Design and development of a high throughput airborne line-of-sight communication link
Line-of-sight (LOS) communication links have an ever increasing demand for high throughput IP-based data transmission. Such LOS systems are of particular interest for bi-directional communications from an aircraft to a ground station. A key requirement for the operation in various countries is carrier frequency agility because of the regulatory issues. That is why the LOS link developed by JOANNEUM RESEARCH DIGITAL supports adjustable carrier frequencies in the range from 2 GHz to 6 GHz. The used TDD (Time Division Duplex) medium access has the advantage that only one frequency for up- and downlink is required. A further advantage is configurable allocation of the available carrier bandwidth between the downlink to the ground and uplink to the aircraft. The maximum throughput in the downlink is 8 Mbit/s. The system is based on a software defined radio (SDR) approach which leads to high flexibility because of fast development and testing of signal processing algorithms. This fact allows cost effective adaption of the system to different user requirements. The paper is organized in the following way. Section 1 provides a system overview. In Section 2 the modem design parameters are discussed in detail, followed by Section 3 and 4 which present the signal processing algorithms implemented and the RF front end. Finally, Section 5 shows the signal characteristic of a test flight with a DA42 aircraft.