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Alamouti-based space-frequency coding for OFDM

WIRELESS PERSONAL COMMUNICATIONS 2005年第1-2期35卷 173-185页

作者： Hutter, AA Mekrazi, S Getu, BN Platbrood, F CSEM CH-2000 Neuchatel Switzerland Inst EURECOM F-06904 Sophia Antipolis France Univ Aalborg DK-9220 Aalborg Denmark

We investigate space-frequency block coding for OFDM systems with multiple transmit antennas, where coding is applied in the frequency domain (OFDM carriers) rather than in the time domain (OFDM symbols). In particular we consider Alamouti's code, which was shown to be the optimum block code for two transmit antennas and time domain coding. We show that the standard decoding algorithm results in significant performance degradation depending on the frequency-selective nature of the transmission channels, such that a low coherence bandwidth results in a huge degradation. The optimum decoding algorithm that alleviates this problem is the maximum-likelihood decoder for joint symbol detection. We present a performance analysis for the investigated space-frequency decoders in terms of the achievable BER results. Furthermore we compare space-time and space-frequency coding and discuss the respective advantages and drawbacks of the different decoding algorithms in terms of their complexity. It should be noted that for the space-time approach we introduce the so-called matched-filter receiver, which shows significantly lower complexity compared to the maximum-likelihood decoder known from literature. The HIPERMAN system serves as an example OFDM system for quantitative comparisons.

关键词： space-frequency coding joint maximum-likelihood detection/decoding transmit diversity OFDM

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Alamouti-based space-frequency coding for OFDM

Alamouti-based space-frequency coding for OFDM

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International Symposium on Wireless Personal Multimedia Communications

作者： Hutter, AA Mekrazi, S Getu, BN Platbrood, F CSEM CH-2000 Neuchatel Switzerland Inst EURECOM F-06904 Sophia Antipolis France Univ Aalborg DK-9220 Aalborg Denmark

关键词： space-frequency coding joint maximum-likelihood detection/decoding transmit diversity OFDM

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Transmit Beamforming for space-frequency Coded MIMO-OFDM Systems with Spatial Correlation Feedback

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IEEE TRANSACTIONS ON COMMUNICATIONS 2008年第10期56卷 1647-1655页

作者： Sadek, Ahmed K. Su, Weifeng Liu, K. J. Ray Qualcomm Inc Corp R&D San Diego CA 92121 USA SUNY Buffalo Dept Elect Engn Buffalo NY 14260 USA Univ Maryland Dept Elect & Comp Engn College Pk MD 20742 USA Univ Maryland Syst Res Inst College Pk MD 20742 USA

This paper addresses the problem of joint optimization of transmit beamforming and space-frequency (SF) coding for MIMO-OFDM systems with spatial correlation feedback in broadband communications. This problem is challenging in the sense that the transmitter should be designed to beamform across multiple eigenspaces associated with the multipath environment simultaneously. With arbitrary transmit spatial correlation, the performance analysis for SF-coded MIMO-OFDM systems with beamforming is provided, and a general optimization problem for the beamforming design is formulated. Three suboptimal approaches to design the beamformer based on the derived design criteria are proposed i) Eigenvalue selection scheme;ii) Eigenspace selection scheme;and iii) Per-subcarrier approach based on decoding at each subcarrier. The proposed schemes take into account the multiple eigenspace information associated with the multipath-delay channel. Improvement in the performance over SF coding without beamforming is shown through simulations in terms of bit error rate. The Eigenvalue selection scheme provides the best performance among the proposed algorithms. This scheme locates the subspace associated with the largest eigenvalues in the eigenspace of the covariance matrices. With the Eigenvalue selection scheme, the performance improvement is about 3 dB over the SF coding without beamforming for highly correlated channels as shown in our simulations.

