Successive Interference Cancellation and its Implications for the Design of Layered MIMO-Algorithms

In rich scattering environments, wireless systems with multiple transmit and receive antennas (MIMO) offer large capacity gains. They are in general based on a parallel transmission of 1 ≤ M ≤ NT signal steams called layers (NT is the number of transmit antennas). If the channel is not known to the transmitter the best strategy would be to exploit transmit diversity for each layer. This ensures, that all layer achieve full diversity of the MIMO-channel and therefore would perform equally. D-BLAST [1] is able to exploit the transmit diversity through channel coding and multiplexing parts of the code words over different antennas. MultiStratum-Space-Time-Coding [2] (MSSTC) uses Space-TimeBlock-Codes (STBC) for the same purpose. MSSTC suffers from rate loss for more than two transmit antennas due to the Space-Time-Block-Coding. D-BLAST needs guard intervals which leads also to some capacity loss. Multi-StratumPermutation-Codes (MSPC) [3] avoid this rate loss by using orthogonal transformations over space (antennas) and time (successive symbols). This ensures a good reparability of the layers at the receiver. Remark, that different from BLAST approaches, all antennas are used all time even if M < NT , whereas BLAST would have to leave out antennas for transmission in this case. A detailed description of the construction of MSPC can be found in [3].