This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduc...This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduce the walk- off effect and can therefore equalize the nonlinear impairments effectively. Compared with the only other existing nonlinearity pre-compensation method, the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system, but also effective for high- dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation. The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method. For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20 × 80 km standard single-mode fibre system, the suggested method can improve the nonlinear threshold （for Q 〉 10 dB） about 2.7, 1.2 and 1.0 dB, and the maximum Q factor about 1.2, 0.4 and 0.3 dB, for 2, 8 and 16 ps/（nm.km） dispersion coefficients.展开更多
With the development of wireless communication,the 6G mobile communication technology has received wide attention.As one of the key technologies of 6G,terahertz(THz)communication technology has the characteristics of ...With the development of wireless communication,the 6G mobile communication technology has received wide attention.As one of the key technologies of 6G,terahertz(THz)communication technology has the characteristics of ultra-high bandwidth,high security and low environmental noise.In this paper,a THz duplexer with a half-wavelength coupling structure and a sub-harmonic mixer operating at 216 GHz and 204 GHz are designed and measured.Based on these key devices,a 220 GHz frequency-division multiplexing communication system is proposed,with a real-time data rate of 10.4 Gbit/s for one channel and a transmission distance of 15 m.The measured constellation diagram of two receivers is clearly visible,the signal-to-noise ratio(SNR)is higher than 22 dB,and the bit error ratio(BER)is less than 10^(−8).Furthermore,the high definition(HD)4K video can also be transmitted in real time without stutter.展开更多
An optical frequency comb(OFC)frequency-division multiplexing dispersive interference multichannel distance measurement method is proposed.Based on the OFC dispersive interference,the wide OFC spectrum is divided into...An optical frequency comb(OFC)frequency-division multiplexing dispersive interference multichannel distance measurement method is proposed.Based on the OFC dispersive interference,the wide OFC spectrum is divided into multiple channels using a wavelength-division multiplexer.Under the existing light source and spectrometer,a single interference system can realize six channels of the high-precision parallel absolute distance measurement.The influence of the spectrum width and shape on the performance of the distance measurement channel is analyzed.The ranging accuracy of six channels is higher than±4μm under the optimization of a nonuniform discrete Fourier transform and Hanning window.展开更多
The rapidly growing global data usage has demanded more efficient ways to utilize the scarce electromagnetic spectrum resource. Recent research has focused on the development of efficient multiplexing techniques in th...The rapidly growing global data usage has demanded more efficient ways to utilize the scarce electromagnetic spectrum resource. Recent research has focused on the development of efficient multiplexing techniques in the millimeter-wave band(1-10 mm, or 30-300 GHz) due to the promise of large available bandwidth for future wireless networks. Frequency-division multiplexing is still one of the most commonly-used techniques to maximize the transmission capacity of a wireless network.Based on the frequency-selective tunnelling effect of the low-loss epsilon-near-zero metamaterial waveguide, we numerically and experimentally demonstrate five-channel frequency-division multiplexing and demultiplexing in the millimeter-wave range.We show that this device architecture offers great flexibility to manipulate the filter Q-factors and the transmission spectra of different channels, by changing of the epsilon-near-zero metamaterial waveguide topology and by adding a standard waveguide between two epsilon-near-zero channels. This strategy of frequency-division multiplexing may pave a way for efficiently allocating the spectrum for future communication networks.展开更多
Utilizing multi-band and multi-carrier techniques enhances throughput and capacity in Long-Term Evolution(LTE)-Advanced and 5G New Radio(NR)mobile networks.However,these techniques introduce Passive Inter-Modulation(P...Utilizing multi-band and multi-carrier techniques enhances throughput and capacity in Long-Term Evolution(LTE)-Advanced and 5G New Radio(NR)mobile networks.However,these techniques introduce Passive Inter-Modulation(PIM)interference in Frequency-Division Duplexing(FDD)systems.In this paper,a novel multi-band Wiener-Hammerstein model is presented to digitally reconstruct PIM interference signals,thereby achieving effective PIM Cancellation(PIMC)in multi-band scenarios.In the model,transmitted signals are independently processed to simulate Inter-Modulation Distortions(IMDs)and Cross-Modulation Distortions(CMDs).Furthermore,the Finite Impulse Response(FIR)filter,basis function generation,and B-spline function are applied for precise PIM product estimation and generation in multi-band scenarios.Simulations involving 4 carrier components from diverse NR frequency bands at varying transmitting powers validate the feasibility of the model for multi-band PIMC,achieving up to 19 dB in PIMC performance.Compared to other models,this approach offers superior PIMC performance,exceeding them by more than 5 dB in high transmitting power scenarios.Additionally,its lower sampling rate requirement reduces the hardware complexity associated with implementing multi-band PIMC.展开更多
A two-dimensional （2-D） polynomial regression model is set up to approximate the time-frequency response of slowly time-varying orthogonal frequency-division multiplexing （OFDM） systems. With this model the estima...A two-dimensional （2-D） polynomial regression model is set up to approximate the time-frequency response of slowly time-varying orthogonal frequency-division multiplexing （OFDM） systems. With this model the estimation of the OFDM time-frequency response is turned into the optimization of some time-invariant model parameters. A new algorithm based on the expectation-maximization （EM） method is proposed to obtain the maximum-likelihood （ML） estimation of the polynomial model parameters over the 2-D observed data. At the same time, in order to reduce the complexity and avoid the computation instability, a novel recursive approach （RPEMTO） is given to calculate the values of the parameters. It is further shown that this 2-D polynomial EM-based algorithm for time-varying OFDM （PEMTO） can be simplified mathematically to handle the one-dimensional sequential estimation. Simulations illustrate that the proposed algorithms achieve a lower bit error rate （BER） than other blind algorithms.展开更多
