To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox,...To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox, a timing metric related to TSC scheme is put forward and examined. The specific method to select a threshold value provides more precise detection results, which can be shown by performance comparison between the two schemes through Monte Carlo simulation. Taking IEEE 802.1 la WLAN standard as an example, the proposed approach is superior to the most popular Schmidl scheme in terms of BER.展开更多
Multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wide-band (UWB) is a novel wireless communication technology. It has many advantages and is being actively researhed. In this study, we constructed ...Multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wide-band (UWB) is a novel wireless communication technology. It has many advantages and is being actively researhed. In this study, we constructed and implemented a simulation model of UWB communication systems in Simulink. We found the MB-OFDM UWB system has the best performance in distance between 4 m to 10 m without the line-of-sight requirement.展开更多
The orthogonal space-frequency block coding (OSFBC) with orthogonal frequency division multiplexing (OFDM) system reduces complexity in the receiver which improves the system performance significantly. Motivated by th...The orthogonal space-frequency block coding (OSFBC) with orthogonal frequency division multiplexing (OFDM) system reduces complexity in the receiver which improves the system performance significantly. Motivated by these advantages of OSFBC-OFDM system, this paper considers a secure wireless multicasting scenario through multiple-input multiple-output (MIMO) OFDM system employing OSFBC over frequency selective α-μ fading channels. The authors are interested to protect the desired signals from eavesdropping considering the impact of the number of multicast users and eavesdroppers, and the fading parameters α and μ. A mathematical model has been developed based on the closed-form analytical expressions of the probability of non-zero secrecy multicast capacity (PNSMC) and the secure outage probability for multi-casting (SOPM) to ensure the security in the presence of multiple eaves-droppers. The results show that the security in MIMO OSFBC OFDM system over α-μ fading is more sensitive to the magnitude of α and μ and this effect increases in the high signal-to-noise ratio (SNR) region of the main channel.展开更多
The carrier frequency offset（CFO）and impulse noise always affect the performance of underwater acoustic communication_systems.The CFO and impulse noise could be estimated by using the null subcarriers to cancel the ...The carrier frequency offset（CFO）and impulse noise always affect the performance of underwater acoustic communication_systems.The CFO and impulse noise could be estimated by using the null subcarriers to cancel the effects of the two types of interference.The null subcarriers estimation methods include optimal separate estimation and joint estimation.The separate estimation firstly estimates the CFO value and then estimates the impulse noise value.However,the CFO and impulse noise always affect each other when either of them is estimated separately.The performance could be improved by using the joint estimation.The results of simulations and experiments have showed that these two optimization methods have good performance and the joint estimation has better performance than the separate estimation method.There is 3 dB performance gain at the BER value of 10^（-2）when using the joint estimation method.Thus these methods could improve the system robustness by using the CFO compensation and impulse noise suppression.展开更多
Optical spatial modulation （OSM） is a multiple-transmitter technique that can provide higher data rates with low system complexity as compared with single-input single-output systems. Orthogonal frequency division m...Optical spatial modulation （OSM） is a multiple-transmitter technique that can provide higher data rates with low system complexity as compared with single-input single-output systems. Orthogonal frequency division multiplexing （OFDM） is widely implemented to achieve better spectral efficiency in wireless channels. Asymmetrically clipped optical OFDM （O-OFDM） and DC-biased O-OFDM are two well-known O-OFDM techniques suitable for intensity-modulation direct-detection optical systems. In this work, sample indexed spatial OFDM （SIS-OFDM） is proposed to combine OSM and O-OFDM in a novel way and achieve significant per- formance gain. By assigning time-domain samples of the O-OFDM transmit symbol to different transmitters, SIS-OFDM achieves much better spectral efficiency and reduces computational complexity at the transmitter as compared with previous work that combines OSM with O-OFDM in the frequency domain. We also consider the impact of optical source biasing on overall performance, and the relative performance of imaging receiver （ImR） versus non-imaging receiver （NImR） design for our proposed SIS-OFDM technique. Results indicate that for an Ntx x Nrx multiple-input multiple-output configuration where Nix = N = 4, SIS-OFDM using ImR can achieve up to 135 dB of signal-to-noise ratio gain over comparable system using a NImR. Also, using Nc number of O-OFDM subcarriers provides up to Nsc × log2（Ntx） additional bits per symbol of spectral efficiency over technioues that combine OSM and O-OFDM in the freollencv domain.展开更多
