Also known as: UMTS, W-CDMA, WCDMA, Universal Mobile Telecommunications System, 3G
UMTS (Universal Mobile Telecommunications System) is the third-generation (3G) cellular standard from 3GPP, and W-CDMA (Wideband CDMA) is its primary air interface. Rather than assigning each user a slot or a narrow channel, W-CDMA spreads every user across a shared 5 MHz carrier with a unique spreading code, so many calls occupy the same spectrum at once and are separated by code correlation.1
Overview
UMTS was the European-led branch of the ITU’s IMT-2000 3G family. Its W-CDMA radio access network (UTRAN) uses direct-sequence CDMA: each user’s data is multiplied by a fast spreading code (chip rate 3.84 Mchip/s) that widens the signal across the 5 MHz carrier. All users share that carrier simultaneously, and tight power control keeps every signal at the base station near the same level so no one user drowns out the others. The design brought far higher data rates and true simultaneous voice-and-data to mainstream phones.
Technical characteristics
| Property | Value |
|---|---|
| Generation | 3G |
| Access | Direct-sequence CDMA (W-CDMA) |
| Carrier spacing | 5 MHz |
| Chip rate | 3.84 Mchip/s |
| Duplex | FDD (paired) and TDD variants |
| Modulation | QPSK; HSPA adds 16-QAM and 64-QAM |
| Vocoder | AMR / AMR-WB (adaptive multi-rate) |
| Core network | Evolved from the GSM/GPRS packet core |
Fast closed-loop power control (1500 times per second) is essential to CDMA and is one of the features that distinguishes W-CDMA from the TDMA of GSM.
History
3GPP specified UMTS in its Release 99, and the first commercial W-CDMA networks launched in 2001–2003. Operators bid heavily for 3G spectrum around the turn of the millennium. Later releases added the HSPA family (HSDPA and HSUPA), sharply raising throughput and turning 3G into a practical mobile broadband platform.
Deployment
UMTS/W-CDMA became the dominant 3G technology in Europe, much of Asia, and beyond, often deployed by the same operators who ran GSM so that handsets could fall back to 2G outside 3G coverage. It has since been superseded by LTE and 5G, and many carriers have shut down their 3G networks to reclaim the 5 MHz carriers for newer technology.
Decoding it with GopherTrunk
GopherTrunk is a trunked-radio and utility-signal scanner; cellular telephony such as UMTS/W-CDMA is out of scope and is not decoded. Its wideband CDMA carriers hold private, authenticated, ciphered subscriber traffic on licensed spectrum. UMTS appears here to explain how 3G’s code-division approach differs from the time- and frequency-division schemes used by land-mobile systems.