"The Verge has now confirmed with sources familiar with Samsung's plans that March 14th is "definitely" the day that the Korean giant plans on revealing one or more new devices, one of which is presumed to be the Galaxy S IV. As SamMobile says, we are also hearing that the event will be in the US, though it's unclear whether carrier availability will be announced at that time." Quoted on the site.
Previous rumors said that internally-dubbed Project J family of products is comprised of three products, all of which could be unveiled at the same time, the Samsung Galaxy S4, the Samsung Galaxy S4 mini and maybe even a Galaxy Smartwatch.
Also, it looks like that early Samsung Galaxy Note 8 leak that we saw a few days ago could be just an early design, expect the tablet to look different when Samsung presents it to the world at MWC 2013 next week.
source: The Verge