Design and performance of quasi-synchronous multi-carrier CDMA system
S. Tsumura, Shinsuke Hara · 2002
Multicarrier (MC)-CDM/CDMA is one of the promising code division-based multiple access/multiplexing techniques for fourth-generation mobile communications systems, where high data rate services will be provided even for high speed-cruising mobiles. Investigations so far made in Japan have shown that the MC-CDM scheme has superiority over the direct sequence (DS)-CDM scheme in the downlink; on the other hand, the MC-CDMA scheme is not so advantageous over the DS-CDMA scheme in the uplink. This is because the code orthogonality among users can be kept in the downlink, whereas it is totally distorted by frequency selective fading in the uplink. First, we show a new signal design for MC-CDM/CDMA transmission. The new signal format has head/tail guard intervals in one symbol duration, for accurate DFT window synchronization in downlink and uplink, and establishment of quasi-synchronous transmission in uplink. Then, we show the bit error rate performance for MC-CDM with minimum mean square error (MMSE)-based combining in downlink and MC-CDMA with MMSE-based multiuser detection in uplink.