Low-loss splicing of a 62.4 km single-mode-fibre link

A 62.4 km single-mode-fibre link containing 35 splices has been made in the laboratory using equipment and techniques suitable for landline installations. Mean splice attenuations of 0.1 dB at 1.3 ?m and 0.08 dB at 1.55 ?m were measured. The mean attenuation of the complete spliced link was 0.5 dB/km at 1.3 ?m and 0.34 dB/km at 1.55 ?m. In addition, the attenuations of 200 splices measured at 1.3 ?m are reported.     

Attenuation of 8.6 and 3.2 mm radio waves by clouds

Measured attenuations associated with a variety of cloud conditions at wavelengths near 8.6 and 3.2 mm are reported. Two specific events, during which heavy rain clouds covered the sky, are examined and statistical data collected over a six-month period on a variety of cloud types are presented. The number of observations of some cloud types was not large and it was not possible to account for the gaseous attenuation with sufficient accuracy to get reliable values for the attenuation by the cloud droplets for a number of cloud types. The clouds causing the largest attenuations were the rain-bearing cumulonimbus ones. Of the nonrain clouds the two types for which the sample sizes are adequate and attenuations are sufficient for meaningful conclusions are stratocumulus and cumulus, their 35 GHz/95 GHz mean attenuation values being 0.18/0.61 dB and 0.12/0.34 dB, respectively.     

Roadside tree attenuation measurements at UHF for land mobile satellite systems

Tree attenuation results at 870 MHz are described for experiments conducted in October 1985 and March 1986 in Central Maryland. These experiments employed a helicopter as a source platform and a van with receiver and data acquisition instrumentation. Tree attenuation results were obtained for the cases in which the van was stationary and in motion. The experiments were performed for the purpose of providing the designers of planned land mobile satellite systems with important elements in the determination of link parameter requirements; namely, the expected fading statistics due to roadside trees for both mobile and stationary vehicles. Single tree attenuation results gave worst case median fades as high as 15 dB although roadside tree values were noted to produce fades in excess of 20 dB for small percentages of time. The cumulative fade distributions and their relative contributions as a function of path elevation angle, right side versus left side driving, and different road types are derived from the field measurements. Upon comparing the attenuations from bare deciduous trees (March 1986) with those due to trees in full foliage (October 1985), the increase in dB attenuations were, in general, less than 25 percent for the dynamic cases, and less than 40 percent for the worst case static configuration. This result demonstrates thai the dominant fading is caused by the wooded tree branches as opposed to the leaves on these branches. The tail end of the observed fade distributions was observed to follow lognormal distributions with respect to dB attenuation.     

Copolar and cross-polar signals received at 30 GHz from ATS-6

From the end of July 1975 until August 1976 the reception of signals from the geostationary satellite ATS-6was possible since at that time the satellite was brought into a position above Victoria Lake at 35° East. The copolar signal showed attenuation which varies strongly with the amount of rain. The rain was measured by a rain gauge located close to the 3 meter precision Cassegrain antenna. The attenuation measured at the satellite link did not always correspond with the attenuation measured at the nearby line of sight link at 34 GHz. For example during heavy thunderstorms the attenuation might have reach values as high as 20 dB or more. For smaller attenuations comparison is possible with a radiometer experiment at 30.1 GHz. In general this comparison shows good results for attenuations less than 10 dB. The crosspolar signal measured showed values of — 55 dB to about — 20 dB relative to the copolar depending upon several reasons. First of all the rain showed mostly a strong increase in the crosspolar signal but satellite movements and errors in the antenna pointing will also increased this level. Various examples are shown. It appears that the copolar — cross-polar isolation reached the lowest value at attenuations of 3–6 dB. Although the time that the satellite was available for measurements was limited, some statistic results can be given despite the fact the signal transmitted from the satellite was not always constant.     

Cascaded Noise Penalty for Amplified Long-Haul Analog Fiber-Optic Links

The noise penalty (NP) metric is useful in long-haul analog link design, as it predicts degradation of the RF noise figure (NF), 1-dB compression dynamic range (CDR), and the spurious-free dynamic range (SFDR) for a single-amplifier link. We extend the NP theory to predict the cascaded NP of a multiamplifler fiberoptic link from the NP due to each of the individual amplifiers. A cascaded NP expression is derived and compared to experimental results from a 60-km link consisting of three amplifiers. The measured NP of 11.8 dB for the link matches well with our theoretical prediction. The link gain of -7 dB, RF NF of 31 dB, 1-dB CDR of 148 dB ldrHz, and of 108 dB ldrHz^2/3 are also measured and matched to predicted values for the measured NP.     

