In this paper, a subspace method is proposed for blind channel estimation in orthogonal frequency-division multiplexing (OFDM) systems over time-dispersive channel. The proposed method does not require a cyclic prefix (CP) and thus leading to higher spectral efficiency. By exploiting the block Toeplitz structure of the channel matrix, the proposed blind estimation method performs satisfactorily with very few received OFDM blocks. Numerical simulations demonstrate the superior performance of the proposed algorithm over methods reported earlier in the literature.
Spectrum-efficiency parametric channel estimation scheme for massive MIMO sys...Qian Han
This document proposes a parametric channel estimation method for massive MIMO systems that exploits the spatial correlation of wireless channels. It aims to improve channel estimation accuracy and reduce pilot overhead. The key points are:
1) Wireless MIMO channels exhibit common sparse patterns and similar path delays across transmit antennas due to shared scatterers.
2) A parametric channel estimation method is proposed that exploits this common sparsity. It can achieve super-resolution path delay estimation and improved accuracy using fewer pilots.
3) Counterintuitively, the required number of pilots per transmit antenna can decrease as the number of transmit antennas increases, making the method well-suited for massive MIMO systems.
The document proposes a new method for frame synchronization in OFDMA mode of wireless networks. The method uses a timing metric based on the preamble structure specified for OFDMA, which consists of real BPSK symbols on every third subcarrier. In an ideal scenario with a DFT size of 2046, the timing metric results in four significant peaks, with the true frame boundary indicated by one of the peaks. Thresholding and detection strategies are discussed to identify the frame boundary in noisy channels. Simulations show the proposed method performs better than existing techniques, especially in fading channels.
This document proposes a simultaneous multi-channel reconstruction method for TDS-OFDM systems using distributed compressive sensing. It utilizes an interference-free region within the received pseudorandom noise sequence to reconstruct multiple sparse channels simultaneously, without requiring interference cancellation. A simultaneous CoSaMP algorithm is developed to achieve better channel estimation performance in fast fading channels. Simulation results show the proposed scheme improves performance over conventional solutions.
Blind channel estimation for mimo ofdm systemstrungquang0207
This document presents a blind channel estimation technique for MIMO-OFDM systems. It generalizes existing subspace-based methods for single-input single-output OFDM systems to operate with multiple transmit and receive antennas. The proposed method establishes conditions for channel identifiability. It obtains accurate channel estimates using a small number of OFDM symbols and is insensitive to overestimates of the true channel order. The method can work with no or insufficient cyclic prefix if virtual carriers are present, potentially increasing channel utilization. Simulation results show the mean-square error performance of the proposed method.
On Channel Estimation of OFDM-BPSK and -QPSK over Nakagami-m Fading ChannelsCSCJournals
This paper evaluates the performance of OFDM - BPSK & -QPSK based system with and without channel estimation over Nakagami-m fading channels. Nakagami-m variants are generated by decomposition of Nakagami random variable into orthogonal random variables with Gaussian distribution envelopes. Performance of OFDM system in Nakagami channel has been reported here. The results yield the optimum value of m based on BER and SNR. Using this optimum value of m, Channel estimation over flat fading has been reported here. It has been depicted clearly from simulated graphs that channel estimation has further reduced the BER. However, threshold value of m has played a vital role during channel estimation.
This document discusses using implicit training via the MUSIC algorithm to approximate the capacity of an MMSE equalizer in fading channels without full channel state information. It shows that for a slow fading channel, the MUSIC algorithm can approach the explicit MMSE training capacity of 5 bits/Hz within 1 dB. For a faster fading channel, implicit training via MUSIC can realize up to a 2 dB improvement in capacity compared to explicit training, achieving over 4 bits/Hz capacity. The document outlines the MMSE equalizer, MUSIC algorithm, and a proposed method to use MUSIC to implicitly train an MMSE equalizer without explicit training symbols.
Method for Converter Synchronization with RF InjectionCSCJournals
This paper presents an injection method for synchronizing analog to digital converters (ADC). This approach can eliminate the need for precision routed discrete synchronization signals of current technologies, such as JESD204. By eliminating the setup and hold time requirements at the conversion (or near conversion) clock rate, higher sample rate systems can be synchronized. Measured data from an existing multiple ADC conversion system was used to evaluate the method. Coherent beams were simulated to measure the effectiveness of the method. The results show near theoretical coherent processing gain.
Spectrum-efficiency parametric channel estimation scheme for massive MIMO sys...Qian Han
This document proposes a parametric channel estimation method for massive MIMO systems that exploits the spatial correlation of wireless channels. It aims to improve channel estimation accuracy and reduce pilot overhead. The key points are:
1) Wireless MIMO channels exhibit common sparse patterns and similar path delays across transmit antennas due to shared scatterers.
2) A parametric channel estimation method is proposed that exploits this common sparsity. It can achieve super-resolution path delay estimation and improved accuracy using fewer pilots.
3) Counterintuitively, the required number of pilots per transmit antenna can decrease as the number of transmit antennas increases, making the method well-suited for massive MIMO systems.
The document proposes a new method for frame synchronization in OFDMA mode of wireless networks. The method uses a timing metric based on the preamble structure specified for OFDMA, which consists of real BPSK symbols on every third subcarrier. In an ideal scenario with a DFT size of 2046, the timing metric results in four significant peaks, with the true frame boundary indicated by one of the peaks. Thresholding and detection strategies are discussed to identify the frame boundary in noisy channels. Simulations show the proposed method performs better than existing techniques, especially in fading channels.
This document proposes a simultaneous multi-channel reconstruction method for TDS-OFDM systems using distributed compressive sensing. It utilizes an interference-free region within the received pseudorandom noise sequence to reconstruct multiple sparse channels simultaneously, without requiring interference cancellation. A simultaneous CoSaMP algorithm is developed to achieve better channel estimation performance in fast fading channels. Simulation results show the proposed scheme improves performance over conventional solutions.