The ergodic information rate for Orthogonal Frequency-Division Multiplexing / Orthogonal Frequency-Division Multiple Access with amplify-and-forward （AF） relaying systems in the presence of frequency offsets is eval...The ergodic information rate for Orthogonal Frequency-Division Multiplexing / Orthogonal Frequency-Division Multiple Access with amplify-and-forward （AF） relaying systems in the presence of frequency offsets is evaluated. Unlike previous work, per-subcarrier adaptive power allocation is performed on each relay to optimize the system ergodic information rate. For a given frequency offset and total number of relays M, the AF ergodic information rate is proven to be a monotonically increasing function of α （the ratio of the power allocated to the source node and the total transmit power）, implying that the maximum ergodic information rate can be obtained at α=1 （i.e., there is no cooperative relay）. Furthermore, the proof of ＂cooperative relays cannot improve the AF ergodic information rate in a quasi-static wireless channel＂ is also provided in this letter.展开更多
The dynamic resource allocation problem in high-speed railway downlink orthogonal frequency-division multiplexing（OFDM） systems with multiple-input multiple-output（MIMO） antennas is investigated.Sub-carriers,anten...The dynamic resource allocation problem in high-speed railway downlink orthogonal frequency-division multiplexing（OFDM） systems with multiple-input multiple-output（MIMO） antennas is investigated.Sub-carriers,antennas,time slots,and power are jointly considered.The problem of multi-dimensional resource allocation is formulated as a mixed-integer nonlinear programming problem.The effect of the moving speed on Doppler shift is analyzed to calculate the inter-carrier interference power.The optimization objective is to maximize the system throughput under the constraint of a total transmitted power that is no greater than a certain threshold.In order to reduce the computational complexity,a suboptimal solution to the optimization problem is obtained by a two-step method.First,sub-carriers,antennas,and time slots are assigned to users under the assumption of equal power allocation.Next,the power allocation problem is solved according to the result of the first-step resource allocation.Simulation results show that the proposed multi-dimensional resource allocation strategy has a significant performance improvement in terms of system throughput compared with the existing one.展开更多
A novel adaptive ordered LDPC （low-density parity-check） coded OFDM （orthogonal frequency-division multiplexing） transmission technique is proposed to exploit different error probabilities of irregular LDPC coded ...A novel adaptive ordered LDPC （low-density parity-check） coded OFDM （orthogonal frequency-division multiplexing） transmission technique is proposed to exploit different error probabilities of irregular LDPC coded bits in OFDM systems. Assuming that the CSI （channel state information） is known at the transmitter, the irregular LDPC coded bits are ordered according to their degrees and then allocated into subcarriers adaptively. Bits with higher degrees are allocated into less attenuated subcarriers and bits with lower degrees are allocated into deep attenuated subcarriers. Quantization on CSI feedback can be applied to minimize the signaling overhead. Performance of this strategy is analyzed by density evolution and numerical simulation. Simulation results show that about a 1 to 1.5 dB gain in terms of SNR （ signal to noise ratio） can be achieved over frequency-selective fading channels compared to conventional LDPC coded OFDM systems without ordering, and the proposed scheme is robust to CSI quantization.展开更多
In this paper,a novel efficient continuous piecewise nonlinear companding scheme is proposed for reducing the peak-to-average power ratio(PAPR)of orthogonal frequency division multiplexing(OFDM)systems.In the proposed...In this paper,a novel efficient continuous piecewise nonlinear companding scheme is proposed for reducing the peak-to-average power ratio(PAPR)of orthogonal frequency division multiplexing(OFDM)systems.In the proposed companding transform,signal samples with large amplitudes is clipped for peak power reduction,and the signal samples with medium amplitudes is nonlinear transformed with power compensation.While the signal samples with small amplitudes remain unchanged.The whole companding function is continuous and smooth in the range of positive numbers,which is beneficial for guaranteeing the bit error rate(BER)and power spectral density(PSD)performance.This scheme can achieve a significant reduction in PAPR.And at the same time,it cause little increment in BER and PSD performance.Simulation results indicate the superiority of the proposed scheme over existing companding schemes.展开更多
A space-time coded multiple-input multiple-output orthogonal frequency-division multiplexing （MIMO-OFDM） system is considered as a solution to the future wideband wireless communication system. This paper proposes a...A space-time coded multiple-input multiple-output orthogonal frequency-division multiplexing （MIMO-OFDM） system is considered as a solution to the future wideband wireless communication system. This paper proposes an extended Kalman filtering-based （EKF-based） channel estimation method for space-time coded MIMO-OFDM systems. The proposed method can exploit pilot symbols and an extended Kalman filter to estimate channel without any prior knowledge of channel statistics. In comparison with the least square （LS） and the least mean square （LMS） methods, the EKF-based approach has a better performance in theory. Computer simulations demonstrate the proposed method outperforms the LS and LMS methods. Therefore it can offer draznatic system performance improvement at a modest cost of computational complexity.展开更多
