Convolutionally - Coded and Spectrum - Overlapped Multicarrier DS - CDMA Systems in a Multipath Fading Channel

Jung-Hun Oh et al. 177 Multicarrier DS-CDMA is an effective approach to combat fading and various kinds of interference. In this paper, we present an overlapped multicarrier DS-CDMA system, wherein each of the rate M / 1 convolutionally-encoded symbols is also repetition coded and transmitted using overlapped multicarriers. However, since the frequency spectrums of successive carriers are allowed to overlap, the transmission bandwidth is more efficiently utilized. The effect of the overlapping percentage between successive carriers of a multicarrier DS-CDMA system on the performance is investigated to determine the overlapping percentage showing the best performance. We suggest two methods for sub-band overlapping variation. One is to allow variation of sub-band overlapping percentage when the total number of subcarriers is fixed. The other is to increase the number of sub-bands (the number of repetitions R ) with fixed subband bandwidth. Given a total number of subcarriers MR , we show that the BER variation is highly dependent on the roll-off factor β of a raised-cosine chip wave-shaping filter irrespective of convolutional encoding rate M / 1 and repetition coding rate R / 1 . We also analyze the possibility of reduction in total multi-user interference by considering the variation of both the roll-off factor ( 1 0 ≤ < β ) and the sub-band overlapping factor ( 2 0 ≤ < λ ), and show that the proposed system may outperform the multicarrier DSCDMA system in [3].