Full digital beamforming for future aerospace applications based on software-defined radios

Nowadays, wireless devices request always higher data rates and more reliable connections. Omnidirectional antennas, used in smartphones, WIFI modems or even planes no longer fit these requirements as the power is distributed in all directions, which reduces the reachable data rates and favors the creation of interferences. Beamforming is a solution for these problems as the radiated power can be concentrated in a particular direction while interferences in other directions are suppressed. Analog beamforming has limited performance and significant size and cost. Full Digital Beamforming (DBF) allows more flexible implementations using SDR platforms, where the signal processing is fully digital and controlled by software. Moreover, SDR platforms are available at a much lower price as ADCs and DACs became significantly cheaper with respect to 10 years ago.\\ DBF is a mix of RF and digital technologies. It improves the flexibility of the transceiver as it allows to use the different digital signal processing methods and algorithms. The main characteristic of DBF is the conversion of the RF signal fed at each antenna of the array into two baseband signals called I and Q. Beamforming is made by giving complex weights to these digital signals to tune their amplitudes and phases and in adding them to create the signals transmitted to the array elements. In full DBF, the adjustments are made by software, to produce one or multiple beams and implement beam scanning, spatial multiplexing and beam shaping.\\ This thesis focuses on full DBF on the TX side using an SDR platform (AD9361 from Analog Devices) and an antenna array made of two omnidirectional antennas. The thesis is structured in the following way: Some basic knowledge is given on beamforming, an analysis is made on full DBF and the OFDM data modulation scheme, and the hardware and software configurations of the demonstrator is presented. Finally, experiments are made using first an integrated DDS generating sinewaves and then a DMA controller to transmit customized signals from memory (OFDM symbols). In both cases, a receiving antenna is placed in front of the array at different angles and the received power is measured with a spectrum analyzer. For each configuration, the radio beam is steered by changing the relative phase between the two antennas, and the measured powers confirm that the beam is moving to or out of the receiving antenna.