IEEE 802.11ax,which is an emerging WLAN standard,aims at providing highly efficient communication in ultra-dense wireless networks.However,due to a large number of stations(STAs)in the ultra-dense device deployment sc...IEEE 802.11ax,which is an emerging WLAN standard,aims at providing highly efficient communication in ultra-dense wireless networks.However,due to a large number of stations(STAs)in the ultra-dense device deployment scenarios,the potentially high packet collision rate significantly decreases the communication efficiency of WLAN.In this paper,we propose an adaptive STA grouping scheme to overcome this dense network challenge in IEEE 802.11ax by using Buffer State Report(BSR)based Two-stage Mechanism(BTM).In order to achieve the optimal efficiency of BSR delivery,we analyze the functional relationship between STA number in group and Resource Unit(RU)efficiency.Based on this analysis results,an adaptive STA grouping algorithm with variable group size is proposed to achieve efficient grouping in BTM.The numerical results demonstrate that the proposed adaptive BTM grouping algorithm significantly improves the BSR delivery efficiency and the throughput of overall system and each STA in the ultra-dense wireless network.展开更多
This paper is focused on the multiuser implementation of fusion of radar and communication(RadCom)in internet-of-vehicles(IoV)scenarios.Traditional time-division multiple access(TDMA)technology degrades the velocity d...This paper is focused on the multiuser implementation of fusion of radar and communication(RadCom)in internet-of-vehicles(IoV)scenarios.Traditional time-division multiple access(TDMA)technology degrades the velocity detection performance of orthogonal frequency-division multiplexing(OFDM)-based RadCom systems.We propose a new TDMA approach for OFDM-based RadCom systems,where multiuser communication and radar detection are completed synchronously.We consider a continuous-wave TDMA OFDM structure in which random user data or Zadoff-Chu(ZC)sequences are transmitted in one symbol duration to ensure detection performance.As an application of interference cancellation method,user data demodulation and environment sensing can be simultaneously accomplished by our proposed approach.We carry out numerical evaluation and show wireless communication and radar detection performance over the continuous-wave TDMA OFDM-based RadCom approach.展开更多
The Peak to Average power Ratio (PAR) of a Multi-Band Orthogonal Frequency-Division Multiplexing (MB-OFDM) Ultra-Wide Band (UWB) signals can be substantially larger than that of single carrier or carrier-less ultra-wi...The Peak to Average power Ratio (PAR) of a Multi-Band Orthogonal Frequency-Division Multiplexing (MB-OFDM) Ultra-Wide Band (UWB) signals can be substantially larger than that of single carrier or carrier-less ultra-wideband signals. In this letter, a novel PAR reduction scheme for the MB-OFDM UWB system based on spreading and interleaving is proposed. By spreading the coded bits over each subcarrier in corresponding band and interleaving the spread symbols across all bands, the PAR statistics of the MB-OFDM signals can be improved and the PAR is reduced obviously. In the PAR reduction scheme, there is no loss in transmission data rate or Bit Error Rate (BER) performance decreasing. Since the spreading and interleaving operation are implemented by unitary Hadamard sequences and used for an approach to provide the robustness of the UWB system to narrowband interference, there is no additional implementation burden. Simulation results show that the investigated scheme gives the PAR reduction of 3dB compared with that of the original MB-OFDM signals.展开更多
The existing recognition algorithms of space-time block code(STBC)for multi-antenna(MA)orthogonal frequencydivision multiplexing(OFDM)systems use feature extraction and hypothesis testing to identify the signal types ...The existing recognition algorithms of space-time block code(STBC)for multi-antenna(MA)orthogonal frequencydivision multiplexing(OFDM)systems use feature extraction and hypothesis testing to identify the signal types in a complex communication environment.However,owing to the restrictions on the prior information and channel conditions,these existing algorithms cannot perform well under strong interference and noncooperative communication conditions.To overcome these defects,this study introduces deep learning into the STBCOFDM signal recognition field and proposes a recognition method based on the fourth-order lag moment spectrum(FOLMS)and attention-guided multi-scale dilated convolution network(AMDCNet).The fourth-order lag moment vectors of the received signals are calculated,and vectors are stitched to form two-dimensional FOLMS,which is used as the input of the deep learning-based model.Then,the multi-scale dilated convolution is used to extract the details of images at different scales,and a convolutional block attention module(CBAM)is introduced to construct the attention-guided multi-scale dilated convolution module(AMDCM)to make the network be more focused on the target area and obtian the multi-scale guided features.Finally,the concatenate fusion,residual block and fully-connected layers are applied to acquire the STBC-OFDM signal types.Simulation experiments show that the average recognition probability of the proposed method at−12 dB is higher than 98%.Compared with the existing algorithms,the recognition performance of the proposed method is significantly improved and has good adaptability to environments with strong disturbances.In addition,the proposed deep learning-based model can directly identify the pre-processed FOLMS samples without a priori information on channel and noise,which is more suitable for non-cooperative communication systems than the existing algorithms.展开更多