Contrary to the other multi-carrier modulation systems, the coherent optical orthogonal frequency division multiplexing communication system with an offset quadrature amplitude modulation (CO-OFDM-OQAM) possesses inhe...Contrary to the other multi-carrier modulation systems, the coherent optical orthogonal frequency division multiplexing communication system with an offset quadrature amplitude modulation (CO-OFDM-OQAM) possesses inherent imaginary interference (IMI). This has an important impact on the channel estimation process. Currently, a variety of frequency-domain channel estimation methods have been proposed. However, there are various problems that still exist. For instance, in order to reduce the influence of IMI, it is necessary to insert more guard intervals between the training sequence and the payload, leading to the occupation of excessive spectrum resources. In order to address this problem, this work designs a high spectral efficient frequency-domain channel estimation method for the polarization-division-multiplexing CO-OFDM-OQAM systems. First, the working principle of the proposed method is described in detail. Then, its spectral efficiency, power peak-to-average ratio, and channel estimation performance are studied based on simulations. The simulation results show that the proposed method improves the spectral efficiency without worsening the power peak-to-average ratio. The channel estimation capability of this method is verified in three scenarios of long-distance transmissions, including back-to-back, 100 km, and 200 km transmissions. .展开更多
Pilot data aided feed forward （PAFF） carrier recovery is essential for phase noise tracking in coherent optical receivers. This paper describes a new PAFF system based on new pilot arrangement and maximum likelihood...Pilot data aided feed forward （PAFF） carrier recovery is essential for phase noise tracking in coherent optical receivers. This paper describes a new PAFF system based on new pilot arrangement and maximum likelihood （ML） to estimate the phase jitter in coherent receiver- induced by local oscillator＇s lasers and sampling clock errors. Square M-ary quadrature amplitude modulation （M-QAM） （4, 16, 64, and 256） schemes were used. A detailed mathematical description of the method was presented. The system performance was evaluated through numerical simulations and compared to those with noisefree receiver （ideal receiver） and feed forward without ML. The simulation results show that PAFF performs near the expected ideal phase recovery. Results clearly suggest that ML significantly improves the tolerance of phase error variance. From bit error rate （BER） sensibility evaluation, it was clearly observed that the new estimation method performs better with a 4-QAM （or quadrature phase shift keying （QPSK）） format compared to three others square QAM schemes. Analog to digital converter （ADC） resolution effect on the system performance was analyzed in terms of Q-factor. Finite resolution effect on 4-QAM is negligible while it negatively affects the system performance when M increases.展开更多
This paper deals with optimal training design and placement over multiple orthogonal frequency division multiplexing(OFDM) symbols for the least squares(LS) channel estimation in multiple-input multipleoutput(MIMO) OF...This paper deals with optimal training design and placement over multiple orthogonal frequency division multiplexing(OFDM) symbols for the least squares(LS) channel estimation in multiple-input multipleoutput(MIMO) OFDM systems.First,the optimal pilot sequences over multiple OFDM symbols are derived by co-cyclic Jacket matrices based on the minimum mean square error(MSE) of the LS channel estimation.Then,an enhanced channel estimation method using sliding window is proposed to improve further the performance for the optimal pilot sequences in fast-varying channels.Simulation results show that the enhancedmethod can efficiently improve the performances for the optimal pilot sequences over two and four OFDM symbols,especially in fast-varying channels.展开更多
This paper describes field trials of two-way digital video transmissions over a 700-m long medium-voltage power cable using a frequency division duplex scheme. The purpose is to check the feasibility of using time-dom...This paper describes field trials of two-way digital video transmissions over a 700-m long medium-voltage power cable using a frequency division duplex scheme. The purpose is to check the feasibility of using time-domain synchronous orthogonal frequency division multiplexing （TDS-OFDM） technology in powerline communication （PLC）. TDS-OFDM is the core technology in digital multimedia broadcasting-terrestrial （DMB-T）, developed by Tsinghua University for digital television terrestrial multimedia broadcast applications and successfully adopted in the Chinese Digital Terrestrial Television Broadcasting Standard. PLC systems are widely believed to be bandwidth or data throughput limited. However, the use of known pseudo random sequences as guard intervals for synchronization and channel estimation in TDS-OFDM greatly reduces the system overhead and increases the spectrum efficiency. These experiments show that TDS-OFDM is appropriate not only for broadcasting but also for PLC applications with appropriate modifications.展开更多
In this paper, we reviewed our common phase error （CPE） and intercarrier interference （ICI） compensation methods for coherent optical orthogonal frequency division multiplexing （CO-OFDM） system. We first present...In this paper, we reviewed our common phase error （CPE） and intercarrier interference （ICI） compensation methods for coherent optical orthogonal frequency division multiplexing （CO-OFDM） system. We first presented a unified CPE estimation framework combining decision-aided （DA）, pilot-aided （PA） and decision feed- back （DF） algorithms. The DA method is used to estimate the CPE of the current OFDM symbol based on the decision statistics of the previous symbol. DA ＋ PA helps increase the phase noise tolerance of DA and reduce the overhead of PA, while DA ＋ DF reduces the overhead to zero, achieving best performance with one more step of estimation, compensation and demodulation. We also described a modified time-domain blind intercarrier interference （BL-ICI） mitigation algorithm over non- constant amplitude formats. The new algorithm is derived from the BL-ICI algorithm over constant amplitude format for wireless networks. A new power estimation scheme was proposed for the BL-ICI algorithm to adapt to non- constant amplitude format. It has the same order of complexity with frequency domain decision-aided ICI （DA-ICI） compensation method and does not suffer from symbol decision errors. The effectiveness of both CPE and ICI compensation algorithms were demonstrated in a simulated 56-Gbit/s CO-OFDM system with various modulation formats.展开更多
