This work presents a single-carrier massive MIMO transmission system for the frequency selective Gaussian multi-user channel. It considers both cases of spatially uncorrelated and correlated channel and compares them in terms of the user sum-rate as well as the general performance. We consider a channel with M antennas at the base station which provides services for K single- antenna users. We develop a general expression for the achievable rate among users in the channel with a correlation among antennas at the base station. It has been shown that, when there is no correlation between base station antennas or users, the channel matched filter precoder outperforms any other precoder. In a highly- correlated massive MIMO channel however, the conventional channel matched filter precoder does not perform as expected. We show the failure of the channel matched filter in the presence of a correlation pattern among antennas at the base station with theoretical analysis and simulations. We apply three different precoders to enhance the achievable rate and their performances are determined by simulations. We show that the precoders outperform the channel matched filter in a highly-correlated channel with a large number of users. By increasing the number of users in the system, the conventional precoders show even better performance in terms of the user's sum- rates.