The rapid time-variation of a fading multipath environment can impair the performance of multiple-input multiple-output orthogonal frequency division multiplexing (MIMO OFDM). This paper proposes a pilot placement met...The rapid time-variation of a fading multipath environment can impair the performance of multiple-input multiple-output orthogonal frequency division multiplexing (MIMO OFDM). This paper proposes a pilot placement method for MIMO OFDM systems under time-varying channels with the guard band. The time-varying channel is described by complex exponential basis expansion model (BEM). We discuss the least square (LS) channel estimation to obtain the minimum mean square error (MSE) and derive the pilot allocation that can satisfy the minimum MSE with regard to guard band in time-varying channels. It is shown that optimal pilot clusters can distribute non-uniformly in frequency domain and minimize the MSE. We generalize our scheme over G OFDM symbols and compare it with comb pilots. It is demonstrated that the proposed approach is more effective than previous work. Simulation results validate our theoretical analysis.展开更多
To overcome the unbalanced signal-to-noise ratio(SNR)among data-carrying subcarriers(SCs)induced by the imperfect frequency response of optoelectronic devices and various interferences,a channel-independent partial da...To overcome the unbalanced signal-to-noise ratio(SNR)among data-carrying subcarriers(SCs)induced by the imperfect frequency response of optoelectronic devices and various interferences,a channel-independent partial data-carrying SCs precoding(PDSP)method based on orthogonal circular matrix transform(OCT)is proposed and experimentally investigated in an intra-symbol frequency average(ISFA)-enabled discrete multi-tone(DMT)visible light communication(VLC)system.After transmission over 1.9 m free space,at the optimal bias current of 100 mA,the experimental results show that the bit error ratio(BER)performance can be improved by up to an order of magnitude with conventional full data-carrying SCs precoding(FDSP)and PDSP scheme,compared to that without a precoding scheme.Moreover,the BER performance can further be enhanced when the ISFA algorithm with optimal taps is employed.Compared with the FDSP scheme,the proposed PDSP scheme owns a similar BER performance and a significant reduction in required multiplication and addition operations,and it may be a good option to efficiently combat the unbalanced impairments of DMT-VLC transmission systems.展开更多
This paper investigates subcarrier and power allocation in a multi-UAV OFDM system.The study considers a practical scenario,where certain subcarriers are unavailable for dynamic subcarrier allocation,on account of pre...This paper investigates subcarrier and power allocation in a multi-UAV OFDM system.The study considers a practical scenario,where certain subcarriers are unavailable for dynamic subcarrier allocation,on account of pre-allocation for burst transmissions.We first propose a novel iterative algorithm to jointly optimize subcarrier and power allocation,so as to maximize the sum rate of the uplink transmission in the multiUAV OFDM system.The key idea behind our solution is converting the nontrivial allocation problem into a weighted mean square error(MSE) problem.By this means,the allocation problem can be solved by the alternating optimization method.Besides,aiming at a lower-complexity solution,we propose a heuristic allocation scheme,where subcarrier allocation and transmit power allocation are separately optimized.In the heuristic scheme,closedform solution can be obtained for power allocation.Simulation results demonstrate that in the presence of stretched subcarrier resource,the proposed iterative joint optimization algorithm can significantly outperform the heuristic scheme,offering a higher sum rate.展开更多
Efficient and reliable subcarrier power joint allocation is served as a promising problem in cognitive OFDM-based Cognitive Radio Networks (CRN). This paper focuses on optimal subcarrier allocation for OFDM-based CRN....Efficient and reliable subcarrier power joint allocation is served as a promising problem in cognitive OFDM-based Cognitive Radio Networks (CRN). This paper focuses on optimal subcarrier allocation for OFDM-based CRN. We mainly propose subcarrier allocation scheme denoted as Worst Subcarrier Avoiding Water-filling (WSAW), which is based on Rate Adaptive (RA) criterion and three constraints are considered in CRN. The algorithm divides the assignment procedure into two phases. The first phase is an initial subcarrier allocation based on the idea of avoiding selecting the worst subcarrier in order to maximize the transmission rate; while the second phase is an iterative adjustment process which is realized by swapping pairs of subcarriers between arbitrary users. The proposed scheme could assign subcarriers in accordance with channel coherence time. Hence, real time subcarrier allocation could be implemented. Simulation results show that, comparing with the similar existing algorithms, the proposed scheme could achieve larger capacity and a near-optimal BER performance.展开更多
An expendable conductivity-temperature-depth profiler(XCTD)is one of the most important instruments used to obtain hydrological data,such as temperature and conductivity,and detect ocean depth in a large area.However,...An expendable conductivity-temperature-depth profiler(XCTD)is one of the most important instruments used to obtain hydrological data,such as temperature and conductivity,and detect ocean depth in a large area.However,the XCTD channel provides poor time-varying performance,narrowband,and low signal-to-noise ratio(SNR),which severely restricts the data transmission rate.In contrast to conventional single-carrier modulation techniques,such as amplitude-shift keying and differential phase-shift keying,this article provides a new method,based on orthogonal frequency division multiplexing(OFDM)to enhance the data transmission rate of deep-sea abandoned profilers.We apply the OFDM to enhance the SNR of the XCTD,which is achieved by reducing the data transmission rate of each sub-channel.Moreover,the bandwidth utilization may be improved by increasing the number of subcarriers in a given bandwidth,which enhances the data transmission rate.Based on analysis of the XCTD channel model,OFDM with different parameters such as constellation mapping,number of subcarriers,subcarrier spacing,signal period and cyclic prefix are achieved.To verify the effectiveness of the OFDM,this study investigates the influence of different parameters on the data transmission rate at different noise levels,i.e.,-20 dB and-40 d B.展开更多