Rain Attenuation Statistics from a 19 and 28 GHz COMSTAR Beacon Propagation Experiment: One Year Cumulative Distributions and Relationships Between the Two Frequencies

Cumulative attenuation distributions for one year and relationships between attenuations at 19 GHz and 28 GHz are presented for an earth-space propagation path terminating at Crawford Hill, New Jersey. An example from the distributions indicates that 20 dB attenuation was exceeded for 0.012% of the year at 19.04 GHz and for 0.06% at 28.56 GHz. For both frequencies the polarization was linear and oriented 21° from vertical at the receiver. When the attenuation at 19 GHz was less than 20 dB, the attenuation in dB at 28 GHz averaged 2.1 times that at 19 GHz. This ratio was lower at higher attenuations.     

Rain attenuation at 15 and 35 GHz

In order to satisfy future earth-to-space communications needs, new regions of the electromagnetic spectrum must be exploited. A program to determine the feasibility of using millimeter waves for this application has been conducted at Air Force Cambridge Research Laboratories (AFCRL) for approximately 6 years and it has been shown that at frequencies of 15 GHz (lambda = 2.0cm) and 35 GHz (lambda = 8.6mm) atmospheric attenuation is relatively low except for conditions of heavy clouds and precipitation. A portable radiometric system designed to measure attenuation at 15 and 35 GHz under conditions of precipitation was constructed and located in Hilo, Hawaii, a region where it rains frequently thus making it possible to conduct many attenuation measurements for varying rainfall rates. Attenuation was determined from both extinction and emission measurements as a function of zenith angle and rain rate. On the basis of the results that were obtained, it is concluded that for orographic rain up to rates of 50 mm/h in Hawaii: 1) attenuations up to approximately 10 dB can be calculated quite accurately from an emission measurement; 2) zenith attenuations are well correlated with rain rate and can be estimated from the regression lines which have been obtained; 3) attenuations at angles off zenith are not as well correlated with rain rate and thus the values obtained from the regression lines are only approximate; 4) attenuations at 15 and 35 GHz are well correlated.     

Wavelength demultiplexing heterojunction phototransistor

Experimental and theoretical results on a wavelength demultiplexing receiver composed of an AlGaAs/GaAs heterojunction phototransistor (HPT) integrated within a resonant cavity are reported. A high quality factor cavity was formed using a very thin In/sub 0.05/Ga/sub 0.95/As active absorption layer in the collector depletion region of the HPT. Crosstalk attenuations of 15 dB for dual and 12 dB for triple wavelength demultiplexing were demonstrated. The individual HPTs had an optical gain of 500 at the resonant modes. Theoretical calculations predict crosstalk attenuation levels as high as 40 dB with high reflection mirrors on both ends of the cavity.<>     

Antenna beamwidth independence of measured rain attenuation on a 28-GHz Earth-space path

Rain attenuation measured at 28 GHz on an earth-space path is independent of antenna beamwidth for beamwidths as small as0.1degand for attenuations up to 30 dB. The measurements imply that angle-of-arrival fluctuations are less than0.02deg.     

COCHANNEL INTERFERENCE IN SATELLITE COMMUNICATION SYSTEMS DERIVED FROM RAIN ATTENUATION MEASUREMENTS AT 20 GHz

This paper reports experimental results on cochannel interference during rain, derived from measurements of simultaneous and copolar rain attenuations, in the 20 GHz band, in two convergent slant paths to fixed receivers at Spino d'Adda (Northern Italy), from the geostationary satellites Olympus (19°W) and Italsat (13°E). The results show that during rain the interference can be larger than that in clear sky, with probability 0.5 and that, in this case, the interfering level I = A_C − A_n (dB), i.e. the difference between the simultaneous rain attenuations (dB) in the interfered path, A_C (dB), and in the interfering path, A_n (dB), increases as the system power margin increases. For system design, the paper reports the cumulative distributions of I, conditioned to the maximum value of the attenuation not exceeded (i.e. system power margin) in the interfered link. It is shown how the results could be used in systems with regenerative or transparent transponders on board.     

