Showing papers on "Fading distribution published in 1986"

Direct-Sequence Spread-Spectrum Multiple-Access Communications Over Nonselective and Frequency-Selective Rician Fading Channels

Abstract: An accurate approximation is obtained for the average probability of error in an asynchronous binary direct-sequence spreadspectrum multiple-access communications system operating over nonselective and frequency-selective Rician fading channels. The approximation is based on the integration of the characteristic function of the multiple-access interference which now consists of specular and scatter components. For nonselective fading, the amount of computation required to evaluate this approximation grows linearly with the product KN , where K is the number of simultaneous transmitters and N is the number of chips per bit. For frequency-selective fading, the computational effort grows linearly with the product KN2. The resulting probability of error is also compared with an approximation based on the signal-to-noise ratio. Numerical results are presented for specific chip waveforms and signature sequences.

The effect of sample timing on bit error rate performance in a multipath fading channel

Abstract: Digital mobile radio often suffers from fatal effects caused by frequency-selective fading, resulting in severe bit error rate (BER) degradation. The feasibility of digital mobile radio largely depends on the multipath-distortion tolerant capability of modulation technique. The BER performance is compared among four digital modulation techniques in a frequency selective fading channel with large multipath delay spread. In particular, taking the timing fluctuation of eye patterns due to delay distortion of a fading channel into account, the effect of sample timing on BER is analyzed. The analyses have revealed that BER performance markedly depends on the choice of sample timing, and also an interesting fact that BPSK is outstanding in the multipath-distortion tolerance, if coupled with adaptive sampling, and its BER curves remain almost the same as that of frequency-flat fading as long as multipath delay difference is less than a bit interval.

Multi-path equalization for digital cellular radio operating at 300 Kbit/s

Abstract: Using TDMA transmission in digital cellular radio gives several advantages over conventional FDMA systems. However the higher bit rate that is necessary in TDMA makes the multi-path fading take the form of frequency selective fading. This type of distortion destroys the function of a conventional demodulator. In this paper it is shown that a decision feedback equalizer can remove the inter symbol interference created by the frequency selective fading. It is also shown that over a two-ray fading channel a diversity function is achieved. This means that the BER-performance of a TDMA system is better than the BER-performance of a FDMA system over a fading channel.

Signal-to-noise ratio requirements for detection of multiple pulses subject to partially correlated fading with chi-squared statistics of various degrees of freedom

Abstract: : The transmitted signal in a fading medium is composed of several pulses separated in time so as to achieve diversity and thereby combat deep fades and loss of signal Receiver processing consists of matched filtering of each of the pulses, followed by summation of the squared envelopes of all the filter outputs In addition to additive Gaussian background noise, the signal is subject to slow medium fading which has a chi-squared first-order distribution and which may be correlated from pulse to pulse to an arbitrary degree The false alarm and detection probabilities of this system are derived in various series expansions which are amenable to efficient computer evaluation Programs are presented and exercised for various combinations of signal-to-noise ratio, number of pulses, degree of correlated fading, and (noninteger) number of degrees of freedom of the chi-squared fading Required input signal-to-noise ratios for several false alarm and detection probabilities are computed and plotted for cases of the fading normalized correlation coefficient ranging from 0 to 1; results for a nonfading medium are superposed for easy comparison As special cases of the above formulation, we have independent Rayleigh amplitude fading, as well as completely dependent Rayleigh amplitude fading

The effects of Rayleigh distributed multipath fading on carrier recovery performance

Abstract: Multipath fading as encountered in the portable radio communications environment produces rapid and large carrier phase changes coincident with rapid fades. Any phase-locked loop (PLL) used for carrier recovery must accurately track these phase changes. This experiment studies the effects of PLL parameters on carrier recovery performance in the presence of noise-free multipath fading by use of a hardware fading simulator and a typical analog carrier recovery circuit. The Doppler spread, PLL damping factor, and PLL 3dB loop bandwidth were individually and jointly varied to determine their relationships to loop phase error performance. The key parameter affecting the loop phase error behavior is the ratio of the 3dB loop bandwidth to the Doppler spread, not their individual values. Important relationships between this ratio and performance measures of the carrier recovery loop were also found.

Towards a more accurate method of predicting the distribution of multipath fading on terrestrial microwave links

Abstract: Initial work is described towards the development of a more accurate asymptotic prediction method for the high fade depth range of the fading distribution on line-of-sight terrestrial microwave links. The influence of parameters such as path length, frequency, terrain roughness, path inclination, antenna beamwidth and path clearance is analysed using multipath fading data from a large number of links in the UK.

Robust and Nonparametric Detection of Fading Narrowband Signals

Abstract: : This thesis deals primarily with the design and analysis of algorithms for detection of narrow-band slowly fading signals, embedded in noise of uncertain distribution. The signal's phase and amplitude are random, but are random, but are essentially constant over the observation interval; in addition, the Doppler frequency of the signal is unknown. This is the most common model of target echoes received by radar or sonar systems. Attention is focused on i.i.d. noise samples whose marginal distribution belongs to an epsilon-mixture family, where the scale (variance) of the nominal part of the distribution is also unknown. This is an important generalization of the model. The purpose of the derived detection algorithms is two-fold: first, to assure constant probability of false alarm, regardless of the noise distribution (DF-CFAR); and second, to achieve optimal maximin probability of detection (Pd) performance. Keywords: fading narrow-band signals, robust detection, nonparametric detection, and scale invariance.

Laboratory evaluation of a mobile radio data system

Abstract: A mobile communications system has been built to study the parameters affecting data transmitted at 9.6 Kb/s over a laboratory simulated VHF mobile radio channel with additive white gaussian noise and Rayleigh fading. The signal is demodulated by a conventional mobile FM radio and its error distribution is recorded. The performances of different modulation schemes are presented and their BER are compared in a static and a fading environment. The simple and pratical technique of optimum threshold diversity switching by pre-detection of the signal's envelope is used at the receiver to combat fading. The data sequences received are recorded and analysed by computer in order to determine the error distributions and the performances of BCH and Reed-Solomon error-correcting codes.

Analysis of GMSK with differential detection in land mobile radio channels

Abstract: The effect of intersymbol interference (ISI) of Gaussian Filtered Minimum Shift Keying (GMSK) on the probability of error of one bit differential detection is analyzed theoretically in fast Rayleigh fading characterizing land mobile radio channels. A closed form expression is derived for the probability of error as a function of the fading rate, IF Filter Bandwidth, signal-to-noise ratio and ISI. Numerical results are presented for cases of practical interest to researchers and designers of cellular land mobile radio systems.

Equalization with few adaptive frequency gains for rapidly evolutive selective fading

Abstract: In this correspondence, we present a new equalizer with a reduced number of adaptive taps for rapid selective fading in data transmission channels. The equalization is performed in the frequency domain with a bank of frequency sampling filters. Only the gains of the filters whose passbands lie in the fading area are updated. The fading area is adaptively identified by an auxiliary coarse equalizer.

Packet Error Probability for Diversity Systems in Slow Rayleigh Fading and Gaussian Noise

Abstract: Analytical results on packet error probability for noncoherent frequency-shift-keying (NCFSK) and differential phase-shift-keying (DPSK) systems with diversity reception operating over slow Rayleigh fading channels with Gaussian noise are derived. Expressions obtained are applicable to two linear combining schemes: selection combining and maximal-ratio combining.