INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS Int. J. Commun. Syst. 2008; 21:1033–1045 Published online 21 May 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/dac.936 On the error probability of quasi-orthogonal space–time block codes Jae-Dong Yang 1, ∗, † , Xianglan Jin 1 , Jong-Seon No 1 and Dong-Joon Shin 2 1 Department of Electrical Engineering and Computer Science, INMC, Seoul National University, Seoul 151-744, Korea 2 Department of Electronics and Computer Engineering, Hanyang University, Seoul 133-791, Korea SUMMARY In this paper, we derive the exact pairwise error probabilities (PEPs) of various quasi-orthogonal space– time block codes (QO-STBCs) using the moment generating function. By classifying the exact PEPs of QO-STBCs into three types, we derive the closed-form expression for each type of PEP. Based on these closed-form expressions, we obtain the union bounds on the symbol error probability and bit error probability for QPSK modulation. Through simulation, it is shown that these union bounds are quite tight. Copyright 2008 John Wiley & Sons, Ltd. Received 3 September 2006; Revised 29 December 2007; Accepted 26 February 2008 KEY WORDS: bit error probability; pairwise error probability; quasi-orthogonal space–time block codes; symbol error probability 1. INTRODUCTION In a multiple-input multiple-output communication system, transmit diversity is a very attractive technique to achieve high reliability and spectral efficiency, and space–time code is a good solution to achieve transmit diversity. Tarokh et al. [1] introduced space–time codes and derived their performance criterion. Alamouti [2] introduced a simple transmit diversity scheme with two transmit antennas. Space–time block codes (STBCs) from orthogonal designs were proposed [3], which have low decoding complexity and achieve full diversity and full rate. Full rate means that one symbol is effectively transmitted during one symbol duration. However, it is known that the complex linear ∗ Correspondence to: Jae-Dong Yang, Department of Electrical Engineering and Computer Science, INMC, Seoul National University, Seoul 151-744, Korea. † E-mail: yjdong@ccl.snu.ac.kr Contract/grant sponsor: MOE Contract/grant sponsor: MOCIE Contract/grant sponsor: MOLAB Copyright 2008 John Wiley & Sons, Ltd.