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A new reduced-complexity detection scheme for zero-padded OFDM transmissions  [cached]
Eghbali Homa,Muhaidat Sami
EURASIP Journal on Wireless Communications and Networking , 2011,
Abstract: Recently, zero-padding orthogonal frequency division multiplexing (ZP-OFDM) has been proposed as an alternative solution to the traditional cyclic prefix (CP)-OFDM, to ensure symbol recovery regardless of channels nulls. Various ZP-OFDM receivers have been proposed in the literature, trading off performance with complexity. In this paper, we propose a novel low-complexity (LC) receiver for ZP-OFDM transmissions and derive an upper bound on the bit error rate (BER) performance of the LC-ZP-OFDM receiver. We further demonstrate that the LC-ZP-OFDM receiver brings a significant complexity reduction in the receiver design, while outperforming conventional minimum mean-square error (MMSE)-ZP-OFDM, supported by simulation results. A modified (M)-ZP-OFDM receiver, which requires the channel state information (CSI) knowledge at the transmitter side, is presented. We show that the M-ZP-OFDM receiver outperforms the conventional MMSE-ZP-OFDM when either perfect or partial CSI (i.e., limited CSI) is available at the transmitter side. Index Terms-Zero-padding, orthogonal frequency division multiplexing (OFDM), equalization.
Frequency Domain Soft-Decision Feedback Equalization for SC-FDMA with Insufficient Cyclic Prefix
Qiucai Wang,Chaowei Yuan,Yingxue Li
International Journal of Computer Science Issues , 2012,
Abstract: Single-carrier frequency-division multiple access (SC-FDMA) system suffers performance degradation when the length of the cyclic prefix (CP) is less than the channel delay spread. In this paper, based on MMSE criterion, we proposed an efficient frequency domain soft-decision feedback equalization (FD-SDFE) scheme for SC-FDMA system. The proposed scheme employs residual inter-symbols cancellation (RISIC) algorithm, combining a prior information to reduce inter-block interference (IBI) and inter-carrier interference (ICI) component caused by the absence of CP in multipath fading channel. In addition, an FD-SDFE is derived to further mitigate the residual interference. Simulation results show that the proposed scheme has a significant performance improvement.
Coded OFDM by Unique Word Prefix  [PDF]
Mario Huemer,Christian Hofbauer,Johannes B. Huber
Mathematics , 2010,
Abstract: In this paper we propose a novel transmit signal structure and an adjusted and optimized receiver for OFDM (orthogonal frequency division multiplexing). Instead of the conventional cyclic prefix we use a deterministic sequence, which we call unique word (UW), as guard interval. We show how unique words, which are already well investigated for single carrier systems with frequency domain equalization (SC/FDE), can also be introduced in OFDM symbols. Since unique words represent known sequences, they can advantageously be used for synchronization and channel estimation purposes. Furthermore, the proposed approach introduces a complex number Reed-Solomon (RS-) code structure within the sequence of subcarriers. This allows for RS-decoding or to apply a highly efficient Wiener smoother succeeding a zero forcing stage at the receiver. We present simulation results in an indoor multipath environment to highlight the advantageous properties of the proposed scheme.
Interference Cancellation Schemes for Single-Carrier Block Transmission with Insufficient Cyclic Prefix  [cached]
Hayashi Kazunori,Sakai Hideaki
EURASIP Journal on Wireless Communications and Networking , 2008,
Abstract: This paper proposes intersymbol interference (ISI) and interblock interference (IBI) cancellation schemes at the transmitter and the receiver for the single-carrier block transmission with insufficient cyclic prefix (CP). The proposed scheme at the transmitter can exterminate the interferences by only setting some signals in the transmitted signal block to be the same as those of the previous transmitted signal block. On the other hand, the proposed schemes at the receiver can cancel the interferences without any change in the transmitted signals compared to the conventional method. The IBI components are reduced by using previously detected data signals, while for the ISI cancellation, we firstly change the defective channel matrix into a circulant matrix by using the tentative decisions, which are obtained by our newly derived frequency domain equalization (FDE), and then the conventional FDE is performed to compensate the ISI. Moreover, we propose a pilot signal configuration, which enables us to estimate a channel impulse response whose order is greater than the guard interval (GI). Computer simulations show that the proposed interference cancellation schemes can significantly improve bit error rate (BER) performance, and the validity of the proposed channel estimation scheme is also demonstrated.