High-speed train communication system is a typical high-mobility wireless communication network. Resource allocation problem has a great impact on the system performance. However, conventional resource allocation appr...High-speed train communication system is a typical high-mobility wireless communication network. Resource allocation problem has a great impact on the system performance. However, conventional resource allocation approaches in cellular network cannot be directly applied to this kind of special communication environment. A multidomain resource allocation strategy was proposed in the orthogonal frequency-division multiple access(OFDMA) of high-speed. By analyzing the effect of Doppler shift, sub-channels, antennas, time slots and power were jointly considered to maximize the energy efficiency under the constraint of total transmission power. For the purpose of reducing the computational complexity, noisy chaotic neural network algorithm was used to solve the above optimization problem. Simulation results showed that the proposed resource allocation method had a better performance than the traditional strategy.展开更多
This paper investigates Carrier Frequency Offset (CFO) estimation in the uplink of the Orthogonal Frequency-Division Multiple Access (OFDMA) systems with the interleaved subcarrier assignment. CFOs between the transmi...This paper investigates Carrier Frequency Offset (CFO) estimation in the uplink of the Orthogonal Frequency-Division Multiple Access (OFDMA) systems with the interleaved subcarrier assignment. CFOs between the transmitters and the uplink receiver will destroy orthogonality among different subcarriers, hence resulting in inter-carrier interference and multiuser interference. A two-stage frequency offset estimation algorithm based on subspace processing is proposed. The main advantage of the proposed method is that it can obtain the CFOs of all users simultaneously using only one OFDMA block. Compared with the previously known methods, it not only has a relatively low implementation complexity but is also suitable for random subchannel assignment.展开更多
When coexisting with dual-link primary systems,secondary systems in cognitive radios should first distinguish between the primary downlinks and uplinks in order to efficiently explore their respective spectrum opportu...When coexisting with dual-link primary systems,secondary systems in cognitive radios should first distinguish between the primary downlinks and uplinks in order to efficiently explore their respective spectrum opportunities.Because of the assumptive prior knowledge about the time-frequency locations of primary downlinks and uplinks,this procedure is usually not considered in the design of cognitive radios.In this paper,a cooperative method is proposed for the downlink/uplink identification of time-division duplex-based orthogonal frequency-division multiple access systems.In this method,the power level of the primary link is extracted as the key feature,which also contributes to the subsequent cognitive behaviours.The effects of the primary and secondary systems and the effects of the detection parameters on the identification accuracy are all analysed in detail.The simulation results show that the proposed method can identify the primary links precisely and quickly with low complexity.展开更多
Carrier frequency offset （CFO） in MIMO-OFDM systems can be decoupled into two parts： fraction frequency offset （FFO） and integer frequency offset （IFO）. The problem of IFO estimation is addressed and a new IFO ...Carrier frequency offset （CFO） in MIMO-OFDM systems can be decoupled into two parts： fraction frequency offset （FFO） and integer frequency offset （IFO）. The problem of IFO estimation is addressed and a new IFO estimator based on the Bayesian philosophy is proposed. Also, it is shown that the Bayesian IFO estimator is optimal among all the IFO estimators. Furthermore, the Bayesian estimator can take advantage of oversampling so that better performance can be obtained. Finally, numerical results show the optimality of the Bayesian estimator and validate the theoretical analysis.展开更多
As the combining form of the orthogonal frequency-division multiplexing (OFDM) technique and the vertical Bell Labs layered space-time (V-BLAST) architecture, the V-BLAST OFDM system can better meet the demand of next...As the combining form of the orthogonal frequency-division multiplexing (OFDM) technique and the vertical Bell Labs layered space-time (V-BLAST) architecture, the V-BLAST OFDM system can better meet the demand of next-generation (NextG) broadband mobile wireless multimedia communications. The symbols detection problem of the V-BLAST OFDM system is investigated under the frequency-selective fading environment. The joint space-frequency demultiplexing operation is proposed in the V-BLAST OFDM system. Successively, one novel half-rate rotational invariance joint space-frequency coding scheme for the V-BLAST OFDM system is proposed. By elegantly exploiting the above rotational invariance property, we derive one direct symbols detection scheme without knowing channels state information (CSI) for the frequency-selective V-BLAST OFDM system. Extensive simulation results demonstrate the validity of the novel half-rate rotational invariance joint space-frequency coding scheme and the performance of the direct symbols detection scheme.展开更多
基金supported by the National High Technology Research and Development Program of China(Grant No.2009AA01A345)the National Basic Research Program of China(Grant No.2011CB302702)the National Natural Science Foundation of China(Grant No.60932004)
文摘This paper introduces a joint nonlinearity and chromatic dispersion pre-compensation method for coherent optical orthogonal frequency-division multiplexing systems. The research results show that this method can reduce the walk- off effect and can therefore equalize the nonlinear impairments effectively. Compared with the only other existing nonlinearity pre-compensation method, the joint nonlinearity and chromatic dispersion pre-compensation method is not only suitable for low-dispersion optical orthogonal frequency-division multiplexing system, but also effective for high- dispersion optical orthogonal frequency-division multiplexing transmission system with higher input power but without optical dispersion compensation. The suggested solution does not increase computation complexity compared with only nonlinearity pre-compensation method. For 40 Gbit/s coherent optical orthogonal frequency-division multiplexing 20 × 80 km standard single-mode fibre system, the suggested method can improve the nonlinear threshold （for Q 〉 10 dB） about 2.7, 1.2 and 1.0 dB, and the maximum Q factor about 1.2, 0.4 and 0.3 dB, for 2, 8 and 16 ps/（nm.km） dispersion coefficients.
