Fading

About: Fading is a research topic. Over the lifetime, 55489 publications have been published within this topic receiving 1061665 citations. The topic is also known as: fading channel & shadow fading.

Modulation and Detection for Simple Receivers in Rapidly Time-Varying Channels

Abstract: We investigate the performance degradation of basic modulation schemes in a rapidly time-varying channel using a first-order autoregressive channel model. Various performance metrics are used to indicate the relative advantages of each modulation scheme. We find that noncoherent frequency-shift keying (FSK) is suitable for operating at very high mobility and high signal-to-noise ratio, ideal for some military applications. We then propose a partially coherent detector for FSK and differential phase-shift keying that exploits partial channel knowledge to enable the receiver to operate effectively in both fast and slow fading. The maximum-likelihood rule obtained for the partially coherent FSK turns out to be a linear combination of coherent and noncoherent detection rules. Results demonstrate that significant performance improvement can be achieved over the best of coherent and noncoherent FSK detection. The detector is robust to estimation errors present in the channel statistics. We also propose a few adaptive schemes that employ various combinations of modulation schemes to increase the robustness of the system in fast fading

Closed-Form Error Probability of Network-Coded Cooperative Wireless Networks with Channel-Aware Detectors

Abstract: In this paper, we propose a simple analytical methodology to study the performance of multi-source multi-relay cooperative wireless networks with network coding at the relay nodes and Maximum-Likelihood (ML-) optimum channel-aware detectors at the destination. Channel-aware detectors are a broad class of receivers that account for possible decoding errors at the relays, and, thus, are inherently designed to mitigate the effect of erroneous forwarded and network-coded data. In spite of the analytical complexity of the problem at hand, the proposed framework turns out to be simple enough yet accurate and insightful to understand the behavior of the system, and, in particular, to capture advantages and disadvantages of various network codes and the impact of error propagation on their performance. It is shown that, with the help of cooperation, some network codes are inherently more robust to decoding errors at the relays, while others better exploit the inherent spatial diversity and redundancy provided by cooperative networking. Finally, theory and simulation highlight that the relative advantage of a network code with respect to the others might be different with and without decoding errors at the relays.

Underwater Acoustic Networks - Survey on Communication Challenges with Transmission Simulations

Abstract: Underwater sensor networks may be used in many underwater applications and some of these applications may transmit large amounts of data. Underwater acoustic communication is limited by several physical factors affecting communication. Time spread caused by multipath effects and frequency selective fading are major concerns.The choice of modulation technique is important. Due to the high data rate required in network applications coherent modulation techniques should be considered. In the choice of multiple access method Code Division Multiple Access is considered the most promising technique because of its robustness and resistance against frequency selective fading. Also by using a Rake receiver multipath arrivals can coherently be combined.To get an idea of multipath effects for different propagation conditions the acoustic modeling program EasyPLR is used. Sound speed profiles from different seasons of 2005 are implemented to display the seasonal variations. The results indicate multipath effects and time spread for all seasons at short range. For ranges up to 3 km time spread is kept at tens of micro seconds.

Error Performance of Double Space Time Transmit Diversity System

Abstract: The theoretical error performance of double space time transmit diversity (DSTTD) system is analyzed in this paper. By employing both spatial multiplexing and transmit diversity in one system, DSTTD provides practical tradeoff between system spectral efficiency and diversity gain. We derive exact analytical expressions to describe the symbol error rate for DSTTD systems. The effects of both diversity gain and antenna interference introduced by spatial multiplexing are quantified in the results. In addition, the performance of DSTTD system with successive interference cancellation is also investigated. Simulation results are in excellent agreement with the theoretical results obtained in this paper.

Physical Layer Security Performance of Wireless Mobile Sensor Networks in Smart City

Abstract: In smart cities, the ubiquitous network connections and high data rate services are provided to afford effective service of real-time monitoring and responses. With the development of the 5G mobile communication technology, the wireless sensor mobile communication networks in the smart city have become a hot issue for academic researches. Due to the openness of wireless channels, the physical layer security of the wireless mobile sensor mobile communication networks in smart city encounters severe challenges. In this paper, based on Wyner’s wiretap model, the secrecy performance of the wireless mobile sensor communication networks over 2-Nakagami fading channels is investigated. We derive the exact secure outage probability (SOP) and the probability of strictly positive secrecy capacity expressions for two transmit antenna selection (TAS) schemes. The exact closed-form expressions for the lower bound on the SOP are also derived using the optimal TAS scheme. Then, the system secrecy performance is verified and analyzed by Monte Carlo simulations under different conditions. The simulation results show that the analytical results match perfectly with the Monte Carlo simulation results. Increasing the number of transmit antennas can improve secrecy performance.