Wavelet-based OFDM Research Articles

Peak-to-Average Power Ratio reduction in Wavelet based OFDM using Modified Selective Mapping for Cognitive Radio Applications

The prospect of guaranteed quality of service for primary and secondary users in the expression of regulated Peak-to-Average Power Ratio (PAPR) and Bit Error Rate (BER) can be increased in Cognitive Radios using Wavelet based OFDM systems which localize spectrum in realms of time and frequency. However, cutting the Gordian knot of high PAPR associated with the Multi-Carrier Modulation schemes to operate in the linear part of the power amplifier nourishing the balance between PAPR and BER is difficult. In this paper, the phase of the subcarriers is altered by a value of finite, equally spaced phase shifts. The frame of Wavelet-based OFDM (WOFDM) with minimum PAPR guarantees the minimum quality of service (QoS) in terms of Throughput. BER is then identified and transmitted. This modification is applied to various Wavelets and compared amongst WOFDM and FFT-based OFDM schemes. The novelty of this paper lies in using Hadamard and/or Toeplitz matrix to generate phase sequences in a modified SLM technique of Wavelet-based OFDM systems while maintaining the minimum required QoS in Cognitive Radios. The result shows that the proposed technique reduces the PAPR compared to unmodified SLM techniques. HIGHLIGHTS Wavelet based OFDM systems localize spectrum in realms of time and frequency The sinusoid bases function in OFDM has been replaced by Wavelet bases Selective Mapping (SLM) is a popular technique towards PAPR reduction The primary function of the Cognitive Radio system is to identify the spectrum holes GRAPHICAL ABSTRACT

Performance of FFT-OFDM versus DWT-OFDM under Compressive Sensing

In this work, we present a comparative study on the performance of Fourier-based OFDM (FFT-OFDM) and wavelet-based OFDM (DWT-OFDM) under compressive sensing (CS). Transmission over FFT-OFDM and DWT-OFDM, which has been made under different baseband modulation schemes such as Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Key (QPSK), Quadrature amplitude modulation (16QAM) and (64QAM) has been considered. From numerical simulation results, it is observed that the Wavelet-based OFDM system outperforms Fourier based OFDM when the Quadrature Amplitude Modulation is 16QAM and 64QAM within the signal to noise ratios range 30 to 40 dB. Although CS is more efficient in compression than classical compression techniques, it introduces more errors over OFDM transmission. Future directions of this work are also suggested.

Analysis of WOFDM over LTE 1.25 MHz Band

Orthogonal Frequency Division Multiplexing (OFDM) is the one of the most preferred multiplexing technique for realizing high-speed wireless communication, like Long Term Evolution (LTE) and LTE-Adv. In the era of digital wireless communication, applications of wavelet theory have been favorably applied in many areas of signal processing. Orthogonality, flexible time-frequency analysis, and the ability to characterize signals accurately have attracted the attention of the telecommunication community to use wavelet as a basis function for OFDM. In this paper, discrete wavelet transform (DWT) has been proposed as an alternative signal analysis with multiple merits such as support high-speed applications, immune to distortion, wavelet diversity, better error performance, and efficient bandwidth utilization. A simulative analysis of various wavelets, at different modulation techniques, over OFDM has been presented to demonstrate the improvement in BER performance. Further, in accordance with the LTE parameterization over 1.25 MHz band, the performance of wavelet-based OFDM (WOFDM) is found significantly higher in terms of maximum achievable data rate and system spectral efficiency.

Performance evaluation of ICI self-cancellation schemes in fractional wavelet-based OFDM system

The widely used multi carrier modulation technique in the current wireless scenario is orthogonal frequency division multiplexing (OFDM). It is severely affected by frequency offsets and leads to inter carrier interference (ICI). Fractional wavelet transforms (FrWT)-based OFDM model is proposed to mitigate the effect of ICI by its orthogonal fractional wavelets. The performance of FrWT involved OFDM model is comparatively analysed through various mapping schemes of ICI self-cancellation in order to mitigate frequency offsets. This system overcomes the drawback of ICI self-cancellation and shows improved bandwidth efficiency without any cyclic prefix. Simulation results are carried out for the proposed model and compared with exiting Fourier transform and wavelet transform-based OFDM system. The analysis is performed for a range of normalised frequency offsets values. The proposed model performance is tested with various mapping schemes against a frequency offset of 0.05. It is proved that FrWT-based OFDM with ICI self-cancellation gives reduced bit error rate (BER) of 10–5 at 8 dB signal to noise ratio (SNR). From various graphs, it states that weighted conjugated transformation results in effective mitigation of ICI with BER achievement of 10-4.4 at frequency offset of 0.1.

