  A Multiple Target, Multiple Type Filtering (MTMTF) algorithm is developed
using Random Finite Set (RFS) theory. First, we extend the standard Probability
Hypothesis Density (PHD) filter for multiple types of targets, each with
distinct detection properties, to develop a multiple target, multiple type
filtering, N-type PHD filter, where $N\geq2$, for handling confusions among
target types. In this approach, we assume that there will be confusions between
detections, i.e. clutter arises not just from background false positives, but
also from target confusions. Then, under the assumptions of Gaussianity and
linearity, we extend the Gaussian mixture (GM) implementation of the standard
PHD filter for the proposed N-type PHD filter termed the N-type GM-PHD filter.
Furthermore, we analyze the results from simulations to track sixteen targets
of four different types using a four-type (quad) GM-PHD filter as a typical
example and compare it with four independent GM-PHD filters using the Optimal
Subpattern Assignment (OSPA) metric. This shows the improved performance of our
strategy that accounts for target confusions by efficiently discriminating
them.
