Orthogonal Time Frequency and Space(OTFS) modulation is expected to provide high-speed and ultra-reliable communications for emerging mobile applications, including low-orbit satellite communications. Using the Dopple...Orthogonal Time Frequency and Space(OTFS) modulation is expected to provide high-speed and ultra-reliable communications for emerging mobile applications, including low-orbit satellite communications. Using the Doppler frequency for positioning is a promising research direction on communication and navigation integration. To tackle the high Doppler frequency and low signal-to-noise ratio(SNR) in satellite communication, this paper proposes a Red and Blue Frequency Shift Discriminator(RBFSD) based on the pseudo-noise(PN) sequence.The paper derives that the cross-correlation function on the Doppler domain exhibits the characteristic of a Sinc function. Therefore, it applies modulation onto the Delay-Doppler domain using PN sequence and adjusts Doppler frequency estimation by red-shifting or blue-shifting. Simulation results show that the performance of Doppler frequency estimation is close to the Cramér-Rao Lower Bound when the SNR is greater than -15dB. The proposed algorithm is about 1/D times less complex than the existing PN pilot sequence algorithm, where D is the resolution of the fractional Doppler.展开更多
Orthogonal time frequency space(OTFS)technique, which modulates data symbols in the delayDoppler(DD) domain, presents a potential solution for supporting reliable information transmission in highmobility vehicular net...Orthogonal time frequency space(OTFS)technique, which modulates data symbols in the delayDoppler(DD) domain, presents a potential solution for supporting reliable information transmission in highmobility vehicular networks. In this paper, we study the issues of DD channel estimation for OTFS in the presence of fractional Doppler. We first propose a channel estimation algorithm with both low complexity and high accuracy based on the unitary approximate message passing(UAMP), which exploits the structured sparsity of the effective DD domain channel using hidden Markov model(HMM). The empirical state evolution(SE) analysis is then leveraged to predict the performance of our proposed algorithm. To refine the hyperparameters in the proposed algorithm,we derive the update criterion for the hyperparameters through the expectation-maximization(EM) algorithm. Finally, Our simulation results demonstrate that our proposed algorithm can achieve a significant gain over various baseline schemes.展开更多
An enhanced expectation maximization （ with channel time variation is proposed for mobile EM） based iterative channel estimator for coping multiple input multi output orthogonal frequency division multiplexing （MIM...An enhanced expectation maximization （ with channel time variation is proposed for mobile EM） based iterative channel estimator for coping multiple input multi output orthogonal frequency division multiplexing （MIMO OFDM） systems. In the proposed scheme, the recursive least squares （RLS） algorithm is applied to track the time varying channel impulse response （CIR） within several symbols. By using the tracked time varying CIR, the ICI are constructed and then cancelled from the received signal, thus reducing their impactions on the channel estimation. Moreover, based on an o ver sampled complex exponential basis expansion model （ OCE BEM）, an improved channel predic tor is derived in order to improve the initial channel estimates accuracy of the iterative estimator. Simulation results show that ying scenarios with a smaller the proposed scheme outperforms the classic counterpart in time var cost of complexity.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
