MIMO i.i.d Channel Capacity When the Channel is Known and Unknown to the Transmitter for Different Antenna Configurations

In this paper, the authors study the capacity of MIMO i.i.d channels for different antenna configurations with and without channel knowledge at the transmit side (CSIT). When (CSIT) is available, waterfilling algorithm is used to allocate the power among the transmitter antennas. In this case, channel capacity is greatly improved, especially in the low SNR regime and/or large antenna systems. However, this capacity gain approaches zero in the high SNR regime. Simulation shows that the lack in the knowledge about (CSIT) can be compensated for by increasing the number of antennas in the receive side (M_r). When M_r is three times the number of antennas in the transmit side (M_t), meaning that M_r/M_t ap 3, the (CSIT) is no longer beneficial. On the other hand, using waterfilling is necessary when M_t is larger than M_r to get the optimum capacity