For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum(DSSS) systems,a new single decision algorithm is presented.The maximum value of correlation results is co...For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum(DSSS) systems,a new single decision algorithm is presented.The maximum value of correlation results is conventionally detected.However,there may be not only one strong peak among correlation results when the cross-correlation noise is strong enough to affect the correlation results.The proposed algorithm decreases the false alarm probability through the decision of the ratio of the maximum value and the second maximum value of the correlation results.Theoretical analysis and simulation results indicate that the proposed algorithm effectively suppresses the acquisition problem of multiple access interference in DSSS system.展开更多
Frequency Hopping Spread Spectrum (FHSS) system is often deployed to protect wireless communication from jamming or to preclude undesired reception of the signal. Such themes can only be achieved if the jammer or unde...Frequency Hopping Spread Spectrum (FHSS) system is often deployed to protect wireless communication from jamming or to preclude undesired reception of the signal. Such themes can only be achieved if the jammer or undesired receiver does not have the knowledge of the spreading code. For this reason, unencrypted M-sequences are a deficient choice for the spreading code when a high level of security is required. The primary objective of this paper is to analyze vulnerability of linear feedback shift register (LFSRs) codes. Then, a new method based on encryption algorithm applied over spreading codes, named hidden frequency hopping is proposed to improve the security of FHSS. The proposed encryption security algorithm is highly reliable, and can be applied to all existing data communication systems based on spread spectrum techniques. Since the multi-user detection is an inherent characteristic for FHSS, the multi-user interference must be studied carefully. Hence, a new method called optimum pair “key-input” selection is proposed which reduces interference below the desired constant threshold.展开更多
With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based ...With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based underwater acoustic communication system using dual spread spectrum code is proposed. To solve the contradictions between the information data rate and the accuracy of Doppler estimation, channel estimation, and frame synchronization, a data frame structure based on dual spread spectrum code is designed. A long spread spectrum code is used as the training sequence, which can be used for data frame detection and synchronization, Doppler estimation, and channel estimation. A short spread spectrum code is used to modulate the effective information data. A delay cross-correlation algorithm is used for Doppler estimation, and a correlation algorithm is used for channel estimation. For underwater networking, each user is assigned a different pair of spread spectrum codes. Simulation results show that the system has a good anti-multipath, anti-interference, and anti-Doppler performance, the bit error rate can be smaller than 10^(-6) when the signal-to-noise ratio is larger than-10 dB, the data rate can be as high as 355 bits/s, and the system can be used in the downlink of CDMA based networks.展开更多
针对具有空时分组码的多载波CDMA(Space Time Block Coding Multi Carrier Code Division Multiple Access,STBC-MC-CDMA)信号扩频码及信息序列的联合估计问题,结合序贯蒙特卡罗(Sequential Monte Carlo,SMC)算法和卡尔曼滤波技术,充分...针对具有空时分组码的多载波CDMA(Space Time Block Coding Multi Carrier Code Division Multiple Access,STBC-MC-CDMA)信号扩频码及信息序列的联合估计问题,结合序贯蒙特卡罗(Sequential Monte Carlo,SMC)算法和卡尔曼滤波技术,充分利用STBC和OFDM(Orthogonal Frequency Division Multiplexing)调制的正交属性,提出了一种快速的盲解扩算法.该算法通过将信号模型按不同符号路数和天线数目进行分段处理,采用卡尔曼滤波方法对均值和协方差进行迭代更新,并用一组带有权值的抽样粒子来近似建立的联合后验概率分布,根据抽样值和重要性权值大小进行参量状态估计,大大提高了算法的计算效率.理论分析和仿真结果验证了本文算法的有效性.展开更多
基金supported by the National High Technology ResearchDevelopment Program of China (863 Program) (2008AA0248)
文摘For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum(DSSS) systems,a new single decision algorithm is presented.The maximum value of correlation results is conventionally detected.However,there may be not only one strong peak among correlation results when the cross-correlation noise is strong enough to affect the correlation results.The proposed algorithm decreases the false alarm probability through the decision of the ratio of the maximum value and the second maximum value of the correlation results.Theoretical analysis and simulation results indicate that the proposed algorithm effectively suppresses the acquisition problem of multiple access interference in DSSS system.
文摘Frequency Hopping Spread Spectrum (FHSS) system is often deployed to protect wireless communication from jamming or to preclude undesired reception of the signal. Such themes can only be achieved if the jammer or undesired receiver does not have the knowledge of the spreading code. For this reason, unencrypted M-sequences are a deficient choice for the spreading code when a high level of security is required. The primary objective of this paper is to analyze vulnerability of linear feedback shift register (LFSRs) codes. Then, a new method based on encryption algorithm applied over spreading codes, named hidden frequency hopping is proposed to improve the security of FHSS. The proposed encryption security algorithm is highly reliable, and can be applied to all existing data communication systems based on spread spectrum techniques. Since the multi-user detection is an inherent characteristic for FHSS, the multi-user interference must be studied carefully. Hence, a new method called optimum pair “key-input” selection is proposed which reduces interference below the desired constant threshold.
基金Project supported by the National Natural Science Foundation of China(Nos.61431005,51409235,and 61401111)the Fundamental Research Funds for the Central Universities,China(No.201213004)
文摘With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based underwater acoustic communication system using dual spread spectrum code is proposed. To solve the contradictions between the information data rate and the accuracy of Doppler estimation, channel estimation, and frame synchronization, a data frame structure based on dual spread spectrum code is designed. A long spread spectrum code is used as the training sequence, which can be used for data frame detection and synchronization, Doppler estimation, and channel estimation. A short spread spectrum code is used to modulate the effective information data. A delay cross-correlation algorithm is used for Doppler estimation, and a correlation algorithm is used for channel estimation. For underwater networking, each user is assigned a different pair of spread spectrum codes. Simulation results show that the system has a good anti-multipath, anti-interference, and anti-Doppler performance, the bit error rate can be smaller than 10^(-6) when the signal-to-noise ratio is larger than-10 dB, the data rate can be as high as 355 bits/s, and the system can be used in the downlink of CDMA based networks.
文摘针对具有空时分组码的多载波CDMA(Space Time Block Coding Multi Carrier Code Division Multiple Access,STBC-MC-CDMA)信号扩频码及信息序列的联合估计问题,结合序贯蒙特卡罗(Sequential Monte Carlo,SMC)算法和卡尔曼滤波技术,充分利用STBC和OFDM(Orthogonal Frequency Division Multiplexing)调制的正交属性,提出了一种快速的盲解扩算法.该算法通过将信号模型按不同符号路数和天线数目进行分段处理,采用卡尔曼滤波方法对均值和协方差进行迭代更新,并用一组带有权值的抽样粒子来近似建立的联合后验概率分布,根据抽样值和重要性权值大小进行参量状态估计,大大提高了算法的计算效率.理论分析和仿真结果验证了本文算法的有效性.
