The Rician K-fator is widely used to characterize multipath fading channels as the ratio between the power of the line-of-sight (LoS) and the secondary paths. As a practical stochastic model for multipath fading in radio propagation, racian fading occurs when LoS is much stronger than the secondary paths. Random shadowing effects make the LoS component fluctuating, thus leading to a performance degradation of the conventional estimator.
Aimed at avoiding the bias error of the conventional estimator when the LoS component is Nakagami-m distributed, Professor HAO Chengpeng from Institute of Acoustics (IOA) of Chinese Academy of Sciences, together with researchers from Italy, proposed a novel estimation procedure of the Rician K-factor.
The paper entitled “Estimation of Rician K-Factor in the Presence of Nakagami-m Shadowing for the LoS Component” was published in the IEEE Wireless Communications Letters.
The signal propagates through a line-of-sight (LoS) channel from a source location to a destination, where other channels are called secondary paths. The received signal in Rician multipath channels is modeled as a complex constant, accounting for the main path, the constant is then added to a circular complex Gaussian random variable, modeling all the diffusive secondary paths.
The conventional algorithm allocates any signal variation to the diffusive component, although due to a randomly fluctuating LoS signal. Motivated by this lack and with focus on Land Mobile Satellite (LMS) communications, researchers proposed a new estimation procedure to avoid the bias error in case of LoS fluctuations in the presence of Nakagami-m shadowing.
In mobile communications, random fluctuations of the LoS component may occur due to the relative motion between transmitters and receivers. Specifically, when buildings, trees and hills yield complete or partial blockage of the LoS, its amplitude becomes a random variable.
In the presence of a set of admissible solutions, the proposed procedure uses the joint likelihood function of the received samples to select the solution returning the maximum likelihood value. As a final remark, the proposed procedure can also be applied to the estimation of unknown parameters of Nakagami-m fading channels in the presence of thermal noise.
This work was supported by the National Natural Science Foundation of China.
Gaetano Giunta, HAO Chengpeng, Danilo Orlando. Estimation of Rician K-Factor in the Presence of Nakagami-m Shadowing for the LoS Component. IEEE Wireless Communications Letters (Early Access 2018). DOI:10.1109/LWC.2018.2794447.
Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China