systems may correspond to the frequency-hopping and direct-sequence spread spectrum systems in the past second- and third-generation wireless communications. Similar to the current and future wireless communications generations, in this paper, we propose the orthogonal frequency-division multiplexing (OFDM) SAR imaging, where a sufficient Cyclic Prefix (CP) is added to each OFDM pulse. The sufficient CP insertion converts an intersymbol interference (ISI) channel from multipaths into multiple ISI-free subchannels as the key in a wireless communications system, and analogously, it provides an inter-range-cell interference (IRCI)-free (high range resolution) SAR image in a SAR system. The sufficient CP insertion along with our newly proposed SAR imaging algorithm, particularly for the OFDM signals, also differentiates this paper from all the existing studies in the literature on OFDM radar signal processing. Simulation results are presented to illustrate the high-range-resolution performance of our proposed CP-based OFDM SAR imaging algorithm.
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IRCI Free Colocated MIMO Radar Based on Sufficient Cyclic Prefix OFDM Waveforms
arXiv: Information Theory, 2014Co-Authors: Yunhe Cao, Xiang-gen Xia, Shenghua WangAbstract:In this paper, we propose a Cyclic Prefix (CP) based MIMO-OFDM range reconstruction method and its corresponding MIMO-OFDM waveform design for co-located MIMO radar systems. Our proposed MIMO-OFDM waveform design achieves the maximum signal-to-noise ratio (SNR) gain after the range reconstruction and its peak-to-average power ratio (PAPR) in the discrete time domain is also optimal, i.e., 0dB, when Zadoff-Chu sequences are used in the discrete frequency domain as the weighting coefficients for the subcarriers. We also investigate the performance when there are transmit and receive digital beamforming (DBF) pointing errors. It is shown that our proposed CP based MIMO-OFDM range reconstruction is inter-range-cell interference (IRCI) free no matter whether there are transmit and receive DBF pointing errors or not. Simulation results are presented to verify the theory and compare it with the conventional OFDM and LFM co-located MIMO radars.
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MIMO OFDM Radar IRCI Free Range Reconstruction with Sufficient Cyclic Prefix
arXiv: Information Theory, 2014Co-Authors: Xiang-gen Xia, Tianxian Zhang, Lingjiang KongAbstract:In this paper, we propose MIMO OFDM radar with sufficient Cyclic Prefix (CP), where all OFDM pulses transmitted from different transmitters share the same frequency band and are orthogonal to each other for every subcarrier in the discrete frequency domain. The orthogonality is not affected by time delays from transmitters. Thus, our proposed MIMO OFDM radar has the same range resolution as single transmitter radar and achieves full spatial diversity. Orthogonal designs are used to achieve this orthogonality across the transmitters, with which it is only needed to design OFDM pulses for the first transmitter. We also propose a joint pulse compression and pulse coherent integration for range reconstruction. In order to achieve the optimal SNR for the range reconstruction, we apply the paraunitary filterbank theory to design the OFDM pulses. We then propose a modified iterative clipping and filtering (MICF) algorithm for the designs of OFDM pulses jointly, when other important factors, such as peak-to-average power ratio (PAPR) in time domain, are also considered. With our proposed MIMO OFDM radar, there is no interference for the range reconstruction not only across the transmitters but also across the range cells in a swath called inter-range-cell interference (IRCI) free that is similar to our previously proposed CP based OFDM radar for single transmitter. Simulations are presented to illustrate our proposed theory and show that the CP based MIMO OFDM radar outperforms the existing frequency-band shared MIMO radar with polyphase codes and also frequency division MIMO radar.
Sumit Roy - One of the best experts on this subject based on the ideXlab platform.
