  When we have knowledge of the positions of nearby walls and buildings,
estimating the source location becomes a very efficient way of characterizing
and estimating a radio channel. We consider localization performance with and
without this knowledge. We treat the multipath channel as a set of "virtual
receivers" whose positions can be pre-stored in a channel database. Using wall
knowledge, we develop a generalized MUSIC algorithm that treats the wall
reflection parameter as a nuisance variable. We compare this to a classic MVDR
direct positioning algorithm that lacks wall knowledge. In a simple scenario,
we find that lack of wall knowledge can increase location error by 7-100x,
depending on the number of antennas, SNR, and true reflection parameter.
Interestingly, as the number of antennas increases, the value of wall knowledge
decreases.
