Generalized Frequency Division Multiplexing Research Articles

Deep learning-based receiver design for generalized frequency division multiplexing (GFDM)

Generalized frequency division multiplexing (GFDM) is a new efficient multi-carrier system in highly dispersive channels. In a conventional GFDM receiver, if the length of a GFDM block is the power of two (an even number), the equalizer can be implemented with low complexity using the fast Fourier transform (FFT). On the downside, if the block length is even, the GFDM matrix will be singular, leading to severe performance loss. Thus, in the conventional GFDM system, high performance and low complexity cannot be achieved jointly. This paper proposes a new GFDM receiver based on deep learning (DL) methods that can achieve high performance regardless of the GFDM block length. In the proposed GFDM receiver, a deep neural network (DNN) is used to demodulate GFDM symbols. A particular case of a convolutional neural network (CNN) and a fully connected layer are employed in the DNN block. We simulate the proposed DL-based GFDM system in additive white Gaussian noise (AWGN) and multipath channels. Simulation results show that the proposed receiver achieves a significantly higher bit error rate (BER) performance than the conventional GFDM receiver when the length of the GFDM block is even in both AWGN and fading channels. Therefore, the proposed DL-based GFDM receiver can achieve low complexity and high performance simultaneously.

Low-complexity GFDM transmission scheme for low earth orbit satellite communications

As a promising multi-carrier modulation scheme, Generalized Frequency Division Multiplexing (GFDM) has certain advantages in low earth orbit satellite communications. However, the cost of GFDM to obtain these advantages is the self-interference caused by non-orthogonality and the increase of computational complexity. This paper proposes two low-complexity transceiver schemes for GFDM based on matrix sparsity. Firstly, the paper summarizes two GFDM modulation structures, referred to as structure types I and II, based on modulation data. Next, the modulation matrix in both structures is divided into sub-matrices, and the modulation sub-matrix is made sparse by leveraging the properties of the Fourier transform, so as to reduce the complexity of the transmitter. Similarly, by performing sparse processing on the received matrix and converting it into a block diagonal matrix form, the complexity of the receiver can be effectively reduced. The computational costs of our proposed schemes are analyzed in detail and compared with the existing solutions that are known to have the lowest complexity. The simulation results demonstrate that the two proposed schemes can provide satisfactory low-complexity performance depending on the time–frequency structure.

Advanced NOMA-aided indoor optical wireless communications using improved quantum optimized resource

At present, Non-Orthogonal Multiple Access (NOMA) has become the most efficient technique to solve Data Rate (DR) requirements in Visible Light Communication (VLC) systems. However, present NOMA systems show high interference and increase the Peak-to-Average Power Ratio (PAPR), especially in wider applications. To overcome this issue, several techniques have been undertaken in the past and proven to better communication performance. However, the existing studies fail to provide a better Quality of Services (QoS) for the recent multi-carrier Optical Communication System (OCS). Hence, this study put forth a novel Generalized Frequency Division Multiplexing (GFDM) scheme to minimize the PAPR in an indoor-based NOMA-VLC system. To enhance the performance of the GFDM system, a novel Offset-based Quadrature Amplitude Modulation (OQAM) technique is introduced that enhances the signal quality and prevents the Co-Channel Interference (CCI) problems effectively. Moreover, the proposed study introduces a novel Quantum-enabled Rabbit Optimization (QRO) technique for solving Resource Allocation (RA) problems in the NOMA-VLC system. The proposed method is processed via the MATLAB platform and various performance measures like Sum Rate (SR), Signal-to-Interference Noise Ratio (SINR), and Symbol Error Rate (SER) are analyzed and distinguished with various existing studies. In the simulation scenario, the proposed method achieves the SR of 178Mbps, SINR of 16 dB, and SER of compared to conventional techniques.

PAPR reduction using polynomial based compressing with Rapp model in GFDM

Generalized Frequency Division Multiplexing (GFDM) has been considered as an attractive candidate to replace Orthogonal Frequency Division Multiplexing (OFDM) for the fifth generation (5 G) mobile networks. GFDM system has better spectral characteristics compared to the OFDM system due to the usage of properly selected pulse shaping filters. Non-causal ideal filters, such as the raised cosine (RC), are commonly used in the GFDM systems. Here, Generalized frequency division multiplexing is a promising candidate to deploy. However, as an intrinsic property of multi-carrier modulation, the high signal amplitude fluctuation can cause several degradation effects when the signal is affected by nonlinearities. The pulse shaping filters are designed using the computationally efficient quadratic programming (QP) approach. Therefore, the aim of this paper is to evaluate the performance of Generalized frequency division multiplexing systems undergoing nonlinear amplification. We evaluate the bit error ratio using high power amplifier, namely the Rapp model. The results show that the fault rate is apparently affected according to the particular high power amplifier model and its transmission parameters.

