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The performance of wireless communication system is degraded by the burst errors due to deep fades under multipath environment. So, techniques like forward error correction algorithms or automatic repeat request (ARQ) or a combination of both (hybrid ARQ) eliminates the bit error rate (BER). The paper focuses on the performance comparison analysis of different error control codes that gives the near Shannon capacity.

Abstract-Channel estimation plays an important role in wireless communication due to its random nature of the channel. Randomness creates the constructive or destructive fading. The combination of Orthogonal frequency-division multiplexing (OFDM) with multiple antennas at both the base station and mobile terminal converts frequency selectivity of the channel fading into flat fading parallel sub-channels. The performance can be improved by perfect channel estimations, used for non coherent detection. The paper compares different types of channel estimators and proposed a reduced complexity channel estimator.Keyword-MIMO, OFDM, fading, non coherent detection I. INTRODUCTION The wireless multipath environment is usually suffered from fading, mobility and delay spread phenomenon. In such channels, the equalization at the receiver side of the single carrier modulation systems is complex due to multipath fading, results in Inter Symbol Interference (ISI) [1]-[4]. This causes a high probability of errors, the system's overall performance becomes very poor. An efficient approach used to mitigate the detrimental multipath effects is including OFDM-based wireless systems to combat hostile frequency-selective fading encountered in mobile communications, especially for high-speed data transmission [5]. Combining OFDM with MIMO yields synergistic effects, such as enhanced robustness against frequency-selective fading and high scalability in possible data-transmission rates. The function of the channel estimator is to compensate the effect of the channel based on channel state information (CSI) [6]- [8]. For a coherent detection, the channel state information is derived from training sequence or pilot symbols which are known to both transmitter and receiver. For non-coherent detection, the channel gains are tracked at the receiver by efficient channel estimation procedures [9]. There are in general three categories in channel estimations which are training-based, blind and semi-blind methods. The training-based method requires extra bandwidth to accommodate the periodic known symbols and thus reduces the spectral efficiency [10]- [11]. The blind method saves the spectral efficiency by utilizing the statistics of received signals. But, this method requires many received signals to obtain accurate statistics [12]-[13]. Semi-blind methods, on the other hand, combine the blind method with few pilot symbols to solve the ambiguity problem occurred in blind methods [14]-[15]. The accuracy of channel estimator directly affects the performance of MIMO-OFDM systems. Therefore, channel estimation is an important topic to facilitate MIMO-OFDM for wireless communications. The structure of the paper is organized as below. Section II describes the system model. Section III describes the analysis of types of channel estimations and section IV presents simulation results and discussion is given. Section V concludes the paper.

The concatenation of channel coding and diversity schemes are essential in the 4G communication systems to improve the reliable data rate transmission. To address Bit Error Rate performance enhancement, the paper presents the coding gain and diversity gain benefits using the proposed CTSTC scheme by adding modified Turbo features and Space Time encoding features. Simulation results of are provided using MATLAB and compared the results with convolutional coded Space Time Coding technique.

The demand for high data rates in fourth generation wireless communication systems (4G) is to provide low complexity and high reliable system. Orthogonal Frequency Division Multiplexing (OFDM) technique with multiple inputs and multiple outputs (MIMO) system are used to support 4G requirements under unstable fading channels. We propose a combined decision directed channel estimation with an expectation maximization algorithm (DDCE-EM) scheme under the dispersive Rayleigh fading channel. The simulation results are compared with the single iteration channel estimation schemes and demonstrated that the proposed scheme exhibits better performance under different practical conditions.