Blind channel estimation for mimo ofdm systemstrungquang0207
This document presents a blind channel estimation technique for MIMO-OFDM systems. It generalizes existing subspace-based methods for single-input single-output OFDM systems to operate with multiple transmit and receive antennas. The proposed method establishes conditions for channel identifiability. It obtains accurate channel estimates using a small number of OFDM symbols and is insensitive to overestimates of the true channel order. The method can work with no or insufficient cyclic prefix if virtual carriers are present, potentially increasing channel utilization. Simulation results show the mean-square error performance of the proposed method.
On Channel Estimation of OFDM-BPSK and -QPSK over Nakagami-m Fading ChannelsCSCJournals
This paper evaluates the performance of OFDM - BPSK & -QPSK based system with and without channel estimation over Nakagami-m fading channels. Nakagami-m variants are generated by decomposition of Nakagami random variable into orthogonal random variables with Gaussian distribution envelopes. Performance of OFDM system in Nakagami channel has been reported here. The results yield the optimum value of m based on BER and SNR. Using this optimum value of m, Channel estimation over flat fading has been reported here. It has been depicted clearly from simulated graphs that channel estimation has further reduced the BER. However, threshold value of m has played a vital role during channel estimation.
This document discusses using implicit training via the MUSIC algorithm to approximate the capacity of an MMSE equalizer in fading channels without full channel state information. It shows that for a slow fading channel, the MUSIC algorithm can approach the explicit MMSE training capacity of 5 bits/Hz within 1 dB. For a faster fading channel, implicit training via MUSIC can realize up to a 2 dB improvement in capacity compared to explicit training, achieving over 4 bits/Hz capacity. The document outlines the MMSE equalizer, MUSIC algorithm, and a proposed method to use MUSIC to implicitly train an MMSE equalizer without explicit training symbols.
Method for Converter Synchronization with RF InjectionCSCJournals
This paper presents an injection method for synchronizing analog to digital converters (ADC). This approach can eliminate the need for precision routed discrete synchronization signals of current technologies, such as JESD204. By eliminating the setup and hold time requirements at the conversion (or near conversion) clock rate, higher sample rate systems can be synchronized. Measured data from an existing multiple ADC conversion system was used to evaluate the method. Coherent beams were simulated to measure the effectiveness of the method. The results show near theoretical coherent processing gain.
This document summarizes a student's DSP project on linear prediction models presented to Viet Nam National University- Ho Chi Minh City. It covers topics such as linear predictive coding (LPC), the least mean square error, the Levinson-Durbin algorithm, sub-band linear prediction models, and using prediction models for frequency-domain signal restoration. LPC is introduced as a powerful speech analysis technique that models the spectral envelope of digital speech signals using a linear predictive model of past samples. The prediction error signal and mean square prediction error are also discussed.
International Journal of Engineering and Science Invention (IJESI)inventionjournals
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
1) The document proposes simultaneous multi-channel reconstruction for TDS-OFDM based next-generation broadcasting systems using compressive sensing. It introduces several OFDM transmission schemes and issues with interference cancellation in TDS-OFDM.
2) It then describes a new algorithm called Simultaneous CoSaMP (S-CoSaMP) that exploits joint time-frequency processing to improve channel reconstruction over existing algorithms.
3) Simulation results show S-CoSaMP achieves higher signal recovery rates and lower estimation errors than other algorithms, demonstrating its effectiveness for supporting technologies like 256QAM.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
MMSE and ZF Analysis of Macrodiversity MIMO Systems and Wimax Networks over F...IJERA Editor
We consider the large scale MIMO systems in which the number of users are gradually increased at that time the receiving antennas performance also decreased gradually. In contrast, almost no analytical results are available for macro diversity systems where both the sources and receive antennas are widely separated. Here, receive antennas experience unequal average SNRs from a source and receiver antenna receives a different average SNR from each source. Although this is an extremely difficult problem,In this paper, we provide approximate distributions for the output SNR of a ZF receiver and the output signal to interference plus noise ratio (SINR) of an MMSE receiver. In addition, simple high SNR approximations are provided for the symbol error rate (SER) of both receivers assuming M-PSK or M-QAM modulations .For better performance of receivers we can also implement the MMSE and ZF analysis in Wimax networks.
A New Approach for Speech Enhancement Based On Eigenvalue Spectral SubtractionCSCJournals
In this paper, a phase space reconstruction-based method is proposed for speech enhancement. The method embeds the noisy signal into a high dimensional reconstructed phase space and uses Spectral Subtraction idea. The advantages of the proposed method are fast performance, high SNR and good MOS. In order to evaluate the proposed method, ten signals of TIMIT database mixed with the white additive Gaussian noise and then the method was implemented. The efficiency of the proposed method was evaluated by using qualitative and quantitative criteria.
Multi carrier equalization by restoration of redundanc y (merry) for adaptive...IJNSA Journal
This paper proposes a new blind adaptive channel shortening approach for multi-carrier systems. The
performance of the discrete Fourier transform-DMT (DFT-DMT) system is investigated with the proposed
DST-DMT system over the standard carrier serving area (CSA) loop1. Enhanced bit rates demonstrated
and less complexity also involved by the simulation of the DST-DMT system.