Performance evaluation of ICI self-cancellation schemes in fractional wavelet-based OFDM system

Performance evaluation of ICI self-cancellation schemes in fractional wavelet-based OFDM system

A Novel Selected Subcarrier Method for Digital Video Broadcasting

In Digital Video broadcasting there are two types of information namely global and local content. Broadcasting both information using multifrequency network requires large spectrum. To overcome that single frequency network is incorporated.Inorder to transmit both the information in a single frequency network, a novel technique, namely selected subcarrier method of Digital Video Broadcasting is proposed. This technique is well suited in a scenario where the transmission of two different information is targeted over the entire globe at the same time. This methodology proficiently handles the concept of Orthogonality principles among the OFDM subcarrier. In this technique certain dedicated subcarrier is used for transmission of Local content in the network.Also, wavelet-based OFDM has been proposed, which outperforms the existing Fourier based OFDM

A Novel Selected Subcarrier Method for Digital Video Broadcasting

In Digital Video broadcasting there are two types of information namely global and local content. Broadcasting both information using multifrequency network requires large spectrum. To overcome that single frequency network is incorporated.Inorder to transmit both the information in a single frequency network, a novel technique, namely selected subcarrier method of Digital Video Broadcasting is proposed. This technique is well suited in a scenario where the transmission of two different information is targeted over the entire globe at the same time. This methodology proficiently handles the concept of Orthogonality principles among the OFDM subcarrier. In this technique certain dedicated subcarrier is used for transmission of Local content in the network.Also, wavelet-based OFDM has been proposed, which outperforms the existing Fourier based OFDM

Fractional Wavelet Transform based PAPR Reduction Schemes in Multicarrier Modulation System

The future mobile communication system stimulates researcher to improve the spectral efficiency with reduced data loss by carrying out several works. High peak to average power ratio (PAPR) of the transmitted signal is the major drawback in the multicarrier transmission like orthogonal frequency division multiplexing. This study presents a novel way to improve the performance of the multicarrier transmission system with the reduction of PAPR. It is achieved by reconstructing the Fourier-based OFDM block with the help of fractional wavelet transform. This transform provides the accurate joint information of time and fractional frequency contents of the signal which highlights the proposed system. In this system, the wavelet transform is utilized to remove the usage of cyclic prefix and to improve the bandwidth efficiency. In addition, the analysis of PAPR in the FrWT-based OFDM is carried out with the help of selective mapping (SLM) and partial transmit sequences (PTSs) techniques. The simulated results are compared with the existing PAPR analysis of Fourier and wavelet-based OFDM systems. The proposed system shows reduced PAPR of 6.6 dB with SLM scheme and 4.8 dB with PTS scheme to achieve complementary cumulative distribution function of 10−3. The overall performance of the FrWT-OFDM transceiver is analyzed by means of bit error rate (BER) plots and it also shows BER reduction of 0.0028 with SLM scheme and 0.0012 with PTS scheme at high SNR of 16 dB.

