## 3 Transmitter and Receiver Structure
### System-Level Simulations  
Using the PT-GSFIM link-level results, in this subsection we describe several system-level simulations that were performed for a C-RAN incorporating PT-GSFIM, considering different scenarios and 5G NR numerologies. The signal-to-noise ratio (SNR) in dB considered in the system-level simulations is obtained from \(SNR=(E_{s}/N_{0})+10\log(Rs/B)\) dB, where \(Rs\) is the total transmitted symbol rate per antenna and user, \(B\) is the total bandwidth (we considered 20 MHz at 3.5 GHz and 50 MHz at 28 GHz) and \(E_{s}/N_{0}\) is the ratio of symbol energy to noise spectral density in dB. Values of \(E_{s}/N_{0}\) are obtained from the link-level BLER results. 5G NR frame structure has both frequency division duplex (FDD), used in the paired spectrum, and time division duplex (TDD), used for the unpaired spectrum. We chose TDD in this work and 5G NR numerology 1 for UMi and UMa scenarios at 3.5 GHz and numerology 2 for InD scenario at 28 GHz [44]. For UMi and UMa scenarios, \(B=20\) MHz with normal CP, where the subcarrier spacing is 30 kHz and 28 OFDM symbols are transmitted in every subframe of 1 ms. For InD scenario, \(B=50\) MHz, the subcarrier spacing is 60 kHz and 28 OFDM symbols are transmitted in every subframe of 0.5 ms. Other simulator parameters are as follows: maximum TRP transmit power of 49 dBm for UMa, 44 dBm for UMi and 30 dBm for InD, receiver spectral noise power density \(-174\) dBm/Hz, CP overhead 5%, pilots/TRP = 50 and uniform linear arrays with uni-polarized antennas. Each user feedbacks all CSI and signal-to-interference-plus-noise ratio (SINR) to TRPs during uplink time slots. Equal duration of downlink and uplink time slots is assumed. Users are placed uniformly around TRPs and random waypoint mobility around TRPs is employed. We must consider that the full buffer is used. The static clustering technique partitions the network into three adjacent TRP sets where each user is served by at least one TRP, while the others perform inter-user interference. When C-RAN cluster size is one it means that there is no C-RAN BS clustering; this is the traditional cellular system. The UMi street canyon scenario is a high-density urban one where 80% of users are inside buildings and 20% of users are in the streets (such as UMa). However, the intersite distance is 200 m, which allows decreasing the total transmitted power from 49 dBm (UMa) to 44 dBm. Scenarios UMa and UMi street canyon can be directly compared because they both use numerology 1 and the same carrier frequency (3.5 GHz) and bandwidth \(B=20\) MHz. However, the scenario InD cannot be directly compared with the others because it uses numerology 2 with double the transmitted symbols per 1 ms, having a different bandwidth, \(B=50\) MHz, and a carrier frequency of 28 GHz. Based on the parameters of Figure 6, and noting that we considered \(N_{u}=50,5\) transmit antennas per user \(N_{tx}=5N_{u}\) and \(N_{rx}=5\) receive antennas per user, there are a total of 250 active antennas at each sector (one TRP per sector). 64 QAM requires a higher SNR compared to 4 QAM. InD is expected to offer the highest throughput due to its smaller size. This occurs independently of the modulation. UMi scenario assures the next best throughput performance, whereas UMa is the scenario with the lowest throughput. It is observed that the highest throughput performance is for InD with 4 QAM-modulated packets. This is due to the InD scenario having twice the bit rate compared to the other scenarios. Moreover, InD has strong inter-interference and high propagation losses; however, most of the 4 QAM packets are received correctly due to its required SINR being small. By contrast, most of the 64 QAM packets are received with error because of its required SINR being high, resulting in lower average throughput. In other words, 64 QAM packets are only correctly received close to the BS, while 4 QAM packets are correctly received almost everywhere.