ll PDCCH blind decoding candidates in carrier aggregation, higher modem processing capability is required for shorter service latency, compared to 4G LTE. Figure 13.19 shows the timeline for a modem to complete secondary carrier activa- tion in carrier aggregation. The time for cell search, AGC tuning, and synchronization 13 5G Modem Design Challenges SCell Activation MAC CE HARQ ACK Slot, Slot, Slot n+i 'n+i+1 MAC CE decoding MAC CE parsing Cell search CSI measurement and RF preparation AGC tuning reporting Modem Synchronization actions Note: Duration function of the periodicity of SS/PBCH block Figure 13.19 Secondary carrier activation timeline for 15 kHz subcarrier spacing. account for the largest portion of the secondary carrier activation time. Due to sparse common pilots (e.g. SS/PBCH block) in 5G NR, it takes a longer time for a modem to get ready for signal reception, compared to 4G LTE. For example, it takes around 30 ms for a modem to activate the secondary carrier if the periodicity of the SS/PBCH block is 20 ms. Unless the modem performs CSI measurement periodically over a secondary carrier before receiving the secondary carrier activation command, it is very difficult for it to further reduce the secondary carrier activation time. However, it consumes more modem power in this way. 13.6 Summary Compared to 4G LTE, 5G NR offers much lower latency, greater reliability, higher data rates operating in a wider bandwidth, and above all, an unprecedented level of flexi- bility in mobile communication systems. As a result, 5G modem designers are facing mounting challenges in keeping computational and control complexity under control, optimizing the modem architecture to save costs, and lowering the power consumption and mitigating overheating to improve the user experience. This chapter provides a systematic analysis of the interconnection between the NR advancements and their impacts on modem design for mobile devices. One aspect that is examined is the new NR features and their requirements that raise the m