Showing papers on "Channel state information published in 1987"

Capacity of Slotted ALOHA in Rayleigh-Fading Channels

Abstract: Fading channels may improve the capacity of slottedALOHA networks. Rayleigh fading and spatially distributed packet transmitters diminish mutual packet interference and thus reduce the average blocking probability of a shared receiver. A transmission model, combining Poisson statistics of the offered data traffic with Rayleigh statistics for the fading channel, is developed. Analytical and numerical results are presented, indicating significant improvements to signaling in cellular mobile networks and in packet radio systems with fading radio channels.

Fading Channel Issues in System Engineering

Abstract: The character of multipath-induced propagational fading is reviewed, along with the interpretations underlying use of the Rayleigh fading model to describe the process statistics. The relationship between this model and contemporary laboratory fading simulators is also outlined. The effects of the fading upon data communications are described, along with the techniques of modulation, diversity, coding, and adaptive equalization used in modern modem designs for operation over such channels. Finally, the system engineering problems are discussed of attempting to provide quantitative estimates of long-term link or network performance that takes into account the longer term channel variabilities.

Trellis Coded Modulation for 4800-9600 bits/s Transmission Over a Fading Mobile Satellite Channel

Abstract: The combination of trellis coding and MPSK signaling with the addition of asymmetry to the signal set is discussed with regard to its suitabllity as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing the average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in this paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, our results will only reflect the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.

Forward Error Correction Coding for Fading Compensation in Mobile Satellite Channels

Abstract: Fading in mobile satellite communications severely degrades the performance of data transmission. The channel is modeled with nonfrequency selective Rice and Rayleigh fading. Also, stored channel simulation is used for hardware data transmission. FEC coding with Viterbi decoding of convolutional codes, and Berlekamp-Massey decoding of Reed-Solomon codes, are used to compensate for the fading. In addition to interleaving, channel state and erasure information improve the performance of the decoder. The BER after decoding is calculated for specific codes on several channels and for different transmission schemes. Using very simple channel state and erasure information gives 2-7 dB additional coding gain. These gains have been verified by hardware data transmission on synthetic fading channels and stored mobile satellite channels.

Error Probability Evaluation for Systems Employing Differential Detection in a Rician Fast Fading Environment and Gaussian Noise

Abstract: A method is presented for determining the error probability of a receiver using differential detection in the presence of Gaussian noise and fast Rician fading. Equations for the covariances of the fading component are derived, which include the effect of IF filter distortion. It is shown that these equations may be readily evaluated numerically. A simple formula for the error probability is derived for systems using BPSK and a matched filter receiver. An example of the error probability is given using this receiver. Also given is an example of a system using MSK with a practical IF filter. Different spectral shapes and bandwidths for the fading process are investigated for this example and their effect on the error probability is determined.

Direct-Sequence Spread-Spectrum Receiver for Communication on Frequency-Selective Fading Channels

Abstract: The reception of direct-sequence spread-spectrum signals on frequency-selective fading communication channels is considered. The fading statistics are described using the wide-sense-stationary uncorrelated-scattering (WSSUS) channel model. It is shown that, under certain assumptions about this channel such as time-invariance over the duration of a data symbol, an orthogonal representation for the received distorted signal can be found. The optimum incoherent receiver can then be realized with reasonable complexity. The analysis shows that exploiting the inherent diversity of a frequency-selective channel can reduce the receiver error probability by several orders of magnitude. The optimum selective channel and the jamming susceptibility of the receiver are discussed.

The Maritime Satellite Communication Channel--Channel Model, Performance of Modulation and Coding

Abstract: Towards the year 2000, maritime satellite communications using the INMARSAT system will employ a second and third generation of satellites and new ship earth stations (SES). The new SES standards will use very small antennas with gains between 0 and 15 dBi. At the lower end of SES there will be no antenna stabilization. The communication channel for such small stations is described by a model including multipath fading, Doppler shift, and noise. The results of an extensive measurement program were used to determine the parameters of the channel model, which depend on antenna type and elevation angle. Analytical calculations as well as synthetic and stored channel hardware simulations have been used to determine the performance of several modulation schemes. A complete data link using PSK modems with AFC/Costas loop, interleaving, and FEC codecs at 1.2 kbits/s was built up around a hardware maritime channel simulator, to study the performance of data transmission on the small SES maritime channel. Theoretical and measured results are given for interleaved Viterbi decoding with channel state information and Reed-Solomon codes. The measurements show that with interleaved FEC schemes, the required E_{b}/N_{o} for a BER 10-5is in the range of 9-15 dB and the effects of multipath fading are almost compensated for.