Interference Cancellation Schemes for Single-Carrier Block Transmission with Insufficient Cyclic Prefix  [cached]
Kazunori Hayashi,Hideaki Sakai
EURASIP Journal on Wireless Communications and Networking , 2007, DOI: 10.1155/2008/130747
Abstract: This paper proposes intersymbol interference (ISI) and interblock interference (IBI) cancellation schemes at the transmitter and the receiver for the single-carrier block transmission with insufficient cyclic prefix (CP). The proposed scheme at the transmitter can exterminate the interferences by only setting some signals in the transmitted signal block to be the same as those of the previous transmitted signal block. On the other hand, the proposed schemes at the receiver can cancel the interferences without any change in the transmitted signals compared to the conventional method. The IBI components are reduced by using previously detected data signals, while for the ISI cancellation, we firstly change the defective channel matrix into a circulant matrix by using the tentative decisions, which are obtained by our newly derived frequency domain equalization (FDE), and then the conventional FDE is performed to compensate the ISI. Moreover, we propose a pilot signal configuration, which enables us to estimate a channel impulse response whose order is greater than the guard interval (GI). Computer simulations show that the proposed interference cancellation schemes can significantly improve bit error rate (BER) performance, and the validity of the proposed channel estimation scheme is also demonstrated.
Turbo Per-tone Equalization for MIMO OFDM Systems
MIMO OFDM系统中的Turbo子载波均衡

Liu Zhan-li,Zhao Chun-ming,Wang Jing,Meng Qing-min,
刘占利
,赵春明,王静,孟庆民

电子与信息学报 , 2007,
Abstract: To handle co-antenna interference, intersymbol interference (ISI) and intercarrier interference (ICI) caused by insufficient cyclic prefix, a MMSE-based Turbo per-tone equalization is presented for MIMO OFDM systems in this paper. A Soft-Input Soft-Out (SISO) per-tone equalizer exchanges soft information with SISO channel decoder through iterative process. Simulation results show that the proposed Turbo per-tone equalizers can effectively exploit time diversity and space diversity and offer performance gain over non-iterative equalizers.
BER PERFORMANCE OF OFDM SYSTEM WITH CYCLIC PREFIX & ZERO PADDING
Prafulla. D. Gawande,Sirddharth. A. Ladhake
International Journal of Advances in Engineering and Technology , 2013,
Abstract: Multicarrier schemes are supported to high data rate. Orthogonal Frequency Division Multiplexing (OFDM) and Filtered Multi-Tone (FMT) are two techniques of multicarrier schemes. OFDM is an attractive air-interface for next-generation wireless network without complex equalizer. OFDM is an emerging multi-carrier modulation scheme. It has been adopted by several wireless standards such as IEEE 802.11a, IEEE 802.16 and HiperLAN2. OFDM is designed such a way that it sends data over hundreds of parallel carrier which increases data rate. OFDM scheme is suffer by inter-symbol interference (ISI) problem. ISI is distortion in a signal in which one symbol interferes with subsequent symbols, this will degrade performance of OFDM system. There are several methods for reducing the effects of ISI. A guard interval insertion (cyclic prefix and Zero Padding) method is effective method to reduce the effect of ISI. Zero padding (ZP) of multicarrier transmissions has recently been proposed as an appealing alternative to the traditional CP to ensure symbol recovery. In this paper, we are studied the effect of CP and ZP on Bit Error Rate (BER) of OFDM technique with AWGN channel and Rayleigh fading channel. Through simulations, it is shown that the both techniques are effective in mitigating the effects of ISI. For high value of the CP and ZP, performances of both methods are better for Rayleigh fading channel as compared to AWGN channel. Simulation is performed by using MATLAB R2010a.
