FLEX: Low-Complexity 5D Beamspace Channel Estimation for mmWave MIMO-OFDM

Paper in proceeding, 2025

We introduce FLEX, a family of fast Fourier transform(FFT)-based low complexity beamspace channel estimation algorithms for mmWave MIMO-OFDM systems, enabling five-dimensional parameter estimation; delay, two-dimensional angles of arrival (AoAs), and two-dimensional angles of departure (AoDs). FLEX operates without prior knowledge of the number of propagation paths and automatically pairs multidimensional parameters. The proposed methods first estimate path delays using an FFT-based approach, then compensate for these delays to decouple the spatial dimensions. Angle estimation is performed using either a correlation-based or shift-invariance propertybased methods, accommodating different precoder structures. A modified approach resolves paths that share a delay bin but are separable in angular domain. Simulation results demonstrate that FLEX significantly reduces computational complexity while achieving accuracy comparable to state-of-the-art methods, converging to theoretical bounds at lower transmit power. Its efficiency and adaptability make FLEX well-suited for real-time channel estimation in wideband communication systems.