Frequency-selective Rayleigh Fading Channels Research Articles

A use-case efficient DFrFT-based index modulated-OFDM system in the presence of CFO

Index modulated orthogonal frequency division multiplexing (OFDM-IM) only utilizes partial resources to transmit signals according to use case requirement, it leads to higher energy efficiency and spectral efficiency than the classical OFDM. However, in the presence of inter-carrier interference (ICI) due to carrier frequency offset (CFO), the performance of index modulated OFDM system severely deteriorates. To mitigate this issue, a novel discrete fractional Fourier transform (DFrFT) based OFDM-IM scheme over Rayleigh frequency selective fading channel is proposed in this paper. The optimum DFrFT angle (αopt) for this new scheme at various CFO values has been calculated theoretically. Incorporating these estimated αopt, the proposed system achieves a gain of 8 dB over conventional FFT-based OFDM-IM at bit error rate (BER) = 10−3 in a high normalized CFO (ϵ) environment (ϵ=0.2). The system model is also verified for different user applications, i.e., high data rate and low data rate applications. Simulation and analytical results show that the proposed model has a robust and superior performance compared to the conventional FFT-based OFDM-IM, DFrFT-based OFDM, and classical OFDM. Moreover, the proposed DFrFT-OFDM-IM model achieves all these superiorities with the same complexity as the conventional FFT-based OFDM-IM system.

Design and Simulation of MIMO Systems over Rayleigh Fading Channel and Using Near-Maximum-Likelihood Detection

While coding is the main element for the success of the MIMO system implementation, the communication channel is the main component that ascertains this. This paper describes the design and simulation of a 2x2, 4x4, and 8x8 MIMO system which is used exclusively in 5G mobile systems. The detection performed in such a system is near-maximum-likelihood detection. The noise added at the front end of the receiver is additive white Gaussian noise with zero mean and variance which depends upon the signal-to-noise ratio (SNR) while the signal is transmitted over a frequency-selective Rayleigh fading channel. The MIMO system operates at a much higher level of complexity to exploit the channel space-time resources. Orthogonal space-time block codes are used at the transmitter. An Image is transmitted and the received image is compared with the transmitted image and BER is calculated. This is done for varying SNRs. The whole project is performed over a front-end application where the various parameters are populated and run. This makes the simulation extremely easy for the 2x2 or 4x4 or 8x8 MIMO application with varying channel parameters. The modulation scheme used in this work is BPSK.

Performance analysis of FBMC/OQAM systems in frequency-selective channels

Filter bank multicarrier (FBMC) systems based on offset QAM modulation (FBMC/OQAM) represent an interesting alternative to the widely used OFDM scheme for machine type communications or cognitive radio. In this paper the performance of FBMC/OQAM systems exploiting a single-tap receiver in frequency-selective Rayleigh fading channels, is analyzed. In particular, the SER and the asymptotic SER (i.e., for a large number of subcarriers) for any prototype filter, is derived. Moreover, a simple closed-form approximate expression of the asymptotic SER is obtained by taking into account, for each active subcarrier, only intersymbol interference terms due to the considered subcarrier and the adjacent subacarriers, and intercarrier interference terms due to the adjacent subcarriers. The numerical results show that the obtained SER expression can predict the actual performance of the system while the asymptotic SER expression provides a useful upper-bound. Moreover, the curves obtained by exploiting the derived simple closed-form approximate expression can be used to predict the asymptotic upper-bound when the considered prototype filter is adopted.

Impact of carrier frequency offset and in-phase and quadrature imbalance on the performance of wireless precoded orthogonal frequency division multiplexing

<p>Precoding in orthogonal frequency division multiplexing (OFDM) system proved to reduce the peak-to-average power ratio (PAPR), so that it improves BER. However, from the existing literature, the effect of carrier frequency offset (CFO), in-phase and quadrature (IQ) imbalance on precoded wireless OFDM systems has not been carried out. Therefore, this study evaluated the precoded OFDM (P-OFDM) system performance by considering the impact of CFO and IQ imbalance. P-OFDM performance evaluation is expressed in signal-to-interference noise ratio (SINR) and bit error rates (BER). The communication channels used are the additive white Gaussian noise (AWGN) channel and the frequency-selective Rayleigh fading (FSRF) channel, while the channel equalization process is considered perfect. The results of the analysis and simulation show that P-OFDM is greater affected by the presence of CFO and IQ imbalance than conventional OFDM system. In AWGN channel, P-OFDM experiences different SINR for each subcarrier. This is different from conventional OFDM system, where all SINRs are the same for all subcarriers. In the FSRF channel, both the POFDM system and the OFDM system experience different SINR for each subcarrier, where the SINRs fluctuation in the P-OFDM system is much larger than in the OFDM system.</p>

