wer Saving Features PSM timer Release 12 Power T3412 Saving Mode (PSM) = Transmission/reception UE reachable UE off during T3324 = Monitoring paging Figure 14.17 Power Saving Mode (PSM) in Release 12. tracking area updates (TAUs) periodically. After performing the TAU, the UE will then remain in idle mode and monitor paging for some time, specified by T3324, which allows the network to send data to the UE. If no transmission need be sent to the UE, the UE will go to sleep mode until the next TAU. The sleep time is the difference between the PSM timer T3412 and the idle mode timer T3324. During the sleep time, no data transmission from the network to the UE is possible. It is possible to set T3324 = 0 such that the UE enters PSM directly. The PSM solution is illustrated in Figure 14.17. In comparison with powering the UE completely OFF, the UE using PSM avoids the detach procedure, and it may potentially also store system information, which makes the connection reestablishment faster. Release 13 allows the use of the longer Discontinuous Reception (DRX) to minimize the device power consumption. The feature is called extended DRX (eDRX). The maxi- mum DRX cycle in Release 12 was 2.56 both in idle and in connected modes. The cycle was increased to 10.24 S in the connected mode and even 44-175 min in the idle mode. The benefit of the Release 13 eDRX solution is that the network can more frequently send data to the UE compared to PSM. It provides a lower application layer latency at the cost of higher energy consumption. The concept is described in Figure 14.18, and the maximum DRX cycle lengths are listed in Table 14.6. Network Access Stratum (NAS) and RRC states with PSM are shown in Figure 14.19. The UE remains RRC idle in the eDRX state, while it does not have any RRC state in PSM. Release 13 extended UE reachable = Transmission/reception = Monitoring paging Long DRX period Figure 14.18 Long DRX period in Release 13. Table 14.6 Maximum DRX cycle lengths. Release 8-12 DRX Release 13 eDRX Release 12 PSM Connected mo