This paper analyzes the necessity of the measurement of one-way delay, and it also points out the errors caused by the time offset between measurement devices. Then we propose an algorithm to estimate time offset betw...This paper analyzes the necessity of the measurement of one-way delay, and it also points out the errors caused by the time offset between measurement devices. Then we propose an algorithm to estimate time offset between measurement devices in network. With the estimated time offset, we can correct our measuring results. Simulation shows the effectiveness of our algorithm.展开更多
Due to the neglect of the retrieval of communication parameters(including the symbol rate,the symbol timing offset,and the carrier frequency),the existing non-cooperative communication mode recognizers suffer from the...Due to the neglect of the retrieval of communication parameters(including the symbol rate,the symbol timing offset,and the carrier frequency),the existing non-cooperative communication mode recognizers suffer from the generality ability degradation and severe difficulty in distinguishing a large number of modulation modes,etc.To overcome these drawbacks,this paper proposes an efficient communication mode recognizer consisting of communication parameter estimation,the constellation diagram retrieval,and a classification network.In particular,we define a 2-D symbol synchronization metric to retrieve both the symbol rate and the symbol timing offset,whereas a constellation dispersity annealing procedure is devised to correct the carrier frequency accurately.Owing to the accurate estimation of these crucial parameters,high-regularity constellation maps can be retrieved and thus simplify the subsequent classification work.Numerical results show that the proposed communication mode recognizer acquires higher classification accuracy,stronger anti-noise robustness,and higher applicability of distinguishing multiple types,which presents the proposed scheme with vast applicable potentials in non-cooperative scenarios.展开更多
针对北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)精密单点定位(precise point positioning,PPP)服务PPP-B2b在同一时刻可用于PPP的卫星数量有限,以及其实时钟差解算评估研究较少的问题,本文提出了一种基于BDS PPP-B2b与G...针对北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)精密单点定位(precise point positioning,PPP)服务PPP-B2b在同一时刻可用于PPP的卫星数量有限,以及其实时钟差解算评估研究较少的问题,本文提出了一种基于BDS PPP-B2b与Galileo高精度服务(high accuracy service,HAS)融合的改进方案,并对其实时钟差解算性能进行了系统性评估.该方法利用两个卫星系统的PPP服务改正数进行融合,显著提升了同一时刻内可用卫星数量.相较于单一PPP-B2b服务方案,在钟差解算的精度和稳定性方面具有明显提升.同时,实验结果表明,该方法在经过一定时间的收敛后,其性能优于德国波兹坦地学研究中心(German Research Centre for Geosciences,GFZ)提供的超快速(UTL)产品.因此,本文不仅为提高PPP-B2b服务的实际应用能力提供了有效途径,也为多系统融合下的实时时间解算方法设计与性能优化提供了新的思路和实验验证.展开更多
随着GNSS的不断发展,基于精密单点定位(precise point positioning,PPP)技术的高精度时间传递研究已成为时频领域的关键技术之一.本文以北斗三号系统解算接收机钟差为研究对象,分析了无电离层(ionospheric-free,IF)组合和非组合(uncombi...随着GNSS的不断发展,基于精密单点定位(precise point positioning,PPP)技术的高精度时间传递研究已成为时频领域的关键技术之一.本文以北斗三号系统解算接收机钟差为研究对象,分析了无电离层(ionospheric-free,IF)组合和非组合(uncombined,UC)PPP模型对时间传递的影响.首先推导了两种PPP数学模型差异,选取2024年年积日第79~81天的BRUX和USN7两个外接氢原子钟测站观测数据进行分析.结果表明:两种PPP模型解算的接收机钟差差值在0.15 ns内波动,修正的Allan方差数值接近;对BRUX-USN7时间链路对比分析,3天内时间传递结果均在0.8 ns内波动,两种模型解算钟差修正的Allan方差数值近似.综上,两种PPP模型虽然钟差数值解算的理论模型不同,但在钟差解算和时间传递方面无明显差异,非组合模型可以用来进行时间传递且在保留电离层信息方面更具有优势.展开更多
For multiple-input multiple-output （MIMO） orthogonal frequency division multiplexing （OFDM） systems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform ...For multiple-input multiple-output （MIMO） orthogonal frequency division multiplexing （OFDM） systems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform （FRFT） is proposed. The linear frequency modulation signals superimposed on the data signals are used as the training signals. By performing FRFT on the received signals and searching the peak value of the FRFT results, the receiver can realize timing synchronization and frequency offset acquisition simultaneously. Compared with the existing methods, the proposed algorithm can provide better timing synchronization performance and larger frequency offset acquisition range even under multi-path channels with low signal to noise ratio. Theoretical analysis and simulation results prove this point.展开更多
In this paper, we consider the frequency offset estimation for Orthogonal Frequency-Division Multiple Access (OF-DMA) uplink (UL) transmissions. We first analyze the negative effect of Multi-Access-Interference (MAI) ...In this paper, we consider the frequency offset estimation for Orthogonal Frequency-Division Multiple Access (OF-DMA) uplink (UL) transmissions. We first analyze the negative effect of Multi-Access-Interference (MAI) on OFDMA UL, and then propose two interference reduction/elimination methods, i.e., the Reduced-Rank-Projector (RRP) and Shift-Sampling-Projector (SSP) methods, to eliminate/reduce the heavy MAI due to the frequency offsets. Finally, we propose a new training sequence group named the Round-Robin Training Sequence Group (RRTSG), which has a high interference mitigation capabilities for OFDMA UL transmission. The Cramer-Rao Lower Bound (CRLB) for an unbiased frequency offset estimator in a Multiple Access (MA) system is also derived. Numerical results show that the proposed methods are suitable to eliminate/mitigate the effect of the frequency offset on OFDMA UL transmission.展开更多