Orthogonal time frequency space(OTFS)technique,which modulates data symbols in the delay-Doppler(DD)domain,presents a potential solution for supporting reliable information transmission in highmobility vehicular netwo...Orthogonal time frequency space(OTFS)technique,which modulates data symbols in the delay-Doppler(DD)domain,presents a potential solution for supporting reliable information transmission in highmobility vehicular networks.In this paper,we study the issues of DD channel estimation for OTFS in the presence of fractional Doppler.We first propose a channel estimation algorithm with both low complexity and high accuracy based on the unitary approximate message passing(UAMP),which exploits the structured sparsity of the effective DD domain channel using hidden Markov model(HMM).The empirical state evolution(SE)analysis is then leveraged to predict the performance of our proposed algorithm.To refine the hyperparameters in the proposed algorithm,we derive the update criterion for the hyperparameters through the expectation-maximization(EM)algorithm.Finally,Our simulation results demonstrate that our proposed algorithm can achieve a significant gain over various baseline schemes.展开更多
A least square （IS） parametric channel estimation method in broadband mt/ltiple input multiple output （MIMO） orthogonal frequency division multiplexing （OFDM） systems is proposed. The mean square error （MSE） p...A least square （IS） parametric channel estimation method in broadband mt/ltiple input multiple output （MIMO） orthogonal frequency division multiplexing （OFDM） systems is proposed. The mean square error （MSE） performance using optimal training pilots is also given, which proves the method can improve the estimation precision greatly in sparse channel.. Since such method needs the multi-path time delays information of the channel, the probabilistic data association （PDA） method is employed to estimate the time delay of each path. Simulation results show that both the bit error rate （BER） and the MSE performance of the proposed method are better than the traditional LS channel estimation method.展开更多
Studies have indicated that the distributed compressed sensing based(DCSbased) channel estimation can decrease the length of the reference signals effectively. In block transmission, a unique word(UW) can be used as a...Studies have indicated that the distributed compressed sensing based(DCSbased) channel estimation can decrease the length of the reference signals effectively. In block transmission, a unique word(UW) can be used as a cyclic prefix and reference signal. However, the DCS-based channel estimation requires diversity sequences instead of UW. In this paper, we proposed a novel method that employs a training sequence(TS) whose duration time is slightly longer than the maximum delay spread time. Based on proposed TS, the DCS approach perform perfectly in multipath channel estimation. Meanwhile, a cyclic prefix construct could be formed, which reduces the complexity of the frequency domain equalization(FDE) directly. Simulation results demonstrate that, by using the method of simultaneous orthogonal matching pursuit(SOMP), the required channel overhead has been reduced thanks to the proposed TS.展开更多
This paper addresses the problem of channel estimation in 5G-enabled vehicular-to-vehicular(V2V) channels with high-mobility environments and non-stationary feature. Considering orthogonal frequency division multiplex...This paper addresses the problem of channel estimation in 5G-enabled vehicular-to-vehicular(V2V) channels with high-mobility environments and non-stationary feature. Considering orthogonal frequency division multiplexing(OFDM) system, we perform extended Kalman filter(EKF) for channel estimation in conjunction with Iterative Detector & Decoder(IDD) at the receiver to improve the estimation accuracy. The EKF is proposed for jointly estimating the channel frequency response and the time-varying time correlation coefficients. And the IDD structure is adopted to reduce the estimation errors in EKF. The simulation results show that, compared with traditional methods, the proposed method effectively promotes the system performance.展开更多
