4G Cellular Systems

As of 2004, UMTS/WCDMA and cdma2000 3G services have been rolled out in a number of countries and continue to gain some ground among business professionals. It is widely agreed that 3G will replace 2G and 2.5G systems in the next several years, providing a seemingly high throughput of several megabits per second for a mobile station. While this data rate seems sufficiently large for popular applications such as text messaging and web browsing on a cell phone, it cannot meet the relentless demand of emerging applications such as fullmotion video broadcasting and videoconferencing. In response, researchers have moved on to 4G cellular systems, which provide even higher data rates of 20 to 100 Mbps. It has to be noted that wireless LANs can now provide data rates of up to 54 Mbps, much higher than current and future variants of 3G systems, whether UMTS or cdma2000. On the other hand, a signifi cant effort has been made to coalesce voice and data communication in all 3G systems to leverage the legacy systems as much as possible. As voice over IP technology matures, an all-IP wireless network that supports voice and data over the same packet-switching infrastructure will become technically feasible to build and will be more cost-effective than current 3G frameworks. Emerging technologies for 4G wireless networks are summarized as follows; note that the application of these technologies is not limited to cellular systems:

• Smart antenna technologies exploit spatial separation of signals to allow an antenna to focus on desired signals as a way to reduce interference and improve system capacity.

• MIMO utilizes antenna arrays at both the transmitter end and receiver end to boost the link data rate and system capacity. MIMO takes advantages of multipath propagation of signals by which more data can be sent in a single channel by splitting and recombining data onto multiple paths.

• OFDM, multiple-carrier-code-division multiple access (MC-CDMA), modulation, and multiplexing technologies will improve the robustness of signal transmission and the data rate.

• Software radio or software-defi ned radio will make it possible to reconfi gure channel modulation and multiplexing on the fly.

In a broader vision, 3G cellular systems are merely one type of wireless access in the world of mobile computing. Other wireless access technologies, such as wireless LANs and WiMax, have demonstrated great potential to become a primary means of network access. These technologies may complement each other and may certainly compete head-on with each other in a variety of industry segments, leading to coexistence and integration of these systems and spurring new services and applications. The following section talks about a galaxy of new services and applications in the wireless arena.


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