Implementation of a real-time wireless interference alignment network

Interference alignment (IA) is a cooperative transmission technique for the interference channel. This paper describes two testbeds that implement real-time Multiple-input multiple-output (MIMO) IA for a network with three 2-antenna user pairs using software defined radio techniques: a PC-based testbed for rapid prototyping of potential IA protocols and an embedded testbed for evaluating IA under real-world computational constraints. The IA implementations rely on a wired backbone to share global channel state information (CSI) and a shared clock for frequency and timing synchronization. The testbeds are used to demonstrate the viability of IA, and to compare its robustness with several alternative transmission strategies, such as 2 × 2 MIMO TDMA, in terms of sum-rates. Results show that we are able to successfully achieve over-the-air IA in our three-user 2×2 MIMO testbed. The paper highlights key challenges with the practical realization of IA that are encountered while developing the testbed and identifies areas for future research.