Convolutionally interleaved PSK and DPSK trellis codes forshadowed, fast fading mobile satellite communication channels

Using a model from the literature, the performance of convolutionally interleaved phase-shift-keying (PSK) and differential phase-shift-keying (DPSK) trellis codes for digital speech transmission over shadowed mobile satellite communication channels is determined by computer simulation. First the characteristics of fading channels are examined and analyzed in terms of the probability distributions of amplitude, phase, and burst errors. A statistical method, using a histogram approach, is utilized along with the simulations of fading channels to generate these probability distributions. A test for channel burst error behavior is presented. A periodic convolutional interleaver/deinterleaver to be used with trellis coding to combat slow fading in digital, shadowed mobile satellite channels is designed. This interleaver ha less than half the time delay for the same bit error performance than a block interleaver. The results show that the periodic convolutional interleaver provides considerable improvement in the error and time delay performance of mobile satellite communication channels for up to average shadowing conditions as compared to other techniques     

Study on application of CMA to land mobile LEO satellite communication systems based on a deterministic channel model

This paper studies the application of the constant modulus algorithm (CMA) in land mobile low earth orbit (LEO) satellite communication systems. Two propagation phenomena prevail in narrow band land mobile LEO satellite channel, namely, adjacent channel interference (ACI) and frequency‐non‐selective fading. The performance of CMA for ACI cancellation and the behaviours of CMA in frequency‐non‐selective fading channels are evaluated using a digital beamforming (DBF) array antenna simulation scheme. All these evaluations are based on a simple but efficient channel model which provides a good and fast simulation method for land mobile LEO satellite channels. The restricted Jakes Doppler power spectral density (psd) function is incorporated into the model to ensure that it will be appropriate for the evaluation of a DBF antenna. Our results reveal that CMA can reject ACI and work well in frequency‐non‐selective fading channels. Copyright © 2002 John Wiley & Sons, Ltd.     

Q2DPSK in the satellite mobile channel with ISI and CSI

The authors analyze the performance of quadrature-quadrature differential phase shift keying (Q²DPSK) in the satellite mobile channel. The expression for the bit error probability takes into account both intersymbol and cross-symbol interference (ISI and CSI). Numerical results are presented for three different pulse pairs. It is shown that Q²DPSK with 4 symbols outperforms DPSK with 8 symbols. They conclude that Q²DPSK is both power and bandwidth efficient for the satellite mobile channel which includes as special cases the Gaussian and Rayleigh channels     

Performance of Hybrid Error Control Schemes of Satellite Channels

The effectiveness of hybrid error control schemes involving forward error correction (FEC) and automatic repeat request (ARQ) is examined for satellite channels. The principal features of the channel are: large round-trip transmission delay due to the satellite link, and burst errors introduced by the terrestrial links that connect the users to the satellite link. The performance is estimated for two channels described by Fritchman's simple partitioned finite-state Markov model, and is compared to that obtainable if the channel is considered as a binary symmetric channel of the same bit error probability. Results show that the hybrid schemes offer substantial improvement over ARQ and FEC, and that an optimum exists for the number of errors corrected to obtain maximum throughput efficiency.     

Error floors in the satellite and land mobile channels

In a satellite mobile channel (SMC) and land mobile channel (LMC) because of fading and nonlinear power amplifiers, constant envelope modulation and noncoherent detection methods may outperform other schemes. It is shown how to compute the error floor for four noncoherent digital communication systems in satellite and land mobile channels. Differential phase shift keying (DPSK) with differential phase detection (DPD) or frequency shift keying (FSK) with DPD, limiter discriminator integrator detection. (LDID), or limiter discriminator detection (LDD) are studied. The error floor is the residual error probability when SNR is infinity, i.e. the error probability in the system is limited by the error floor. The error floor is computed as a function of Doppler frequency, modulation index, and ratio of powers in the specular and diffuse signal components for DPSK-DPD, FSK-DPD, FSK-LDID and FSD-LDD systems     

Computer Modeling and Simulation of Communications Satellite Channels

Computer modeling of satellite communications channels is a valuable adjunct to analytical modeling and hardware simulation for predicting and verifying communications link performance. In the computer simulation approach, sampled signals are created in the computer and operated on by algorithms that simulate the effects of filtering, channel nonlinearities, interference, and noise. After passage through the simulated channel, the distorted signals are demodulated to determine the performance degradation introduced by the channel. This paper describes the approach used in simulating communications channels on the computer. Examples are given that apply to the communications satellite channel; however, the techniques described are applicable to general channel configurations.     

Estimation of the sampled impulse-response of a channel

The paper describes various techniques for estimating the sampled impulse-response of a noisy linear channel. The estimators are suitable for use with maximum-likelihood detection processes such as the Viterbi-algorithm detector, in applications where a digital data signal is transmitted over a channel introducing severe intersymbol interference and where the receiver may or may not have some prior knowledge of the channel. Results of computer simulation tests are presented, showing, for each estimator, the magnitude of the error in the channel estimate over the reception of a typical data signal. Both time-invariant and time-varying channels are used in the tests and the performances of the estimators are compared for the different cases where the receiver initially has some or no knowledge of the channel and where the detected data symbols are all correct or contain some errors. It is shown that, even under quite unfavourable conditions, a surprisingly good estimate of the channel can be obtained by means of a relatively simple estimator.     