A novel channel estimation algorithm is presented in this paper for the recently proposed cyclic postfix based on orthogonal frequency division multiplexing （OFDM） systems. Phase equalization with the erasure decisi...A novel channel estimation algorithm is presented in this paper for the recently proposed cyclic postfix based on orthogonal frequency division multiplexing （OFDM） systems. Phase equalization with the erasure decision is used to reduce both the channel estimation error and the computational complexity. Simulation results show that the proposed channel estimation algorithm can effectively estimate the channel impulse response （CIR） and the performance of the proposed phase equalization with erasure decision is comparable with the minimal mean square error （MMSE） equalization, but it offers less computational complexity.展开更多
A new channel estimation method for orthogonal frequency division multiplexing （OFDM） system with large subcarriers and serious intercarrier interference （ICI） is proposed. The channel frequency-domain （ CFD ） m...A new channel estimation method for orthogonal frequency division multiplexing （OFDM） system with large subcarriers and serious intercarrier interference （ICI） is proposed. The channel frequency-domain （ CFD ） matrix of each delay path is factorized to the product of a diagonal delay matrix and a circular ICI matrix in this model. To reduce the coefficient number, the circular ICI ma- trix is squeezed by using Hamming-window as the reshaping pulse in the transmitter. Meanwhile, the elements of the diagonal delay matrix are approximated with a discrete prolate spheroidal basis ex- pansion model （DPS-BEM）. A least-square （LS） estimator is used to estimate the reduced channel coefficients. The proposed method is theoretically derived and simulated. The simulation results in- dicate that the model has good performance and is appropriate for various channel environments. The method also has low complexity and good spectral efficiency.展开更多
A semi-blind channel estimation algorithm based on subspace approach for orthogonal frequency division multiplexing（OFDM） systems over the frequency-selective channel is proposed. A linear preeoding is applied on ea...A semi-blind channel estimation algorithm based on subspace approach for orthogonal frequency division multiplexing（OFDM） systems over the frequency-selective channel is proposed. A linear preeoding is applied on each block before the IFFT operation and a low-rank structure is created in the received signal. Then subspace properties can be exploited to identify the channel up to a scalar ambiguity. The residual scalar ambiguities eliminated by inserting pilots into data stream. Simulation results illustrate the performance of the proposed semi-blind algorithm.展开更多
An adaptive bit loading and power-allocation scheme is proposed in order to augment the performance of the system based on orthogonal frequency division multiplexing （OFDM）, which is based on the maximum power margi...An adaptive bit loading and power-allocation scheme is proposed in order to augment the performance of the system based on orthogonal frequency division multiplexing （OFDM）, which is based on the maximum power margin. Coinciding with the adaptive loading scheme, a semi-blind channel estimation algorithm using subspace decomposition method is proposed, which uses the information in the cyclic prefix. An initial channel state information is estimated by using the training sequences with the method of interpolation filtering. The proposed adaptive scheme is simulated on an OFDM wireless local area network（WLAN） system in a time-varying channel. The performance is compared to the constant loading scheme.展开更多