Classical Discrete-Time Fourier TransformBased Channel Estimation for MIMO-OF...IJCSEA Journal
In this document, we look at various time domain channel estimation methods with this constraint of null carriers at spectrumborders.We showin detail howto gauge the importance of the “border effect” depending on the number of null carriers, which may vary from one system to another. Thereby we assess the limit of the technique discussed when the number of null carriers is large. Finally the DFT with the truncated singular value decomposition (SVD) technique is proposed to completely eliminate the impact of the null subcarriers whatever their number. A technique for the determination of the truncation threshold for any MIMO-OFDM system is also proposed.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Hybrid Adaptive Channel Estimation Technique in Time and Frequency Domain for...Tamilarasan N
This document summarizes a research paper that proposes a hybrid adaptive channel estimation technique for MIMO-OFDM wireless communication systems. The technique integrates channel estimation in the time domain and frequency domain. It uses column-based time domain estimation initially and switches to row-based frequency domain estimation when channel quality is good and bit error rate is low. It switches back to time domain estimation when channel quality worsens. The goal is to adaptively estimate the channel under different conditions. Experimental results showed the proposed hybrid technique outperformed other methods.
This document proposes using a hybrid model and structured sparsity for under-determined convolutive audio source separation. It presents a mathematical model that combines a convex cost function with sparse regularization terms. A hybrid model is introduced using a union of two Gabor frames, each adapted to a different "morphological layer" of the signal. Structured sparsity is incorporated using a windowed group lasso operator to better exploit time-frequency structure. Experiments on speech and music mixtures show improved source separation performance compared to baseline methods, confirming the benefits of the proposed hybrid and structured sparsity approaches.
A novel and efficient mixed-signal compressed sensing for wide-band cognitive...Polytechnique Montreal
In cognitive radio (CR) networks, unlicensed (cognitive) users can exploit the licensed frequency bands by using spectrum sensing techniques to identify spectrum holes. This paper proposes a distributed compressive spectrum sensing scheme, in which the modulated wide-band converter can apply compressed sensing (CS) directly to analog signals at the sub-Nyquist rate and the central fusion receives signals from multiple CRs and exploits the multiple-measurements-vectors (MMV) subspace pursuit (M-SP) algorithm to jointly reconstruct the spectral support of the wide-band signal. This support is then used to detect whether the licensed bands are occupy or not. Finally, extensive simulation results show the advantages of the proposed scheme. Besides, we also compare the performance of M-SP with M-orthogonal matching pursuit (M-OMP) algorithms.
Projected Barzilai-Borwein Methods Applied to Distributed Compressive Spectru...Polytechnique Montreal
Cognitive radio allows unlicensed (cognitive) users to use licensed frequency bands by exploiting spectrum sensing techniques to detect whether or not the licensed (primary) users are present. In this paper, we present a compressed sensing applied to spectrum-occupancy detection in wide-band applications. The collected analog signals from each cognitive radio (CR) receiver at a fusion center are transformed to discrete-time signals by using analog-to-information converter (AIC) and then employed to calculate the autocorrelation. For signal reconstruction, we exploit a novel approach to solve the optimization problem consisting of minimizing both a quadratic (l2) error term and an l1-regularization term. In specific, we propose the Basic gradient projection (GP) and projected Barzilai-Borwein (PBB) algorithm to offer a better performance in terms of the mean squared error of the power spectrum density estimate and the detection probability of licensed signal occupancy.
A COMPARATIVE PERFORMANCE STUDY OF OFDM SYSTEM WITH THE IMPLEMENTATION OF COM...ijcsa
This paper presents a comparative performance analysis of wireless orthogonal frequency division multiplexing (OFDM) system with the implementation of comb type pilot-based channel estimation algorithm over frequency selective multi-path fading channels. The Minimum Mean Square Error (MMSE) method is used for the estimation of channel at pilot frequencies. For the estimation of channel at data frequencies different interpolation techniques such as low-pass, linear, and second order interpolation are employed. The OFDM system simulation has been carried out with Matlab and the performance is analyzed in terms of bit error rate (BER) for various signal mapping (BPSK, QPSK, 4QAM, 16QAM, and 64QAM) and channel (Rayleigh and Rician) conditions. The impact of selecting number of channel taps on the BER performance is also investigated.
This document summarizes research on designing the transmitted beampattern for non-uniform MIMO radar arrays. It first reviews covariance-based beampattern design methods for MIMO radar. It then analyzes how the transmitted beampattern is affected by the locations of transmitter antennas. Numerical examples demonstrate that optimizing the beampattern with respect to antenna locations is a non-convex problem that requires heuristic approaches like genetic algorithms. The document concludes that antenna position is an important parameter that can influence the transmitted beampattern in MIMO radar systems.
This paper aims, a 3D-Pilot Aided Multi-Input Multi-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) Channel Estimation (CE) for Digital Video Broadcasting -T2 (DVB-T2) for the 5 different proposed block and comb pilot patterns model and performed on different antenna configuration. The effects of multi-transceiver antenna on channel estimation are addressed with different pilot position in frequency, time and the vertical direction of spatial domain framing. This paper first focus on designing of 5-different proposed spatial correlated pilot pattern model with optimization of pilot overhead. Then it demonstrates the performance comparison of Least Square (LS) & Linear Minimum Mean Square Error (LMMSE), two linear channel estimators for 3D-Pilot Aided patterns on different antenna configurations in terms of Bit Error Rate. The simulation results are shown for Rayleigh fading noise channel environments. Also, 3x4 MIMO configuration is recommended as the most suitable configuration in this noise channel environments.
Ieee 802.20 working group on mobile broadband wireless accessNguyen Minh Thu
This document discusses inconsistencies in the path loss models recommended for evaluating mobile broadband wireless access (MBWA) proposals for the IEEE 802.20 working group. It proposes additions to clarify the frequency dependence of the path loss models for different environments (macrocell suburban/urban, microcell LOS/NLOS, indoor). Models are provided for path loss as a function of carrier frequency and distance. It recommends adopting the proposed path loss formulations and accounting for carrier frequency and bandwidth when evaluating proposals using different channel models.
