improved battery life of handsets among many other attributes. Then cdma2000 1xEV-DO systems were introduced to support higher data rates and multimedia applications. The two successful revisions of EV-DO technology are Revision 0 and Revision A. In 2007, multi carrier EV-DO Revision B was standardized and commercial deployments are expected in the coming years. The latest OFMDA-based revision called EV-DO Release C or Ultra Mobile Broadband (UMB) was standardized in 2007 to compete with WiMAX and 3G-LTE. UMB did not receive much attention from the industry and almost all the R&D activities have been suspended and it is no longer on the roadmap of any operator. Thus, EV-DO systems were continuously evolving till the industry decided to shelve the UMB in favor of competing EPS and WiMAX technologies. The evolution of CDMA standards is shown in Figure 5.1. This chapter is designed for readers who are already familiar with the EV-DO technology which is stated as HRPD (High Rate Packet Data) in standards. To understand the basics and standard specifications of EV-DO readers can refer to [2]. The chapter will focus on the key techniques and enhancements that are introduced in the different revisions of EV-DO (Revisions 0, A, and B) and we will very briefly touch upon UMB. Since UMB has been discontinued, we will also look into the possibilities of migration to LTE (Long Term Evolution). The second section will look into the current revisions (0 and A) of EV-DO while the third section explains multi-carrier EV-DO Rev. B. UMB air interface and CDMA 450 are described in Sections 4 and 5 respectively. EV-DO network architecture and performance of different revisions, evolution of CDMA2000 and migration to LTE are listed in the following sections. Lastly, the current statistics of EV-DO subscribers, deployments and the future outlook is presented. 1 In simple terms 3GPP2 (3rd Generation Partnership Project 2) provides CDMA2000 specifications. 2 1X means 1.25 MHz single carrier. Next Generation Mobile Communications Ecosyst