The traditional orthogonal multiple access(OMA)is unable to satisfy the needs of large number of smart devices.To increase the transmission rate in the limited spectrum resource,implementation of both non-orthogonal m...The traditional orthogonal multiple access(OMA)is unable to satisfy the needs of large number of smart devices.To increase the transmission rate in the limited spectrum resource,implementation of both non-orthogonal multiple access(NOMA)and successive interference cancelation(SIC)is essential.In this paper,an optimal resource allocation algorithm in NOMA is proposed to maximize the total system rate in a multi-sector multi-subcarrier relay-assisted communication network.Since the original problem is a non-convex problem with mixed integer programming which is non-deterministic polynomial-time(NP)-hard,a three-step solution is proposed to solve the primal problem.Firstly,we determine the optimal power allocation of the outer users by using the approach of monotonic discrimination,and then the optimal user pairing is determined.Secondly,the successive convex approximation(SCA)method is introduced to transform the non-convex problem involving central users into convex one,and the Lagrangian dual method is used to determine the optimal solution.Finally,the standard Hungarian algorithm is utilized to determine the optimal subcarrier matching.The simulation results show that resource allocation algorithm is able to meet the user performance requirements with NOMA,and the total system rate is improved compared to the existing algorithms.展开更多
The idea of cooperation and the clustering amongst cognitive radios(CRs) has recently been focus of attention of research community, owing to its potential to improve performance of spectrum sensing(SS) schemes. This ...The idea of cooperation and the clustering amongst cognitive radios(CRs) has recently been focus of attention of research community, owing to its potential to improve performance of spectrum sensing(SS) schemes. This focus has led to the paradigm of cluster based cooperative spectrum sensing(CBCSS). In perspective of high date rate 4th generation wireless systems, which are characterized by orthogonal frequency division multiplexing(OFDM) and spatial diversity, there is a need to devise effective SS strategies. A novel CBCSS scheme is proposed for OFDM subcarrier detection in order to enable the non-contiguous OFDM(NC-OFDM) at the physical layer of CRs for efficient utilization of spectrum holes. Proposed scheme is based on the energy detection in MIMO CR network, using equal gain combiner as diversity combining technique, hard combining(AND, OR and Majority) rule as data fusion technique and antenna diversity based weighted clustering as virtual sub clustering algorithm. Results of proposed CBCSS are compared with conventional CBCSS scheme for AND, OR and Majority data fusion rules. Moreover the effects of antenna diversity, cooperation and cooperating clusters are also discussed.展开更多
In the current multi-carrier communications,Orthogonal Frequency Division Multiplexing(OFDM)is widely considered as a leading technology.For mobile applications,however,the orthogonality between subcarriers is deterio...In the current multi-carrier communications,Orthogonal Frequency Division Multiplexing(OFDM)is widely considered as a leading technology.For mobile applications,however,the orthogonality between subcarriers is deteriorated by Doppler frequency shift,which will introduce serious subcarrier phase rotation in the received signals and degrade the system performance.Thus,a method of differential grouping weighted symmetry data-conjugate(DWSCC)have been previously presented to obtain a better inter-carrier interference(ICI)suppressing effect and Bit Error Rate(BER)performance with no loss of spectral efficiency.In this paper,a novel scheme applying a completely different method of subcarrier interactive mapping is put forward.By mapping two different symbols which are both conjugated or multiplied by a complex weighting factor onto a pair of symmetric subcarriers,the presented scheme can greatly reduce the influence of subcarriers phase rotation caused by Doppler frequency shift in highly mobile environments.Analysis and simulation results indicate that comparing with the DWSCC method,our formulated scheme can not only maintain the spectrum utilization with no loss,but also have the advantages of an improvement on reduction effect and BER performance as well as a lower computational complexity in highly mobile environments.展开更多
In this paper, we investigate the power-minimizing resource allocation problem in multiuser cooperative relay communication systems. A joint optimization problem involving subcarrier assignment, relay selection and po...In this paper, we investigate the power-minimizing resource allocation problem in multiuser cooperative relay communication systems. A joint optimization problem involving subcarrier assignment, relay selection and power allocation is formulated. Since the problem cannot be solved directly, we decompose it into three subproblems. According to the equivalent channel gains and the target rates of users, the subcarrier assignment and relay selection are conducted. Motivated by the water-filling algorithm, we propose a power allocation algorithm with cooperative features. Simulations results indicate that the proposed algorithm performs better in terms of the total transmit power consumption than the existing algorithms.展开更多
Aiming at the problems of underwater acoustic communication such as narrowband, low speed and multipath effect, this paper studies the high-speed communication technology of electromagnetic wave in short distance at s...Aiming at the problems of underwater acoustic communication such as narrowband, low speed and multipath effect, this paper studies the high-speed communication technology of electromagnetic wave in short distance at sea. The channel model of seawater electromagnetic wave is given, and the performance of different modulation modes in this channel is analyzed. A meth-od of seawater short-range high-speed electromagnetic wave communication based on OFDM is proposed. In order to reduce the BER of the system, a method of allocating different modulation modes to subcarriers in seawater channel is introduced, which combines frequency domain equalization. This method has low complexity, improves the utilization of frequency band, and improves the reliability. It can realize high-speed and reliable communication in short distance in seawater.展开更多
