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The paper considers the impact of the UMTS synchronisation channel (SCH) on bearer performance. The SCH is described, and it is shown that it has significantly different characteristics from other interference and noise sources. For this reason, it is important to understand whether it can be generally modelled in a simple way, e.g. by using its average received power. In reality, it is found that this is not the case, and that the performance degrades when the SCH is present for the same average level of Eb/Nt. This shows that the coding/interleaving schemes used are not sufficient to average the temporally selective interference. In particular, it is found that convolutionally coded bearers show higher sensitivity than turbo coded ones, resulting in an increase in the Eb/Nt targets set by the outer loop. A basic analysis indicates that the resulting system capacity loss is not significant. However, a full evaluation of this effect is going to require a more complex analysis based on system simulation.