# A Software-Defined Radio Platform for Teaching Beamforming Principles
## 1 Introduction  
Beamforming has emerged as an essential technology in today's wireless communication landscape, enabling more efficient, reliable, and high-speed data transmission in fifth-generation mobile communication (5G) and wireless-fidelity (Wi-Fi) networks by focusing signals to end-user devices. This is achieved through signal processing techniques that steer the beam in specific directions by combining outputs from multiple antennas or arrays. As the demand for bandwidth and connectivity continues to increase, beamforming plays a crucial role in optimizing signal directivity, by minimizing interference and enhancing overall performance in both indoor and outdoor wireless communication environments [1]. In indoor environments, where radio waves must propagate through walls, furniture, and other obstructions, beamforming dynamically directs signals towards the end-user receivers, reducing the effects of multipath propagation and attenuation. In outdoor environments, wave propagation is impacted by factors such as longertransmission distances, diverse weather conditions, and the presence of buildings and foliage [2]. By directing radio beams towards user devices, beamforming aims to compensate signal fading and scattering, common propagation phenomena in outdoor environments. Figure 1 presents 5G and Wi-Fi beamforming networks deployed in indoor and outdoor environments. Beamforming can be implemented using analog, digital, or hybrid architectures [3; 4; 5; 6; 7], each with its own advantages and limitations. Analog beamforming is more cost-effective as it uses fewer radiofrequency (RF) chains [4], but it is limited in flexibility due to its inability to independently control the signal on each antenna element. On the other hand, digital beamforming has been proved to be highly flexible and convenient for implementing complex algorithms as it relies on software-based signal processing [5]. However, this comes at a higher cost and greater complexity compared to analog beamforming. Hybrid beamforming, which combines analog and digital components, can significantly reduce hardware complexity and power consumption while approaching the performance of fully digital beamforming [3; 6]. Hybrid beamforming is a promising approach offering a balance between performance and hardware efficiency [6; 7]. Coupled with the agility and flexibility of software-defined radio (SDR) technology, this approach enables convenient, rapid, and cost-effective deployment of communication systems in multiple frequency bands [8; 9]. To this extent, several papers document the use of SDR for beamforming systems [8; 9; 10; 11]. The authors of [8] demonstrate that their proposed SDR-based beamforming system effectively cancels interference in multipath environments without compromising signal quality or performance. In [9], the authors present a flexible SDR-based radio beamforming architecture operating in the 28 GHz frequency band with potential application in radar and 5G systems. SDR-based beamforming systems are also presented in [10; 11; 12; 13], with demonstrated usability and robustness together with good agreement between simulation and measurement results. The main documented challenge associated with the use of SDR for beamforming is the need of phase calibration in the case of multiple transmitters for precise beam directivity [14]. Despite these advancements, gaps and limitations still exist in the current literature, particularly concerning the documentation of phase synchronization, as well as the validation and testing of these systems in real-life deployment scenarios in the sub 6 GHz frequency range [15], where propagation impact is more significant than in mm-wave. Multichannel transmit/receive SDR recently became available from NI Ettus Research [16] or Per Vices Corporation [17], supporting a variety of RF developing environments. Building on this accessibility, this work presents the development of an SDR-based beamforming platform designed for laboratory experimentation of telecom engineering students.