The emergence of various commercial and industrial Internet of Things(IoT)devices has brought great convenience to people’s life and production.Both low-power,massively connected mMTC devices(MDs)and highly reliable,...The emergence of various commercial and industrial Internet of Things(IoT)devices has brought great convenience to people’s life and production.Both low-power,massively connected mMTC devices(MDs)and highly reliable,low-latency URLLC devices(UDs)play an important role in different application scenarios.However,when dense MDs and UDs periodically initiate random access(RA)to connect the base station and send data,due to the limited preamble resources,preamble collisions are likely to occur,resulting in device access failure and data transmission delay.At the same time,due to the highreliability demands of UDs,which require smooth access and fast data transmission,it is necessary to reduce the failure rate of their RA process.To this end,we propose an intelligent preamble allocation scheme,which uses hierarchical reinforcement learning to partition the UD exclusive preamble resource pool at the base station side and perform preamble selection within each RA slot at the device side.In particular,considering the limited processing capacity and energy of IoT devices,we adopt the lightweight Qlearning algorithm on the device side and design simple states and actions for them.Experimental results show that the proposed intelligent scheme can significantly reduce the transmission failure rate of UDs and improve the overall access success rate of devices.展开更多
Worldwide Interoperability for Microwave Access(WiMAX)trusts Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing(MIMO-OFDM)combination for the deployment of physical layer functions and for conne...Worldwide Interoperability for Microwave Access(WiMAX)trusts Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing(MIMO-OFDM)combination for the deployment of physical layer functions and for connecting the medium access control to the wireless media.Even though Orthogonal Frequency Division Multiplexing(OFDM)facilitates reliable digital broadband transmission in the fading wireless channels,the presence of synchro-nization errors in the form of Carrier Frequency Offset(CFO)and Time Offset(TO)adversely affect the performance of OFDM based physical layers.The objective of this work is to improve the accuracy of the frequency and the time offset estimation in the WiMAX physical layer.A method to enhance the synchro-nization accuracy byfine-tuning the merit factor of the preamble sequence is sug-gested in this paper.Also,a new preamble with improved synchronization accuracy is proposed for the WiMAX system.The performance of the proposed preamble is evaluated in a Rayleigh fading channel and the results of simulations show that the Mean Square Error(MSE)in offset estimation is significantly reduced and it outperforms the standard WiMAX preamble.展开更多
Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window,...Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window, and the carrier frequency offset （CFO） due to Doppler frequency shift or the frequency mismatch between the transmitter and receiver oscil ators, can bring severe inter-symbol interference （ISI） and inter-carrier interference （ICI） for the OFDM system. Relying on the relatively good correlation charac-teristic of the pseudo-noise （PN） sequence, a joint frame offset and normalized CFO estimation algorithm based on PN preamble in time domain is developed to realize the frame and frequency synchronization in the OFDM system. By comparison, the perfor-mances of the traditional algorithm and the improved algorithm are simulated under different conditions. The results indicate that the PN preamble based algorithm both in frame offset estimation and CFO estimation is more accurate, resource-saving and robust even under poor channel condition, such as low signal-to-noise ratio （SNR） and large normalized CFO.展开更多
Timing and carrier frequency offset estimation are critical issue for OFDM cooperative communications. In view of the complexity and high accuracy requirement, 1/2 and 1/4 pilot symbol cycle CAZAC sequence structures ...Timing and carrier frequency offset estimation are critical issue for OFDM cooperative communications. In view of the complexity and high accuracy requirement, 1/2 and 1/4 pilot symbol cycle CAZAC sequence structures are defined as the pilot frequency sequence. Estimation within one symbol cycle is carried out through averaging samples of two neighboring symbol cycles, after which the operation is expanded to all the symbol cycles in one band group. Taking multipath effect into account, the concept of phase rotation is proposed for a further step. Adjust the phase difference of estimated symbols by phase rotation, and cross estimation could be done. Meanwhile, timing scheme works within one cycle training sequence. Theoretical and simulation analysis indicate that CRLB does not only relate to estimation symbol length, but also be influenced by phase difference of estimation symbols seriously. In the condition that the length of estimation is fixed, the bigger the phase rotation angle is, the smaller the CRLB is. The complexity of proposed algorithm is less than full cycle average estimation method for almost 50%. Meanwhile, the estimation accuracy is approximate with the full cycle average estimation method as well. Timing scheme with the defined preamble structure is also proposed. Simulation proves its efficiency.展开更多