Subcarrier intensity modulation with direct detection is a modulation/detection technique for optical wireless communication systems,where a pre-modulated and properly biased radio frequency signal is modulated on the...Subcarrier intensity modulation with direct detection is a modulation/detection technique for optical wireless communication systems,where a pre-modulated and properly biased radio frequency signal is modulated on the intensity of the optical carrier.The most important benefits of subcarrier intensity modulation are as follows:1) it does not provide irreducible error floor like the conventional on-off keying intensity modulation with a fixed detection threshold;2) it provides improved spectral efficiency and supports higher order modulation schemes;and 3) it has much less implementation complexity compared to coherent optical wireless communications with heterodyne or homodyne detection.In this paper,we present an up-to-date review of subcarrier intensity modulated optical wireless communication systems.We survey the error rate and outage performance of subcarrier intensity modulations in the atmospheric turbulence channels considering different modulation and coding schemes.We also explore different contemporary atmospheric turbulence fading mitigation solutions that can be employed for subcarrier intensity modulation.These solutions include diversity combining,adaptive transmission,relay assisted transmission,multiple-subcarrier intensity modulations,and optical orthogonal frequency division multiplexing.Moreover,we review the performance of subcarrier intensity modulations due to the pointing error and synchronization error.展开更多
Single-carrier frequency-division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) systems are new orthogonal multiple access systems. They have been adopted in the 3GPP long term ev...Single-carrier frequency-division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) systems are new orthogonal multiple access systems. They have been adopted in the 3GPP long term evolution (3GPP-LTE). In these systems, there are only two types of subcarrier mapping schemes which are the interleaved and the localized. So, introducing a new subcarrier mapping scheme is an important issue, which is the main objective of this paper. In this paper, a hybrid subcarrier mapping scheme is proposed and examined for the SC-FDMA system. Monte Carlo simulations are performed to compare the performance of the proposed scheme with that of the interleaved and the localized schemes. It is shown that a hybrid scheme provides better performance than that of the localized and the same performance as that of the interleaved scheme and increased robustness to carrier frequency offset (CFO) at the expense of increased envelope fluctuations.展开更多
Multicarrier systems such as orthogonal frequency division (OFDM) are considered as a promising candidate for wireless networks that support high data rate communication. In this article, we investigate the perform-an...Multicarrier systems such as orthogonal frequency division (OFDM) are considered as a promising candidate for wireless networks that support high data rate communication. In this article, we investigate the perform-ance of a multiuser OFDM system under imperfect synchronization. Analytical results indicate that the SNR degrades as the average power of the channel impairments such as AWGN, carrier frequency offset due to Doppler frequency and fading gain is increased. The SNR degradation leads to imperfect synchronization and hence decreases the total number of subcarriers available for allocation. Monte Carlo analysis shows up to 22% loss in the number of allocatable subcarriers can be expected under a specific imperfect synchroniza-tion condition as compared to perfect synchronization. We utilize empirical modelling to characterize the available number of subcarriers as a Poisson random variable. In addition, we determine the percentage de-crease in the total number of allocatable subcarriers under varying channel parameters. The results indicate 19% decrease in the number of available subcarriers as average AWGN power is increased by 10dB;44% decrease as the Doppler frequency is varied from 10Hz to 100Hz;and 56% decrease as the fading gain is varied from 0dB to -30dB.展开更多
In this paper, an adaptive subcarrier allocation scheme with reconfiguration of operating parameters for Cognitive Radio Networks (CRN) is presented. A QoS-conscious spectrum decision frame work is projected, where sp...In this paper, an adaptive subcarrier allocation scheme with reconfiguration of operating parameters for Cognitive Radio Networks (CRN) is presented. A QoS-conscious spectrum decision frame work is projected, where spectrum bands are determined by considering the application requirements as well as the dynamic nature of the spectrum bands. The novel subcarrier allocation algorithm is developed to fulfill different performance objective as a solution for subcarrier allocation and power allocation problem for Cognitive Radio (CR) users in CRNs. It employs operating frequency parameter modification using Proportional Resource Algorithm and Genetic Algorithm (GA). The multi objective optimization problem with equality and inequality constraint is considered. Moreover, a dynamic subcarrier allocations scheme is developed based on GA to decide on the spectrum bands adaptively dependent on the time-varying CR network capacity. The proposed algorithm targets to achieve maximum data rate for each subcarrier, maximize the overall network throughput and maximize the number of satisfied user under the constraints of bandwidth and guarantee Quality of Service (QoS) requirement from dynamic spectrum management (DSM) perspective. Moreover, it determines the best available channel.展开更多
A method for online dispersion monitoring by adding a single in-band subcarrier tone isintroduced.According to the theoretical analysis,the dispersion monitor and measurement range aredetermined by the specific freque...A method for online dispersion monitoring by adding a single in-band subcarrier tone isintroduced.According to the theoretical analysis,the dispersion monitor and measurement range aredetermined by the specific frequency of the subcarrier tone.By using simulation tools,figures aboutrelationship between power of subcarrier tone and transmission distance in ideal condition are shown.展开更多
