The avalanche in mobile data consumption represents a big challenge for mobile operators. The efficient use of radio resources, e.g. technology, infrastructure and spectrum, is needed to meet the new capacity requirement in the mobile networks. This thesis aims at quantifying the real-life spectrum opportunities for deploying a massive low-power indoor secondary system. Our studies have mainly focused in two frequency bands: the digital TV and the aeronautical band. Indoor secondary access to these bands presents different technical challenges: Limited adjacent channel rejection capabilities and no information about the location of the primary receivers are key challenges in the digital TV band. Instead for the aeronautical band, the control of the aggregate interference over a large area due to the high sensitivity levels and the extremely low permissible outage probability at the primary system are the key issues for secondary access. We have proposed a research methodology for determining the availability of spectrum opportunities in both frequency bands: digital TV and aeronautical band. Our methodology mainly emphasizes on establishing the realistic limits of tolerable interference at the primary, devising practical sharing schemes and determining the operational conditions and constraints for the secondary system. Based on our numerical results and measurement campaigns, we conclude that there is significant amount of spectrum opportunities for the deployment of massive low-power indoor secondary access in the digital TV and aeronautical band. The availability of spectrum opportunities highly depends on the sharing mechanisms, the primary protection criteria and the secondary system parameters. Future work should consider how the secondary users share the available spectrum in order to optimize the performance of secondary system in realistic scenarios. Another interesting investigation is the business viability assessment of secondary access in both frequency bands. / <p>QC 20121002</p>