This paper proposes a TSK fuzzy approach to channel estimation for Orthogonal Frequency Division Multiplexing （OFDM） systems. The information of dispersive fading channel is described by using TSK fuzzy model, which...This paper proposes a TSK fuzzy approach to channel estimation for Orthogonal Frequency Division Multiplexing （OFDM） systems. The information of dispersive fading channel is described by using TSK fuzzy model, which is updated by the pilot symbols. The proposed approach can trace the variation of channel and it is computationally simple. Its performance is tested via simulations. Results show that it is comparable to that of ideal Minimum Mean-Square-Error （MMSE） method, especially at the low Signal to Noise Ratio （SNR）.展开更多
针对现有信道估计方案导致正交时频空间(Orthogonal Time Frequency Space,OTFS)调制系统峰均功率比(Peak-to-Average Power Ratio,PAPR)高或频谱效率(Spectral Efficiency,SE)低的问题,提出一种多叠加导频的低PAPR、高SE信道估计方法...针对现有信道估计方案导致正交时频空间(Orthogonal Time Frequency Space,OTFS)调制系统峰均功率比(Peak-to-Average Power Ratio,PAPR)高或频谱效率(Spectral Efficiency,SE)低的问题,提出一种多叠加导频的低PAPR、高SE信道估计方法。发送端利用时域正交性和离散傅里叶域相位的随机性,在时延多普勒域中嵌入与数据相叠加的5导频符号的导频图案实现低PAPR,提高SE。接收端以数据符号与噪声之和的能量均值为基准,实现导频信号检测,同时根据每个导频的不同位置信息恢复出存在相位旋转的数据信号。基于能量准则,利用多个独立的接收信号进行联合信道估计,以降低数据符号的干扰,并采用消息传递算法进行数据恢复。仿真结果表明,该方法比单叠加导频信道估计的PAPR低,同时较嵌入式导频信道估计的SE提高约14.4%。展开更多
水声通信作为海洋信息传输的核心技术,广泛应用于海洋探测、海事监管及海底工程等领域。然而,水声信道因双重色散特性而极具挑战性,对系统设计构成重大障碍。尽管正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)技术...水声通信作为海洋信息传输的核心技术,广泛应用于海洋探测、海事监管及海底工程等领域。然而,水声信道因双重色散特性而极具挑战性,对系统设计构成重大障碍。尽管正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)技术已在水声通信中得到广泛应用,但其性能仍受限于信道状态估计的准确性。正交时频空(Orthogonal Time Frequency Space, OTFS)调制技术通过将数据转换到时延-多普勒域内传输,能够有效地应对水声信道中的多径效应和多普勒频移,提高通信系统的性能和可靠性。综述了OTFS在水声通信中的关键处理技术,涵盖信道估计、信道均衡及多址接入技术三个核心方面,并从天线拓展、机器学习融合及同步创新等方面探讨了未来发展趋势,同时详细分析了复杂信道环境下的信号检测、计算复杂度与实时性平衡、参数估计准确性及水下环境对数据可靠性的影响面临的技术挑战。展开更多
针对多输入多输出正交时频空间(multiple-input multiple-output orthogonal time frequency space,MIMO-OTFS)系统由最大时延、多普勒扩展、天线数量增加带来信道估计计算开销大、准确率下降的问题,提出了一种基于感知辅助和原子选择...针对多输入多输出正交时频空间(multiple-input multiple-output orthogonal time frequency space,MIMO-OTFS)系统由最大时延、多普勒扩展、天线数量增加带来信道估计计算开销大、准确率下降的问题,提出了一种基于感知辅助和原子选择门限的广义正交匹配追踪(sensing aided generalized orthogonal matching pursuit algorithm based on atomic threshold,SA-TGOMP)信道估计算法。该算法首先将雷达探测的用户和周围环境信息转化为OTFS信道的初始索引集,然后引入以固定值选取相关性原子进行迭代的策略和原子选择门限进行支撑集更新。实验结果表明,本文算法能够有效提高信道估计精度的同时减少导频开销。展开更多
针对低轨卫星星地通信高动态信道特点,采用正交时频空(Orthogonal Time Frequency Space, OTFS)调制方式,提出一种低导频开销、高精度的两阶段信道估计方法,实现对时延、多普勒频移和信道增益3个参数的精细估计。所提TP-CSIE(Two Phase ...针对低轨卫星星地通信高动态信道特点,采用正交时频空(Orthogonal Time Frequency Space, OTFS)调制方式,提出一种低导频开销、高精度的两阶段信道估计方法,实现对时延、多普勒频移和信道增益3个参数的精细估计。所提TP-CSIE(Two Phase Channel State Information Estimation)方案采用时域训练序列为导频结构,解决时延-多普勒(Delay-Doppler, DD)域嵌入式导频方案在高动态星地链路下导频开销过大的问题。由于DD域信道的固有稀疏性,OTFS信道估计问题被转化为稀疏信号的恢复问题。在算法第一阶段,选用稀疏信号恢复算法进行信道参数的初始估计,利用重叠相加法获得部分先验信息以提高压缩采样匹配追踪(Compressive Sampling Matching Pursuit, CoSAMP)算法的准确性。在算法第二阶段,设计增强型旋转不变子空间算法实现信道参数的准确估计。仿真结果表明,与现有方案相比,所提算法归一化均方误差性能约有7 dB性能的提升,误码率性能约有10 dB的提升。展开更多
正交时频空(Orthogonal Time Frequency Space, OTFS)调制技术是近年提出的新型信号调制方式,旨在应对下一代无线通信网络典型的高移动性多径传输场景中存在的大多普勒频移导致的通信质量下降问题。OTFS技术将符号映射至时延-多普勒(Del...正交时频空(Orthogonal Time Frequency Space, OTFS)调制技术是近年提出的新型信号调制方式,旨在应对下一代无线通信网络典型的高移动性多径传输场景中存在的大多普勒频移导致的通信质量下降问题。OTFS技术将符号映射至时延-多普勒(Delay-Doppler, DD)域,并通过二维变换将其变换到时频域,以应对大多普勒频移和时延导致的载波间干扰与符号间干扰。分析并总结了OTFS技术的基本原理、信道估计、符号检测及与多址技术结合等方向的研究现状,对未来OTFS技术的发展趋势进行了展望。展开更多
