Is there a producer quality wage premium similar to the exporter wage premium

Exporter wage premium has been widely studied in the literature on international trade. The aim of this paper is analyze whether there is also a producer quality wage premium at firm level, and if so, analyze whether its origin is similar to the exporter wage premium. In other words, I test whether firms that increase their product quality become more productive and pay higher wages (as with the learning by exporting hypothesis, we can speak of learning by producing quality), or, in contrast, more-productive firms with higher wages opt to increase product quality because their higher productivity means these kinds of decisions and investments can be taken with more guarantees (self-selection hypothesis).