8Multiple Input Multiple Output

The Multiple Input Multiple Output (MIMO) techniques are an essential part of wireless communication systems because it significantly increases wireless communication system performances. The MIMO techniques enable us to obtain diversity gain, array gain, and multiplexing gain. Each different gain is related to different types of system performances. The diversity gain improves link reliability and transmission coverage by mitigating multipath fading. The array gain improves transmission coverage and QoS. The multiplexing gain increases spectral efficiency by transmitting independent signals via different antennas. In this chapter, we focus on space time codes and MIMO detection techniques. In addition, we look into the encoding and decoding process of a space time trellis code.

8.1 MIMO Antenna Design

The performance of MIMO systems depends on channel correlation caused by spatial correlation and antenna mutual coupling. In practical MIMO systems, each MIMO channel is related to another channel with different degrees. We call this spatial correlation. It depends on multipath channel environments. When one element of MIMO antennas transmits a signal, a power is radiated everywhere and a neighboring antenna element absorbs the power. This is undesirable situation. We call this antenna mutual coupling. It is caused by the interaction among transmit antennas [1]. This effect becomes a very serious problem if antenna spacing is very small. For ...

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