关键词： Broadband wireless communications MIMO-OFDM systems transmit beamforming across multiple eigenspaces multiple antennas space-frequency coding correlation feedback

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Cooperative Spectrum Sensing with Transmit and Relay Diversity in Cognitive Radio Networks

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2008年第12期7卷 4761-4766页

作者： Zhang, Wei Ben Letaief, Khaled Univ New S Wales Sch Elect Engn & Telecommun Sydney NSW 2052 Australia Hong Kong Univ Sci & Technol Dept Elect & Comp Engn Kowloon Hong Kong Peoples R China

In the letter the problem of cooperative spectrum sensing is investigated in cognitive radio (CR) networks over Rayleigh fading channels. By taking into account the error effect on the decision reporting, a general performance analysis of cooperative spectrum sensing is given. The analytical detection results show that the performance of cooperative spectrum sensing is limited by the probability of reporting errors. To deal with this limitation, we propose a transmit diversity based cooperative spectrum sensing method. By regarding multiple CRs as a virtual antenna array, space-time coding and space-frequency coding are applied into CR networks over flat-fading and frequency-selective fading channels, respectively. Moreover, we propose a relay diversity based cooperative spectrum sensing approach to increase the diversity of detection when some CRs are in heavy shadowing. It is then shown that, when combined with algebraic coding, relay diversity can further improve the cooperative spectrum sensing performance.

关键词： Cognitive radio diversity technique relay channels space-frequency coding space-time coding

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Blind channel estimation in MIMO-OFDM systems using semi-definite relaxation

Blind channel estimation in MIMO-OFDM systems using semi-def...

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33rd IEEE International Conference on Acoustics, Speech and Signal Processing

作者： Sarmadi, Nima Gershman, Alex B. Shahbazpanahi, Shahram Tech Univ Darmstadt Commun Syst Grp D-64283 Darmstadt Germany Inst Technol Univ Ontario Fac Engn & Appl Sci London ON L1H7K4 Canada

ISBN: (纸本)9781424414833

A new blind channel estimation technique for multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems is proposed. It estimates the channel parameters in the time domain jointly for all subcarriers instead of doing this in the frequency domain independently for each subcarrier. This results in a substantially improved parsimony of the channel parameterization along with the ability to use coherent processing across the subcarriers. It is shown that using semi-definite relaxation (SDR), our channel estimation problem can be transferred to a convex form and then solved efficiently using modem convex optimization tools.

关键词： blind channel estimation space-frequency coding MIMO-OFDM systems semi-definite relaxation

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Performances of differential-encoded FFHMA systems with space-frequency coding over Nakagami-m fading channels

Performances of differential-encoded FFHMA systems with spac...

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60th IEEE Vehicular Technology Conference

作者： Khemapatapan, C Benjapolakul, W Chulalongkorn Univ Dept Elect Engn Bangkok 10330 Thailand

ISBN: (纸本)0780385217

Performances and capacities of differential-encoded fast frequency-hopping multiple-access (FFHMA) systems under Nakagami-m fading channels are studied. The space-frequency coding (SFC) scheme is applied to gain diversity order. The proposed FFHMA transmitter can operate without an output hopping filter. The simulation results show that the receiver can detect the transmitted signal when maximum Doppler frequency closes to 350 Hz. The performances of synchronous FFHMA systems can be improved by spreading factor and average SNR per bit. In Rayleigh fading channel, the system capacity of FFHMA for BER about 10(-3) is derived from simulation and it is about 5, 24, and 61 users for spreading factor of 1, 2, and 4 respectively.

关键词： fast frequency-hopping multiple-access space-frequency coding Nakagami-m fading channel

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Iterative channel estimation and decoding of turbo coded SFBC-OFDM systems

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2007年第8期6卷 3090-3101页

作者： Dogan, Hakan Cirpan, Hakan A. Panayirci, Erdal Istanbul Univ Dept Elect & Elect Engn Istanbul Turkey Kadir Has Univ Dept Elect Engn Istanbul Turkey

We consider the design of turbo receiver structures for space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) systems in the presence of unknown frequency and time selective fading channels. The Turbo receiver structures for SFBC-OFDM systems under consideration consists of an iterative MAP Expectation/Maximization (EM) channel estimation algorithm, soft MMSE-SFBC decoder and a soft MAP outer-channel-code decoder. MAP-EM employs iterative channel estimation and it improves receiver performance by re-estimating the channel after each decoder iteration. Moreover, the MAP-EM approach considers the channel variations as random processes and applies the Karhunen-Loeve (KL) orthogonal series expansion. The optimal truncation property of the KL expansion can reduce computational load on the iterative estimation approach. The performance of the proposed approaches are studied in terms of mean square error and bit-error rate. Through computer simulations, the effect of a pilot spacing on the channel estimator performance and sensitivity of turbo receiver structures on channel estimation error are studied. Simulation results illustrate that receivers with turbo coding are very sensitive to channel estimation errors compared to receivers with convolutional codes. Moreover, superiority of the turbo coded SFBC-OFDM systems over the turbo coded STBC-OFDM systems is observed especially for high Doppler frequencies.

