question: What is the generic definition of the MIMO detection problem? option 1: The estimation of the input vector based on the received signal vector and the channel matrix. option 2: The estimation of the received signal vector based on the input vector and the channel matrix. option 3: The estimation of the channel matrix based on the received signal vector and the input vector. option 4: The estimation of the channel matrix based on the input vector and the received signal vector. 