An Impulse Response Model and $Q$ -Factor Estimation for Vehicle Cavities

To facilitate efficient communications (i.e., minimum power consumption and maximum information throughput) in vehicle cavities, it is necessary to fully understand the underlying physics of the propagation process. This can be characterized as a statistical model of the channel impulse response, which we derive from a general starting point. The impulse response model is useful in its own right for ultrawideband pulse radio communications, channel simulations, and time-of-arrival positioning systems, and it also allows us to verify the generally accepted property that the energy retained in the cavity exponentially decays with time after an impulse input. This property can be characterized as a cavity Q-factor, and we investigate methods of Q-factor estimation in vehicle cavities, using only a limited amount of data, such as would typically be available to a deployed in-vehicle wireless network. We find that the most reliable approach utilizes an inverse-discrete-Fourier-transform-based method, which finds the maximum-likelihood instantaneous Q-factor, given measured data across various spatial links and frequency channels.