IFFT频谱相除技术在罗兰C接收机中的应用

罗兰C无线电导航接收机接收带有天波干扰的地波信号，其中天波的到达相对于地波的到达时间有一定的延迟。但是，由于接收机的有限带宽的影响，使得天波干扰的存在严重影响了接收机的性能。应用IFFT频谱相除技术不但能够精确的检测到天波相对于地波的延迟时间、天地波强度之比，同时能够精确的得到地波的到达时间．因此，这种方法不但可以有效的实现天波和地波的分离，而且应用地波到达的精确时间可以实现准确的周期识别，大大减小了周期识别的计算量。     

罗兰C接收机天波识别技术研究

使用现代谱估计技术进行罗兰C接收机的天波延迟估计,有效地解决了常规接收机基准点固定的问题。文章提出的方法,在不断变化的天波干扰环境下根据数据调节相应的采样点,在低信噪比条件下分离出了地波和天波的到达时刻,且具有较高的分辨率。本文对基于参数建模和特征值分解的算法进行了讨论,充分说明了现代谱估计技术能减少对准基准点的时间,可提高现有罗兰C接收机的性能。     

罗兰C天波授时信号研究

介绍了长波天波传播特性,阐述了罗兰C天波信号实测试验的原理,通过对试验数据的研究分析,得出罗兰C天波信号覆盖范围、修正精度及昼夜变化规律,给出了天波使用的有关建议。     

多微处理器系统及其在罗兰C接收机中的应用

多微处理器系统是目前被广泛应用的一种计算机技术，也是计算机技术的发展方向之一，对多微处理器系统在两种罗兰Ｃ接收机中的应用进行了分析与比较，指出在高性能罗兰Ｃ接收机的嵌入式系统设计中，采用多微处理器系统是一种比较理想的方案。     

GPS传感器与罗兰C接收机镶嵌技术

介绍了把ＧＰＳ传感器镶嵌入已定型的罗兰Ｃ接收机的构想，并且详细讲述了具体的镶嵌方法，对大量正在使用中的罗兰Ｃ接收机的升级改造十分有用。镶嵌后的接收机将是一个ＧＰＳ／罗兰Ｃ组合导航系统。     

各向同性电离层低频一跳天波时延特性研究

低频天波的准确预测对于低电离层探测、远程导航授时具有重要意义。该文基于传统“波跳”理论和FDTD方法对地-电离层波导中天波传播时延特性进行研究。结合天地波时域分离技术,给出了100 kHz载频罗兰-C信号在均匀/指数渐变各向同性电离层条件下,距发射台200 km范围内采用两种方法计算的一跳天波时延随收发距离的变化规律。与“波跳”理论相比,该方法可同时考虑地面不规则、电离层昼夜参数分布不均匀的影响,计算精度更高。     

一种基于短时傅里叶变换的罗兰C信号频谱分析方法

当前对罗兰 C 信号的频谱分析基本上采用的是基于傅里叶变换法的频谱分析方法, 此类方法无法实现对信号频谱的实时监测。采用短时傅里叶变换法(STFT)对不同信干比、天波幅度和时延条件影响下的罗兰 C 信号进行理论建模与仿真,并建立信号的时频数据库。通过对罗兰 C 信号的 STFT 分析,并与时频数据库进行谱峰比对,可有效解决实时性要求较高的天地波识别与天波时延测量问题。     

水下罗兰C接收机的电磁兼容设计

介绍了罗兰C接收机电磁兼容的设计思想，详细叙述了电磁屏蔽设计方法及干扰抑制方法，给出了电磁兼容的测试结果。     

对罗兰C信号处理方法的探讨

通过提出新的处理罗兰C信号的方法，对有效提高空用罗兰C接收机的性能有重要的意义。     

基于DSP的新型罗兰C接收机

介绍了一种采用DSP芯片技术的新型罗兰C接收机。它利用DSP的高速数据处理能力，实力自适应滤波和16位ADC技术，来提高接收机的性能。     

Loran-C skywave delay estimation using eigen-decompositiontechniques

A novel eigen-decomposition technique for estimating the delays of Loran-C skywave components is presented. This provides the basis for a new generation of receivers which implement adaptive skywave interference monitoring, enhancing reliability and positioning accuracy. Performance of the new technique is demonstrated using off-air data     

High resolution techniques for Loran-C skywave delay estimation

Two high-resolution estimation techniques are applied to the problem of estimating the delays of the skywave components of signals input to Loran-C receivers. Their performance is evaluated and compared with that of a Fourier-based spectral-division technique. Simulation results show that the high-resolution algorithms improve the accuracy of the estimates significantly and estimate the skywave delay successfully in situations in which the Fourier-based method fails     

天波超视距雷达中瞬态干扰定位方法研究

为了对抗天波超视距雷达中的瞬态干扰,现有时域算法一般有干扰定位、干扰剔除与数据恢复3个步骤,其中干扰定位的精度直接决定了后续处理的性能。目前工程中应用的固定门限方法定位精度不够,而现有文献中提出的方法运算量较大,且对参数的选择较为敏感。针对这一问题,该文提出一种迭代剔除平均检测器。此检测器将判决为干扰的样本点剔除出迭代平均的过程,并采用前-后向检测的定位方法,保证了背景估计与干扰定位的可靠性。天波超视距雷达的实测数据处理结果证明了所提方法的有效性。     

