New Direction of Wireless Technology

The 3^rd generation (3G) mobile wireless communications systems based on direct-sequence code division multiple access (DS-CDMA) technique were put into services, with much higher data rates than the present 2G systems, in many countries and their deployment speed has since accelerated. 3G systems will be continuously evolving with high speed downlink packet access (HSDPA) technique, multiple-input/multiple-output (MIMO) antenna technique, etc, for providing packet data services of around 14 Mbps as the mid-term evolution and of 50~100 Mbps as the long-term evolution. However, the capabilities of 3G wireless networks will sooner or later be insufficient to cope with the increasing demands for broadband services. The evolution of 3G systems will be followed by the development of 4G systems, that support extremely high-speed packet data services of e.g., 100 M~1 Gbps. The most important technical challenge for the realization of 4G systems is two-fold: (a) to overcome the severely frequency-selective fading channel, and (b) to significantly reduce the transmit power from mobile terminals. Frequency-domain equalization (FDE) can take advantage of channel frequency-selectivity and improve the transmission performance of single carrier (SC) DS-CDMA signal transmissions as well as multicarrier (MC) signal transmissions. MIMO can also be combined with FDE in SC transmission. Frequency-domain signal processing is believed to play an important role in 4G systems. Either SC or MC, both with FDE, can be used for the downlink (base-to-mobile) to achieve almost the same transmission performance. However, for the uplink (mobile-to-base) applications, SC transmission with FDE is more appropriate since it requires less peak transmit power. Transmit power reduction is a very important issue. Applying wireless multi-hop technique or distributed antenna technique is a possible solution to this issue. In this presentation, we will discuss about some important 4G wireless tech- niques.