  We consider the two-hop interference channel (IC) with constant real channel
coefficients, which consists of two source-destination pairs, separated by two
relays. We analyze the achievable degrees of freedom (DoF) of such network when
relays are restricted to perform scalar amplify-forward (AF) operations, with
possibly time-varying coefficients. We show that, somewhat surprisingly, by
providing the flexibility of choosing time-varying AF coefficients at the
relays, it is possible to achieve 4/3 sum-DoF. We also develop a novel outer
bound that matches our achievability, hence characterizing the sum-DoF of
two-hop interference channels with time-varying AF relaying strategies.