High power broadcasting skywave transmitters interference analysisfor navigation and communication systems

The operation of high-power broadcasting transmitters (Tx) can strongly interfere with collocated and even remote radio communication and navigation systems on broad frequency ranges. In these cases, extensive analysis and computation method developments are essential in order to assess the feasibility of reliable operation of indispensable radio communication links. The magnitudes of the interference effects are computed, based on specifications of 500 kW skywave Tx parameters and the important airborne VHF radio navigation and communication systems. The critical interference (i.e. desensitization or blocking of the victim airborne receivers) and other interference modes are analyzed using semiempirical state-of-the-art computation methods. Limits for victim receiver distances and frequency intervals for no-interference situations and optimal reception conditions are obtained     

Performance of Partial Response CPM in the Presence of Adjacent Channel Interference and Gaussian Noise

Partial response continuous phase modulation (CPM) schemes have found wide acceptance because of their compact spectra and comparable performance with other traditional modulation schemes. Although optimum receivers are complex, simple suboptimum receivers are found to yield very good performance in special cases. Performance of such modulation schemes is of interest in a multiple user environment where adjacent channels are spaced closely to improve the system capacity. This paper presents the performance of partial response CPM in the presence of adjacent channel interference and Gaussian noise. The meansquare crosstalk in CPM systems employing MSK-type receivers is formulated. Based on this formulation, a number of modulation schemes employing different receiver filters are analyzed for their ACI rejection. Comparison of results proves that receiver filters, in addition to the spectral occupancy of the signal, play an important role in deciding the crosstalk. The error performance of various schemes evaluated using simulation technique is compared, and it is found that in the presence of adjacent channel interference, certain schemes perform better than minimum shift keying (MSK). The results of the simulation further prove the inadequacy of Gaussian assumption for the adjacent channel interference. It is seen that judicious choice of modulation scheme and receiver filter can result in better spectrum utilization.     

LF/MF skywave propagation at daytime

Interference from the daytime skywave signal of one broadcasting station to the groundwave signal of a co-channel station located several hundred kilometers away has been observed in certain parts of the world. The need for a better of skywave propagation at daytime, the Radiocommunications Sector of the International Telecommunications Union (ITU-R, formerly known as the International Radio Consultative Committee, CCIR) adopted Question 215/3 at its 1993 Radio Assembly. This paper is in direct response to this Question. Daytime measurements of more than 30 paths are believed to be skywave and have been studied for detailed information of these paths. The purpose of this paper is twofold: to discuss daytime skywave propagation in a qualitative manner and to present a simple procedure for estimating daytime skywave field strength and interference levels     

Linear multiuser receivers: effective interference, effectivebandwidth and user capacity

Multiuser receivers improve the performance of spread-spectrum and antenna-array systems by exploiting the structure of the multiaccess interference when demodulating the signal of a user. Much of the previous work on the performance analysis of multiuser receivers has focused on their ability to reject worst case interference. Their performance in a power-controlled network and the resulting user capacity are less well-understood. We show that in a large system with each user using random spreading sequences, the limiting interference effects under several linear multiuser receivers can be decoupled, such that each interferer can be ascribed a level of effective interference that it provides to the user to be demodulated. Applying these results to the uplink of a single power-controlled cell, we derive an effective bandwidth characterization of the user capacity: the signal-to-interference requirements of all the users can be met if and only if the sum of the effective bandwidths of the users is less than the total number of degrees of freedom in the system. The effective bandwidth of a user depends only on its own SIR requirement, and simple expressions are derived for three linear receivers: the conventional matched filter, the decorrelator, and the MMSE receiver. The effective bandwidths under the three receivers serve as a basis for performance comparison     

Reducing the effects of intersymbol interference with correlation receivers

This paper considers the problem of intersymbol interference in a binary communication system and the optimization of a class of linear receivers to minimize the effects of this interference. The class of correlation receivers is chosen for investigation, and maximizing the probability of correct reception is used as the performance criterion. The optimum decision level as well as optimum impulse response is determined for receivers with and without memory where a priori knowledge of the channel characteristics are available. The performances of these receivers are evaluated and compared with nonoptimum linear receivers.     

Adjacent-Cell Interference in Direct-Sequence CDMA Forward Traffic Channels

Each transmission from a base station in a mobile cellular direct-sequence CDMA network is a source of interference for the receivers in the mobile handsets that are operating in adjacent cells. This interference can limit the capacity of the forward traffic channels. The effect of adjacent-cell interference on the performance of the handset receivers is evaluated for a mobile cellular CDMA network that employs quadriphase-shift-key spreading, convolutional coding, and soft-decision decoding. It is demonstrated that acceptable performance may not be possible for a fully loaded cellular network. Of particular interest in this paper are cellular networks in which the base stations are mobile and must be interconnected by wireless communication links. Such networks are important for military applications and certain civilian emergency communications services.