The complete solution for third-generation wireless communications: two modes on air, one winning strategy

mobile subscribers has increased much faster than anticipated. This trend is expected to continue in the future. According to the Universal Mobile Telecommunication System (UMTS) Forum [1], there will be around 400 million mobile subscribers worldwide in the year 2000 and almost 1800 million subscribers in the year 2010. In recent years, the number of subscribers to analog firstgeneration mobile radio systems has started to decrease. On the other hand, the number of subscribers to second-generation systems that use digital transmission technology is increasing steadily. Second-generation systems include timedivision multiple access (TDMA)-based systems such as the Global System for Mobile Communications (GSM), Digital AMPS (D-AMPS or IS-136), and Personal Digital Cellular (PDC) as well as code-division multiple access (CDMA)based systems like IS-95 or cdmaOne. Currently, GSM is the mobile radio standard with the highest penetration worldwide. According to the UMTS Forum, the percentage of mobile multimedia users will increase significantly after 2000. About 60 percent of the traffic in Europe will be created by multimedia applications in 2010. A similar growth of mobile data traffic is expected worldwide with an expected growth rate on the order of 70 percent per year within the next five years (starting from about 3 million data users in 1998 up to about 77 million data users in 2005). In addition to the current voice and low-data-rate services, there will be advanced high-data-rate services. Due to their limited data rate, second-generation systems will not be able to cope with all these challenges. Therefore, third-generation mobile radio systems are currently one of the key communication technologies in research, development, and international standardization bodies. This article is organized as follows. First, we summarize the international standardization activities for third-generation mobile radio systems and describe some key application areas of the UMTS Terrestrial Radio Access (UTRA). After that, we provide an overview of the UTRA Network (UTRAN) architecture. The basic system parameters of UTRA are then summarized. Moreover, we describe capacity enhancement techniques such as joint (multi-user) detection and smart antennas. Finally, a vision of future wireless communication systems beyond the third generation is outlined.