Nonselective Fading Research Articles

Adaptive Diversity Reception Over a Slow Nonselective Fading Channel

We extend some previous results on adaptive receivers with memory for slow nonselective Rayleigh fading channels to the case of diversity reception. The Bayes receiver in this case is shown to be a generalized maximal ratio combiner. Error probability performance is obtained for antipodal signals such as BPSK. A simple performance upper bound is also derived. Numerical performance results are presented for the particular case of a Markov channel model.

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

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.

Coding and Modulation Techniques for Frequency-Hopped Spread-Spectrum Communications Over a Pulse-Burst Jammed Rayleigh Fading Channel

In this paper, the results of comparing the performance of various forward error correction techniques and several modulation formats when used over a nonselective Rayleigh fading channel in the presence of a pulse-burst jammer are presented. Both binary and nonbinary codes are considered, as well as concatenated codes consisting of either a block or a convolutional inner code and a Reed-Solomon outer code. Finally, the use of side information to allow the decoding of both erasures and errors is also analyzed.

Reception of PSK Signals Over Fading Channels Via Quadrature Amplitude Estimation

We consider here a new approach to PSK signal detection over a slow nonselective Rayleigh fading channel which does not require a carrier recovery loop. The receiver achieves coherent demodulation by making use of estimates of the quadrature amplitudes of the received PSK signals in its likelihood ratio test. The receiver is assumed to have a memory containing information on the past received signals which enables it to generate the estimates. The error rate of the receiver can be evaluated analytically and computer simulation results are presented to verify the predicted performance.

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

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.

Error Performance of Direct Sequence Spread Spectrum Systems on Non-Selective Fading Channels

The effects of fading on the performance of a spread spectrum multiple-access communication system using direct sequence modulation are investigated. General series expansions are developed for the average probability of error and specific results are given for the irreducible error rate associated with propagation over independent Rician fading channels or correlated Rayleigh fading channels. Simple single-term approximations for the irreducible error rate, which are proportional to the second moment of the cross-correlation between the spreading codes employed by the users, are derived for these cases.

Effect of Fading on FM Reception with Cochannel Interference

The combined effect of cochannel interference and nonselective Rayleigh fading on the reception of analog FM signals in additive Gaussian noise is analyzed. Rice's click model for the breaking region is used. Analysis in the absence of interference is performed first and the effect of modulation on the click rate is found to be nearly negligible. For the case with cochannel interference the click rate is computed in the absence of modulation. Curves are given for detected signal-to-noise ratio (SNR) versus carrier-to-noise ratio (CNR) with signal-to-interference ratio (SIR) as a parameter and SNR versus SIR with CNR as a parameter. The results agree well with recently published results of a simulation study.

Performance of an M-ary p.s.k. system in the presence of additive noise, intersymbol interference and fading

The results of an investigation of the evaluation of energy signal degradation of an M-ary p.s.k. system due to intersymbol interference and fading are analysed. Attention is concentrated upon the influence of intersymbol interference caused by the limited band of the receiver filter as well as the transmitter one. As far as the channel is concerned, it has been assumed there is nonselective fading in it. Part 1 presents the analysis method being applied; Part 2 analyses the energy degradation characteristics of M-ary signals resulting from intersymbol interference in the case when no fading occurs in the channel; Part 3 analyses the influence of intersymbol interference and fading jointly.

Multipath Fading in FSK Communication Links - An Experimental al Investigation

The results of an experimental investigation of binary error rates in an FSK channel experiencing nonselective fading are presented. For all cases considered, the received frequency uncertainty is large compareded to the bit rate, requiring the use of an envelope detector rather than a matched filter. Both slow and fast fading rates are considered and include the effects of differential Doppler shift between the direct and reflected energy. A simplified mathematical analysis is presented to support the observed results. Both the theoretical examination and the data obtained demonstrate that fast fading and/or differential Doppler generally improve the link error rate performance with respect to the nonfading case.

