Doppler Fading Research Articles

A Proposal of Pulse-Pair Doppler Operation on a Spaceborne Cloud-Profiling Radar in the W Band

Pulse-pair Doppler operation is considered for the spaceborne mission. In a formalism, the condition that a measured Doppler velocity on pulse-pair operation corresponds to that on the FFT operation is derived. The coherent coupling effect of the spectral broadenings between Doppler fading and vertical wind shears is shown to strongly depend on the flight direction of a platform. This coupling effect, which has been ignored for ground-based and airborne radars, is characteristic for the space mission. Two kinds of pulse-pair operations, polarization diversity method and conventional contiguous pulse-pair method, are studied to determine the accuracy of Doppler velocity as a function of cloud reflectivity and pulse-pair interval. Advantages and disadvantages of these operations, including adverse effects of beam-pointing error, ground clutters, and sidelobes, are discussed along with a variety of parameters to design the optimum operation. In the assessment of the Doppler feasibility, new features suitable to the space mission are also proposed.

A Unified Formalism of Incoherent, Quasi-coherent, and Coherent Correlation Signals on Pulse-Pair Doppler Operation for a Cloud-Profiling Radar: Aiming for a Space Mission

The correlation signals of the incoherent, quasi-coherent, and coherent backscatterings from clouds have been analytically calculated from a unified formalism based on the Eulerian description for a generic weather radar with pulse-pair function, especially aiming for a space-/airborne mission. The spectral broadening due to Doppler fading and wind shears is calculated from this formalism. Since the coupling of these two effects in the spectral broadening is substantial, a conventional estimation is found not to be adapted for the space-/airborne radar. The condition of pulse-pair interval to make data treatment of this operation correspond to that of the fast Fourier transform (FFT) operation is also derived. Further, comparing the derivation of the quasi-coherent scattering to that of the incoherent scattering within the unified formalism, as concerns the Fraunhofer region, it is proven that the former scattering can be represented in a similar form to the latter one, even for nonuniformly illuminated clouds, despite the difference in scattering properties. In addition, the reestimation of the volumetric reflectivity for the quasi-coherent scattering is performed. Finally, the Doppler correlation signals for the coherent backscattering and for the optical partial reflection from a keen boundary of cloud density are formulated.

Analysis of observed Doppler fading signal in low-VHF band

Short-term amplitude variations of a tropospheric radio signal are presented and discussed. Radio wave transmissions from Newbury on 46.95 MHz were received at the University of Hull. These fluctuating signals were recorded, edited and finally analysed using time-frequency and regression techniques.

Semianalytical simulation for evaluation of block-error rates on fading channels

A semianalytical (SA) simulation method is proposed as a means to improve the efficiency of computer simulation in estimating block-error rates (BKERs) in the presence of Doppler fading and additive white Gaussian noise. Frequency-nonselective Rayleigh, Rician, and Nakagami fading with diversity combining for binary noncoherent frequency-shift keying (NCFSK) modulation are considered. The reduction in required computer simulation time of the SA method compared to the conventional Monte Carlo (MC) simulation is assessed.

Effects of directional antennas at the base station on the Doppler spectrum

We analyze the effect of directional antennas at the base station on the Doppler spectrum. It is well known that the Doppler spectrum is dependent on the probability density function (pdf) of the angle-of-arrival (AOA) of the multipath components at the mobile unit and the direction of the motion of the mobile. The Doppler spectrum is U-shaped, when the pdf of the AOA of the multipath components at the mobile is uniform. Here, however, we study the Doppler fading at the base station and assume that the scatterers are uniformly located around the mobile within a circle and derive the pdf of the AOA of the multipath components at the mobile when directional antennas are used at the base station.

Capacity of a cellular time division duplex CDMA system

A time division duplex (TDD) technique is considered for a CDMA cellular system. Its use enables all the multipath combining (using a RAKE type receiver) to be located in the base site rather than in the mobile unit. This is possible due to the reciprocal uplink and downlink channels which are created by time division, and employ the same carrier frequency. Simulations show that at low Doppler fading rates TDD is only marginally lower in cell capacity than conventional frequency division duplex (FDD) techniques. However, at higher Doppler fading rates (for high speed mobiles) the cell capacity degrades in a nonlinear manner and will breakdown suddenly, unlike that of a comparable FDD CDMA system. The limitation of the TDD technique results from the noncontinuous receiver training caused by the bursty nature of the communications. Losses in cell capacity are also due to the guard times inserted between the uplink and downlink transmissions.

Convolutionally coded binary PSAM for Rayleigh fading channels

Recently proposed, pilot symbol assisted modulation (PSAM) uses a known pilot sequence to derive amplitude and phase references at the receiver. The Letter presents convolutional coding for such systems and derives the exact pairwise error probability and the Chernoff upper bound of it A comparison among PSAM, coherent and differential detected coded systems indicates that, even at 5% Doppler fading rate, coded PSAM requires 3.5 dB more than the ideal coherent case but less than the differential case.

Interfade Interval Statistics of a Rayleigh-Distributed Wave

This paper presents distributions of the intervals between fades measured on a hardware-simulated Rayleigh-fading mobile radio channel. For intervals between deep fades, these distributions take on a Poisson form. Measured results are in good agreement with a simple analytical model. Distributions for the intervals between shallower fades exhibit preferred durations caused by peaks in the Doppler fading spectrum.

On the characterization of multipath and Doppler fading in earth-scatter communication, navigation, and radar links (Ph.D. Thesis abstr.)

On the characterization of multipath and Doppler fading in earth-scatter communication, navigation, and radar links (Ph.D. Thesis abstr.)

Some measurements on the sunset fading effect

The sunset fading effect, or flutter fading, is a phenomenon sometimes observed on radio signals reflected from the F region of the ionosphere when the reflection point is near the magnetic equator. The effect was investigated in Ghana using direct observation of the carrier level, a fading-rate meter, and the Doppler fading technique. It is found that flutter fading occurs between sunset and midnight, has equinoctial maximums, and correlates positively with the sunspot cycle. The fading rate is directly proportional to the frequency. It is suggested that coherent scatter from elongated irregularities could account for the observed correlation with radio-star scintillations and for the Doppler fading results. (auth)