International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 3 (2015) pp. 8827-8839 © Research India Publications http://www.ripublication.com Low Complexity of ACS architecture For Space Time Trellis Code Viterbi Decoder Mohd Azlan Abu 1,2 , Harlisya Harun 1,3 , Mohammad Yazdi Harmin 1 & Noor Izzri Abdul Wahab 4 1 Department of Aerospace Engineering, Faculty of Engineering, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia 2 Electronics Technology Section, University Kuala Lumpur British Malaysian Institute, 53100 Gombak, Selangor, Malaysia 3 University Kuala Lumpur Malaysian Institute of Aviation Technology, 43900 Dengkil, Selangor, Malaysia 4 Department of Electrical and Electronic Engineering, Faculty of Engineering, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia mohdazlan@unikl.edu.my Abstract Space time trellis codes (STTC) and Viterbi algorithm is used to offer a combination of strong forward error correction system, which has been widely used in digital communication systems such as noisy wireless communications. A traditional Viterbi decoder consists of three main units, namely Branch Metric Computation Unit (BMC), Add Compare Select Unit (ACS) and the path metric updater (PMU). Mergers between STTC and complexity of the Viterbi algorithm will result in the STTC Viterbi decoding algorithm and will increase power consumption and reduced battery life in a system. To reduce the complexity of the algorithm, a new method to calculate the ACS STTC Viterbi decoder is proposed. This paper proposes to remove the mold parts in the calculation of ACS and replaced by comparing and choosing the minimum value calculation only. The simulation results show that under the same conditions of BER , ACS proposed algorithm outperform the state of the art by about 1 dB and the proposed ACS algorithm can reduce the computational complexity significantly. Introduction Mobile communication consists of different types of technology, services, and applications that already exists to meet the specific needs of users in different