On the Compound MIMO Broadcast Channels with Confidential Messages

TL;DR

This paper analyzes the secrecy capacity of compound MIMO broadcast channels with confidential messages, deriving achievable secrecy degrees of freedom for different models and demonstrating improvements through temporal state variation.

Contribution

It introduces new achievable secrecy degrees of freedom regions for compound MIMO-BCC models, highlighting the benefits of exploiting temporal variations in channel states.

Findings

Temporal variation enhances secrecy degrees of freedom.

Achievable s.d.o.f. regions differ between Gaussian and ergodic fading models.

Delay increases with improved secrecy performance.

Abstract

We study the compound multi-input multi-output (MIMO) broadcast channel with confidential messages (BCC), where one transmitter sends a common message to two receivers and two confidential messages respectively to each receiver. The channel state may take one of a finite set of states, and the transmitter knows the state set but does not know the realization of the state. We study achievable rates with perfect secrecy in the high SNR regime by characterizing an achievable secrecy degree of freedom (s.d.o.f.) region for two models, the Gaussian MIMO-BCC and the ergodic fading multi-input single-output (MISO)-BCC without a common message. We show that by exploiting an additional temporal dimension due to state variation in the ergodic fading model, the achievable s.d.o.f. region can be significantly improved compared to the Gaussian model with a constant state, although at the price of a larger delay.