sion multiple access aimed at third-generation mobile communications systems is reviewed. W-CDMA is designed t o flexibly offer wideband services which cannot be provided by present cellular systems, with various data rates as high as 2 Mb/s. The important concept of W-CDMA is the introduction of intercell asynchronous operation and t h e pilot channel associated w i t h individual data channels. Intercell asynchronous operation facilitates continuous system deployment from outdoors t o indoors. Other technical features of W-CDMA include fast cell search under intercell asynchronous operation, fast transmit power control, coherent spreading code tracking, a coherent Rake receiver, orthogonal multispreading factor forward link, and variable-rate transmission w i t h blind rate detection. The introduction o f the data-channel-associated pilot channel allows W-CDMA t o support interference cancellation and adaptive antenna array techniques that can significantly increase the link capacity and coverage. This article presents radio link performance evaluated by computer simulation. Field experiment radio link performance results are also presented. ecently, mobile communications services are pen-R etrating into our society at an explosive growth rate. All of the current second-generation cellular communications systems (e.g., PDCIGSMIIS54 and IS95) have adopted digital technology. However, the major services they provide are limited to basic services, such as voice, facsimile, and low-bit-rate (far less than 64 kb/s) data. We are now approaching the 21st century, when demands for a variety of wideband services such as high-speed Internet access and videolhigh-quality image transmission, will continue to increase. The third-generation mobile communication systems, called International Mobile Telecommunications-2000 (IMT-2000) in the International Telecommunication Union (ITU) [l], must be designed to support wideband services at data rates as high as 2 Mbis, with the same quality as fixed networks. Direct sequence code-division multiple access (DS-CDMA) technology [a] is attractive for wireless access because of its numerous advantages over time-division multiple access (TDMA) and frequency-division multiple access (FDMA), including soft handoff (or site diversity), exploitation of multipath fading through Rake combining, and direct capacity increase by the use of cell sectorization. However, the current IS-95 is based on narrowband DS-CDMA technology optimized for basic services. To realize true IMT-2000 systems, a new wideband wireless access technology incorporating as many recent technology developments as possible is necessary. The most promising candidate, wideband DS-CDMA (W-CDMA), is being developed throughout the world [3, 41. In January 1998, the European Telecommunications Standards Institute (ETSI) decided to adopt W-CDMA technology for frequency-division duplex (FDD) bands. In Japan, the Association of Radio Industries and Businesses (ARIB), the standardization body of the radio sector, is now developing a...

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The broadband orthogonal frequency and code division multiplexing (OFCDM) system with two-dimensional spreading (time and frequency domain spreading) is becoming a very attractive technique for high-rate data transmission in future wireless communication systems. In this paper, a quasianalytical study is presented on the downlink performance of the OFCDM system with hybrid multi-code interference (MCI) cancellation and minimum mean square error (MMSE) detection. The weights of MMSE are derived and updated stage by stage of MCI cancellation. The effects of channel estimation errors and sub-carrier correlation are also studied. It is shown that the hybrid detection scheme performs much better than pure MMSE when good channel estimation is guaranteed. The power ratio between the pilot channel and all data channels should be set to 0.25, which is a near optimum value for the two-dimensional spreading system with time domain spreading factor ( ) of 4 and 8. On the other hand, in a slow fading channel, a large value of the channel estimation window size , where is an odd integer, is expected. However, = 3 is large enough for the system with = 8 while = 5 is more desirable for the system with = 4.Although performance of the hybrid detection degrades in the presence of the sub-carrier correlation, the hybrid detection still works well even the correlation coefficient is as high as 0.7. Finally, given , although performance improves when the frequency domain spreading factor ( ) increases, the frequency diversity gain is almost saturated for a large value of (i.e., 32).

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