838 research outputs found
On SDoF of Multi-Receiver Wiretap Channel With Alternating CSIT
We study the problem of secure transmission over a Gaussian multi-input
single-output (MISO) two receiver channel with an external eavesdropper, under
the assumption that the state of the channel which is available to each
receiver is conveyed either perfectly () or with delay () to the
transmitter. Denoting by , , and the channel state information
at the transmitter (CSIT) of user 1, user 2, and eavesdropper, respectively,
the overall CSIT can then alternate between eight possible states, i.e.,
. We denote by the
fraction of time during which the state occurs. Under these
assumptions, we first consider the Gaussian MISO wiretap channel and
characterize the secure degrees of freedom (SDoF). Next, we consider the
general multi-receiver setup and characterize the SDoF region of fixed hybrid
states , , and . We then focus our attention on the symmetric
case in which . For this case, we establish bounds
on SDoF region. The analysis reveals that alternating CSIT allows synergistic
gains in terms of SDoF; and shows that, by opposition to encoding separately
over different states, joint encoding across the states enables strictly better
secure rates. Furthermore, we specialize our results for the two receivers
channel with an external eavesdropper to the two-user broadcast channel. We
show that, the synergistic gains in terms of SDoF by alternating CSIT is not
restricted to multi-receiver wiretap channels; and, can also be harnessed under
broadcast setting.Comment: To Appear in IEEE Transactions on Information Forensics and Securit
On the Degrees-of-freedom of the 3-user MISO Broadcast Channel with Hybrid CSIT
The 3-user multiple-input single-output (MISO) broadcast channel (BC) with
hybrid channel state information at the transmitter (CSIT) is considered. In
this framework, there is perfect and instantaneous CSIT from a subset of users
and delayed CSIT from the remaining users. We present new results on the
degrees of freedom (DoF) of the 3-user MISO BC with hybrid CSIT. In particular,
for the case of 2 transmit antennas, we show that with perfect CSIT from one
user and delayed CSIT from the remaining two users, the optimal DoF is 5/3. For
the case of 3 transmit antennas and the same hybrid CSIT setting, it is shown
that a higher DoF of 9/5 is achievable and this result improves upon the best
known bound. Furthermore, with 3 transmit antennas, and the hybrid CSIT setting
in which there is perfect CSIT from two users and delayed CSIT from the third
one, a novel scheme is presented which achieves 9/4 DoF. Our results also
reveal new insights on how to utilize hybrid channel knowledge for multi-user
scenarios
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