室内单载波太赫兹无线信号传播及覆盖性能分析

针对太赫兹无线信号与传统频谱的差异性制约其应用于室内通信场景的问题,提出了一种室内太赫兹无线信号传播的修正模型,并分析了宽带单载波太赫兹无线信号传播及覆盖性能.具体地,考虑障碍物厚度导致的吸收损耗问题,建立了宽带太赫兹信道传递函数模型.基于射线追踪技术,阐明了障碍物厚度、信号带宽对上述性能的影响.研究表明,非视距障碍物...     

On radio propagation through earth

The electromagnetic fields of a vertical electric dipole in a conducting half-space are considered. A numerical method for predicting the transfer between two receiving sites is outlined and the results are applied to a configuration used in an experimental test over the frequency range from 1 to 10 MHz.     

Frequency domain measurements of indoor radio channels

Frequency responses of the indoor radio channel for 128 locations in an office and a research laboratory are analysed. Some statistics on the number of fades are determined. The cumulative distribution function (CDF) of the 3 dB bandwidth of the frequency correlation function is presented, and experimental results relating the RMS delay spread of the channel and the inverse of the 3 dB width of the frequency correlation function are given.<>     

Impulse response modeling of indoor radio propagation channels

If indoor radio propagation channels are modeled as linear filters, they can be characterized by reporting the parameters of their equivalent impulse response functions. The measurement and modeling of estimates for such functions in two different office buildings are reported. The resulting data base consists of 12000 impulse response estimates of the channel that were obtained by inverse Fourier transforming of the channel's transfer functions. It is shown that the number of multipath components in each impulse response estimate is a normally-distributed random variable with a mean value that increases with increasing antenna separations; a modified Poisson distribution shows a good fit to the arrival time of the multipath components; amplitudes are lognormally distributed over both local and global areas, with a log-mean value that decreases almost linearly with increasing excess delay; for small displacements of the receiving antenna, the amplitude of the multipath components are correlated; the amplitudes of adjacent multipath components of the same impulse response function show negligible correlations; and the RMS delay spread over large areas is normally distributed with mean values that increase with increasing antenna separation     

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     

Ray-optical modeling of simulcast radio propagation channels in tunnels

Simulcast radio propagation channel characteristics inside tunnels are considered in this paper. Based on the image theory of ray optics, a simulcast radio propagation channel in a rectangular tunnel is exactly formulated. As only the field components of horizontal and vertical polarization are of interest in real implementation, the exact formulation is approximated to facilitate the numerical computation. The calculated simulcast radio propagation channels are comparable fairly to measurements at 900 MHz and 2.0 GHz. The validated ray-optical modeling approach is then applied to simulate simulcast radio propagation channel characteristics at 900 MHz and 2.0 GHz to gain deeper insight and better understanding of this type of channels in tunnels. Results show that large fluctuations occur in the capture regions of the distributed antennas for both 900 MHz and 2.0 GHz. The fluctuations in the simulcast regions are larger at 2.0 GHz than at 900 MHz. The root-mean-squared (rms) delay spread is greater in the simulcast regions than in the capture regions of the distributed antennas. This larger delay spread is mainly due to the delay introduced by the transmission medium. Large values of the rms delay spread can be avoided by a careful design of the distance between the distributed antennas.     

Slant-path microwave radio propagation through distorted raindrops

Attenuation and phase coefficients are evaluated for microwave radio propagation through oblate spheroidal raindrops on slant radio paths. From these coefficients, it is evident that the resultant crosspolarisation for linearly or circularly polarised waves should be significantly less on satellite radio paths than on horizontal radio paths.     

