Evaluation and verification of the VHF/UHF propagation channelbased on a 3-D-wave propagation model

This paper is intended to increase and improve the knowledge concerning the characterization of digital VHF/UHF communication channels. This characterization of the propagation channel is based on the field strength-delay-spectrum (FDS) of the three-dimensional (3-D) multipath wave propagation. A statistical superposition of the predicted multipath signals yields the probability density function of the narrowband signal and the averaged channel impulse response of the wideband propagation channel. Thereof, the relevant parameters, e.g., standard deviations, mean values, delay spread, and correlation coefficients, are derived both in time and frequency domain. The angles-of-arrival of the multipath signals are used to calculate the Doppler spectra of moving receivers for the characterization the time-variant properties of the propagation channel. In total, a rather complete summary of derivations, algorithms and characteristics of the VHF/UHF propagation channel is presented. Narrowband and wideband measurements are included for verification     

A new wideband high frequency channel simulation system

This paper provides a technical overview of a high frequency (HF) channel simulation system that is applicable to either narrowband or wideband HF channels. Although narrowband models of the HF channel have existed for many years, they are applicable only to a limited set of actual narrowband channel conditions. The need for an HF channel model that is valid for both narrow and wide bandwidths over a more extensive range of channel conditions motivated the research reported in this paper. Wideband propagation, noise, and interference models have been developed and implemented in a real-time digital simulator that utilizes state-of-the-art signal processing hardware with a throughput in excess of 1 mega samples/s. The simulator architecture has the flexibility to permit its application to future simulator designs as faster signal processing components become available. The current simulation system can be used for simulating radio channels other than HF because the propagation, noise, and interference models are implemented in software. This flexibility results in a very powerful test instrument     

宽带聚合雷达稀疏频率配置及距离估计

雷达高距离分辨力需要大带宽发射信号,而雷达发射连续大带宽信号受硬件成本和频谱资源限制。利用多个窄带发射信号进行宽带合成时,由于窄带信号频谱不连续性和步进量的增大,会出现距离旁瓣增大、不模糊距离范围缩小的问题。为解决上述问题,并充分利用不连续或跨波段的频谱资源,提出一种用于宽带聚合的雷达稀疏频率配置方式。通过子频带之间的差分处理,获得等效的连续均匀步进虚拟频率信号,在获得高分辨力的同时避免距离旁瓣增大和距离模糊;对于频率跨度较大的子频带,提出了基于几何绕射理论(GTD)模型的目标散射特性频率一致性校正方法,并仿真分析了不同频率跨度对宽带聚合效果的影响和跨波段宽带聚合的可能性。该研究可进一步为雷达系统的后续兼容研究提供参考。     

An approximate performance model for a multislot integratedservices system

An approximate model (with finite or infinite waiting room) is presented for an integrated service system with three types of traffic: a first-offered narrowband traffic, an overflow narrowband traffic, and a wideband traffic. A narrowband call requires a single server, while the number of servers required to serve a wideband call is N. The blocked narrowband calls are lost while the blocked wideband calls are delayed in a finite or infinite waiting room. Based on two assumptions with regard to the characteristics of the system, the system is resolved by decomposition. The corresponding improvements in numerical efficiency as well as in computational storage requirements are significant enough to enable use of the model within network optimization algorithms. The model provides a very good approximation for the system performance, i.e. the blocking probabilities of the two narrowband traffics, the loss probability (in the case of finite waiting room), the probability of nonwaiting, and the average waiting time of wideband traffic     

多输入多输出宽带时变信道分布散射模型研究

基于多输入多输出(MIMO)窄带分布式散射模型和Kronecker信道模型,导出了宽带分布式散射模型的信道冲激响应矩阵,并利用蒙特卡洛方法和离散傅里叶变换,分别得到随机的时域信道矩阵和频域信道矩阵,建立了MIMO宽带分布式散射模型.在此基础上,通过对复高斯白噪声进行多普勒滤波的方法,实现了对MI-MO时变、宽带信道时域...     

