共查询到20条相似文献，搜索用时 562 毫秒
1.
With the proposed new GNSS signals, enhanced navigation performance is expected in both civil and military applications. However, these new signals introduce the difficulty of combining multiple signal components into a constant-envelope signal. For the Compass B1 band, the problem is to multiplex a QPSK(2) signal and a new multiplexed binary offset carrier (MBOC) signal with a center frequency difference of 14.322 MHz. One approach for multiplexing spreading codes is the phase-optimized constant-envelope transmission (POCET) method proposed for the GPS L1 band. However, only binary spreading codes are considered in POCET. We first generalize the POCET method as a multilevel POCET (MPOCET) algorithm for multilevel coded signals. A new implementation of the alternative binary offset carrier (AltBOC) generator is derived from MPOCET. Secondly, the multiplexing problem for Compass is modeled by MPOCET. Multilevel subcarriers of AltBOC are adopted in the model. As a result, an 8-PSK unbalanced AltBOC (UAltBOC) modulation, which has a QPSK(2) signal at the lower sideband and a TMBOC signal at the upper sideband, is obtained. Simulations for signal model validation and power spectrum analysis are conducted. Numerical results indicate that UAltBOC successfully combines the QPSK and TMBOC signals with only 0.16-dB additional combining loss compared to AltBOC. The proposed MPOCET technique is demonstrated as a unified multiplexing method for navigation signals. 相似文献
2.
Emilie Rebeyrol Olivier Julien Christophe Macabiau Lionel Ries Antoine Delatour Laurent Lestarquit 《GPS Solutions》2007,11(3):159-171
Spectrum limitations for navigation systems require that the various navigation signals broadcast by the Galileo system must
be combined and must utilize bandwidth-efficient modulations. At the L1 band, one of the most important questions is how to
combine all the Open Service signals and the Public Regulated Service signal at the payload level, while maintaining good
performance at reception. The Interplex modulation, a particular phase-shifted-keyed/phase modulation (PSK/PM), was chosen
to transmit these signals because it is a constant-envelope modulation, thereby allowing the use of saturated power amplifiers
with limited signal distortion. The Interplex modulation was also taken as baseline at the E6 band to transmit the three channels
and the services associated on the same carrier frequency. At the E5 band, the modulation must combine two different services
on a same constant envelope composite signal, while keeping the simplicity of a BOC implementation. The constant envelope
Alternate Binary Offset Carrier (ALTBOC) modulation was chosen as the solution to transmit the Galileo E5 band signal. The
main objective of this paper is to study these Galileo modulations. After the introduction, the E5 band signals are described,
followed by the Alternate BOC modulation which has been chosen to transmit them. The second part describes the general formulation
of the Interplex modulation and its key parameters for an optimal multiplexing of the Galileo L1 band signals. Since the Galileo
Open Service signals at the L1 band are still not yet completely specified, different test cases are considered and their
impact on the resulting choice for the Interplex modulation parameters is exposed. 相似文献
3.
针对传统的互复用调制方法中,8种不同的输入信号组合值与6个不同相位量之间对应关系模糊的问题,提出了三码八相的互复用调制方法。基于三码八相互复用调制方法,利用与3路输入信号相关的指数因子,推导出了新的互复用基带调制信号表达式,实现了复用调制信号的相位翻转,得到了8个不同的相位值。仿真结果显示,三码八相互复用调制方法,保证了复用调制信号的恒包络特性,解决了输入码组合值与相位量之间对应关系的模糊度问题,研究结果对于GNSS组合中的信号调制有一定的参考价值。 相似文献
4.
运用Hilbert-Huang变换（HHT）从时频域的角度对大坝监测资料进行了分析。通过经验模态分解（empirical mode decomposition,EMD）,测值序列被分解为以不同频率波动的内在模态分量（IMF）和代表序列变化趋势性的余量,其分解所得的各IMF分量的变化具有调幅调频特征,余量则可以反映测值趋势性变化的局部特征。效应量和环境量测值的Hilbert谱存在一定的相似性,测值变化的调幅调频特征反映了大坝、基岩和周围环境组成的复杂系统的非线性和非平稳性。 相似文献
5.
在Galileo系统建设和GPS现代化的进程中，为实现与BPSK（Bi-phase Shift Keying）的频谱分离，采用了BOC（Binary Offset Carrier）调制。BOC调制在码跟踪精度、多径抑制等方面比BPSK调制具有更好的性能，但其自相关函数的多相关峰特性使得在测距中可能产生偏差，因此，消除相关峰的模糊度是BOC信号接收中非常关键的问题。介绍了一种基于QBOC码的BOC信号码跟踪环路（“BOC十QBOC-BOC”），并推导出该环路码跟踪性能的解析表达式，最后的仿真结果验证了理论推导的正确性，可为BOC信号接收机的设计提供参考。 相似文献
6.
Xiaoli Liu Muqing Liang Yu Morton Pau Closas Ting Zhang Zhigang Hong 《GPS Solutions》2014,18(2):163-175
The objective of this work is to investigate the performances of orthogonal frequency division multiplexing (OFDM) and minimum frequency shift keying (MSK) modulations as potential future global navigation satellite systems (GNSS) signal modulation schemes. MSK is used in global system for mobile communications because of its spectral efficiency, while OFDM is used in WLAN and digital video broadcast-terrestrial because of its multipath mitigation capability. These advantages of MSK and OFDM modulations render them as promising modulation candidates for future GNSS signals to offer enhanced performances in challenging environments. Gabor bandwidth and multipath error envelopes of these two modulations were computed and compared with those of the current global positioning system (GPS), Galileo, and Beidou signal modulations. The results show that OFDM modulation demonstrated promises as a viable future GNSS modulation, especially for signals that require pre-filtering bandwidths larger than 2 MHz, while MSK modulation is more desirable for pre-filtering bandwidth below 2 MHz where it exhibits the largest Gabor bandwidth. 相似文献
7.
