Highly accurate indoor positioning is still a hard problem due to interference caused by multipath propagation and the resulting high complexity of the infrastructure. We focus on the possibility of exploiting information contained in specular multipath components (SMCs) to increase the positioning accuracy of the system and to reduce the required infrastructure, using a-priori information in form of a floor plan. The system utilizes a single anchor equipped with array antennas and wideband signals to allow separating the SMCs. We derive a closed form of the Cramér-Rao lower bound for array-based multipath-assisted positioning and examine the beneficial effect of spatial aliasing of antenna arrays on the achievable angular resolution and as a direct consequence onto the positioning accuracy. It is shown that ambiguities that arise due to the aliasing can be resolved by exploiting the information contained in SMCs. The theoretic results are validated by simulations.