Metasurface Based Positional Modulation Design

Abstract

Directional modulation (DM) can transmit information to the desired direction or directions with known constellation mappings, but with scrambled ones in other directions. However, one problem of the design is that when desired receivers and eavesdroppers are in the same transmission direction, their beam responses cannot be distinguished, as steering vectors for these locations are the same. To solve the problem, positional modulation (PM) is introduced where a given modulation pattern can only be received at certain desired positions. In this work, the multi-path effect is exploited for positional modulation with the aid of metasurface acting as a low-cost flexible reflecting surface. Design examples are provided to show the effectiveness of the proposed design.

Sparse Antenna Array Based Positional Modulation Design With a Low-Complexity Metasurface

“…The PM design proposed in [25] is based on ULAs with a maximum half wavelength spacing to avoid grating lobes. The performance of the PM design can be improved by optimizing the antenna locations, leading to a sparse array based design; on the other hand, the number of active micro electromagnetic units on the metasurface can be minimised for reduced implementation complexity.…”

“…One is using a fixed reflecting surface [23], and the other one is applying multiple antenna arrays at different locations [24]. Recently, a PM design was proposed in [25] using metasurface as a low-cost flexible reflecting material to control the modulation pattern at different spatial locations. The benefit of using metasurface over reflecting surface is the flexibility in direction control and reflected signal strength, while the benefit of using metasurface over antenna arrays is the low cost.…”

Constant Reflection Attenuation Constraint for Incoming Signals on Metasurface in Positional Modulation Design

“…, R − 1, with steering matrices S L , S E ,Ŝ,S L and S E . Similarly, we can classify beam responses for desired locations p m,L and beam responses for eavesdroppers p m,E , respectively [23].…”

“…Similar to [23], an alternating optimization method can be adapted, with the process below 1) Randomly generate the vectorw with all magnitudes the same as a given value. 2) With the providedw, W in ( 14) can be optimised.…”

“…Recently, to further increase the degree of freedom in PM design, metasurface has been introduced as a replacement of reflecting surface [23]. As a newly proposed material, metasurface has been applied quickly in wireless communication-s [24]- [28].…”