A computer simulation of XPD degradation due to multipath propagation

A computer program has been constructed to study degradation in Xpd (cross-polarization discrimination) due to multipath propagation. The geometric optics limit is used. The program will accept any analytic index of refraction including those with discontinuities in n or ?n. Antenna effects are included and all reflected, refracted, direct and ground reflected rays can be considered. Using a realistic index of refraction and realistic discontinuity, we have found that, after the antenna pattern, the major influence on Xpd is interference between the ground-reflected wave and the direct wave. There is also significant interference due to the waves reflected from the refractive index discontinuity which may arrive without ground reflection or may be reflected once or twice from the ground.     

Approximation of SNR degradation due to carrier frequency offset for OFDM in shadowed multipath channels

We derive an approximate expression for signal-to-noise ratio (SNR) degradation of orthogonal frequency division multiplexing due to carrier frequency offset over a shadowed multipath channel, to explicitly show the effects of system and channel parameters on the degradation of the received SNR. The results show that, for small frequency offset, the SNR degradation is proportional to the square of the frequency offset and the square of the number of subcarriers. It is also shown that, if E/sub s//N/sub 0/ is reasonably large, the SNR degradation becomes insensitive to E/sub s//N/sub 0/, which is contrary to the case of the additive white Gaussian noise channel.     

Performance degradation due to cross-phase modulation in optical fdm ask coherent detection systems

The performance degradation due to cross-phase modulation in optical FDM ASK coherent detection systems has been investigated in this paper. The effect of modulation statistics and phase tracking of the receivers is taken into account. Based on the theoretical treatment, power penalty and allowable launched power per channel have been estimated.     

Amplifier-induced crosstalk in multichannel coherent lightwave systems

When an in line semiconductor laser amplifier is used to amplify several channels simultaneously, it can induce inter channel crosstalk if the amplifier gain is channel-dependent. It is shown that modulation of the carrier density at the beat frequency of two neighbouring channels can lead to considerable crosstalk even when the amplifier is operated well below the saturation level. An analytic expression for the channel gains of a travelling-wave amplifier is used to discuss and compare the crosstalk for ASK and FSK systems. The relatively short carrier lifetime in high-gain amplifiers may ultimately limit the channel spacing of such multichannel systems.     

Outage intensity due to multipath fading in terrestrial links

Measured data of multipath fading from 20 microwave line-of-sight links, operating in the 4 and 6 GHz frequency bands, were analysed to provide statistics of fade durations as a function of the attenuation threshold. From these results, an empirical method for predicting outage intensity due to multipath propagation was derived, which shows good agreement with the measurements.     

A vector space approach to direction finding in a coherent multipath environment

The superresolution methods of spatial spectrum estimation heretofore reported are known to break down when arriving signals from different directions are coherent. It is shown here that this deficiency can be overcome by replacing the direction-of-arrival (DOA) search vector ordinarily used with a linear combination of such vectors. Particular attention is here given to extending the multiple signal classification (MUSIC) method to cover such cases. A procedure for determining the proper linear combination is presented so that determination of the separate coherent signal arrival angles involves a multidimensional search in angle only. Such a search is demonstrated for coherent two-ray and three-ray multipath environments.     

WDM光网络相干串扰实验研究

同频串扰可以分为同源串扰和非同源串扰 ,文中分析了 WDM光网络系统相干串扰的起源与特征 ,设计并模拟实验研究了不同相干串扰代价下 ,WDM光网络系统的功率代价。对应 1 d B功率代价下 ,WDM光网络系统对应相干串扰代价容限小于 - 1 9.7d B,对于 WDM系统实用化组网具有一定参考价值     

相干多径环境下自适应阵列的性能改进

针对传统自适应波束形成算法无法抑制相干干扰的问题,引入了一种预处理技术--自适应加权空间平滑(Weighted Spatial Smoothing,WSS)算法,结合线性约束最小方差准则,可以有效地抑制相干干扰.同时,针对WSS引起的孔径损失,提出了一种对子阵进行相位补偿,利用全阵做波束形成的方法.理论分析和仿真结果表明,该方法对相干干扰的抑制能力明显优于常规均匀空间平滑(Uniform Spatial Smoothing,USS)算法,而且避免了孔径损失.     

