MIMO systems, with its reliability and high growth in sum-rate without increasing the transmission power or bandwidth, have been used in several recent wireless communication standards. Meanwhile microcell and distributed antenna systems have received the most attention, due to the reduction of distance between the transmitter and the receiver, and the resulting increase in data rates. When the antenna elements of a central antenna unit in a big cellular area are divided into several separate antenna units and distributed around the area - so that every element is connected to a central processing unit placed in the center of the area - a distributed antenna system is created. In addition to spatial diversity, this kind of system allows for large-scale and small-scale performance improvements such as reducing radiation power (which in turn reduces inter-cell interference) as well as increasing coverage and spectral efficiency. Nevertheless, the different degrees of path loss due to different distances between users and the distributed units create noticeable challenges in analyzing the efficiency of these systems. Using MIMO capability in each smaller antenna unit, in order to increase spectral efficiency and also concentrating radio signals in a particular direction, can improve reliability of the communication link as well. However according to the propagation loss in high frequencies (millimeter-wave frequencies), in order to have a better coverage in every macrocell, the direction of transmission should be changed towards the desired receiver and vice versa. Moreover, it is necessary to ensure a long range reception by compensating for the path loss in an optimal fashion. The objective of an antenna array, in form of a spatial (angular) filter, is to successfully send (or receive) a beam to (from) a desired direction, and to create an effective null, both in reception and transmission, in order to eliminate transmission (or reception) of signals to (from) undesirable directions. This process is as effective in reducing interference as using a large directional antenna. The formation of this spatial filter in high frequencies (millimeter wave frequencies) in the presence of uniform random line of sight (UR-LoS) stochastic channel provides a desired propagation phenomenon. In this thesis, in order to improve the performance of the communication network in millimeter-wave frequencies we propose a method for beam forming based on the main beam forming and effective null forming. Accordingly, three communication scenarios have been analyzed. In the first scenario (the centralized scenario) we consider a point to point communication between a multi-antenna unit and a single multi-antenna user. In the second scenario (cooperative scenario) several multi-antenna units send same information to a single multi-antenna user. In the third scenario (multi user scenario) each multi-antenna unit is connected to the nearest multi-antenna user independently. According to the fact that each multi-antenna unit has an antenna array, spatial multiplexing can also be provided in addition to the frequency-time multiplexing of the beams. It is noteworthy that the proposed beam forming scheme used at the transmitter and receiver is based on the SIR maximization approach. Considering the design criteria, simulation results confirm the efficiency of the proposed technique in terms of the sum throughput of the network. Key Words : MIMO , Distributed MIMO (D-MIMO) , Smart antenna array, Beamforming and Precoding, Nullforming