The emerging trend to provide users with ubiquitous seamless wireless access leads to the development of multi-mode terminals able to smartly switch between heterogeneous wireless networks. This switching process known as vertical handover requires the terminal to first measure various network metrics relevant to decide whether to trigger a vertical handover (VHO) or not. This paper focuses on current and next generation networks that rely on an OFDM physical layer with either a CSMA/CA or an OFDMA multiple-access technique. A synthesis of several signal feature estimators is presented in an unify way in order to propose a set of complementary metrics (SNR, Channel occupancy rate, collision rate) relevant as inputs of vertical handover decision algorithms. All the proposed estimators are ``non-data aided'' and only rely on a physical layer processing so that they do not require multi-mode terminals to be first connected to the handover candidate networks. Results based on a detailed performance study are presented to demonstrate the efficiency of the proposed algorithms. In addition, some experimental results have been performed on a RF platform to validate one of the proposed approach on real signals.