DATA TRANSMISSION IN MIMO-OFDM TECHNOLOGIES FOR CURRENT AND FUTURE WIRELESS COMMUNICATION SYSTEMS: FROM THEORY TO PRACTICE

This paper presents a Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) communication system with space-time and space-Frequency block coded (STBC/SFBC) of present generation downlink channel. Space-time block coding (STBC) and space-frequency block coding are transmit diversity schemes used in a wireless communication system to mitigate the effect of channel fading. The system is aimed to reduce the error rate (BER) by mitigating the effect of multipath fading which increase the quality of the system. In the proposed system, 2 transmit and 2 receive antennas are used, to transmit modulated symbols of block N across an OFDM channel, using SFBC Alamouti’s based encoding algorithm (SFBC-OFDM) derives from the basic criteria for space-time block codes (STBC). The signals from the first and second antennas are encoded and transmitted simultaneously in space and frequency over frequency-selective Rayleigh fading channel using two adjacent carriers. The work examines the SFBC and spatial diversity benefits realized based on the BER performance. The result is simulated effectively using MATLAB application software and the BER performance is compared with the conventional STBC-OFDM. It is shown that both STBC and SFBC techniques achieve similar performance with a diversity gain of four (4) over a slow fading channel with 2 antennas at both ends of the link under simple processing across the transmit and receive antennas.

Asymptotic performance of FBMC-PAM systems in frequency-selective Rayleigh fading channels

This paper deals with the performance analysis of the recently introduced FBMC-PAM system, a multicarrier scheme that represents a promising alternative to OFDM to meet the requirements of cognitive radio or machine type communications. An analytical expression of the symbol error-rate (SER) of the single-tap sub-channel (SC) equalizer designed as the inverse of the complex gain that multiplies the symbol of interest at the output of the filter matched to each subcarrier, is derived. Specifically, an asymptotic (i.e., for a large number of subcarriers) analytical expression of the SER of the SC receiver operating in frequency-selective Rayleigh fading channel is obtained and compared via simulation results. Moreover, a simple approximate closed-form expression of the asymptotic SER of the SC receiver is obtained by taking into account, for each active subcarrier, only inter-symbol interference (ISI) terms due to the considered subcarrier and adjacent subcarriers, and, moreover, inter-carrier interference (ICI) terms due to adjacent subcarriers.

The effects of DC offset in direct-conversion receivers for WLAN systems

In this paper, the effects DC offset in direct-conversion receivers for WLAN systems are analyzed using both experimental and simulation data. DC offset estimation is performed by using data-aided methods which are based on the short training sequence of WLAN preamble. In the simulations, DC offset and frequency offset estimations are carried out on the signals affected by frequency selective Rayleigh fading channel and additive white Gaussian noise. Estimation performance of the methods is compared for different SNR levels and frequency offset values in terms of mean square error. Experimental data which is in the form of WLAN packets and transmitted through a wireless channel is captured by using a software defined radio. The experimental performance of the DC offset compensation methods is evaluated in terms of transmission success ratio.

Maximum-Likelihood-Based Performance Enhancement of Clipped and Filtered OFDM Systems With Clipping Noise Cancellation

Clipping and filtering (CAF) technique is known as a simple and effective approach that reduces the peak-to-average power ratio (PAPR) of orthogonal frequency-division multiplexing (OFDM) signals at the cost of increasing in-band distortion. Clipping noise cancelation (CNC) can compensate for the performance degradation due to the in-band distortion caused by CAF, especially when the number of subcarriers is large, but its achievable symbol error rate (SER) performance is in general worse than that of the unclipped OFDM systems. In this letter, we propose an additional compensation scheme based on the maximum likelihood (ML) metric. We reveal that the proposed approach can even outperform the unclipped OFDM systems, only with moderate increase of complexity from the conventional CNC. Furthermore, we demonstrate that significant gain resulting from the diversity effect can be achieved in the case of frequency-selective Rayleigh fading channels.

