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Throughout
the history of wireless communications, researchers have found ways to pack
more information into wireless communications channels. The evolution of mobile
technology, from AMPS (1G) to LTE Advanced (4G), has introduced a myriad of
multichannel, multicarrier, and multiple-access schemes to more efficiently use
spectrum.

In
the early 2000s, new mobile standards such as UMTS and CDMA2000 were designed
to use spread-spectrum technology to achieve improved spectral efficiency. At
the same time, IEEE 802.11 was pioneering the use of orthogonal frequency
division multiplexing (OFDM) technology to better take advantage of wideband
channels through the use of orthogonal subcarriers. In 2011, the deployment of
LTE introduced OFDM technology into mobile applications with the uplink using a
variant of OFDM known as single-carrier frequency division multiple access
(SC-FDMA).

Although
each evolution of wireless communications allows for higher data throughput,
the resulting waveform complexity places stringent requirements on the physical
radio. Not only do modern wireless radios use significantly wider bandwidths
(up to 160 MHz for 802.11ac), but also signal characteristics such as the peak
to average power ratio (PAPR) drive difficult linearity and efficiency
requirements on RF power amplifiers.

To address these linearity and efficiency
requirements, system designers frequently use linearization techniques such as
digital pre-distortion (DPD) to improve linearity and use dynamic power supply
(DPS) techniques such as envelope tracking (ET) or direct polar (DP) modulation
to improve efficiency. The use of these techniques tasks engineers with new
test methods and requirements. Today, key power amplifier (PA) metrics such as
power added efficiency (PAE) or LTE adjacent channel leakage ratio (ACLR) must
be measured under DPD or DPS conditions. This document examines test practices
for several advanced PA test techniques including DPD and DPS.