Multi-Modal Communications for Reliable UAV and UGV Connectivity, BWAC Core Project

More Details

Reliable communications are a cornerstone of safe UAV deployments. For example, the proposed NASA UTM system relies entirely on reliable air-to-ground and air-to-air communications. Unfortunately, wireless communications are affected by a variety of impediments, from interference, to multipath propagation, lack of network coverage, etc. For UAVs (as well as for UGVs), two-ray ground reflection is assumed to be the main source of fast fading. However, despite a number of papers in the research literature making this assumption, to the best of our knowledge there are limited studies validating that two-ray ground reflection is indeed affecting UAV and UGV communications as expected, and no clear solution to the problem.

The goal of this proposal is to first validate the nature of communications impairments in carefully conducted experiments, and then solve the problem by using multi-modal communications. For this purpose we will be using the AERPAW testbed, which has been specifically designed for studying problems at the intersection between wireless communications and unmanned aerial and ground vehicles. The AERPAW vehicles are equipped with high precision (real-time kinematic (RTK)) GPS receivers and are able to maneuver in extremely controlled and precise ways, allowing for high-density, geo-tagged wireless measurements that can then be used to study the root cause of the wireless impairments. Furthermore, using software defined radios (SDRs) AERPAW offers very flexible control over the frequency of operation (from DC to 6GHz, and potentially higher with extensions), the waveform, transmit and receive gains, antenna polarization, front ends, etc.

As part of AERPAW testing we have already measured the received signal strength LTE links from one of our fixed nodes to a portable node on an UAV that changed its altitude and distance from the fixed node. Our preliminary results show almost 30dB variation in signal strength even when the receiver is near the transmitter, consistent with our hypothesis of the two ray ground reflection being the main communication impairment. We will first carefully validate this assumption.

Furthermore, we will consider different types of radio communications to alleviate (or better yet, eliminate) the impediments encountered by employing a single radio. We will consider using multiple similar radios but with different settings (e.g., frequency of operation, antenna polarization, modulation and coding, etc.), or different types of radios altogether. While the expectation is that each single type of radio will have its impairments, the locations of deep fading caused by two-ray ground reflections are frequency dependent, and are therefore expected to occur at different locations on the trajectory of the UAV or UGV. Hence, multi-mode links will improve reliability due to the inherent frequency diversity introduced for a given UAV or UGV location.

Our objective is to develop an accurate model of wireless communication from and to UAVs while using one or more types of radios, and thus quantify the reliability of the radio communications system.