In the 5G New Radio standard, millimeter wave (mmWave) frequencies, in addition to sub-6 GHz frequencies, are utilized to enhance throughput. The use of mmWave frequencies provides unique opportunities for a drastic increase in data throughput while presenting new implementation challenges. This article explores architectural differences between sub-6 GHz and mmWave base station radios, with particular emphasis on the challenges and benefits of implementing DPD on these systems. While digital predistortion (DPD) is a wellestablished technique commonly used in sub-6 GHz wireless communication systems to improve the power efficacy, most mmWave radios do not use DPD. Using a prototype 256 element mmWave array, built with ADI beamformers and transceivers, we are able to demonstrate that DPD improves the effective isotropic radiated power (EIRP) by up to 3 dB. This allows for a 30% reduction in the number of array elements, relative to an array without DPD, for the same target EIRP.
The purpose of this article is to draw a comparison between a traditional sub-6 GHz macrocellular and a mmWave base station radio and antenna design. It further covers how these design differences impact DPD implementation in mmWave arrays relative to sub-6 GHz radios.
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