This paper presents a study on the benefit of observing several signals of opportunity for positioning purposes. Several static emitters are placed over a defined area where an user is moving and acquiring measurements to each of these emitters. The simulation considers that the user is capable of acquiring time of arrival measurements from several wireless protocols, such as WCDMA, 802.11b, 802.11g and 802.11ac. The variance in the measurements is modelled through the Crámer-Rao bound and a propagation model for each technology. As conclusions, this paper discusses the benefits of using multiple signals of opportunity in the context of positioning and how much the positioning performance is affected by considering different measurements combinations from several wireless technologies.