The expansion and improvement of synthetic aperture radar (SAR) technology have greatly enhanced its practicality. SAR imaging requires real-time processing with limited power consumption for large input images. Designing a specific heterogeneous array processor is an effective approach to meet the power consumption constraints and real-time processing requirements of an application system. In this paper, taking a commonly used algorithm for SAR imaging—the chirp scaling algorithm (CSA)—as an example, the characteristics of each calculation stage in the SAR imaging process is analyzed, and the data flow model of SAR imaging is extracted. A heterogeneous array architecture for SAR imaging that effectively supports Fast Fourier Transformation/Inverse Fast Fourier Transform (FFT/IFFT) and phase compensation operations is proposed. First, a heterogeneous array architecture consisting of fixed-point PE units and floating-point FPE units, which are respectively proposed for the FFT/IFFT and phase compensation operations, increasing energy efficiency by 50% compared with the architecture using floating-point units. Second, data cross-placement and simultaneous access strategies are proposed to support the intra-block parallel processing of SAR block imaging, achieving up to 115.2 GOPS throughput. Third, a resource management strategy for heterogeneous computing arrays is designed, which supports the pipeline processing of FFT/IFFT and phase compensation operation, improving PE utilization by a factor of 1.82 and increasing energy efficiency by a factor of 1.5. Implemented in 65-nm technology, the experimental results show that the processor can achieve energy efficiency of up to 254 GOPS/W. The imaging fidelity and accuracy of the proposed processor were verified by evaluating the image quality of the actual scene.

Improving flight endurance limited by on-board energy is a critical issue in UAV-assisted communication systems. Due to the natural gliding capabilities of fixed-wing UAVs, the aerodynamic forces can be leveraged to reduce the propulsion energy consumption. In this paper, we investigate a UAV attitude control strategy to optimize the energy consumption for data collection. A dynamic model is developed to capture the key aerodynamic effects on the propulsion energy consumption and trajectory of UAV. Then, an energy minimization problem is formulated with the flight angle selection constraints and the data collection requirements. To efficiently solve this problem, a piecewise attitude control strategy is proposed to obtain the values of yaw angle and pitch angle. This is the first attempt which considers the effect of aerodynamic forces on designing energy efficient data collection scheme for fixed-wing UAVs. Simulation results show that the proposed strategy wisely adjusts the attitude of UAV based on wind field to complete the data collection mission with less energy consumption.

Steering motor is of vital importance in UAV’s health-monitoring system, to which its supply current is the most critical characteristic representing health statue of UAV. In order to conduct continuous measuring on the steering motor’s current of large dynamic range, in this paper, a current measurement method is therefore proposed on the basis of twin nonlinear shunt. The proposed method adopts the twin diode as the current sampling device, which not only realizes measurement range and relative constant resolution, but also ensures continuity of the measurement due to the eliminated operation of range switching. The associated diode is used to compensate the temperature of core temperature of the shunt diode, and to make the nonlinear-shunt more adaptive for the case of junction being heated under larger current. The working principle, real-time compensation method and circuit implementation of our method are discussed in detail. Experimental test results suggest that the measurement error of the proposed method is less than 4.5% when the measurement current varies between 10 mA to 10 A, maintaining the relative resolution at an almost constant level, while preventing the conventional method of frequent range switching from generating glitches. In addition to the ensured continuity, information-rich details of the current are sustained, contributing to the UAV’s health-monitoring system. The proposal can also be applied to other applications concerning large dynamic current detection, including, but not limited to, industrial control, motor control, etc.