Measured Characteristics of 800/900 MHz Fading Radio Channels with High Angle Propagation Through Moderately Dense Foliage

Abstract: The probability of error for the transmission of digital information on fading radio channels is influenced by the statistical behavior of fading. This is characterized by the cumulative distribution function (CDF) for the received signal envelope, and the correlation of random variations across the channel bandwidth. It is therefore important for system design purposes to determine the distribution function for envelope fading, and the frequency correlation characteristics of radio channels in propagation environments where the use of digital radio systems is planned. This paper details experiments that were conducted under conditions similar to those which would be typical on 800/900 MHz band satellite-mobile channels in rural environments. The impulse response functions of measured channels were estimated by operating a pseudonoise channel probe from a 65 m tower through deciduous trees to a receiver at close range. Measurement results include: channel impulse response estimates, envelope fading statistics, and double-sided frequency correlation plots. Comparisons are made between channel characteristics during the summer and during the autumn after the leaves have fallen from the trees. Estimates of digital channel capacity limitations are also given. Aside from the fading statistics, these channel characteristics have not previously been reported.

Adaptive Receiver for Digital Communication Over HF Channels

Abstract: The fading characteristics of the HF channel make communication over this channel difficult, even at moderate data rates. In this correspondence, a practical communication system is presented which has a near-optimal receiver for data detection and adaptive optimization of the receiver to channel parameters. The channel tracking is performed during the training sequence as well as during the detected data sequence. The receiver is fast converging, therefore suitable for frequency hopping. The correspondence presents the performance obtained on fading HF channels and the computational complexity via comparisons to previously published results. The performance is shown to be superior at comparable computational complexity.

The Effects of Fading on Antijam Performance Requirements

Abstract: The purpose of this paper is to analyze the impact of fading on the performance of both conventional and spread spectrum systems. The analyses presented herein take into account the effects of fading on the jamming signal as well as fading of the communications signal. It is assumed that the envelopes of both the desired signal and the jamming signal fade with a Rice distribution. The distribution of the signal-to-jammer ratio ( S/J ) is thus the result of squaring the ratio of two independent Rice random variables. An expression for the distribution of the ratio of two Rice random variables is obtained and this expression is used to evaluate the effects of fading on performance. Two cases are considered. In the first case, the fading is assumed to be slow compared to the duration of a message. In this case, the system performance is described by the probability that the message is successfully transmitted, averaged over all possible values of the S/J . This performance measure is often referred to as the availability of the system. In the second case, the fading is assumed to be slow compared to the symbol duration but fast compared to the message duration. In this case, the performance is best described by averaging the bit error rate over all possible values of the S/J . A number of numerical examples is presented. In general, these results show that, for the case of very slow fading (case 1), the communicators suffer a performance loss of up to 10 dB compared to the nonfading case, depending on the required availability and the fading parameters. In case 2, fading appears to have little impact on the jammer but a major impact on the communicators, so that losses of up to 20 dB compared to the nonfading case are observed. In case 2, the performance for the situation in which both the signal and the jammer fade is approximately the same as the performance in the situation where only the signal fades. It is shown that, as in the standard fading model in which only the signal fades, error correction coding with interleaving can be effective in reducing the losses caused by fading.

Discriminator-MLSE Detection of a GTFM Signal in the Presence of Fast Rayleigh Fading

Abstract: This paper examines the influence of fast Rayleigh fading and cochannel interference on GTFM with discriminator-MLSE detection using a hardware fading simulator. The degradation in BER performance, due to fading, can be largely recovered by using two-branch selection diversity. The resultant bit error patterns are also presented.

Diversity and Coding for FH/MFSK Systems with Fading and Jamming--Part I: Multichannel Diversity

Abstract: The performance of diversity and/or coding is evaluated for FH/MFSK signaling over Rayleigh fading channels in the presence of jamming. The effects of partial-band tone and partial-band noise jamming on uncoded and coded systems are considered. The results indicate that FH/MFSK signaling with diversity provides satisfactory performance for jammed fading channels. For coded FH/MFSK signaling over fading channels, noise jamming may be more effective than tone jamming. The amount of improvement resulting from the use of diversity in conjunction with coding depends upon many factors, including the nature of the channel, the degree of channel state information available at the decoder, the type of decoding, and the modulation alphabet size.