基金supported by the National Natural Science Foundation of China under Grant Nos.62022022 and 62101107the National Key R&D Program of China under Grant No.2018YFB1801502+1 种基金China Postdoctoral Science Foundation under Grant No.2021TQ0057ZTE Industry-Uni⁃versity-Institute Cooperation Funds.
文摘With the development of wireless communication,the 6G mobile communication technology has received wide attention.As one of the key technologies of 6G,terahertz(THz)communication technology has the characteristics of ultra-high bandwidth,high security and low environmental noise.In this paper,a THz duplexer with a half-wavelength coupling structure and a sub-harmonic mixer operating at 216 GHz and 204 GHz are designed and measured.Based on these key devices,a 220 GHz frequency-division multiplexing communication system is proposed,with a real-time data rate of 10.4 Gbit/s for one channel and a transmission distance of 15 m.The measured constellation diagram of two receivers is clearly visible,the signal-to-noise ratio(SNR)is higher than 22 dB,and the bit error ratio(BER)is less than 10^(−8).Furthermore,the high definition(HD)4K video can also be transmitted in real time without stutter.
基金the finanical support from National Natural Science Foundation of China(52127810,51835007,51721003).
文摘An optical frequency comb(OFC)frequency-division multiplexing dispersive interference multichannel distance measurement method is proposed.Based on the OFC dispersive interference,the wide OFC spectrum is divided into multiple channels using a wavelength-division multiplexer.Under the existing light source and spectrometer,a single interference system can realize six channels of the high-precision parallel absolute distance measurement.The influence of the spectrum width and shape on the performance of the distance measurement channel is analyzed.The ranging accuracy of six channels is higher than±4μm under the optimization of a nonuniform discrete Fourier transform and Hanning window.
基金supported by the National Natural Science Foundation of China(Grant Nos.11734012,62105213,12074267,516022053,and 12174265)the Young Innovative Talents Project of Universities in Guangdong Province(Grant No.2019KQNCX123)+4 种基金the Guangdong Basic and Applied Basic Research Fund(Grant No.2020A1515111037)the Science and Technology Project of Guangdong(Grant No.2020B010190001)the Guangdong Natural Science Foundation(Grant No.2020A1515010467)the Shenzhen Fundamental Research Program(Grant No.20200814113625003)the Open Fund of State Key Laboratory of Applied Optics(Grant No.SKLAO2020001A06)。
文摘The rapidly growing global data usage has demanded more efficient ways to utilize the scarce electromagnetic spectrum resource. Recent research has focused on the development of efficient multiplexing techniques in the millimeter-wave band(1-10 mm, or 30-300 GHz) due to the promise of large available bandwidth for future wireless networks. Frequency-division multiplexing is still one of the most commonly-used techniques to maximize the transmission capacity of a wireless network.Based on the frequency-selective tunnelling effect of the low-loss epsilon-near-zero metamaterial waveguide, we numerically and experimentally demonstrate five-channel frequency-division multiplexing and demultiplexing in the millimeter-wave range.We show that this device architecture offers great flexibility to manipulate the filter Q-factors and the transmission spectra of different channels, by changing of the epsilon-near-zero metamaterial waveguide topology and by adding a standard waveguide between two epsilon-near-zero channels. This strategy of frequency-division multiplexing may pave a way for efficiently allocating the spectrum for future communication networks.
基金supported by the National Natural Science Foun-dation of China under Grant 11901209,Grant 62374061,and Grant 62271217.
