Aggressive frequency reuse in a multibeam satellite system offers wider bandwidths per beam at the cost of increased co-channel interference. Focussing on the return link of interactive mobile satellite systems, emphasis has been laid on Minimum Mean Squared Error (MMSE) receivers at the gateway to reduce the co-channel interference arising out of aggressive reuse. Performance of such receivers have been evaluated in presence of perfect channel information and synchronization showing impressive gains in throughput. Towards bringing such receivers closer to system implementation, this work aims at understanding the effect of imperfect channel estimates on the resulting performance. In particular, utilizing first order approximations, closed-form expressions for the MMSE receiver and the resulting Mean Squared Error (MSE) have been derived. These expressions provide insight into the effect of channel, noise levels and the estimation error on performance while indicating the robustness of MMSE receiver.