Overview
The third generation of mobile networks was driven by the ITU's IMT-2000 programme, which set minimum requirements for a new standard: 2 Mbps for stationary users, 384 kbps for pedestrian users, and 144 kbps for vehicular users. Two primary 3G families emerged: the UMTS family (based on Wideband CDMA, championed by 3GPP and the European / Japanese industry) and the CDMA2000 family (an evolution of IS-95, championed by 3GPP2 and North American CDMA operators). Japan's NTT DoCoMo launched the world's first 3G service in October 2001; UMTS/WCDMA commercial services began across Europe in 2003.
3G's defining contribution was establishing packet-switched broadband as the primary mode of mobile data — supporting streaming video, always-connected email, and eventually the application ecosystem that made the smartphone the defining device of the 21st century.
UMTS / WCDMA Radio Interface
UMTS employs Wideband Code Division Multiple Access (WCDMA), operating over a 5 MHz channel (much wider than 2G's 200 kHz channels). Users are separated using individual orthogonal spreading codes (similar to IS-95 CDMA) at a chip rate of 3.84 Mcps. The wide bandwidth provides greater multipath diversity and allows more simultaneous users with better statistical multiplexing than narrowband CDMA.
UMTS operates in paired spectrum using Frequency Division Duplex (FDD): uplink and downlink are transmitted on separate frequency bands simultaneously. A Time Division Duplex (TDD) variant also exists for unpaired spectrum deployments. The UMTS air interface supports variable spreading factors from 4 to 512, allowing data rates to be traded against range and interference tolerance on a per-channel basis.
WCDMA's universal frequency reuse (all cells use the same 5 MHz channel) means the system is interference-limited: capacity is directly determined by how well inter-cell interference is managed. This is fundamentally different from the frequency-planning approach of GSM.
HSPA: High-Speed Packet Access
The most significant 3G upgrade came not from a new generation, but from the HSPA family of enhancements standardised by 3GPP from Release 5 (2002) onwards. HSPA transformed UMTS from a reasonably quick mobile internet system into a genuine mobile broadband service.
- HSDPA (High-Speed Downlink Packet Access, Release 5): Introduced a shared high-speed downlink channel (HS-DSCH), adaptive modulation (QPSK and 16-QAM), a fast Node B scheduler that could allocate capacity every 2 ms, and HARQ (Hybrid Automatic Repeat Request) retransmission at the base station layer. Peak rates: 14.4 Mbps.
- HSUPA (High-Speed Uplink Packet Access, Release 6): Applied similar techniques to the uplink, with the Enhanced Uplink channel (E-DCH). Peak rates: 5.76 Mbps.
- HSPA+ (Release 7 / 8): Added 64-QAM modulation (downlink), MIMO spatial multiplexing (2×2), and eventually dual-carrier operation combining two 5 MHz channels. Theoretical peaks of 42 Mbps downlink.
Network Architecture
The UMTS network architecture introduced a clear separation between radio and core network functions. The UMTS Terrestrial Radio Access Network (UTRAN) consists of Node B (the base station) and the Radio Network Controller (RNC), which handles handover decisions, resource management, and protocol termination. The core network connects through Iu interfaces and handles mobility, authentication, and interconnection with the internet and PSTN.
3G introduced a fully packet-switched data plane alongside the circuit-switched voice plane. Data sessions used the Packet Data Protocol (PDP) context, establishing a tunnel through GPRS Tunnelling Protocol (GTP) from the serving GPRS Support Node (SGSN) to the Gateway GPRS Support Node (GGSN). Voice calls continued to use circuit-switched bearers — a dual-mode architecture that persisted until VoLTE in the 4G era.
CDMA2000 and EV-DO
The competing North American 3G path evolved IS-95 into CDMA2000 1x (doubling voice capacity and adding basic data at up to 153 kbps) and then EV-DO (Evolution-Data Optimised). EV-DO Rev. 0 provided 2.4 Mbps downlink; Rev. A added QoS mechanisms and 3.1 Mbps downlink; Rev. B (multi-carrier) reached 73 Mbps theoretically. Verizon and Sprint deployed extensive EV-DO networks in the US, while markets in South Korea and China used CDMA2000 widely before transitioning to LTE.
Social Impact
3G coincided with and enabled the smartphone era. Apple's original iPhone launched in 2007 on EDGE (2.5G); the iPhone 3G, released a year later, made 3G ubiquitous in consumer expectations. The combination of capable touchscreen hardware, an application distribution ecosystem (App Store, Google Play), and sufficient mobile broadband transformed the mobile phone from a communication device into a pocket computer. By 2011, mobile web traffic had overtaken desktop in several developing markets — a shift that 3G infrastructure, however imperfect, made possible.