一种改进的窄带短波信道模型及仿真实现方法

针对短波信道具有多径衰落和不可逆性等特点,提出了改进的窄带短波信道模型及仿真实现算法。该模型以美国电信科学协会（ITS）提出的宽带短波信道模型为基础,经过适当的近似与简化,得到了适于计算机仿真的实现结构。改进的窄带短波信道仿真模型考虑了各个传播模式内的时延扩展,消除了经典Watterson窄带短波信道模型的使用限制,能够仿真更广泛的短波信道条件。     

A stochastic multipath channel model including path directions for indoor environments

A novel stochastic channel model for the indoor propagation channel is presented. It is especially for, but not limited to future communication systems with multiple antennas like space division multiple access (SDMA), spatial filtering for interference reduction (SFIR), or multiple-input/multiple-output (MIMO). The model is designed for indoor scenarios, straight forward extendable to urban environments. It is based on physical wave propagation. The new approach describes the channel by multipath components, each characterized by its transfer matrix (including loss), delay, direction of arrival, and departure. The appearance and disappearance of multipath components over time is modeled as a birth and death process, a marked Poisson process. This enables first-time the correct modeling of spatial and temporal correlations. In each modeling step, path properties change according to the motion of transmitter and receiver. The changing delay times of propagation paths yield a realistic Doppler behavior of the channel. Deterministic ray tracing results are used to produce the huge data sets required for the statistical evaluation of the parameters of the proposed model. This method enables an automated parameter extraction for new environments or frequencies. The ray tracing tool has been verified by narrowband, wideband, and directional channel measurements. The novel stochastic spatial channel model allows the simulation of third-generation broadband radio systems including arbitrary antenna configurations and patterns. System simulations for the bit-error rate of radio links can be performed including intelligent antenna configurations like SDMA, SFIR, or MIMO. Furthermore, the capacity of complete systems can be investigated.     

A new simple model for land mobile satellite channels: first- and second-order statistics

We propose a new shadowed Rice (1948) model for land mobile satellite channels. In this model, the amplitude of the line-of-sight is characterized by the Nakagami distribution. The major advantage of the model is that it leads to closed-form and mathematically-tractable expressions for the fundamental channel statistics such as the envelope probability density function, moment generating function of the instantaneous power, and the level crossing rate. The model is very convenient for analytical and numerical performance prediction of complicated narrowband and wideband land mobile satellite systems, with different types of uncoded/coded modulations, with or without diversity. Comparison of the first- and the second-order statistics of the proposed model with different sets of published channel data demonstrates the flexibility of the new model in characterizing a variety of channel conditions and propagation mechanisms over satellite links. Interestingly, the proposed model provides a similar fit to the experimental data as the well-accepted Loo's (1985) model but with significantly less computational burden.     

Channel Models for Body Surface Communications in Ultra Wideband-Based Wireless Body Area Networks

Body area networks are being developed to serve a wide range of purposes ranging from providing health care to patients on the move to tracking patients and motion sensing for gaming controls. There has been significant and sizeable amount of research in the various areas and applications of body area networks. Ultra wideband which operates in the 3.1–10.6 GHz band is slowly being preferred for high data rate communication in body area networks. The development of suitable applications and techniques for communication depends significantly on the channel models. The wireless channel is a crucial parameter as it provides significant information about the propagation characteristics and losses involved in the transmission medium. The existing channel models proposed are mostly in the spectra involving the wideband 3.1–10.6 GHz bands or the 3.1–6 GHz bands. However, the IEEE 802.15.6 specifies operation in various sub-bands of 499.2 MHz width. And the channel characteristics are significantly different for wideband and narrowband channels. In this article, we propose empirical channel models for body surface communication in the various sub-bands specified by the IEEE 802.15.6. The body surface scenario is chosen as the combination of propagation through wireless media and losses due to absorption from body tissues make it challenging. The proposed path loss models are developed from more than 300,000 received power measurements collected over a span of hours.     