对未来移动通信中高速移动性场景下的新型正交时频空(Orthogonal Time Frequency Space,OTFS)接收机关键技术进行研究。首先,概述了OTFS技术的系统模型,对其主要优势与特性进行阐述。其次,分析OTFS系统在时频域和时延-多普勒域的输入-...对未来移动通信中高速移动性场景下的新型正交时频空(Orthogonal Time Frequency Space,OTFS)接收机关键技术进行研究。首先,概述了OTFS技术的系统模型,对其主要优势与特性进行阐述。其次,分析OTFS系统在时频域和时延-多普勒域的输入-输出关系。然后,通过与传统正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术的性能比较,总结OTFS在不同通信条件下的技术优势,并进一步介绍和分析现有OTFS系统的信道估计、信号检测以及分集增益方案。最后,探讨OTFS技术在下一代通信关键技术及潜在场景下的应用前景。展开更多
文摘Orthogonal Time Frequency and Space(OTFS) modulation is expected to provide high-speed and ultra-reliable communications for emerging mobile applications, including low-orbit satellite communications. Using the Doppler frequency for positioning is a promising research direction on communication and navigation integration. To tackle the high Doppler frequency and low signal-to-noise ratio(SNR) in satellite communication, this paper proposes a Red and Blue Frequency Shift Discriminator(RBFSD) based on the pseudo-noise(PN) sequence.The paper derives that the cross-correlation function on the Doppler domain exhibits the characteristic of a Sinc function. Therefore, it applies modulation onto the Delay-Doppler domain using PN sequence and adjusts Doppler frequency estimation by red-shifting or blue-shifting. Simulation results show that the performance of Doppler frequency estimation is close to the Cramér-Rao Lower Bound when the SNR is greater than -15dB. The proposed algorithm is about 1/D times less complex than the existing PN pilot sequence algorithm, where D is the resolution of the fractional Doppler.
基金supported by the Key Scientific Research Project in Colleges and Universities of Henan Province of China(Grant Nos.21A510003)Science and the Key Science and Technology Research Project of Henan Province of China(Grant Nos.222102210053)。
文摘Orthogonal time frequency space(OTFS)technique, which modulates data symbols in the delayDoppler(DD) domain, presents a potential solution for supporting reliable information transmission in highmobility vehicular networks. In this paper, we study the issues of DD channel estimation for OTFS in the presence of fractional Doppler. We first propose a channel estimation algorithm with both low complexity and high accuracy based on the unitary approximate message passing(UAMP), which exploits the structured sparsity of the effective DD domain channel using hidden Markov model(HMM). The empirical state evolution(SE) analysis is then leveraged to predict the performance of our proposed algorithm. To refine the hyperparameters in the proposed algorithm,we derive the update criterion for the hyperparameters through the expectation-maximization(EM) algorithm. Finally, Our simulation results demonstrate that our proposed algorithm can achieve a significant gain over various baseline schemes.
基金Supported by the National Natural Science Foundation of China(6096200161071088)
文摘An enhanced expectation maximization （ with channel time variation is proposed for mobile EM） based iterative channel estimator for coping multiple input multi output orthogonal frequency division multiplexing （MIMO OFDM） systems. In the proposed scheme, the recursive least squares （RLS） algorithm is applied to track the time varying channel impulse response （CIR） within several symbols. By using the tracked time varying CIR, the ICI are constructed and then cancelled from the received signal, thus reducing their impactions on the channel estimation. Moreover, based on an o ver sampled complex exponential basis expansion model （ OCE BEM）, an improved channel predic tor is derived in order to improve the initial channel estimates accuracy of the iterative estimator. Simulation results show that ying scenarios with a smaller the proposed scheme outperforms the classic counterpart in time var cost of complexity.
