n (Li-Ion) batteries been constant over this time span, the need for doubling battery capacity would have led to doubling weight. This would translate into a severe penalty in the smartphone weight budget. In reality, battery energy efficiency keeps on improving at a rate of approximately 5-7% every year [9]. For example, LTE Small Cell Optimization Average power consumption = 1.7 W Time (s) Average power consumption = 0.7 W Time (s) Figure 16.38 UE power consumption in flight mode. (a) animated wallpaper; (b) static picture in 2014, an advanced 2100 mA-h battery weighs 35 g. This represents an energy density of approximately 230 Wh/Kg. The same battery built with the average 190 Wh/Kg density of the 2009-2010 timeframe would have weighed 42 g. Alternatively, a 2009 35 g battery pack would have delivered a capacity of 1750 mA-h. These examples are only a simplistic summary of improvements in Li-Ion batteries because energy density does not depend purely on weight/volume of the cell, but also on its thickness [9]. These slow improvements explains why device manufacturers have had no other choice but to increase battery weight and/or volume and to put a lot of pressure on chipset vendors to always deliver more power-efficient cellular subsystems. At the other end of the food chain, advanced 3GPP features give tele- com operators plenty of tools which can further reduce smartphone power consumption. For example, activating discontinuous reception (DRX) and transmission (DTX) is one option. Deploying small cells is another. Smartphone Optimization Section 16.8.2 presents the efforts accomplished in successive generations of LTE chipsets to improve power efficiency. The benefits of small cell deployments are presented in Sec- tion 16.8.3. 16.8.2 Trends in Cellular Chipset Power Consumption Assessing the contribution of an entire smartphone, whether it be in idle or in 'active/busy' states, is a rather complex task. When idle, numerous OS-related and application 'keep-alive' specific tasks wake up several hardware bloc