International OPEN ACCESS Journal Of Modern Engineering Research (IJMER) | IJMER | ISSN: 2249–6645 | www.ijmer.com | Vol. 4 | Iss. 6| June. 2014 | 21| MIMO System Performance Evaluation for High Data Rate Wireless Networks using Space Time Block Codes with Orthogonal Structure Sandeep Narain 1 , Dr. Syed Hasan Saeed 2 1, 2 (Department of ECE, Integral University, India) I. INTRODUCTION Due to fading in a multipath wireless channels makes it becomes very tough for the receiver antenna to differentiate the transmitted signal if the receiver is adjusted with some specific type of diversity having some less-faded replica of the signal transmi tted by sending end antenna. In today’s many applications one of the popular practical way of achieving diversity is multiplication of number of the antenna at the transmitter and may also be on the receiver additionally. But there is a desired need that receivers should be of small size. Hence under this consideration it may not be practical to use multiple receiving side antennas at the mobile remote station. This justifies the consideration of mainly transmit side diversity. Transmit diversity is treated as a method of removing data errors in wireless fading channels [2]. It is very popular due to its simplicity of design and the reliability of multiple antennas at the base station. In terms of the cost of multiple transmit chains at the base can be applied over numerous users. Space–time trellis coding [10] is a new coding scheme that combines signal processing at the receiver with coding techniques appropriate to multiple transmit antennas. Specific space–time trellis codes designed for 2–4 transmit antennas perform extremely well in slow-fading environments (typical of indoor transmission) and come close to the outage capacity computed by Telatar [3] and independently by Foschini and Gans [4]. However, when the number of transmit antennas is fixed, the decoding complexity of space–time trellis codes (measured by the number of trellis states in the decoder) increases exponentially with transmission rate. In reference to the matter of the complexity in decoding recently a remarkable scheme is proposed for transmission using only two transmit antennas. This scheme is simplicity on compared with the space–time trellis coding for two transmit antennas but a loss in performance is found as compared to space–time trellis codes. Despite this loss of performance, Alamouti’s scheme [1] is applying in many places due to its simplicity and performance and it motivated researchers of all the world for discovering similar schemes using more than or equal to two transmit antennas based communication systems. Abstract: Space–time block coding is used for data communication in fading channels by multiple transmit antennas. Message data is encoded by applying a space–time block code and after the encoding the data is break into ‘n’ streams of simultaneously transmitted strings through n transmit antennas. The received signal at the receiver end is the superposition of the n transmitted signals distorted due to noise .For data recovery maximum likelihood decoding scheme is applied through decoupling of the signals transmitted from different antennas instead of joint detection. The maximum likelihood decoding scheme applies the orthogonal structure of the space–time block code (OSTBC) and gives a maximum-likelihood decoding algorithm based on linear processing at the receiver. In this paper orthogonal space –time block codes based model is developed using Matlab/Simulink to get the maximum diversity order for a given number of transmit and receive antennas subject with a simple decoding algorithm. The simulink block of orthogonal space coding block with space –time block codes is applied with and without gray coding. The OSTBC codes gives the maximum possible transmission rate for any number of transmit antennas using any arbitrary real constellation such of M-PSK array. For different complex constellation of M- PSK space–time block codes are applied that achieve 1/2 and 3/4 of the maximum possible transmission rate for MIMO transmit antennas using different complex constellations. Keywords: Transmit diversity, Multipath channels, Multiple input multiple output, Wireless communication and OSTBC.