In this paper, the sum secure degrees of freedom (SDoF) of the $K$-user Multiple Input/Single Output (MISO) Broadcast Channel with Confidential Messages (BCCM) and alternating Channel State Information at the Transmitter (CSIT) is investigated. In the MISO BCCM, a $K$-antenna transmitter (TX) communicates toward $K$ single-antenna receivers (RXs), so that message for RX $k$ is kept secret from RX $j$ with $j<k$. For this model, we consider the scenario in which the CSI of the RXs from $2$ to $K$ is instantaneously known at the transmitter while CSI of RX $1$ is known at the transmitter (i) instantaneously for half of the time and (ii) with a unit delay for the remainder of the time. We refer to this CSIT availability as \emph{alternating} CSIT. Alternating CIST has been shown to provide synergistic gains in terms of SDoF and is thus of a viable strategy to ensure secure communication by simply relying on the CSI feedback strategy. Our main contribution is the characterization of sum SDoF for this model as $SDoF_{\rm sum}= (2K-1)/2$. Interestingly, this $SDoF_{\rm sum}$ is attained by a rather simple achievability in which the TX uses artificial noise to prevent the decoding of the message of the unintended receivers at RX $1$. For simplicity first, the proof for the case $K=3$ is discussed in detail and after that, we have presented the results for any number of RXs.
翻译:在本文中,对以K$用户多重投入/单一输出(MISO)广播频道中含有机密信息(BCM)和传输器中交替频道国家信息(CSIT)的自由度总安全度(SDoF)进行了调查。在MSISO BCM中,一个K$-antenna发报机(TX)向美元单安纳接收机(RX)发送信息,因此,RX $k$的信息以人工度(j) < k$)保密。对于这一模型,我们认为,RX 的CSI 美元从2美元到K$(CCCMM)即时知道,而CSI $(CX) 的CSI 立即知道, 半时间是瞬间,(TX) 安全度(S) 美元(RX) 的信息以memph{contratingting} CS.SIT 。 解说,以SDF 的协同值提供SDRF的增益。因此,一个简单的战略是S-x的S=xnalalal 。