Dynamic behaviour of radio channels due to trans-horizon propagation mechanisms

To study the propagation mechanisms of trans-horizon radio links, the authors propose an event-based approach. Data from one year captured on a trans-horizon link of 156 km are divided into different groups according to the signal amplitude signature of the chart recordings. The propagation mechanisms for each group are investigated using the cross-correlation between received signal amplitudes along the same path. These amplitudes are obtained using two different transmitter antenna heights.<>     

Low-complexity blind carrier frequency recovery for OFDM signals over frequency-selective radio channels

This paper introduces a blind (i.e., data independent) algorithm for carrier frequency offset recovery in an orthogonal frequency-division multiplexing (OFDM) receiver operating over frequency-selective fading channels. The main idea behind this algorithm is to exploit the time-frequency-domain exchange inherent to the modulation scheme. Due to this feature, a carrier frequency offset has a similar impact on OFDM as a clock timing offset has in a quadrature amplitude modulation (QAM) system. The scheme we propose is a variant of Oerder-Meyr's (1988) feedforward clock recovery. Its performance is assessed by simulation, and the results are compared to those obtained from Van de Beek-Sandell-Borjesson's (1997) frequency synchronizer, which bears comparable complexity. The new scheme is shown to outperform the latter over frequency-selective fading channels, notably at medium to high signal-to-noise ratios. We also evaluated the efficiency of two different (time domain and frequency domain) offset correction strategies embedded in a particular OFDM receiver.     

Performance of digital code tracking loops for direct-sequencespread-spectrum signals in mobile radio channels

The performance of first- and second-order non-coherent digital delay lock loops (DDLL) for direct-sequence spread-spectrum (DS-SS) signals is investigated in the mobile radio environment. The mobile radio channel is first characterized by Rayleigh fading and Doppler shift. A closed-form expression for the timing error transition probability density function of the Chapman-Kolmogorov (C-K) equation is proposed. The probability density function of the steady-state timing error for the first- and second-order DDLL is obtained by solving the C-K equation numerically, and the results are confirmed by computer simulations. Furthermore, the mean time to lose lock (MTLL) of the first-order loop is evaluated, and some numerical results and simulation results are reported. Finally, the steady-state timing error and MTLL of the first-order loop for DS-SS signals in the log-normal fading environment are also presented, and the results are compared with those of Rayleigh and AWGN channels     

Multistage block-spreading for impulse radio multiple access through ISI channels

Transmitting digital information using ultra-short pulses, impulse radio (IR) has received increasing interest for multiple access (MA). When IRMA systems have to operate in dense multipath environments, the multiple user interference (MUI) and intersymbol interference (ISI) induced, adversely affect system capacity and performance. Analog IRMA utilizes pulse position modulation (PPM) and random time-hopping codes to mitigate ISI and suppress MUI statistically. We develop an all-digital IRMA scheme that relies on multistage block-spreading (MS-BS), and judiciously designed transceiver pairs to eliminate MUI deterministically, and regardless of ISI multipath effects. Our proposed MS-BS-IRMA system can accommodate a large number of users and is capable of providing different users with variable transmission rates, which is important for multimedia applications. Unlike conventional IRMA systems, MS-BS-IRMA exhibits no degradation in bit-error rate performance, as the number of users increases.     

近红外激光水面传输热晕效应缩比实验研究

为了验证近红外激光在水面大气传输时的热晕效应,采用缩比实验方法,克服了大口径和高功率系统复杂、实验成本高等实际问题,以理论分析为基础设计了高效的实验方案,对1000nm左右的激光水面大气传输热晕效应进行了实验研究,取得了重要的外场实验数据。结果表明,在选择合适的功率和发射口径情况下,1000nm左右的高能激光水面传输热晕效应可忽略。这一结果对大口径和高功率激光系统设计是有帮助的。     

Frequency fluctuation of spacecraft radio signals in the circumsolar plasma

Frequency fluctuation data of monochromatic radio waves propagating through the circumsolar plasma in 1975–2002 are systematized and analyzed. The radial dependences of the intensity of the frequency fluctuations are obtained for the decimeter radio waves in the circumsolar plasma from the results of radio sounding using the Ulysses and Galileo spacecrafts. It is demonstrated that the radial profile of the rms frequency fluctuations can be approximated by a power-law function whose exponent is determined by the intensity of the plasma inhomogeneities, the velocity of solar wind, the spectral index of the spatial spectrum of the plasma fluctuations, and the outer scale of turbulence. It is also shown that three different frequency fluctuation regimes are found in the solar wind acceleration region and in the inner and outer regions of the stable solar wind.     