Delay calculation capturing crosstalk effects due to coupling capacitors

A driver model to calculate gate and interconnect delays accurately for a chip with coupling capacitors is presented. The crosstalk effects between simultaneously switching victim and aggressors are effectively captured by iteratively solving an N-port RC network. The algorithm was implemented in a delay calculation tool called XINT and its accuracy demonstrated for industrial designs.     

Error probability due to Gaussian noise and near-end crosstalk

The error probability is calculated of a baseband digital system operating on multipair cable subject to Gaussian noise and near-end crosstalk from a number of interfering plesiochronous digital systems carrying a.m.i.-coded random binary signals.     

Analysis of DPSK error rate due to multipath delay spread

The intersymbol interference (ISI) produced by multipath channel delay spread can be approximated as Gaussian noise. The equivalent average signal-to-noise power ratio (SNR) is defined. Very simple expressions for average bit error rate (BER) due to delay spread are derived for linear quaternary DPSK (QDPSK) transmission with differential detection over mobile radio Rayleigh fading channels.<>     

Characteristics of L-band multipath fading due to sea surface reflection

For lowG/Tship-based earth stations in future maritime satellite communications, the effect of multipath fading due to sea surface reflection will be very important at low elevation angles. However, a practical model of theL-band multipath fading for fade prediction has not been available so far. A practical fading model is presented based on the shadowed Kirchhoff approximation theory for the coherent and incoherent components of the scattered power as a function of sea surface conditions. Using this model, theoretical fading depths are presented as a function of elevation angle, wave height, and antenna gain. The results indicate that intense fading occurs for wave heights greater than 50 cm, and the dependence on wave height is small under these conditions atL-band frequencies. Theoretical results presented agree well with experimental results obtained by field experiments.     

Channel allocation and crosstalk penalty in coherent opticalfrequency division multiplexing systems

Theoretically studies the crosstalk penalty of coherent optical frequency division multiplexing systems by varying the intermediate frequency and the channel spacing. Results, applicable to ASK, PSK and CPFSK modulation formats, provide a quantitative criterion for designing a practical multichannel coherent lightwave system     

Holographic prediction of ray parameters in line-of-sight links due to tropospheric multipath

Ducting in LOS radio links is investigated. A technique is proposed to estimate the number of refracted rays that could reach the receiver due to the presence of a duct, their angle of arrival and their relative amplitude in comparison to the direct ray.<>     

Nonlinear crosstalk due to stimulated Raman scattering in a two-channel wavelength-division-multiplexed system

The effects of stimulated Raman crosstalk on two binary PCM channels, wavelength-multiplexed in a single optical fibre, are minimised by optimising the ratio of powers launched into each channel. The longest repeater spacings that could be achieved by increasing the launched powers are thereby obtained for two WDM channels of equal group velocity.     

Intense spontaneous violet emission due to coherent two-photon excitation in potassium

This paper describes the measured result of intense violet emission at 4048 Å that is due to the strong coherent two-photon excitation in potassium vapor. Anomalous delay and narrowing of the emitted pulse was observed in contrast to the incident pulse. The intensity dependence on the atomic density also is reported.     

Scaling limitations in transparent optical networks due tolow-level crosstalk

As transparent optical networks are scaled up in size, stringent constraints must be placed on the in-band crosstalk generated by their components. Measurements show that transparent networks corrupted by interferometric signal-crosstalk beat noise from only 8 crosstalk fields require component crosstalk levels <-35 dB. Good agreement with theory is shown     

Prony technique for prediction of ray parameters in LOS links due to tropospheric multipath

A Prony algorithm is utilised in the process of predicting relative amplitudes and angles of arrival of rays in line of sight (LOS) links using phase and amplitude data. The technique showed much better performance compared with the use of Fourier transform.     

Structure-enhanced MOSFET degradation due to hot-electron injection

Device degradation due to channel hot-electron injection in several nonconventional MOSFET structures including minimum-overlap gate, offset gate, graded drain, and lightly doped drain (LDD) structures are evaluated. In these nonconventional structures the device degradation is much faster than that in conventional devices when biased with the same amount of hot electrons in the channel. This faster degradation rate is proposed to be due to external channel pinchoff at the more lightly doped drain edge. This behavior implies even more severe constraints on the operating regime for these nonconventional device structures at submicrometer gatelengths to maintain adequate reliability margins.