The fourth generation (4G) wireless technology known as Long Term Evolution (LTE) allows cellular operators to use new and wider spectrum and complements third generation (3G) networks with higher user data rates, lower latency, and a flat Internet Protocol (IP)-based network architecture. The LTE standard was first published in March 2009 as part of the Third Generation Partnership Project (3GPP) Release 8 specifications. The specifications have been in development since 2005 when 3GPP defined LTE requirements and performance goals to significantly improve on the 3GPP Release 6 standard, which was at that point the state of the art. Achieving those goals required an evolution of both the air interface and the network architecture, now known as Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) and Evolved Packet Core (EPC), respectively. The very first commercial LTE networks were deployed on a limited scale in Scandinavia at the end of 2009, and currently, large-scale deployments are taking place in several regions, including North America, Europe, and Asia.