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ABSTRACT: This paper proposes spectral efficient relay-assisted transmit diversity techniques, i.e., space-time and space-frequency block codes (STBC/SFBC), for single carrier frequency-domain equalization (SC-FDE). The proposed systems achieve spatial diversity over frequency selective channels in a distributed fashion without cyclic prefix (CP), which increases spectral efficiency of conventional relay-assisted systems. In practical mobile applications, the CP-less distributed STBC (D-STBC) SC-FDE suffers from the time selectivity of wireless fading channels, resulting in a deviation from the basic assumption of Alamouti codeword. In order to obtain a reliable performance over doubly selective channels, the CP-less D-SFBC SC-FDE and its efficient implementation are presented. Further, the performance of these two distributed SC transmissions is analytically compared over fast fading (i.e., time selective) environments. For evaluation of mean square error over fast fading channels, we present a channel model that captures the time-varying nature of wireless channels. It is shown through analysis that the CP-less DSFBC SC-FDE outperforms the CP-less D-STBC SC-FDE when there exists a severe Doppler spread. Timing synchronization and highly accurate channel estimation of the proposed systems are also addressed for practical implementations. Simulation results show that the proposed systems approach the lower bound of full-CP systems, thus increasing the spectral efficiency.
IEEE Transactions on Communications 03/2010; · 1.68 Impact Factor
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IEEE Transactions on Communications. 01/2010; 58:3480-3490.
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IEEE Transactions on Communications. 01/2010; 58:568-577.
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ABSTRACT: This paper proposes a full-rate cooperative communication technique with spatial diversity for single-carrier transmissions. In order to achieve both the spatial diversity and the full-rate, data streams are simultaneously transmitted through all direct and relay channels with different phase rotation and cyclic delay patterns. The phase rotation and cyclic delay patterns are derived in the sense of minimizing interlayer interference and a corresponding destination structure is presented for decoupling each layer at the destination. Simulation results show that the proposed technique achieves spatial diversity without sacrificing spectral efficiency and outperforms conventional full-rate cooperative communication techniques.
IEEE Transactions on Wireless Communications 12/2009; · 2.59 Impact Factor
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ABSTRACT: Peak-to-average power ratio (PAPR) regrowth after clipping is one disadvantage of space-frequency block coded orthogonal frequency-division multiplexing (SFBC-OFDM). In this letter, we propose an effective PAPR reduction technique of SFBC-OFDM for multinode cooperative transmission. To reduce PAPR at the source (mobile equipment), the relay applies SFBC encoding, which enables the source to transmit clipped single-input single-output (SISO)-OFDM signals without any increase of PAPR. Simulation results show that the clipped signals of proposed scheme are effectively recovered, and the proposed scheme achieves the diversity of SFBC without the complexity of multiple antennas at the source.
IEEE Signal Processing Letters 12/2009; · 1.39 Impact Factor
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ABSTRACT: Space-time block coded (STBC) single carrier (SC) transmission was extended in a distributed fashion for practical implementation of user cooperation. However, STBC was designed under the assumption that the channel is static over the duration of a space-time codeword. Thus, the distributed STBC SC system suffers from the time selectivity of wireless fading channels. To achieve a reliable performance over fast fading channels, we propose a distributed space-frequency block coded (D-SFBC) SC transmission. This paper analytically compares the performance of these two distributed SC transmissions over fast fading environment. For evaluation of mean square error (MSE) over fast fading channels, we present a channel model that captures the time-varying nature of wireless channels. It gives an insight into the characteristics of inter-carrier interference and simplifies the evaluation of MSE. Using this model, it is proven that the D-SFBC SC transmission outperforms the D-STBC SC transmission when there exists a severe Doppler spread. Simulation results are also provided to validate our analysis and to compare two distributed single carrier transmission schemes.