Reconfigurable intelligent surfaces(RISs)have the capability to change the wireless environment smartly Considering the attenuation of subchannels and crowding users involved in the wideband system,we introduce RISs i...Reconfigurable intelligent surfaces(RISs)have the capability to change the wireless environment smartly Considering the attenuation of subchannels and crowding users involved in the wideband system,we introduce RISs into the multi-user multi-input single-output(MU-MISO)system with orthogonal frequency division multiplexing(OFDM)for performance enhancement.Maximizing the minimum rate of dense users in an MU-MISO-OFDM system assisted by RIS with an approximate practical model is formulated as the joint optimization problem involving subcarrier allocation,transmit precoding(TPC)matrices at the base station,and RIS passive beamforming.A coalition-game subcarrier allocation(CSA)algorithm is proposed to solve space–frequency resource allocation on subcarriers,which reforms the interference topology among dense users.Fractional programming and convex optimization method are used to optimize the TPC matrices and the RIS passive beamforming,which improves the spectral efficiency synthetically across all subchannels in the wideband system.Simulation results indicate that the CSA algorithm provides a significant gain for dense users.Besides,the proposed joint optimization method shows the considerable advantage of the RISs in the MU-MISO-OFDM system.展开更多
Chaotic sequence has been applied in Cognitive Radio(CR)to exert the enormous potential spectral utilization and enhance the transmission security.However,since there is not strict orthogonality between chaotic signal...Chaotic sequence has been applied in Cognitive Radio(CR)to exert the enormous potential spectral utilization and enhance the transmission security.However,since there is not strict orthogonality between chaotic signals,intra-signal interference(ISI)will be introduced into the demodulation.Here,an anti-interference orthogonal-frequency-division-multiplexing(OFDM)chaotic modulation named Walsh-sequence chaotic CR(WS-CCR)is proposed for cognitive radio.By constructing the strictly orthogonal chaotic signal based on Walsh sequence,the ISI component,which is produced by frequency offset in previous CR,can be eliminated during the demodulation.Moreover,the chaotic sequence can also be applied to scramble subcarriers to relieve the interference caused by malicious attacks.Gaussian approximation method is adopted to obtain the exact performance analysis of WS-CCR over Additive White Gaussian Noise(AWGN)channel and Rayleigh multipath fading channel.Results show that,with subcarriers scrambling by chaotic sequence,anti-interference performance and transmitting security can be signi?cantly improved in WS-CCR.Importantly,due to the absence of ISI component,the bit-error ratio(BER)performance of WS-CCR is better than that of the previous CR system.展开更多
In this paper,we study the problem of optimal resource allocation for lifetime maximization in an orthogonal-frequencydivision multiplexing(OFDM)system with decode-and-forward relay.The goal is to minimize total energ...In this paper,we study the problem of optimal resource allocation for lifetime maximization in an orthogonal-frequencydivision multiplexing(OFDM)system with decode-and-forward relay.The goal is to minimize total energy cost of the system by jointly optimizing power allocation,subcarrier pairing and relay selection.We present a heuristic solution that is composed of two parts.The first part is an optimal power allocation approach to allocate power to a subcarrier pair of the source and the relay.The second part is a modified Hungarian algorithm to make subcarrier pairing and relay selection.Evaluations show that the presented scheme outperforms other schemes in the total transmitted data and the network lifetime.展开更多
In this Letter,we have experimentally verified a low-complexity subcarrier pairwise-averaging(SPA)-enhanced channel estimation(CE)method for small-size fast Fourier transform(FFT)non-Hermitian symmetric orthogonal fre...In this Letter,we have experimentally verified a low-complexity subcarrier pairwise-averaging(SPA)-enhanced channel estimation(CE)method for small-size fast Fourier transform(FFT)non-Hermitian symmetric orthogonal frequency-division multiplexing(NHS-OFDM)transceivers.Compared with intra-symbol frequency averaging(ISFA),more than 20% look-up tables and 10%logic power consumption can be saved.The least-square(LS),ISFA,and SPA CE methods are compared by offline and real-time digital signal processing approaches.The results show that the receiver sensitivity of the SPA NHS-OFDM transmission system with 64/128-point FFT can be improved by more than 1 dB at the bit error rate of 3.8 ×10^(-3) compared to the LS.展开更多
This paper considers the design of a low-complexity and high-performance precoder for multiple-input multiple-output(MIMO)systems.The precoder is designed by combining both nonlinear and non-iterative processing strat...This paper considers the design of a low-complexity and high-performance precoder for multiple-input multiple-output(MIMO)systems.The precoder is designed by combining both nonlinear and non-iterative processing strategies.The proposed nonlin-ear precoding techniques employ a nonlinear constellation precoding technique based on maximum distance sepa-rable codes at the transmitter.We propose to reduce the computational complexity in iterative-based precoding algorithms by using less complex non-iterative singular value decomposition-based joint precoder and decoder pair design.The maximum likelihood detection for the lin-ear MIMO channel is considered.The simulation results showed that the proposed nonlinear and non-iterative precoding schemes outperform the conventional linear MIMO precoder design,even when a reduced-complexity suboptimal strategy is adopted,considering the bit error rate performance.展开更多
文摘The rapid time-variation of a fading multipath environment can impair the performance of multiple-input multiple-output orthogonal frequency division multiplexing (MIMO OFDM). This paper proposes a pilot placement method for MIMO OFDM systems under time-varying channels with the guard band. The time-varying channel is described by complex exponential basis expansion model (BEM). We discuss the least square (LS) channel estimation to obtain the minimum mean square error (MSE) and derive the pilot allocation that can satisfy the minimum MSE with regard to guard band in time-varying channels. It is shown that optimal pilot clusters can distribute non-uniformly in frequency domain and minimize the MSE. We generalize our scheme over G OFDM symbols and compare it with comb pilots. It is demonstrated that the proposed approach is more effective than previous work. Simulation results validate our theoretical analysis.