In this paper,analyzed is the symbol synchronization algorithm in orthogonal frequency division multiplex(OFDM)system,and accomplished are the hardware circuit design of coarse and elaborate synchronization algorithms...In this paper,analyzed is the symbol synchronization algorithm in orthogonal frequency division multiplex(OFDM)system,and accomplished are the hardware circuit design of coarse and elaborate synchronization algorithms.Based on the analysis of coarse and elaborate synchronization algorithms,multiplexed are,the module accumulator,division and output judgement,which can evidently save the hardware resource cost.The analysis of circuit sequence and wave form simulation of the design scheme shows that the proposed method efficiently reduce system resources and power consumption.展开更多
Space-Time Block Coded(STBC)Orthogonal Frequency Division Multiplexing(OFDM)satisfies higher data-rate requirements while maintaining signal quality in a multipath fading channel.However,conventional STBCs,including O...Space-Time Block Coded(STBC)Orthogonal Frequency Division Multiplexing(OFDM)satisfies higher data-rate requirements while maintaining signal quality in a multipath fading channel.However,conventional STBCs,including Orthogonal STBCs(OSTBCs),Non-Orthogonal(NOSTBCs),and Quasi-Orthogonal STBCs(QOSTBCs),do not provide both maximal diversity order and unity code rate simultaneously for more than two transmit antennas.This paper targets this problem and applies Maximum Rank Distance(MRD)codes in designing STBCOFDM systems.By following the direct-matrix construction method,we can construct binary extended finite field MRD-STBCs for any number of transmitting antennas.Work uses MRD-STBCs built over Phase-Shift Keying(PSK)modulation to develop an MRD-based STBC-OFDM system.The MRD-based STBC-OFDM system sacrifices minor error performance compared to traditional OSTBC-OFDM but shows improved results against NOSTBC and QOSTBC-OFDM.It also provides 25%higher data-rates than OSTBC-OFDM in configurations that use more than two transmit antennas.The tradeoffs are minor increases in computational complexity and processing delays.展开更多
This paper investigates the fundamental data detection problem with burst interference in massive multiple-input multiple-output orthogonal frequency division multiplexing(MIMO-OFDM) systems. In particular, burst inte...This paper investigates the fundamental data detection problem with burst interference in massive multiple-input multiple-output orthogonal frequency division multiplexing(MIMO-OFDM) systems. In particular, burst interference may occur only on data symbols but not on pilot symbols, which means that interference information cannot be premeasured. To cancel the burst interference, we first revisit the uplink multi-user system and develop a matrixform system model, where the covariance pattern and the low-rank property of the interference matrix is discussed. Then, we propose a turbo message passing based burst interference cancellation(TMP-BIC) algorithm to solve the data detection problem, where the constellation information of target data is fully exploited to refine its estimate. Furthermore, in the TMP-BIC algorithm, we design one module to cope with the interference matrix by exploiting its lowrank property. Numerical results demonstrate that the proposed algorithm can effectively mitigate the adverse effects of burst interference and approach the interference-free bound.展开更多
In this paper,we study the accuracy of delay-Doppler parameter estimation of targets in a passive radar using orthogonal frequency division multiplexing(OFDM)signal.A coarse-fine joint estimation method is proposed to...In this paper,we study the accuracy of delay-Doppler parameter estimation of targets in a passive radar using orthogonal frequency division multiplexing(OFDM)signal.A coarse-fine joint estimation method is proposed to achieve better estimation accuracy of target parameters without excessive computational burden.Firstly,the modulation symbol domain(MSD)method is used to roughly estimate the delay and Doppler of targets.Then,to obtain high-precision Doppler estimation,the atomic norm(AN)based on the multiple measurement vectors(MMV)model(MMV-AN)is used to manifest the signal sparsity in the continuous Doppler domain.At the same time,a reference signal compensation(RSC)method is presented to obtain highprecision delay estimation.Simulation results based on the OFDM signal show that the coarse-fine joint estimation method based on AN-RSC can obtain a more accurate estimation of target parameters compared with other algorithms.In addition,the proposed method also possesses computational advantages compared with the joint parameter estimation.展开更多
Power line communication(PLC)has the potential to become the preferred technique for providing broadband communication to homes and offices with advantage of eliminating the need for new wiring infrastructure and redu...Power line communication(PLC)has the potential to become the preferred technique for providing broadband communication to homes and offices with advantage of eliminating the need for new wiring infrastructure and reducing the cost.But it suffers from the impulsive noise because it introduces significant time variance into the power line channel.In this paper,a polar codes based orthogonal frequency division multiplexing(OFDM)PLC system is proposed to deal with the impulsive noise and thereby improve the transmission performance.Firstly,the impulsive noise is modelled with a multi-damped sine function by analyzing the time behavior of impulse events.Then the polar codes are used to combat the impulsive noise of PLC channel,and a low complexity bit-flipping decoding method based on CRC-aided successive cancellation list(CA-SCL)decoding algorithm is proposed.Simulations evaluate the proposed decoding algorithm and the results validate the suggested polar codes based OFDM-PLC scheme which can improve the BER performance of PLC with impulsive interference.展开更多
