MIMO is one of the key enabling technologies of broadband wireless. It makes use of multiple antennas in communication. Multi-antenna is not new; it has been used in diversity reception for decades.
Traditionally, fading in wireless channels was regarded as a nuisance, which was combated by means of diversity, namely, receiving many copies of a signal from different antennas. In contrast, fading is now seen as a beneficial factor in MIMO communication. In MIMO communication, antennas are usually far spaced so as to achieve independent fading. It in fact takes advantage of independence naturally provided by fading to create multiple spatial channels in parallel. Hence, higher channel capacity is obtained over the same bandwidth, thereby higher spectral efficiency.
Contemporary wireless systems are supposed to achieve high efficiency, capacity and reliability simultaneously, and using multiple transmission antennas is a feasible solution that has been applied ubiquitously. This paper analyses a typical 2-by-2 multi-input multi-output (MIMO) communication system. We investigate the influence of fading phenomenon and utilise the effect to achieve transmission diversity. Capacity of generated ergodic channels on different signal-to-noise (SNR) are simulated with Monte Carlo method (MCM), and quadrature amplitude modulation (QAM) together with space-time coding are employed for symbol mapping. Detection schemes of maximum-likelihood (ML), zero-forcing (ZF) and minimum-mean-square-error (MMSE) are examined and compared in terms of bit error rate (BER) and complexity. It is proved that the ML detector is optimal to recover the signal with high complexity, while the MMSE one achieves a balance on criterion. The result also show that the reliability can be further enhanced by combining the conventional detectors with Alamouti code.