Ser performance analysis of decode-and-forward cooperative scheme in satellite mobile channel

In this paper, Symbol-Error-Rate (SER) performance analysis is provided for a Decode-and-Forward (DF) cooperative scheme in satellite mobile channel environment. We present a satellite mobile cooperative communication system model and derive two generalized error probability expressions with Cyclical Redundancy Check (CRC) or not. We also derive and simulate SER of the proposed system over different satellite mobile channels. The results show that the analytical results are in great accordance with the ones obtained by simulation. Also, it was shown that, whether or not adopt CRC depends on the channel link quality between the source node and the relay node.     

SER PERFORMANCE ANALYSIS OF DECODE-AND-FORWARD COOPERATIVE SCHEME IN SATELLITE MOBILE CHANNEL

In this paper,Symbol-Error-Rate (SER) performance analysis is provided for a Decodeand-Forward (DF) cooperative scheme in satellite mobile channel environment.We present a satellite mobile cooperative communication system model and derive two generalized error probability expressions with Cyclical Redundancy Check (CRC) or not.We also derive and simulate SER of the proposed system over different satellite mobile channels.The results show that the analytical results are in great accordance with the ones obtained by simulation.Also,it was shown that,whether or not adopt CRC depends on the channel link quality between the source node and the relay node.     

峰值检读方式下磁光盘系统误码特性与检偏方式的关系

分析了在峰值检读方式下磁光存储系统产生误码的原因．并考虑多种定时误差的存在，导出了描述信道误码特性的数学模型．在此基础上分析了磁光信号检偏方式与信道误码特性的关系，分析结果表明平衡差分信道的容错能力略高于非平衡差分信道．     

磁光存储系统数据信道误码特性分析

本文分析了磁光存储系统产生误码的原因，针对系统在读取数据“１”和“０”时信道噪声强度不同这一特殊性，导出了描述信道误码特性的数学模型，并在此基础上研究了磁光信号检偏方式与信道误码特性的关系。分析结果表明：平衡差分信道的容功错能力略高于非平衡差分信息道。     

Impact of diversity reception on fading channels with codedmodulation. III. Co-channel interference

For pt.II see ibid., vol.45, no.6, p.55-67, 1997. In previous work, we have studied the impact of diversity on coded digital communication systems operating over fading channels. In particular, we have shown that diversity may be thought of as a way of making the channel more similar to a Gaussian one. The present paper extends this analysis to fading channels affected by co-channel interference (CCI). Three receiver models are examined, namely, with coherent detection and perfect channel-state information (CSI), with differential; and with pilot-tone detection. We study the effect of diversity on the irreducible error floor caused by CCI and fading, and the asymptotic behavior of the channel as the diversity order increases. Our results show that, when perfect CSI is available, diversity is able to turn asymptotically the channel into a CCI-free additive white Gaussian noise (AWGN) channel with the same signal-to-noise ratio (SNR). On the other hand, differential and pilot-tone detection do not remove interference in the limit. Nevertheless, also with these detection schemes, diversity achieves significant gains when the SNR is large enough. Calculation of the channel cutoff rate provides guidelines for the design of coded systems with CCI in fading environments. A wide range of examples, validated by computer simulation, illustrates our conclusions     

On the robustness of decision-feedback detection of DPSK and differential unitary space-time modulation in Rayleigh-fading channels

Decision-feedback differential detection (DFDD) of differential phase-shift keying (DPSK) and differential unitary space-time modulation (DUST) in Rayleigh-fading channels exhibits significant performance improvement over standard single-symbol maximum-likelihood detection. However, knowledge of channel fading correlation and signal-to-noise ratio (SNR) is required at the receiver to compute the feedback coefficients used in DFDD. In this letter, we investigate the robustness of the DFDD to imperfect knowledge of the feedback coefficients by modeling the mismatch between estimated feedback coefficients and ideal coefficients in terms of mismatch between the estimated values of fading correlation and SNR and the true values. Under the assumption of a block-fading channel when nondiagonal DUST constellations are used and a continuous fading channel otherwise, we derive exact and Chernoff bound expressions for pair-wise word-error probability and then use them to approximate the bit-error rate (BER), finding close agreement with simulation results. The relationships between BER performance and various system parameters, e.g., DFDD length and Doppler mismatch, are also explored. Furthermore, the existence of an error floor in the BER-vs-SNR curve is investigated for the infinite-length DFDD. For the special case of Jakes' fading model, it is shown that the error floor can be removed completely even when the Doppler spread is over-estimated.     