As time goes by,Journal of Landscape Research has withessed ten years of publication in spite of difficulties and hardships,which is attributed to the team’s persistent efforts.In the past year,we expanded the editor...As time goes by,Journal of Landscape Research has withessed ten years of publication in spite of difficulties and hardships,which is attributed to the team’s persistent efforts.In the past year,we expanded the editorial board in order to broaden the horizon of the journal and get more professional guidance.In 2019,we will,as always,work hard to introduce more industry leaders to participate in the construction of the journal.展开更多
A new preamble structure and design method for orthogonal frequency division multiplexing（OFDM）systems is described,which results a two-symbol long training preamble.The preamble contains four parts,the first part i...A new preamble structure and design method for orthogonal frequency division multiplexing（OFDM）systems is described,which results a two-symbol long training preamble.The preamble contains four parts,the first part is the same as the third,and the four parts are calculated by using nonlinear programming（NLP）model such that the moving correlation of the preamble results a steep rectangular-like pulse of certain width,whose step-down indicates the timing offset.Simulation results in AWGN channel are given to evaluate the perf o rmance of the proposed preamble design.展开更多
Based on the analysis of the performance of Boumard＇s SNR method for wireless orthogonal frequency division multiplexing （OFDM） systems, a new estimation algorithm of the noise variance is proposed by only using th...Based on the analysis of the performance of Boumard＇s SNR method for wireless orthogonal frequency division multiplexing （OFDM） systems, a new estimation algorithm of the noise variance is proposed by only using the data samples of the two training symbols in the preamble, and the second order moment of these data samples is employed to estimate the signal power. The average SNR and the SNRs on the subchannels can all be estimated by the proposed algorithm, and its performance is independent of the channel＇s frequency selectivity. Simulation results show that the performance of the proposed method is highly improved and much better than that of Boumard＇s method.展开更多
Two years after assuming a new name and format change, the year 2010 marks the 8th anniversary of Particuology. To commemorate this special occasion for the journal, the thematic editors met in Montreal at the 8th Wor...Two years after assuming a new name and format change, the year 2010 marks the 8th anniversary of Particuology. To commemorate this special occasion for the journal, the thematic editors met in Montreal at the 8th World Congress of Chemical Engineering and decided to compile a truly special issue. Instead of producing another ＂conventional＂ special issue of the more ＂regular＂ research papers on some given subjects, we have decided to take a more innovative format for this issue to present short discussion papers that provide quick overviews of the current status of selected subiects and then discuss forward thinking for the future.展开更多
In cellular systems,establishing the initial symbol timing of potential preambles is the first step of a cell search.The envelope fluctuation of the downlink signal hinders the successful timing of conventional symbol...In cellular systems,establishing the initial symbol timing of potential preambles is the first step of a cell search.The envelope fluctuation of the downlink signal hinders the successful timing of conventional symbol timing methods.To solve this problem,a hybrid timing strategy is proposed with two novel detectors,namely the normalized replica-based detector and normalized differential detector.The strategy first detects all potential preambles via the normalized replica-based detector and then employs the normalized differential detector to verify the target preamble,which comes from the target cell and has the highest power.The strategy is unaffected by envelope fluctuation and has computational complexity comparable to that of conventional methods.Simu-lations and real-data tests show that the hybrid timing strategy is robust and practical for initial symbol timing.展开更多
Table of Contents Preamble 1 Prevalence of hypertension in Chinese population 1.1 Prevalence,incidence and epidemic trend of hypertension in Chinese population 1.2 Awareness,treatment and control of Hypertension in Ch...Table of Contents Preamble 1 Prevalence of hypertension in Chinese population 1.1 Prevalence,incidence and epidemic trend of hypertension in Chinese population 1.2 Awareness,treatment and control of Hypertension in China 1.3 Important risk factors for hypertension in Chinese population 2 Hypertension and cardiovascular risk 2.1 Relationship between blood pressure and cardiovascular risk 2.2 Cardiovascular risk characteristics of hypertension population in China 3 Diagnostic evaluation 3.1 Medical history 3.2 Physical examination 3.3 Laboratory examinations 3.4 Genetic analysis 3.5 BP measurement 3.6 Evaluation of target organ damage.展开更多