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subspace based blind channel estimation for ofdm by exploiting virtual carriers
IEEE Transactions on Wireless Communications, 2003Co-Authors: Sumit RoyAbstract:Reliable channel estimation is indispensable for orthogonal frequency-division multiplexing (OFDM) systems employing coherent detection and adaptive loading in order to achieve high data rate communications. Several options exist in practical OFDM systems-including training symbols, Cyclic Prefix, virtual carriers, pilot tones, and receiver diversity-to facilitate channel estimation. In this paper, a subspace blind channel estimation method based on exploiting the presence of virtual carriers is proposed for OFDM systems over a time-dispersive channel. The method can be applied to conventional OFDM systems with Cyclic Prefix as well as OFDM systems with no Cyclic Prefix. The reduction/elimination of Cyclic Prefix thereby provides the OFDM systems the potential to achieve higher channel utilization than most previously reported Cyclic Prefix based estimators. Sufficient channel identifiability condition is developed as well. Comparison with two other recently reported subspace methods is presented via computer simulations to support the effectiveness of the proposed method.
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a subspace blind channel estimation method for ofdm systems without Cyclic Prefix
IEEE Transactions on Wireless Communications, 2002Co-Authors: Sumit RoyAbstract:We propose a subspace based blind channel estimation method for orthogonal frequency-division multiplexing (OFDM) systems over a time-dispersive channel. Our approach is motivated by the resemblance of the multichannel signal model resulting from oversampling (or use of multiple receive sensors) of the received OFDM signal to that in conventional single carrier system. The proposed algorithm distinguishes itself from many previously reported channel estimation methods by the elimination of the Cyclic Prefix, thereby leading to higher channel utilization. Comparison of the proposed method with other two reported subspace channel estimation methods is presented by computer simulations to support its effectiveness.
P P Vaidyanathan - One of the best experts on this subject based on the ideXlab platform.
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generalized geometric mean decomposition and dfe mmse transceiver design for Cyclic Prefix systems
International Conference on Acoustics Speech and Signal Processing, 2011Co-Authors: Chihhao Liu, P P VaidyanathanAbstract:This paper considers the decomposition of a complex matrix as the product of several sets of semi-unitary matrices and upper triangular matrices in iterative manner. The innermost triangular matrix has its diagonal elements equal to the geometric mean of the singular values of the complex matrix. This decomposition, generalized geometric mean decomposition (GGMD), has one order less complexity than the geometric mean decomposition (GMD) if the target matrix is a diagonal matrix. GGMD can be used to design the optimal decision feedback equalizer (DFE) MMSE transceiver for arbitrary multi-input-multi-output (MIMO) channels. The GGMD transceiver shares the same performance as the transceiver designed by using GMD. For the applications over Cyclic Prefix system, the GGMD transceiver has K/ log 2 (K) times lower complexity1 than the GMD transceiver, where K is the number of subchannels and is a power of 2.
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subspace based blind channel identification for Cyclic Prefix systems using few received blocks
IEEE Transactions on Signal Processing, 2007Co-Authors: P P VaidyanathanAbstract:In this paper, a novel generalization of subspace-based blind channel identification methods in Cyclic Prefix (CP) systems is proposed. For the generalization, a new system parameter called repetition index is introduced whose value is unity for previously reported special cases. By choosing a repetition index larger than unity, the number of received blocks needed for blind identification is significantly reduced compared to all previously reported methods. This feature makes the method more realistic especially in wireless environments where the channel state is usually fast-varying. Given the number of received blocks available, the minimum value of repetition index is derived. Theoretical limit allows the proposed method to perform blind identification using only three received blocks in absence of noise. In practice, the number of received blocks needed to yield a satisfactory bit-error-rate (BER) performance is usually on the order of half the block size. Simulation results not only demonstrate the capability of the algorithm to perform blind identification using fewer received blocks, but also show that in some cases system performance can be improved by choosing a repetition index larger than needed. Simulation of the proposed method over time-varying channels clearly demonstrates the improvement over previously reported methods.
M Engels - One of the best experts on this subject based on the ideXlab platform.
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ofdm versus single carrier with Cyclic Prefix a system based comparison
Vehicular Technology Conference, 2001Co-Authors: Jan Tubbax, Luc Deneire, B Come, L Van Der Perre, S Donnay, M EngelsAbstract:In recent years, wireless indoor networks have received a lot of scientific and industrial attention. Most systems rely on the use of orthogonal frequency division multiplexing (OFDM) because of its capability to elegantly cope with multipath interference. However, while OFDM provides a nice solution for the digital modem, its front-end requirements should be investigated as well. To that goal, we have set up a simulation environment which comprises both the digital modem and the most important front-end nonidealities. We show that for the same data rate, bandwidth and transmit power constraints, Single-Carrier with Cyclic Prefix (SC-CP) allows the design of a more power-efficient modem than OFDM and is therefore a better candidate for portable wireless terminals.
