The Expectation-Maximization (EM) algorithm is studied to perform channel estimation in a low cost and high data rate impulse radio UWB receiver. The system under consideration uses a pulse position modulation with a simple analog energy detector. In order to overcome the problems inherent to high data rates, such as inter-symbol interferences, a probabilistic equalizer is used. The EM algorithm and the equalizer are embedded into the loop of an iterative channel decoder. This permits to refine both the channel parameters and the signal probability at each iteration. We present numerical results performed on the channel models from the IEEE 802.15.3a task group. These results show that the EM algorithm contributes to achieve data rate greater than 100Mb/s with a simple impulse radio UWB receiver.