The major constraint on the performance of orthogonal frequency division multiplexing （OFDM） based underwater acoustic （UWA） communication is to keep subcarriers orthogonal. In this paper, Doppler estimation and t...The major constraint on the performance of orthogonal frequency division multiplexing （OFDM） based underwater acoustic （UWA） communication is to keep subcarriers orthogonal. In this paper, Doppler estimation and the respective compensation technique along with various diversity techniques were deliberated for OFDM-based systems best suited for underwater wireless information exchange. In practice, for mobile communication, adjustment and tuning of transducers in order to get spatial diversity is extremely difficult. Considering the relatively low coherence bandwidth in UWA, the frequency diversity design with the Doppler compensation function was elaborated here. The outfield experiments of mobile underwater acoustic communication （UWAC） based on OFDM were carried out with 0.17 bit/（s-Hz） spectral efficiency. The validity and the dependability of the scheme were also analyzed.展开更多
This paper presents an algorithm that aims to reduce the peak-to-average power ratio（PAPR） of orthogonal frequency division multiplexing（OFDM） communication systems while maintaining frequency tracking.The algorit...This paper presents an algorithm that aims to reduce the peak-to-average power ratio（PAPR） of orthogonal frequency division multiplexing（OFDM） communication systems while maintaining frequency tracking.The algorithm achieves PAPR reduction by applying the complex conjugates of the data symbol obtained from the frequency domain to cancel the phase of the data symbol.A likelihood estimator is used to obtain the sub-carrier phase error due to the residual carrier frequency offset（RCFO） using the same complex conjugates as a pilot signal.Furthermore,a joint time and frequency domain multicarrier phase locked loop（MPLL） is developed to compensate additional frequency offset.Simulation results show that this algorithm is capable of reducing PAPR without impacting the frequency tracking performance.展开更多
For multiple-input multiple-output （MIMO） orthogonal frequency division multiplexing （OFDM） systems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform ...For multiple-input multiple-output （MIMO） orthogonal frequency division multiplexing （OFDM） systems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform （FRFT） is proposed. The linear frequency modulation signals superimposed on the data signals are used as the training signals. By performing FRFT on the received signals and searching the peak value of the FRFT results, the receiver can realize timing synchronization and frequency offset acquisition simultaneously. Compared with the existing methods, the proposed algorithm can provide better timing synchronization performance and larger frequency offset acquisition range even under multi-path channels with low signal to noise ratio. Theoretical analysis and simulation results prove this point.展开更多
Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window,...Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window, and the carrier frequency offset （CFO） due to Doppler frequency shift or the frequency mismatch between the transmitter and receiver oscil ators, can bring severe inter-symbol interference （ISI） and inter-carrier interference （ICI） for the OFDM system. Relying on the relatively good correlation charac-teristic of the pseudo-noise （PN） sequence, a joint frame offset and normalized CFO estimation algorithm based on PN preamble in time domain is developed to realize the frame and frequency synchronization in the OFDM system. By comparison, the perfor-mances of the traditional algorithm and the improved algorithm are simulated under different conditions. The results indicate that the PN preamble based algorithm both in frame offset estimation and CFO estimation is more accurate, resource-saving and robust even under poor channel condition, such as low signal-to-noise ratio （SNR） and large normalized CFO.展开更多
The problem of channel estimation for multiple an- tenna orthogonal frequency division multiplexing （OFDM） systems subject to unknown carrier frequency offset （CFO） is addressed. Multiple signal classification （M...The problem of channel estimation for multiple an- tenna orthogonal frequency division multiplexing （OFDM） systems subject to unknown carrier frequency offset （CFO） is addressed. Multiple signal classification （MUSIC）-Iike algorithm, which generally has been used for direction estimation or frequency estimation, is used for channel estimation in multiple antenna OFDM systems. A reduced dimensional （RD）-MUSIC based algorithm for channel estimation is proposed in multiple antenna OFDM systems with unknown CFO. The Cramer-Rao bound （CRB） of channel estimation in multiple antenna OFDM systems with unknown CFO is derived. The proposed algorithm has a superior performance of channel estimation compared with the Capon method and the least squares method.展开更多
文摘To improve frame synchronization precision, a scheme named training symbol correlation （TSC） is presented for orthogonal frequency division multiplexing （ OFDM ） system. Based on the solution from Schmidl and Cox, a timing metric related to TSC scheme is put forward and examined. The specific method to select a threshold value provides more precise detection results, which can be shown by performance comparison between the two schemes through Monte Carlo simulation. Taking IEEE 802.1 la WLAN standard as an example, the proposed approach is superior to the most popular Schmidl scheme in terms of BER.
