Power amplifier linearity is relevant in the design of communication systems. High peak-to-average ratios (“PARs”) tend to exist in wideband communication systems. A PAR may be considered a function of a transmission waveform, such as for example an orthogonal frequency division multiplexing (“OFDM”) waveform for a 3GPP Long-Term Evolution (“LTE”) system or a wideband code division multiple access (“W-CDMA”) waveform for a Universal Mobile Telecommunications System (“UMTS”) system. Because such waveforms have high PARs, power amplifiers with high degrees of linearity may be used to reduce spectral artifacts in the output of such power amplifiers, namely in transmission waveforms. Unfortunately, conventionally a power amplifier with a high degree of linearity also comes with a high cost. Further, unfortunately, conventionally a low cost power amplifier has a low degree of linearity. One approach to power amplifier linearization for operating in an efficient input-to-output operating range of a power amplifier involves use of digital pre-distortion.
Digital predistortion or digital pre-distortion is used to linearize a nonlinear response of a power amplifier over a power range of such power amplifier. More particularly, a baseband signal may be distorted before amplification by a power amplifier. A type of digital predistorter may be one that employs a conventional memory polynomial. Such conventional memory polynomial configured digital predistorter may be used for power amplification in a variety of applications, including without limitation an amplification of power for a wireless signal (e.g., for a wideband wireless communication system as indicated above), an amplification of power for a land-line signal (e.g., a backhaul link between a cellular base station and a gateway to an Internet Protocol network), and an amplification of power a signal for a satellite link. However, a conventional memory polynomial configured digital predistorter may involve a time-consuming heuristic selection process for selection of nonlinearity order (“K”), and memory length (“Q”).
With respect to selection of K and Q for digital predistortion to condition a signal subsequently provided to a power amplifier, selecting K and Q too large may significantly increase compute complexity, and thus power consumption, without a sufficient return in power amplifier performance, while selecting K and Q too small may underutilize power amplifier performance. Heretofore, a power amplifier was generally heuristically characterized in a laboratory by iteratively feeding such power amplifier signals to determine K and Q. However, this process for power amplifier characterization does not lend itself to determining K and Q in the field, namely apart from such a laboratory setting. Furthermore, setting a digital predistorter heretofore involved prior knowledge of a power amplifier to which such digital predistorter was to be coupled.
Accordingly, it would be desirable and useful to be able to select K and/or Q in the field.