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Digital multimedia broadcasting (DMB) is a reliable multi-service system for mobile and portable receivers. DMB system allows interference-free reception under the conditions of multipath propagation and transmission errors using coded orthogonal frequency division multiplexing modulation (COFDM) and unequal error protection (UEP) scheme. For error correction of portable DMB receivers, punctured convolutional code and viterbi decoder is developed but it needs lots of computations for real-time operation. So, it is desired to design a high speed and low-power hardware scheme for viterbi decoder. This paper proposes a combined add-compare-select (ACS) and path metric normalization (PMN) unit using pre-computation technique for DMB system. The proposed PMN unit reduces the critical path by applying fixed value selection algorithm using the comparison tree properties. We also propose an ACS structure using the decomposition and pre-computation technique for reducing the complexity of the adder, comparator and multiplexer. Simulation results shows that area, gate delay and power consumption are reduced about 3.78%, 23.80%, and 12.22%, respectively.