Showing papers on "Fading distribution published in 1985"

Performance of nondiversity receivers for spread spectrum in indoor wireless communications

Abstract: In this work we have considered direct-sequence spread-spectrum transmission for indoor wireless communications. We have modeled the indoor communications medium, which is a multipath fading channel, by a discrete set of Rayleigh faded paths. We have proposed new analytical techniques to evaluate the probability of error for the receiver terminals studied in this work. Numerical results reveal that, for the nondiversity receivers considered here, Rayleigh fading is very hostile to this form of modulation/multipleaccess technique. The results also indicate that either some form of operation to prevent Rayleigh fading or diversity operation to counteract Rayleigh fading is required.

Method for improving the reliability of data transmission over Rayleigh fading channels

Abstract: A method and apparatus for reducing the bit error probability of data transmitted over a Rayleigh fading channel are disclosed. A relatively high bit rate serial stream of data is divided into N parallel relatively low bit rate streams of data. A controlled amount of intersymbol interference is introduced in the parallel streams. The N parallel streams are then transmitted simultaneously over the Rayleigh fading channel. Each bit in the N parallel stream of data has a duration longer than the duration of the typical Rayleigh fade. Thus there is a reduced probability that a Rayleigh fade will cause a bit error.

Outage probability in a mobile radio system subject to fading and shadowing

Abstract: Outage probability calculations are presented for the case when the transmission from a wanted base station is received at a mobile in the presence of an interfering cochannel signal, and reception is subject to fading and shadowing. These calculations consider the joint requirement that for satisfactory reception both an adequate signal and an acceptable signal/interference ratio are required simultaneously.

Space and frequency correlation characteristics of L‐band multipath fading due to sea surface reflection

Abstract: When maritime satellite communication is conducted at low elevation angles, fading due to sea surface reflection becomes a problem. For suppression of the fading, space diversity and frequency diversity may be employed. This paper studies the correlation characteristics of multipath fading due to sea reflection in the spatial and frequency domains in L-band operation. This is important in investigating the diversity effect. First, from the theoretical model of sea surface reflection, the correlation scattering cross sections of the coherent and incoherent components of the reflected wave are obtained. Next, from numerical calculations, the correlation characteristics are obtained with the antenna elevation angle and the height over the sea as the parameters. It is found that in space diversity good diversity effects can be expected from two antennas- separated in the vertical direction by about 40 cm. It is also seen that fading reduction cannot be expected with frequency diversity in the case of narrowband communications such as in maritime satellite communications. The effects of various fading reduction measures in the up and down links are considered.

An Analysis of the Sensitivity of Digital Modulation Techniques to Frequency-Selective Fading

Abstract: This Paper investigates the sensitivity to frequency-selective fading of different modulation techniques commonly used in digital radio systems. The modulation methods considered are phase-shift-keying ( M ary PSK), nonoffset and offset quadrature amplitude modulation ( M -ary QAM), and quadrature partial response signaling (QPRS). The performances of these methods during multipath fading are compared on the basis of the "signatures" calculated for idealized systems. Results are presented from which the relative outage probability was determined, assuming a propagation channel with frequency-selective Rician fading.

Generating rice processes with given spectral properties

Abstract: The autocorrelation function (acf) of a stochastic Rician fading process is numerically evaluated, and useful approximations are given. The spectral properties of the fading are related to the component processes constituting the fading process. The result is that for Rayleigh fading and first-order Butterworth characteristic of the component processes the fading bandwidth is double the component bandwidth. The fading bandwidth decreases to the component bandwidth, however, when the Gaussian channel is approached or when high-order faltered components are assumed.

Statistical model for amplitude and delay of selective fading

Abstract: The transmission performance of digital radio systems is controlled by spectral distortion caused by multipath fading. To evaluate this performance for digital systems with high-order modulation schemes, a statistical model for frequency-selective fading is needed. New propagation data obtained in Gainesville, Florida, were used to generalize Rummler's model to include group delay response. The introduction of the delay response data into the model of the fading channel enabled the classification of the fades as minimum phase and nonminimum phase. We found that 24 percent of all fades have significant delay distortion, and can be characterized as being minimum phase or non-minimum phase. In the range of practical interest, there are as many minimum phase as nonminimum phase fades. The results of this work will facilitate a better understanding of the fading channel, which will be beneficial in the engineering of radio routes and digital radio design. The results also demonstrate the need for a description of the geographical occurrence of dispersion, which will differ from that for multipath fading at a single frequency. This is based on the observation, presented in this paper, that the relative amount of dispersive fading is significantly greater in Gainesville, Florida, than in Palmetto, Georgia. The availability of a dispersive fading map will facilitate the accurate engineering of digital radio routes.