文摘Utilizing multi-band and multi-carrier techniques enhances throughput and capacity in Long-Term Evolution(LTE)-Advanced and 5G New Radio(NR)mobile networks.However,these techniques introduce Passive Inter-Modulation(PIM)interference in Frequency-Division Duplexing(FDD)systems.In this paper,a novel multi-band Wiener-Hammerstein model is presented to digitally reconstruct PIM interference signals,thereby achieving effective PIM Cancellation(PIMC)in multi-band scenarios.In the model,transmitted signals are independently processed to simulate Inter-Modulation Distortions(IMDs)and Cross-Modulation Distortions(CMDs).Furthermore,the Finite Impulse Response(FIR)filter,basis function generation,and B-spline function are applied for precise PIM product estimation and generation in multi-band scenarios.Simulations involving 4 carrier components from diverse NR frequency bands at varying transmitting powers validate the feasibility of the model for multi-band PIMC,achieving up to 19 dB in PIMC performance.Compared to other models,this approach offers superior PIMC performance,exceeding them by more than 5 dB in high transmitting power scenarios.Additionally,its lower sampling rate requirement reduces the hardware complexity associated with implementing multi-band PIMC.
基金The National Natural Science Foundation of China(No60472026)
文摘A two-dimensional （2-D） polynomial regression model is set up to approximate the time-frequency response of slowly time-varying orthogonal frequency-division multiplexing （OFDM） systems. With this model the estimation of the OFDM time-frequency response is turned into the optimization of some time-invariant model parameters. A new algorithm based on the expectation-maximization （EM） method is proposed to obtain the maximum-likelihood （ML） estimation of the polynomial model parameters over the 2-D observed data. At the same time, in order to reduce the complexity and avoid the computation instability, a novel recursive approach （RPEMTO） is given to calculate the values of the parameters. It is further shown that this 2-D polynomial EM-based algorithm for time-varying OFDM （PEMTO） can be simplified mathematically to handle the one-dimensional sequential estimation. Simulations illustrate that the proposed algorithms achieve a lower bit error rate （BER） than other blind algorithms.
基金the 863 project No.2014AA01A701,the National Natural Science Foundation of China，Program for New Century Excellent Talents in University，the open research fund of National Mobile Communications Research Laboratory Southeast University，the Research Foundation of China Mobile,and the Foundation of Beijing Engineering and Technology Center for Convergence Networks and Ubiquitous Services
文摘The ergodic information rate for Orthogonal Frequency-Division Multiplexing / Orthogonal Frequency-Division Multiple Access with amplify-and-forward （AF） relaying systems in the presence of frequency offsets is evaluated. Unlike previous work, per-subcarrier adaptive power allocation is performed on each relay to optimize the system ergodic information rate. For a given frequency offset and total number of relays M, the AF ergodic information rate is proven to be a monotonically increasing function of α （the ratio of the power allocated to the source node and the total transmit power）, implying that the maximum ergodic information rate can be obtained at α=1 （i.e., there is no cooperative relay）. Furthermore, the proof of ＂cooperative relays cannot improve the AF ergodic information rate in a quasi-static wireless channel＂ is also provided in this letter.
基金The National Science and Technology Major Project (No.2011ZX03001-007-03)the National Natural Science Foundation of China(No.61271182)
文摘The dynamic resource allocation problem in high-speed railway downlink orthogonal frequency-division multiplexing（OFDM） systems with multiple-input multiple-output（MIMO） antennas is investigated.Sub-carriers,antennas,time slots,and power are jointly considered.The problem of multi-dimensional resource allocation is formulated as a mixed-integer nonlinear programming problem.The effect of the moving speed on Doppler shift is analyzed to calculate the inter-carrier interference power.The optimization objective is to maximize the system throughput under the constraint of a total transmitted power that is no greater than a certain threshold.In order to reduce the computational complexity,a suboptimal solution to the optimization problem is obtained by a two-step method.First,sub-carriers,antennas,and time slots are assigned to users under the assumption of equal power allocation.Next,the power allocation problem is solved according to the result of the first-step resource allocation.Simulation results show that the proposed multi-dimensional resource allocation strategy has a significant performance improvement in terms of system throughput compared with the existing one.
基金The National High Technology Research and Devel-opment Program of China (863Program) (No2002AA123031)
文摘A novel adaptive ordered LDPC （low-density parity-check） coded OFDM （orthogonal frequency-division multiplexing） transmission technique is proposed to exploit different error probabilities of irregular LDPC coded bits in OFDM systems. Assuming that the CSI （channel state information） is known at the transmitter, the irregular LDPC coded bits are ordered according to their degrees and then allocated into subcarriers adaptively. Bits with higher degrees are allocated into less attenuated subcarriers and bits with lower degrees are allocated into deep attenuated subcarriers. Quantization on CSI feedback can be applied to minimize the signaling overhead. Performance of this strategy is analyzed by density evolution and numerical simulation. Simulation results show that about a 1 to 1.5 dB gain in terms of SNR （ signal to noise ratio） can be achieved over frequency-selective fading channels compared to conventional LDPC coded OFDM systems without ordering, and the proposed scheme is robust to CSI quantization.
