Abstract
We improve upon our previous upper bound on the secrecy capacity of the wiretap channel with multiple transmit antennas and single-antenna receivers, with noisy main channel state information (CSI) at the transmitter (CSI-T). Specifically, we show that if the main CSI error does not scale with the power budget at the transmitter (P) over bar, then the secrecy capacity is bounded above essentially by log log ((P) over bar) yielding a secure degree of freedom ( sdof) equal to zero. However, if the main CSI error scales as O((P) over bar (-beta)), for beta is an element of[0, 1], then the sdof is equal to beta.