A channel estimation method for MIMO-OFDM Mobile WiMax systems

This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder. Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.In this paper, channel estimation for Space-Time Block Code (STBC) - Orthogonal Frequency Division Multiplexing (OFDM) is investigated for Mobile WiMax systems. A new channel estimation approach is proposed using the dedicated pilot subcarriers defined at constant intervals by the WiMax standard. The estimation method has low computation as only linear operations are needed due to orthogonal pilot coding. The performances of the proposed method have been demonstrated by extensive computer simulations. For the OFDM system with two transmit antennas and one to four receive antennas and using QPSK modulation, the simulated results under different Stanford University Interim (SUI) channels show that the proposed method has only a 4dB loss compared to the ideal case where the channel is known at the receiver

Detection scheme for space-time block codes wireless communications without channel state information

“This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder." “Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.” DOI: 10.1109/ICCS.2008.4737147In this paper, the new detection scheme proposed by Tarokh and Alamouti is investigated and expanded to two schemes of two transmit two receive antennas and four transmit one receive antennas. Previously, Tarokh and Alamouti, based on the simple transmit diversity scheme proposed by Alamouti, have provided two new detection methods to decode signals at the receiver without channel information. We expand their work to two and four transmit antennas with different number of receive antennas. We also demonstrate that the two methods are in fact the same with one being a special case of the other. The theory and detailed derivation of detection formulas for three cases, Tarokh and Alamouti work, two transmit two receive antennas and four transmit one receive antennas are presented.Peer reviewe

Source-assisting strategy for distributed space-time block codes

This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder. Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Most of the previous works on distributed space-time coding assume that there is no direct link between the source and the destination, which means that the source is not actively involved in cooperation. In order to present the benefits that can be extracted when the source is actively involved in cooperation, we propose a source-assisting (SA) strategy for distributed orthogonal and quasi-orthogonal space-time block coded cooperative multi-hop networks. We adopt a two time-slot protocol using the decode-and-forward model, where in the first time slot, the source transmits while the relay and destination nodes all receive, and in the second time slot, the source and relay nodes transmit and the destination node receives. Numerical and simulation results show that our SA strategy exhibits improved diversity performance compared to the conventional distributed orthogonal and quasi-orthogonal designs, at the expense of slightly increased complexity of the ML detector. An explanation on the modified structure of the ML detector is provided

MIMO-OFDM with pilot-aided channel estimation for WiMax systems

This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder. Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.This paper describes a channel estimation scheme for Multiple Input Multiple Output (MIMO)-Orthogonal Frequency Division Multiplexing (OFDM) systems based on training sequence. We first develop an approach to channel estimation which is crucial for the decoding of the transmitted data. We then discuss the implementation of the proposed method for WiMax systems under various channel conditions. The efficiency of the new algorithm is demonstrated through the simulation of the MIMO-OFDM system for two and four transmit antennas and different number of receive antennas. The Space-Time Coding with 192 information subcarriers per codeword is used as defined in the WiMax standard. Through simulations, it is shown that the proposed method has between 1.5 dB and 2dB loss compared to the ideal case where the channel coefficients are known at the receiver. In summary, with the proposed channel estimation technique, combining diversity using Space-Time Codes with OFDM is proved to be a promising technique for the present and future wireless communications

Performance of SFBC-OFDM system with pilot aided channel estimation

“This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder." “Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.”This paper introduces a computationally efficient pilot aided channel estimation method for space-frequency block coding (SFBC) Orthogonal Frequency Division Multiplexing (OFDM) systems under frequency selective channels. The proposed method, simulated under WiMax requirements, is based on the use of eight pilots defined in the standard to estimate the channel parameters at constant interval. The pilots are also coded in the same SFBC format to simplify the estimation computations, but can be modulated by different modulation scheme to reduce the estimation error. The method offers tradeoff between accurate channel estimation and efficient bandwidth usage as more pilots would allow the algorithm to perform a more accurate estimation but at the cost of less transmitted data. Performances are evaluated for high mobility applications and with pilots modulated using different modulation schemes. Simulation results are presented for different number of antenna at the receiver, different values of Doppler shifts and different modulations for pilot and data subcarriers

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Pilot-aided channel estimation and performance of ASTC-MIMO-OFDM system in a correlated Rayleigh frequency-selective channel

“This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder." “Copyright IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.”Algebraic Space-Time Codes (ASTC) for MIMO systems are based on quaternion algebras. Thanks to their algebraic construction, the ASTC codes are full-rank, full-rate and have the non-vanishing determinant property. These codes have been proposed for MIMO flat fading channels in order to increase the spectral efficiency and to maximize the coding gain. The purpose of this work is to analyze the performance of the ASTC in a frequency selective Rayleigh channel. To deal with the frequency selectivity, we use the OFDM modulation. Methods for channel estimation using pilot symbol have been proposed. BER performances of ASTC-MIMO-OFDM system, under several propagation conditions, have been evaluated