re fully digital and supported voice and circuit-switched data communication at low rates up to 14.4 Kbps. GSM adopted a hybrid of FDMA and time-division multiple access (TDMA), while IS-95 used hybrid FDMA and code-divi- sion multiple access (CDMA) techniques. 2.5G was the first technology to introduce packet-switched data services in addition to circuit- switched voice and data services in the mobile networks. The main 2.5G standard, General Packet Radio Service (GPRS), introduced the packet-switched (PS) domain to the GSM core network. GPRS coding schemes adopted error correction and more than one time-slot to achieve higher data rates in a GSM-based radio access network (RAN). For the cdmaOne family, packet-switching was introduced by IS-95B, and was deployed by South Korea starting in 1999. In 1998, the 3rd Generation Partnership Project (3GPP) was initiated to define a third-generation (3G) mobile system based on 2G GSM and to standardize network protocols across different vendors. In parallel, the 3rd Generation Partnership Project 2 (3GPP2) defined an alternate 3G net- work based on CDMA. 3G was first lunched by NTT Docomo in 2001. The first 3G systems were as follows: Enhanced Data rate for GSM Evolution (EDGE), also widely referred as pre-3G or 2.75G, was a superset to GPRS and could function on any GPRS-based network. EDGE used 8PSK modu- lation techniques to achieve higher data rates; for example, a downlink rate up to 384 kbps. Universal Mobile Telecommunication System (UMTS) shared the same core network as GSM/GPRS or EDGE. However, the UMTS RAN architecture was completely different, as the radio used wideband code-division multiple access (WCDMA). UMTS could achieve the same download speed, 384 kbps, as EDGE. cdma2000 1xRTT (Single-Carrier Radio Transmission Technology), specified in IS-2000, achieved downlink rate up to 153.6 kbps using the quadrature phase-shift keying (QPSK) mod- ulation technique. 1x Evolution-Data Optimized (1xEV-DO), which was defined in IS-856, and High Speed Packet Access (