文摘Multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wide-band (UWB) is a novel wireless communication technology. It has many advantages and is being actively researhed. In this study, we constructed and implemented a simulation model of UWB communication systems in Simulink. We found the MB-OFDM UWB system has the best performance in distance between 4 m to 10 m without the line-of-sight requirement.
文摘The orthogonal space-frequency block coding (OSFBC) with orthogonal frequency division multiplexing (OFDM) system reduces complexity in the receiver which improves the system performance significantly. Motivated by these advantages of OSFBC-OFDM system, this paper considers a secure wireless multicasting scenario through multiple-input multiple-output (MIMO) OFDM system employing OSFBC over frequency selective α-μ fading channels. The authors are interested to protect the desired signals from eavesdropping considering the impact of the number of multicast users and eavesdroppers, and the fading parameters α and μ. A mathematical model has been developed based on the closed-form analytical expressions of the probability of non-zero secrecy multicast capacity (PNSMC) and the secure outage probability for multi-casting (SOPM) to ensure the security in the presence of multiple eaves-droppers. The results show that the security in MIMO OSFBC OFDM system over α-μ fading is more sensitive to the magnitude of α and μ and this effect increases in the high signal-to-noise ratio (SNR) region of the main channel.
基金supported by the Reasearch Fund for the Visiting Scholar Program by the China Scholarship Council(2011631504)The U.S.Science Foundation(CNS-1205665)+1 种基金the Fundamental Research Funds for the Central Universities(201112G020,201212G012)the National Natural Science Foundation of China(41176032)
文摘The carrier frequency offset（CFO）and impulse noise always affect the performance of underwater acoustic communication_systems.The CFO and impulse noise could be estimated by using the null subcarriers to cancel the effects of the two types of interference.The null subcarriers estimation methods include optimal separate estimation and joint estimation.The separate estimation firstly estimates the CFO value and then estimates the impulse noise value.However,the CFO and impulse noise always affect each other when either of them is estimated separately.The performance could be improved by using the joint estimation.The results of simulations and experiments have showed that these two optimization methods have good performance and the joint estimation has better performance than the separate estimation method.There is 3 dB performance gain at the BER value of 10^（-2）when using the joint estimation method.Thus these methods could improve the system robustness by using the CFO compensation and impulse noise suppression.
基金supported by the Engineering Research Centers Program of the National Science Foundation under Grant No.EEC-0812056
文摘Optical spatial modulation （OSM） is a multiple-transmitter technique that can provide higher data rates with low system complexity as compared with single-input single-output systems. Orthogonal frequency division multiplexing （OFDM） is widely implemented to achieve better spectral efficiency in wireless channels. Asymmetrically clipped optical OFDM （O-OFDM） and DC-biased O-OFDM are two well-known O-OFDM techniques suitable for intensity-modulation direct-detection optical systems. In this work, sample indexed spatial OFDM （SIS-OFDM） is proposed to combine OSM and O-OFDM in a novel way and achieve significant per- formance gain. By assigning time-domain samples of the O-OFDM transmit symbol to different transmitters, SIS-OFDM achieves much better spectral efficiency and reduces computational complexity at the transmitter as compared with previous work that combines OSM with O-OFDM in the frequency domain. We also consider the impact of optical source biasing on overall performance, and the relative performance of imaging receiver （ImR） versus non-imaging receiver （NImR） design for our proposed SIS-OFDM technique. Results indicate that for an Ntx x Nrx multiple-input multiple-output configuration where Nix = N = 4, SIS-OFDM using ImR can achieve up to 135 dB of signal-to-noise ratio gain over comparable system using a NImR. Also, using Nc number of O-OFDM subcarriers provides up to Nsc × log2（Ntx） additional bits per symbol of spectral efficiency over technioues that combine OSM and O-OFDM in the freollencv domain.
