# Non-Orthogonal eMBB-URLLC Radio Access for Cloud Radio Access Networks with Analog Fronthauling
## 6 Numerical Results
However, when the cable crosstalk increases, the rate degradation is severe, and fair performance are achieved only if the cable bandwidth is large enough to accommodate the redundant transmission of radio signals over all pairs, i.e., \(\mu=1\). Figure 11 shows URLLC and eMBB rates as a function of the URLLC packet arrival probability \(q\). eMBB rates under OMA are compared with those achieved by NOMA under puncturing, TIN and SIC. We consider here full cable bandwidth availability \(\mu=1\) and \(\gamma^{2}=1\), so that, as in Figure 10, the rates achieved for both OMA and NOMA for low \(q\) (say, \(q<10^{-2}\)) coincide with those achieved over the ideal fronthaul. Inter-cell interference is set to \(\alpha^{2}=0.2\). As noted in [32], under OMA, when \(q\) increases, the probability of an URLLC packet to be dropped due to blockage becomes very high, preventing URLLC transmission from meeting the strict reliability constraints, and results in a vanishing URLLC rate. This is unlike in NOMA, whereby the URLLC rate is not affected by \(q\), and the access latency is minimal, i.e., \(L_{U}=1\). For eMBB under NOMA, TIN always outperforms puncturing. This is because TIN does not discard any received minislot, thus contributing to the overall eMBB rate. The result is in contrast with the conventional digital capacity-constrained fronthaul considered in [32]. In fact, in the latter, for sufficient low \(q\), it is preferable not to waste fronthaul capacity resources by quantizing samples received in minislots affected by URLLC interference in order to increase the resolution of the interference-free samples. Additional gains are achieved by SIC, which takes advantages of the high reliability, and thus high probability to be cancelled, of the URLLC signal at the EN. Implementing SIC in a fully analog fashion is practically not trivial, and there is generally some residual URLLC interference. The effect of residual interference on the achievable eMBB rate is investigated in Figure 12 for \(q=0.3\), \(\alpha^{2}=0.4\), \(\gamma^{2}=0.5\), \(\mu=1\) and for different power of URLLC UE \(P_{U}\). Once again, in case of perfect interference cancellation, i.e., \(\rho=0\), SIC approaches the ideal fronthaul performance, while for more severe values of the residual interference power \(\rho\), the eMBB performance progressively decreases. Nevertheless, even in the worst-case SIC scenario, i.e., \(\rho=1\), the achievable rates are never worse than those achieved by TIN irrespective of the value of \(P_{U}\). This is once again due to the high reliability of URLLC transmission. It is in fact easy to prove that for \(\rho=1\) and low values of \(\epsilon_{U}^{D}\), the SIC eMBB rate in (42) converges to the one of TIN in (39). For completeness, Figure 13 shows the trade-off between eMBB and URLLC per-UE rates as a function of the access latency \(L_{U}\) for OMA and NOMA with puncturing, and considering \(q=10^{-3}\), \(\alpha^{2}=0.2\) and \(\gamma^{2}=0.5\). The behavior of the RoC-based C-RAN system versus the access latency \(L_{U}\) is similar to the one observed for digital capacity-constrained fronthaul [32] for both \(\mu=1\) and \(\mu=1/4\). While under OMA it is not possible to achieve a non-zero URLLC rate at even relatively low access latency such as \(L_{U}>3\), NOMA provides a reliable communication with constant minimal \(L_{U}=1\) access latency, but with lower rate. For eMBB, NOMA achieves an higher per-UE rate regardless of the value of the normalized bandwidth \(\mu\). Figure 11: URLLC and eMBB rates vs. probability of URLLC arrival \(q\) for OMA and NOMA by puncturing, treating interference as noise (TIN), and successive interference cancellation (SIC). Figure 12: eMBB rates for NOMA by SIC vs. power of residual URLLC interference \(\rho^{2}\).