## 6 Numerical Results  
In this section, appropriate numerical results are illustrated, using the derived closed-form expressions (19) and (21). Several parameter values are chosen for the CDMA RoFSO link with receivers' spatial diversity. Firstly, we assume two different cases for the atmospheric turbulence conditions. In the first case we assume strong irradiance fluctuations with the value of the Rytov variance equal to \(\sigma_{R}^{2}=2.5\) and in the second case we choose saturate turbulence conditions with \(\sigma_{R}^{2}=25\). The aperture radius for each receiver is chosen equal to \(R_{m}=5\) cm. The beam spot radius at each transmitter is \(W_{0,m}=3\) cm, the operational wavelength \(\lambda=1.55\)\(\upmu\)m, the link distance \(L_{5,m}=1.5\) km and the phase front radius is \(F_{0,m}=500\) m. The beam spot radius at each receiver aperture is calculated equal to \(W_{z,m}=9\) cm for \(\sigma_{R}^{2}=2.5\) and \(W_{z,m}=25\) cm for \(\sigma_{R}^{2}=25\). For the CDMA RoFSO link we have the IMD3 coefficient equal to \(\alpha_{3}=1/3\), \(G_{p}=512\), \(T=300\) K and \(RIN=-155\) dB/Hz. The load resistance is \(R_{L}=50\)\(\Omega\) and \(<\)\(\text{s}_{k}(t)\)\(>=1\). Also, the bandwidth for the forward link is chosen \(B=20\) MHz while for the reverse link is \(B=10\) MHz. For the influence of the PE effect, two cases are considered. For the first case, we select weak spatial jitters with normalized values at \(\sigma_{x}/R=0.2\) and \(\sigma_{y}/R=0.1\) and zero boresight displacement i.e., \(\mu_{x}/R=0\) and \(\mu_{y}/R=0\). In the second case, enhanced spatial jitters are considered, with \(\sigma_{x}/R=0.5\), \(\sigma_{y}/R=0.2\) and NZB displacement with \(\mu_{x}/R=0.1\) and \(\mu_{y}/R=0.1\). The selected modulation scheme for the forward link is the 16-QAM, while for the reverse link is the QPSK. The ABER results for the CDMA RoFSO link with receivers' diversity are illustrated among the Figures 3-6 wherein cases with \(M=2\times 2\) and \(M=4\times 4\) transceivers are shown. In Figures 2 and 3 the ABER performance of the forward link is presented. In Figure 3 the weak PE case is depicted and in Figure 4 the strong PE impact is shown. It is deduced that an average received optical power per diversity branch (\(P_{R,m}\)) above \(-10\) dBm is required for the case of the forward link when \(M=4\) transceivers are used in order to attain an ABER at \(10^{-4}\) even in the saturated turbulence conditions, i.e., \(\sigma_{R}^{2}=25\). In the case of enhanced PE impact, i.e., Figure 3, the performance slightly worsens and the required \(P_{R,m}\) increases proportionally. Figure 4: The ABER performance for the forward CDMA RoFSO link with receivers’ diversity, over strong turbulence and enhanced PE impact for different values of the number of users \(K\). Figure 5: The ABER performance for the reverse CDMA RoFSO link with receivers’ diversity, over strong turbulence and weak PE impact for different values of the number of users \(K\). Figure 3: The ABER performance for the forward CDMA RoFSO link with receivers’ diversity, over strong turbulence and weak PE impact for different values of the number of users \(K\). The ABER performance for the reverse link of the CDMA RoFSO system is illustrated in Figures 5 and 6. Firstly, as it is illustrated in both figures the simultaneous access of 80 users is feasible, especially when \(M=4\) transceivers are employed. In this case, the required \(P_{R,m}\) is \(-15\) dBm for ABER at \(10^{-4}\) with saturated turbulence conditions. The case of enhanced PE is presented in Figure 4, where the performance exacerbates primarily in the case of \(\sigma_{R}^{2}=2.5\). Eventually, the OP outcomes are depicted in Figures 7 and 8. It is worth noting that the outage performance estimation is implemented as a function of the \(\textit{CNIR}_{k,m,EX}\), providing the advantage for performance assessment of both directions of the forward and the reverse link.