Measurement of propagation effects for high-speed, digital UHF channels

The work described here relates to an effort to assess the reliability and robustness of datacasting for use in the mobile environment. Datacasting employs the excess bandwidth from digital television signals for use in one-way data transmission and it is being used successfully for high-speed downloads at fixed receiver locations. It is being considered as a means for providing data-rich information to police and emergency personnel in the field, and the work reported here is part of the evaluation process. Datacasting operates in the UHF television band and employs 8-level vestigial sideband (8-VSB) modulation to provide data rates in excess of 2.5 Mb/sec. Datacast reception is known to be very vulnerable to multipath interference, particularly time-varying multi- path interference. Because of this, an estimation of coverage area based upon signal strength alone does not accurately predict where the signal will be available. While propagation models are available that can predict both signal strength and multipath, they cannot provide the type of statistical information about signal availability and reliability that is sought in this study. In order to get the desired information, datacasting receivers and data logging equipment were installed in police vehicles to measure the channel over a wide range of operating conditions. This paper reports on some of the key findings from that study.