CS Based Channel Estimation for OFDM Systems under Long Delay Channels Using ...IJERA Editor
Orthogonal frequency division multiplexing (OFDM) is a technique which are used in the next-generation wireless communication. Channel estimation in the OFDM technique is one of the big challenges, ever since high-resolution channel estimation can significantly improve the equalization at the receiver and consequently enhance the communication performances. Channel computation using superimposed pilot sequences is also a fully new area, idea for using superimposed pilot sequences has been proposed by various authors for different applications. In this paper, we are introduced a high accurate, low complexity compressive sensing (CS) based channel estimation namely Auxiliary information based Subspace Pursuit (ASP) in TFT-OFDM systems. ASP based channel estimation in TFT-OFDM system is based on two steps. First is, by exploiting the signal structure of recently proposed TDM-OFDM scheme, the supporting channel information is obtained. Second is, we propose the supporting information based subspace pursuit (SP) algorithm to use a very small amount of frequency domain pilots embedded in the OFDM block used for the exact channel estimation. Moreover, the obtained auxiliary channel information is adopted to reduce the complexity of the conventional SP algorithm. Simulation results demonstrate a important reduction of the number of pilots relative to least-squares channel estimation and supporting high-order modulations like 256 QAM.
In this paper, we analyzed a numerical evaluation of the performance of MIMO radio systems in the LTE network environment. Downlink physical layer of the OFDM-MIMO based radio interface is considered for system model and a theoretical analysis of the bit error rate of the two space-time codes (SFBC 2×1 and FSTD 4×2 codes are adopted by the LTE norm as a function of the signal to noise ratio. Analytical expressions are given for transmission over a Rayleigh channel without spatial correlation which is then compared with Monte-Carlo simulations. Further evaluated channel capacity and simulation results show throughput almost reaches to the capacity limit.
1. The document proposes a scheme called Superimposed Spatial Modulation (SSM) that allows for doubling of information conveyed in the spatial position of transmitting antennas.
2. SSM superimposes two independent spatial modulation systems on the same antenna array. Each system transmits different components of orthogonal symbols.
3. This approach increases spectral efficiency over conventional spatial modulation by doubling the size of the possible antenna constellations.
Pilot based channel estimation improvement in orthogonal frequency-division m...IJECEIAES
Pilot based least square (LS) channel estimation is a commonly used channel estimation technique in orthogonal frequency-division multiplexing based systems due to its simplicity. However, LS estimation does not handle the noise effect and hence suffers from performance degradation. Since the channel coefficients are correlated in time and hence show a slower variation than the noise, it is possible to encode the channel using linear predictive coding (LPC) without the noise. In this work, the channel is estimated from the pilots using LS estimation and in a second step the channel’s LS estimation is encoded as LPC coefficients to produce an improved channel estimation. The estimation technique is simulated for space-time block coding (STBC) based orthogonal frequency-division multiplexing (OFDM) system and the bit error rate (BER) curves show improvement of the LPC estimation over the LS estimation of the channel.
The document proposes a novel joint carrier frequency offset (CFO) and channel estimation scheme for MIMO-OFDM systems using recursive least squares (RLS) algorithms. It first introduces a joint CFO and channel estimator using two iterative RLS algorithms. It then derives a more precise pilot-aided RLS algorithm to estimate residual CFO errors and enhance channel estimation accuracy. Simulation results show the proposed estimation scheme achieves fast convergence and performance close to theoretical bounds for a wide range of signal-to-noise ratios and an initial CFO up to half the subcarrier spacing.
This document summarizes a student's DSP project on linear prediction models presented to Viet Nam National University- Ho Chi Minh City. It covers topics such as linear predictive coding (LPC), the least mean square error, the Levinson-Durbin algorithm, sub-band linear prediction models, and using prediction models for frequency-domain signal restoration. LPC is introduced as a powerful speech analysis technique that models the spectral envelope of digital speech signals using a linear predictive model of past samples. The prediction error signal and mean square prediction error are also discussed.
International Journal of Engineering and Science Invention (IJESI)inventionjournals
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
1) The document proposes simultaneous multi-channel reconstruction for TDS-OFDM based next-generation broadcasting systems using compressive sensing. It introduces several OFDM transmission schemes and issues with interference cancellation in TDS-OFDM.
2) It then describes a new algorithm called Simultaneous CoSaMP (S-CoSaMP) that exploits joint time-frequency processing to improve channel reconstruction over existing algorithms.
3) Simulation results show S-CoSaMP achieves higher signal recovery rates and lower estimation errors than other algorithms, demonstrating its effectiveness for supporting technologies like 256QAM.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
MMSE and ZF Analysis of Macrodiversity MIMO Systems and Wimax Networks over F...IJERA Editor
We consider the large scale MIMO systems in which the number of users are gradually increased at that time the receiving antennas performance also decreased gradually. In contrast, almost no analytical results are available for macro diversity systems where both the sources and receive antennas are widely separated. Here, receive antennas experience unequal average SNRs from a source and receiver antenna receives a different average SNR from each source. Although this is an extremely difficult problem,In this paper, we provide approximate distributions for the output SNR of a ZF receiver and the output signal to interference plus noise ratio (SINR) of an MMSE receiver. In addition, simple high SNR approximations are provided for the symbol error rate (SER) of both receivers assuming M-PSK or M-QAM modulations .For better performance of receivers we can also implement the MMSE and ZF analysis in Wimax networks.
A New Approach for Speech Enhancement Based On Eigenvalue Spectral SubtractionCSCJournals
In this paper, a phase space reconstruction-based method is proposed for speech enhancement. The method embeds the noisy signal into a high dimensional reconstructed phase space and uses Spectral Subtraction idea. The advantages of the proposed method are fast performance, high SNR and good MOS. In order to evaluate the proposed method, ten signals of TIMIT database mixed with the white additive Gaussian noise and then the method was implemented. The efficiency of the proposed method was evaluated by using qualitative and quantitative criteria.
