Codeword scrambling for multi-stream transmission in MIMO channel

We propose to independently scramble the codewords of the parallel data streams which are transmitted through multiple antennas in the multiple-input-multiple-output (MIMO) wireless channel. The codeword scrambling converts any possibly competing codewords of the interfering streams into invalid random words in the viewpoint of the decoder of the desired stream when the channel coefficient vectors of two or more parallel streams become very close. It also plays a role of effective interference variance reduction when the code rate is low enough to use a repetition rate matching after a baseline channel encoding. Simulation results show that the scrambling can improve the decoding performance especially when the MIMO channel is highly correlated in the transmitter side or the repetition rate is high.