Book produced by participants to the European project: COST action IC0905 TERRA (2010-2014). Title: Cognitive radio policy and regulation - Techno-economic studies to facilitate dynamic spectrum access. Two contributions to chapter 3: Technical approaches for improved spectrum sharing. The aim of this chapter is to showcase several important contributions towards identification of techniques for spectrum sharing and coexistence. Contribution 1: potential of a multicarrier approach based on filter banks for cognitive radio and comparison with the existing OFDM technique. Contribution 2:intoduction of a new method to achieve efficiency and coexistence in a multi-user context with opportunistic access.