Performance of selected block and convolutional codes on a fading HF channel

This paper describes the application of selected block and convolutional coding techniques to digital transmission over an HF radio channel. Performance results are presented for interleaved binary Bose-Chaudhuri-Hocquenghem (BCH) codes, interleaved two-stage concatenated codes, and diffuse convolutional codes. The performance results are based upon raw error data recorded in transmission over a 640-km HF path, with various data runs representing the typical effects of frequency-selective and non-selective fading, atmospheric impulse noise, and interference from other users of the HF band. The performance of binary BCH codes with bit interleaving is presented and the selection of a code to meet a specified performance criterion is described. The sensitivity of specific codes to changing channel conditions is presented, along with the cost, in terms of interleaving, of designing for one set of channel conditions rather than others. Concatenated codes are discussed as a means of effective error control on channels with clustered errors. Performance data are presented for selected two-stage codes used with inner-stage word interleaving and the effects of varying certain of the code parameters are shown. Emphasis is placed on code designs that use the inner-stage code only for error detection and the outer-stage code mainly for erasure filling with only a small amount of symbol error correction. The impact of error clustering on the performance of concatenated codes is discussed. Two diffuse convolutional codes are evaluated with the use of recorded error data in computer simulations of their threshold-decoding algorithms. Performance of various configurations of these convolutional codes is given and a comparison is made with that of a simple block coding scheme having the same decoder storage requirements. The various coding techniques studied are compared on the basis of achievable performance as well as certain factors affecting the feasibility of implementation.

Response of an FM Discriminator to a Digital FM Signal in Randomly Fading Channels

The calculation of the error rate resulting from the detection of a binary FSK signal using an FM discriminator-lowpass filter detector is described for an FM signal undergoing nonselective fading in additive Gaussian noise. The results extend the error rate calculations of Schilling et al. [1], [2] which were performed for a nonfading channel. While the technique employed is quite general, examples considering Rayleigh fading and an alternating mark-space sequence are given. Following a CCIR recommendation for Rayleigh fading, the percentage of time that the signal envelope is below a minimum level is ignored, since in this case the circuit would be completely cut off or switched to a better path. Thus, the results also depend on the depth of fade or ratio of the minimum signal amplitude squared to the average carrier power. The use of diversity is studied, and the error rate for a discriminator using predetection combining diversity is found. In this case the possibility of infinitely deep fades is considered. The analysis is based on the work of Nelson[9], [14], who considered signal-to-noise ratio performance of an FM discriminator with an analog FM signal undergoing nonselective fading. Experimental results are shown to verify the theory.

Performance of Digital Communications Systems in an Arbitrary Fading Rate and Jamming Environments

Performance of Digital Communications Systems in an Arbitrary Fading Rate and Jamming Environments

Error Probabilities for Binary Symmetric Ideal Reception through Nonselective Slow Fading and Noise

One of two correlated, equal energy, equiprobable waveforms is transmitted through a channel during a given time interval. The signal is corrupted in the channel by slowly-varying, frequency-nonselective fading and by additive, Gaussian noise. On reception, the corrupted signal is processed by an ideal receiver, which guesses that the transmitted waveform was the one which it computes to be a posteriori most probable. Expressions for the probability of committing an error in making such a guess are derived for both coherent and noncoherent receivers; these are studied in detail, and some general trends and system design considerations are noted. In an illustrative example, the results are applied to binary frequency-shift keyed (FSK) systems with various pulse shapes and frequency separations.

71. A peculiar type of scintillation of solar radio radiation

Some authors (Payne-Scott and Little (1952) [1]; Owren (1952) [2]) have mentioned a phenomenon in the enhanced solar radio emission which they call ‘non-selective fading’. The present paper is meant to call attention to another, rather peculiar, type of scintillation in the radio emission of the sun, which differs from the non-selective fading in some important respects. This scintillation has been observed since 1952 by the division ‘Ionosphere and Radio Astronomy’ of the Netherlands Telecommunications Service in the course of a continuous survey of solar radio radiation. It has been found at the radio frequencies 140, 200 and 545 Mc./s.