Showing papers on "Channel state information published in 1982"

Error Probabilities for Slow-Frequency-Hopped Spread-Spectrum Multiple-Access Communications Over Fading Channels

Abstract: Bounds and approximations are obtained for the average probability of error in an asynchronous slow-frequency-hopped spread-spectrum multiple-access communications system with noncoherent binary frequency-shift-keyed (FSK) data transmission. Both nonselective fading and wide-sense-stationary uncorrelated-scattering fading are considered.

Wideband characterisation of fading mobile radio channels

Abstract: A description of the physical mechanism causing multipath propagation in built-up areas is followed by a discussion of the various ways in which fading radio communiction channels can be described. It is shown that characterisation in the time-delay/Doppler-shift domain explicitly illustrates the multipath nature of the channel and provides parameters relevant to system design. A brief discussion of channel-sounding techniques is followed by a description of a wideband channel sounder using matched-filter signal processing in the receiver.

Packet radio in a Rayleigh channel

Abstract: Statistical multiple access is analysed for a number of independent transmitter-receiver pairs exchanging data packets over a shared mobile-radio channel. Rayleigh fading ‘softens’ the channel, resulting in less packet contentions and higher traffic capacity than for the standard Aloha channel.

Coding for the Turbulent Atmospheric Optical Channel

Abstract: In the presence of atmospheric or aircraft boundary layer turbulence, an optical channel may need large amounts of link margin to combat fading and beam spreading. Channel coding can reduce the average transmitter power required for reliable communication. This paper analyzes the performance of a coded PPM optical communication system that suffers log-normal fading during transmission. For moderate turbulence strengths, the coding gain in link margin is shown to be substantial.

A Comparison of Calculated and Observed Performance of Digital Radio in the Presence of Interference

Abstract: A statistical model of muitipath fading and detailed radio characterization measurements made in the laboratory provide the basis for a calculation of the time, during a heavy fading month, that a given digital radio system will be unavailable because of high bit error rates induced by multipath fading, thermal noise, and interference. We show that a simple algebraic expression for outage agrees with the detailed calculation over a wide range of possible interference levels. The simple expression also agrees with field observations. Performance is shown to depend on five parameters: three of these (dispersive fade margin, flat fade margin, and carrier-to-noise ratio at critical BER) are characteristic of the radio system as installed on a given path, one describes the interference environment, and one specifies the incidence of fading on the path.

Optimized Selection Diversity for Rayleigh Fading Channels

Abstract: This paper considers the choice of the number of diversity branches for minimizing the bit error rate of a selection diversity system using noncoherent binary frequency-shift keying modulation for transmission over a Rayleigh fading Gaussian channel. An exact expression for the optimum number of branches, L_{sel}^{\ast} , is given. The resulting probability of bit error decreases exponentially with the square root of the energy per bit.

Analysis of FH/MFSK Systems in Non-Uniform Rayleigh Fading Channels

Abstract: This paper examines several FH/MFSK systems in a noise jammed channel consisting of many sub-bands In each sub-band there is independent Rayleigh fading and distinct noise and propagation parameters General expressions for bit error bounds and cutoff rates are presented and plotted for the special case of worst jammer noise distribution and identical sub-bands

Effects of Frequency-Selective Fading on Slow-Frequency-Hopped DPSK Spread-Spectrum Multiple-Access Communications

Abstract: This paper is concerned with the performance of frequency-hopped spread-spectrum multiple-access communications in a fading environment. The data is transmitted on the carrier using differential phase-shift keying with multiple data bits per hop (i.e., slow frequency hopping). The frequency hopping and dehopping are noncoherent. Frequency-selective fading channels are considered for systems with various data pulse waveforms and channel delay power-density spectra. Analytical results for the average probability of error are presented, and numerical examples of the most interesting cases are given.

Fading Signals in the MF Band

Abstract: In the MF band, interfering signals from one or more broadcast stations can be received. During nighttime periods, this interference is caused by fading signals, propagated from distances of more than about 200 miles. It is the purpose of this report to provide the techniques needed to properly determine the degree of interference from one or more distant broadcasting stations. Computer algorithms are developed which determine the actual overall fading distribution of one or a combination of two fading signals, when the short–term fading of each is represented by a Rayleigh distribution and the long–term fading of median values is given by a log-normal distribution. Also, a simple approximate means of determining the distribution of the median value of a signal given by the sum of any number of fading signals is given. This approximate method is accurate only for the smaller percentage points. It is found that the techniques described here lead to somewhat higher values for the sum of the signals than previous methods.

Equalization of rapid selective fadings with unknown and time-varying forms

Abstract: This paper presents a new equalizer for rapidly time varying selective fading without an apriori information about the shape of that fading in frequency domain. The basic idea is to analyze the output of the channel by a set of adjacent filters covering the band of channel. Then, a gradient algorithm is used to identify frequency bands at which fading takes place and an other gradient algorithm is used to adapt only the gains of filters lying in vicinity of fading. This idea enables a high tracking speed for the equalizer and enables equalization of rapid fadings that are beyond the capabilities of presently existing equalizers.