Mitigating Impulsive Noise for Wavelet-OFDM Powerline Communication

Advanced metering infrastructure (AMI) is an important application of smart grid communication technology used for the remote monitoring and control of smart meters. Broadband powerline communication (BB-PLC) systems could perhaps be used for AMI; however, impulsive noise (IN) greatly degrades performance. In addition to the fast Fourier transform (FFT)-based orthogonal frequency-division multiplexing (OFDM), IEEE 1901 specifications have defined the other physical layer called wavelet-based OFDM. Even though many existing studies have reported the IN mitigation algorithms for the FFT-based OFDM system, these approaches may not directly apply to the wavelet-OFDM-based PLC systems. In this paper, we propose a robust receiver for PLC systems based on wavelet-OFDM. The proposed receiver comprises a pre-IN mitigation block, an adaptive inverse discrete wavelet transform, and an iterative IN reconstruction block. The iterative cancellation of strong IN samples leads to a gradual improvement in the quality of the received signal. Instead of using the frequency domain approach, we reduce the inter-dependency of the channel estimation and per-subchannel equalization by using the time domain signal processing. Besides, we apply variable step-size adaptive algorithms to reduce the impact of IN during the training processes for the channel estimator and per-subchannel equalizer. In accordance with IEEE 1901 specifications, we built a simulation environment to evaluate the effectiveness of the proposed method. Simulation results demonstrated that conventional blanking devices fall short in terms of IN mitigation, and that the proposed scheme is able to achieve performance values approaching those obtained in cases without IN.

Performance comparison of DFT, DCT and DWT based OFDM with wavelet family to minimize PAPR

The paper presents the analysis of peak average power ratio (PAPR) performance of wavelet based OFDM (WOFDM) using wavelet families. We study on several wavelet from different wavelet families to find out the PAPR performance. The WOFDM system using, Haar, Daubechies, Symlets, Coiflets, Biorthogonal, and discrete Meyer. WOFDM using QPSK modulation to reduce PAPR. Discrete Fourier transform (DFT) and discrete cosine transform (DCT) to compare discrete wavelet transform (DWT). These transform, that DCT with ‘Haar’ and ‘biorthogonal’ shows better improvement among the wavelet families since the PAPR achieve almost 5 dB. Keywords: OFDM, PAPR, DCT, DFT, DWT, Wavelet family

Comparative Analysis of Modulation Techniques in LTE: A Ber Study of Conventional and Wavelet-Based OFDM

Comparative Analysis of Modulation Techniques in LTE: A Ber Study of Conventional and Wavelet-Based OFDM

Analysis and Simulation of Wavelet Carrier Modulation with Clipping Techniques in Mobile WiMAX

The implementation of OFDM results in relatively high peak-to-average power ratio (PAPR) due to IFFT process to generate orthogonal subcarriers. A number of studies have attempted to apply various techniques to minimize PAPR by apllying the Wavelet transform as a substitution for Fourier transform. Another technique used to reduce the PAPR is clipping. In this thesis, the clipping technique was applied on the Wavelet based OFDM in mobile WiMAX standard to obtain better performance. The results indicate that Wavelet based OFDM has better immunity to noise and more resistant to Doppler shift than Fourier based OFDM. Sym 7 with Classical clipping and CR 1.2 can be selected and applied on wavelet-based OFDM in mobile WiMAX.

Optimal deactivated sub‐carriers guard bands for spectrum pooling systems based on wavelet‐based orthogonal frequency division multiplexing

Cognitive radio (CR) is an advanced technology for efficient use of radio resources. In the CR system, the spectrum pooling technique is used to enhance spectrum utilisation, which enables public access to the spectral ranges of the licenced frequency bands which are seldom used by overlaying an unlicenced user (unLU) on an existing licenced user (LU). The spectrum pooling system constructed by implementing wavelet-based orthogonal frequency division multiplexing (WOFDM) owns better flexibility and bandwidth efficiency. However, the interference between the LU and the unLU is severe in the multipath wireless channel. In the study, the intercarrier interference (ICI) interference energy of the spectrum pooling-based WOFDM is analysed and an optimal deactivated subcarriers algorithm for the guard bands is proposed to mitigate the ICI between the unLU and the LU by intelligently deactivating one or more of the optimal deactivated subchannels which generates the maximum ICI interference in the LU. The numerical and the simulation results show that the data transmission rate of the unLU is ensured, the ICI of the LU is reduced and the bit error rate performance of the LU is, respectively, improved by implementing the algorithm.

Performance comparison of wavelet based and conventional OFDM systems in multipath Rayleigh fading channels

In this work, the performance of wavelet based OFDM (WOFDM) is studied and compared to that of conventional OFDM over multipath Rayleigh fading channels with exponential power delay profile. Results show that WOFDM has better bit error rate (BER) performance than conventional OFDM without cyclic prefix (CP) for all signal-to-noise ratios (SNRs) and also outperforms OFDM with CP for low SNR values in indoor and outdoor environments. Therefore, WOFDM might be an alternative to conventional OFDM since it also has better bandwidth efficiency.

