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With imperfect channel state information (CSI) acquired by channel estimation at the receiver, the performance of basic automatic-repeat-request (ARQ) and hybrid ARQ (HARQ) systems is evaluated as a function of the accuracy of channel estimation. A link between data-link-layer performances and physical-layer parameters is therefore established. Upper and lower bounds on the accepted packet error rate (APER), the goodput, and the drop rate are derived. These upper and lower bounds are close to one another and therefore enable the behavior of the exact performance parameters to be investigated. The results show that the effect of the MSE on the system performance is nonlinear. At high values of the MSE, the performance very rapidly deteriorates, whereas, at low values of the MSE, the performance gently improves toward that of the perfect CSI case. The study here shows how accurate the CSI should be to achieve a specified performance level in ARQ schemes.