Diversity Fading Channels Research Articles

Examination of the multiple-input multiple-output space-time block-code selective decode and forward relaying protocol over non-homogeneous fading channel conditions

With the tremendous increase in wireless user traffic, investigation on the end-to-end reliability of wireless networks in practical conditions such as non-homogeneous fading channel conditions is becoming increasingly widespread. Because they fit well to the experimental data, generalized channel fading distributions like κ–μ are well suited for modeling diverse fading channels. This paper analyzes the symbol error rate (SER) and outage probability (OP) performance of multiple-input multiple-output (MIMO) space-time block-code (STBC) selective decode and forward (S-DF) network over κ–μ fading channel conditions considering the additive white Gaussian noise (AWGN). First, the closed-form (CF) analytical expressions for the probability density function (PDF) and the cumulative distribution function (CDF) of the received signal-to-noise ratio (SNR) as well as its moment generating function (MGF) are derived. Second, the OP performance is then investigated for various values of the channel fading parameter and SNR regimes. The simulation findings show an increase in SER performance with an improved line-of-sight (LOS) component. Furthermore, the results show that the S-DF relaying systems can function properly even when there is no fading or LOS component. The OP has been increasing with the increase in the value of μ and κ. In medium and high SNR regimes, simulation results exactly match with analytical results.

Asymptotic SER Analysis and Optimal Power Sharing for Dual-Phase and Multi-Phase Multiple-Relay Cooperative Systems

The asymptotic high-signal-to-noise ratio (SNR) symbol error rate (SER) performance of selective decode-and-forward cooperative multiple relay-aided wireless systems is derived for $M$ -PSK and $M$ -QAM modulations. The proposed analysis considers both dual-phase and multi-phase relaying protocols. Furthermore, analytical results are also presented for optimal power allocation both at the source and at each of the relays, since it significantly influences the performance of cooperative communication. A novel aspect of the proposed framework is that the SER and optimal power allocation results derived are applicable to diverse fading channels such as $\eta -\mu $ , $\kappa -\mu $ , and shadowed-Rician scenarios and each for non-identical fading for the source–destination, source–relay (SR), and relay–destination (RD) links. The applicability of the proposed framework is also demonstrated for diverse PHY layer schemes, such as multiple-input multiple-output-orthogonal space–time block codes, cooperative beamforming, joint transmit/receive antenna selection, and free-space optical scenarios. This high-SNR analysis provides the valuable insights into the impact of the diversity orders of the SR and RD links on the end-to-end SER as well as on the optimal power allocation factors both in the dual-phase and multi-phase protocols of various fading channels and schemes. Our simulation results verify the analytical results derived.

Unified Stochastic Geometry Modeling and Analysis of Cellular Networks in LOS/NLOS and Shadowed Fading

Statistical characterization of the signal-to-interference-plus-noise ratio (SINR) via its cumulative distri- bution function is ubiquitous in a vast majority of technical contributions in the area of cellular networks, since it boils down to averaging the Laplace transform of the aggregate interference, a benefit accorded at the expense of confinement to the simplistic Rayleigh fading. In this paper, to capture diverse fading channels that arise in realistic outdoor/indoor wireless communication scenarios, we tackle the problem differently. By exploiting the moment generating function of the SINR, we succeed in analytically assessing cellular networks performance over the shadowed $\kappa$ – $\mu$ , $\kappa$ – $\mu$ , and $\eta$ – $\mu$ fading models. These channel models offer high flexibility by capturing diverse fading channels, including Rayleigh, Nakagami- $m$ , Rician, and Rician shadow fading distributions. These channel models have been recently promoted for their capability to accurately model dense urban environments, future femtocells, and device-to-device shadowed channels. In addition to unifying the analysis for different channel models, this paper integrates the coverage, the achievable rate, and the bit error probability, which are largely treated separately in the literature. The developed model and analysis are validated over a broad range of simulation setups and parameters.

Optimized WiMAX System over Fading Channels Using FEC Codes

The Wireless Interoperability Microwave Access (WiMAX) system in this paper makes use of various forward error correction codes to improve and hence optimize the performance of the system. Two diverse fading channels have been used to study the response of the WiMAX system based on Forward Error Correction (FEC) encoding and M-ary Phase Shift Keying (M-PSK) modulation. Since WiMAX is used for both Line Of Sight (LOS) and Non Line-Of-Sight (NLOS) communication so, Rayleigh and Rician channels have been used, out of which one has LOS component, and other has no LOS component. The performance of WiMAX system has been studied by analyzing the graphs between Bit Error Rate (BER) and Signal to Noise Ratio (SNR) for all the different cases. It is observed that out of all coding techniques reed Solomon (RS) encoding techniques performs better at lower order modulation schemes by providing the BER of 10-3 at lower values of SNR in comparison to all other FEC encoding techniques. But, at higher order modulation level turbo encoding scheme outperform all other FEC schemes. Also, out of channels rician channel has a better response because of one strong line of sight constituent in comparison to Rayleigh fading channel. Further, modified FEC encoding schemes can be incorporated to enhance the BER performance of the WiMAX system.

