Orthogonal Vector Approach for Synthesis of Multi-Beam Directional Modulation Transmitters

Abstract

An orthogonal vector approach is proposed for the synthesis of multi-beam directional modulation (DM) transmitters. These systems have the capability of concurrently projecting independent data streams into different specified spatial directions while simultaneously distorting signal constellations in all other directions. Simulated bit error rate (BER) spatial distributions are presented for various multi-beam system configurations in order to illustrate representative examples of physical layer security performance enhancement that can be achieved.

A Synthesis-Free Directional Modulation Transmitter Using Retrodirective Array

“…3 it can be observed that the standard QPSK constellation diagram, i.e., four symbols with identical amplitude and 90° phase intervals, can be detected only along the selected communication direction, 60° in this example. As it has been pointed out previously in [1] and [21] that the achievable secrecy performance is determined by the chosen PEDM, the BER simulation results presented here show the same conclusion, i.e., the smaller PEDM the narrower the BER main beams become and the greater the BER sidelobes are suppressed, as is evident in Fig. 4 under different signal to noise ratios (SNRs).…”

“…This approach is relatively universal as it is compatible with both static and dynamic DM systems [19], and can be readily deployed into modern digital wireless transmitters [20]. Furthermore, the orthogonal vector approach can be readily extented to endow DM transmitters with the ability for multiple independent secure beam transmissions [21]- [23] and to make the DM technology applicable in multipath environment [24], [25]. Using the orthogonal vector concept the DM synthesis can be considered as a process of injecting artificial interference that is orthogonal to the transmitted information signals along selected direction(s) in free space or at desired location(s) within a multipath environment.…”

“…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.…”

“…The generation of orthogonal interference that is used to achieve DM functionality [1], i.e., signal waveform distortion along all spatial directions other than the secure communication direction, is independent of the selected secure direction, and, importantly, can be performed using low-cost low-complexity analogue solutions for real-time behaviour; 3) The proposed DM architecture can operate in the scenario where multiple legitimate receivers located along different directions in free space acquire the same information that is required to be conveyed securely. This is completely un-related to the 'dual-beam' DM in [37], which utilizes two beams transmitted along the same direction to construct a single-beam DM transmitter, and is also different to the multi-beam DM in [21]- [23], where multiple DM beams for independent information transmissions are formed; 4) The proposed DM architecture can operate in a multipath environment. It should be noted that the RDA and the DM technologies were previously linked together in [24], [25].…”

Directional-modulation-enabled physical-layer wireless security

“…Here the limited states of the phase shifters reduce the number of independent users that can be supported in the DM systems. 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].…”