Positioning in wireless networks has recently concentrated the interest of the research community. Outdoor positioning has been addressed successfully, but location indoors poses some open issues. Time-based ranging techniques, such as 2-way time-of-arrival (TOA), are promising for indoor positioning but present issues such as scalability and landmark dependency. Handling these problems separately makes it difficult to find solutions that can be implemented over communication networks on which positioning solutions rely. The passive TDOA algorithm was proposed for overcoming both issues together. Preliminary results indicate that scalability can be improved. This work assesses the performance of the passive TDOA in scenarios where there are not enough landmarks to run a regular 2-way TOA algorithm. Results show that the accuracy provided is worse than in scenarios with enough landmarks but, depending on the power of the ranging noise, good enough for most of the location-based services indoors.