This paper proposes a simple method to enlarge the estimation range of conventional carrier frequency offset (CFO) estimation methods based on correlations among the identical parts of the preamble. A novel preamble i...This paper proposes a simple method to enlarge the estimation range of conventional carrier frequency offset (CFO) estimation methods based on correlations among the identical parts of the preamble. A novel preamble is designed, which is composed of one regular OFDM training block with even numbers of identical parts and one irregular OFDM training block with odd numbers of identical parts. The initial estimates obtained over the two training blocks are next exploited to jointly estimate the CFO. By elaborately selecting the numbers of identical parts for the two training blocks, the proposed CFO estimator can estimate frequency offset over tens of the subcarrier spacing. Simulation results showed that the proposed CFO estimator satisfies the estimate range requirement for the practical OFDM systems, while achieving a very good estimate performance.展开更多
This paper presents a novel carrier frequency offset estimation (CFO) algorithm for orthogonal frequency division multiplexing (OFDM)-based Wireless Local Area Networks (WLANs). Compared with previous approaches, this...This paper presents a novel carrier frequency offset estimation (CFO) algorithm for orthogonal frequency division multiplexing (OFDM)-based Wireless Local Area Networks (WLANs). Compared with previous approaches, this paper extends the whole frequency offset acquisition range by embedding a synthetic algorithm according to the preamble structure of WLANs symbols. The numerical results presented support the effectiveness of this algorithm by which the estimation error of the whole carrier frequency offset in the WLANs is effectively decreased.展开更多
基金supported by National Key R&D Program of China (2022YFB3104200)in part by National Natural Science Foundation of China (62202386)+3 种基金in part by Basic Research Programs of Taicang (TC2021JC31)in part by Fundamental Research Funds for the Central Universities (D5000210817)in part by Xi’an Unmanned System Security and Intelligent Communications ISTC Centerin part by Special Funds for Central Universities Construction of World-Class Universities (Disciplines) and Special Development Guidance (0639022GH0202237 and 0639022SH0201237)
文摘The emergence of various commercial and industrial Internet of Things(IoT)devices has brought great convenience to people’s life and production.Both low-power,massively connected mMTC devices(MDs)and highly reliable,low-latency URLLC devices(UDs)play an important role in different application scenarios.However,when dense MDs and UDs periodically initiate random access(RA)to connect the base station and send data,due to the limited preamble resources,preamble collisions are likely to occur,resulting in device access failure and data transmission delay.At the same time,due to the highreliability demands of UDs,which require smooth access and fast data transmission,it is necessary to reduce the failure rate of their RA process.To this end,we propose an intelligent preamble allocation scheme,which uses hierarchical reinforcement learning to partition the UD exclusive preamble resource pool at the base station side and perform preamble selection within each RA slot at the device side.In particular,considering the limited processing capacity and energy of IoT devices,we adopt the lightweight Qlearning algorithm on the device side and design simple states and actions for them.Experimental results show that the proposed intelligent scheme can significantly reduce the transmission failure rate of UDs and improve the overall access success rate of devices.
文摘Worldwide Interoperability for Microwave Access(WiMAX)trusts Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing(MIMO-OFDM)combination for the deployment of physical layer functions and for connecting the medium access control to the wireless media.Even though Orthogonal Frequency Division Multiplexing(OFDM)facilitates reliable digital broadband transmission in the fading wireless channels,the presence of synchro-nization errors in the form of Carrier Frequency Offset(CFO)and Time Offset(TO)adversely affect the performance of OFDM based physical layers.The objective of this work is to improve the accuracy of the frequency and the time offset estimation in the WiMAX physical layer.A method to enhance the synchro-nization accuracy byfine-tuning the merit factor of the preamble sequence is sug-gested in this paper.Also,a new preamble with improved synchronization accuracy is proposed for the WiMAX system.The performance of the proposed preamble is evaluated in a Rayleigh fading channel and the results of simulations show that the Mean Square Error(MSE)in offset estimation is significantly reduced and it outperforms the standard WiMAX preamble.
