  Spatial filtering based on multiple-input multiple-output (MIMO) processing
is a promising approach to jammer mitigation. Effective MIMO data detectors
that mitigate smart jammers have recently been proposed, but they all assume
perfect time synchronization between transmitter(s) and receiver. However, to
the best of our knowledge, there are no methods for resilient time
synchronization in the presence of smart jammers. To remedy this situation, we
propose JASS, the first method that enables reliable time synchronization for
the single-user MIMO uplink while mitigating smart jamming attacks. JASS
detects a randomized synchronization sequence based on a novel optimization
problem that fits a spatial filter to the time-windowed receive signal in order
to mitigate the jammer. We underscore the efficacy of the proposed optimization
problem by proving that it ensures successful time synchronization under
certain intuitive conditions. We then derive an efficient algorithm for
approximately solving our optimization problem. Finally, we use simulations to
demonstrate the effectiveness of JASS against a wide range of different jammer
types.
