Transmitted Orthogonal Frequency Division Multiplexing Signal Research Articles

Adaptive polarization transmission of OFDM signals in channels with polarization mode dispersion and polarization-dependent loss

A 2times2 multiple-input multiple-output (MIMO) architecture using dual-polarized antennas (DPAs) is considered with orthogonal frequency division multiplexing (OFDM). The performance of DPAs is evaluated for adaptive polarization (AP) transmission techniques in time-varying multipath channels impaired by polarization mode dispersion (PMD) and polarization-dependent loss (PDL). AP transmission techniques considered include power gain maximization, polarization dispersion minimization for interference avoidance, polarization multiplexing with water-filling, and a suboptimal multiplexing strategy that enables direct recovery of the polarization multiplexed streams, thereby simplifying the design of the receiver. Measured time-varying dual-polarized channel realizations from mobile-to-mobile experiments are used to estimate the capacity, diversity, and interference avoidance performance of the adaptive approaches.

An Effective SLM-PRSC Hybrid Scheme for OFDM PAPR Reduction

In order to improve OFDM (Orthogonal Frequency Division Multiplexing) PAPR (Peak-to-Average Power Ratio) reduction performance of the conventional SLM (SeLective Mapping), we propose an effective SLM-PRSC (PAPR Reduction Sub-Carrier) hybrid scheme. In the proposed scheme, after performing the SLM for the frequency domain OFDM symbol excluding pre-determined PRSC positions, the SLM-PRSC hybrid sequence with the lowest PAPR, which is generated by adding the time domain PRSC sequence to the results of the SLM, is selected as the transmitted OFDM signal. Since the identical PRSC sequences generated a priori are repeatedly used for every OFDM symbol, excessive IFFT (Inverse Fast Fourier Transform) calculation is avoided. Simulation results reveal that the proposed scheme significantly improves the PAPR reduction performance of the conventional SLM, while avoiding excessive increase of IFFT and PAPR calculation.

Theoretical Analysis of Decision Directed Block Iterative Channel Estimation for OFDM Mobile Radio

Orthogonal frequency division multiplexing (OFDM) is one of the promising transmission techniques for next generation mobile communication systems. Accurate channel estimation is essential for coherent OFDM signal transmission. So far, many pilot-assisted channel estimation schemes have been proposed. In the case of packet transmission, each received packet can be repeatedly processed by decision feedback to improve the channel estimation accuracy, resulting in a decision directed block iterative channel estimation (DD-BICE). However, decision feedback of erroneously detected data symbols degrades the packet error rate (PER) or bit error rate (BER) performance. In this paper, theoretical analysis is presented for the DD-BICE taking into account the decision feedback errors assuming quadrature phase shift keying (QPSK) data modulation. A 2-dimensional (2D) averaging filter is used for reducing the negative impact of decision feedback errors. The impacts of 2D averaging filter and antenna diversity reception are discussed and the validity of the theoretical analysis is confirmed by computer simulation.

A novel search method to reduce PAPR of an OFDM signal using partial transmit sequences

AbstractOne of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak‐to‐average power ratio (PAPR) of the transmitted OFDM signal. Partial transmit sequence (PTS) technique can improve the PAPR statistics of an OFDM signal. As ordinary PTS technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of sub‐blocks. In this paper, we propose a novel PTS technique with reduced complexity that each level inverts twice of phase factor bits from previous level. Then we also use initial random phase sequence to find the better search way of PAPR reduction. Numerical results show that the proposed method can achieve significant reduction in search complexity with little performance degradation. Copyright © 2006 John Wiley & Sons, Ltd.

PAPR Reduction of an OFDM Signal by Use of PTS With Low Computational Complexity

One of the major drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the transmitted OFDM signal. Partial transmit sequence (PTS) technique can improve the PAPR statistics of an OFDM signal. However optimum PTS (OPTS) technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of sub-blocks. By combining sub-optimal PTS with a preset threshold, a novel reduced complexity PTS (RC-PTS) technique is presented to decrease the computational complexity. Numerical results show that the proposed approach can achieve better performance with lower computational complexity when compared to that of other PTS approaches.

Nonlinear Companding Transform for Reducing Peak-to-Average Power Ratio of OFDM Signals

A new nonlinear companding transform scheme is proposed to reduce the peak-to-average ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) signals. By exploiting statistical distribution of transmitted OFDM signals, the proposed scheme effectively reduces the PAPR by compressing the peak signals and expanding the small signals, while maintaining the average power unchanged by properly choosing transform parameters. The fact that the proposed companding scheme is described by a single-valued function allows to be transformed before amplification and to be restored the signals at the receiver. The proposed scheme can be applicable with any modulation format and subcarriers. Our simulations results confirm that the suggested scheme exhibits a good ability to reduce PAPR and a good BER performance with a solid state power amplifier (SSPA) in an additive white Gaussian noise (AWGN) channel.

Effects of clipping and filtering on the performance of OFDM

Orthogonal frequency division multiplexing (OFDM) is an attractive technique for wireless communication applications. However, an OFDM signal has a large peak-to-mean envelope power ratio, which can result in significant distortion when passed through a nonlinear device, such as a transmitter power amplifier. We investigate, through extensive computer simulations, the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the crest factor, and the bit-error rate. Our results show that clipping and filtering is a promising technique for the transmission of OFDM signals using realistic linear amplifiers.