Uplink and Downlink Mc-ds-cdma Sensitivity to Static Clock Frequency Offsets

We study the effect of fixed clock frequency offsets on the performance of multicarrier direct-sequence CDMA (MCDS-CDMA) for both uplink and downlink communication, assuming orthogonal spreading sequences. We show that for both uplink and downlink MC-DS-CDMA, the performance in the presence of a clock frequency offset rapidly degrades with an increasing number of carriers. It turns out that this degradation is larger in the uplink than in the downlink, because the former suffers from a higher level of multiuser interference. For a given maximum clock frequency offset, enlarging the spreading factor in a fully loaded system does not affect the downlink degradation, but strongly increases the uplink degradation.