What is the origin of paleolithic people in Portugal?

The original tribe that we now call the proto-Indo-Europeans came from somewhere in the region in which modern Georgia and Anatolia lie, roughly 4000BCE. It split into two branches.

One branch, called the Western or "Kentum" branch (so called because their languages retained the original K in the word kmtom for "hundred," as in Latin centum and Greek hekaton) migrated northward into the vague boundary between Europe and Asia. Then they fragmented into a succession of migrations westward into Europe. The Celts were the first to enter Europe. With the more advanced agricultural and other technologies they had picked up by living on the fringe of Mesopotamian civilization, they easily became dominant over the people who already lived there, including the Lusitanians and other tribes in Iberia. They assimilated them more-or-less peacefully by intermarriage, but their superior numbers resulted in their descendants' DNA being primarily of Indo-European stock. By 1500BCE the Celts reigned over all of sub-Scandinavian Europe, including the British Isles, with only a few pockets of the earlier ethnic groups surviving as communities, such as the Basques, Etruscans and (perhaps) Picts.

The migration of the Germanic Western Indo-European tribes took place later, perhaps 2000BCE (you can find more precise dates with a little research), but they went north and populated Scandinavia. It would be more than a thousand years before they came down through Denmark and began spreading across the main part of the continent. By this time the Hellenic Western Indo-European tribes had migrated into what is now Greece and nearby regions. By using what they remembered of Mesopotamian technology plus what they picked up in their trading with the seagoing Phoenicians, they established the first offshoot of Mesopotamian civilization in Europe, which spread into Italy, the Balkans, Asia Minor, and eventually much further. A few centuries later the Romans became prominent, another Western Indo-European tribe; we're not sure of their chronology, they might have somehow sauntered in under the noses of the Celtic, Germanic and Greek tribes, or some linguists suggest that they were cousins of the Celts who had been there for a long time, since Latin looks a little like a distant member of the Celtic language group. In any case, the Roman Empire spread out across southern Europe rather swiftly, displacing the Celtic and pre-Indo-European tribes in Iberia, Italy, France and elsewhere. Based on their DNA, the modern Spanish and Portuguese people are primarily the descendants of Romans, with a large sub- and superstratum of Moorish, Celtic, and pre-Indo-European.

The Germanic tribes did the same thing in northern Europe, to the point that the only remaining communities of identifiably Celtic people with Celtic languages are at the very fringe of Europe: Ireland, Scotland, Cornwall, Wales, the Isle of Man, and Brittany (and the Bretons are refugees from the Anglo-Saxon occupation of Celtic Britannia).

But to get back to your original question, the Indo-European migrants to Europe did not come from India; as I noted, they came from somewhere around Anatolia. It was the Eastern branch of the Indo-European tribes who went to India (and elsewhere) while the Western tribes were going to Europe. We call them the Satem branch because the K in proto-Indo-European kmtom became S in all of their languages. Various tribes from this branch settled in India, Persia, Armenia, and some of them went north and became the Baltic and Slavic peoples. (E.g., Russian sto and Sanskrit satem for "hundred.")

The Portuguese are related to the Indo-Iranian peoples, but they are not descended from them. They share the same ancestors.

We call this entire ethnic group the "Indo-Europeans" because they have covered a huge swath of Eurasia from India to Europe. Of course subsequent to their assuming dominance over those regions, other unrelated peoples have moved in. The Turks and their cousins in the remnants of the Ottoman Empire from Turkmenistan through Uzbekistan to Xinjiang are descendants of the Mongols or "Mughals." The Hungarians, Finns, Sami ("Lapps") and Bulgarians are descendants of Eastern tribes, possbily cousins of the Mongols. Many of the people in eastern India are of Dravidian origin. The Semitic Arabs have taken over much of the old Persian Empire and the Semitic Jewish people have communities throughout the Indo-European lands.