The upcoming IEEE 802.11ax standard is intended to enhance wireless connectivity, offering more consistent and reliable high-throughput Wi-Fi in crowded user environments. Such environments include places like busy airports and stadiums. The power amplifier (PA) is a critical component in a Wi-Fi transmitter, because its performance affects wireless coverage area, data-rate capacity, and battery life. Achieving the desired PA performance becomes even more challenging in IEEE 802.11ax applications for a number of reasons—all of which are discussed in LitePoint’s application note, “Testing Power Amplifiers for 802.11ax.”
IEEE 802.11ax is expected to improve spectral efficiency in real-world environments, leveraging a number of technologies from cellular 4G LTE. Unlike the IEEE 802.11ac standard, which only operates in the 5-GHz frequency band, IEEE 802.11ax is intended to operate in both 2.4- and 5-GHz bands. IEEE 802.11ax also utilizes orthogonal-frequency-division multiple-access (OFDMA) technology. Another key aspect is the utilization of 1024-quadrature amplitude modulation (1024-QAM).
Some of the challenges associated with IEEE 802.11ax PAs surround error-vector-magnitude (EVM) requirements, which will be more stringent than those put forth by IEEE 802.11ac. The aforementioned OFDMA technology also impacts PA transmit performance and PA test requirements. Yet another challenge surrounding IEEE 802.11ax PA testing concerns dc voltage supply errors.
Digital pre-distortion (DPD) is an important feature likely to be deployed with next-generation IEEE 802.11ax chipsets. PA performance must therefore be validated when DPD is implemented. As a result, the PA linearization that can be achieved with DPD is able to be quantified. Furthermore, OFDMA technology adds other variables that must be considered.
The application note concludes with a description of an IEEE 802.11ax test setup, explaining that all test system errors must be minimized. In essence, the entire integrated test system must be optimized to imitate real-world operating conditions. The test setup shown includes a number of LitePoint’s instruments, including the z8653 vector signal analyzer (VSA), the z8751 vector signal generator (VSG), and the z5211 arbitrary waveform generator (AWG).
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