A Comparative Performance Analysis of Channel Equalizer in OFDM System Under Jamming Attacks

In this article, the accomplishment of OFDM systems under different jamming attacks is analyzed. Partial band jamming signal suppressing OFDM data packets partially and full band jamming signal suppressing all OFDM data packets are examined in this study. Computer simulation works are carried out to analyze the achievement of the OFDM system over AWGN and frequency selective Rayleigh fading channels under both jamming attacks. In addition, comparative performance analysis of different equalizer structures in frequency selective Rayleigh fading channel environment is performed. From the obtained results, it is seen that frequency domain equalizers combat jamming attack signals in the best way and provide the best performances.

On Low-Complexity MMSE Channel Estimation for OCDM Systems

In this letter, we first present a time-domain model for pilot-assisted MMSE channel estimation in the orthogonal chirp division multiplexing (OCDM) systems. Then by proposing a pilot selection criterion, the complexity of MMSE channel estimation is reduced by the simplification of matrix inversion. Meanwhile, we prove that the criterion can lead to the optimal mean square error (MSE) performance. Furthermore, based on the criterion, by adopting the Zadoff-Chu sequences as pilots and presenting a split-and-decomposition algorithm, we propose a low-complexity channel estimator for OCDM. The complexity of the proposed estimator is <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> (Nlog\frac L2), while the estimator in existing literature for OCDM is <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> (NlogN), where L is the channel length and N is the number of subcarriers. Numerical results are provided to verify the performance of the proposed algorithm over frequency-selective Rayleigh fading channels. It turns out that the proposed estimator can significantly reduce the computational complexity without any MSE performance loss.

Performance Analysis of p/4 DQPSK for FrFT-OFDM System with Carrier Frequency Offset

The Orthogonal Frequency Division Multiplexing (OFDM) has widely been used in broadband wireless communication due to its ability to efficiently utilize the spectrum with mu lticarrier communication. In this paper BER expression for π/4 DQPSK modulation has been derived from FrFT based OFDM system in the presence of carrier frequency offset (CFO) under frequency selective Rayleigh fading channel. The performance of proposed system has been evaluated and compared with the FFT based OFDM system. It is found that the FrFT based OFDM system outperforms the FFT based OFDM. BER analysis has also been done for various values of α (FrFT angle parameter) on said FrFT based OFDM system, however the system responds best at α = 0.9 as compared with other values of α. Improvement as high as up to 23 dB in SNR has been achieved with the proposed FrFT based OFDM system at α = 0.9 for said modulation with carrier frequency offset of 0.1 under frequency selective Rayleigh fading channel.

On the performance of FBMC-PAM systems in frequency-selective Rayleigh fading channels

Filter bank multicarrier (FBMC) techniques are emerging alternatives to the widely used orthogonal frequency division multiplexing (OFDM) schemes for applications such as machine type communications or cognitive radio. Recently an FBMC scheme based on a sine prototype filter with overlapping factor K=2 termed FBMC-PAM has been introduced. It assures an interesting performance, a reduced system latency and is robust to carrier-frequency offset. After presentation of the system model, an analytical expression of the BER of the single-tap sub-channel equalizer for the considered FBMC-PAM system operating in frequency-selective Rayleigh fading channel is obtained and compared with simulation results. Moreover, a performance comparison with an approximate single-tap sub-channel equalizer and with the previously proposed FBMC-PAM-2M, is presented.

High-Dimensional OFDM With In-Phase/Quadrature Index Modulation

In this paper, we propose a new modulation scheme for wireless communications called high-dimensional orthogonal frequency division multiplexing with in-phase/quadrature index modulation (HD-OFDM-IQ-IM). In the proposed scheme, coordinate values of a symbol of the HD signal constellations are separated. A part of the coordinate values of an HD symbol are mapped to the active in-phase component subcarriers and the rest are mapped to the active quadrature component subcarriers in each OFDM subblock. A simple rule to design the HD constellation using the Gray coding and mapping is also presented. The method increases the minimum Euclidean distance between symbols of an HD signal constellation by increasing the Hamming distance of the binary sequences. As the dimension of the constellation increases, more index patterns can be produced, thus improving spectral and energy efficiency of the HD-OFDM-IQ-IM scheme. A feasible selection of subcarrier component active patterns can also produce additional index patterns to enhance spectral efficiency without additional energy consumption. In the receiver, both maximum likelihood (ML) and reduced-complexity log-likelihood ratio (LLR) detection can be exploited. As a result, the proposed scheme has better bit error performance than the conventional OFDM system with IM techniques in the frequency selective Rayleigh fading channel. In particular, it is noted that the bit error rate (BER) in the high signal-to-noise ratio (SNR) region is tightly limited by the upper bound on bit error probability derived in this paper.

