Digital Communications

13MIMO Systems

MIMO systems improve the performance of communication systems by employing multiple antennas at both transmitter and receiver. In MIMO systems the fading is exploited as a channel resource for possible performance improvement. Multiple antenas both at transmit and receive sides provide space (antenna) diversity. The diversity order is defined as the number of paths through which a transmitted signal reaches the receiver, hence is equal to the product of the number of transmit and receive antennas. Increase in the diversity order leads to a significant increase in diversity gain and improvement in the bit error probability performance. On the other hand, the mean SNR at the receiver output also increases; this implies that either the transmit power may be reduced or the range (coverage area) of the telecommunication system may be increased. MIMO systems may also be used in order is to increase the transmission rate since they may also be considered to provide multiple spatial channels for message transmission between transmit and receive antennas. In virtue of the so‐called multiplexing gain, the channel capacity (spectral efficiency) may be increased significantly. Performance improvements in MIMO systems are achieved at the expense of computational complexity while maintaining the primary communication resources (that is, total transmit power and channel bandwidth) fixed. Space‐time coding, that is, the data is transmitted over multiple antennas by coding symbols ...