基金supported by the Scientific Research Fund of Hunan Provincial Education Department(Nos.20B330 and 21A0562)the Construct Program of the Key Discipline in Hunan Province,China。
文摘To overcome the unbalanced signal-to-noise ratio(SNR)among data-carrying subcarriers(SCs)induced by the imperfect frequency response of optoelectronic devices and various interferences,a channel-independent partial data-carrying SCs precoding(PDSP)method based on orthogonal circular matrix transform(OCT)is proposed and experimentally investigated in an intra-symbol frequency average(ISFA)-enabled discrete multi-tone(DMT)visible light communication(VLC)system.After transmission over 1.9 m free space,at the optimal bias current of 100 mA,the experimental results show that the bit error ratio(BER)performance can be improved by up to an order of magnitude with conventional full data-carrying SCs precoding(FDSP)and PDSP scheme,compared to that without a precoding scheme.Moreover,the BER performance can further be enhanced when the ISFA algorithm with optimal taps is employed.Compared with the FDSP scheme,the proposed PDSP scheme owns a similar BER performance and a significant reduction in required multiplication and addition operations,and it may be a good option to efficiently combat the unbalanced impairments of DMT-VLC transmission systems.
基金supported by China NSF Grants(61631020)the Fundamental Research Funds for the Central Universities(NP2018103,NE2017103,NC2017003)
文摘This paper investigates subcarrier and power allocation in a multi-UAV OFDM system.The study considers a practical scenario,where certain subcarriers are unavailable for dynamic subcarrier allocation,on account of pre-allocation for burst transmissions.We first propose a novel iterative algorithm to jointly optimize subcarrier and power allocation,so as to maximize the sum rate of the uplink transmission in the multiUAV OFDM system.The key idea behind our solution is converting the nontrivial allocation problem into a weighted mean square error(MSE) problem.By this means,the allocation problem can be solved by the alternating optimization method.Besides,aiming at a lower-complexity solution,we propose a heuristic allocation scheme,where subcarrier allocation and transmit power allocation are separately optimized.In the heuristic scheme,closedform solution can be obtained for power allocation.Simulation results demonstrate that in the presence of stretched subcarrier resource,the proposed iterative joint optimization algorithm can significantly outperform the heuristic scheme,offering a higher sum rate.
基金Supported by the National Natural Science Foundation of China (NSFC) (No. 61102066)the China Postdoctoral Science Foundation (Grant No. 2012M511365)the Scientific Research Project of Zhejiang Provincial Education Department (No. Y201119890)
文摘Efficient and reliable subcarrier power joint allocation is served as a promising problem in cognitive OFDM-based Cognitive Radio Networks (CRN). This paper focuses on optimal subcarrier allocation for OFDM-based CRN. We mainly propose subcarrier allocation scheme denoted as Worst Subcarrier Avoiding Water-filling (WSAW), which is based on Rate Adaptive (RA) criterion and three constraints are considered in CRN. The algorithm divides the assignment procedure into two phases. The first phase is an initial subcarrier allocation based on the idea of avoiding selecting the worst subcarrier in order to maximize the transmission rate; while the second phase is an iterative adjustment process which is realized by swapping pairs of subcarriers between arbitrary users. The proposed scheme could assign subcarriers in accordance with channel coherence time. Hence, real time subcarrier allocation could be implemented. Simulation results show that, comparing with the similar existing algorithms, the proposed scheme could achieve larger capacity and a near-optimal BER performance.
