Guest editorial: wideband CDMA II

M OBILE communications services are penetrating our society at an explosive rate. The major services that the second-generation mobile systems provide are limited to basic services (e.g., voice and low-bit rate data). We have entered the 21st century, when demands for a variety of wideband services (e.g., high-speed Internet access and the video/high-quality images transmission) will continue to increase. The third-generation (3G) mobile systems (called IMT-2000) are being designed to support wideband services, at data rates as high as 2 Mb/s, with the same quality as fixed networks. It is everyone's wish that wireless could act like a wired connection. To realize true IMT-2000 systems, a new wideband wireless access technology incorporating as many recent technology developments as possible is necessary. Wideband direct sequence code division multiple access (wideband CDMA) is emerging as the predominant wireless access technology for the 3G systems, and is being developed throughout the world. Wideband CDMA is designed to flexibly offer wideband services, such as wireless Internet services (i.e., peak rate of 384 kb/s to download information from the Web) and video transmissions (data rate up to 2 Mb/s). Wideband is essentially about data rate. The physical limitations and impairments to radio channels (bandwidth constraints, multipath fading, noise, and interference) present a fundamental technical challenge to the goal of reliable high data rate communications. The emphasis of this special issue is on advanced wireless wideband CDMA techniques. Wideband CDMA supports in-tercell asynchronous/synchronous operation, adaptive (variable rate) transmission, and applications of advanced techniques such as adaptive antenna arrays and turbo codes. • One objective is cell acquisition for intercell asynchronous operation, which does not require interbase-station synchronization ; therefore, there is no requirement on any external system such as GPS to allow for easy deployment in all types of environments. • Adaptive (variable rate) transmission provides multimedia services. To achieve higher bit rates, multiple downlink physical channels (or multicode) can be transmitted in parallel in one direction. • The adaptive antenna array directs beam nulls to interference sources to maximize the signal-to-interference ratio of each user. In the case of voice-only services, the appli-Publisher Item Identifier S 0733-8716(01)03456-4. cation of the antenna arrays is rather impractical because a large number of antenna elements is required. However, antenna arrays are particularly useful for multimedia communications in which different users are transmitting at different data rates. High-rate users (Internet and video), although their numbers are not large, give …