Arafat J. Al-Dweik

PAPR Reduction Scheme using Maximum Cross Correlation

This letter presents an efficient technique to reduce the impact of nonlinear power amplifiers on the bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) systems. The proposed technique is based on the well-established Partial Transmit Sequence (PTS), a power amplifier model, and a simple single point cross correlator. Unlike the conventional PTS, the optimum phase sequence in the proposed system is selected by maximizing the correlation between the input and output of the power amplifier model. Simulation results have confirmed that the BER using the proposed technique is almost identical to the state-of-the-art while the complexity of the proposed optimization metric is significantly reduced.

Exact Performance Analysis of Synchronous FH-MFSK Wireless Networks

In this paper, a new approach is presented to derive the exact bit-error-rate (BER) performance of frequency-hopping spread-spectrum (FHSS) wireless networks with noncoherent M-ary frequency-shift keying (MFSK) in additive white Gaussian noise (AWGN) and Rayleigh fading channels. The new approach has enabled an exact evaluation of the BER, regardless of the modulation order M or the number of interferers. Theoretical results validated by simulations have shown that system performance is dominated by the first two hits, which lead to an accurate and computationally efficient approximation for the AWGN channel case. The exact and approximated results are compared with the simulation and semianalytic results presented in the literature.

Blind iterative frequency offset estimator for orthogonal frequency division multiplexing systems

This study presents an iterative carrier frequency offset estimator for orthogonal frequency division multiplexing (OFDM) systems. The proposed estimator is based on the efficient Viterbi-and-Viterbi (VAV) algorithm. The proposed estimator is blind and can be used with non-constant modulus subcarrier modulations such as quadrature amplitude modulation (QAM). The performance of the proposed estimator is assessed theoretically and via Monte Carlo simulations over various channel models and compared to the performance of other well established blind techniques in addition to the Cramer–Rao lower bound. The comparison results demonstrate that the proposed estimator outperforms other well-established blind estimators by more than 12u2005dB at moderate and high signal-to-noise ratios (SNRs).

The effect of timing errors on frequency offset estimation in OFDM systems

This work considers the effect of timing errors on the carrier frequency offset (CFO) estimation for orthogonal frequency division multiplexing (OFDM) systems. In general, most of the research conducted on OFDM systems assume that a wide range of timing errors can be tolerated due to the use of cyclic prefix (CP). Although such assumption might be valid for bit error rate (BER) analysis, it might not be the case for other processes such as CFO estimation. In this work, Monte Carlo simulations have been used to evaluate the effect of timing errors on the performance of several state-of-the-art CFO estimators for OFDM systems. The considered estimators include time domain, frequency domain, data-aided (DA) and blind estimators. Simulation results confirmed that particular CFO estimators, which are known to be highly accurate in perfect timing conditions, are very sensitive to timing offsets even if the offsets are within the inter-symbol-interference (ISI) free region of the CP. Other estimators offered high robustness for timing offsets in the entire range of the CP region. However, most of the considered estimators suffered from a severe performance degradation for timing errors out of the CP region.

Time- and Frequency-Domain Impulsive Noise Spreader for OFDM Systems

In this work, a new technique for mitigating the impulsive noise impact on the orthogonal frequency division multiplexing (OFDM) system is proposed, and its performance is compared with a previously published technique (referred to as time-domain interleaving (TDI) technique). In the TDI technique, the samples contaminated by impulsive noise are spread in timedomain over N OFDM symbols by using an interleaver after the inverse fast Fourier transform (IFFT) process. Accordingly, the effect of the impulsive noise burst will be averaged over N OFDM symbols, which reduces the impact on the bit error rate (BER) considerably. However, to achieve the same goal, the proposed system is using an additional orthogonal transform in form of an IFFT at the output of the interleaver. In general, the two techniques have shown a superior improvement in BER performance compared to that of the standard OFDM system, which suffers from error floors at high values of signal to noise ratio (SNR). However, for quadrature phase shift keying (QPSK) modulation with low signal to impulsive noise ratio (SIR), the proposed technique outperforms the TDI technique for different impulsive noise distributions. For high modulation order 16 and 64 quadrature amplitude modulation (QAM) in severe impulsive noise channels, the proposed technique demonstrates more robustness than the TDI, which suffers from error floors for the considered values of SIR and impulsive noise distributions.

