Optimal Power Allocation in Block Fading Channels with Confidential Messages

Arsenia Chorti, Katerina Papadaki, H. Vincent Poor

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The optimal power allocation for block fading (BF) networks with confidential messages is investigated under an $M$-block delay and power constraint. First, we study networks without channel state information (CSI) feedback to the transmitter and demonstrate that the optimal power allocation is the equidistribution of the power budget, denoted as the 'blind policy.' In blind scenarios secrecy can be achieved through receiver diversity; the probability of secrecy outage (PSO) is shown to decay exponentially with the diversity order of the legitimate user. Then, we investigate networks with CSI feedback. For comparison purposes, we restate the acausal secure waterfilling algorithm with full CSI before moving to the causal feedback scenario. In the latter, an approximate 'threshold policy' for the low SNR and an approximate 'high power policy' for the high SNR regimes are derived. Furthermore, a novel universal transmission policy is proposed across all SNRs, denoted as the 'blind horizon approximation' (BHA). Through numerical results, the BHA policy is shown to outperform both the threshold and high power policies when the legitimate user has an SNR advantage with respect to the eavesdropper, while it also compares well with the secure waterfilling policy.

Original languageEnglish (US)
Article number7091949
Pages (from-to)4708-4719
Number of pages12
JournalIEEE Transactions on Wireless Communications
Issue number9
StatePublished - Sep 2015
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Computer Science Applications
  • Electrical and Electronic Engineering
  • Applied Mathematics


  • BF-AWGN channel
  • Secrecy capacity
  • block fading
  • causal channel state information feedback
  • dynamic program
  • probability of secrecy outage


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