文摘Contrary to the other multi-carrier modulation systems, the coherent optical orthogonal frequency division multiplexing communication system with an offset quadrature amplitude modulation (CO-OFDM-OQAM) possesses inherent imaginary interference (IMI). This has an important impact on the channel estimation process. Currently, a variety of frequency-domain channel estimation methods have been proposed. However, there are various problems that still exist. For instance, in order to reduce the influence of IMI, it is necessary to insert more guard intervals between the training sequence and the payload, leading to the occupation of excessive spectrum resources. In order to address this problem, this work designs a high spectral efficient frequency-domain channel estimation method for the polarization-division-multiplexing CO-OFDM-OQAM systems. First, the working principle of the proposed method is described in detail. Then, its spectral efficiency, power peak-to-average ratio, and channel estimation performance are studied based on simulations. The simulation results show that the proposed method improves the spectral efficiency without worsening the power peak-to-average ratio. The channel estimation capability of this method is verified in three scenarios of long-distance transmissions, including back-to-back, 100 km, and 200 km transmissions. .
文摘Pilot data aided feed forward （PAFF） carrier recovery is essential for phase noise tracking in coherent optical receivers. This paper describes a new PAFF system based on new pilot arrangement and maximum likelihood （ML） to estimate the phase jitter in coherent receiver- induced by local oscillator＇s lasers and sampling clock errors. Square M-ary quadrature amplitude modulation （M-QAM） （4, 16, 64, and 256） schemes were used. A detailed mathematical description of the method was presented. The system performance was evaluated through numerical simulations and compared to those with noisefree receiver （ideal receiver） and feed forward without ML. The simulation results show that PAFF performs near the expected ideal phase recovery. Results clearly suggest that ML significantly improves the tolerance of phase error variance. From bit error rate （BER） sensibility evaluation, it was clearly observed that the new estimation method performs better with a 4-QAM （or quadrature phase shift keying （QPSK）） format compared to three others square QAM schemes. Analog to digital converter （ADC） resolution effect on the system performance was analyzed in terms of Q-factor. Finite resolution effect on 4-QAM is negligible while it negatively affects the system performance when M increases.
基金the National Natural Science Foundation of China (Nos. 60332030 and 60625103)the Science and Technology Commission of Shanghai Municipality (STCSM) (No. 05DZ22102)the National High Technology Research and Development Program(863) of China (No. 2007AA01Z237)
文摘This paper deals with optimal training design and placement over multiple orthogonal frequency division multiplexing(OFDM) symbols for the least squares(LS) channel estimation in multiple-input multipleoutput(MIMO) OFDM systems.First,the optimal pilot sequences over multiple OFDM symbols are derived by co-cyclic Jacket matrices based on the minimum mean square error(MSE) of the LS channel estimation.Then,an enhanced channel estimation method using sliding window is proposed to improve further the performance for the optimal pilot sequences in fast-varying channels.Simulation results show that the enhancedmethod can efficiently improve the performances for the optimal pilot sequences over two and four OFDM symbols,especially in fast-varying channels.
文摘This paper describes field trials of two-way digital video transmissions over a 700-m long medium-voltage power cable using a frequency division duplex scheme. The purpose is to check the feasibility of using time-domain synchronous orthogonal frequency division multiplexing （TDS-OFDM） technology in powerline communication （PLC）. TDS-OFDM is the core technology in digital multimedia broadcasting-terrestrial （DMB-T）, developed by Tsinghua University for digital television terrestrial multimedia broadcast applications and successfully adopted in the Chinese Digital Terrestrial Television Broadcasting Standard. PLC systems are widely believed to be bandwidth or data throughput limited. However, the use of known pseudo random sequences as guard intervals for synchronization and channel estimation in TDS-OFDM greatly reduces the system overhead and increases the spectrum efficiency. These experiments show that TDS-OFDM is appropriate not only for broadcasting but also for PLC applications with appropriate modifications.
文摘In this paper, we reviewed our common phase error （CPE） and intercarrier interference （ICI） compensation methods for coherent optical orthogonal frequency division multiplexing （CO-OFDM） system. We first presented a unified CPE estimation framework combining decision-aided （DA）, pilot-aided （PA） and decision feed- back （DF） algorithms. The DA method is used to estimate the CPE of the current OFDM symbol based on the decision statistics of the previous symbol. DA ＋ PA helps increase the phase noise tolerance of DA and reduce the overhead of PA, while DA ＋ DF reduces the overhead to zero, achieving best performance with one more step of estimation, compensation and demodulation. We also described a modified time-domain blind intercarrier interference （BL-ICI） mitigation algorithm over non- constant amplitude formats. The new algorithm is derived from the BL-ICI algorithm over constant amplitude format for wireless networks. A new power estimation scheme was proposed for the BL-ICI algorithm to adapt to non- constant amplitude format. It has the same order of complexity with frequency domain decision-aided ICI （DA-ICI） compensation method and does not suffer from symbol decision errors. The effectiveness of both CPE and ICI compensation algorithms were demonstrated in a simulated 56-Gbit/s CO-OFDM system with various modulation formats.
