The strength of the attenuated received signal and the 3D path loss in mmWave transmission are shown. To enhance spectral efficiency and transmission latency a CP-less OCDM system and to reduce both out-of-band (OOB) spectrum power and consumption of additional resources due to cyclic prefixing a proper subcarrier mapping is proposed. For achieving negligible BER and increased channel capacity a QR decomposition and Gram Schmidt orthogonalization (QR-GSO)-based multi-user, multiple-input, multiple-output (MU-MIMO) precoding system is also proposed in this paper.