Major focus of this lecture is to explain 4G Mobile Communications history and system. here also focus on OFDMA Based WiMAX Network. We consider a single cell in a WiMAX network which has a base station and multiple subscriber channels. Each subscriber section serves multiple associations. Admission control can be used at each customer station to limit the quantity of ongoing connections as a result of that subscriber section. At each customer station, traffic from most users for uplink associations are aggregated right single queue.