MULTIUSER SCHEDULING IN MIMO OFDM SYSTEMS

Abstract

There are a tiumber of challenges in wireless communication. These challenges inclwles the limited spectrum or bandwidth for communication and a complex space-time varying environment. There is also requirement of high data rates, high quality of service and high capacity systems. To fulfill these requirements several technologies has been developed in past years. One of these technologies is multiple input multiple output systems . It is also known as MIMO systems. 'space time wireless' communication or 'smart' antennas. Mul-tiple input multiple output uses multiple antennas at transmitter and at receiver. vIII\IO technology overcomes on both impairments of fading channel and resource constraints. MIMO technology exploits spatial (limentions as well as time and frequency dimension. Because of these properties MIMO is widely used in IEEE 802.11n(Wi-Fi), IEEE 802.116m, 4G, 3GPP Long Term evolution(HSPA+ and WiMax). Multiuser MIMO achieves multiplexing gain by transmitting multiple users at a time. Multiplexing gain achieved by MU MIMO depends on no. of transmitting antennas and no. of receive antennas. The multiuser mirno achieves large multiplexing gain by slecting optimum users from total users present in cell. In MIMO multiuser diversity gain also can he achieved by scheduling transmissions for best users. For this several algorithms has been developed that schedules users. These algorithms schedule users which has high desirable channel conditions. To measure these channel conclitiomis feedback is also provided by users to transmitter. The feedback can he Channel quality indicator, Precoding matrix indicator, Rank indicator etc. These are parameters of scheduling algorithms of user equipment. In Multiuser i\lfl\IO scheduling several parallel data streams are sent simultaneously to multiple users equipment with same time and frequency. This increases the multiuser diversity gain and utilizes available radio resources efficiently. There are some power and bandwidth resource allocation strategies. These strategies optimally allocate power and bandwidth for selected users and increase cell throughput.