Table 6 Application specific comparison of range-angular DM techniques

Frequency range-angular DM

1

FDA based DM and its variants [97, 98, 101,102,103, 107,108,109]

Suitable for point-to-point applications in which both angular direction and range of the legitimate user are known to transmitter

2

Multi-directional FDA [99, 100, 104]

Enhanced directional capability of FDA is demonstrated. Particularly useful for multi-user FDA security applications

3

Multi-carrier FDA [105] [106]

Well-suited for integration with OFDM transmitters

4

Frequency index modulation for FDA [110]

Decoupling of range and angle is achieved for better security compared to simple FDA

5

Discular FDA [111]

Two-dimensional array geometry for FDA has been proposed. Suitable for applications in which secure transmission is required in a very narrow region of interest

Temporal range-angular DM

6

Time-modulated FDA [112]

Resolves the issue of range-angular coupling in traditional FDA by time-modulation of antenna array

7

Time-invariant time-modulated FDA [113]

Logarithmic frequency offsets has been proposed to mitigate the time-variance issue associated with conventional FDA

Spatial range-angular DM

8

Antenna index modulation for FDA [114]

Antenna array is both spatially modulated and diversified in frequency. This scheme not only enhances security but also increases throughput at the expense of increased receiver complexity

9

Quadrature spatial modulation based FDA [115]

A combination of QSM and FDA for enhanced security has been proposed

Polarization range-angular DM

10

Polarization sensitive beamforming for FDA [116]

Polarization sensitive FDA technique provides not only range-angular security but also polarization dependent beam. An added complexity is the polarization control of array