Effect of Cyclic Prefix on OFDM System
Miss Rashmi Mishra,Dr. Baibaswata Mohapatra,Mr. Nitin Naiyar
International Journal of Recent Technology and Engineering , 2012,
Abstract: Orthogonal Frequency Division Multiplexing(OFDM), because of its resistance to multipath fading, hasattracted increasing interest in recent years as a suitablemodulation scheme for commercial high-speed broadbandwireless communication systems. OFDM can provide large datarates. Orthogonal frequency division multiplexing (OFDM) isone of the Multi-Carrier Modulation (MCM) techniques thattransmit signals through multiple carriers. These carriers(subcarriers) have different frequencies and they are orthogonalto each other. There are different parameters which alters theperformance of OFDM system. This thesis analyzes OFDMsystem and the effect of cyclic prefix and length of cyclic prefixon OFDM system. Besides, compare the performance of thesystem with and without cyclic prefix and with differentRSF(Repeated Symbol Fraction).BER performance of theOFDM system is carried out with emphasis on the cyclic prefixand RSF. The simulation results show how a tradeoff is neededbetween reduction in multi-path effects and Transmissionefficiency.
Single Carrier Cyclic Prefix-Assisted CDMA System with Frequency Domain Equalization for High Data Rate Transmission  [cached]
Madhukumar AS,Chin Francois,Liang Ying-Chang,Yang Kai
EURASIP Journal on Wireless Communications and Networking , 2004,
Abstract: Multiple-access interference and interfinger interference limit the capacity of conventional single-carrier DS-CDMA systems. Even though multicarrier CDMA posses the advantages of conventional CDMA and OFDM, it suffers from two major implementation difficulties such as peak-to-average power ratio and high sensitivity to frequency offset and RF phase noise. A novel approach based on single-carrier cyclic prefix-assisted CDMA has been proposed to overcome the disadvantages of single-carrier CDMA and multicarrier modulation. The usefulness of the proposed approach for high-speed packet access with simplified channel estimation procedures are investigated in this paper. The paper also proposes a data-dependent pilot structure for the downlink transmission of the proposed system for enhancing pilot-assisted channel estimation in frequency domain. The performance of the proposed pilot structure is compared against the data-independent common pilot structure. The proposed system is extensively simulated for different channel parameters with different channel estimation and equalization methods and the results are compared against conventional multicarrier CDMA systems with identical system specifications.
Single Carrier Cyclic Prefix-Assisted CDMA System with Frequency Domain Equalization for High Data Rate Transmission  [cached]
Madhukumar A. S.,Chin Francois,Liang Ying-Chang,Yang Kai
EURASIP Journal on Wireless Communications and Networking , 2004,
Abstract: Multiple-access interference and interfinger interference limit the capacity of conventional single-carrier DS-CDMA systems. Even though multicarrier CDMA posses the advantages of conventional CDMA and OFDM, it suffers from two major implementation difficulties such as peak-to-average power ratio and high sensitivity to frequency offset and RF phase noise. A novel approach based on single-carrier cyclic prefix-assisted CDMA has been proposed to overcome the disadvantages of single-carrier CDMA and multicarrier modulation. The usefulness of the proposed approach for high-speed packet access with simplified channel estimation procedures are investigated in this paper. The paper also proposes a data-dependent pilot structure for the downlink transmission of the proposed system for enhancing pilot-assisted channel estimation in frequency domain. The performance of the proposed pilot structure is compared against the data-independent common pilot structure. The proposed system is extensively simulated for different channel parameters with different channel estimation and equalization methods and the results are compared against conventional multicarrier CDMA systems with identical system specifications.
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