Analysis and Simulation of MRC Diversity Reception in Correlated Composite Nakagami-Lognormal Fading Channels

The physical meaning of the composite Nakagami-lognormal fading model is not well understood by many researchers using the model. The signal power transfer and transform at the interface between the global lognormal shadowing sub-channels and the local Nakagami multipath sub-channels in the presence of correlation between these diversity sub-channels is rather complex. This is the main reason why a thorough analysis or a simulation model is absent to date for the case of correlated composite Nakagami-lognormal diversity channels. This paper presents a novel technique for the estimation of the probability density function (PDF) of the signal-to-noise (SNR) at the output of a maximum ratio combining (MRC) receiver operating in correlated composite diversity fading channels. The PDF is estimated using the recently proposed two-point lossless moment generating function (MGF) matching technique and a closed-form expression for the bit-error rate (BER) for QPSK signal is consequently presented using the Gauss-Hermite polynomial approximation. The paper also presents the complex Monte-Carlo simulation model for the MRC reception and BER counting in correlated composite Nakagami-lognormal fading channels.

Energy optimal scheduler for diversity fading channels with maximum delay constraints

We present a minimal energy packet scheduling and rate control scheme with a strict maximum delay constraint. This problem occures natually in real-time wireless multimedia transmission where a hard delay limit is imposed on each packet. In general, the communication link is assumed to be a diversity channel with multiple parallel sub-channels(e.g. OFDM, or MIMO eigenchannels.) We present both the theoretical optimal solution, which assumes prescient traffic and channel knowlodge, and a causal scheduler where the future is only known statistically. We show that the causal scheduler performs well, to within 3 dB of the prescient optimal in a single channel, and is even better with diversity channels.

Adaptive modulation for limited diversity fading channels

In this study, the authors propose a novel technique for adaptive modulation over limited diversity fading channels with channel state information at the transmitter. Limited diversity channels such as those encountered in indoor orthogonal frequency division multiplexing systems are characterised by the fact that achievable diversity orders are limited by the channel and not by code-free distances. The authors first propose a novel analysis technique for the performance of coded modulation on limited diversity block fading channels with different modulation sets on each block. The authors then propose adaptive modulation techniques for maximising the throughput at a fixed bit error probability and also for minimising the bit error probability at a fixed rate. Lastly, the authors show simulation results that support the arguments presented in the paper.

Power Allocation in Concatenated Trellis Coded Modulation

In this paper, power loading algorithms are presented for limited diversity fading channels with channel state information at the transmitter. Limited diversity channels are those that offer moderate levels of diversity (about 3-5) such as those encountered in orthogonal frequency division multiplexing (OFDM) based indoor wireless networks. We propose our ideas in the framework of a recently proposed coding approach for limited diversity channels although key aspects of the paper are valid for any coding scheme. We develop the optimal transmitter loading algorithm and also a low complexity suboptimal algorithm based on a linear objective function that maximizes the effective signal to noise ratio of the coded system. We compare the performances of different coding approaches with the proposed power allocation algorithms. Simulation results supporting the ideas presented in this paper are given.

On achievable performance of spatial diversity fading channels

Channel time-variation and frequency selectivity [causing intersymbol interference (ISI)] are two major impairments in transmission for a wireless communication environment. Spatial diversity on the transmitter or the receiver side has been traditionally used to combat multipath fading. Previous results indicate significant gains in using multiple transmitter and receiver antenna diversity. By deriving the mutual information and cutoff rate we characterize the gains on these channels. We show that gains linear in the number of antennas can be achieved either when the signal-to-noise ratio (SNR) becomes very large or when the number of antennas becomes large. We show that some of these gains can be achieved by lower complexity linear receiver structures. By evaluating the cutoff rate for phase-shift keying (PSK) constellations we further quantify the gains of using spatial diversity at both the transmitter and the receiver. Next, we examine the expected mutual information for slowly fading ISI channels where the channel is assumed to be block time-invariant. We then examine the impact of fast channel time variation (time variation within a transmission block) on multicarrier transmission schemes. We derive the average mutual information for orthogonal frequency-division multiplexing (OFDM) in time-varying ISI environments. Using this we examine the impact of transmitter and receiver diversity on OFDM transmission over time-varying ISI channels. We also study the effect of time variation on OFDM packet-size design.