  Wireless systems must be resilient to jamming attacks. Existing mitigation
methods based on multi-antenna processing require knowledge of the jammer's
transmit characteristics that may be difficult to acquire, especially for smart
jammers that evade mitigation by transmitting only at specific instants. We
propose a novel method to mitigate smart jamming attacks on the massive
multi-user multiple-input multiple-output (MU-MIMO) uplink which does not
require the jammer to be active at any specific instant. By formulating an
optimization problem that unifies jammer estimation and mitigation, channel
estimation, and data detection, we exploit that a jammer cannot change its
subspace within a coherence interval. Theoretical results for our problem
formulation show that its solution is guaranteed to recover the users' data
symbols under certain conditions. We develop two efficient iterative algorithms
for approximately solving the proposed problem formulation: MAED, a
parameter-free algorithm which uses forward-backward splitting with a box
symbol prior, and SO-MAED, which replaces the prior of MAED with soft-output
symbol estimates that exploit the discrete transmit constellation and which
uses deep unfolding to optimize algorithm parameters. We use simulations to
demonstrate that the proposed algorithms effectively mitigate a wide range of
smart jammers without a priori knowledge about the attack type.
