ental Uplink (SUL) transmission. In that case, a device transmits on the SUL frequency, which is at a lower carrier frequency than the normal UL frequency, or the normal frequency depending on dynamic signaling from the network. The PUSCH transmission charac- teristics over SUL and UL can be very different, for example, subcarrier spacing, and hence different baseband and RF processing are needed for SUL and UL. 13.3 Low Latency, Flexible Timing, and Modem Control Flow Complexity This section addresses the UE modem design challenges for supporting low latency and high system flexibility. Low latency is an important design characteristic of 5G NR, 13.3 Low Latency, Flexible Timing, and Modem Control Flow Complexity reflected not only in the intrinsic details of its radio interface but also in the entities processing the related radio signals. The processing time requirements on the device side have been considerably tightened compared to LTE. In addition, with the goal of addressing the diverse requirements of a plethora of services, 5G NR features a very high degree of flexibility. By means of flexible configurations, the network can adapt its many parameters to meet the required capabilities of any particular service of various use cases and usage scenarios. High flexibility coupled with low latency pose various challenges for modem processing. In Section 13.3.1, the impacts of 5G NR low latency on the modem processing capability are investigated. That is, the physical layer techniques used to produce low latency, including shorter slot duration, mini-slot transmission, multiple PDCCH monitoring occasions per slot, and SO on, are addressed in terms of the challenges they pose to the modem. For each technique, four main aspects are discussed (when applicable): Identifying the new NR features and requirements for low latency that increase modem design complexity The modem design challenges to support these features The methods introduced in 3GPP specifications to mitigate the impact on the modem What can be expect