In this study, a series of tests have been conducted in order to investigate the machinability evaluation of austenitic Hadfield manganese steel in the Wire Electrical Discharge Machine (WEDM). Experimental investigat...In this study, a series of tests have been conducted in order to investigate the machinability evaluation of austenitic Hadfield manganese steel in the Wire Electrical Discharge Machine (WEDM). Experimental investigations have been carried out to relate the effect of input machining parameters such as pulse on-time (Ton), pulse off-time (Toff), wire feed (WF), and average gap voltage (V) on the wire offset in WEDM. No analytical approach gives the exact amount of offset required in WEDM and hence experimental study has been undertaken. In this paper, a mathematical model has been developed to model the machinability evaluation through the response surface methodology (RSM) capable of predicting the response parameter as a function of Ton, Toff, WF and V. The samples are tested and their average prediction error has been calculated taking the average of all the individual prediction errors. The result shows that this mathematical model reflects the independent, quadratic and interactive effects of the various machining parameters on cutting speed in WEDM process.展开更多
One of the important aspects in wireless sensor networks is time synchronization. Many applications such as military activity monitoring, environmental monitoring and forest fire monitoring require highly accurate tim...One of the important aspects in wireless sensor networks is time synchronization. Many applications such as military activity monitoring, environmental monitoring and forest fire monitoring require highly accurate time synchronization. Time synchronization assures that all the sensor nodes in wireless sensor network have the same clock time. It is not only essential for aforementioned applications but it is mandatory for TDMA scheduling and proper duty cycle coordination. Time synchronization is a challenging problem due to energy constraints. Most of the existing synchronization protocols use fixed nodes for synchronization, but in the proposed synchronization, algorithm mobile nodes are used to synchronize the stationary nodes in the sensing field. In this paper, we propose a new time synchronization algorithm, named controlled mobility time synchronization (CMTS) with the objective to achieve the higher accuracy while synchronizing the nodes. The proposed approach is used in this paper to synchronize the nodes externally by using the mobile nodes. Simulation results exhibit that proposed controlled mobility time synchronization increases the synchronization precision and reduces the energy consumption as well as synchronization error by reducing the collisions and retransmissions.展开更多
Time synchronization is one of the important aspects in wireless sensor networks. Time synchronization assures that all the sensor nodes in wireless sensor network have the same clock time. There are various applicati...Time synchronization is one of the important aspects in wireless sensor networks. Time synchronization assures that all the sensor nodes in wireless sensor network have the same clock time. There are various applications such as seismic study, military applications, pollution monitoring where sensor nodes require synchronized time. Time synchronization is mandatory for many wireless sensor networks protocols such as MAC protocols and also important for TDMA scheduling for proper duty cycle coordination. Time synchronization is a stimulating problem in wireless sensor networks because each node has its own local clock which keeps on varying due to variation in the oscillator frequency. The oscillator frequency is time varying due to ambient conditions which leads to re-synchronization of nodes time and again. This re-synchronization process is energy consuming whereas energy is constraints in WSN. This paper proposes a novel cluster based time synchronization technique for wireless sensor networks in which cluster head rotation is based on minimum clock offset. Simulation results based on energy analysis of the proposed model demonstrate that proposed novel cluster based time synchronization technique reduces the energy consumption and also the synchronization error compared with other existing protocols.展开更多
文摘This paper analyzes the necessity of the measurement of one-way delay, and it also points out the errors caused by the time offset between measurement devices. Then we propose an algorithm to estimate time offset between measurement devices in network. With the estimated time offset, we can correct our measuring results. Simulation shows the effectiveness of our algorithm.
