the receiver processes the received signal in order to obtain received bits in the end. Channel estimation is a part of the receiver which aims to estimate the channel coefficients H. This estimated channel is then exploited by the equalizer (where equalizer is referred to as the receiver method in the simulator since it is the main part of the linear receiver chain) that aims to mitigate the channel distortion of the received signal. In other words the equalizer tries to cancel the influence of H to the received signal Y. In the simplest case, the so called zero forcing equalizer, the received signal Y is divided by the channel coefficient H (that was estimated beforehand).
However, the problem if estimating the wireless channel coefficients from the received signal, which is known as channel estimation, and the problem of reconstructing the transmitted signal x from the received signal, which is known as detection problem, are very basic problems of communication theory.