I am submitting my journal article to IEEE Transactions on Vehicular Technology. This is a completely new work. However, initial results have been submitted to IEEE Globecom 2018 (the result will be announced on July 15th).
My question is, should I upload my conference paper to the journal submission?
IEEE (at least in Computer Science) has a 30% new materials rule to make a journal submission out of a conference proceedings. You seem to have no problem meeting this threshold. Reviewers will be asked to speak to the novelty of your submission and whether this mark is there. Therefore, it is customary to mention the conference paper in the cover letter to the editor and to include the conference proceedings. When reviewing for IEEE, I often to Google scholar searches, and I would likely come across your conference paper. If you include it, everyone's life is easier, so do it.
As @Buffy said, it is best to check with the journal. However, in the social sciences, the normal practice is to write up a conference paper and present it for discussion with your peers.
Based on the feedback you receive, you will often rework your paper and then submit it to a journal. Most journals have the stipulation that they will accept articles based on conference papers as long as there is (at least) 20% or 25% new content.
If you have no new content, that might be a problem because the journal is not publishing something "new."
