The structure and the evolution of essential patents for standards: Lessons from three IT standards

This paper examines the structure and the evolution of the patents declared as essential for three major technical standards in information technology (MPEG2, DVD and W-CDMA). These standards have many essential patents, which are owned by many firms with different interests. Many patents have been applied even after the standard was set. We analyze three important reasons for why the essential patents are many and increase over time: they cover a number of different technology fields, there exist R&D competition even in a narrowly defined technology field and a firm can expand its patent portfolio by using continuations and other practices based on the priority dates of its earlier filed patent applications in the USA. Around 40% of the essential US patents for MPEG2 and DVD standards have been obtained by using these applications. However, our empirical analysis suggests that a firm with pioneering patents does not obtain more essential patents, using these practices.