ons even if there is no data to be sent LTE Small Cell Optimization Power consumption Active transmission Average over 185 S 10 MHz no CA 20 MHz no CA 10 + 10 MHz CA Figure 16.9 UE current consumption during large file download CA configured, avg. 44.2 mA CA activated, avg. 48 mA CA OFF, avg. 26.8 mA Time (s) Figure 16.10 UE current consumption while RRC connected but without activity (DRX ON) Smartphone Optimization = UE monitors PDCCH = Short DRX cycle = DRX short cycle timer = Long DRX cycle Figure 16.11 DRX diagram or received. This continuous PDCCH monitoring requires relatively high current consumption which in the long term can have an impact on the battery life experienced by users. Energy savings are possible in RRC idle state, when UE remains in sleep mode and only wakes up periodically to check if there is any paging indication from the network. Power saving is possible also in connected mode. Connected mode discontinuous reception (cDRX) allows the UE to monitor the PDCCH periodically and enter sleep mode between the monitoring periods while still remaining in RRC-connected state. Thus cDRX reduces UE current consumption in RRC-connected state when no data is transmitted. DRX concept is illustrated in Figure 16.11. Every time that a packet is sent or received, the DRX inactivity timer is re-started, and the UE keeps monitoring the PDCCH until the timer expires. After this happens, the UE goes to DRX sleep mode for a time period defined by the DRX cycle. The UE comes back to DRX active mode periodically to monitor the PDCCH for few milliseconds, and in case there is no new data for the UE in that period the UE will go back to DRX sleep. This process continues until the RRC Inactivity timer expires and the UE switches to RRC Idle state. The DRX cycle pattern can be divided into two parts: the long DRX cycle, which can range from 20 ms to 2.5 seconds, and the optional short DRX cycle, which is usually defined between two and four times smaller than the long DRX cycle. Using a combination of short cycle a