Performance Bounds for Very Large Multiuser MIMO Systems

The last ten years have seen significant advances of multiuser MIMO (MUMIMO) in wireless communication. MU-MIMO is now being introduced in several new generation wireless standards (e.g., LTE-Advanced, 802.16m). The number of users is increasing with more and more applications. At the same time, high transmission data rates and communication reliability are required. Furthermore, there is a growing concern about green communication which relates to the effects of the radiation emitted from wireless devices on the human body. Therefore, future MU-MIMO systems have to satisfy three main requirements: i) serving many autonomous users in the same time-frequency resource, ii) having high data rate and communication reliability, and iii) less energy consumption/radiation. These are seemingly contradictory requirements since the more users are served, the more interference the systems will suffer from, and the higher the data rate is, the more power is required. MU-MIMO with very large antenna arrays seems to meet the above demands and hence, it can be considered as a promising technology for next generation wireless systems. With very large antenna arrays (we mean arrays comprising say a hundred of antennas), the channel vectors are nearly-orthogonal and hence, multiuser interference can be significantly reduced. As a result, many users can be simultaneously served with high data rate. In particular, with coherent processing, transmit power can be reduced dramatically owing to the array gain. In this thesis, we focus on performance bounds of MU-MIMO with very large antenna arrays. We study the fundamental limits on the system performance when using large antenna arrays under practical constraints such as low complexity processing, imperfect channel state information, intercell interference, and finite-dimensional channels.