In the development of beyond-line-of-sight (BLOS) Unmanned Aerial Vehicle (UAV) systems, communication between the UAVs and the ground control station (GCS) is of critical importance. The commonly used economical wireless modules are restricted by the short communication range and are easily blocked by obstacles. The use of a communication relay system provides a practical way to solve these problems, improving the performance of UAV communication in BLOS and cross-obstacle operations. In this study, a communication relay system, in which a quadrotor was used to relay radio communication for another quadrotor was developed and tested. First, the UAVs used as the airborne platform were constructed, and the hardware for the communication relay system was selected and built up. Second, a set of software programs and protocol for autonomous mission control, communication relay control, and ground control were developed. Finally, the system was fully integrated into the airborne platform and tested both indoor and in-flight. The Received Signal Strength Indication (RSSI) and noise value in two typical application scenarios were recorded. The test results demonstrated the ability of this system to extend the communication range and build communication over obstacles. This system also shows the feasibility to coordinate multiple UAVs’ communication with the same relay structure.

this paper presents a kind of three-phase multifunctional networked electric meter based on GPRS transmission technology. Hardware and software of the meter were designed in this paper, data information security protection of the electric meter were also been studied at the same time. The system introduces an ESAM module, the SM1 encryption algorithm the module uses can encrypt the data information of smart meters, so it guarantees the safety of the data information. The networked intelligent meter is low cost and has complete functions, and the active power energy measurement accuracy can reach 0.5s-class, reactive power energy measurement accuracy can reach 2-class.