IEEE Transactions on Communications 10/2009; · 1.68 Impact Factor
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ABSTRACT: This letter proposes a multiple-input multiple-output (MIMO) technique for single carrier frequency-domain equalization (SC-FDE). The proposed system achieves spatial multiplexing and transmit diversity gains altogether, thus improving error performance and increasing spectral efficiency compared to conventional spatial multiplexing and transmit diversity techniques, respectively. In order to achieve both of the gains, independent data streams are transmitted simultaneously through all transmit antennas with different cyclic delay patterns for each data stream. Corresponding receiver structure is also presented, where a successive interference cancellation (SIC) algorithm without ordering process is introduced. Simulation results show that the proposed system with iterative receiver structure provides considerable performance gains over conventional MIMO techniques.
IEEE Signal Processing Letters 08/2009; · 1.39 Impact Factor
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ABSTRACT: Cyclic delay diversity (CDD) is an attractive diversity technique due to its low complexity and compatibility to existing wireless communication systems. This letter proposes a CDD with frequency domain turbo equalization (FDTE) for single carrier (SC) transmission, in order to achieve the full spatial diversity of frequency-selective multi-antenna channels. The frequency diversity inherent in SC is picked up from the increased channel selectivity of CDD. The noise or intersymbol interference enhanced by equalization for highly selective channels is then mitigated through applying FDTE at the receiver. Simulation results show that the performance of proposed system approaches the corresponding orthogonal spacetime block coding (STBC) system in slowly fading channels without any data rate loss, and considerably outperforms the STBC system in fast fading channels.
IEEE Communications Letters 04/2009; · 0.98 Impact Factor
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ABSTRACT: Multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) has become a promising candidate for next generation broadband wireless communications. However, like a single-input single-output (SISO)-OFDM, one main disadvantage of the MIMO-OFDM is the high peak-to-average power ratio (PAPR), which can be reduced by using an amplitude clipping. In this paper, we propose clipped signal reconstruction methods for the MIMO-OFDMs with spatial diversity, such as space-time and space-frequency block codes (STBC/SFBC). The proposed methods are based on the technique called iterative amplitude reconstruction (IAR) for SISO-OFDM. It is shown that the IAR can be easily employed for the STBC-OFDM, but it cannot be directly applied to the SFBC-OFDM, because the transmitted sequences over different antennas are dependent due to the use of space-frequency code. We propose a new SFBC transmitter for clipped OFDM, which has approximately half the computational complexity of conventional SFBC-OFDM. The proposed clipping preserves the orthogonality of transmitted signals, and the clipped signals are iteratively recovered at the receiver. Further, we theoretically analyze the performance of IAR with optimum equalization, and also provide highly accurate channel estimation of the OFDM with amplitude clipping. Simulation results show that the proposed receivers effectively recover contaminated OFDM signals with a moderate computational complexity.
IEEE Transactions on Wireless Communications 02/2009; · 2.59 Impact Factor
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ABSTRACT: Relay-assisted space-time block code (STBC) and space-frequency block code (SFBC) for single carrier frequency-domain equalization (SC-FDE) were presented. They achieve spatial diversity over fading relay channels under the assumption of perfect channel state information (CSI). In this paper, we propose a pilot position selection/detection technique for channel estimation of those systems. Unlike the conventional block-type channel estimation techniques, the proposed scheme superimposes pilots on data-carrying tones whose positions are selected to minimize the distortion of original signals. Without additional pilot overhead, the proposed technique can track the CSI even when the mobile equipment speed is high. The corresponding destination structure and frequency domain equalization are also presented, where the pilot positions are blindly detected and the distorted data symbols are iteratively reconstructed. Simulation results show that the proposed method gives better BER performance than the block-type channel estimation for the distributed SFBC (D-SFBC) SC-FDE over fast fading relay channels, without the loss of spectral efficiency.
Global Telecommunications Conference, 2008. IEEE GLOBECOM 2008. IEEE; 01/2009
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IEEE Transactions on Communications. 01/2009; 57:2799-2807.
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IEEE Transactions on Wireless Communications. 01/2009; 8:268-277.
