Experiments on aeronautical satellite communications using ETS-Vsatellite

The world's first aeronautical satellite communication experiments, conducted at L-band frequencies using a commercial aircraft, are described. An airborne antenna with electronically steerable beam and communication equipment was installed in a B-747F freighter flying over transoceanic flight routes. The satellite used in these experiments is the Engineering Test Satellite-Five (ETS-V). During the test period, various experiments, such as antenna pattern measurements, transmission performances, and voice quality evaluation were conducted. As the airborne antenna is the key component for the aeronautical satellite communication system, emphasis has been placed on antenna characteristics. Its performance is found to be closely related to the fading characteristics in low-elevation areas and to transmission error performance     

无线光通信系统中极化码编译码技术

大气无线光通信系统中的湍流运动会降低系统误码性能。为此,将Polar编译码技术引入无线光通信系统中,研究了极化码编码方法及其加入循环冗余校验的列表连续消除(Cyclic Redundancy Check-Successive Cancella-tion List,CRC-SCL)译码原理,并分别在高斯和湍流信道条件下进行了误码性能的蒙特卡洛仿真。结果分析表明,Polar编码对大气湍流信道的无线光通信系统可靠性有明显改善,在误码率为10-3时,相较于未编码系统,基于CRC-SCL译码的Polar编码技术可获得约6.3 dB的编码增益。同时,码长越长,码率越低,编码系统误码性能越佳。     

拉普拉斯白噪声下的分组Turbo码

目前,传统航空测控通信所采用的纠错码大多是建立在高斯信道基础上的。然而,航空测控环境中不可避免存在着多种尖锐的噪声,测控通信纠错码的可靠性能在非高斯信道中尚未得到充分的研究。分析了一类国际航空遥测的分组Turbo码（BTC）在拉普拉斯白噪声信道下的译码和性能。将传统Chase迭代译码算法引入到拉普拉斯白噪声信道中,建立相应的数学模型,同时,基于该数学模型设计了3种不同的译码接收器下的BTC译码方案。仿真结果验证了该数学模型的正确性与可行性,在误码率为10^-4时最佳译码方案相比于硬限幅接收机有3.7 dB的增益,相比原有的高斯信道下的接收机仅有0.6 dB的性能损失。     

PSK communications systems using fully saturated power amplifiers

Quasiconstant envelope phase-shift keying (PSK) is analyzed to assess its ability to overcome nonlinearities caused by fully saturated RF power amplifiers in communications systems. These modulations can achieve bit error rate (BER) performance comparable to linear BPSK in additive white Gaussian noise (AWGN) channel. Quasiconstant envelope offset quadrature PSK (OQPSK) is presented as a design example. At a BER = 10/sup -5/, the SNR degradation caused by fully saturated power amplifiers is 0.1 dB. The simulated BER matches analytically derived results. For a communications system employing the quasiconstant envelope OQPSK and a rate 1/2 convolutional code with K = 7, the demodulation performance is degraded by 0.25 dB at a BER = 10/sup -5/ when a fully saturated power amplifier is employed.     

多载波调制结合Turbo编码技术的性能分析

多载波调制是一种有效克服衰落信道频率选择性的技术,从而显著减少码间干扰(ISI)。Turbo码以其接近香农极限的工作性能受到人们的注目,它能在极低信噪比条件下提供可靠通信。把多载波调制与Turbo 编码结合起来能够对整个系统提供显著的性能增益。本文试图对采用这两种技术的通信系统给出性能上的评估。     

The split symbol moments SNR estimator in narrow-band channels

The split symbol moments estimator (SSME) is an algorithm that is designed to estimate symbol signal-to-noise ratio (SNR) in the presence of additive white Gaussian noise (AWGN). The performance of the SSME algorithm in bandlimited channels is examined, and the effects of the resulting intersymbol interference (ISI) are quantified. All results obtained are in closed form and can be easily evaluated numerically for performance-prediction purposes. The results are also validated through digital simulations     

JTIDS链路性能分析与仿真

从链路层的角度出发,介绍了美军联合信息分发系统(JTIDS)的技术体制;并对其传输性能进行了分析;在用SPW软件建立的系统的链路仿真平台上,系统在不同条件下,例如高斯白噪声、多网干扰、点频及部分频带干扰以及非理想同步,对误码性能进行了仿真测试;最后,还对JTIDS系统的抗干扰能力进行了评估。     

Statistical Analysis of Digital Phase-Locked Loops Fading Channiels

Statistical analyses of zero-crossing sampling first- and second order digital phase-locked loops in fading channls (DPLFC) are presented. A DPLFC is defined as one where the incoming signal is not only corrupted by additive Gaussian noise channel (AGN) but also by a fading communication channel. The three fading channels considered are the log-normal, Rayleigh, and Rician channels. The performance degradation of the DPLFC operation is characterized by the steady-state phase-error process probability density function and phase-error variance. Approximate analytic expressions for the phase-error statistics of a first-order DPLFC for both phase-step and frequency-step inputs are obtained by solving the Chapman-Kolmogorov equation associated with the phase-error process. The second-order DPLFC is analyzed for a frequency-step input. Numerical and simulation results are provided confirming the analyses presented for the three fading channels considered.     

Error Probability for Fading CPSK Signals in Gaussian and Impulsive Atmospheric Noise Environments

Recently the performance of digital communication systems in the presence of impulsive atmospheric noise has been evaluated assuming a noise model which is in excellent agreement with experimental results. We evaluate the bit error probability for coherent phase-shift keying (CPSK) signaling assuming the same atmospheric noise model but considering a more reasonable representation of the communication channel which accounts for the simultaneous presence of Gaussian (always present) atmospheric noise and signal fading.     

