Predicting and adapting satellite channels with weather-induced impairments

Efficiency improvements using predictive and adaptive methods over satellite channels with weather-induced impairments are presented. Scintillation and rain attenuation are the two dominant factors for signal fading over satellite-Earth paths at operating frequencies over 10 GHz. We develop statistical and spectral analyses of these processes, and obtain simple linear predictors for received signal attenuation using autoregressive (AR) models. For adaptation, we propose changing signal transmission power, modulation symbol size, and/or code rate as the state of the channel changes. In particular, we introduce a continuous power control and discrete rate control strategy. Quantitative analyses of power consumption and channel capacity indicate that there can be a substantial gain in performance with such adaptive schemes.     

Modeling and performance of HF/OTH radar target classificationsystems

The effects of a class of multipath propagation channels on the performance of a over-the-horizon (OTH) radar target classification system are considered. A Rician frequency-selective fading channel model is employed to characterize the effects of the multipath propagation medium and evaluate the performance of radar target classification systems. The performance of classification algorithms that employ relative amplitude, relative phase, and absolute amplitude measurements as features is investigated. Performance estimates of the various classification algorithms for interesting sets of channel parameters are obtained by means of Monte-Carlo simulations     

A One-bit Memory Receiver for Channels with Memory

A receiver is investigated with one-bit memory for communication channels with memory. The memory of the channel is characterized by the statistical correlation of the received bits due to fading. An optimal solution to the problem is considered but is found to be quite complex to implement. Therefore, a suboptimal receiver having a decision-feedback structure is examined. The performance of the receiver is shown to be better than a receiver without memory. Binary on-off keying system is considered as an example and numerical results are obtained.     

Multipath Fading in FSK Communication Links?An Experimental al Investigation

The results of an experimental investigation of binary error rates in an FSK channel experiencing nonselective fading are presented. For all cases considered, the received frequency uncertainty is large compareded to the bit rate, requiring the use of an envelope detector rather than a matched filter. Both slow and fast fading rates are considered and include the effects of differential Doppler shift between the direct and reflected energy. A simplified mathematical analysis is presented to support the observed results. Both the theoretical examination and the data obtained demonstrate that fast fading and/or differential Doppler generally improve the link error rate performance with respect to the nonfading case.     

Nonredundant error correction DQPSK for the aeronautical-satellitechannel

The performance of differentially encoded quadrature phase-shift keying (DQPSK) system employing nonredundant error correction (NEC) receivers with single- and double-error correction capability is analyzed and evaluated for the aeronautical satellite channel. The NEC is an attractive coding technique which employs differential detectors with more than one symbol delay elements and which does not introduce any redundancy as other coding schemes do. As typical for aeronautical satellite communications, a Rician fading channel with Gaussian power spectrum has been considered. Unlike the additive, uncorrelated from symbol to symbol interference such as additive white Gaussian noise (AWGN) or static cochannel interference (CCI) which has been investigated in the past, analysis of the performance in a fading channel is much more difficult. The difficulty arises from the multiplicative and correlative nature of the fading interference. Bit error rate (BER) performance evaluation results have been obtained by means of computer simulation for various channel conditions, including different values of the K-factor and the fading B_DT. These results have indicated that considerable performance gains as compared with conventional differentially detected systems are achieved for high values of K and for very fast fading. Both of these conditions are encountered in typical aeronautical communication systems. Wherever possible, heuristic explanations of the trend of the obtained BER performance evaluation results are also given     

基于Simulink?的复合衰落信道仿真与分析

基于Simulink平台建立了Rayleigh-Lognormal、Ricean-Lognormal、Nakagami-Lognormal复合衰落信道的仿真模型,这些模型可用于进行单频组网的DRM系统的设计和性能分析。给出了各种复合衰落的概率密度函数、累积分布函数、平均电平交叉率、平均衰落时间的统一表达式。仿真结果验证了理论分析结果的正确性。     

Decision fusion rules in multi-hop wireless sensor networks

The decision fusion problem for a wireless sensor network (WSN) operating in a fading environment is considered. In particular, we develop channel-aware decision fusion rules for resource-constrained WSNs where binary decisions from local sensors may need to be relayed through multi-hop transmission in order to reach a fusion center. Each relay node employs a binary relay scheme whereby the relay output is inferred from the channel impaired observation received from its source node. This estimated binary decision is subsequently transmitted to the next node until it reaches the fusion center. Under a flat fading channel model, we derive the optimum fusion rules at the fusion center for two cases. In the first case, we assume that the fusion center has knowledge of the fading channel gains at all hops. In the second case, we assume a Rayleigh fading model, and derive fusion rules utilizing only the fading channel statistics. We show that likelihood ratio (LR) based optimum decision fusion statistics for both cases reduce to respective simple linear test statistics in the low channel signal-to-noise ratio (SNR) regime. These suboptimum detectors are easy to implement and require little a priori information. Performance evaluation, including a study of the robustness of the fusion statistics with respect to unknown system parameters, is conducted through simulations.     

