AMP-based Joint Activity Detection and Channel Estimation for OFDM-based Grant-Free Access

To realize orthogonal frequency division multiplexing (OFDM)-based grant-free access for wide-band systems under frequency-selective fading, the existing device activity detection and channel estimation methods need substantial accuracy improvement or computation time reduction. In this paper, we aim to resolve this issue. First, we present an exact time domain signal model for OFDM-based grant-free access under frequency-selective fading. Then, we build a new factor graph and propose an approximate message passing (AMP) algorithm for joint device activity detection and channel estimation, unleashing AMP’s full potential. Next, we analyze the state evolution of the AMP algorithm and the error probability and mean square error (MSE) of the estimated device activities and active devices’ channels, respectively. Finally, numerical results validate the theoretical results and show the superior performance of the proposed AMP algorithm.