K. Deepak Babu et al, International Journal of Computer Science and Mobile Computing, Vol.3 Issue.1, January- 2014, pg. 533-538 © 2014, IJCSMCAll Rights Reserved 533 Available Online at www.ijcsmc.com International Journal of Computer Science and Mobile Computing A Monthly Journal of Computer Science and Information Technology ISSN 2320–088X IJCSMC, Vol. 3, Issue. 1, January 2014, pg.533 – 538 RESEARCH ARTICLE PERFORMANCE EVALUATION FOR FEEDBACK ROTATE- QUASI- ORTHOGONAL SPACE-TIME BLOCK CODES IN MULTIPLE TRANSMIT ANTENNAS 1 K. Deepak Babu, 2 Rajesh Durgam, 3 P. Anil Kumar 1, 2, 3 Assistant professor, Mallareddy College of Engineering, Hyderabad, India Abstract SPACE-time coding is a transmit diversity scheme with optional receive diversity to achieve high data rate and to improve the reliability of a wireless channel. In the past, STBC has full rate and full diversity for four transmit antennas. This technique has high cost and high complexity due to the more feedback information. In this paper, feedback-rotated QOSTBC technique is used to improve its transmit diversity with one bit feedback.. The experimental result shows that the bit error rate of feedback-rotated QOSTBC has better performance compare to other techniques. Index terms: QOSTBC, feedback, closed-loop, rotation, circulant. 1. INTRODUCTION A space-time code [1] is in general any modulation scheme which is designed for a multiple transmitter wireless system that tries to achieve antenna (space) diversity. The very first designs of space-time codes were in the form of trellis coded modulation, and suffered from exponential decoding complexity as the number of transmit antennas increased. After a while, Alamouti [2] proposed a simple transmitter diversity scheme which benefited both full diversity of a two-transmit antenna channel as well as simple Maximum-Likelihood (ML) decoding. The good properties of this code inspired Tarokh et al. [3] to inspect the existence of similar designs for more numbers of transmit antennas. In the case of complex codes, i.e. modulation schemes using complex constellation members, the authors proposed a structured modulation scheme, called Orthogonal Space-time Block Code that could send on average one symbol in every two time slots, and achieved full diversity as well as simple ML decoding. They presented examples for three and four transmit antennas with average rate of 3/4, or in case of real constellations they presented rate1 codes for any number of transmit antennas.