Nowadays, accurate localization plays an essential role in many fields, such as target tracking and path planning. The challenges of indoor localization include inadequate localization accuracy, unreasonable anchor deployment in complex scenarios, lack of stability, and the high cost. So, the universal positioning technologies cannot meet the real application requirements scarcely. To overcome these shortcomings, a comprehensive ultra wide-band (UWB)-based real-time localization system (RTLS) is presented in this paper. We introduce the architecture of a real-time localization system, then propose a new wireless clock synchronization (WCS) scheme, and finally discuss the time difference of arrival (TDoA) algorithm. We define the time-base selection strategy for the TDoA algorithm, and we analyze the relationship between anchor deployment and positioning accuracy. The extended Kalman filter (EKF) method is presented for non-linear dynamic localization estimation, and it performs well in terms of stability and accuracy on moving targets.

In this paper, a three-dimensional (3D) non-stationary geometry-based stochastic model (GBSM) is proposed for low-altitude unmanned aerial vehicles (UAVs) multiple-input-multiple-output (MIMO) air-to-ground (A2G) channel. In the proposed model, both UAV rotation and arbitrary trajectories are taken into account. UAV rotation is described by a 2D Gauss-Markov random mobility model (RMM), while UAV arbitrary trajectories are characterized by a 3D revised Gauss-Markov RMM. The time-varying parameters of multipath components (MPCs), such as distances, angles of arrival (AoAs), and angles of departure (AoDs), are calculated based on the proposed model. In addition, the expressions of the space-time correlation function (CF) and Doppler power spectral density (PSD) are also derived. Numerous numerical simulations are conducted and the simulation results reveal that the UAV rotational motion causes channel non-stationarity in space domain, and the mobility characteristics of UAV along with arbitrary trajectories cause channel time domain non-stationary. Finally, the accuracy of the model is verified by comparing with the available measurement data.

In this paper, a priority based adaptive MAC protocol (PM-MAC) is proposed for UAV ad hoc networks. Firstly, in the protocol, the arriving packets are classified into different queues according to the priority of services. A Markov chain model is proposed to analyze the channel access probabilities of different queues. And it is ensured that packets with high priority can access the channel with high probability. Secondly, the size of contention window is adaptively adjusted based on backoff times and the current packet size. Finally, simulation results show that PM-MAC can guarantee the access requirements of high priority packets, and compared with the traditional backoff method, the backoff mechanism in PM-MAC achieves better performance in access success rate, channel utilization and backoff delay.