 processors as shown in Figure 13.1. Consider as an example the reception of the PDCCH with flexible configurations. A PDCCH candidate is first blindly decoded at the hardware. The decoding result is passed to other modules for the cyclic redundancy check and parsing of the DCI to judge whether the decoding result is valid. If it is considered valid, the DCI is passed to the software to proceed to the next actions. However, due to flexible configuration, the software is generally not waiting for the result of the PDCCH decoding but rather is car- rying out some other tasks. In this case, the software will be interrupted to handle the PDCCH decoding result as well as the associated upcoming tasks and goes back to the original work after that. Complex system scheduling and data traffic management are essential to realize low device cost, small latency, and power saving. This causes software programming burden. In the following, two NR features that enable system flexibility are identified, as well as the challenges they pose to the design of the modem. 13.3.2.1 Flexible Slot Format Indication In NR, the link direction of an OFDM symbol in a slot can be classified as "downlink," "flexible," or "uplink." One of the key features of NR is the support for very flexible con- figurations for link directions. Four different signaling mechanisms can provide infor- mation to the UE on the link directions: (1) Semi-static higher-layer signaling of slot format indication: three possible states "downlink," "flexible," or "uplink" for the link direction (2) UE-specific RRC configuration from which a link direction "downlink" or "uplink" can be inferred: for instance, the link direction of an OFDM symbol can be assumed as "uplink" if a UE is configured to perform periodic Sounding Reference Signal (SRS) transmission at the symbol (3) Dynamic data scheduling signaling from which a link direction "downlink" or "uplink" can be inferred: for instance, the link direction of an OFDM symbol can be assumed as "downlink" if a UE is schedu