tates in HSPA and in LTE networks are illustrated in Figure 16.7. Optimizing the usage of RRC states is critical for the smartphone performance in terms of network resource consumption and terminal power consumption. 16.3 Smartphone Power Consumption Optimization Device's battery life is one of the main concerns of the active smartphone users. Since the battery technology is improving only slowly compared to the developments in the digital processing and RF integration, there is a clear need to minimize the terminal power con- sumption. The following sections present the terminal power consumption measurements and optimization solutions. 16.3.1 Impact of Downlink Carrier Aggregation Downlink CA is one of the key features of LTE-Advanced, aimed to increase the peak throughput and improve the efficiency of radio resource management by allowing one UE to be scheduled on up to five LTE carriers simultaneously. The exact combinations of intra- and inter-band CA allowed are explicitly defined in 3GPP specifications according to the requests from different operators and the spectrum organization in different areas of the world. The simplest form of CA consists in pairing two co-located cells serving the same geo- graphical sector, although more complex configurations are possible where more than two carriers of up to 20 MHz could be combined. The cell pairing can optionally be bi-directional, meaning that the same cell can play a role of the Primary (PCell) and Secondary Cell (SCell) at the same time, or unidirectional, where only one of the cells is allowed to behave as PCell and the other as SCell. Both cells can in any case be used as regular LTE carriers for UEs Smartphone Optimization CA UE Non-CA UE PCell SCell Figure 16.8 Carrier aggregation (CA) principle which do not support CA, and mobility between them is controlled by same cell reselection and handover settings as in case of unpaired cells. Figure 16.8 illustrates the CA concept. When additional carriers (SCells) are configured via RRC signalling, the UE may