Analysis of Atmospheric Effects Due to Atmospheric Oxygen on a Wideband Digital Signal in the 60 Ghz Band

As lower microwave frequency bands become saturated with users, there is a motivation for the research of applications that utilize higher frequencies, especially the 60 GHz band. This band is plagued with high atmospheric absorption due to atmospheric oxygen, but has a lot of bandwidth, which makes it desirable for multi-media applications. Recently, research of wideband digital links within the 60 GHz band gained the interest of the wireless communication industry when the FCC announced that a license is not required for a wideband digital signal in this band.

Previous research on 60 GHz signals focused on how much attenuation due to atmospheric oxygen exists in the link. But a look at the physical properties of atmospheric oxygen reveals both the reason why atmospheric oxygen absorbs electromagnetic waves and how pressure affects atmospheric oxygen. Atmospheric oxygen resonates at 60 GHz due to transitions between its three closely spaced rotational states. These transitions, combined with the magnetic dipole moment of atmospheric oxygen, cause attenuation and phase dispersion in electromagnetic waves.

At lower pressures, the individual resonance lines of atmospheric oxygen appear in the attenuation and the phase dispersion plots. As pressure increases, the resonance lines broaden and contribute to neighboring resonant lines. The effect of attenuation and phase dispersion in a wideband signal becomes greater at lower atmospheric pressures, which results in signal distortion. The signal distortion leads to more bit errors and results in the presence of inter-symbol interference (ISI) in the received signal.

This thesis aims to analyze the effects of atmospheric oxygen on a wideband digital link, especially at lower pressures and higher data rates. In order to simulate the effects of atmospheric oxygen in the atmosphere, an empirical atmospheric model was used, which characterizes the behavior of oxygen under various atmospheric pressures. A wideband communication system was simulated with the absorption and dispersion due to atmospheric oxygen represented as a transfer function and placed in the link part of the system. Eye diagrams were used to view the impact of the atmospheric oxygen attenuation and phase dispersion in the signal. Also bit error rate plots were computed in order to determine the extra margin needed.