Fading distribution

About: Fading distribution is a research topic. Over the lifetime, 5732 publications have been published within this topic receiving 114193 citations.

On communication over fading channels

Abstract: The channel capacity in the presence of Gaussian noise is the same whether the signal suffers fluctuations or not, so high gains may be expected in the fading case. The main tool considered towards this goal is rotation of constellations in signal space, as applied by Boutros (1996) to lattices.

The Jakes fading model for antenna arrays incorporating azimuth spread

Abstract: A new method for simulating the multiplicative fading of the narrow-band, flat wireless channel for antenna array receivers is presented. The new approach produces a set of fading waveforms, one waveform associated with each receiver element, in which the waveforms are appropriately correlated to take into account the spread, or dispersion, in the azimuth (arrival angle) of the received signal. The new method is an extension of the Jakes (1974) method of simulating fading in which the appropriate correlation of the set of waveforms is accomplished by directly considering the azimuth of scatterers in a particular distribution about the mobile transmitter. The models used for this cluster of scatterers are a ring and a disk of scatterers. Further modifications of the disk model permit the generation of fading waveforms which are correlated in a manner which reflect actual field measurements of azimuth dispersion. Analytical correlation of these models is reviewed for purposes of verification with the waveforms generated by the method.

Performance evaluation and analysis of space-time coding in unequalized multipath fading links

Abstract: This paper investigates the use of space-time (ST) coding for high-speed data transmission, as well as studies the effect of time delay spread on such scheme over unequalized fading channels. Using a random variable decomposition technique, we present an analytical model and obtain an approximate bound of the pairwise-error probability for ST coded systems over multipath and time-dispersive fading channels. It is shown that the presence of multipath does not reduce the diversity gain provided by the original design criteria, which is adopted to construct specific ST codes in quasi-static flat fading, but the coding gain diminishes due to the effect of multipath fading.

Diversity transform for fading channels

Abstract: This paper investigates a transform that provides diversity to words of symbols transmitted over fading channels. This diversity transform (DRT) does not alter the distance between the input words nor the bandwidth or the information rate. The transform is based on an orthonormal transform and thus increases the channel alphabet. A considerable diversity gain is achieved over Rayleigh fading channel with perfect channel state information (CSI) and interleaving. The transform performances are evaluated both analytically and by simulation, and optimal transforms are determined for specific channels. Finally, a simple nonoptimal decoding scheme is developed, which provides a powerful and practical technique to transfer information over fading channels with or without coding.

Multiuser demodulation for DS-CDMA systems in fading channels

Abstract: Multiuser demodulation algorithms for centralized receivers of asynchronous direct-sequence (DS) spread-spectrum code-division multiple-access (CDMA) systems in frequency-selective fading channels are studied. Both DS-CDMA systems with short (one symbol interval) and long (several symbol intervals) spreading sequences are considered. Linear multiuser receivers process ideally the complete received data block. The approximation of ideal infinite memory-length (IIR) linear multiuser detectors by finite memory-length (FIR) detectors is studied. It is shown that the FIR detectors can be made near-far resistant under a given ratio between maximum and minimum received power of users by selecting an appropriate memory-length. Numerical examples demonstrate the fact that moderate memory-lengths of the FIR detectors are sufficient to achieve the performance of the ideal IIR detectors even under severe near-far conditions. Multiuser demodulation in relatively fast fading channels is analyzed. The optimal maximum likelihood sequence detection receiver and suboptimal receivers are considered. The parallel interference cancellation (PIC) receiver is demonstrated to achieve better performance in known channels than the decorrelating receiver, but it is observed to be more sensitive to channel coefficient estimation errors than the decorrelator. At high channel loads the PIC receiver suffers from bit error rate (BER) saturation, whereas the decorrelating receiver does not. Choice of channel estimation filters is shown to be crucial if low BER is required. Data-aided channel estimation is shown to be more robust than decision-directed channel estimation, which may suffer from BER saturation caused by hang-ups at high signal-to-noise ratios. Multiuser receivers for dynamic CDMA systems are studied. Algorithms for ideal linear detector computation are derived and their complexity is analyzed. The complexity of the linear detector computation is a cubic function of KL, where K and L are the number of users and multipath components, respectively. Iterative steepest descent, conjugate gradient, and preconditioned conjugate gradient algorithms are proposed to reduce the complexity. The computational requirements for one iteration are a quadratic function of KL. The iterative detectors are also shown to be applicable for parallel implementation. Simulation results demonstrate that a moderate number of iterations yields the performance of the corresponding ideal linear detectors. A quantitative analysis shows that the PIC receivers are significantly simpler to implement than the linear receivers and only moderately more complex than the conventional matched filter bank receiver.