连续时变信道对协作通信性能影响的研究

协作通信能够抵抗无线信道衰落,是提高无线通信系统性能的有效手段。但是,其性能优势的发挥受信道时变的影响。文章研究了连续时变信道下协作通信系统的性能,为了准确反映信道连续时变情况,采用内插滤波高斯噪声法构建连续时变信道模型,选取误包率作为性能指标。仿真结果表明,连续时变信道下,随数据传输逐渐加重程度的过时信道状态信息将导致协作通信误包率性能大幅恶化。     

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.     

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.     

Design and Performance of an Adaptive Kalman Receiver for Synchronous Data Transmission

A class of multilevel linear-modulation data-transmission systems, over unknown, slowly time-varying, and bandlimited channels is considered. It is shown how sequence estimation in the presence of Gaussian noise and intersymbol interference can be carried out by means of a discrete Kalman estimator. Moreover, the receiver can be provided with data-aided adaptive loops for performing channel identification, carrier recovery, and timing extraction. A computational method is presented to evaluate the average probability of error of the overall system in the presence of inter-symbol interference, additive noise, and phase-and sampling-synchronization errors. The method is based upon nonclassical one-and two-dimensional quadrature rules, which are outlined in the Appendix. As an example, numerical performance results related to a phase-shift-keying (PSK) system are given. The results are obtained by means of general-purpose and system-oriented computers.     

航空通信中基于PN码的信道估计算法研究

航空移动通信系统（空空信道）中,大的多径时延和多普勒频移会造成非常严重的符号间干扰,高速宽带下尤为突出,使得传统的频域信道估计算法不得不通过提高运算长度和复杂度来实现性能,而航空通信对实时性的要求使其难以工程实现。本文针对空空信道时延长而衰落小的条件,提出一种基于PN码的时域信道估计算法,连续发送N段m序列作为训练序列...     

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。     

PCM/FM aeronautical telemetry in frequency selective multipath interference

The performance of PCM/FM using a delay-line detector in multipath interference is analyzed. In aeronautical telemetry applications, the multipath interference causes a in the signal spectrum which is web modeled by a channel composed of a line-of-sight signal and a strong specular reflection with magnitude /spl Gamma/ and excess delay less than a bit time. Analysis shows that the bit error probability is strongly dependent on the location of the within the spectrum. The bit error probability averaged over the location is also analyzed. For the case of no predetection filtering, the average bit error probability is dependent on the depth of the but not on the width. The loss in performance (relative to the AWGN environment) is bounded by (1-/spl Gamma/)/sup -2/ which is the depth of the . For the case of predetection filtering, the average bit error probability is dependent on both the width and depth of the . The performance loss is bounded by (1-/spl Gamma/)/sup -2/spl Gamma// which is less than that for the case of no predetection filtering.     

星基ADS-B接收机监视容量分析

星基广播式自动相关监视（ADS-B）系统是实现广域范围内航空器监视的重要技术手段。星基ADS-B系统内部存在严重的共信道干扰,共信道干扰限制了系统的监视性能。为了定量给出星基ADS-B接收机监视容量的计算方法,首先,给出了星基ADS-B系统的模型;随后,通过理论分析得到了星基ADS-B接收机报文冲突概率及报文正确接收概率,以此为基础理论,分析得出星基ADS-B接收机位置报文更新间隔及监视容量的计算方法;最后,构建了星基ADS-B仿真系统,仿真验证了理论计算公式的正确性。研究表明：星基ADS-B接收机的监视容量由飞机-卫星空天链路的误码率及ADS-B应用子系统所要求的位置报文更新间隔联合决定。     

Effect of Fading on FM Reception with Cochannel Interference

The combined effect of cochannel interference and nonselective Rayleigh fading on the reception of analog FM signals in additive Gaussian noise is analyzed. Rice's click model for the breaking region is used. Analysis in the absence of interference is performed first and the effect of modulation on the click rate is found to be nearly negligible. For the case with cochannel interference the click rate is computed in the absence of modulation. Curves are given for detected signal-to-noise ratio (SNR) versus carrier-to-noise ratio (CNR) with signal-to-interference ratio (SIR) as a parameter and SNR versus SIR with CNR as a parameter. The results agree well with recently published results of a simulation study.     

一种基于信道模拟的测速精度评估方法

为了评估单向多普勒测速动态测量精度,构建了一种基于卫星信道模拟器的测速精度评估系统,通过在卫星信道模拟器装订卫星飞行轨迹,利用卫星信道模拟器对上行信号加入传播时延、多普勒频率,对卫星在轨飞行状态下的单向多普勒测速进行场景仿真,并对场景仿真获取的测速数据进行O-C残差序列分析,得到动态测量条件下的测速精度。给出了O-C残差序列的计算方法,分析了单向多普勒测速体制下时钟偏差对测速结果的影响,并给出了一种简单的时钟误差修正方法。     

Optimal generator matrix G

Multiple antenna transmission methods are currently being developed all around the world for evolving 3G wireless standards. Space–Time Trellis Code (STTC) has been proven to use transmit diversity efficiently. It effectively exploits the effects of multipath fading to increase the information capacity of the multiple antenna transmission systems. STTC is a channel coding technique that maximises the ‘distance’ between different symbol matrices such that the probability of transmission errors are decreased when transmitting redundant symbol or in other words, to maximise the minimum determinant. Maximising the minimum determinant is equivalent to obtaining optimal generator matrix G. Instead of using state diagrams, optimal generator matrix G discussed in this paper is obtained using an improved algorithm which is based on Lisya tree structure. Optimal generator matrix G in this paper has a minimum determinant of 48 which is the highest coding gain obtained so far.