Multi carrier equalization by restoration of redundanc y (merry) for adaptive...IJNSA Journal
This paper proposes a new blind adaptive channel shortening approach for multi-carrier systems. The
performance of the discrete Fourier transform-DMT (DFT-DMT) system is investigated with the proposed
DST-DMT system over the standard carrier serving area (CSA) loop1. Enhanced bit rates demonstrated
and less complexity also involved by the simulation of the DST-DMT system.
Classical Discrete-Time Fourier TransformBased Channel Estimation for MIMO-OF...IJCSEA Journal
In this document, we look at various time domain channel estimation methods with this constraint of null carriers at spectrumborders.We showin detail howto gauge the importance of the “border effect” depending on the number of null carriers, which may vary from one system to another. Thereby we assess the limit of the technique discussed when the number of null carriers is large. Finally the DFT with the truncated singular value decomposition (SVD) technique is proposed to completely eliminate the impact of the null subcarriers whatever their number. A technique for the determination of the truncation threshold for any MIMO-OFDM system is also proposed.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Hybrid Adaptive Channel Estimation Technique in Time and Frequency Domain for...Tamilarasan N
This document summarizes a research paper that proposes a hybrid adaptive channel estimation technique for MIMO-OFDM wireless communication systems. The technique integrates channel estimation in the time domain and frequency domain. It uses column-based time domain estimation initially and switches to row-based frequency domain estimation when channel quality is good and bit error rate is low. It switches back to time domain estimation when channel quality worsens. The goal is to adaptively estimate the channel under different conditions. Experimental results showed the proposed hybrid technique outperformed other methods.
This document proposes using a hybrid model and structured sparsity for under-determined convolutive audio source separation. It presents a mathematical model that combines a convex cost function with sparse regularization terms. A hybrid model is introduced using a union of two Gabor frames, each adapted to a different "morphological layer" of the signal. Structured sparsity is incorporated using a windowed group lasso operator to better exploit time-frequency structure. Experiments on speech and music mixtures show improved source separation performance compared to baseline methods, confirming the benefits of the proposed hybrid and structured sparsity approaches.
A novel and efficient mixed-signal compressed sensing for wide-band cognitive...Polytechnique Montreal
In cognitive radio (CR) networks, unlicensed (cognitive) users can exploit the licensed frequency bands by using spectrum sensing techniques to identify spectrum holes. This paper proposes a distributed compressive spectrum sensing scheme, in which the modulated wide-band converter can apply compressed sensing (CS) directly to analog signals at the sub-Nyquist rate and the central fusion receives signals from multiple CRs and exploits the multiple-measurements-vectors (MMV) subspace pursuit (M-SP) algorithm to jointly reconstruct the spectral support of the wide-band signal. This support is then used to detect whether the licensed bands are occupy or not. Finally, extensive simulation results show the advantages of the proposed scheme. Besides, we also compare the performance of M-SP with M-orthogonal matching pursuit (M-OMP) algorithms.
Projected Barzilai-Borwein Methods Applied to Distributed Compressive Spectru...Polytechnique Montreal
Cognitive radio allows unlicensed (cognitive) users to use licensed frequency bands by exploiting spectrum sensing techniques to detect whether or not the licensed (primary) users are present. In this paper, we present a compressed sensing applied to spectrum-occupancy detection in wide-band applications. The collected analog signals from each cognitive radio (CR) receiver at a fusion center are transformed to discrete-time signals by using analog-to-information converter (AIC) and then employed to calculate the autocorrelation. For signal reconstruction, we exploit a novel approach to solve the optimization problem consisting of minimizing both a quadratic (l2) error term and an l1-regularization term. In specific, we propose the Basic gradient projection (GP) and projected Barzilai-Borwein (PBB) algorithm to offer a better performance in terms of the mean squared error of the power spectrum density estimate and the detection probability of licensed signal occupancy.
A COMPARATIVE PERFORMANCE STUDY OF OFDM SYSTEM WITH THE IMPLEMENTATION OF COM...ijcsa
This paper presents a comparative performance analysis of wireless orthogonal frequency division multiplexing (OFDM) system with the implementation of comb type pilot-based channel estimation algorithm over frequency selective multi-path fading channels. The Minimum Mean Square Error (MMSE) method is used for the estimation of channel at pilot frequencies. For the estimation of channel at data frequencies different interpolation techniques such as low-pass, linear, and second order interpolation are employed. The OFDM system simulation has been carried out with Matlab and the performance is analyzed in terms of bit error rate (BER) for various signal mapping (BPSK, QPSK, 4QAM, 16QAM, and 64QAM) and channel (Rayleigh and Rician) conditions. The impact of selecting number of channel taps on the BER performance is also investigated.
This document summarizes research on designing the transmitted beampattern for non-uniform MIMO radar arrays. It first reviews covariance-based beampattern design methods for MIMO radar. It then analyzes how the transmitted beampattern is affected by the locations of transmitter antennas. Numerical examples demonstrate that optimizing the beampattern with respect to antenna locations is a non-convex problem that requires heuristic approaches like genetic algorithms. The document concludes that antenna position is an important parameter that can influence the transmitted beampattern in MIMO radar systems.