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training sequence vs Cyclic Prefix a new look on single carrier communication
Global Communications Conference, 2000Co-Authors: Luc Deneire, Bert Gyselinckx, M EngelsAbstract:Frequency domain equalization has gained a lot of attention in the last decade, mainly pushed by the OFDM (orthogonal frequency division multiplexing) communication scheme. It has been adopted, in various flavours, for, among others, wireless LANs and xDSL. The technique is indeed leading to low complexity implementation, at the cost of a Cyclic Prefix, used to avoid inter block interference (IBI). The idea has been adapted to single carrier communication, almost "as is", yielding the same computational advantages and avoiding the high crest factor of OFDM. We name this scheme CP-SC (Cyclic Prefix-single carrier). We take a new look at this single carrier scheme, and, with a slight modification, show that the Cyclic Prefix can be implemented as a training sequence, and hence play two important roles: avoid IBI and help in synchronisation and channel estimation. The latter topic is of utter importance in fast fading situations (e.g. mobile). This new training aided frequency domain equalized single carrier (we name it TASC) scheme offers these advantages at the expense of only a small fraction of a dB (in terms of E/sub b//N/sub 0/). All these arguments make TASC an interesting candidate in situations where multipath and fast fading are present, while in other situations it has hardly no drawback compared to CP-SC.
Chardir Chung - One of the best experts on this subject based on the ideXlab platform.
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Spectrally Precoded OFDM and OFDMA with Cyclic Prefix and Unconstrained Guard Ratios
IEEE Transactions on Wireless Communications, 2011Co-Authors: Hao-ming Chen, Wei-chang Chen, Chardir ChungAbstract:Spectrally precoded orthogonal frequency-division multiplexing with Cyclic Prefix (SP-CP-OFDM) and SP-CP-OFDM multiple access (SP-CP-OFDMA) are investigated in this paper. A general constraint on spectral precoding is developed for both SP-CP-OFDM and SP-CP-OFDMA signal formats with unconstrained guard ratios and arbitrary input data statistics to ensure very small power spectral sidelobes decaying asymptotically as f-2J-2, with J a predesigned integer-valued parameter. In the SP-CP-OFDM signaling format, new spectral precoders are devised to meet the constraint. It is shown that the proposed SP-CP-OFDM signals can provide much smaller spectral sidelobes than the previously designed SP-CP-OFDM signals with block partitioning and constrained guard ratios. In the SP-CP-OFDMA signaling format, a general procedure is proposed to facilitate the precoder design for SP-CP-OFDMA signals with arbitrary subcarrier allocation for each user and some spectral precoders are accordingly devised. It is shown that the proposed SP-CP-OFDMA signals can suppress sidelobe powers effectively and thus achieve higher spectral compactness than nonprecoded rectangularly-pulsed CP-OFDMA.
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spectrally precoded ofdm with Cyclic Prefix
International Conference on Communications, 2007Co-Authors: Chardir ChungAbstract:Spectrally precoded orthogonal frequency-division multiplexing (OFDM) is a promising rectangularly pulsed OFDM signaling format which can provide very small power spectral sidelobes, while allowing for efficient implementation by fast Fourier transform and guard insertion. In this paper, a general constraint on spectral precoding is developed for OFDM signals with Cyclic Prefix (CP-OFDM) to warrant the desirable spectral property that the power spectral sidelobes decay as f-2K-2, with K a preassigned integer. Specifically, block partitioning is adopted to facilitate the precoder design of such spectrally precoded CP-OFDM. New correlative and orthogonal precoders are also devised. It is analytically shown that the proposed spectrally pre- coded OFDMs can provide better choices of spectral efficiency and average error performance than conventional spectrally precoded OFDMs.
