a multi- stage parallel interference cancellation (PIC) may suite well WCDMA systems with a single spreading factor (SF). The parallel interference cancellation implies that interfer- ence gets cancelled from all users concurrently. MUD techniques for multi-service WCDMA with a variable spreading factor has been studied in Ref. [27], where a group- wise serial interference cancellation (GSIC) receiver [28-30] appears to be the most promising of the present receiver designs. In this technique, users with a given SF are also detected concurrently, after which the MAI9 originated by them gets suppressed by the users having different SF. 1.3.3 Software Radio Applications Although 3G wireless communications concepts, e.g. IMT-2000 family of networks, aim towards global standardization to break away with multiple standards deployed in particular geographical areas, there is a need for multi-frequency transceivers operating in common hardware platforms for practical solutions in the medium and long-term. This solution appears more realistic today through Software Radio (SR), the application of flexible and programmable transceivers. Thus, SR sets itself as a key technology to drive the realization of global standards in 3G systems. The evolution of GSM to UMTS alone will benefit multi-band multi-mode (GSM 900, 1800, 1900, GPRS, UMTS (FDD and TDD) terminals. On the other hand, SR not only applies to terminals or Mo- 9 Multiple Access Interference. The UMTS Network and Radio Access Technology bile Stations (MS) but also the to the Base Stations (BS). In the sequel we cover SR as part of the enabling techniques in the MS and BS. The main limitation of the feasibility of MUD in real commercial systems has been the disproportionate processing speeds afforded by current DSP10 technology and the re- quirement of the detection and estimation algorithms. Although overall performance of DSPs has increased and keeps increasing, 3G systems also are pushing the signal proc- essing capabilities higher and higher. Tasks such as high-d