This paper aims, a 3D-Pilot Aided Multi-Input Multi-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) Channel Estimation (CE) for Digital Video Broadcasting -T2 (DVB-T2) for the 5 different proposed block and comb pilot patterns model and performed on different antenna configuration. The effects of multi-transceiver antenna on channel estimation are addressed with different pilot position in frequency, time and the vertical direction of spatial domain framing. This paper first focus on designing of 5-different proposed spatial correlated pilot pattern model with optimization of pilot overhead. Then it demonstrates the performance comparison of Least Square (LS) & Linear Minimum Mean Square Error (LMMSE), two linear channel estimators for 3D-Pilot Aided patterns on different antenna configurations in terms of Bit Error Rate. The simulation results are shown for Rayleigh fading noise channel environments. Also, 3x4 MIMO configuration is recommended as the most suitable configuration in this noise channel environments.
Ieee 802.20 working group on mobile broadband wireless accessNguyen Minh Thu
This document discusses inconsistencies in the path loss models recommended for evaluating mobile broadband wireless access (MBWA) proposals for the IEEE 802.20 working group. It proposes additions to clarify the frequency dependence of the path loss models for different environments (macrocell suburban/urban, microcell LOS/NLOS, indoor). Models are provided for path loss as a function of carrier frequency and distance. It recommends adopting the proposed path loss formulations and accounting for carrier frequency and bandwidth when evaluating proposals using different channel models.
CS Based Channel Estimation for OFDM Systems under Long Delay Channels Using ...IJERA Editor
Orthogonal frequency division multiplexing (OFDM) is a technique which are used in the next-generation wireless communication. Channel estimation in the OFDM technique is one of the big challenges, ever since high-resolution channel estimation can significantly improve the equalization at the receiver and consequently enhance the communication performances. Channel computation using superimposed pilot sequences is also a fully new area, idea for using superimposed pilot sequences has been proposed by various authors for different applications. In this paper, we are introduced a high accurate, low complexity compressive sensing (CS) based channel estimation namely Auxiliary information based Subspace Pursuit (ASP) in TFT-OFDM systems. ASP based channel estimation in TFT-OFDM system is based on two steps. First is, by exploiting the signal structure of recently proposed TDM-OFDM scheme, the supporting channel information is obtained. Second is, we propose the supporting information based subspace pursuit (SP) algorithm to use a very small amount of frequency domain pilots embedded in the OFDM block used for the exact channel estimation. Moreover, the obtained auxiliary channel information is adopted to reduce the complexity of the conventional SP algorithm. Simulation results demonstrate a important reduction of the number of pilots relative to least-squares channel estimation and supporting high-order modulations like 256 QAM.
In this paper, we analyzed a numerical evaluation of the performance of MIMO radio systems in the LTE network environment. Downlink physical layer of the OFDM-MIMO based radio interface is considered for system model and a theoretical analysis of the bit error rate of the two space-time codes (SFBC 2×1 and FSTD 4×2 codes are adopted by the LTE norm as a function of the signal to noise ratio. Analytical expressions are given for transmission over a Rayleigh channel without spatial correlation which is then compared with Monte-Carlo simulations. Further evaluated channel capacity and simulation results show throughput almost reaches to the capacity limit.
1. The document proposes a scheme called Superimposed Spatial Modulation (SSM) that allows for doubling of information conveyed in the spatial position of transmitting antennas.
2. SSM superimposes two independent spatial modulation systems on the same antenna array. Each system transmits different components of orthogonal symbols.
3. This approach increases spectral efficiency over conventional spatial modulation by doubling the size of the possible antenna constellations.
Pilot based channel estimation improvement in orthogonal frequency-division m...IJECEIAES
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A Subspace Method for Blind Channel Estimation in CP-free OFDM Systems
1. Xiaodong Yue & Xuefu Zhou
Signal Processing: An International Journal (SPIJ), Volume (5): Issue (1) : 2011 12
A Subspace Method for Blind Channel Estimation in CP-free
OFDM Systems
Xiaodong Yue yue@ucmo.edu
Department of Mathematics and Computer Science
University of Central Missouri
Warrensburg, MO 64093, USA
Xuefu Zhou xuefu.zhou@uc.edu
School of Electronics and Computing Systems
University of Cincinnati
Cincinnati, OH 45221, USA
Abstract
In this paper, a subspace method is proposed for blind channel estimation in orthogonal
frequency-division multiplexing (OFDM) systems over time-dispersive channel. The proposed
method does not require a cyclic prefix (CP) and thus leading to higher spectral efficiency. By
exploiting the block Toeplitz structure of the channel matrix, the proposed blind estimation
method performs satisfactorily with very few received OFDM blocks. Numerical simulations
demonstrate the superior performance of the proposed algorithm over methods reported earlier in
the literature.
Keywords: OFDM, Channel Estimation, Dispersive Channel, Wireless Communications.
1. INTRODUCTION
Due to its high spectral efficiency, robustness to frequency selective fading as well as the low
cost of tranceiver implementations, orthogonal frequency-division multiplexing (OFDM) has been
receiving considerable interest as a promising candidate for high speed transmission over wired
and wireless channels [1][2].
Several channel identification methods for the OFDM systems with or without CP have been
proposed in [3]-[13]. In [3][4], blind subspace methods were proposed for OFDM systems with
CP. In practical OFDM systems operating over a dispersive channel, a cyclic prefix longer than
the anticipated multipath channel spread is usually inserted in the transmitted sequence. And, in
the IEEE 802.11a standard, CP’s length is 25% of an OFDM symbol duration, indicating a
significant loss in bandwidth efficiency. In order to improve the spectral efficiency, In [5]-[13],
channel identification methods were introduced for OFDM systems without CP. Specifically, blind
subspace based methods were introduced in [10]-[13]. The methods in [10][11] ignored the inter-
block interference (IBI) in the received OFDM blocks by assuming that the number of sub-carriers
is much larger than the channel length. In [12][13], IBI was not discarded. Furthermore, a block
subspace method [13] was proposed to increase equivalent sample vectors which resulted in
better performance than those of [10]-[12]. Unlike the method in [13], we propose a new blind
channel estimation method without using sub-vectors of the received OFDM blocks. As a result,
the rank of the noise subspace in our proposed method is larger than that of the block subspace
method which results in lower channel estimation error. Computer simulations are presented to
verify the effectiveness of the proposed method.