Wideband Probing of the Trans-Auroral HF Channel

Abstract: HF probe measurements of the channel pulse response were made over a 2300 km trans-auroral path between a transmitter site at Frobisher Bay, Canadian Northwest Territories, and a receiver site near Rome, New York Data are presented in the form of ionograms, pulse response time histories, and channel scattering functions The distinguishing characteristics between a well behaved mid-latitude channel and a trans-auroral channel, as seen with a coherent channel probe, are discussed Inferences regarding signalling strategies for coping with multipath fading and bandwidth for maximizing spread spectrum processing gain are discussed Examples showing the variety of the trans-auroral channel are presented

Channel estimation for land mobile radio systems

Abstract: The paper describes a number of novel and promising techniques for use in the estimation of a flat fading channel with a rapid fading rate, such as occurs in many land mobile radio systems. The algorithms of the various techniques are first presented, followed by the results of a series of computer simulation tests, carried out on these algorithms when operating with an idealised model of the channel. The quantities measured in the tests include the mean-square error in the channel estimate, with the correct detection of the data symbols, and the error rate in the detected data symbols, with perfect channel estimation and also when operating with a channel estimator. The channel estimate considered here is the one- or two-step prediction of the channel that is fed to the detector. A further aim of this investigation is to study the feasibility of the simultaneous transmission of two bandlimited 4-level QAM (quaternary PSK) signals simultaneously over two independent Rayleigh fading channels to a single receiver, where both signals occupy the same frequency band and no coding or diversity techniques are employed to improve the performance, other than differential coding needed to avoid prolonged error bursts. The results obtained suggest that it should be possible to achieve the satisfactory coherent detection of a single Rayleigh-fading 4-level QAM signal, under conditions of even quite severe and rapid fading, but for the simultaneous transmission of two independently Rayleigh-fading signals over the same frequency band, the appropriate diversity techniques will be required to reduce the resultant depth of the fades. The techniques proposed here should make it possible to achieve a significantly more efficient use of bandwidth in cellular mobile radio systems than is possible by conventional methods.

Performance of binary multi-h modulation for fast fading, shadowed, mobile satellite communication channels

Abstract: The performance of bandwidth efficient multih modulation is determined for a class of fading models for mobile satellite communication. The fading model has the structure of a Rician model except that the line-of-sight component is subjected to a lognormal transformation. This models shadow fading due to foliage attenuation. The multi-h codes are considered under conditions of perfect and partial coherence. The phase jitter due to fading is found to be a major impairment to system performance. A fast fading assumption is used with system fading bandwidths of 5 to 10 percent of the baud rate. The fading spectrum follows a third-order-Butterworth spectral shaping and uses fading model parameters based on measured data. The system average bit error probability is determined via a digital computer simulation on an additive white Gaussian noise channel with received signal fading.

Limits of data rates in the urban mobile channel

Abstract: The bit error rate performance of data transmission schemes is evaluated when operating over the Rayleigh fading urban radio mobile channel. Two typical situations are analysed : the fast fading with differential detection and the frequency-selective fading with coherent detection, for BPSK, QPSK and MSK modulations. Conditions for which the fast fading or the frequency-selective fading effects may be neglected are given in terms of the data rate. The influence of the shape of different spatial and frequency correlation functions on the bit error rates is also analysed.

Pdomance of Binary Multi-h Modulation for Fast Fading, Shadwed, Mobile Satellite Cmication Channels t

Abstract: The performance of bandwidth efficient multi-h modulation is determined for a class of fading models for mobile satellite communication. The fading model has the structure of a Rician model except that the line-of-sight component is subjected to a lognormal transformation. This models shadow fading due to foliage attenuation. The multi-h codes are considered under conditions of perfect and partial coherence, The phase jitter due to fading is found to be a major impairment to system performance. A fast fading assunption is used with system fading bandwidths of 5 to 10 percent of the baud rate. The fading spectrum follows a third-order-Butterworth spectral shaping and uses fading model parameters based on measured data. The system average bit error probability is determined via a digital computer simulation on an additive white Gaussian noise channel with received signal fading.

Laboratory measurements and a theoretical analysis of the TCT fading channel radio system. [Tone Calibrated Technique]

Abstract: This paper documents the laboratory and theoretical performance of a pilot-aided digital radio system. The technique considered transmits a midband pilot tone to improve the receiver data detection performance in a multipath fading channel and is referred to as the tone calibrated technique (TCT). We report on the performance of a 860 MHz prototype system carrying 2.4 kbit/s data under Rician fading conditions. Both experimental and analytical results show that the error floor experienced with nonpilot-aided transmission methods is effectively removed by the TCT scheme, resulting in significant performance gains at high signal-to-noise ratio (SNR) values. The paper also examines the TCT system performance under typical operating conditions and presents a new analysis of the TCT theoretical error probability.

Performance Analysis of Multiple Chips Per Symbol M-ary FSK in Fast, Slow and Partially Correlated Rayleigh Fading

Abstract: Error rate performance analysis is presented in this paper for the multiple chips per symbol M-ary FSK in the fast, slow and partially correlated Rayleigh fading environments Exact error rate expressions are given for the three fading situations considered Numerical results are provided for the 8-FSK waveform Error performance with forward error control coding is also presented to show the improvement over the uncoded cases These results have direct application to the design of ionospheric communication systems