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 Key Scientific Research Project in Colleges and Universities of Henan Province of China(Grant Nos.21A510003)Science and the Key Science and Technology Research Project of Henan Province of China(Grant Nos.222102210053).
文摘Orthogonal time frequency space(OTFS)technique,which modulates data symbols in the delay-Doppler(DD)domain,presents a potential solution for supporting reliable information transmission in highmobility vehicular networks.In this paper,we study the issues of DD channel estimation for OTFS in the presence of fractional Doppler.We first propose a channel estimation algorithm with both low complexity and high accuracy based on the unitary approximate message passing(UAMP),which exploits the structured sparsity of the effective DD domain channel using hidden Markov model(HMM).The empirical state evolution(SE)analysis is then leveraged to predict the performance of our proposed algorithm.To refine the hyperparameters in the proposed algorithm,we derive the update criterion for the hyperparameters through the expectation-maximization(EM)algorithm.Finally,Our simulation results demonstrate that our proposed algorithm can achieve a significant gain over various baseline schemes.
文摘A least square （IS） parametric channel estimation method in broadband mt/ltiple input multiple output （MIMO） orthogonal frequency division multiplexing （OFDM） systems is proposed. The mean square error （MSE） performance using optimal training pilots is also given, which proves the method can improve the estimation precision greatly in sparse channel.. Since such method needs the multi-path time delays information of the channel, the probabilistic data association （PDA） method is employed to estimate the time delay of each path. Simulation results show that both the bit error rate （BER） and the MSE performance of the proposed method are better than the traditional LS channel estimation method.
基金support by National Key Technology Research and Development Program of the Ministry of Science and Technology of China (2015BAK05B01)
文摘Studies have indicated that the distributed compressed sensing based(DCSbased) channel estimation can decrease the length of the reference signals effectively. In block transmission, a unique word(UW) can be used as a cyclic prefix and reference signal. However, the DCS-based channel estimation requires diversity sequences instead of UW. In this paper, we proposed a novel method that employs a training sequence(TS) whose duration time is slightly longer than the maximum delay spread time. Based on proposed TS, the DCS approach perform perfectly in multipath channel estimation. Meanwhile, a cyclic prefix construct could be formed, which reduces the complexity of the frequency domain equalization(FDE) directly. Simulation results demonstrate that, by using the method of simultaneous orthogonal matching pursuit(SOMP), the required channel overhead has been reduced thanks to the proposed TS.
基金supported by the National Natural Science Foundation of China (No.61501066,No.61572088,No.61701063)Chongqing Frontier and Applied Basic Research Project (No.cstc2015jcyjA40003,No.cstc2017jcyjAX0026,No.cstc2016jcyjA0209)+1 种基金the Open Fund of the State Key Laboratory of Integrated Services Networks (No.ISN16-03)the Fundamental Research Funds for the Central Universities (No.106112017CDJXY 500001)
文摘This paper addresses the problem of channel estimation in 5G-enabled vehicular-to-vehicular(V2V) channels with high-mobility environments and non-stationary feature. Considering orthogonal frequency division multiplexing(OFDM) system, we perform extended Kalman filter(EKF) for channel estimation in conjunction with Iterative Detector & Decoder(IDD) at the receiver to improve the estimation accuracy. The EKF is proposed for jointly estimating the channel frequency response and the time-varying time correlation coefficients. And the IDD structure is adopted to reduce the estimation errors in EKF. The simulation results show that, compared with traditional methods, the proposed method effectively promotes the system performance.
基金the research grant of New Century Excellent Talent Support Project from Minister of EducationHigh-tech R&D Program of China (863 Program) with Grant No. 2007AA01Z2B6.
