Purpose: Given the increased levels of fine and ultrafine dust, as well as the spread of COVID-19, current opinion is that most people will wear a face mask such a KF94 mask for a long time. To test speech transmission through the face masks, various types of masks including dust masks available in the market at the time of the study were tested under laboratory conditions.Methods: Fourteen types of masks worn on a head and torso simulator (HATS) and test signals were played on a speaker installed in the mouse position of the HATS. Speech Transmission Index (STI) and the speech level in the octave band were measured at distances of 1 m and 2 m.Results: STI at a distance of 2 m was decreased to 3.4-5.7% and speech levels in the octave band at 4 kHz or higher were also decreased when wearing disposable masks and a cotton mask. KF80 and KF94 masks showed decreased STI similar to those of disposable masks; however, a decrease in the speech level was observed at the octave bands of above 2 kHz. Dust masks and single-cartridge half-face respirators showed approximately 11.2% and 33.7% to 39.3% decreases in STI levels, respectively.Conclusion: When wearing masks, STI and the speech level was decreased in the high-frequency bands. However, speech level differences at high frequencies may be related to the increased voice level of the speaker and the understanding of consonants with the masks for several hours in living and working environments.

Power line communication (PLC) technology is used in various areas of a smart grid. The extensive use of PLC technology has proved its key role in smart grids throughout the world. Despite PLC's advantages, it suffers from a difficulty in modeling and analysis of its power line channel. Many researchers have experimented and proposed channel models for their own defined environments; as a result, a unified model for the power line has not been presented. To overcome this problem partially, we used a Nakagami-m distribution like background noise and analyzed the performance of the binary transmission system in our previous work. In this paper, we compare the analytical and simulated BER (bit error rate) performances of QPSK (quadrature phase shift keying) transmission system with Gray encoding. We verify that the analyzed and simulated performances are well matched for different values of m.

In this paper, we present the design of the analog front end (AFE) module for power-line communication (PLC) which complies with the Korean industrial standard (KS) specifications. We measured the electromagnetic emission of the implemented AFE and verified that the measurement satisfies the regulation for PLC.