No abstract

Since the National Highway Traffic Safety Administration mandated the incorporation of tire pressure monitoring systems (TPMSs) in all newly produced passenger vehicles, most vehicle manufacturers have adopted direct pressure measurement. Direct TPMS sensors embedded in each tire require a wireless radio frequency (RF) communications link that broadcasts tire status to the vehicle once per minute from each tire when at speed. Each TPMS message communicates benign information that includes pressure and temperature as well as a static unique identifier that may be exploited, which raises concerns about privacy and spoofing. To focus on concerns related to the TPMS-RF interface, vehicle motion simulations were integrated with live propagation modeling measurements from three classes of passenger vehicles: subcompact car, full-size sedan, and full-size pickup. The RF link and channel models for this TPMS interface with the vehicle resulted in surprisingly long ranges away from the vehicle for the radiation of the unique identifiers. A TPMS sensor redesign could use the proposed RF channel propagation measurements to change the directions of signal propagation while reducing battery consumption by the TPMS sensor (which is affected primarily by RF transmission).

In Earth-to-Space communications, well-known propagation effects such as path loss and atmospheric loss can lead to fluctuations in the strength of the communications link between a satellite and its ground station. Additionally, a less-often considered effect of shadowing due to the geometry of the satellite and its solar panels can also lead to link degradation. As a result of these anticipated channel impairments, NASA communication links have been traditionally designed to handle the worst-case impact of these effects through high link margins and static, lower rate, modulation formats. This thesis first characterizes the propagation environment experienced by a software-defined radio on the NASA SCaN Testbed through a full link-budget analysis. Then, the following chapters propose, design, and model a link adaptation algorithm to provide an improved trade-off between data rate and link margin through varying the modulation format as the received signal-to-noise operate at the most robust transmitting configuration, ensuring a low error-rate. However, with this worst-case method, the trade-off manifests in the very constrained data rate-although the data is transmitted with minimal errors, the throughput also remains low. This thesis first outlines the propagation environment experienced by a communications signal originating in Cleveland, OH and traveling to a software-defined radio on the NASA SCaN Testbed. Then, a link adaptation algorithm is designed and simulated to provide an improved trade-off between data rate and bit error rate. This flexibility between transmitting configurations allows for communications to be more efficient, as the transmitter can adapt as the signal strength improves.