Opportunistic user scheduling and beamforming for physical layer security in multicast and interference networks

Abstract

In this dissertation, we study the transmission schemes for physical layer security in the single-cell multicast network with wireless information and power transfer, and the bursty interference network with opportunistic user scheduling. In the multiuser scenario, one of severe problems is the inter-group/user interference, which significantly degrades the reliable transmission quality in general. For this reason, a critical issue for multiuser networks is to resolve the inter-group/user interference issue. Interestingly, in two specific multiuser networks where we want to consider, the inter-group/user interference might be beneficial in terms of secure transmissions. As described above, it is very important to deal with the inter-group/user interference properly since it has both advantage and disadvantage simultaneously for reliable and secure transmissions. In this dissertation, we propose novel secure transmission schemes to solve the challenging inter-group/user interference problem in two specific multiuser networks by utilizing the artificial noise (AN) aided transmit beamforming and the opportunistic user scheduling, respectively.

The main focus of this dissertation is to improve physical layer security, which is essential for reliable and secure transmissions. To this end, we adopt the secrecy rate criterion for physical layer security. We resolve the interference issue as well as enhance network performance by minimizing the transmit power under the secrecy rate constraint in the single-cell multicast network with wireless information and power transfer, and maximizing the ergodic secrecy rate per transmitter-receiver pair in the bursty interference network with opportunistic user scheduling.

Firstly, we address the AN aided transmit beamforming problem for physical layer security in a multiple-input single-output (MISO) single-cell multicast network with wireless information and power transfer. To solve the inter-group interference issue and minimize the transmit power, we derive the closed-form suboptimal beamforming based on the null-space beamforming. The suboptimal beamforming is shown to be optimal when the number of transmit antennas goes to infinity. To further improve the performance in the finite regime of the number of transmit antennas, we propose an efficient iterative algorithm based on the successive convex approximation.

Secondly, we investigate the opportunistic user scheduling problem for physical layer security in a MISO symmetric bursty interference network. To solve the inter-user interference issue, we propose a signal-to-interference-plus-noise ratio (SINR) based opportunistic transmission scheme. Then, the ergodic secrecy rate per transmitter-receiver pair is mathematically analyzed. To obtain the achievable ergodic secrecy rate per transmitter-receiver pair, we also propose a two-level iterative algorithm based on the golden section search and the damped Newton method.

Thirdly, we consider the opportunistic user scheduling problem for physical layer security in a MISO asymmetric bursty interference network. To solve the inter-user interference issue, we propose a SINR based opportunistic transmission scheme. Then, the ergodic secrecy rate per transmitter-receiver pair is mathematically analyzed. Using the derived analytical expression, the achievable ergodic secrecy rate per transmitter-receiver pair is obtained through a proposed two-level iterative algorithm based on the interior point method and the damped Newton method. To catch more insights behind the mathematical expressions, we analyze asymptotic characteristics of the achievable ergodic secrecy rate per transmitter-receiver pair in interference limited and nose limited scenarios.

Our analytic and numerical results verify the gains of the proposed schemes compared to the conventional or benchmark schemes.