Modal attenuation in multilayered coated waveguides

Propagation and attenuation constants of low-order normal modes in a circular waveguide lined with lossy coating layers are calculated using a generalized dispersion equation. It is found that the use of multilayered coating can significantly enhance modal attenuations over a broader frequency range compared to that for a single-layer coated structure. For a cylinder with radius a=2λ, the attenuation constants for the dominant modes are shown to increase by 20 dB per a by adding a lossless padding layer to a lossy magnetic coating. Application of this result in radar cross-section (RCS) reduction is discussed     

太赫兹波大气分层传输特性

基于修正的Van-Vleck Weisskopf(VVW)线型,辐射传输色散理论和水汽连续体吸收模型,结合HITRAN数据库,建立了太赫兹(THz)波大气传输衰减和色散模型,并与毫米波传播模型(MPM)的结果进行了对比分析。加入新的天顶分层方法,形成了对宽频THz波在真实大气中纵向传输吸收衰减和色散的数值模拟能力。研究了不同传输距离下THz波大气分层传输衰减与色散特性、340 GHz和410 GHz窗口特性。研究结果表明：340 GHz和410 GHz大气窗口垂直传输10 km以上,衰减分别低于25 dB和45 dB,群速色散很低,相位变化在0.01个量级,信号传输失真度小。     

Measurements of rainfall attenuation at 8 and 15 GHz

Measurements of attenuation at frequencies of 8 and 15 GHz, and their correlation with rainfall rate, along a 15.78 km path near Ottawa, are described. Empirical expressions which relate the observed attenuation to the measured rainfall rate are derived and compared with similar expressions obtained on the basis of earlier theoretical studies of the problem. It is concluded that while the theoretical predictions of attenuation in rain are reasonably satisfactory, at least for rains observed at Ottawa, there is a definite tendency for observed attenuations at low rainfall rates to be somewhat higher than the expected values. The cumulative distribution of rainfall attenuation over a six-month period is compared with the attenuation predicted on the basis of average rainfall data obtained during the last five years. Although the agreement between observation and prediction, using the theoretical relation between rainfall rate and attenuation, is good for path attenuations greater than 2 dB, it can be greatly improved if the empirical expression relating rainfall rate to attenuation is used.     

An adaptive resource sharing strategy for TDMA

A satellite-based TDMA network consisting of four stations within different rain climatic zones has been operated in the 20/30 GHz frequency range using a recently developed flexible TDMA system allowing for FEC code rate and transmission bit rate variation. In this paper a strategy is presented to counteract overall link degradations due to atmospheric attenuation by dynamic allocation of resources. A spare time slot within the TDMA frame as a ‘common resource’ for bit rate and code rate switching offers up to 12 dB gain, whereas up-link power control, as it is implemented in this configuration, can cope with fades of 8 dB at maximum. For an experimental network configuration the expected long-term performance in terms of system availability is estimated for a viable version of the resource sharing strategy. Thereby, a model to calculate the probability of concurrent attenuation at the individual earth-station sites (‘satellite based diversity’) has been applied and the resulting probability to exhaust the resources is considered as a function of the degrading correlation between attenuations. Simulations with measured data via a ‘channel simulator’ and satellite measurements during the summer months of 1994 with the adaptive TDMA system are planned to test the functionality of the fade countermeasure strategy. Long-term propagation measurements on large-scale site diversity are required to verify predictions on the effective utilization of common resources.     

High-performance and wideband amplifier using bismuth-oxide-based EDF with cascade configurations

We demonstrate high-performance and wideband-bismuth-oxide-based erbium-doped fiber amplifiers (BI-EDFAs) with multi-stage configurations. Cascade configurations that gain flattening filters and isolators inserted between the doped fibers are applied in order to suppress amplified spontaneous emission (ASE). As a result of the optimization of the fiber length, the gain characteristics of the two-stage BI-EDFAs were improved in extended L-band region. The BI-EDFAs for four-channel coarse wavelength division multiplexing (CWDM) systems ranging from 1550–1610 nm are then presented. Three-stage configurations are applied, and a gain of 20 dB and an output power of 20 dB m are simultaneously achieved with practical pumping condition.     

