Analysis of adaptive downlink multiuser mimo wireless communication system.

Omar Jabbar Ibrahim
Dr. Ra'ad S. Fyath

Abstract:Multiple-input multiple-output (MIMO) wireless communication systems have received significant attention due to their enormous channel capacity potential in rich scattering environment. Such systems need to consider multiuser transmission / reception in their design. This thesis investigates theoretically the ergodic capacity of multiuser MIMO systems operating with adaptive techniques to enhance their performance. The ergodic capacity of multiuser MIMO system is analyzed and simulated for three types of channels: additive white Gaussian noise (AWGN) channel, uncorrelated Rayleigh fading (URF) channel, and semicorrelated Rayleigh fading (SRF) channel. The downlink SRF channel for each user is modeled by assuming that the fading is correlated at the transmitter but uncorrelated at the receiver side. The simulation results are compared to those related to a single-user system and used as a guideline to present an adaptive technique to enhance the capacity of MIMO system operating in SRF channel. The adaptive technique is based on a tradeoff between time division multiple access (TDMA) and block diagonalization (BD). Simulation results are presented using MATLAB environment to address the dependence of ergodic capacity of a MIMO communication on various system and channel parameters. The results indicate clearly that the threshold level of angle between users ø employed in the adaptive system must be chosen carefully to maximize the ergodic capacity. The optimum threshold øth is equal to 24°, 42° and 47°, for angle spread ö = 5°, 50° and 75°, respectively.