基金Guangdong Province Science and Technology Guiding Project(2005B10101013)
文摘In this paper,analyzed is the symbol synchronization algorithm in orthogonal frequency division multiplex(OFDM)system,and accomplished are the hardware circuit design of coarse and elaborate synchronization algorithms.Based on the analysis of coarse and elaborate synchronization algorithms,multiplexed are,the module accumulator,division and output judgement,which can evidently save the hardware resource cost.The analysis of circuit sequence and wave form simulation of the design scheme shows that the proposed method efficiently reduce system resources and power consumption.
基金supported by the Excellent Foreign Student scholarship program,Sirindhorn International Institute of Technology.
文摘Space-Time Block Coded(STBC)Orthogonal Frequency Division Multiplexing(OFDM)satisfies higher data-rate requirements while maintaining signal quality in a multipath fading channel.However,conventional STBCs,including Orthogonal STBCs(OSTBCs),Non-Orthogonal(NOSTBCs),and Quasi-Orthogonal STBCs(QOSTBCs),do not provide both maximal diversity order and unity code rate simultaneously for more than two transmit antennas.This paper targets this problem and applies Maximum Rank Distance(MRD)codes in designing STBCOFDM systems.By following the direct-matrix construction method,we can construct binary extended finite field MRD-STBCs for any number of transmitting antennas.Work uses MRD-STBCs built over Phase-Shift Keying(PSK)modulation to develop an MRD-based STBC-OFDM system.The MRD-based STBC-OFDM system sacrifices minor error performance compared to traditional OSTBC-OFDM but shows improved results against NOSTBC and QOSTBC-OFDM.It also provides 25%higher data-rates than OSTBC-OFDM in configurations that use more than two transmit antennas.The tradeoffs are minor increases in computational complexity and processing delays.
基金supported by the National Key Laboratory of Wireless Communications Foundation,China (IFN20230204)。
文摘This paper investigates the fundamental data detection problem with burst interference in massive multiple-input multiple-output orthogonal frequency division multiplexing(MIMO-OFDM) systems. In particular, burst interference may occur only on data symbols but not on pilot symbols, which means that interference information cannot be premeasured. To cancel the burst interference, we first revisit the uplink multi-user system and develop a matrixform system model, where the covariance pattern and the low-rank property of the interference matrix is discussed. Then, we propose a turbo message passing based burst interference cancellation(TMP-BIC) algorithm to solve the data detection problem, where the constellation information of target data is fully exploited to refine its estimate. Furthermore, in the TMP-BIC algorithm, we design one module to cope with the interference matrix by exploiting its lowrank property. Numerical results demonstrate that the proposed algorithm can effectively mitigate the adverse effects of burst interference and approach the interference-free bound.
基金supported by the National Natural Science Foundation of China(6193101562071335)+1 种基金the Technological Innovation Project of Hubei Province of China(2019AAA061)the Natural Science F oundation of Hubei Province of China(2021CFA002)。
文摘In this paper,we study the accuracy of delay-Doppler parameter estimation of targets in a passive radar using orthogonal frequency division multiplexing(OFDM)signal.A coarse-fine joint estimation method is proposed to achieve better estimation accuracy of target parameters without excessive computational burden.Firstly,the modulation symbol domain(MSD)method is used to roughly estimate the delay and Doppler of targets.Then,to obtain high-precision Doppler estimation,the atomic norm(AN)based on the multiple measurement vectors(MMV)model(MMV-AN)is used to manifest the signal sparsity in the continuous Doppler domain.At the same time,a reference signal compensation(RSC)method is presented to obtain highprecision delay estimation.Simulation results based on the OFDM signal show that the coarse-fine joint estimation method based on AN-RSC can obtain a more accurate estimation of target parameters compared with other algorithms.In addition,the proposed method also possesses computational advantages compared with the joint parameter estimation.
基金Supported by Headquarters Technology Project of State Grid Corporation of China(No.5700-202118203A-0-0-00)。
文摘Power line communication(PLC)has the potential to become the preferred technique for providing broadband communication to homes and offices with advantage of eliminating the need for new wiring infrastructure and reducing the cost.But it suffers from the impulsive noise because it introduces significant time variance into the power line channel.In this paper,a polar codes based orthogonal frequency division multiplexing(OFDM)PLC system is proposed to deal with the impulsive noise and thereby improve the transmission performance.Firstly,the impulsive noise is modelled with a multi-damped sine function by analyzing the time behavior of impulse events.Then the polar codes are used to combat the impulsive noise of PLC channel,and a low complexity bit-flipping decoding method based on CRC-aided successive cancellation list(CA-SCL)decoding algorithm is proposed.Simulations evaluate the proposed decoding algorithm and the results validate the suggested polar codes based OFDM-PLC scheme which can improve the BER performance of PLC with impulsive interference.
