Establishing Secrecy Region for Directional Modulation Scheme with Random Frequency Diverse Array

TL;DR

This paper analyzes the secrecy region in RFDA-based directional modulation, deriving antenna and bandwidth requirements, and examining how artificial noise impacts secrecy capacity in secure communications.

Contribution

It introduces the concept of a secrecy region around the receiver and derives key parameters for RFDA-DM-AN schemes, highlighting when artificial noise is beneficial.

Findings

Artificial noise can reduce secrecy capacity under certain conditions.

Increasing bandwidth enlarges the secrecy region and capacity.

More antennas are needed for higher secrecy transmission rates.

Abstract

Random frequency diverse array (RFDA) based directional modulation (DM) was proposed as a promising technology in secure communications to achieve a precise transmission of confidential messages, and artificial noise (AN) was considered as an important helper in RFDA-DM. Compared with previous works that only focus on the spot of the desired receiver, in this work, we investigate a secrecy region around the desired receiver, that is, a specific range and angle resolution around the desired receiver. Firstly, the minimum number of antennas and the bandwidth needed to achieve a secrecy region are derived. Moreover, based on the lower bound of the secrecy capacity in RFDA-DM-AN scheme, we investigate the performance impact of AN on the secrecy capacity. From this work, we conclude that: 1) AN is not always beneficial to the secure transmission. Specifically, when the number of antennas is sufficiently large and the transmit power is smaller than a specified value, AN will reduce secrecy capacity due to the consumption of limited transmit power. 2) Increasing bandwidth will enlarge the set for randomly allocating frequencies and thus lead to a higher secrecy capacity. 3) The minimum number of antennas increases as the predefined secrecy transmission rate increases.