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IEEE Transactions on Wireless Communications. 01/2009; 8:5449-5454.
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IEEE Communications Letters. 01/2009; 13:184-186.
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ABSTRACT: This paper proposes a relay-based transmit diversity technique for single carrier frequency-domain equalization (SC-FDE). The proposed system achieves spatial diversity over fading channels in a distribution fashion without cyclic prefix (CP), which increases spectral efficiency of conventional relay- based systems. The destruction of channel cyclicity due to the lack of CP is recovered at the input of relay and destination. In order to obtain spatial diversity, the transmit sequence of relay is efficiently generated in time domain, realizing space-frequency block code (SFBC). Corresponding destination structure using FDE, timing synchronization, and highly accurate channel estimation for the proposed system are also presented. Simulation results show that the proposed system approaches the lower bound of full-CP system.
Communications, 2008. ICC '08. IEEE International Conference on; 06/2008
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ABSTRACT: In this letter, we propose a simple pilot position selection/detection technique for channel estimation of single- carrier frequency domain equalization (SC-FDE). Unlike the conventional channel estimation techniques such as frequency domain superimposed pilot technique (FDSPT), the proposed scheme selects the pilot positions to minimize the distortion of original signals caused by the loss of useful data tones in frequency domain. The corresponding receiver structure is also presented, where the pilot positions are blindly detected and the distorted data symbols are iteratively reconstructed. Simulation results show that the proposed system gives better BER performance than the FDSPT and approaches the lower bound of SC-FDE.
IEEE Communications Letters 06/2008; · 0.98 Impact Factor
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ABSTRACT: This letter proposes a relay-based single carrier frequency-domain equalization (SC-FDE) with space-frequency block code (SFBC) in a distributed fashion. The proposed scheme achieves spatial diversity in uplink fast fading channels without the complexity of multiple antennas at source (mobile equipment). The source of the proposed system has a very simple transmitter structure without any increase of peak-to-average power ratio (PAPR). In order to obtain spatial diversity, the transmit sequence of relay is efficiently generated in the time domain, which realizes the SFBC. The corresponding destination structure and frequency domain equalization are also presented. Simulation result shows that the proposed system considerably outperforms the distributed space-time block code (D-STBC) SC-FDE over fast fading channels.
IEEE Communications Letters 01/2008; · 0.98 Impact Factor
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ABSTRACT: This paper proposes a relay-assisted space- frequency block code (SFBC) for single carrier frequency-domain equalization (SC-FDE) in a distributed fashion. The proposed scheme achieves spatial diversity over uplink fast fading channels without the complexity of multiple antennas. The source (mobile equipment) of the proposed system has a very simple transmitter structure with constant amplitude transmit sequences. In order to obtain spatial diversity, the transmit sequence of relay is efficiently generated in the time domain, which is equivalent to the SFBC. The corresponding destination structure and frequency domain equalization are also presented. Simulation results show that the proposed system considerably outperforms the distributed space-time block code (D-STBC) SC-FDE over fast fading channels.
Global Telecommunications Conference, 2007. GLOBECOM '07. IEEE; 12/2007
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ABSTRACT: As with orthogonal frequency-division multiplexing (OFDM), one main disadvantage of multi-input multi-output (MIMO) OFDM is the prohibitively large peak-to-average power ratio (PAPR) of transmitted signals on different antennas, which can be reduced by a deliberate amplitude clipping. However, clipping causes distortion that degrades the system performance. In this letter, we propose clipping noise mitigation techniques for space-time and space-frequency block coded (STBC/SFBC)-OFDMs. A new SFBC transmitter for clipped OFDM is proposed, and the optimum equalizer is derived for reconstruction of the clipped signals. Simulation results show that the proposed receivers effectively recover contaminated STBC/SFBC-OFDM signals with a moderate computational complexity.
IEEE Signal Processing Letters 12/2007; · 1.39 Impact Factor
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IEEE Communications Letters. 01/2007; 11:928-930.