基金Supported by the National High Technology Research and Development Program of China (2009AA093601-2)the National Defense Foundation Research (B2420110007)
文摘The major constraint on the performance of orthogonal frequency division multiplexing （OFDM） based underwater acoustic （UWA） communication is to keep subcarriers orthogonal. In this paper, Doppler estimation and the respective compensation technique along with various diversity techniques were deliberated for OFDM-based systems best suited for underwater wireless information exchange. In practice, for mobile communication, adjustment and tuning of transducers in order to get spatial diversity is extremely difficult. Considering the relatively low coherence bandwidth in UWA, the frequency diversity design with the Doppler compensation function was elaborated here. The outfield experiments of mobile underwater acoustic communication （UWAC） based on OFDM were carried out with 0.17 bit/（s-Hz） spectral efficiency. The validity and the dependability of the scheme were also analyzed.
基金supported by the National Natural Science Foundation of China(60872026)the Natural Science Foundation of Tianjin(09JCZDJC16900)
文摘This paper presents an algorithm that aims to reduce the peak-to-average power ratio（PAPR） of orthogonal frequency division multiplexing（OFDM） communication systems while maintaining frequency tracking.The algorithm achieves PAPR reduction by applying the complex conjugates of the data symbol obtained from the frequency domain to cancel the phase of the data symbol.A likelihood estimator is used to obtain the sub-carrier phase error due to the residual carrier frequency offset（RCFO） using the same complex conjugates as a pilot signal.Furthermore,a joint time and frequency domain multicarrier phase locked loop（MPLL） is developed to compensate additional frequency offset.Simulation results show that this algorithm is capable of reducing PAPR without impacting the frequency tracking performance.
基金supported by the National Natural Science Foundation of China(60672047).
文摘For multiple-input multiple-output （MIMO） orthogonal frequency division multiplexing （OFDM） systems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform （FRFT） is proposed. The linear frequency modulation signals superimposed on the data signals are used as the training signals. By performing FRFT on the received signals and searching the peak value of the FRFT results, the receiver can realize timing synchronization and frequency offset acquisition simultaneously. Compared with the existing methods, the proposed algorithm can provide better timing synchronization performance and larger frequency offset acquisition range even under multi-path channels with low signal to noise ratio. Theoretical analysis and simulation results prove this point.
基金supported by the National Natural Science Foundation of China(6130110561102069)+2 种基金the China Postdoctoral Science Foundation Funded Project(2013M531351)the Nanjing University of Aeronautics and Astronautics Founding(NN2012022)the Open Fund of Graduate Innovated Base(Laboratory)for the Nanjing University of Aeronautics and Astronautics(KFJJ120219)
文摘Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window, and the carrier frequency offset （CFO） due to Doppler frequency shift or the frequency mismatch between the transmitter and receiver oscil ators, can bring severe inter-symbol interference （ISI） and inter-carrier interference （ICI） for the OFDM system. Relying on the relatively good correlation charac-teristic of the pseudo-noise （PN） sequence, a joint frame offset and normalized CFO estimation algorithm based on PN preamble in time domain is developed to realize the frame and frequency synchronization in the OFDM system. By comparison, the perfor-mances of the traditional algorithm and the improved algorithm are simulated under different conditions. The results indicate that the PN preamble based algorithm both in frame offset estimation and CFO estimation is more accurate, resource-saving and robust even under poor channel condition, such as low signal-to-noise ratio （SNR） and large normalized CFO.
基金supported by the National Natural Science Foundation of China(6137116961301108+1 种基金61071164)the Fundamental Research Funds for the Central Universities(NS2013024)
文摘The problem of channel estimation for multiple an- tenna orthogonal frequency division multiplexing （OFDM） systems subject to unknown carrier frequency offset （CFO） is addressed. Multiple signal classification （MUSIC）-Iike algorithm, which generally has been used for direction estimation or frequency estimation, is used for channel estimation in multiple antenna OFDM systems. A reduced dimensional （RD）-MUSIC based algorithm for channel estimation is proposed in multiple antenna OFDM systems with unknown CFO. The Cramer-Rao bound （CRB） of channel estimation in multiple antenna OFDM systems with unknown CFO is derived. The proposed algorithm has a superior performance of channel estimation compared with the Capon method and the least squares method.