Characterisation of propagation in 60 GHz radio channels

Narrowband as well as wideband measurements have been performed in various indoor and outdoor environments in order to enable the development of reliable prediction models for 60 GHz radio channels. In addition, results of deterministic modelling on the basis of geometric ray-tracing have been compared with measurement results, showing that simple ray-tracing can be used to estimate both the narrowband and wideband characteristics of a 60 GHz radio channel. This paper reviews the measurement and modelling activities performed by various research institutes     

Deterministic Wideband Modeling of Satellite Propagation Channel With Buildings Blockage

The article presents an example of satellite propagation modeling, applying the radio channel transfer function analysis as described and experimentally verified in scientific literature. The simulation of a satellite radio channel is executed by employing "ray tracing" and the uniform geometric theory of diffraction-based method for an assumed urban and suburban environment and different polarizations. Derived results regarding the channel transfer function are analyzed via a simulation of the wideband propagation measurement system and the Fourier transform procedures. It has been concluded that, contrary to ground cell radio system situations, where two-ray models usually suffice, a more detailed calculation should be considered for wideband satellite radio systems. Moreover, it is shown that the conclusions derived for the path loss and the delay spread depend not only on the specific propagation scenario, but also on the building permittivity.     

码片占空因子对DS-UWB系统的影响

由于超宽带系统与窄带系统频谱重叠,窄带信号不可避免会干扰超宽带系统,严重影响其性能。信道模型采用IEEE 802.15.3a工作组建议的标准UWB室内信道模型,并使用最大比例合并Rake接收机,系统地研究了在不同窄带信号干扰情况下,可变的码片占空因子对直接序列超宽带(DS-UWB)系统的性能影响,并进行了仿真。仿真结果表明,使用低的码片占空因子得到的超宽带信号,能有效抵抗窄带干扰和多径衰落,较大提高UWB系统误比特性能。     

Propagation prediction for hilly terrain using GTD wedge diffraction

A terrain sensitive propagation model based on the geometrical theory of diffraction (GTD) modified for finite conductivity and local surface roughness is applied to hilly terrain including multiple diffraction, with the results compared with measurements and the Longley-Rice model. Even though the approach used to calculate multiple-wedge diffraction is known to be invalid in certain situations, the comparison is favorable to the GTD model results.     

A ray-tracing propagation model for digital broadcast systems inurban areas

A propagation model is presented for characterizing the channel response for digital systems in urban areas where multiple reflections from buildings are encountered. A deterministic ray-tracing propagation model is used to predict the time delay and fading characteristics for the channel in a hypothetical urban area. The analysis shows that due to multiple reflection and diffraction sources, the RMS delay spread of the channel in urban areas can be several hundred nanoseconds, so that very effective equalizers will be required to achieve successful performance of high-data-rate digital systems such as 20-Mb 16-QAM digital HDTV. The channel response results presented also suggest that polarization diversity may be a useful technique for mitigating some of the channel impairments predicted by the propagation model     

基于雷达宽窄带多特征信息融合的空中目标识别

宽带高分辨一维距离像(HRRP)含有丰富的目标特征信息,是进行型号识别的良好特征。窄带特征所携带的目标信息虽不如宽带丰富,但其与宽带特征有很强的互补性,且有识别距离远、受目标姿态影响小等优点。因此,综合利用目标的宽、窄带特征进行识别能够提高识别系统性能。文中分析了以HRRP的功率谱和目标速度、高度为识别特征的宽窄带识别系统的特点,利用DS证据理论,实现了基于宽窄带识别结果的决策层融合目标识别;外场实测数据的实验结果表明了该方法的有效性。     

An Alternative Algorithm for Both Narrowband and Wideband Lorentzian Dispersive Materials Modeling in the Finite-Difference Time-Domain Method