无人机中继平台覆盖区域统计模型

针对中继信号覆盖区域确定性模型没有考虑信道随机衰落影响的问题,提出了一种基于中断概率的无人机（UAVs）中继平台信号覆盖半径统计模型。通过将中继链路建模为包含路径损耗、阴影衰落和多径衰落的复合分布模型,推导获得中继信号覆盖半径的概率分布,并给出一种利用中断概率数值求解覆盖半径的方法。仿真结果表明,信道衰落对覆盖半径影响非常大,当中断概率小于10%时,覆盖半径仅为无衰落信道时的一半。研究结果对移动自组织网络（MANETs）中的中继网络的无人机最优布置、飞行策略以及网络性能评估等具有重要的参考价值。     

无人机中继平台覆盖区域统计模型简

 针对中继信号覆盖区域确定性模型没有考虑信道随机衰落影响的问题,提出了一种基于中断概率的无人机（UAVs）中继平台信号覆盖半径统计模型。通过将中继链路建模为包含路径损耗、阴影衰落和多径衰落的复合分布模型,推导获得中继信号覆盖半径的概率分布,并给出一种利用中断概率数值求解覆盖半径的方法。仿真结果表明,信道衰落对覆盖半径影响非常大,当中断概率小于10%时,覆盖半径仅为无衰落信道时的一半。研究结果对移动自组织网络（MANETs）中的中继网络的无人机最优布置、飞行策略以及网络性能评估等具有重要的参考价值。     

On Finite-Lag Receivers for Fading Channels

This paper reports some results on the development of finite-lag receivers for reception via fading channels. The receivers are given in discrete form and clearly show the additional complexity due to introduction of delay between the instants of reception and estimation of the signal. The channel noise has been assumed to have a multiplicative component due to fading. This results in the optimal demodulators being nonlinear and unrealizable. However, the receivers proposed are suboptimal, but realizable. Simulation studies evaluating the performance of the various receivers are also discussed.     

空射倾斜转弯导弹制导控制系统设计

讨论了空射 BTT 导弹的制导命令的生成,特别是针对纵向通道降高问题,设计了一种新的降高段控制指令,然后给出了三个通道的 PID 控制器。六自由度的仿真结果表明这种制导控制设计是成功的。     

Satellite mobile communication and radio positioning systemplanning aspects

System aspects of mobile communication and position determination by satellite are described. Topics of discussion are the choice of frequency, type of modulation/multiple access and system design, and considering the effects of active and passive intermodulation and multipath interference. Communication performance and position determination analyses are conducted with respect to small-scale domestic mobile communication systems, where the satellite mobile transponder constitutes only a fraction of the otherwise fixed services C-band or Ku-band payload, and where the orbit position of the spare satellite(s) is dictated by considerations other than purely radio positioning. The system tradeoffs and arguments presented lead to a particular modulation/multiple access system, which provides high channel capacity, good ranging accuracy, and high resistance to multipath fading     

多渐消因子Kalman滤波器在SINS初始对准中的应用(英文)

针对系统模型和统计信息不能精确已知的条件下Kalman滤波无法给出最优解这一问题,单一渐消因子Kalman滤波算法对于简单的系统是有效的,但是对于复杂的多变量系统,仅仅利用单个的渐消因子是不够的。本文提出了一种多渐消因子滤波算法,通过利用开窗法计算新息序列协方差的无偏估计获得渐消因子矩阵。利用渐消因子矩阵调节一步预测均方误差矩阵k|k1P,对不同的滤波通道提供不同的渐消速率。将该方法应用于SINS的初始对准中,仿真和试验结果表明:当真实系统噪声统计特性同设定参数不一致时,对准精度明显高于其他滤波算法。其对不确定性噪声具有较低的敏感度,对系统参数具有较好的滤波效果。因而,在实际应用中具有重要的参考价值。     

Spectral Location of Rayleigh and "m" Fading Signals in White Gaussian Noise

The classical problem is considered of locating a fading sinusoidal signal known to be present in one of several frequency " cells," each of which contains additive white Gaussian noise. The signal fading is assumed to follow the popular Rayleigh distribution, but generalizations tions to non-Rayleigh fading are included in terms of the " in" distribution due to Nakagami. The channel observation time is allowed to be either predetermined or variable (corresponding, respectively, to " fixed sample size" and " sequential" reception), and the practically important situation of intermittent signal transmissions is also examined. Results are in the form of optimal and near-optimal receiver structures, and of measures of performance.     