文摘A novel channel estimation algorithm is presented in this paper for the recently proposed cyclic postfix based on orthogonal frequency division multiplexing （OFDM） systems. Phase equalization with the erasure decision is used to reduce both the channel estimation error and the computational complexity. Simulation results show that the proposed channel estimation algorithm can effectively estimate the channel impulse response （CIR） and the performance of the proposed phase equalization with erasure decision is comparable with the minimal mean square error （MMSE） equalization, but it offers less computational complexity.
基金Supported by the National Natural Science Foundation of China(61101131)
文摘A new channel estimation method for orthogonal frequency division multiplexing （OFDM） system with large subcarriers and serious intercarrier interference （ICI） is proposed. The channel frequency-domain （ CFD ） matrix of each delay path is factorized to the product of a diagonal delay matrix and a circular ICI matrix in this model. To reduce the coefficient number, the circular ICI ma- trix is squeezed by using Hamming-window as the reshaping pulse in the transmitter. Meanwhile, the elements of the diagonal delay matrix are approximated with a discrete prolate spheroidal basis ex- pansion model （DPS-BEM）. A least-square （LS） estimator is used to estimate the reduced channel coefficients. The proposed method is theoretically derived and simulated. The simulation results in- dicate that the model has good performance and is appropriate for various channel environments. The method also has low complexity and good spectral efficiency.
文摘A semi-blind channel estimation algorithm based on subspace approach for orthogonal frequency division multiplexing（OFDM） systems over the frequency-selective channel is proposed. A linear preeoding is applied on each block before the IFFT operation and a low-rank structure is created in the received signal. Then subspace properties can be exploited to identify the channel up to a scalar ambiguity. The residual scalar ambiguities eliminated by inserting pilots into data stream. Simulation results illustrate the performance of the proposed semi-blind algorithm.
文摘An adaptive bit loading and power-allocation scheme is proposed in order to augment the performance of the system based on orthogonal frequency division multiplexing （OFDM）, which is based on the maximum power margin. Coinciding with the adaptive loading scheme, a semi-blind channel estimation algorithm using subspace decomposition method is proposed, which uses the information in the cyclic prefix. An initial channel state information is estimated by using the training sequences with the method of interpolation filtering. The proposed adaptive scheme is simulated on an OFDM wireless local area network（WLAN） system in a time-varying channel. The performance is compared to the constant loading scheme.
文摘This paper proposes a TSK fuzzy approach to channel estimation for Orthogonal Frequency Division Multiplexing （OFDM） systems. The information of dispersive fading channel is described by using TSK fuzzy model, which is updated by the pilot symbols. The proposed approach can trace the variation of channel and it is computationally simple. Its performance is tested via simulations. Results show that it is comparable to that of ideal Minimum Mean-Square-Error （MMSE） method, especially at the low Signal to Noise Ratio （SNR）.
