A Measurement-Based Model for Outdoor Near-Ground Ultrawideband Channels

Deployment of wireless devices with transceivers in close proximity to the ground has become increasingly attractive for a wide range of applications such as distributed sensor networks and broadband tactical communications. Furthermore, the use of ultrawideband (UWB) signals is attractive for these communications due to their robustness and their suitability for precision ranging and localization. For the development and performance simulation of such systems, accurate channel models are required. The current paper thus presents details of an extensive measurement campaign for near-ground UWB propagation channels and a channel model-based thereon. The measurements were performed with a self-built channel sounder based on arbitrary waveform generation at the transmitter, high-bandwidth sampling oscilloscope at the receiver, and synchronization via electro-optical connections. Various combinations for the antenna height at transmitter and receiver, ranging from 10 cm to 2 m above ground, were measured. We find that the pathloss coefficient (γ) depends significantly on the Tx-Rx antenna heights, while shadowing variance (σ2) and rms delay-spread (τrms) shows smaller dependence. The pathloss shows a slight dependence on frequency; the frequency-dependent pathloss exponent (κ) increases as antennas get closer to the ground. We also found a linear dependency of the rms delay-spread on distance for various antenna height configurations measured. Statistical distributions of all parameters including γ, τrms, σ2, and κ are extracted from the measurements. Results are verified by comparing with a second measurement campaign.