Fading from Irregular Surfaces for Line-of-Sight Communications

This paper is concerned with the communications channel between a planetary flyby or orbiting spacecraft and an ejected probe that is traveling toward the planet. Since the mission requires that a significant part of the probe's transmitted energy be reflected from the irregular planet's surface, we will be concerned with the effect of the scattered signal for line-of-sight communications. The statistical distribution of the received field and the fading rate are considered so that the fading margin may be determined for some required probability of satisfactory performance. Typical examples are given for a Martian atmospheric probe.     

衰落信道中不同集分割的Turbo TCM方案的性能研究

比较了衰落信道下两种不同的集分割方式,UP（Ungerboeck分割）和BP（分组分割）对Turbo TCM性能的影响。研究了在两种不同映射以及不同帧长度下Turbo TCM的性能。并给出了在8PSK和8ASK两种调制方式下的仿真试验结果,通过比较得出了很有意义的结果。     

π-TFSK时频调制信号的功率谱分析

 高速移动数据传输时,由高速移动而产生的衰落以及多径波的干扰,传输特性及差错率特性恶化,相移时频调制正是为了对抗衰落与多径延迟而产生。建立了π-TFSK时频调制的数学模型及其复数包络模型,在π-TFSK信号的复包络自相关函数的基础上计算了π-TFSK信号的功率谱密度,并对其进行了特性分析。     

Cross-layer design of LT codes and LDPC codes for satellite multimedia broadcast/multicast services

According to large coverage of satellites, there are various channel states in a satellite broadcasting network. In order to introduce an efficient rateless transmission method to satellite multimedia broadcasting/multicast services with finite-length packets, a cross-layer packet transmission method is proposed with Luby transform （LT） codes for efficiency in the network layer and low density parity check （LDPC） codes for reliability in the physical layer jointly. The codewords generated from an LT encoder are divided into finite-length packets, which are encoded by an LDPC encoder subsequently. Based on noise and fading effects of satellite channels, the LT packets received from an LDPC decoder either have no error or are marked as erased, which can be mod- eled as a binary erasure channels （BECs）. By theoretical analysis on LT parameters and LDPC parameters, the relationships between LDPC code rates in the physical layer and LT codes word lengths in the network layer are investigated. With tradeoffs between the LT codes word lengths and the LDPC code rates, optimized cross-layer solutions are achieved with a binary search algorithm. Verified by simulations, the proposed solution for cross-layer parameters design can provide the best transmission mode according to satellite states, so as to improve throughput performance for satellite multimedia transmission.     

Single Channel Per Carrier Satellite Repeater Channel Capacity

This paper analyzes the performance of a number of modulation and speech processing techniques that have been considered for single voice channel per carrier transmissions via satellite. This transmission mode is applicable to demand assignment systems, which make possible the most efficient loading of the satellite transponder in applications where the traffic at individual Earth terminals is not sufficient to justify a substantial number of dedicated channels. The analysis basically determines the operating point for the satellite transponder which minimizes the required Earth terminal G/T. The fraction of the total link noise allocated to uplink noise is treated as a parameter, so that the cost of improving G/T may be traded against the cost of providing increased Earth terminal transmitter power. Both analog and digital modulation techniques are considered, together with various practical combinations of syllabic companding, voice-actuated carriers, and error-correcting codes. The results are presented in general analytic form, applicable to any modulation technique for which carrier-to-noise density ratio, channel width, and guardband width may be specified. Curves showing required G/T as a function of the total number of voice channels per transponder are also presented for the above-mentioned signal processing techniques, assuming "CCIR/CITT type" speech quality and transponder EIRP and bandwidth typical of current domestic satellite configurations.     

Single Channel Per Carrier Satellite Repeater Capacity, Part 2

This paper analyzes the performance of a number of speech processing techniques that have been considered for single voice channel per carrier transmissions via satellite. This transmission mode is applicable to demand assigiment systems, which make possible the most efficient loading of the satellite transponder applications where the traffic at individual earth terminals is not sufficient to justify a substantial number of dedicated channels. The analysis basically determines the operating point for the satellite transponder which minimizes the required earth terminal G/T. Both analog and digital modulation techniques are considered, and the effects of syllabic companding and voice actuation of carriers are demonstrated. The results are presented in general analytic form, applicable to any modulation technique for which carrier-to-noise density ratio, channel width, and guardband width may be specified. Full carrier modulation is assumed. Curves are also furnished showing the required G/T and uplink per carrier EIRP as a function of the number of voice channels per transponder and the transponder gain. "CCIR/CCITT type" speech quality is assumed, together with a transponder El RP and bandwidth typical of current domestic satellite configurations.