蒸发波导微波超视距信道衰落特性研究

针对利用海上蒸发波导效应的微波超视距通信,在三条不同距离跨海电路上开展了外场试验。基于测试数据,统计L、S、C和X频段超视距信道的衰落幅度、深度和速率,对比分析了蒸发波导和对流层散射信道的快衰落特性。并根据大气波导和对流层散射传播预测模型,统计比较了实测和模型预测路径传播损耗。结果表明与对流层散射信道相比,蒸发波导信道衰落幅度、衰落深度和衰落速率均较小,传播预测模型可有效的预测蒸发波导的慢衰落特性。     

Fading depth dependence on system bandwidth in mobile communications - an analytical approximation

A simple and computationally inexpensive analytical approach is proposed for the evaluation of the dependence of short-term fading depth on system bandwidth and environmental characteristics. The approach, accounting for the maximum difference in propagation path length and having the Rice factor as a parameter, is derived by fitting simulated data from a model in the literature. Application examples are presented for GSM, UMTS, HIPERLAN, and mobile broadband systems (MBS), giving some insight into the fading depth observed under different conditions with regard to system bandwidth and environmental characteristics. Macro-, micro-, and picocell environments are considered. In the microcellular environment, the fading depth experienced by UMTS is below the one for GSM by 0.1 to 5.5 dB, while in the picocellular one, the difference between GSM and UMTS is not significant, being almost independent of environment characteristics. When considering HIPERLAN or systems with larger bandwidths, the fading depth, both in micro and picocellular environments, is smaller than the one verified by UMTS; however, there is an increased dependence on environmental characteristics. In the macrocellular environment, the fading depth experienced by UMTS is about 6 to 11 dB below the one for GSM. Hence, different short-term fading margins should be considered for each system and working environment.     

Propagation analysis of signal fading for basic exchange radios

Although empirical multipath fading models are available for microwave links above 2 GHz, these models are not directly applicable to basic exchange radio (BEXR) links because of the substantial differences in frequency, antenna beamwidth, and radio path clearance. A method for obtaining a scaling factor which accounts for the differences between BEXR and microwave links is presented. First, the terrain scattering is studied using a rough surface model, and the atmospheric refraction is studied using a ray tracing approach. Then, the received signal powers of a microwave link and two BEXR links on the same path under the same propagation condition are calculated. The signal characteristics are investigated and used to simulate the fading distributions for all three links. From the simulation results, a scaling factor is derived and used to modify the existing microwave multipath fading models for BEXR application. The predictions of the modified model agree well with measured BEXR data. This study shows that the probability distribution of signal fading on BEXR links is a strong function of antenna height and beamwidth     

考虑混合SC/MRC分集的层叠分布式天线系统SER性能分析

针对Nakagami/lognormal复合衰落信道,研究了层叠分布式天线系统(Cascade Distributed Antenna System-CDAS)在CDMA网络中的平均误符号率性能.推导出了采用混合SC/MRC分集接收机的层叠分布式天线系统平均误符号率性能公式.利用推导出的平均误符号率表达式,分析了多径密度函数(Multipath Intensity Profile-MIP)衰减因子、空时分集维数、活动用户数以及阴影衰落因子对平均误符号率性能的影响.仿真表明层叠分布式天线系统可以有效对抗衰落,提高系统容量以及削弱对数正态阴影衰落的影响.     

无线接入信道损耗特性分析

小尺度衰落中的瑞利衰落和莱斯衰落是2种最为常见的无线接入信道衰落。从工程设计角度出发,重点分析了莱斯和瑞利信道条件下的2个重要指标——衰落深度和衰落速度,推导了相应的计算公式,特别是莱斯和瑞利信道条件下的衰落中值进行分析和计算。给出了在瑞利和不同莱斯因子条件下的PSK误码性能,为进行多径衰落无线接入信道的系统工程设计提供了参考。     

Propagation model for simulating shadowing and multipath fading inland-mobile satellite channel

A land-mobile satellite propagation model which includes multipath fading and shadowing effects using five-state Markov transitions between fade states and nonfade states is proposed. This generates a time-series of the fading, very closely matching statistical characteristics such as fade duration, nonfade duration and fade depth obtained from measured data     

Trellis code design for periodic interleavers

A standard technique for correlated fading combines trellis codes designed for independent fading with interleaving that makes correlated fading appear to be independent for symbols within the Viterbi traceback depth. When the fading correlation is persistent and delay constraints preclude deep interleaving, some correlation remains among symbols within the traceback depth. Incorporating this post-interleaver correlation improves the trellis code design. This article presents such a trellis code design technique for periodic interleavers. Bit error rate simulations demonstrate that the new design technique can provide a dramatic performance improvement when fading or interference is severe and persistent     

