## 4 Performance Analysis
### Discussion  
In this section, we present a comparison with some previous works in Table 2, which fully compares different schemes from different aspects of power efficient (PE), neighbor security (the location of Eve is close to or the same as that of LU, NS), control of received power (CR), range-angle security (RA), and spectral efficiency (SE). From Table 2, we generalize the advantages of our proposed scheme as follows. (1) Compared with PA-based DM schemes, the proposed scheme can achieve the range-angle security due to the FDA characteristics. (2) The high overall spectral efficiency. The idea of SM is to map a block of information bits to symbols that are chosen from the constellation diagram and numbers information of LUs that are chosen from the sets of LUs. The numbers information of multiple LUs can be directly used as additional sources to transmit information simultaneously. (3) Compared with AN-aided DM schemes, our proposed scheme is power efficient due to MP-WFRFT technique which realizes the embedding process of \"AN\" from the modulation level of digital baseband signal. (4) Our proposed scheme can guarantee security of confidential message in some challenging application scenarios. Based on conventional DM schemes, as long as an Eve is close enough to the LU, the confidential messages can be intercepted by the Eve due to constraint on beamwidth. To illustrate the advantage of the proposed schemes, we consider the worst case where Eve s know the MP-WFRFT operation with perfect parameters, and these Eves with same number of LUs can cooperate with each other. Therefore, the received symbol vectors of Eves are first operated by the inverse MP-WFRFT with the shared parameters \((\alpha_{e},\mathbf{m}_{e},\mathbf{c}_{e})\), which yields  
\[\mathbf{y}_{E}(t) =\mathfrak{F}_{\alpha_{e},\mathbf{c}_{e}}^{(\mathbf{m}_{e}, \mathbf{c}_{e})}(\mathbf{H}_{E}^{H}(t)\mathbf{D}\mathbf{v}(t))+\mathfrak{F}_{ \alpha_{e}}^{(\mathbf{m}_{e},\mathbf{c}_{e})}(\mathbf{n}_{E}(t))\] \[=\mathbf{H}_{E}^{H}(t)\mathbf{D}\mathfrak{F}_{\alpha_{e}}^{( \mathbf{m}_{e},\mathbf{c}_{e})}\mathfrak{F}_{\alpha_{s}}^{(\mathbf{m}_{e}, \mathbf{c}_{s})}(\mathbf{u}(t))+\mathfrak{F}_{\alpha_{e}}^{(\mathbf{m}_{e}, \mathbf{c}_{e})}(\mathbf{n}_{E}(t)) \tag{26}\]  
Here, we assume [PERSON] know the MP-WFRFT operation with perfect parameters, which means  
\[(\alpha_{e},\mathbf{m}_{e},\mathbf{c}_{e})=(-\alpha_{s},\mathbf{m}_{s}, \mathbf{c}_{s}), \tag{27}\] \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**ITEM** & **PA-DM** & **AN-DM** & **WFRFT-DM** & **PROPOSED-DM** \\ \hline PE & NO & NO & YES & YES \\ NS & NO & NO & YES & YES \\ CR & NO & NO & NO & YES \\ RA & NO & YES & YES & YES \\ SE & LOW & LOW & LOW & HIGH \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparisons for different schemes. Then the (35) can be further written as  
\[\mathbf{y}_{E}(t)=\mathbf{H}_{E}^{H}(t)\mathbf{D}\mathfrak{F}_{-\alpha_{s}}^{( \mathbf{m}_{\
u},\mathbf{c}_{s})}\mathfrak{F}_{\alpha_{s}}^{(\mathbf{m}_{\
u}, \mathbf{c}_{s})}(\mathbf{u}(t))+\mathfrak{F}_{-\alpha_{s}}^{(\mathbf{m}_{\
u}, \mathbf{c}_{s})}(\mathbf{n}_{E}(t)){=}\mathbf{H}_{E}^{H}(t)\mathbf{D}\mathbf{u }(t){+}\mathbf{n}_{E}^{{}^{\prime}}(t) \tag{28}\]  
Specifically, the received signal of \(ith\) [PERSON] intercepting \(kth\) LU's information can be obtained by  
\[y_{E_{j}}(t)=\mathbf{h}_{E_{k}}^{H}(t)\mathbf{D}u_{k}(t)+n_{E_{j}}^{{}^{\prime} }(t){=}\underbrace{\mathbf{h}_{E_{k}}^{H}(t)\mathbf{d}_{k}u_{k}(t)}_{\text{ Scrambled signal}}+\underbrace{\mathbf{h}_{E_{k}}^{H}(t){\sum_{i=1,j\
eq k}^{K} \mathbf{d}_{i}u_{i}(t)}}_{\text{Interference from others}}+\underbrace{n_{E_{j}}^{{}^{ \prime}}(t)}_{\text{AWAG}} \tag{29}\]  
From (38), in the worst case, we can see that WFRFT operation cannot achieve encryption security. When the [PERSON]'s location is the same as the LUs--i.e., \(\mathbf{h}_{E_{j}}(t)=\mathbf{h}_{L_{k}}(t)\), \(\mathbf{h}_{E_{k}}^{H}(t)\mathbf{d}_{k}=1\), \(\mathbf{h}_{E_{k}}^{H}(t)\mathbf{d}_{i}=0(i\
eq k)\)--the AN-DM scheme and WFRFT-aided DM scheme both fail.