Abstract
Directional modulation (DM) as a physical layer security technique has been studied from many different aspects recently. Normally all existing designs based on antenna arrays lead to varying weight coefficients for different antennas and for different signal symbols, which poses a particular challenge for feed circuits design in analogue implementation. In this paper, to reduce the implementation complexity, a constant magnitude constraint is proposed for the first time, and the resultant non-convex constraint can be modified to a convex form so that the problem can be solved conveniently by existing convex optimisation toolboxes. Design examples are provided to show the effectiveness of the proposed design.
Highlights
With the fast development of the Fifth Generation (5G) network, communication has been more important than ever [1], [2]
Compared with a given antenna array design, to further reduce the number of antennas, directional modulation (DM) design was extended to sparse antenna arrays [6]
To overcome the inherent limitation of DM, where eavesdroppers and the desired users share the same received signal when they are in the same spatial direction of the antenna array, two positional modulation (PD) designs were proposed, with one based on a reflecting surface [7], and the other employing multiple antenna arrays [8]
Summary
With the fast development of the Fifth Generation (5G) network, communication has been more important than ever [1], [2]. Where δm represents the given magnitude for each weight coefficient for the m-th symbol, so that we only need to change the phase response of the feed circuit for different antennas. The DM design under the constant magnitude constraint for weight coefficient can be formulated as follows min ||pm,SL − wHm SSL ||2 subject to wHm SML = pm,ML. Note that for the above formulation to work, the maximum magnitude response in the mainlobe can only be located at one single direction (θ0 in our case), i.e., a flat top main beam can not be achieved We will prove this later at the end of Section III. Another note is that the proposed constraint cannot only be applied to a linear antenna array, and a planar antenna array or a circular antenna array by changing the corresponding steering vectors
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