Capacity of slotted ALOHA in generalised fading environments

The channel throughput of the slotted ALOHA protocol is evaluated for a Nakagami fading channel model. General expressions for different values of the fading figure m and receiver capture ratio are presented. Evaluations of these expressions show that the throughput increases as the fade depth increases     

An empirical model for high elevation angle land-mobile satellitechannels at urban environment

A land mobile satellite system (LMSS) propagation measurement campaign at 1.8 GHz was launched in Athens city center during June 1996 for high elevation angle (60°, 70° and 80°) channels. Four narrow streets with large building blocks and heavy traffic were tested. A new empirical model is extracted to calculate the link margin required to compensate for multipath fading in urban environments. A comparison with an existing model is presented. The results show a considerable increase in the fade depth compared to suburban and rural environments. In general, the fade depth decreases with increasing elevation angle, and the overall analysis indicates a strong dependence of the signal attenuation on the width of the streets, the average building height and the vegetation at the edges of the streets     

基于多维乘积码的编码协作方案研究

多维乘积码是一种成熟的编码技术,其性能较好,且具有灵活的多维结构。本文提出一种基于多维乘积码的协作方案,利用不同维数的校验位进行协作,达到获取分集增益的目的。文中以分量码为扩展汉明码的多维乘积码为例,在慢衰落、快衰落瑞利信道下进行了理论性能分析和计算机仿真,仿真结果显示:慢衰落信道下,BER为10-3时,协作程度为50%,用户间信道SNR大于10dB时,增益大于8dB;在快衰落信道下,可以通过该协作方案可达到帮助上行信道较差的用户的目的。从实用性和良好性能的角度来看,该编码协作将具有较好的应用前景。      

Nondata-aided error vector magnitude performance analysis over κ−μ shadowed fading channel

The performance prediction of wireless system over κ?μ shadowed fading channels was a challenging problem of wireless communications,which affects transmission scheme design seriously.To solve this problem,a novel method of quantifying the κ?μ shadowed fading channels performance based on nondata-aided error vector magnitude (NDA-EVM) was proposed.NDA-EVM was considered as a new metric to evaluate the change of the channels.The unified model to calculate different modulation order of NDA-EVM was analytically derived by maximum likelihood criterion.Moreover,the relationship between the κ?μ distribution and the NDA-EVM was built by using the attenuation factor of the channel as intermediate variable.Thereafter,the lower bounds of the NDA-EVM over the κ?μ shadowed fading channels were formulated,which was also simplified for various typical channels.The theoretical analysis was taken,moreover,numerical results were also conducted to verify the effectiveness of the derived formulation.It shows that NDA-EVM estimation has the lest root mean square error than data-aided signal to noise ratio (DA-SNR) estimation and error vector magnitude (DA-EVM) estimation over the κ?μ shadowed fading channels.The derived lower bounds closely match the theoretical values,especially at low SNR.In addition,the lower bounds are negatively related to all of the parameters of the κ?μ shadowed fading channels,which make it sensitive to the change of the fading channels.     

Unified performance analysis over Mckay–Meijer G shadowed fading channel

ABSTRACT

Composite fading models have been considered as the suitable fading models for scenarios such as indoor communication and free space optical. Most of the composite fading models are based on Nakagami-m fading distribution in which amount of fading parameter ranges from 0.5 (most severe fading) to infinity (no fading). However, using the McKay–Meijer G function, one of the recent article presents McKay shadowed fading distribution which shows that the fading severity may have values more than that of the most severe case of Nakagami-m fading. In this paper, using the conditional unified expression for conditional bit error rate (BER), a unified expression of the average bit error rate (ABER) over McKay–Meijer G shadowed fading model has been proposed. The proposed unified expression includes the ABER of almost all the modulation schemes. In addition, expression for ABER of binary phase shift keying modulation over McKay fading channel under generalised Gaussian distribution has been derived. Finally, analytical expressions of adaptive capacity under different adaptive schemes namely, COPRA, CORA, CCIFR and truncated CIFR have been presented. Through numerical analysis, different results have been compared with similar results available in the literature.     

