dB NF and 20 MHz bandwidth, we have a signal level of -90dB and a Noise level of 174 + 73-2 = 103dB or an SNR of 13 dB which should be enough to sustain QPSK operation or better. This 13 dB (with margins added, see below) also defines the required ADC performance. 130 Open Radio Access Network (O-RAN) Systems Architecture and Design Radio unit latency and delay Refer to the figure below from CUS fronthaul specifications for key reference points associ- ated with timing and delay management between DU ( = Low Level Split Central Unit or lls-CU in the O-RAN fronthaul specification) and RU (Fig. 3-17): Key latencies are Tiamin/Tiamax-latency range from DU egress port to Antenna. This defines the "window" for transmission of downlink radio frames from by the DU. T2a.min/T2a.max-latency range from reception at the RU ingress port to Antenna or RU Processing Latency including the "window" for reception of downlink radio frames from by the RU. Ta4,min/Ta4,max-latency range from Antenna to DU ingress port. Ta3.min/Ta3.max-latency range from Antenna to RU egress port. Or summarized as shown in Fig. 3-18 - below. In this figure, the DU Processing Latency represents the time spent in the Physical Layer of the DU, from MAC layer Transport Block generation to eCPRI I/Q sample generation. During the DU Transmit Window, the I/Q samples are transferred from the DU to Ethernet using eCPRI encapsulation. The RU Receive Window defines a buffer time that compensates for any jitter in the fronthaul interface. Remainder time is spent in the RU Processing stage which are the low-PHY and DFE components which are typically highly deterministic. Ils-CU FIGURE 3-17 Fronthaul and radio unit latencies per O-RAN specifications. gNB Transmit Processing Delay (summed) DU Processing DU Tx Latency Window RU Rx RU Processing Window Latency Front Haul Latency FIGURE 3-18 Transmit fronthaul and radio unit internal latencies. Chapter 3 Hardware system dimensioning 131 Analog latency is defined as the time it takes for the analog signal to transfer fr