A Study of HVAC Channel for 60 GHz Indoor High-Speed Wireless Communications




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With the deployment of the fifth generation (5G) wireless communications systems, research and practical implementation work on millimeter wave (mm-wave) technology has gained tremendous momentum. With the evident advantages and obstacles with employing higher frequency signals, there is a demand for technological advancements required for the implementation of the millimeter wave systems in indoor communication settings. The wavelength of the mm-wave at 60 GHz is 5 mm, due to which the reception of mm-wave suffers from the propagation loss which is around 50 dB for a distance of 1 meter. Further, the small wavelength also leads to substantial losses by objects present inside a building. To gain further insight on this, wooden walls and doors lead to an attenuation loss of 20 dB, concrete walls would cause 40 dB, glass door would lead to an attenuation of around 16 dB and lastly human body accounts for an attenuation of 35 dB. Hence, the wireless mm-wave channels with substantial path and multipath propagation losses turn out to be the biggest hurdles in the implementation of the mm-wave wireless systems. In order to circumvent this limitation, in this study, we propose the use of heating, ventilation and air conditioning (HVAC) ducts for the transmission of mm-wave signals. These ducts act as waveguides, providing an electrically insulated, linear channels which are already present in most indoor constructions. To establish the viability of HVAC duct mm-wave channels, we conduct experiments using the WiGig compliant transceiver chipsets as the transmitter and receiver. The experiments involve measuring the various RF parameters, such as signal-to-noise ratio (SNR), error vector magnitude (EVM), received signal strength indicator (RSSI), received signal power indicator (RSPI), packet transmission and reception percentage, and bit rate. Initial experimentation involves comparison of the results between a straight HVAC duct and free space for various transmitter-receiver separation, alignment of the transmitter and receiver, and variation in the height of the transmitter/receiver from the ground. Subsequent experiments are performed considering the different bend angles, such as 45°, 90°, 180° (U shape), and S shape of the HVAC duct, resulting in results which are similar to that of a straight duct. The dissertation provides theoretical calculation of the duct channel frequency response for the overall duct system using transfer matrix theory and calculation of the power delay profile. Different dispersion phenomena are also explored. To further substantiate the results, imagetheory based ray-tracing algorithms using MATLAB are developed. The experimental, theoretical, and simulation results are shown to correlate favorably, thereby allowing the extension of the results in this study to transmission scenarios of mm-waves for larger distances in indoor environment. We also propose and study a mm-wave microstrip patch antenna, which forms an important sub-component of the mm-wave systems. The proposed antenna is a lowprofile, circularly polarized patch antenna that uses two substrate layers and provides high gain for a broad bandwidth. The results obtained in this dissertation, in terms of the RSSI and throughput, establish the viability of the HVAC duct channel for the transmission of 60 GHz mm-wave wireless signals in indoor environments.



Millimeter waves, Heating and ventilation industry, Indoor positioning systems (Wireless localization), Air ducts