Directional modulation far‐field pattern separation synthesis approach

Abstract

In this study, a far-field power pattern separation approach is proposed for the synthesis of directional modulation (DM) transmitter arrays. Separation into information patterns and interference patterns is enabled by far-field pattern null steering. Compared with other DM synthesis methods, for example, bit error rate-driven DM optimisation and orthogonal vector injection, the approach developed in this study facilitates manipulation of artificial interference spatial distributions. With such capability more interference power can be projected into those spatial directions most vulnerable to eavesdropping, that is, the information side lobes. In such a fashion, information leaked through radiation side lobes can be effectively mitigated in a transmitter power efficient manner. Furthermore, for the first time, the authors demonstrate how multi-beam DM transmitters can be synthesised via this approach.

A review of directional modulation technology

“…Prior to the recent efforts in [11,[14][15][16], the previous DM synthesis attempts were closely bounded up with the physical DM transmitter structures. For passive DM transmitter arrays [20][21][22], termed by authors near-field direct antenna modulation (NFDAM), which rely on the complex transformation between near-field electromagnetic boundaries and far-field behaviours, there is no analytical means to map transmitter settings to vector paths in IQ space, and ultimately to the constellation tracks and secrecy performance.…”

Directional-modulation-enabled physical-layer wireless security

“…Another DM array far-field pattern separation synthesis approach was developed in [32,33]. Here by virtue of the far-field null steering approach, the DM array far-field radiation patterns can be separated into information patterns, which describe information energy projected along each spatial direction, and interference patterns, which represent disturbance on genuine information.…”

“…Further in [40,41] the orthogonal vector approach was successfully adapted for general-case multi-beam DM synthesis. By realising that the orthogonal vectors generate far-field radiation patterns, termed as interference patterns, which have nulls along all desired secure directions, the far-field pattern separation approach was developed [33]. All of the above methods are equivalent.…”

A Synthesis-Free Directional Modulation Transmitter Using Retrodirective Array

“…Bit error rate (BER) driven optimization algorithm assisted approaches were presented in [5], [6], [11], [12]. A variety of DM synthesis methods by constraining different properties of array far-field radiation patterns were described in [13]- [17]. An orthogonal vector approach was firstly proposed in [1] and further refined in [18], which synthesizes DM transmitter arrays by generating orthogonal vectors/interference in the null space of the channel vectors between the DM transmitters and the legitimate receivers.…”

“…These hinder the real-time response of implemented DM transmitters. For example, the BER-driven methods in [5], [12] and the far-field radiation pattern synthesis approaches in [14], [15] require a number of iterations in optimization processes; the far-field pattern separation method [16], [17] and the orthogonal vector approach or the MIMO-inspired approach [1], [21]- [25] involves matrix inversion. In addition when the selected secure communication direction/location or the multipath environment changes all of the DM synthesis processes need to be re-run.…”