Humans have been present on the high Tibetan plateau for at least 20,000 years and permanent villages have been there since 3200BC. Solid evidence of growing crops such as millet, barley and wheat is found from 1600BC onwards, which is remarkable as the plateau is between 2500m (8200feet) and 3400m (11,154 feet) in altitude. Even more remarkable is the fact that wheat and barley are crops more usually identified with western Asia rather than eastern Asia. Is this evidence of migration? (see http://physorg.com/print335713806.html).
If so, what was happening elsewhere around 1600BC. Well, we have that well known low growth tree ring event at 1628-5BC and we know people migrated into Mesopotamia at around this time (the Indic speaking Mitanni and the Kassites etc).