探究模块化短波电台的设计与实现

该文主要围绕着短波电台进行深入分析,对模块化的设计及其实现开展研究和探讨,期望可以为后续更多技术专家和学者对此类课题的实践研究提供有价值的指导或者参考.     

基于OFDM的短波电台改进方案设计

短波电台作为远距离传输的重要载体,有着非常重要的作用。然而传统短波电台受短波信道固有缺点的限制,传输速率较低,频带利用率也不高。正交频分复用(OFDM)技术的各子载波之间的正交性使得其频谱可重叠从而提高了频带利用率,同时能有效对抗频率选择性衰落。为了有效提高短波电台的性能,可以采用OFDM技术。分析了OFDM的基本原理,提出了基于OFDM的短波电台性能增强方案。     

Mobile radio propagation path loss studies at VHF/UHF bands inSouthern India

Field strength measurements at 200, 400 and 450 MHz (VHF/UHF band) were conducted with the field strength meter placed on board a vehicle in Southern India. Observed field strength values were converted into path losses and are compared with different path loss prediction methods like Hata (1980), Egli (1957), Blomquist-Ladell (1974), COST 231 Walfisch-Ikegami (Doble 1996), Walfisch-Bertoni (1988) and ITU-R. These path loss studies are carried out in urban, suburban and open areas in this region. The results showed that Hata's method gave better agreement with observed values in urban, suburban and open regions; the COST 231 Walfisch-Ikegami model is also in good agreement with the observed values in urban and suburban regions, the Egli and Blomquist-Ladell methods showed moderate agreement in open regions only. The agreement of the Walfisch-Bertoni and ITU-R methods with observed values is not good     

Coding for radio channels

The conventional remedy to time and/or frequency variability of radio channels is diversity. Redundant coding is a kind of diversity, as each coded symbol can be recovered from other symbols. Only linear binary block codes are considered. Any binary random variable can be represented by its algebraic value,a real number whose sign indicates its most likely value and whose absolute value measures the probability of this value. The algebraic value of a received binary symbol is itself a random variable, whose distribution obeys a particular constraint. The algebraic value associated with the maximum likelihood decision on a binary symbol, given a set of independent received replicas of it, and that associated with the sum modulo 2 of binary random variables are also considered. The symbol-by-symbol decoding is then analysed in the case of threshold decoding, then in the general case. An approximate bound on the decoding error probability for additive Gaussian noise and coherent demodulation is used to assess the advantage of coding when unequalenergy symbols are received, according to a deterministic or a Rayleigh distribution. Simulation results are given for the Hamming (15,11) code. Coding affords a significant advantage provided the channel is good enough, while conventional diversity always provides gain.     

一种基于HMM的短波电台PACTOR协议识别技术

采用了一种基于HMM的比特流协议识别技术,首先通过模式匹配算法对原比特流进行分类,然后采用隐式马尔科夫模型对量化后的数据进行处理和计算。实验结果表明,它不仅能够对带有混淆协议数据的比特流进行识别,而且可以克服数据包不完整的缺点,并使得协议识别所需时间大大降低。     

Preparation of a CubeSat LEO radio wave propagation campaign at Q and W bands

Due to the congestion of the spectrum and the need for wider bandwidths, ultrahigh throughput satellites (UHTSs) are moving towards the use of higher frequency bands (Q/V and W bands). These frequencies are however severely impaired by atmospheric phenomena causing attenuation, scintillation and depolarization and compromising the quality of service (QoS). In order to study the Earth-space link, several experimental campaigns have been performed up to the Q band with geostationary (GEO) satellites. This paper introduces a new propagation experiment that will extend the characterization of the Earth-space channel up to the W band and low Earth orbits (LEOs).     

短波数字电台PACTOR协议解码的研究与实现

HF数字通信电台协议识别与分析作为现代通信对抗和无线电监测的一项关键技术,受到越来越多的重视。通过基于滑动窗口的协议数据解码算法,根据协议的coding方式,利用VC++和MySQL数据库平台,对短波电台PACTOR协议进行了解码分析和验证。