ts latency. As the fronthaul interface latency goes up, supporting the strict 8-process synchronous HARQ requirement becomes impossible. According to Ref. 2, two strategies can be deployed to mitigate this challenge. The first one is called HARQ process interleaving where an HARQ process is not reused until the corresponding Ack/Nack has been received, rather than assuming the Ack/Nack reception to have taken place at a predefined time. This comes at the cost of throughput (we are not able to use all the allocated time resources in this way). The second strategy is referred to as "predictive HARQ," for example, backing off the target modulation and coding scheme to ensure higher rate of successful decode at the Physical Layer, thus not needing HARQ retransmission. In this type of scheme, the RLC (AM) layer ensures reliability through retransmission. SINR Target, Measurement Report Power Control Algorithm Power Headroom Report FIGURE 2-22 Closed-loop power control in 3GPP. 66 Open Radio Access Network (O-RAN) Systems Architecture and Design Power control Receive side 3GPP systems, including 3G, 4G/LTE, and 5G/NR rely on closed-loop power control to aim for the received power from the multiple clients to the same at the base station. Keeping the received power (close to) the same for all clients allows the base station to decode the signals from multiple simultaneous transmissions such as are happening in an OFDMA waveform. For this purpose, the base station uses Transmit Power Control (TPC) commands (Fig. 2-22) to indi- cate to the client to increase or decrease transmit power, while the client reports back available headroom to the base station through power headroom reports. The power control algorithm is proprietary to the base station implementation, but target performance equations are included in 3GPP 38.213. Given that power control requires a round-trip (closed-loop) connection between base station and client, initial access cannot use this mechanism. For this purpose, initial access uses an open-loop powe