Frequency-selective scintillation effects and decision feedback equalization in high data-rate satellite links

Ionospheric irregularities produce signal amplitude and phase scintillations in transionospheric satellite channels. When the electron-density fluctuation is large, the channel coherence bandwidth is small, causing the scintillations to decorrelate at different frequencies within the bandwidth of a wide-band signal. Frequency-selective scintillation introduces delay spread and intersymbol interference, which can severely limit the usable capacity of the channel. This paper, largely tutorial in nature, relates adaptive equalization techniques, which have been developed previously for other dispersive channels, to the problem of wide-band satellite links operating through a highly disturbed transionospheric channel. Pertinent features of the ionospheric channel and characteristics of signal scintillations are summarized. Effects of frequency-selective scintillation on high data-rate wide-bandwidth digital communication links are described in some detail. Intersymbol interference caused by the loss of channel coherence over the signal bandwidth is shown, via simulations, to severely degrade the performance of a conventional coherent binary PSK receiver. An adaptive decision feedback equalization technique is then shown to be a powerful method of mitigating frequency-selective disturbances in high data-rate satellite links.     

The Effects of Noise Correlation and Power Imbalance on Terrestrial and Satellite DPSK Channels

New results are given for the bit error probability for binary DPSK modulation over both terrestrial and satellite channels taking into account noise correlation and power imbalance. The new expressions are remarkably simpler than their previously published counterparts. For the terrestrial channel, the results are in closed form in terms of tabulated functions and, for the hard-limiting satellite channel, both in terms of integrals readily evaluated by quadrature and in terms of infinite series. Using the results, it is shown that the error rate does not depend on the noise correlation (down-link in the satellite case) so long as the a priori symbol probabilities are equal, thereby solving an "open problem" posed by Lee, French, and Hong. Also, the satellite case in which each of the up-link and down-link channels contains nonzero noise correlations is briefly treated.     

Bit error simulation for π/4 DQPSK mobile radio communicationsusing two-ray and measurement-based impulse response models

An accurate software/hardware bit-by-bit error simulator for mobile radio communications is described. Simulation results in indoor and outdoor channels are compared with theoretical results. Bit error rate (BER) results in simulated frequency-selective fading channels generated by several channel models such as two-ray, constant amplitude, and simulated indoor radio channel impulse models (SIRCIMs) are presented. It is shown that BER is not only dependent on the RMS delay spread, but also on the distribution of temporal and spatial multipath components in local areas. An important result is that a two-ray Rayleigh fading model is a poor fit for indoor wireless channels and, if used, can underestimate the BER by orders of magnitude. A real-time bit error simulation of video transmission using the bit-by-bit error simulator is described. The simulator, called BERSIM, is shown to be a useful tool for evaluating emerging data transmission products for digital mobile communications     

Error-rate performance of digital FM with differential detection in land mobile radio channels

Error-rate performance of a digital FM with differential detection in the presence of both thermal Gaussian noise and cochannel interference is theoretically analyzed in the fast Rayleigh fading environment encountered in the typical UHF or microwave land mobile radio channels. The temporal correlation of the fades is included in the performance analysis. The error probability is presented by a simple closed form for the important situations where both effects of Gaussian noise and cochannel interference predominate in causing errors. Finally, a comparison with the other detection schemes, e.g., discriminator and coherent detections, is given.     

MMSE Equalization of Interference on Fading Diversity Channels

Adaptive equalization is used in digital transmission systems with parallel fading channels. The equalization combines the diversity channels and reduces intersymbol interference due to multipath returns. When interference is present and correlated from channel to channel, the equalizer can also reduce its effect on the quality of information transfer, important applications for interference cancellation occur in diversity troposcatter systems in the presence of jamming, diversity high frequency (HF) systems which must cope with interfering skywaves, and space diversity line-of-sight (LOS) radio systems where adjacent channel interference is a problem. In this paper we develop the general formulation for minimum mean square error (MMSE) equalization of interference in digital transmission diversity systems. The problem formulation includes the use of available receiver decisions to assist in MMSE processing. The effects of intersymhol interference are included in the analysis through a critical approximation which assumes sufficient processor capability to reduce ISI effects to levels small enough for satisfactory communication. The analysis also develops he concept of additional implicit or intrinsic diversity which results from channel multipath dispersion. It shows how the MMSE processor sacrifices diversity to suppress interference even when the interference arrives in the main beams of the receiver antenna patterns. The condition of near synchronous same-path interference is also addressed. Because the spatial angle of arrival of the interference may result in delay differences between interference signals in different antenna channels, interference delay compensation may be required. We show that this effect is compensated for with a small number of appropriately spaced equalizer taps.     

Models for channels with memory and their applications to error control

Errors encountered in digital transmission over most real communication channels are not independent but appear in clusters. Such channels are said to exhibit memory, i.e., statistical dependence in the occurrence of errors; and thus cannot be adequately represented by the classical memoryless binary symmetric channel. The existence of memory implies additional capacity. To exploit this through efficient coding schemes, it is necessary to describe and model the underlying statistical structure of the error process. This paper reviews various channel models, noting the interaction between channel modeling and error control.