基金supported by the National Natural Science Foundation of China(6130110561102069)+2 种基金the China Postdoctoral Science Foundation Funded Project(2013M531351)the Nanjing University of Aeronautics and Astronautics Founding(NN2012022)the Open Fund of Graduate Innovated Base(Laboratory)for the Nanjing University of Aeronautics and Astronautics(KFJJ120219)
文摘Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window, and the carrier frequency offset （CFO） due to Doppler frequency shift or the frequency mismatch between the transmitter and receiver oscil ators, can bring severe inter-symbol interference （ISI） and inter-carrier interference （ICI） for the OFDM system. Relying on the relatively good correlation charac-teristic of the pseudo-noise （PN） sequence, a joint frame offset and normalized CFO estimation algorithm based on PN preamble in time domain is developed to realize the frame and frequency synchronization in the OFDM system. By comparison, the perfor-mances of the traditional algorithm and the improved algorithm are simulated under different conditions. The results indicate that the PN preamble based algorithm both in frame offset estimation and CFO estimation is more accurate, resource-saving and robust even under poor channel condition, such as low signal-to-noise ratio （SNR） and large normalized CFO.
基金supported by the National Natural Science Foundation of China (No. 61371092 , No. 61401175)the Doctoral Fund of Ministry of Education of China (No. 20130061120062)the China Postdoctoral Science Foundation (No. 2014M551184)
文摘Timing and carrier frequency offset estimation are critical issue for OFDM cooperative communications. In view of the complexity and high accuracy requirement, 1/2 and 1/4 pilot symbol cycle CAZAC sequence structures are defined as the pilot frequency sequence. Estimation within one symbol cycle is carried out through averaging samples of two neighboring symbol cycles, after which the operation is expanded to all the symbol cycles in one band group. Taking multipath effect into account, the concept of phase rotation is proposed for a further step. Adjust the phase difference of estimated symbols by phase rotation, and cross estimation could be done. Meanwhile, timing scheme works within one cycle training sequence. Theoretical and simulation analysis indicate that CRLB does not only relate to estimation symbol length, but also be influenced by phase difference of estimation symbols seriously. In the condition that the length of estimation is fixed, the bigger the phase rotation angle is, the smaller the CRLB is. The complexity of proposed algorithm is less than full cycle average estimation method for almost 50%. Meanwhile, the estimation accuracy is approximate with the full cycle average estimation method as well. Timing scheme with the defined preamble structure is also proposed. Simulation proves its efficiency.
文摘As time goes by,Journal of Landscape Research has withessed ten years of publication in spite of difficulties and hardships,which is attributed to the team’s persistent efforts.In the past year,we expanded the editorial board in order to broaden the horizon of the journal and get more professional guidance.In 2019,we will,as always,work hard to introduce more industry leaders to participate in the construction of the journal.
基金supported by the National Natural Science Foundation of China under Grant No. 60501018
文摘A new preamble structure and design method for orthogonal frequency division multiplexing（OFDM）systems is described,which results a two-symbol long training preamble.The preamble contains four parts,the first part is the same as the third,and the four parts are calculated by using nonlinear programming（NLP）model such that the moving correlation of the preamble results a steep rectangular-like pulse of certain width,whose step-down indicates the timing offset.Simulation results in AWGN channel are given to evaluate the perf o rmance of the proposed preamble design.