An Efficient Technique for OFDM Systems over Fading Channels Impaired by Impulsive Noise

In this work, an elegant interleaving process is used not only to mitigate the impact of bursty impulsive noise on the performance of orthogonal frequency division multiplexing (OFDM) systems but also to break bursty multipath fading channel errors. While, conventional OFDM systems implement the interleaving process in the frequency domain, the system proposed here uses a block interleaver of size N2 samples in the time domain. As a result, time diversity has been exploited through the use of the interleaver by spreading the samples contaminated by impulsive noise over the impulse-free OFDM symbols and breaking the correlated behaviour of the multipath fading channel. Nevertheless, the results, given in this work, have shown that the performance of the proposed system depends on the kind of equalization process used. A serious degradation in the performance is noticed when zero forcing (ZF) equalizer is utilized. However, a simple and low complexity solution to improve the ZF equalizer performance is also proposed. On the other hand, utilizing a minimum mean square error (MMSE) equalizer demonstrates better performance than the ZF equalizer. The simulation results have confirmed the validity of the proposed system over different scenarios of the channels considered in this work.

Robust early-late gate system for symbol timing recovery in MIMO-OFDM systems

This paper presents a robust timing recovery scheme for orthogonal space-time block coding (OSTBC) multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with constant modulus constellation. In the proposed system, the symbol timing is achieved either by minimizing the power difference between adjacent subcarriers in one STC block or between subcarriers with similar indices in consecutive STC blocks. The proposed technique is totally blind because it does not require any prior information about the channel state or the transmitted data. The early-late gate (ELG) configuration is utilized to realize the proposed timing recovery scheme efficiently. Monte Carlo simulations are used to assess the performance of the two realizations of the proposed system over fading channels with different frequency-selectivity conditions. Simulation results demonstrated the superiority of the proposed technique to provide accurate symbol timing even in severe frequency-selective fading channels which remarkably outperforms other timing metrics.

Symbol timing offset estimation scheme for OFDM systems based on power difference measurements

This paper presents a new blind symbol timing offset (STO) estimation scheme for wireless orthogonal frequency division multiplexing (OFDM) systems with constant modulus constellation. In the proposed scheme, the STO estimation is performed by minimizing the power difference between either adjacent or consecutive subcarriers, which basically depends on the assumptions made on the channel conditions. Monte Carlo simulation is used to assess the two realizations of the proposed system. The system performance is evaluated by means of mean squared error (MSE) over additive white Gaussian noise (AWGN) and frequency selective mobile radio channels. The simulation results demonstrate that the MSE of the proposed system is well below the MSE of other well-established estimators reported in the literature.

Blind scheme for carrier frequency offset estimation in MIMO-OFDM systems

In this paper, a blind carrier frequency offset (CFO) estimation method for multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems is proposed. The proposed method is based on minimizing the power difference between all subcarriers in two consecutive space-time coding (STC) blocks. The cost function has a simple closed-form expression and the CFO can be estimated accurately using only three trial values. The performance of the proposed estimator is assessed via Monte Carlo simulation. Simulation results illustrate the superior performance of the proposed scheme for MIMO-OFDM systems when compared with other blind techniques.

CORDIC based architecture for blind CFO estimation in OFDM systems

This paper discusses the architectural aspects for the implementation of blind carrier frequency offset (CFO) estimation in orthogonal frequency division multiplexing (OFDM) systems using coordinate rotational digital computer (CORDIC). Multiplexed-stream architecture (MSA) for the considered CFO estimation algorithm has been designed and evaluated for field programmable gate array (FPGA) implementation using Xilinx system generator (XSG) tool. The proposed architecture is a resource-efficient implementation where a single fast Fourier transform (FFT) core can be shared between the parallel-streams. The effect of finite hardware precision on the CFO estimation accuracy is accessed in terms of mean square error (MSE). The simulation results demostrated that the proposed architecture consumes at least 25% less resources compared with the parallel-stream implementation.