G. C. Brock 《The Photogrammetric Record》1968,6(31):32-40
Photography of models and modulation transfer function analysis have been used to investigate the common belief that in aerial photography large-scale images are preferable to small-scale images, even when the resolving power in terms of ground dimensions is the same. The belief was found to be justified for two extreme cases representing, respectively, a small scale, mainly grain-limited system, and a large scale, wholly lens-limited system, for which the ground resolutions were equal on three-bar targets of 3 to 1 contrast (modulation 0–5). Resolving power tests would have been misleading for these two systems even at a target contrast of less than 2 to 1 (modulation less than 0–3). 相似文献
8.
Infrared (IR) imagery of microbreaking waves in the ocean and laboratory showed modulation of breaking by swell and paddle-generated waves, respectively. Skin temperature also was modulated by the long waves, with the maxima occurring on the rear face of the long waves in both the laboratory and the field. The IR imagery from the ocean and laboratory showed that long-wave-induced microbreaking occurred at or near the long wave crest, and the resulting warm wakes occurred on the rear face. Thus, microbreaking waves generated near the crest of low-amplitude long waves can produce modulation with the maxima on the rear face. This mechanism was shown to be responsible for modulation of the measured in the laboratory and also likely contributed to the modulation observed in the field. 相似文献
9.
10.
高空间分辨率影像与多光谱影像融合,为影像处理提供了更加丰富的资源,有利于进行影像的分析和制图。本文以庐山及其周边区域的2009年5月11日LandsatETM＋与2009年5月6日SPOT5影像数据为例,对典型的融合方法进行了对比评价。融合方法包括加权融合法,HIS变换,改进的HIS变换,高频调制融合法（频域采用Butterworth滤波器．指数滤波器）,HSV变换,Brovey变换,CN变换,PC变换,Gram—Schmidt变换11种方法。评价指标为相关系数、信息熵、标准差、平均梯度、相对偏差、标准偏差。结果表明,不同的融合结果突出的侧重点不同。加权融合法、Grain—Schmidt变换,PC变换方法突出了影像的信息量丰富度、清晰度,提高空间分辨率能力。CN波谱锐化,改进的HIS变换,BWO高频调制融合,指数高频调制融合方法光谱保真度较好。改进的HIS变换,BWO高频调制融合,CN波谱锐化,指数高频调制融合法在空间分辨率及光谱保真度、清晰度、信息丰富度方面的能力较均衡。 相似文献
11.
增强型罗兰(eLoran)系统是精确时频信息的一个重要来源,且为全球卫星导航系统(GNSS)的有效备份．本文针对目前eLoran信号调制方式较单一,数据传输速率低的问题,同时为充分运用时频资源、扩大信息播发数据量与应用范围,提出一种提高信号信息携带能力的调制方式和具有更高编码增益的信道编码方式．新型的脉冲调制方式增加仅用于数据传输脉冲组的调制方式,可实现40~200 bps的传输速率．仿真实验表明,数据信息长度为215 bit左右,LDPC编码方式能够较好地兼顾编码增益和信号帧长． 相似文献
12.
13.
面向多接收模式的GNSS互操作信号调制 总被引：1，自引：0，他引：1
针对互操作信号在性能与处理复杂度上平衡点不唯一的特点,提出了一种非匹配接收模式下的信号性能评估方法,在此基础上为北斗二期B1频点互操作信号提出了4种参考调制方案,并从综合接收性能的角度给出了一种优选方案。与国际上现有的互操作信号调制方案相比,本文提出的优选方案可获得最小的解调损失以及最佳的跟踪性能,在处理方式灵活性方面具有其独特的优势,可以作为我国自主GNSS信号体制设计和优化的一种可行的参考方案。 相似文献
14.
15.
对全球导航卫星的信号体制进行了专利检索分析,综合考虑信号调制、多路复用等技术,分别以导航卫星的信号调制方式、信号生成方式、信号编码方式为检索领域,对全球导航卫星系统申请专利进行全面而系统的检索。在初检基础上,以空间段、星上技术为依据进行复检并深入分析,指出该领域未来发展方向。为我国未来全球导航卫星系统信号体制的设计提出知识产权规避措施和发展建议。 相似文献
16.
17.
18.
针对小数据量矢量地理数据的版权保护需求,提出了一种基于压缩感知和多段量化调制的矢量地理数据水印算法。水印信息生成中,对二值水印图像分块稀疏表达并运用压缩感知理论进行测量,构建量化表将测量结果调制为量化值,从而压缩水印信息并保证水印信息的可重构性。在水印嵌入过程中,提出基于角度的多段量化水印嵌入机制,建立水印量化值和角度量化区间的映射关系,对矢量数据相邻节点形成的夹角进行多段量化调制并嵌入水印,提高每个节点承载的水印容量。试验结果表明,算法能够对100个点的矢量数据嵌入并检测水印信息,水印容量达每节点7 bit,且对增点、删点、排序、平移、旋转、缩放等攻击具有好的稳健性,有效解决了水印容量与小数据量之间的矛盾。 相似文献
19.
GPS Solutions - Binary offset carrier (BOC) modulation technology is widely used in newly developed and modernized global navigation satellite systems. BOC signal offers superior performance over... 相似文献
20.
GPS Solutions - Receiver design challenges arising from new GNSS signals include required intermediate frequency, sampling rate, modulation type, spreading code, and secondary code. Several... 相似文献