Bit error distribution in digital mobile radiocommunication-comparison between field measurements and fading simulation

Abstract: It is proposed to test the performance of mobile radio equipment by use of a fading simulator. This procedure has the advantages that the measurements can be made in laboratories, and that the random fading is reproducible in its statistical charcter. It is essential, however, to compare the results of fading simulation with field measurements. The fading simulator used is non-frequency-selective, and produces the two main random processes, Rayleigh and log-normal superimposed. The mobile measurements were made near Darmstadt, F.R.Germany. In most cases the results corresponded well with the simulation. The expected dependences of the signal/noise ratio and speed of the mobile on the bit error rates(BERs) were confirmed. Some measurements, however, revealed higher BERs than expected. Moreover, losses of data synchronism occurred. These irregularities are caused by heavy obstructions of the direct radio path and extremely low obstructions of the waves scattered from mountains, which were so far away that the excess delay can be of the order of magnitude of the clock period of the digital signal.

Performance of First-Order Digital Phase-Locked Loops in Mobile Radio Channels

Abstract: The performance of a first-order digital phase-locked loop (DPLL) using nonuniform sampling is studied in the mobile radio environments The mobile radio channel is characterized by introducing fast Rayleigh fading and random phase variation to the signal envelope and phase, respectively The nonlinear stochastic difference equation describing the loop operation in fading environments is introduced The joint probability density function (pdf) of the random variables of this equation is derived by transformation of random variables for fast Rayleigh fading channels A closed-form expression for the transition probability of the ChapmanKolmogorov (C-K) equation is obtained for phase step plus noise input and for frequency step plus noise input The probability density function of the steady-state phase error is obtained by solving the C-K equation numerically

Experimental Comparison of Angle and Space Diversity for Line-of-Sight Microwave Links

Abstract: In line-of-sight (LOS) links which use space or frequency diversity to combat multipath fading, the fading in each diversity branch is uncorrelated provided the antenna spacing or frequency separation is sufficiently large. Therefore, the availability or outage probability of space and frequency diversity systems is closely described by independent (uncorrelated) Rayleigh fading statistics. In the case of angle diversity, uncorrelated Rayleigh fading does not describe the performance of the angle diversity system. In fact, the fading on the two branches is positively correlated when the fades are shallow and negatively correlated when the fades are deep; i.e., if a deep fade occurs in one branch there is a high probability that the signal in the other diversity branch will not fade. In this paper we discuss briefly the theory of angle diversity and present the results of a short experimental program to compare the performance of angle diversity and space diversity on a fading LOS microwave link.

A unified analysis of multipath degradation in multilevel modulation radio systems

Abstract: In microwave digital radio transmission, waveform distortion due to frequency selective fading becomes a dominant factor of degradation. To evaluate the degradation of different systems in a unified way, the waveform factor is defined first. With the aid of concept “waveform factor,” the eye aperture is easily obtained. We also evaluate the waveform factors for various modulation schemes. Next, on the basis of the relation between propagation parameters and waveform factor in two-ray fading, the estimation formula of the outage probability for various digital radio systems in line-of-sight propagation is derived. The proposed factor is determined uniquely by system parameters, such as modulation scheme, system impulse response, and symbol rate. With the aid of this factor, digital radio system performance during multipath fading is easily evaluated.

lodul Analysis of the Sensitivity of Digital .ation Techniques to Frequency-Selectj

Abstract: Abstruct-This paper investigates the sensitivity to frequency-selective fading ef different modulation techniques commonly used in digital radio systems. The modulation methods considered are phase-shift-keying (Mary PSK), nonoffset and offset quadrature amplitude modulation (M-ary QAM), and quadrature partial response signaling (QPRS). The performances of these methods during multipath fading are compared on the basis of the “signatures” calculated for idealized systems. Results are presented from which the relative outage probability was determined, assuming a propagation channel with frequency-selective Rician fading.