  Channel estimation is challenging in multi-antenna communication systems,
because of the large number of parameters to estimate. One way of facilitating
this task is to use a physical model describing the multiple paths constituting
the channel, in the hope of reducing the number of unknowns in the problem. The
achievable performance of estimation using this kind of physical model is
studied theoretically. It is found that adjusting the number of estimated paths
leads to a bias-variance tradeoff which is characterized. Moreover, computing
the Fisher information matrix of the model allows to identify orthogonal
parameters, ultimately leading to fast and asymptotically optimal algorithms as
a byproduct.
