2.3 Universal Mobile Telecommunication System
This chapter is a short introduction to the universal mobile telecommunication system (UMTS). For more details please refer to References  and .
UMTS (WCDMA) was specified and selected for 3G system for many reasons, one of the main ones being that it is a very efficient way to utilize the radio resources – the radio spectrum. WCDMA has a very high rejection of narrowband interference, and is very robust against frequency-selective fading. It offers good multipath resistance due to the use of rake receivers. The handovers in WCDMA are smooth and imperceptible due to the use of soft handovers. During handover the mobile is serviced by more cells at the same time, offering macro diversity gain.
However, there are challenges to UMTS radio planning, when all cells in the network are using the same frequency. UMTS radio planning is all about noise and power control. Very strict power control is necessary to make sure that all transmitted signals are kept to a target level that insures that all mobiles reach the base station at the exact same power level. Very good radio planning discipline must be applied and cells must only cover the intended area, and not spill into unintended areas. The reason for this is that you need to minimize the inter-cell interference since all cells are operating on the same frequency; this is one of the biggest radio planning challenges when designing UMTS radio systems.
Even though the concept of soft ...