文摘Due to the neglect of the retrieval of communication parameters(including the symbol rate,the symbol timing offset,and the carrier frequency),the existing non-cooperative communication mode recognizers suffer from the generality ability degradation and severe difficulty in distinguishing a large number of modulation modes,etc.To overcome these drawbacks,this paper proposes an efficient communication mode recognizer consisting of communication parameter estimation,the constellation diagram retrieval,and a classification network.In particular,we define a 2-D symbol synchronization metric to retrieve both the symbol rate and the symbol timing offset,whereas a constellation dispersity annealing procedure is devised to correct the carrier frequency accurately.Owing to the accurate estimation of these crucial parameters,high-regularity constellation maps can be retrieved and thus simplify the subsequent classification work.Numerical results show that the proposed communication mode recognizer acquires higher classification accuracy,stronger anti-noise robustness,and higher applicability of distinguishing multiple types,which presents the proposed scheme with vast applicable potentials in non-cooperative scenarios.
文摘针对北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)精密单点定位(precise point positioning,PPP)服务PPP-B2b在同一时刻可用于PPP的卫星数量有限,以及其实时钟差解算评估研究较少的问题,本文提出了一种基于BDS PPP-B2b与Galileo高精度服务(high accuracy service,HAS)融合的改进方案,并对其实时钟差解算性能进行了系统性评估.该方法利用两个卫星系统的PPP服务改正数进行融合,显著提升了同一时刻内可用卫星数量.相较于单一PPP-B2b服务方案,在钟差解算的精度和稳定性方面具有明显提升.同时,实验结果表明,该方法在经过一定时间的收敛后,其性能优于德国波兹坦地学研究中心(German Research Centre for Geosciences,GFZ)提供的超快速(UTL)产品.因此,本文不仅为提高PPP-B2b服务的实际应用能力提供了有效途径,也为多系统融合下的实时时间解算方法设计与性能优化提供了新的思路和实验验证.
文摘随着GNSS的不断发展,基于精密单点定位(precise point positioning,PPP)技术的高精度时间传递研究已成为时频领域的关键技术之一.本文以北斗三号系统解算接收机钟差为研究对象,分析了无电离层(ionospheric-free,IF)组合和非组合(uncombined,UC)PPP模型对时间传递的影响.首先推导了两种PPP数学模型差异,选取2024年年积日第79~81天的BRUX和USN7两个外接氢原子钟测站观测数据进行分析.结果表明:两种PPP模型解算的接收机钟差差值在0.15 ns内波动,修正的Allan方差数值接近;对BRUX-USN7时间链路对比分析,3天内时间传递结果均在0.8 ns内波动,两种模型解算钟差修正的Allan方差数值近似.综上,两种PPP模型虽然钟差数值解算的理论模型不同,但在钟差解算和时间传递方面无明显差异,非组合模型可以用来进行时间传递且在保留电离层信息方面更具有优势.
基金supported by the National Natural Science Foundation of China(60672047).
