  In this letter, we present the first characterization for the achievable
Degrees-of-Freedom (DoF) by Blind Interference Alignment (BIA) using staggered
antenna switching in the $K$-user Gaussian Interference Channel. In such
scheme, each transmitter is equipped with one conventional antenna and each
receiver is equipped with one reconfigurable (multi-mode) antenna. Assuming
that the channel is known to the receivers only, we show that BIA can achieve
$\frac{2K}{K+2}$ DoF, which surpasses the sum DoF achieved by previously known
interference alignment schemes with delayed channel state information at
transmitters (CSIT). This result implies that the sum DoF is upper bounded by
2, which means that the best we can do with BIA is to double the DoF achieved
by orthogonal multiple access schemes. Moreover, we propose an algorithm to
generate the transmit beamforming vectors and the reconfigurable antenna
switching patterns, and apply this algorithm to the 4-user SISO Interference
Channel, showing that $\frac{4}{3}$ sum DoF is achievable.
