We investigate the detector design in generalized space shift keying (GSSK) modulation for large MIMO systems. An orthogonal matching pursuit (OMP) based detector design is adopted due to its low complexity compared with the maximum likelihood (ML) detector. To improve the performance of the OMP algorithm, our first design is to propose an equalizer at the receiver in order to orthogonalize the equivalent channel matrix; our second design is to propose an equalizer whose columns pursue orthonormality to the columns of the channel matrix. We obtain closed-form expressions of the equalizers under the two design objectives. Simulation results demonstrate the performance superiority compared with the standard OMP algorithm.Index Terms-Large MIMO, space shift keying, detection, orthogonal matching pursuit.