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The deployment of the 3G network infrastructure was accelerated in 2008, especially in the U.S. and Europe, to reach a maximum number of subscribers. Several carriers offered relatively inexpensive unlimited data plans with tethering capability and increased the number of net-based applications like video conferencing, Voice over Internet Protocol (VoIP), easy e-mail, and Internet browsing to capture the interest of their subscribers.

The requirement for more battery power has scaled up in proportion to the handset usage profile with greater needs for application time, but no concession on the talk time. Several 3G phones were released with modest usage times ranging from two to three-and-a-half hours without really convincing end users that they would see those totals. The real talk or connection time depended on how good the connection to the basestation was as well as on how intense the data content was during the connection.

Based on the operating RF power level, the PAE for a two-mode W-CDMA RFPA can vary.

From a hardware point of view, the handset designers managed to optimize the power consumption of the RF transmitters, especially the RF power amplifier (RFPA), when operating at low-power mode and servicing voice calls in urban areas. Statistics provided by carriers show that a handset in this situation transmits less than 1 mW.

Most of the RFPAs in use today have a low-power mode that consumes 10 mA or even less when the RF power goes below 1 mW. They are also optimized to achieve the best power added efficiency (PAE) (~33%) at about 500 mW, which is the maximum operating RF power level. PAE is a measure of the efficiency of a power amplifier that considers the RF drive power plus the normal dc power input in ratio to the power output.

A voltage-controlled dc-dc converter can dynamically adjust the RFPA supply voltage to continuously achieve the highest possible power efficiency for each RF power level

The concern at this point is that the RFPA wastes about 1 W and causes excessive heat, which reduces the performance of the surrounding components. Figure 1 shows typical variations of the PAE and power consumption versus the operating RF power level. Indeed, according to the power distribution statistics provided by 3G network carriers, a voice-centric phone operates 90% to 95% of the time below 1 mW in urban zones, which should enable up to five hours of talk time in these conditions.

But for connections with higher data content and for users located in suburban zones or in low-coverage areas, a 3G handset has to increase the transmitted power level beyond 50 mW to achieve a good signal-over-noise ratio. In such conditions, an RFPA without re-optimization would drain the battery energy in less than two-and-a-half hours.