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
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
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
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
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
为了提高网络的接入成功率和有限前导资源利用率,提出了一种基于机器类型设备(machine type devices,MTD)分组和功率控制的前导复用随机接入策略。利用地面MTD与卫星基站之间的实时仰角关系,动态规划同一波束内不同位置的MTD,建立不同...为了提高网络的接入成功率和有限前导资源利用率,提出了一种基于机器类型设备(machine type devices,MTD)分组和功率控制的前导复用随机接入策略。利用地面MTD与卫星基站之间的实时仰角关系,动态规划同一波束内不同位置的MTD,建立不同分组索引与前导序列和发射功率的映射关系;通过不同分组的MTD使用不同发射功率产生的干扰消除效应来降低接入过程中前导序列碰撞率。仿真结果表明,提出的策略在大规模卫星物联网设备接入时具有良好的接入成功率和前导序列利用率,适应性和高效性优于其他资源再分配接入技术。展开更多
在面向卫星物联网的免授权随机接入(Grant-free Random Access,GFRA)系统中,受大规模连接和设备随机激活的影响,前导碰撞成为用户接入性能提升的主要制约因素。鉴于此,借助正交与非正交序列在前导检测和冲突抑制方面的各自优势,提出一...在面向卫星物联网的免授权随机接入(Grant-free Random Access,GFRA)系统中,受大规模连接和设备随机激活的影响,前导碰撞成为用户接入性能提升的主要制约因素。鉴于此,借助正交与非正交序列在前导检测和冲突抑制方面的各自优势,提出一种基于混合ZC(Zadoff-Chu)序列的大容量前导设计和检测方法。该方法利用正交ZC序列与其循环移位映射的不同根ZC序列级联来构建前导序列,并采用一种基于假设检验的两阶段干扰消除活跃用户检测算法,以确保大规模接入场景下的高精度用户识别。此外,对所提前导结构进行扩展,将相位旋转因子与多段非正交序列相结合,在不增加峰均比的前提下进一步扩大前导集容量。所提方法较现有复合和正交前导方法具有显著改善的多用户识别性能,在相同活跃用户下,成功检测概率最大提升约30.3%。展开更多
为解决海量机器类通信(mMTC,massive machine type communications)场景下,机器类通信设备(MTCD,machine type communication device)采用传统随机接入方案时,往往出现网络严重拥塞,导致大量MTCD无法成功接入网络问题,提出了一种基于前...为解决海量机器类通信(mMTC,massive machine type communications)场景下,机器类通信设备(MTCD,machine type communication device)采用传统随机接入方案时,往往出现网络严重拥塞,导致大量MTCD无法成功接入网络问题,提出了一种基于前导码重传辅助的动态接入类别限制(PRT-ACB,preamble retransmission access class barring)方案。利用MTCD的前导码重传次数,将每个随机接入机会(RAO,random access opportunity)中尝试发起接入的MTCD划分为高、低优先级,结合每个RAO中负载数估计模型,分别为其设定随每个RAO中的接入负载动态变化的高、低优先级限制因子和可用前导码池,使更多MTCD能在未达到最大前导码传输次数前成功接入网络。仿真结果表明,所提方案能有效提升MTCD的接入成功概率,降低MTCD接入网络所需时延。所提方案可以作为缓解海量通信设备同时接入网络造成拥塞的一种解决方案。展开更多
基于COSTAS环的载波同步环路在对较大相位差的正交方波远距离无线电(Long Range Radio,LoRa)信号进行载波同步时,入锁时间长甚至出现失锁现象。针对这一问题,首先分析了正交方波LoRa物理层原理,指出其本质为具有前导码的正交相移键控信...基于COSTAS环的载波同步环路在对较大相位差的正交方波远距离无线电(Long Range Radio,LoRa)信号进行载波同步时,入锁时间长甚至出现失锁现象。针对这一问题,首先分析了正交方波LoRa物理层原理,指出其本质为具有前导码的正交相移键控信号(Quadrature Phase Shift Keying,QPSK);然后利用正交方波LoRa的前导码结合同步环路设计了改进算法。仿真结果显示,改进算法适用于有前导码的QPSK信号,相比于传统算法,在相位差大于45°时仍能保持良好的工作性能,在信噪比低于20 dB时具有更小的频率误差。展开更多
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.
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.
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 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.
文摘为了提高网络的接入成功率和有限前导资源利用率,提出了一种基于机器类型设备(machine type devices,MTD)分组和功率控制的前导复用随机接入策略。利用地面MTD与卫星基站之间的实时仰角关系,动态规划同一波束内不同位置的MTD,建立不同分组索引与前导序列和发射功率的映射关系;通过不同分组的MTD使用不同发射功率产生的干扰消除效应来降低接入过程中前导序列碰撞率。仿真结果表明,提出的策略在大规模卫星物联网设备接入时具有良好的接入成功率和前导序列利用率,适应性和高效性优于其他资源再分配接入技术。
文摘在面向卫星物联网的免授权随机接入(Grant-free Random Access,GFRA)系统中,受大规模连接和设备随机激活的影响,前导碰撞成为用户接入性能提升的主要制约因素。鉴于此,借助正交与非正交序列在前导检测和冲突抑制方面的各自优势,提出一种基于混合ZC(Zadoff-Chu)序列的大容量前导设计和检测方法。该方法利用正交ZC序列与其循环移位映射的不同根ZC序列级联来构建前导序列,并采用一种基于假设检验的两阶段干扰消除活跃用户检测算法,以确保大规模接入场景下的高精度用户识别。此外,对所提前导结构进行扩展,将相位旋转因子与多段非正交序列相结合,在不增加峰均比的前提下进一步扩大前导集容量。所提方法较现有复合和正交前导方法具有显著改善的多用户识别性能,在相同活跃用户下,成功检测概率最大提升约30.3%。
文摘为解决海量机器类通信(mMTC,massive machine type communications)场景下,机器类通信设备(MTCD,machine type communication device)采用传统随机接入方案时,往往出现网络严重拥塞,导致大量MTCD无法成功接入网络问题,提出了一种基于前导码重传辅助的动态接入类别限制(PRT-ACB,preamble retransmission access class barring)方案。利用MTCD的前导码重传次数,将每个随机接入机会(RAO,random access opportunity)中尝试发起接入的MTCD划分为高、低优先级,结合每个RAO中负载数估计模型,分别为其设定随每个RAO中的接入负载动态变化的高、低优先级限制因子和可用前导码池,使更多MTCD能在未达到最大前导码传输次数前成功接入网络。仿真结果表明,所提方案能有效提升MTCD的接入成功概率,降低MTCD接入网络所需时延。所提方案可以作为缓解海量通信设备同时接入网络造成拥塞的一种解决方案。
