Flat Rician Research Articles

On the LLR Metrics for DPSK Modulations Over Two-Symbol Observation Intervals for the Flat Rician Fading Channel

We consider the differential phase-shift keying modulation over the flat Rician fading channel with perfect channel model information (PCMI), and derive the two-symbol-observation-interval log-likelihood ratio (LLR) metric from first principles. The work generalizes the previous LLR derivations in [16] – [19] , and demonstrates the necessity of the knowledge of the statistical channel model in the exact LLR computation. Assuming the channel is slowly time-varying, we also propose a simple approximate LLR metric based on the generalized likelihood ratio test (GLRT), which requires only the information of the noise spectral density. The advantage of the newly derived PCMI-LLR metric over the approximate metric and the other LLR metrics in the literature is explained from the information-theoretic perspective via the generalized mutual information. Computer simulations are also provided to demonstrate the superiority of the PCMI-LLR metric in both error rate performance and convergence speed for iterative decoding of turbo and low-density parity-check codes in practical systems. This paper aims to present the fundamental principles of LLR computation, emphasizing the importance of selecting the appropriate metric for iterative decoding over fading channels.

Bayesian Multiple Estimation in Flat Rician Fading MIMO Channels

Bayesian Multiple Estimation in Flat Rician Fading MIMO Channels

Ziv–Zakai Time-Delay Estimation Bounds for Frequency-Hopping Waveforms Under Frequency-Selective Fading

Ziv-Zakai Bayesian lower bounds on time-delay estimation (TDE) are developed for frequency hopping waveforms. These wideband waveforms are readily employed for both communications and TDE. We consider random frequency-selective fading channels, described by a Gaussian tapped delay line model with inter-hop correlation. The receiver does not know the channel realization to assist in estimating the time delay but does know the channel statistics. The development incorporates a random uniform prior on the delay. The bounds provide tight mean-square error prediction for the maximum a posteriori (MAP) estimator performance over a large range of signal-to-noise ratios (SNRs). They also accurately predict the TDE frequency diversity gain from multi-frequency transmission in fading channels. The special case of independent fading is discussed, including both flat Rician and Rayleigh fading, and closed-form expressions enable easy study of the effects of SNR, frequency diversity, and channel statistics on TDE.

Matched Filter Bound for Trellis‐Coded Transmission over Frequency‐Selective Fading Channels with Diversity

AbstractTransmission of trellis‐coded digital information over time‐variant frequency‐selective multipath radio channels leads to receiver design considerations and bit error characteristics fundamentally different from those of links using static channels. Making use of diversity is of prime importance in a fading environment. Explicit antenna diversity, implicit time diversity from interleaved trellis‐coded modulation, and implicit multipath diversity via energy detection/equalization are three methods of transmission quality enhancement that can be jointly employed without loss of power and bandwidth.The matched filter bound (MFB) is a lower bound on the average bit error rate under ideal conditions, i.e. perfect channel estimation, interleaving, and equalization. In this paper, a new method of evaluating the MFB based on an eigenvalue approach is presented and the analysis extended to include transmission of trellis‐coded linearly modulated signals over selective diversity channels having arbitrary fading multipath profiles.MFB results are generated for a number of illuminating examples (trellis codes with effective code lengths up to 5, selective two‐ray and GSM Rayleigh as well as flat Rician channels) that demonstrate the potential benefits of implicit time and multipath diversity. Some simulation results are presented giving rise to concluding remarks on the tightness of the bound.