GRAMMAR (EC FP7) is a project aiming to deliver IP for future Galileo mass market receivers. One of the outcomes of this project will be an advanced Galileo receiver prototype. In this paper we present the research for finding the optimal dual frequency option for a Galileo mass market receiver. We discuss the impact of multiple frequencies on baseband algorithms and the implementation issues of a dual-frequency baseband. From the analysis results, we draw the following conclusions: E1/E5a combination is the optimal dual-frequency solution for Galileo; a common dualfrequency baseband architecture with flexible channels seems to be the best implementation approach for a Galileo E1/E5a dual-frequency receiver.