Energy-Efficient Index Modulation With In-Phase/Quadrature Format in the Generalized Fading Channel

Dual-mode (DM) or multi-mode (MM) index modulation (IM) techniques with the in-phase/quadrature (IQ) format have been investigated for improving the performance of the orthogonal frequency division multiplexing with IM (OFDM-IM) system in the frequency-selective Rayleigh fading channel. However, all subcarriers in these schemes must be activated so that the energy efficiency (EE) of the system inevitably decreases. In this paper, we propose a novel modulation scheme named quadrature tri-mode index modulation (QTM-IM) technique to achieve a trade-off between the spectral efficiency (SE) and EE. The proposed QTM-IM can also be flexibly extended into multi-mode form called MM with enhanced IQ (MM-EIQ). The multi-mode $M$ -ary pulse amplitude modulation (PAM) constellations containing the origin point are designed to map the information bits into the active subcarriers. On the other hand, the theoretical analysis of IM-based schemes over the Rician fading channel has been conducted since most previous papers only considered the Rayleigh fading channel. At the receiver, three kinds of detectors with different algorithm complexities are employed for signal demodulation. Finally, the computer simulation results demonstrate the enhancement of the proposed schemes. More specially, (i) QTM-IM achieves 4dB signal-to-noise ratio (SNR) gain at the BER level of 10−5 compared with quadrature DM (QDM) scheme with the same SE in the Rician fading channel and (ii) MM-EIQ harvests 0.89 bits/s/Hz SE gain and almost doubles the EE compared with MM-IQ scheme without any SNR loss over the Rayleigh fading channel.

A Near-Optimal and Low-Complex Joint Multiuser Detection for QCSS-MC-CDMA System

Joint maximum likelihood (ML) multiuser detection for quasi-synchronous multicarrier code division multiple access (MC-CDMA) system has an excessive computational complexity, and it increases exponentially as the number of users and bits in each of the modulation symbols increases. Recently, sphere decoding (SD) has been adopted for multiuser detection whose complexity is polynomial in nature with the number of users, and it does not rely on the number of bits in the modulation. In this article, first we provide a construction of large size quasi-complementary sequence sets (QCSSs), and then a low-complexity optimum SD algorithm is proposed to detect the multiuser communication in QCSS-based MC-CDMA (QCSS-MC-CDMA) system. The complexity analysis has shown that the proposed SD-based QCSS-MC-CDMA receiver for multiuser communication provides lower complexity than that of ML-based QCSS-MC-CDMA receiver. We also show that peak to average power ratio of the proposed system is lesser than that of complete complementary code (CCC) based MC-CDMA (CCC-MC-CDMA) system. The proposed system overcomes the fractional delay problem which is noticed for CCC-MC-CDMA receiver. The bit error rate performance of the proposed SD-based QCSS-MC-CDMA system is compared with maximum ratio combining based MC-CDMA, ML-based MC-CDMA, frequency domain equalization based MC-CDMA, and CCC-MC-CDMA receivers over Rayleigh frequency selective fading channels. The work is validated through Monte Carlo simulation results.

FFT‐Based Multiband Spectrum Sensing in SIMO In‐band Full‐Duplex Cognitive Radio Networks

AbstractThis paper presents fast Fourier transform (FFT)‐based multiband spectrum sensing over multipath Rayleigh frequency selective fading channels in single input multiple output (SIMO) in‐band full‐duplex (FD) cognitive radio (CR) networks (FDCRNs) under residual self‐interference (RSI). In this work, first, multiband energy detection using Neyman Pearson criterion is proposed in FDCRNs under RSI, where the secondary user is equipped with multiple receive antennas to exploit spatial diversity. Next, a two‐dimensional averaging is done to overcome spectrum leakage problem occurring due to FFT operation in orthogonal frequency division multiplexing (OFDM) system. The closed form expressions for average probability of detection and probability of false alarm are derived for SIMO FDCRNs under RSI. Further, RSI cancelation is performed employing noise robust wavelet decomposition‐based least squares scheme and the corresponding simulation studies indicate that the proposed algorithm further improves the detection performance in SIMO FDCRNs.

