Distributed and I/Q-Swapped Mapping for Chip-Interleaved DS-CDMA in Uplink

This paper describes a new chip-mapping method that reduces multi-path interference for chip-interleaved direct-spread (CIDS) - code division multiple access (CDMA) in fast fading channels. The proposed spreading method consists of a combination of chip distribution and I/Q-swapped mapping (DISM). To reduce the correlation among several paths, chips that come through the ordinary spreading process are distributed. The I/Q-swapped mapping swaps I-phase chips for Q-phase chips at the transmitter and the receiver, to balance out the phase variation due to fading. The I/Q-swapped mapping method loses signal energy in the case of a large phase variation, but it completely compensates for the phase variation instead. The computer simulation results indicate that DISM improves the packet error rate of CIDS-CDMA with 16-QAM signal in fast frequency-selective fading channels.