Universal Mobile Telecommunication System (UMTS)
WCDMA

Since the TDMA and FDMA access at the air interface used in former 2G networks has not been sufficient for 3G networks, the UMTS adopted more sophisticated access method based on CDMA, explained in chapter 7. To be more specific, the WCDMA technique is utilized in UMTS networks. In WCDMA, user information bits are spread over a much wider bandwidth than in conventional CDMA case. This way, the capacity and data bit rates achieved by individual users in the system is increased. Similarly as in case of CDMA, user data are multiplied with quasi-random bits, called chips, derived from CDMA spreading codes. The UMTS uses the chip rate of 3.84 Mcps (Mega chip per second) and carrier bandwidth is equal to 5 MHz. The other distinguished characteristic of WCDMA based system is the frequency reuse factor 1. It means, the frequency used in all cells is the same (contrary to GSM, where each cell uses individual frequencies to minimize interference). Thus, radio resources are better utilized.

The utilization of WCDMA brings several important features into UMTS standard: