Experimental Validation of Interference Alignment Techniques for Homogeneous and Three-Tier HetNets Using USRP-Testbed

Validating the performance of wireless networks using hardware testbeds is an essential task to see networks' performance in real environments. In this paper, we present an experimental evaluation of the performance of different interference alignment techniques for both homogeneous and heterogeneous networks (HetNets) conducted on a wireless testbed comprised of a total of 20 multi-input multi-output (MIMO) software-defined radio (SDR) devices. Four interference alignment (IA) techniques are considered, namely, rank constrained rank minimization (RCRM), weighted rank constrained rank minimization (WRCRM), leakage minimization and maximum signal-to-interference-plus-noise ratio (SINR). The four IA algorithms are first implemented on a downlink three-user homogeneous network using a cluster of 6 USRPs and the LabVIEW programming environment. Then, the comparison is conducted for a three-tier downlink heterogeneous network with a macro base station (BS) of 6 antennas, a small BS with 4 antennas, and a cognitive-radio BS with 2 antennas, giving a mutually interfering broadcast channel (MIBC). Our paper shows the implementation procedures and discusses the systems' configuration from both hardware and software aspects. The experimental real-time results compare the performance of the different IA schemes showing the impact of practical constraints on the evaluation results.