The forthcoming wireless communication networks, commonly referred to as fourth generation (4G) systems, are expected to support extremely high data rates as close as possible to the theoretical channel capacity while satisfying quality of service (QoS) constraints. The development of these systems must take into account the problem of limited radio resources and the harshness of wireless channel conditions. Two emerging technologies that are potential candidates for 4G wireless networks are multiuser multiple-input multiple-output (MU-MIMO) wireless systems and orthogonal frequency division multiplexing (OFDM). The MU-MIMO technique allows the spatial multiplexing gain at the base station to be obtained without the need for multiple antenna terminals, thereby allowing multiple users to receive data over the downlink simultaneously. The use of OFDM provides protection against intersymbol interference (ISI) and allows high data rates to be achieved. Linear precoding schemes for MU-MIMO wireless systems, e.g., zero forcing beamforming (ZF-BF) and minimum mean squared error beamforming (MMSE-BF), have been widely concerned for their high performance in single-carrier MU-MIMO networks where a base station attempts to communicate simultaneously with multiple users. In this paper, we evaluate and extend the ZF-BF and MMSE-BF schemes from single-carrier MU-MIMO to multicarrier MU-MIMO architecture based on OFDM, i.e., MU-MIMO-OFDM system, assuming the availability of channel state information (CSI) at the transmitter. Numerical results demonstrate that both introduced linear precoding strategies provide a higher sum-rate capacity improvement compared to a conventional MU-MIMO-OFDM system where the users are served on a time division multiple access (TDMA) basis.

This letter proposes a novel compact cylindrical Dielectric Resonator Antenna excited by a microstrip feed line. The matching bandwidth is 16.9