A 0.13-/spl mu/m CMOS 5-Gb/s 10-m 28AWG cable transceiver with no-feedback-loop continuous-time post-equalizer

The frequency-dependent attenuation of the transmission lines between chips and printed circuit boards, for example, is an obstacle to improving the performance of a system enhanced with LSI technology scaling. This is because large frequency-dependent attenuation results in poor eye-opening performance and a high bit-error rate in data transmission. This paper presents a 5-Gb/s 10-m 28AWG cable transceiver fabricated by using 0.13-/spl mu/m CMOS technology. In this transceiver, a continuous-time post-equalizer, with recently developed no-feedback-loop high-speed analog amplifiers, can handle up to 9dB of frequency-dependent attenuation in cables and also achieve an 18-dB improvement in the attenuation (27dB total improvement) by using pre- and post-equalization techniques in combination.     

Affaiblissements différentiels a 13 GHz sur 53 km comparaison a des mesures simultanées a 20,5 GHz

Since May 1975, a 53 km link installed in the vicinity of Dijon (France), has been used to measure attenuation due to precipitation at 13 GHz in both vertical and horizontal polarization. A presentation is made of the results covering 1975 and 1976. Differential attenuations are measured on average, 25 % of the horizontal attenuation. This ratio does not vary much with attenuation, yet is higher than those values reported by other research engineers, or predicted by theory on the basis of Laws and Parsons distribution laws. This rather considerable attenuation may be explained by a mean distribution of raindrop diameters differing widely from those of Laws and Parsons. During the summer of 1975, therefore a second 20 GHz link was installed over the same route as the 13 GHz link. Indeed, a given ratio between the differential attenuation and the horizontal attenuation at 13 GHz, assigns the exponent to the distribution of the diameters of drops, assuming this distribution to be exponential (this being verified in the main). This constraint on raindrop diameter distribution, in turn assigns a value to the ratio of horizontal attenuations at 20.5 GHz and 13 GHz, respectively. This has been verified for 9 showers during the summer 1975. The average ratio of attenuation at 20.5 GHz and 13 GHz was 2, and simultaneously, for the same showers, the differential attenuation at 23 GHz equalled 24 % of the horizontal attenuation. Furthermore, it is shown that whatever the chosen exponential distribution is, those two ratios (2 and .24) correspond to the same exponent of the exponential, to which exponent a rainfall intensity can be associated. By way of example for the Laws and Parson distribution, these ratios are accounted for by a rainfall of about 300 mm/h against a rainfall (thunderstorms) of 50 mm/h for Joss.     

Fade counter-measures applied to transmissions at 20/30 GHz

The paper deals with the future use of the 20/30 GHz satellite communications band, especially with regard to small earth terminals. The 20/30 GHz bands are attractive for private link applications, but are subject to large signal attenuations in the presence of rainfall. Methods to overcome the rain attenuation, known as fade counter-measures, are investigated     

Prediction of slant path rain propagation statistics usingdual-polarized radar

The authors conducted a year-long experiment in which a dual-polarized S-band radar probed the volume surrounding two 11.45-GHz satellite downlink paths during rain. Accuracy was assessed by comparison to directly measured link attenuation with two 11-GHz beacon receivers 7.3-km apart at an 18.5° elevation angle, one colocated with the radar. Drop size distributions calculated from the radar horizontal reflectivity (Z_H) and differential reflectivity (ZDR) measurements were used to predict 11.45-GHz satellite beacon attenuations. The radar-predicted attenuations and those measured on the radio links agree, both on an event basis and in terms of annual cumulative distributions     

Statistical analysis of coherent ultrashort light pulse CDMA with multiple optical amplifiers using additive noise model

This paper describes a study of the performance of various configurations for placing multiple optical amplifiers in a typical coherent ultrashort light pulse code-division multiple access (CULP-CDMA) communication system using the additive noise model. For this study, a comprehensive performance analysis was developed that takes into account multiple-access noise, noise due to optical amplifiers, and thermal noise using the saddle-point approximation technique. Prior to obtaining the overall system performance, the input/output statistical models for different elements of the system such as encoders/decoders, star coupler, and optical amplifiers were obtained. Performance comparisons between an ideal and lossless quantum-limited case and a typical CULP-CDMA with various losses exhibit more than 30 dB more power requirement to obtain the same bit-error rate (BER). Considering the saturation effect of optical amplifiers, this paper discusses an algorithm for amplifiers' gain setting in various stages of the network in order to overcome the nonlinear effects on signal modulation in optical amplifiers. Finally, using this algorithm, various configurations of multiple optical amplifiers in CULP-CDMA are discussed and the rules for the required optimum number of amplifiers are shown with their corresponding optimum locations to be implemented along the CULP-CDMA system.