A Novel Haar Wavelet-Based BPSK OFDM System Robust to Spectral Null Channels and with Reduced PAPR

Orthogonal frequency-division multiplexing (OFDM) has lately gained a great deal of attention and is considered as a strong candidate for many next-generation wireless communication systems. However, OFDM is very sensitive to nonlinear effects due to the high peak-to-average power ratio (PAPR) owned by the transmitted signals and does not show robustness to spectral null channels. This paper proposes a novel BPSK OFDM system based on Haar wavelet transformation. The Haar wavelet transformation operates decomposition over the data symbol sequence after binary-to-complex mapping shows that half of the data symbols are zeros and the rest are either \({\sqrt{2}}\) or \({-\sqrt{2}}\). Then, we have the PAPR reduced by \({10\log_{10} 2\approx 3}\) dB at most, compared with the conventional OFDM system. We also propose a novel decoding algorithm for the proposed OFDM system to show robustness to spectral null channels, and derive the bit error rate (BER) performance in theory from unbalanced QPSK modulation. Finally, we compare BER performance of our proposed OFDM with the conventional OFDM over different channels to show the excellent performance of our proposed OFDM system.

Reducing PAPR by selecting optimal wavelet tree structure in WOFDM

The major disadvantage of wavelet based Orthogonal Frequency Division Multiplexing (WOFDM) system is high peak-to-average power ratio (PAPR) of the transmit signal. A new method is presented to obtain a set of optimal wavelet packet basis by constructing the PAPR optimization model and the optimal PAPR of system can be obtain by modulating the signal with the optimal wavelet packet basis. Numerical and simulation results show the new algorithm obtains better bit error rate (BER) performance than the threshold method and the PAPR values of the WOFDM system with fixed wavelet packet tree space and fixed number of sub-channel can be optimized without any side information required.

The performance of multiwavelets based OFDM system under different channel conditions

In wireless communication reception, the reliability of orthogonal frequency division multiplexing (OFDM) is limited because of the time-varying nature of the channel. This causes inter-carrier interference (ICI) and increases inaccuracies in channel tracking. This can effectively be avoided at the cost of power loss and bandwidth expansion by inserting a cyclic prefix guard interval before each block of parallel data symbols. However, this guard interval decreases the spectral efficiency of the OFDM system as the corresponding amount. Recently, it was found that based on Haar-orthonormal wavelets, discrete wavelet-based OFDM (DWT-OFDM) is capable of reducing the inter symbol interference (ISI) and ICI, which are caused by the loss in orthogonality between the carriers. DWT-OFDM can also support much higher spectrum efficiency than discrete Fourier-based OFDM (DFT-OFDM). In this paper the DFT-OFDM is replaced by Multiwavelets OFDM (DMWT-OFDM) in order to further reduce the level of interference and increase spectral efficiency. It is found that proposed Multiwavelet design achieves much lower bit error rates, increases signal to noise power ratio (SNR), and can be used as an alternative to the conventional OFDM. The proposed OFDM system was modeled tested, and its performance was found under different channel conditions.

Better wavelet packet tree based OFDM for multipath powerline channel

In this work, better wavelet packet tree structures are searched to reduce the sum of ISI and ICI powers (integrated power) in Daubechies wavelet-based OFDM system over a practical two path low-voltage powerline channel or two way multipath channel. Better wavelet tree structures are obtained by using a brute-force algorithm. Results show that better wavelet packet tree structures perform better than conventional Mallat structures for the same bandwidth occupancy.

Better wavelet packet tree structures for PAPR reduction in WOFDM systems

This paper presents a proper way to reduce the peak-to-average power ratio (PAPR) in Daubechies (Db) wavelet-based OFDM (WOFDM) by searching better wavelet packet tree (BWPT) structures. These BWPT structures are obtained by using a brute force search algorithm. Numerical and simulation results also show that BWPT structures have lower PAPR values than conventional Mallat structures without any degradation in bit error rate (BER) performance for the same bandwidth occupancy. In addition, this PAPR reduction method does not introduce any additional complexity to WOFDM system since BWPT structures are obtained by selecting the proper ones from wavelet packet tree space.