## 3 Transmitter and Receiver Structure
### System-Level Simulations
Scenario UMi also has strong inter-interference between sites, and there is additional outdoor-to-indoor propagation loss for users that are inside the buildings. The throughput performance of 64 QAM packets is lower than that of 4 QAM packets in all scenarios. The explanation for this is the same given for the InD scenario. Scenario UMa also has strong inter-interference between sites, and due to the highest ISD, users at the cell borders suffer the smallest SINR. It also has additional outdoor-to-indoor propagation loss for users that are inside the buildings. As a consequence, the throughput performance ofIn Figure 7, the RAN cluster size is 3, so the network is partitioned into three adjacent site sets and each user is served at the same time by three sites (generating much less inter-interference). The same maximum \(N_{u}=50\) from the previous scenario is also considered. From the comparison between Figures 6 and 7, it is clear that there is an improved throughput for clusters of three sites, due to much lower inter-interference between sites, especially for 64 QAM in all scenarios. InD continues to offer the highest throughput due to its smaller size and double transmitted bit rate when compared to the other scenarios. The average throughput gain due to cluster size 3 for UMi is 4.6 for 64 QAM and 2.0 for 4 QAM. The gain for UMa is 3.9 for 64 QAM and 2.7 for 4 QAM. The gain for InD is 2.6 for 64 QAM and 1.6 for 4 QAM. For 4 QAM (5.75 bpcu), the increase in throughput between 3C and 1C is less obvious due to its lower SE allowing higher cell coverage. For 50 users in UMi with 3C, the total throughput of 64 QAM is 2.760 Gbps, which corresponds to a sector SE of 138 bps/Hz that is equivalent to almost 2.8 bps/Hz per user. For 50 users in InD, the total throughput of 64 QAM is 3.875 Gbps, which corresponds to a sector SE of 77.5 bps/Hz that is equivalent to 1.55 bps/Hz per user. This is in agreement with higher frequency bands (28 GHz) which imply higher bandwidths (50 MHz) but lower SE, while lower frequency bands (3.5 GHz) result in lower bandwidths (20 MHz) but higher SE. Figure 6: Throughput vs. number of users for different scenarios with \(N_{tx}=5N_{u}\), \(N_{f}=4\), \(N_{df}=3\), \(N_{s}=5\), \(N_{a}=2\), \(N_{rx}=5\), 64-QAM (11.75 bpcu per user) and 4 QAM (5.75 bpcu per user), C-RAN cluster size 1. Figure 8 presents the cumulative distribution function (CDF) of each user served by one TRP of the UMa scenario, based on the throughput results presented in Figures 6 and 7. This CDF statistic is based on the throughput per user achieved as a function of the distance between terminals and serving TRPs. Each TRP has \(N_{tx}\) = 250 active antennas serving 50 users each with \(N_{rx}\) = 5 antennas. We consider the C-RAN UMa scenario with two different cluster sizes, namely a cluster of size 1 (1C) and a cluster of size 3 (3C). As expected, only for 3C there is a percentage of users that achieve the maximum throughput. With 3C, not only users that are close to the TRPs are able to get the maximum throughput. About 20% of users for 64 QAM and 50% of users for 4 QAM are in this situation of achieving maximum throughput. For 4 QAM with 1C, only users that are located quite close to the TRP antenna (less than 1%) are able to get maximum throughput. For 64 QAM with 1C, no user is able to get the maximum throughput due to high inter-interference. For 4 QAM with 1C, only users that are located quite close to the TRP antenna (less than 1%) are able to get maximum throughput. For 64 QAM with 1C, no user is able to get the maximum throughput due to high inter-interference. So, for 64 QAM, most of the packets are not received correctly, while for 4 QAM, many of the packets are correctly received. Figure 9 presents the CDF of a TRP for the UMa scenario serving 20 users, during the simulation run with a duration of 100 s. These statistics are based on the throughput performance of each one of all users measured at each TTI = 0.5 ms during the simulation run.