Enhanced TOA Estimation Using OFDM over Wide-Band Transmission Based on a Simulated Model

This paper presents the advantages of using a wideband spectrum adopting multi-carrier to improve targets localization within a simulated indoor environment using the Time of Arrival (TOA) technique. The study investigates the effect of using various spectrum bandwidths and a different number of carriers on localization accuracy. Also, the paper considers the influence of the transmitters’ positions in line-of-sight (LOS) and non-LOS propagation scenarios. It was found that the accuracy of the proposed method depends on the number of sub-carriers, the allocated bandwidth (BW), and the number of access points (AP). In the case of using large BW with a large number of subcarriers, the algorithm was effective to reduce localization errors compared to the conventional TOA technique. The performance degrades and becomes similar to the conventional TOA technique while using a small BW and a low number of subcarriers.

Impact of Inter-Channel Interference on Shallow Underwater Acoustic OFDM Systems

This paper investigates the impacts of Inter-Channel Interference (ICI) effects on a shallow underwater acoustic (UWA) orthogonal frequency-division multiplexing (OFDM) communication system. Considering both the turbulence of the water surface and the roughness of the bottom, a stochastic geometry-based channel model utilized for a wide-band transmission scenario has been exploited to derive a simulation model. Since the system bandwidth and the sub-carrier spacing is very limited in the range of a few kHz, the channel capacity of a UWA system is severely suffered by the ICI and Doppler effects. For further investigation, we construct the signal-to-noise-plus-interference ratio (SINR) based on the simulation model, then evaluate the channel capacity. Numerical results show that the various factors of a UWA-OFDM system as subcarriers, bandwidth, and OFDM symbols affects the channel capacity under the different Doppler frequencies. Those observations give hints to select the good parameters for UWA-OFDM systems.

Tuning a Two-Chamber Muffler for Wide-Band Transmission Loss

The design of a muffler with wide-band transmission loss (TL) is a basic requirement for automotive exhaust systems where the exhaust noise is spread over several harmonics of the engine firing frequency. This has led to the concept of a double-tuned expansion chamber. In the present paper, the concept of double-tuning is extended to the two-chamber mufflers. The author's classical Velocity Ratio Algorithm is used here to analyze and design such a muffler. The relevant two-row array is manipulated and simplified to arrive directly at the single most significant term out of the 81 non-dimensional terms constituting the relevant Velocity Ratio. Examination of this single term reveals acoustics of the raised wide-band domes of the TL spectrum of the double-tuned two-chamber (DT2C) muffler vis-a-vis that of an equivalent longer double-tuned single-chamber muffler. Except for a low-frequency trough, its TL curve covers the entire frequency range of interest for control of automotive exhaust noise. It is also shown that the corresponding side-inlet side-outlet (SISO) DT2C muffler configuration has an identically similar wide-band TL spectrum to that of the co-axial muffler configuration. Finally, some guidelines are laid out for designing a DT2C muffler.