文摘针对现有信道估计方案导致正交时频空间(Orthogonal Time Frequency Space,OTFS)调制系统峰均功率比(Peak-to-Average Power Ratio,PAPR)高或频谱效率(Spectral Efficiency,SE)低的问题,提出一种多叠加导频的低PAPR、高SE信道估计方法。发送端利用时域正交性和离散傅里叶域相位的随机性,在时延多普勒域中嵌入与数据相叠加的5导频符号的导频图案实现低PAPR,提高SE。接收端以数据符号与噪声之和的能量均值为基准,实现导频信号检测,同时根据每个导频的不同位置信息恢复出存在相位旋转的数据信号。基于能量准则,利用多个独立的接收信号进行联合信道估计,以降低数据符号的干扰,并采用消息传递算法进行数据恢复。仿真结果表明,该方法比单叠加导频信道估计的PAPR低,同时较嵌入式导频信道估计的SE提高约14.4%。
文摘水声通信作为海洋信息传输的核心技术,广泛应用于海洋探测、海事监管及海底工程等领域。然而,水声信道因双重色散特性而极具挑战性,对系统设计构成重大障碍。尽管正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)技术已在水声通信中得到广泛应用,但其性能仍受限于信道状态估计的准确性。正交时频空(Orthogonal Time Frequency Space, OTFS)调制技术通过将数据转换到时延-多普勒域内传输,能够有效地应对水声信道中的多径效应和多普勒频移,提高通信系统的性能和可靠性。综述了OTFS在水声通信中的关键处理技术,涵盖信道估计、信道均衡及多址接入技术三个核心方面,并从天线拓展、机器学习融合及同步创新等方面探讨了未来发展趋势,同时详细分析了复杂信道环境下的信号检测、计算复杂度与实时性平衡、参数估计准确性及水下环境对数据可靠性的影响面临的技术挑战。
文摘针对多输入多输出正交时频空间(multiple-input multiple-output orthogonal time frequency space,MIMO-OTFS)系统由最大时延、多普勒扩展、天线数量增加带来信道估计计算开销大、准确率下降的问题,提出了一种基于感知辅助和原子选择门限的广义正交匹配追踪(sensing aided generalized orthogonal matching pursuit algorithm based on atomic threshold,SA-TGOMP)信道估计算法。该算法首先将雷达探测的用户和周围环境信息转化为OTFS信道的初始索引集,然后引入以固定值选取相关性原子进行迭代的策略和原子选择门限进行支撑集更新。实验结果表明,本文算法能够有效提高信道估计精度的同时减少导频开销。
文摘针对低轨卫星星地通信高动态信道特点,采用正交时频空(Orthogonal Time Frequency Space, OTFS)调制方式,提出一种低导频开销、高精度的两阶段信道估计方法,实现对时延、多普勒频移和信道增益3个参数的精细估计。所提TP-CSIE(Two Phase Channel State Information Estimation)方案采用时域训练序列为导频结构,解决时延-多普勒(Delay-Doppler, DD)域嵌入式导频方案在高动态星地链路下导频开销过大的问题。由于DD域信道的固有稀疏性,OTFS信道估计问题被转化为稀疏信号的恢复问题。在算法第一阶段,选用稀疏信号恢复算法进行信道参数的初始估计,利用重叠相加法获得部分先验信息以提高压缩采样匹配追踪(Compressive Sampling Matching Pursuit, CoSAMP)算法的准确性。在算法第二阶段,设计增强型旋转不变子空间算法实现信道参数的准确估计。仿真结果表明,与现有方案相比,所提算法归一化均方误差性能约有7 dB性能的提升,误码率性能约有10 dB的提升。
文摘正交时频空(Orthogonal Time Frequency Space, OTFS)调制技术是近年提出的新型信号调制方式,旨在应对下一代无线通信网络典型的高移动性多径传输场景中存在的大多普勒频移导致的通信质量下降问题。OTFS技术将符号映射至时延-多普勒(Delay-Doppler, DD)域,并通过二维变换将其变换到时频域,以应对大多普勒频移和时延导致的载波间干扰与符号间干扰。分析并总结了OTFS技术的基本原理、信道估计、符号检测及与多址技术结合等方向的研究现状,对未来OTFS技术的发展趋势进行了展望。
文摘对未来移动通信中高速移动性场景下的新型正交时频空(Orthogonal Time Frequency Space,OTFS)接收机关键技术进行研究。首先,概述了OTFS技术的系统模型,对其主要优势与特性进行阐述。其次,分析OTFS系统在时频域和时延-多普勒域的输入-输出关系。然后,通过与传统正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术的性能比较,总结OTFS在不同通信条件下的技术优势,并进一步介绍和分析现有OTFS系统的信道估计、信号检测以及分集增益方案。最后,探讨OTFS技术在下一代通信关键技术及潜在场景下的应用前景。