In this study, an alternative algorithm is proposed for modeling narrowband and wideband Lorentzian dispersive materials using the finite-difference time-domain (FDTD) method. Previous algorithms for modeling narrowband and wideband Lorentzian dispersive materials using the FDTD method have been based on a recursive convolution technique. They present two different and independent algorithms for the modeling of the narrowband and wideband Lorentzian dispersive materials, known as the narrowband and wideband Lorentzian recursive convolution algorithms, respectively. The proposed alternative algorithm may be used as a general algorithm for both narrowband and wideband Lorentzian dispersive materials modeling with the FDTD method. The second-order motion equation for the Lorentzian materials is employed as an auxilary differential equation. The proposed auxiliary differential-equation-based algorithm can also be applied to solve the borderline case dispersive electromagnetic problems in the FDTD method. In contrast, the narrowband and wideband Lorentzian recursive convolution algorithms cannot be used for the borderline case. A rectangular cavity, which is partially filled with narrowband and wideband Lorentzian dispersive materials, is presented as a numerical example. The time response of the electric field z component is used to validate and compare the results     

Comparison of different order GTD solutions of double-edgediffraction problem

A second order diffraction coefficient for the uniform geometrical theory of diffraction (GTD) is obtained explicitly for two knife edges in terms of the usual complex transition function (a modified Fresnel integral). The results from conventional GTD (zero order), slope diffraction GTD (first order), and second order GTD are compared with those obtained from physical optics (PO), which uses the complex Fresnel double integral. The results from second order GTD are close to those from PO in most of the cases studied     

Discrete time-scale characterization of wideband time-varying systems

Wideband time-varying systems can be found in many applications, including underwater acoustics and ultra-wideband technologies. The time variation due to Doppler scaling effects, coupled with dispersive scattering due to multipath propagation, can severely limit the performance of wideband systems. Just as the discrete time-frequency model can efficiently improve narrowband processing, a discrete time-scale system characterization is important in processing wideband time-varying systems. In this paper, a time-scale model is proposed as a discrete characterization of wideband time-varying systems. This representation decomposes a wideband system output into discrete time shifts and Doppler scalings on the input signal, weighted by a smoothed and sampled version of the wideband spreading function. The proposed transform-based approach uses the Mellin transform that is inherently matched to scalings to geometrically sample the scale parameter and the Fourier transform to arithmetically sample the time-delay parameter. Using this proposed model, and by properly designing the signaling and reception schemes using wavelet techniques, a joint multipath-scale diversity can be achieved over a dyadic time-scale framework in wideband wireless systems. The simulation results demonstrate that, based on the proposed model, performance can be increased by exploiting the diversity intrinsically afforded by the wideband system.     

Finite conductivity uniform GTD versus knife edge diffraction in prediction of propagation path loss

Diffraction propagation over hills and ridges at VHF and UHF is commonly estimated using Fresnel knife edge diffraction. This approach has the advantage of simplicity, and for many geometries yields accurate results. However, since it neglects the shape and composition of the diffracting surface, it can in some cases yield results which are in serious disagreement with measurements. To remedy this, attempts have been made to approximate the diffracting hill or ridge by other shapes, most notably cylinders. These approaches have not been widely adopted, due in large part to their greater numerical complexity. In this paper it is proposed to apply wedge diffraction in the format of the geometrical theory of diffraction (GTD), modified to include finite conductivity and local surface roughness effects. It is shown that, for geometries with grazing incidence and/or diffraction angles, significant improvement in accuracy is obtained. Further, the GTD wedge diffraction form used is based on the Fresnel integral, so that it is only slightly more complex numerically than knife edge diffraction. Finally, the GTD includes reflections from the sides of the ridge (wedge faces), and can be extended to multiple ridge diffraction and three-dimensional terrain variations.     

有序多重签名体制中阈下信道通信方法的研究

本文分析了阈下信道技术在数字签名中的应用，并以一种有序多重数字签名方案为例，对其中存在的宽带和窄带阈下信道进行了具体分析．提出了一种有序多重签名体制下的窄带阈下信道通信方案，通过实时性测试确定阈下信息位数，从而满足了传输信息容量与实时性的要求。