基金the National Natural Science Foundation of China (Grant Nos.60602063, 60532060 and 60772134)the Natural Science Foundation of Shaanxi Province (Grant No.2006F28)
文摘Based on the analysis of the performance of Boumard＇s SNR method for wireless orthogonal frequency division multiplexing （OFDM） systems, a new estimation algorithm of the noise variance is proposed by only using the data samples of the two training symbols in the preamble, and the second order moment of these data samples is employed to estimate the signal power. The average SNR and the SNRs on the subchannels can all be estimated by the proposed algorithm, and its performance is independent of the channel＇s frequency selectivity. Simulation results show that the performance of the proposed method is highly improved and much better than that of Boumard＇s method.
文摘Two years after assuming a new name and format change, the year 2010 marks the 8th anniversary of Particuology. To commemorate this special occasion for the journal, the thematic editors met in Montreal at the 8th World Congress of Chemical Engineering and decided to compile a truly special issue. Instead of producing another ＂conventional＂ special issue of the more ＂regular＂ research papers on some given subjects, we have decided to take a more innovative format for this issue to present short discussion papers that provide quick overviews of the current status of selected subiects and then discuss forward thinking for the future.
基金supported in part by the National Natural Science Foundation of China(61931015,62071335)in part by the Natural Science Foundation of Hubei Province of China(2021CFA002)+2 种基金in part by the Fundamental Research Funds for the Central Universitiesin part by the Technological Innovation Project of Hubei Province of China(2019AAA061)in part by the Science and Technology Program of Shenzhen(JCYJ20170818112037398).
文摘In cellular systems,establishing the initial symbol timing of potential preambles is the first step of a cell search.The envelope fluctuation of the downlink signal hinders the successful timing of conventional symbol timing methods.To solve this problem,a hybrid timing strategy is proposed with two novel detectors,namely the normalized replica-based detector and normalized differential detector.The strategy first detects all potential preambles via the normalized replica-based detector and then employs the normalized differential detector to verify the target preamble,which comes from the target cell and has the highest power.The strategy is unaffected by envelope fluctuation and has computational complexity comparable to that of conventional methods.Simu-lations and real-data tests show that the hybrid timing strategy is robust and practical for initial symbol timing.
文摘Table of Contents Preamble 1 Prevalence of hypertension in Chinese population 1.1 Prevalence,incidence and epidemic trend of hypertension in Chinese population 1.2 Awareness,treatment and control of Hypertension in China 1.3 Important risk factors for hypertension in Chinese population 2 Hypertension and cardiovascular risk 2.1 Relationship between blood pressure and cardiovascular risk 2.2 Cardiovascular risk characteristics of hypertension population in China 3 Diagnostic evaluation 3.1 Medical history 3.2 Physical examination 3.3 Laboratory examinations 3.4 Genetic analysis 3.5 BP measurement 3.6 Evaluation of target organ damage.
基金Project supported by the Hi-Tech Research and Development Pro-gram (863) of China (No. 2003AA12331007) and the National NaturalScience Foundation of China (No. 60572157)
文摘This paper proposes a simple method to enlarge the estimation range of conventional carrier frequency offset (CFO) estimation methods based on correlations among the identical parts of the preamble. A novel preamble is designed, which is composed of one regular OFDM training block with even numbers of identical parts and one irregular OFDM training block with odd numbers of identical parts. The initial estimates obtained over the two training blocks are next exploited to jointly estimate the CFO. By elaborately selecting the numbers of identical parts for the two training blocks, the proposed CFO estimator can estimate frequency offset over tens of the subcarrier spacing. Simulation results showed that the proposed CFO estimator satisfies the estimate range requirement for the practical OFDM systems, while achieving a very good estimate performance.
基金Project supported by the National Natural Science Foundation of China (No. 2004012F33AA), and Education Foundation of Zhe- jiang Education Department (No. 20040125-66), China
文摘This paper presents a novel carrier frequency offset estimation (CFO) algorithm for orthogonal frequency division multiplexing (OFDM)-based Wireless Local Area Networks (WLANs). Compared with previous approaches, this paper extends the whole frequency offset acquisition range by embedding a synthetic algorithm according to the preamble structure of WLANs symbols. The numerical results presented support the effectiveness of this algorithm by which the estimation error of the whole carrier frequency offset in the WLANs is effectively decreased.