关键词： EM algorithm MAP channel estimation OFDM systems space-frequency coding turbo receiver

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Noncoherent sequence detection of differential space-frequency modulation MIMO-OFDM

Noncoherent sequence detection of differential space-frequen...

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8th IEEE Workshop on Signal Processing Advances in Wireless Communications

作者： Wang, Xin Li, Ying Wei, Jibo Natl Univ Def Technol Changsha Peoples R China

ISBN: (纸本)9781424409549

In a multiple-antenna broadband system, differential space-frequency modulation (DSFM) MIMO-OFDM in conjunction with noncoherent detection, which avoids channel state information (CSI) estimation, is attractive for time- and frequency selective channels for its reduced complexity. However, a long power-delay profile (PDP), which we encounter frequently in broadband systems, will deteriorate the performance rapidly. In this paper, a noncoherent sequence detection of DSFM MIMO-OFDM is proposed, which exploits the correlation among subcarriers and utilizes the past several symbols to detect the current one and it can be used to alleviate the performance degradation introduced by long PDPs. We also present an analytical approximation of the symbol-error rate (SER) for DSFM, which enables quick and accurate performance evaluations. Simulation results confirm the efficacy of our approach and it is more flexible than the fixed window multiple-symbols detection under variable numbers of subcarriers.

关键词： MIMO-OFDM space-frequency coding noncoherent sequence detection

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Nondata-aided channel estimation for OFDM systems with space-frequency transmit diversity

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 2006年第2期55卷 449-457页

作者： Çirpan, HA Panayirci, E Dogan, H Istanbul Univ Dept Elect Engn TR-34850 Istanbul Turkey Bilkent Univ Dept Elect & Elect Engn TR-06800 Ankara Turkey

This paper proposes a computationally efficient nondata-aided maximum a posteriori (MAP) channel-estimation algorithm focusing on the space-frequency (SF) transmit diversity orthogonal frequency division multiplexing (OFDM) transmission through frequency-selective channels. The proposed algorithm properly averages out the data sequence and requires a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and estimates the complex channel parameters of each subcarrier iteratively, using the expectation maximization (EM) method. To further reduce the computational complexity of the proposed MAP algorithm, the optimal truncation property of the KL expansion is exploited. The performance of the MAP channel estimator is studied based on the evaluation of the modified Cramer-Rao bound (CRB). Simulation results confirm the proposed theoretical analysis and illustrate that the proposed algorithm is capable of tracking fast fading and improving overall performance.

关键词： expectation maximization (EM) algorithm maximum a posteriori (MAP) channel estimation orthogonal frequency division multiplexing (OFDM) systems space-frequency coding

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Coded OFDM with transmitter diversity for digital television terrestrial broadcasting

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IEEE TRANSACTIONS ON BROADCASTING 2006年第3期52卷 325-335页

作者： Esli, Celal Delic, Hakan Bogazici Univ Wireless Commun Technol Lab TR-34342 Istanbul Turkey Bogazici Univ Wireless Commun Lab TR-34342 Istanbul Turkey

space-frequency coded (SFC) and channel coded orthogonal frequency-division multiplexing (COFDM) is considered under narrow-band interference (NBI). Analytical expressions for the bit error probability (BEP) are derived for OFDM with SFC in a frequency-selective fading environment. It is shown that SFC increases the resistance of COFDM against the NBI and reduces the BEP considerably. Specific attention is paid to Digital Terrestrial Television Broadcasting (DTTB), and the associated coding gains are discussed.

关键词： COFDM digital video broadcasting multitone interference space-frequency coding

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