Secure Information Transmission with Self Jamming SWIPT

This article is focused on implementing simultaneous wireless information and power transmission as a physical layer security measure by using artificial noise. A series of high energy precoded symbols is simultaneously transmitted along with the information symbols over a Rayleigh frequency selective fading channel. The high energy precoded symbols act as an artificial noise for the eavesdroppers. The energy symbols are precoded on the basis of a legitimate user’s channel matrix to form a null space vector, which eliminates the interference of energy symbols at the information symbol receiver antennas, while allowing the rectenna to harvest energy from the superimposed information and energy symbols. We analyze the secrecy rate and error rate performance at the receiver under different circumstances, and we show that the performance of the legitimate user can be improved by using the iterative block decision feedback equalization method at the receiver.

A space-frequency block codes MIMO single-carrier code-frequency-division multiple access system

In this paper, a novel space frequency block codes MIMO single-carrier code-frequency-division multiple access (SFBC MIMO SC-CFDMA) transceiver is proposed. The proposed SFBC SC-CFDMA system allocates a unique spreading code for each user. The proposed SFBC SC-CFDMA system offers robustness against the effect of carrier frequency offsets (CFOs). The proposed SFBC SC-CFDMA system is suggested to improve both of the peak-to-average power ratio (PAPR) performance and the bit error rate (BER) performance. The simulation results show that the proposed SFBC SC-CFDMA system has superior improvements in the BER performance over the traditional SFBC SC-FDMA system. Moreover, the PAPR performance of the proposed SFBC SC-CFDMA system is better than that of the traditional system for the case of a localized mapping scheme. Furthermore, BER analysis for the proposed SFBC SC-CFDMA and traditional SFBC SC-FDMA system over a frequency-selective Rayleigh fading channel is presented for the case of zero-forcing (ZF) equalizer and QPSK modulation.

Review of Channel Estimation for Candidate Waveforms of Next Generation Networks

The advancement in wireless communication applications encourages the use of effective and efficient channel estimation (CE) techniques because of the varying behaviour of the Rayleigh fading channel. In most cases, the emphasis of most proposed CE schemes is to improve the CE performance and complexity for ensuring quality signal reception and improved system throughput. Candidate waveforms whose designs are based on filter bank multi-carrier (FBMC) modulation techniques such as filter bank orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM), universal filtered multicarrier (UFMC) and generalised frequency division multiplexing based on offset quadrature amplitude modulation (GFDM-OQAM) are no exception to the use of these proposed CE techniques in the literature. These schemes are considered as potential waveform candidates for the physical/media access control layer of the emerging fifth generation (5G) networks. Therefore, pinpoint CE techniques represent an important requirement for these waveforms to attain their full potentials. In this regard, this paper reviews the concept of CE as applicable to these waveforms as well as other waveform candidates under consideration in the emerging 5G networks. Since the design of the majority of the waveform candidates is filter based, a review of the general filter design considerations is presented in this paper. Secondly, we review general CE techniques for candidate waveforms of next generation networks and classify some of the studied CE techniques. In particular, we classify the CE schemes used in filter bank OFDM-OQAM and GFDM-OQAM based transceivers and present a performance comparison of some of these CE schemes. Besides, the paper reviews the performances of two linear CE schemes and three adaptive based CE schemes for two FBMC based waveform candidates assuming near perfect reconstruction (NPR) and non-perfect reconstruction (Non-PR) filter designs over slow and fast frequency selective Rayleigh fading channels. The results obtained are documented through computer simulations, where the performances of the studied CE schemes in terms of the normalised mean square error (NMSE) are analysed. Lastly, we summarise the findings of this work and suggest possible research directions in order to improve the potentials of the studied candidate waveforms over Rayleigh fading channels.

A space wavelet block codes MIMO SC-WDMA systems

In this paper, a novel space-wavelet block codes single-carrier wavelet-division multiple access (SWBC SC-WDMA) multiple-input multiple-output (MIMO) transceiver is proposed. The proposed MIMO transceiver system improves both of the bit error rate (BER) performance and the peak-to-average power ratio (PAPR) performance. Bit error rate (BER) analysis of the proposed SWBC SC-WDMA system over a frequency selective Rayleigh fading channel is presented for the case of zero-forcing (ZF) equalization and QPSK modulation. Comparisons of the BER and PAPR performances between the proposed SWBC SC-WDMA system and the conventional space-frequency block codes single-carrier frequency-division multiple access (SFBC SC-FDMA) system are illustrated. The simulation results show that the proposed SWBC SC-WDMA system has superior improvements in both PAPR and the BER performances.