基金supported by the National Key Research and Development Program of China (No. 2016 YFC1400400)the Marine Economic Innovation and Development Demonstration Project in Binhai New Area (No. 1723434C4114194)
文摘An expendable conductivity-temperature-depth profiler(XCTD)is one of the most important instruments used to obtain hydrological data,such as temperature and conductivity,and detect ocean depth in a large area.However,the XCTD channel provides poor time-varying performance,narrowband,and low signal-to-noise ratio(SNR),which severely restricts the data transmission rate.In contrast to conventional single-carrier modulation techniques,such as amplitude-shift keying and differential phase-shift keying,this article provides a new method,based on orthogonal frequency division multiplexing(OFDM)to enhance the data transmission rate of deep-sea abandoned profilers.We apply the OFDM to enhance the SNR of the XCTD,which is achieved by reducing the data transmission rate of each sub-channel.Moreover,the bandwidth utilization may be improved by increasing the number of subcarriers in a given bandwidth,which enhances the data transmission rate.Based on analysis of the XCTD channel model,OFDM with different parameters such as constellation mapping,number of subcarriers,subcarrier spacing,signal period and cyclic prefix are achieved.To verify the effectiveness of the OFDM,this study investigates the influence of different parameters on the data transmission rate at different noise levels,i.e.,-20 dB and-40 d B.
基金This work was partly supported by the Natural Science Foundation of Hebei Province(F2019203095)the National Natural Science Foundation of China(61873223,61803328)the National Key R&D Program of China(2018YFB1702100)。
文摘The traditional orthogonal multiple access(OMA)is unable to satisfy the needs of large number of smart devices.To increase the transmission rate in the limited spectrum resource,implementation of both non-orthogonal multiple access(NOMA)and successive interference cancelation(SIC)is essential.In this paper,an optimal resource allocation algorithm in NOMA is proposed to maximize the total system rate in a multi-sector multi-subcarrier relay-assisted communication network.Since the original problem is a non-convex problem with mixed integer programming which is non-deterministic polynomial-time(NP)-hard,a three-step solution is proposed to solve the primal problem.Firstly,we determine the optimal power allocation of the outer users by using the approach of monotonic discrimination,and then the optimal user pairing is determined.Secondly,the successive convex approximation(SCA)method is introduced to transform the non-convex problem involving central users into convex one,and the Lagrangian dual method is used to determine the optimal solution.Finally,the standard Hungarian algorithm is utilized to determine the optimal subcarrier matching.The simulation results show that resource allocation algorithm is able to meet the user performance requirements with NOMA,and the total system rate is improved compared to the existing algorithms.
文摘The idea of cooperation and the clustering amongst cognitive radios(CRs) has recently been focus of attention of research community, owing to its potential to improve performance of spectrum sensing(SS) schemes. This focus has led to the paradigm of cluster based cooperative spectrum sensing(CBCSS). In perspective of high date rate 4th generation wireless systems, which are characterized by orthogonal frequency division multiplexing(OFDM) and spatial diversity, there is a need to devise effective SS strategies. A novel CBCSS scheme is proposed for OFDM subcarrier detection in order to enable the non-contiguous OFDM(NC-OFDM) at the physical layer of CRs for efficient utilization of spectrum holes. Proposed scheme is based on the energy detection in MIMO CR network, using equal gain combiner as diversity combining technique, hard combining(AND, OR and Majority) rule as data fusion technique and antenna diversity based weighted clustering as virtual sub clustering algorithm. Results of proposed CBCSS are compared with conventional CBCSS scheme for AND, OR and Majority data fusion rules. Moreover the effects of antenna diversity, cooperation and cooperating clusters are also discussed.
基金This work was supported by the National Natural Science Foundation of China(No.61601296,No.61701295,and No.61801286)the Major scientific and technological innovation projects in Chengdu(No.2019-YF08-00082-GX)+1 种基金the Talent Program of Shanghai University of Engineering Science(No.2018RC43)the start-up research project of Shanghai University of Engineering Science(No.2019-39).
文摘In the current multi-carrier communications,Orthogonal Frequency Division Multiplexing(OFDM)is widely considered as a leading technology.For mobile applications,however,the orthogonality between subcarriers is deteriorated by Doppler frequency shift,which will introduce serious subcarrier phase rotation in the received signals and degrade the system performance.Thus,a method of differential grouping weighted symmetry data-conjugate(DWSCC)have been previously presented to obtain a better inter-carrier interference(ICI)suppressing effect and Bit Error Rate(BER)performance with no loss of spectral efficiency.In this paper,a novel scheme applying a completely different method of subcarrier interactive mapping is put forward.By mapping two different symbols which are both conjugated or multiplied by a complex weighting factor onto a pair of symmetric subcarriers,the presented scheme can greatly reduce the influence of subcarriers phase rotation caused by Doppler frequency shift in highly mobile environments.Analysis and simulation results indicate that comparing with the DWSCC method,our formulated scheme can not only maintain the spectrum utilization with no loss,but also have the advantages of an improvement on reduction effect and BER performance as well as a lower computational complexity in highly mobile environments.
文摘In this paper, we investigate the power-minimizing resource allocation problem in multiuser cooperative relay communication systems. A joint optimization problem involving subcarrier assignment, relay selection and power allocation is formulated. Since the problem cannot be solved directly, we decompose it into three subproblems. According to the equivalent channel gains and the target rates of users, the subcarrier assignment and relay selection are conducted. Motivated by the water-filling algorithm, we propose a power allocation algorithm with cooperative features. Simulations results indicate that the proposed algorithm performs better in terms of the total transmit power consumption than the existing algorithms.