基金supported in part by the National Natural Science Foundation of China(No.61821001)。
文摘In this paper,a novel efficient continuous piecewise nonlinear companding scheme is proposed for reducing the peak-to-average power ratio(PAPR)of orthogonal frequency division multiplexing(OFDM)systems.In the proposed companding transform,signal samples with large amplitudes is clipped for peak power reduction,and the signal samples with medium amplitudes is nonlinear transformed with power compensation.While the signal samples with small amplitudes remain unchanged.The whole companding function is continuous and smooth in the range of positive numbers,which is beneficial for guaranteeing the bit error rate(BER)and power spectral density(PSD)performance.This scheme can achieve a significant reduction in PAPR.And at the same time,it cause little increment in BER and PSD performance.Simulation results indicate the superiority of the proposed scheme over existing companding schemes.
基金Project supported by the National Natural Science Foundation of China （Grant No.60572157）, and the National High- Technology Research and Development Program of China （Grant No.2003AA123310）
文摘A space-time coded multiple-input multiple-output orthogonal frequency-division multiplexing （MIMO-OFDM） system is considered as a solution to the future wideband wireless communication system. This paper proposes an extended Kalman filtering-based （EKF-based） channel estimation method for space-time coded MIMO-OFDM systems. The proposed method can exploit pilot symbols and an extended Kalman filter to estimate channel without any prior knowledge of channel statistics. In comparison with the least square （LS） and the least mean square （LMS） methods, the EKF-based approach has a better performance in theory. Computer simulations demonstrate the proposed method outperforms the LS and LMS methods. Therefore it can offer draznatic system performance improvement at a modest cost of computational complexity.
文摘IEEE 802.11ax,which is an emerging WLAN standard,aims at providing highly efficient communication in ultra-dense wireless networks.However,due to a large number of stations(STAs)in the ultra-dense device deployment scenarios,the potentially high packet collision rate significantly decreases the communication efficiency of WLAN.In this paper,we propose an adaptive STA grouping scheme to overcome this dense network challenge in IEEE 802.11ax by using Buffer State Report(BSR)based Two-stage Mechanism(BTM).In order to achieve the optimal efficiency of BSR delivery,we analyze the functional relationship between STA number in group and Resource Unit(RU)efficiency.Based on this analysis results,an adaptive STA grouping algorithm with variable group size is proposed to achieve efficient grouping in BTM.The numerical results demonstrate that the proposed adaptive BTM grouping algorithm significantly improves the BSR delivery efficiency and the throughput of overall system and each STA in the ultra-dense wireless network.
基金supported in part by the National Natural Science Foundation of China(No.61971092,No.62222121)in part by the Sichuan Province Foundation for Distinguished Young Scholars(2020JDJQ0023)in part by the Fundamental Research Funds for the Central Universities(ZYGX2020ZB045,ZYGX2019J123).
文摘This paper is focused on the multiuser implementation of fusion of radar and communication(RadCom)in internet-of-vehicles(IoV)scenarios.Traditional time-division multiple access(TDMA)technology degrades the velocity detection performance of orthogonal frequency-division multiplexing(OFDM)-based RadCom systems.We propose a new TDMA approach for OFDM-based RadCom systems,where multiuser communication and radar detection are completed synchronously.We consider a continuous-wave TDMA OFDM structure in which random user data or Zadoff-Chu(ZC)sequences are transmitted in one symbol duration to ensure detection performance.As an application of interference cancellation method,user data demodulation and environment sensing can be simultaneously accomplished by our proposed approach.We carry out numerical evaluation and show wireless communication and radar detection performance over the continuous-wave TDMA OFDM-based RadCom approach.
基金Supported by the National 863 High Technology Research Program of China (N0.2005AA123320)Universities Natural Science Research Project of Jiangsu Province (No.05KJB510101).
文摘The Peak to Average power Ratio (PAR) of a Multi-Band Orthogonal Frequency-Division Multiplexing (MB-OFDM) Ultra-Wide Band (UWB) signals can be substantially larger than that of single carrier or carrier-less ultra-wideband signals. In this letter, a novel PAR reduction scheme for the MB-OFDM UWB system based on spreading and interleaving is proposed. By spreading the coded bits over each subcarrier in corresponding band and interleaving the spread symbols across all bands, the PAR statistics of the MB-OFDM signals can be improved and the PAR is reduced obviously. In the PAR reduction scheme, there is no loss in transmission data rate or Bit Error Rate (BER) performance decreasing. Since the spreading and interleaving operation are implemented by unitary Hadamard sequences and used for an approach to provide the robustness of the UWB system to narrowband interference, there is no additional implementation burden. Simulation results show that the investigated scheme gives the PAR reduction of 3dB compared with that of the original MB-OFDM signals.
基金supported by the National Natural Science Foundation of China(91538201)the Taishan Scholar Foundation of China(ts201511020).