2. SYSTEM MODELS
Consider an OFDM system with N sub-carriers. The information symbols s(n) are transmitted
through a linear time invariant baseband equivalent channel h(t). Assume h(t) has finite support
2. Xiaodong Yue & Xuefu Zhou
Signal Processing: An International Journal (SPIJ), Volume (5): Issue (1) : 2011 13
[0, (L-1)T] where T is the information symbol interval. Denote u(n) and to be the nth
transmitted and received symbol respectively. The symbol stream s(n) is first serial to parallel
converted into a vector , where i is the block index. After the
IDFT transform, we obtain which is then parallel to serial
converted into u(n) and transmitted. The discrete-time received sequence is then given by
(1)
Where represents the corresponding discrete-time baseband multipath channel, and is
the additive white Gaussian noise. We can write , where is the
dimensional IDFT matrix with its (m,n)th element as , and is the ith
transmitted symbol block. The ith received signal block is grouped as
. Using (1), we obtain
, where is the
corresponding noise vector, and
,
By combining and and the corresponding and into a larger matrix/vector,
we obtain the following signal model
(2)
Where , , is the
inter-block interference and is composed by the last L-1 elements of ,
. Since is not of full column rank, the signal model in (2)
cannot satisfy the identifiability condition (full column rank) which is well known in the blind
channel identification literature [14]. Fortunately, this problem can be easily solved by adopting
multi-antenna in the receive end [9]-[13]. Assuming the number of receive antenna is M, (2) can
be rewritten as
(3)
Where , is the
received signal from the jth receive antenna.
, , and ( denotes the number of
received OFDM blocks). is the channel associated with the jth receive antenna,
and
3. Xiaodong Yue & Xuefu Zhou
Signal Processing: An International Journal (SPIJ), Volume (5): Issue (1) : 2011 14
is the corresponding
noise vector.
3. SUBSPACE METHOD
Since sub-vectors of with length GM were used in the block subspace method [13], the rank
of its noise subspace is MG-G-L+1, where is the sub-block size. It is well known that the
higher the rank of the noise subspace, the lower the channel estimation error is in the least
square minimization problem. If G is chosen to be the same or very close as N in the block
subspace method to increase the rank of its noise subspace, the number of received signal
vectors used to obtain the noise subspace is significantly reduced which offsets the gain from the
increasing rank of the noise subspace. In fact, when G=N, the block subspace method [13]
degenerates to the subspace method in [12] and there are only received OFDM blocks can
be used to calculate the noise subspace. Motivated by this fact, we propose a subspace method
which has large rank of noise subspace and more sample vectors at the same time.
Reconstruct the received signal vector and define
where and . Due to the block Toeplitz structure of the channel
matrix. It is straightforward to show that
(4)
Where and
is the corresponding noise vector. Under signal model (4), there are received
signal vectors can be used to estimate the channel as comparing to vectors in [4] [10]-[12]. As
a result, the proposed method is expected to have better performance than those of [4] [10]-[12].
Since the received signal vector has length NM, the rank of its noise subspace is MN-N-
L+1 which is larger than that of the block subspace method. As a result, the performance of the
proposed subspace method is expected to be better than that of the block subspace method [13].
Performing the singular value decomposition (SVD) on the covariance matrix of the received
signal vector to obtain the noise subspace . Let be the ith column of and
partition into block vector , where each is an
vector. Since , then can be expressed alternatively as ,
where and
(5)
The channel estimation can be obtained by the constrained least square optimization criterion
(6)
Where .
Finally, it is worth mentioning that the proposed subspace method differs the subspace methods
[4] [10] in that 1.) the proposed method processes the received signal vector with IBI; 2.) the rank
of the noise subspace in our proposed method is larger than those of the subspace methods (e.g.
MN-N-L+1 comparing with M(N-L+1)-N); 3.) the proposed method uses vectors
4. Xiaodong Yue & Xuefu Zhou
Signal Processing: An International Journal (SPIJ), Volume (5): Issue (1) : 2011 15
instead of vectors to calculate the noise subspace, which is also a distinguishing factor from
the subspace method [12]. Similarly, our proposed subspace method differs the block subspace
method [13] in that 1.) the rank of the noise subspace in our proposed method is larger than that
of the block subspace method; 2.) our method uses vectors instead of
vectors to calculate the noise subspace.
Computational Complexity: Next we analyze the computational complexity of the proposed
subspace method with the subspace method in [10], the subspace method in [12] and the block
subspace method in [13]. The main computational complexity of the proposed subspace method
is from 1) the singular value decomposition to obtain the noise subspace and 2) EVD used to
estimate the channel vector. These operations are shown in [15] [16] of order
. Similarly, the SVD-related operations for the subspace method [10], the
subspace method [12] and the block subspace method [13] are of order
, and , respectively.
Furthermore, the proposed subspace method, the subspace method [10], the subspace method
[12] and the block subspace method [13] have complexity ,
, and , respectively, for the
computation of the covariance matrix. Since in practice and the subspace
methods [10] [12] require much more OFDM blocks to achieve satisfactory performance than that
of the proposed method, the computational complexity of our subspace method is slightly higher
than those of the subspace methods [10] [12] and the block subspace method [13]. This is the
trade off between computational complexity and estimation accuracy.
