The present invention provides a process for preparing a catalyst useful in gas phase polymerization of olefins wherein the hydrogen response of the catalyst can be improved by using a ketone as the electron donor in the catalyst. During memory read andor memory write operations the corresponding data strobe is sampled at the data destination 5055 according to a local clock signal 7173. When the engine is cold, the ECU determines the amount of fuel injected in accordance with the actual intake flow rate. By way of the dynamic adjustment technique, coupled with the bit-error detection and estimation, workload of the Viterbi decoder in operation is capable of being adjusted according to bit error rate such that less power is consumed in a decoding process.