2-dimensional OVSF Spreading for Chip-interleaved DS-CDMA Uplink Transmission
Le Liu, Fumiyuki Adachi · 2005
Abstract—Multi-access interference (MAI) limits the transmission performance of the DS-CDMA uplink. In this paper, we propose 2-dimensional (2D)-OVSF spreading for chip-interleaved DS-CDMA uplink transmission. By adopting 2D-OVSF spreading, the multiuser channel is transformed into orthogonal single-user channels irrespective of users ’ data rates. Thus, single-user frequency-domain MMSE equalization can be used to take advantage of frequency-selective fading channel for signal detection. For a large Doppler spread, however, the orthogonality among the OVSF spreading codes may be lost, thereby producing the MAI. The decision feedback frequency-domain MAI cancellation is applied to improve the BER performance. The transmission performance in a multiuser and frequency- and time-selective fading environment is evaluated by computer simulation. Key words: MAI, 2-dimensional, OVSF spreading codes, uplink, DS-CDMA.