文摘For multiple-input multiple-output （MIMO） orthogonal frequency division multiplexing （OFDM） systems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform （FRFT） is proposed. The linear frequency modulation signals superimposed on the data signals are used as the training signals. By performing FRFT on the received signals and searching the peak value of the FRFT results, the receiver can realize timing synchronization and frequency offset acquisition simultaneously. Compared with the existing methods, the proposed algorithm can provide better timing synchronization performance and larger frequency offset acquisition range even under multi-path channels with low signal to noise ratio. Theoretical analysis and simulation results prove this point.
文摘In this paper, we consider the frequency offset estimation for Orthogonal Frequency-Division Multiple Access (OF-DMA) uplink (UL) transmissions. We first analyze the negative effect of Multi-Access-Interference (MAI) on OFDMA UL, and then propose two interference reduction/elimination methods, i.e., the Reduced-Rank-Projector (RRP) and Shift-Sampling-Projector (SSP) methods, to eliminate/reduce the heavy MAI due to the frequency offsets. Finally, we propose a new training sequence group named the Round-Robin Training Sequence Group (RRTSG), which has a high interference mitigation capabilities for OFDMA UL transmission. The Cramer-Rao Lower Bound (CRLB) for an unbiased frequency offset estimator in a Multiple Access (MA) system is also derived. Numerical results show that the proposed methods are suitable to eliminate/mitigate the effect of the frequency offset on OFDMA UL transmission.
文摘In this study, a series of tests have been conducted in order to investigate the machinability evaluation of austenitic Hadfield manganese steel in the Wire Electrical Discharge Machine (WEDM). Experimental investigations have been carried out to relate the effect of input machining parameters such as pulse on-time (Ton), pulse off-time (Toff), wire feed (WF), and average gap voltage (V) on the wire offset in WEDM. No analytical approach gives the exact amount of offset required in WEDM and hence experimental study has been undertaken. In this paper, a mathematical model has been developed to model the machinability evaluation through the response surface methodology (RSM) capable of predicting the response parameter as a function of Ton, Toff, WF and V. The samples are tested and their average prediction error has been calculated taking the average of all the individual prediction errors. The result shows that this mathematical model reflects the independent, quadratic and interactive effects of the various machining parameters on cutting speed in WEDM process.
文摘One of the important aspects in wireless sensor networks is time synchronization. Many applications such as military activity monitoring, environmental monitoring and forest fire monitoring require highly accurate time synchronization. Time synchronization assures that all the sensor nodes in wireless sensor network have the same clock time. It is not only essential for aforementioned applications but it is mandatory for TDMA scheduling and proper duty cycle coordination. Time synchronization is a challenging problem due to energy constraints. Most of the existing synchronization protocols use fixed nodes for synchronization, but in the proposed synchronization, algorithm mobile nodes are used to synchronize the stationary nodes in the sensing field. In this paper, we propose a new time synchronization algorithm, named controlled mobility time synchronization (CMTS) with the objective to achieve the higher accuracy while synchronizing the nodes. The proposed approach is used in this paper to synchronize the nodes externally by using the mobile nodes. Simulation results exhibit that proposed controlled mobility time synchronization increases the synchronization precision and reduces the energy consumption as well as synchronization error by reducing the collisions and retransmissions.
文摘Time synchronization is one of the important aspects in wireless sensor networks. Time synchronization assures that all the sensor nodes in wireless sensor network have the same clock time. There are various applications such as seismic study, military applications, pollution monitoring where sensor nodes require synchronized time. Time synchronization is mandatory for many wireless sensor networks protocols such as MAC protocols and also important for TDMA scheduling for proper duty cycle coordination. Time synchronization is a stimulating problem in wireless sensor networks because each node has its own local clock which keeps on varying due to variation in the oscillator frequency. The oscillator frequency is time varying due to ambient conditions which leads to re-synchronization of nodes time and again. This re-synchronization process is energy consuming whereas energy is constraints in WSN. This paper proposes a novel cluster based time synchronization technique for wireless sensor networks in which cluster head rotation is based on minimum clock offset. Simulation results based on energy analysis of the proposed model demonstrate that proposed novel cluster based time synchronization technique reduces the energy consumption and also the synchronization error compared with other existing protocols.