文摘The existing recognition algorithms of space-time block code(STBC)for multi-antenna(MA)orthogonal frequencydivision multiplexing(OFDM)systems use feature extraction and hypothesis testing to identify the signal types in a complex communication environment.However,owing to the restrictions on the prior information and channel conditions,these existing algorithms cannot perform well under strong interference and noncooperative communication conditions.To overcome these defects,this study introduces deep learning into the STBCOFDM signal recognition field and proposes a recognition method based on the fourth-order lag moment spectrum(FOLMS)and attention-guided multi-scale dilated convolution network(AMDCNet).The fourth-order lag moment vectors of the received signals are calculated,and vectors are stitched to form two-dimensional FOLMS,which is used as the input of the deep learning-based model.Then,the multi-scale dilated convolution is used to extract the details of images at different scales,and a convolutional block attention module(CBAM)is introduced to construct the attention-guided multi-scale dilated convolution module(AMDCM)to make the network be more focused on the target area and obtian the multi-scale guided features.Finally,the concatenate fusion,residual block and fully-connected layers are applied to acquire the STBC-OFDM signal types.Simulation experiments show that the average recognition probability of the proposed method at−12 dB is higher than 98%.Compared with the existing algorithms,the recognition performance of the proposed method is significantly improved and has good adaptability to environments with strong disturbances.In addition,the proposed deep learning-based model can directly identify the pre-processed FOLMS samples without a priori information on channel and noise,which is more suitable for non-cooperative communication systems than the existing algorithms.
基金Supported by the National Natural Science Foundation of China(No.61302080)Scientific Research Starting Foundation of Fuzhou University(No.022572)Science and Technology Development Foundation of Fuzhou University(No.2013-XY-27)
文摘High-speed train communication system is a typical high-mobility wireless communication network. Resource allocation problem has a great impact on the system performance. However, conventional resource allocation approaches in cellular network cannot be directly applied to this kind of special communication environment. A multidomain resource allocation strategy was proposed in the orthogonal frequency-division multiple access(OFDMA) of high-speed. By analyzing the effect of Doppler shift, sub-channels, antennas, time slots and power were jointly considered to maximize the energy efficiency under the constraint of total transmission power. For the purpose of reducing the computational complexity, noisy chaotic neural network algorithm was used to solve the above optimization problem. Simulation results showed that the proposed resource allocation method had a better performance than the traditional strategy.
基金the Specialized Research Fund for the Doctoral Program of Higher Education, China Ministry of Education (No.20030003039).
文摘This paper investigates Carrier Frequency Offset (CFO) estimation in the uplink of the Orthogonal Frequency-Division Multiple Access (OFDMA) systems with the interleaved subcarrier assignment. CFOs between the transmitters and the uplink receiver will destroy orthogonality among different subcarriers, hence resulting in inter-carrier interference and multiuser interference. A two-stage frequency offset estimation algorithm based on subspace processing is proposed. The main advantage of the proposed method is that it can obtain the CFOs of all users simultaneously using only one OFDMA block. Compared with the previously known methods, it not only has a relatively low implementation complexity but is also suitable for random subchannel assignment.
基金supported by the National Natural Science Foundation of China under Grants No. 60832008,No. 60902001
文摘When coexisting with dual-link primary systems,secondary systems in cognitive radios should first distinguish between the primary downlinks and uplinks in order to efficiently explore their respective spectrum opportunities.Because of the assumptive prior knowledge about the time-frequency locations of primary downlinks and uplinks,this procedure is usually not considered in the design of cognitive radios.In this paper,a cooperative method is proposed for the downlink/uplink identification of time-division duplex-based orthogonal frequency-division multiple access systems.In this method,the power level of the primary link is extracted as the key feature,which also contributes to the subsequent cognitive behaviours.The effects of the primary and secondary systems and the effects of the detection parameters on the identification accuracy are all analysed in detail.The simulation results show that the proposed method can identify the primary links precisely and quickly with low complexity.
基金supported by the National Science Fund for Distinguished Young Scholars (60725105)National"863"Program of China (2007AA01Z288)+1 种基金the sixth project of the Key Project of National Nature Science Foundation of China (60496316)Teaching Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE,the 111 Project (B08038).
文摘Carrier frequency offset （CFO） in MIMO-OFDM systems can be decoupled into two parts： fraction frequency offset （FFO） and integer frequency offset （IFO）. The problem of IFO estimation is addressed and a new IFO estimator based on the Bayesian philosophy is proposed. Also, it is shown that the Bayesian IFO estimator is optimal among all the IFO estimators. Furthermore, the Bayesian estimator can take advantage of oversampling so that better performance can be obtained. Finally, numerical results show the optimality of the Bayesian estimator and validate the theoretical analysis.
文摘As the combining form of the orthogonal frequency-division multiplexing (OFDM) technique and the vertical Bell Labs layered space-time (V-BLAST) architecture, the V-BLAST OFDM system can better meet the demand of next-generation (NextG) broadband mobile wireless multimedia communications. The symbols detection problem of the V-BLAST OFDM system is investigated under the frequency-selective fading environment. The joint space-frequency demultiplexing operation is proposed in the V-BLAST OFDM system. Successively, one novel half-rate rotational invariance joint space-frequency coding scheme for the V-BLAST OFDM system is proposed. By elegantly exploiting the above rotational invariance property, we derive one direct symbols detection scheme without knowing channels state information (CSI) for the frequency-selective V-BLAST OFDM system. Extensive simulation results demonstrate the validity of the novel half-rate rotational invariance joint space-frequency coding scheme and the performance of the direct symbols detection scheme.