4. SIMULATIONS
In our simulation, the number of receive antenna M=2. Information sequence is QPSK
modulated. A multipath channel [10]
,
is
used in all simulations. The Normalized Root Mean Square Error (NRMSE)
is adopted, where the subscript p refers to the pth Monte Carlo run
and denotes the total number of runs which is 100 in all simulations. is the estimated
channel vector of the pth run, and is the actual channel vector. Channel estimators including
the proposed subspace method, the subspace method [10], the subspace method [12] and the
block subspace method [13] are compared. All methods eliminate the CP and training, but require
multiple receive antenna. 3 OFDM blocks are used for channel estimation for all methods. The
number of sub-carriers N=16.
Example 1: In this experiment, the normalized root mean square error is examined as a function
of SNR. Note that similar as in [10], there is a complex scalar ambiguity in the proposed blind
channel estimator. In our simulation, the same method as in [10] is adopted to determine the
phase ambiguity and compensate the channel estimate prior to the sample MSE computations. It
can be seen from Fig. 1 that the estimator error of the proposed subspace method is consistently
better than [10] [12] [13]. In addition, the subspace methods [10] [12] cannot achieve satisfactory
performance with 3 OFDM blocks.
5. Xiaodong Yue & Xuefu Zhou
Signal Processing: An International Journal (SPIJ), Volume (5): Issue (1) : 2011 16
FIGURE 1: NRMSE vs SNR
Example 2: The effect of the number of sub-carriers N is shown in Fig. 2 with SNR=35dB and
. Larger N indicates larger rank of the noise subspace for the proposed method, yielding
more constraints on the channel vector (6) and thus, leads to improvement in the channel
estimation. Finally, it worth mentioning that under current simulation setting, when N>16, more
sample vectors are available in the block subspace method than that of the proposed subspace
method. Therefore, the performance gap between two methods is closing. Overall, the estimator
error of the proposed subspace method is consistently better than [10] [12] [13].
FIGURE 2: NRMSE vs N
Example 3: The effect of OFDM block is presented in Fig. 3 when SNR=35dB and N=16. It
can be seen from Fig. 3 that the estimation error decreases for all methods when the number of
received OFDM blocks increases. Also notable is that under the simulation setting, when
, more sample vectors are available in the proposed subspace method than that of the
block subspace method. Therefore, the performance gap between two methods is expanding.
Again, the estimator error of the proposed subspace method is consistently better than [10] [12]
[13].
6. Xiaodong Yue & Xuefu Zhou
Signal Processing: An International Journal (SPIJ), Volume (5): Issue (1) : 2011 17
5. CONCLUSION
By exploiting the block Toeplitz structure of the channel matrix, a blind subspace method for
OFDM systems without CP is proposed in this paper. The strength of the proposed method lies in
high data and spectral efficiency, thus being attractive for channel estimation under fast changing
channel environment. Comparison of the proposed method with several existing blind subspace
channel estimation methods illustrates the good performance of the proposed method.
FIGURE 3: NRMSE vs
6. REFERENCES
1. Z. Wang and G. Giannakis. “Wireless Multicarrier Communications”. IEEE Signal Processing
Magazine, 29-48, 2000
2. R. van Nee and R. Prasad. “OFDM for Wireless Multimedia Communications”, Artech House
Publishers, (2000)
3. B. Muquet, M. de Courville, P. Duhamel, and V. Buenac. “Subspace based blind and semi-
blind channel identification method for OFDM systems”. In Proceedings of the IEEE-SP
Workshop on Signal Processing Advances in Wireless Communications. Annapolis, MD,
USA, 1999
4. X. Cai and A. Akansu. “A subspace method for blind channel identification in OFDM
systems”. In Proceedings of the IEEE International Conference on Communications, 2000
5. C. Wang and Z. Zhou. “A new detection algorithm for OFDM system without cyclic prefix”. In
Proceedings of the IEEE Mobile and Wireless Communications, 2004
6. C. Lin, J. Wu and T. Lee. “GSC-based frequency-domain equalizer for Cp-free OFDM
systems”. In Proceedings of the IEEE International Conference on Communications, 2005
7. M. Teoltsch and A. Molisch. “Efficient OFDM transmission without cyclic prefix over
frequency-selective channels”. In Proceedings of the IEEE PIMRC, 2000
8. H. Xuejun and B. Houjie. “Blind channel identification and equalization in OFDM system
without cyclic prefix”. In Proceedings of the International Conference on Communication
Technology, 2003
7. Xiaodong Yue & Xuefu Zhou
Signal Processing: An International Journal (SPIJ), Volume (5): Issue (1) : 2011 18
9. S. Wang and J.anton. “Blind Channel Estimation for non-CP OFDM Systems using Multiple
Receive Antenna”. IEEE Signal Processing Letters, 299-302, 2009
10. S. Roy and C. Li. “A Subspace Blind Channel Estimation Method for OFDM Systems without
Cyclic Prefix”. IEEE Trans. Wireless Communications, 572-579, 2002
11. H. Ali, J. Manton and Y. Hua. “A SOS subspace method for blind channel identification and
equalization in bandwidth efficient OFDM systems based on receive antenna diversity”. In
Proceedings of the IEEE Signal Processing Workshop on Statistical Signal processing, 2001
12. J. Yu, C. Chen and M. Lee. “Blind channel estimation for SIMO OFDM systems without cyclic
prefix”. In Proceedings of the International Conference on Wireless Communications,
Networking and Mobile Computing, 2006
13. J. Yu. “Channel Estimation for SIMO OFDM Systems without Cyclic Prefix”. Electronics
Letters, 1369-1371, 2007
14. H. Liu. “Signal Processing Applications in CDMS Communications”, Artech House Publishers,
(2000)
15. D. Johnson and D. Dudgeon. “Array Signal Processing: Concepts and Techniques”, Prentice
Hall, (1993)
16. G. Golub and F. Van Loan. “Matrix Computation”, The Johns Hopkins University Press,
(1996)