文摘Aiming at the problems of underwater acoustic communication such as narrowband, low speed and multipath effect, this paper studies the high-speed communication technology of electromagnetic wave in short distance at sea. The channel model of seawater electromagnetic wave is given, and the performance of different modulation modes in this channel is analyzed. A meth-od of seawater short-range high-speed electromagnetic wave communication based on OFDM is proposed. In order to reduce the BER of the system, a method of allocating different modulation modes to subcarriers in seawater channel is introduced, which combines frequency domain equalization. This method has low complexity, improves the utilization of frequency band, and improves the reliability. It can realize high-speed and reliable communication in short distance in seawater.
文摘Subcarrier intensity modulation with direct detection is a modulation/detection technique for optical wireless communication systems,where a pre-modulated and properly biased radio frequency signal is modulated on the intensity of the optical carrier.The most important benefits of subcarrier intensity modulation are as follows:1) it does not provide irreducible error floor like the conventional on-off keying intensity modulation with a fixed detection threshold;2) it provides improved spectral efficiency and supports higher order modulation schemes;and 3) it has much less implementation complexity compared to coherent optical wireless communications with heterodyne or homodyne detection.In this paper,we present an up-to-date review of subcarrier intensity modulated optical wireless communication systems.We survey the error rate and outage performance of subcarrier intensity modulations in the atmospheric turbulence channels considering different modulation and coding schemes.We also explore different contemporary atmospheric turbulence fading mitigation solutions that can be employed for subcarrier intensity modulation.These solutions include diversity combining,adaptive transmission,relay assisted transmission,multiple-subcarrier intensity modulations,and optical orthogonal frequency division multiplexing.Moreover,we review the performance of subcarrier intensity modulations due to the pointing error and synchronization error.
文摘Single-carrier frequency-division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) systems are new orthogonal multiple access systems. They have been adopted in the 3GPP long term evolution (3GPP-LTE). In these systems, there are only two types of subcarrier mapping schemes which are the interleaved and the localized. So, introducing a new subcarrier mapping scheme is an important issue, which is the main objective of this paper. In this paper, a hybrid subcarrier mapping scheme is proposed and examined for the SC-FDMA system. Monte Carlo simulations are performed to compare the performance of the proposed scheme with that of the interleaved and the localized schemes. It is shown that a hybrid scheme provides better performance than that of the localized and the same performance as that of the interleaved scheme and increased robustness to carrier frequency offset (CFO) at the expense of increased envelope fluctuations.
文摘Multicarrier systems such as orthogonal frequency division (OFDM) are considered as a promising candidate for wireless networks that support high data rate communication. In this article, we investigate the perform-ance of a multiuser OFDM system under imperfect synchronization. Analytical results indicate that the SNR degrades as the average power of the channel impairments such as AWGN, carrier frequency offset due to Doppler frequency and fading gain is increased. The SNR degradation leads to imperfect synchronization and hence decreases the total number of subcarriers available for allocation. Monte Carlo analysis shows up to 22% loss in the number of allocatable subcarriers can be expected under a specific imperfect synchroniza-tion condition as compared to perfect synchronization. We utilize empirical modelling to characterize the available number of subcarriers as a Poisson random variable. In addition, we determine the percentage de-crease in the total number of allocatable subcarriers under varying channel parameters. The results indicate 19% decrease in the number of available subcarriers as average AWGN power is increased by 10dB;44% decrease as the Doppler frequency is varied from 10Hz to 100Hz;and 56% decrease as the fading gain is varied from 0dB to -30dB.
文摘In this paper, an adaptive subcarrier allocation scheme with reconfiguration of operating parameters for Cognitive Radio Networks (CRN) is presented. A QoS-conscious spectrum decision frame work is projected, where spectrum bands are determined by considering the application requirements as well as the dynamic nature of the spectrum bands. The novel subcarrier allocation algorithm is developed to fulfill different performance objective as a solution for subcarrier allocation and power allocation problem for Cognitive Radio (CR) users in CRNs. It employs operating frequency parameter modification using Proportional Resource Algorithm and Genetic Algorithm (GA). The multi objective optimization problem with equality and inequality constraint is considered. Moreover, a dynamic subcarrier allocations scheme is developed based on GA to decide on the spectrum bands adaptively dependent on the time-varying CR network capacity. The proposed algorithm targets to achieve maximum data rate for each subcarrier, maximize the overall network throughput and maximize the number of satisfied user under the constraints of bandwidth and guarantee Quality of Service (QoS) requirement from dynamic spectrum management (DSM) perspective. Moreover, it determines the best available channel.
文摘A method for online dispersion monitoring by adding a single in-band subcarrier tone isintroduced.According to the theoretical analysis,the dispersion monitor and measurement range aredetermined by the specific frequency of the subcarrier tone.By using simulation tools,figures aboutrelationship between power of subcarrier tone and transmission distance in ideal condition are shown.