A space-time model for frequency nonselective Rayleigh fadingchannels with applications to space-time modems

This paper extends the traditional Clarke/Jakes (1968, 1974) model for a frequency flat fading process in a land mobile radio system to facilitate the examination of coherent space-time demodulation systems. The work develops a space-time correlation function using a ring of scatterers model around the mobile unit. The resulting correlation function permits the investigation of a variety of issues concerning base station configurations in space-time systems. The interrelationship of the fading process between the space and the time domain is explored. A detailed example regarding the effects of antenna separation in a receiver diversity system is considered. A set of design rules for interleaving depth and antenna separation in a space-time modem is presented and quantified     

一种新的临近空间通信信道模型及其仿真分析

分析了临近空间通信信道的衰减特性,从多径衰落和降雨衰减两个方面综合考虑, 建立了一种新的两状态信道统计模型,使用MATLAB进行了计算机仿真。仿真结果表明,该模 型能够较好地反映临近空间通信的信道特性,对于临近空间通信的开发和研究具有重要意义 。     

A Markov model for the mobile propagation channel

A finite-state Markov model is fitted to the mobile propagation channel by the use of contingency tables. Narrow-band Rayleigh and Ricean fading are considered in detail, but the techniques extend to other types of fading. Several criteria may indicate that a first-order finite-state Markov model sufficiently characterizes the channel behavior. The parameters of the model are obtained both from theoretical analysis and simulation. Functional dependence between the transition probabilities and the steady-state probabilities is found in the slow fading case     

一种改进的C.Loo信道模型衰落因子算法

为更好地反映实际无线信道的特性,介绍一种改进的C.Loo信道模型衰落因子算法。原始C.Loo信道模型衰落因子算法中不考虑多普勒频移的影响,本文加载了多普勒频移对衰落因子的影响,并说明其合理性、可行性及优点。     

Optimum transmission ranges in multihop packet radio networks inthe presence of fading

The evaluation of optimum transmission ranges in a packet radio network in a fading and shadowing environment is considered. It is shown that the optimal probability of transmission of each user is independent of the system model and is p_o≃0.271. The optimum range should be chosen so that on the average there are χ(G/b)²η/ terminals closer to the transmitter than the receiver, where G is the spread spectrum processing gain, b is the outage signal-to-noise ratio threshold, η is the power loss factor and χ depends on the system parameters and the propagation model. The performance index is given in terms of the optimal normalized expected progress per slot, given by ϑ(G/b)¹η/ where ϑ is proportional to the square root of χ. A comparison with the results obtained by using deterministic propagation models shows, for typical values of fading and shadowing parameters, a reduction up to 40% of the performance index     

On the performance analysis of wireless receiver using generalized-gamma fading model

In this paper, we provide a unified analysis for wireless system over generalized fading channels that is modeled by the two parameter generalized gamma model. This model is versatile enough to represent short-term fading such as Weibull, Nakagami-m, or Rayleigh as well as shadowing. The performance measures such as the amount of fading, average bit error rate, and signal outage are considered for analysis. With the aid of moment generating function (MGF) approach and Padé approximation (PA) technique, outage probability and average bit error rate have been evaluated for a variety of modulation formats. We first use the PA technique to find a simple way to evaluate compact rational expressions for the MGF of output signal-to-noise ratio, unlike previously derived intricate expressions in terms of Fox’s H and MeijerG functions. Using these rational expressions, we evaluate the performance of wireless receivers under a range of representative channel fading conditions. Our results are validated through computer simulations, which shows perfect match.     

Variable forgetting factor linear least squares algorithm forfrequency selective fading channel estimation

In this article, the variable forgetting factor linear least squares algorithm is presented to improve the tracking capability of channel estimation. A linear channel model with respect to time change describes a time-varying channel more accurately than a conventional stationary channel model. To reduce the estimation error due to model mismatch, we incorporate the modified variable forgetting factor into the proposed algorithm. Compared to the existing algorithms-exponentially windowed recursive least squares algorithm with the optimal forgetting factor and linear least squares algorithm-the proposed method makes a remarkable improvement in a fast fading environment. The effects of channel parameters such as signal-to-noise ratio and fading rate are investigated by computer simulations     

Performance of BPSK Pre-detection MRC Systems over Two-Wave with Diffuse Power Fading Channels

The bit-error rate (BER) analysis for BPSK pre-detection maximal ratio combining (MRC) systems in two-wave with diffuse power (TWDP) fading is presented. In TWDP fading, the received signal is composed of two specular components in addition to the diffuse signal. The analysis shows that in TWDP fading, the BER of the MRC system is given by the weighted sum of the BERs of a number of MRC systems in Rician fading. The methodology used in the analysis is verified through simulation.