When will Microsoft Compete in Mobile Gaming?

With Nintendo having already been competing in the mobile game market for years, they have had a lot of competition. The PSP came along, and has become rivaal to the DS. Recently, the Nintendo 3DS was released, and was a pretty big deal. Next, in late February, the PSVita will be released. This will not have 3D capabilities, but as always, people will compare it to  Nintendo's DS. The following question has been lurking upon us for years; when will Microsoft jump into the mobile gaming market? Sony and Microsoft have been competing with the Xbox and PlayStation, but Microsoft has not showed many signs of a "Xbox Portable", or whatever they want to name their product. So, when will they compete with Nintendo and Sony? My prediction is an announcement in early 2013. Though they might already have something ready to announce at E3 2012, or another big gaming convention.