A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, ease of availability, and ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail when compared to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios

Connecting Disjoint Nodes Through a UAV-Based Wireless Network for Bridging Communication Using IEEE 802.11 Protocols

Cooperative aerial wireless networks composed of small unmanned aerial vehicles(UAVs) are easy and fast to deploy and provide on the fly communication facilities in situations where part of the communication infrastructure is destroyed and the survivors need to be rescued on emergency basis. In this article, we worked on such a cooperative aerial UAV-based wireless network to connect the two participating stations. The proposed method provides on the fly communication facilities to connect the two ground stations through a wireless access point (AP) mounted on a UAV using the IEEE 802.11a/b/g/n. We conducted our experiments both indoor and outdoor to investigate the performance of IEEE 802.11 protocol stack including a/b/g/n. We envisioned two different cases: line of sight (LoS) and non-line of sight (NLoS). In LoS, we consider three different scenarios with respect to UAV altitude and performed the experiments at different altitudes to measure the performance and applicability of the proposed system in catastrophic situations and healthcare applications. Similarly, for NLoS, we performed a single set of experiments in an indoor environment. Based on our observations from the experiments, 802.11n at 2.4 GHz outperforms the other IEEE protocols in terms of data rate followed by 802.11n at 5 GHz band. We also concluded that 802.11n is the more suitable protocol that can be practiced in disastrous situations such as rescue operations and healthcare applications

An Empirical Air-to-Ground Channel Model Based on Passive Measurements in LTE

In this paper, a recently conducted measurement campaign for unmanned-aerial-vehicle (UAV) channels is introduced. The downlink signals of an in-service long-time-evolution (LTE) network which is deployed in a suburban scenario were acquired. Five horizontal and five vertical flight routes were considered. The channel impulse responses (CIRs) are extracted from the received data by exploiting the cell specific signals (CRSs). Based on the CIRs, the parameters of multipath components (MPCs) are estimated by using a high-resolution algorithm derived according to the space-alternating generalized expectation-maximization (SAGE) principle. Based on the SAGE results, channel characteristics including the path loss, shadow fading, fast fading, delay spread and Doppler frequency spread are thoroughly investigated for different heights and horizontal distances, which constitute a stochastic model.Comment: 15 pages, submitted version to IEEE Transactions on Vehicular Technology. Current status: Early acces

Adaptive Link Optimization for 802.11 UAV Uplink Using A Reconfigurable Antenna

This thesis presents a low-cost and flexible experimental testbed for aerial communication research along with an implementation and experimental evaluation of an aerial-to-ground 802.11g link with an adaptive beamsteering antenna system. The system consists of a software-defined radio (SDR) platform, and a pattern reconfigurable antenna mounted on a hexacopter unmanned aerial vehicle (UAV). First, the system design aspects of the testbed are described. The performance of the reconfigurable antenna is characterized through radiation pattern measurements while the antenna is mounted on the underbelly of the UAV. A low complexity reinforcement learning based adaptive antenna selection algorithm is implemented on the aerial SDR testing platform to enhance the link quality. We present SNR measurements obtained during various indoor and outdoor flight scenarios. The results show that utilizing a reconfigurable antenna and intelligent antenna selection strategy onboard a UAV provides a higher mean SNR compared to an omni-directional antenna in both line of sight (LOS) and non-line of sight (NLOS) scenarios, and is more resilient to co-channel interference and reactive jamming.M.S., Electrical Engineering -- Drexel University, 201

Low Altitude Air-to-Ground Channel Characterization in LTE Network

Low altitude unmanned aerial vehicle (UAV)-aided applications are promising in the future generation communication systems. In this paper, a recently conducted measurement campaign for characterizing the low-altitude air-to-ground (A2G) channel in a typical Long Term Evolution (LTE) network is introduced. Five horizontal flights at the heights of 15, 30, 50, 75, and 100 m are applied, respectively. The realtime LTE downlink signal is recorded by using the Universal Software Radio Peripheral (USRP)-based channel sounder onboard the UAV. Channel impulse responses (CIRs) are extracted from the cell specific signals in the recorded downlink data. To shed lights on the physical propagation mechanisms, propagation graph simulation is exploited. Moreover, path loss at different heights are investigated and compared based on the empirical data. The simulated and empirical results provide valuable understanding of the low altitude A2G channels