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.
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