基金Project supported by the Graduate Research and Innovation Foundation of Chongqing,China(No.CYB23050)the National Natural Science Foundation of China(Nos.62271092,62001074)+4 种基金the Fundamental Research Funds for the Central Universities,China(No.2023CDJXY-037)the China Postdoctoral Science Foundation(No.2022M710534)the Natural Science Foundation of Chongqing,China(Nos.CSTB2023NSCQMSX0933,CSTB2022NSCQMSX0327)the Open Fund of the Shaanxi Key Laboratory of Information Communication Network and Security,China(No.ICNS202201)the Opening Project of the Guangxi Wireless Broadband Communication and Signal Processing Key Laboratory,China(No.GXKL06230206)。
文摘Reconfigurable intelligent surfaces(RISs)have the capability to change the wireless environment smartly Considering the attenuation of subchannels and crowding users involved in the wideband system,we introduce RISs into the multi-user multi-input single-output(MU-MISO)system with orthogonal frequency division multiplexing(OFDM)for performance enhancement.Maximizing the minimum rate of dense users in an MU-MISO-OFDM system assisted by RIS with an approximate practical model is formulated as the joint optimization problem involving subcarrier allocation,transmit precoding(TPC)matrices at the base station,and RIS passive beamforming.A coalition-game subcarrier allocation(CSA)algorithm is proposed to solve space–frequency resource allocation on subcarriers,which reforms the interference topology among dense users.Fractional programming and convex optimization method are used to optimize the TPC matrices and the RIS passive beamforming,which improves the spectral efficiency synthetically across all subchannels in the wideband system.Simulation results indicate that the CSA algorithm provides a significant gain for dense users.Besides,the proposed joint optimization method shows the considerable advantage of the RISs in the MU-MISO-OFDM system.
基金the University Science Research Project of Jiangsu Province(16KJB510045,18KJB510033)“333”High-Level Talent Training Project(BRA2020322)。
文摘Chaotic sequence has been applied in Cognitive Radio(CR)to exert the enormous potential spectral utilization and enhance the transmission security.However,since there is not strict orthogonality between chaotic signals,intra-signal interference(ISI)will be introduced into the demodulation.Here,an anti-interference orthogonal-frequency-division-multiplexing(OFDM)chaotic modulation named Walsh-sequence chaotic CR(WS-CCR)is proposed for cognitive radio.By constructing the strictly orthogonal chaotic signal based on Walsh sequence,the ISI component,which is produced by frequency offset in previous CR,can be eliminated during the demodulation.Moreover,the chaotic sequence can also be applied to scramble subcarriers to relieve the interference caused by malicious attacks.Gaussian approximation method is adopted to obtain the exact performance analysis of WS-CCR over Additive White Gaussian Noise(AWGN)channel and Rayleigh multipath fading channel.Results show that,with subcarriers scrambling by chaotic sequence,anti-interference performance and transmitting security can be signi?cantly improved in WS-CCR.Importantly,due to the absence of ISI component,the bit-error ratio(BER)performance of WS-CCR is better than that of the previous CR system.
基金supported by Important National Science and Technology Specific Projects(No.2011ZX03003-001-04 and 2012ZX03003-012)National Natural Science Foundation of China(No.61072069)+2 种基金Fundamental Research Funds for the Central Universities(No.72101859)State Key Laboratory of Integrated Services Networks(No.ISN090105)111 Project(No.B08038)
文摘In this paper,we study the problem of optimal resource allocation for lifetime maximization in an orthogonal-frequencydivision multiplexing(OFDM)system with decode-and-forward relay.The goal is to minimize total energy cost of the system by jointly optimizing power allocation,subcarrier pairing and relay selection.We present a heuristic solution that is composed of two parts.The first part is an optimal power allocation approach to allocate power to a subcarrier pair of the source and the relay.The second part is a modified Hungarian algorithm to make subcarrier pairing and relay selection.Evaluations show that the presented scheme outperforms other schemes in the total transmitted data and the network lifetime.
基金This work was supported in part by the National Natural Science Foundation of China(No.61805079)the Hunan Provincial Natural Science Foundation(No.2020JJ4433)the Hunan Province College Students Research Learning and Innovative Experiment Project,China(No.S202010542058).
文摘In this Letter,we have experimentally verified a low-complexity subcarrier pairwise-averaging(SPA)-enhanced channel estimation(CE)method for small-size fast Fourier transform(FFT)non-Hermitian symmetric orthogonal frequency-division multiplexing(NHS-OFDM)transceivers.Compared with intra-symbol frequency averaging(ISFA),more than 20% look-up tables and 10%logic power consumption can be saved.The least-square(LS),ISFA,and SPA CE methods are compared by offline and real-time digital signal processing approaches.The results show that the receiver sensitivity of the SPA NHS-OFDM transmission system with 64/128-point FFT can be improved by more than 1 dB at the bit error rate of 3.8 ×10^(-3) compared to the LS.
文摘This paper considers the design of a low-complexity and high-performance precoder for multiple-input multiple-output(MIMO)systems.The precoder is designed by combining both nonlinear and non-iterative processing strategies.The proposed nonlin-ear precoding techniques employ a nonlinear constellation precoding technique based on maximum distance sepa-rable codes at the transmitter.We propose to reduce the computational complexity in iterative-based precoding algorithms by using less complex non-iterative singular value decomposition-based joint precoder and decoder pair design.The maximum likelihood detection for the lin-ear MIMO channel is considered.The simulation results showed that the proposed nonlinear and non-iterative precoding schemes outperform the conventional linear MIMO precoder design,even when a reduced-complexity suboptimal strategy is adopted,considering the bit error rate performance.