DHT-based GFDM and STC-GFDM systems for beyond 5G wireless networks

This manuscript endeavours an exploration of Generalized Frequency Division Multiplexing (GFDM) as a promising alternative to the Orthogonal Frequency Division Multiplexing (OFDM) in next-generation cellular networks. GFDM’s exceptional performance in minimizing out-of-band emissions (OOBE) and maximizing spectral efficiency (SE) makes it a compelling candidate, especially when integrated with Multi-Input Multi-Output (MIMO) technology to enhance reliability through spatial diversity. However, ensuring GFDM’s resilience against frequency-selective channels (FSCs), especially in low-latency scenarios, is crucial.This research investigates Discrete Hartley Transform (DHT) based GFDM and Space-Time Coded GFDM (STC-GFDM) systems, proposing a comprehensive framework to enhance performance metrics such as Bit Error Rate (BER) and Achievable Rate (AR). Further enhancements are achieved through a Minimum BER-Power Allocation (MBER-PA) strategy, optimizing BER and AR in QAM-based GFDM and STC-GFDM systems employing a DHT precoding scheme. Analytical expressions for BER and AR are derived and validated via Monte Carlo simulations. Additionally, a comparative analysis against traditional GFDM systems is conducted, evaluating metrics including Peak-to-Average Power Ratio (PAPR), BER, and AR.

Analysis of STC-GFDM with Walsh Hadamard in generalized η−μ fading channel

ABSTRACT This manuscript presents a comprehensive analytical framework for Walsh-Hadamard Transform (WHT) precoding in Space-Time Coded Generalized Frequency Division Multiplexing (STC-GFDM) systems. The investigation specifically targets the η - μ fading channel and employs the moment generating function (MGF) approach to establish an exact closed-form expression for the Symbol Error Rate (SER). The derived expression enables the examination of one-sided Gaussian, Rayleigh, Nakagami-m and Hoyt-q fading channels as specific cases of the η - μ fading channel. Additionally, the paper also delves into the impact of crucial system parameters, including modulation order, channel fading parameters ( η and μ ) and the number of transmit and receive antennas, on the WHT-STC-GFDM system’s performance. Furthermore, the paper conducts an in-depth complexity analysis of the WHT precoder, shedding light on the computational demands associated with its implementation. In summary, this research enhances the understanding of WHT precoding in STC-GFDM systems operating in η - μ fading channels, providing valuable insights for the design and optimisation of future communication systems. The numerical results are validated through Monte-Carlo simulations.

Modified Error Function Companding for reduction of PAPR in GFDM signals

Generalized Frequency Division Multiplexing (GFDM) is a multicarrier modulation technique, nevertheless, it provides high peak to average power ratio (PAPR) which affects the power amplifier (PA) efficiency. In this work, the modified error function companding is proposed for reducing PAPR in GFDM signals. The power scaling parameter (η) and companding parameter (a) are used to reduce the peak power. The average power is not altered in the proposed method, so there is no need to adjust the dynamic gain of PA. The theoretical expressions for the transform gain, achievable PAPR reduction and closed form expression of attenuation factor are derived. Moreover, the transform gain, attenuation factor, power spectral density, PAPR and bit error rate (BER) performance of the proposed method is analysed for different values of companding parameter. The results ensure that the proposed mEFC method at a=1 provides significant PAPR reduction than existing companding methods.

An Optimized Sequence for Sparse Channel Estimation in a 5G MIMO System

ABSTRACT Recently, the massive Multiple-Input Multiple-Output (MIMO) system has been integrated with machine learning approaches to realise automatic channel state information detection. These methods need high computational complexity due to the lack of optimal training sequences and the failure to control the sparsity assembly based on massive MIMO. Moreover, it does not consider optimised training sequences based on a compressive sensing approach in the presence of contamination. Thus, this paper proposed an enhanced deep learning model with an optimised pilot training sequence for sparse channel estimation in a 5 G massive MIMO system. Initially, the system and sparse block channel impulse response model will be constructed by considering the time-domain synchronous Generalized Frequency Division Multiplexing (GFDM) system and additive white Gaussian noise (AWGN). In the proposed work, a seagull optimisation algorithm is developed to design the training pilot sequence depending on the coherence properties of the sensing matrix, which is used to recover the channel impulse response. Then, the sparse massive MIMO channel is evaluated by proposing a new deep channel estimator with an enhanced stacked auto encoder (D-ESAE). The proposed channel MSE is 10−6, the bit error rate is 0.04, and NMSE is 10−9 at 40 dB SNR through Matlab simulation.

Eliminating intrinsic interference in GFDM systems: Design of a complex-valued prototype filter

Prototype filter design is a critical challenge in generalized frequency division multiplexing (GFDM) systems. Poorly designed filters can result in inherent and out-of-band (OOB) interferences, severely impacting system performance. This paper proposes a novel solution to this problem by introducing an optimal prototype filter that mitigates the adverse effects of intrinsic interferences in GFDM systems. Our approach involves using a complex-valued prototype filter, which resembles a single-sideband (SSB) modulation scheme and significantly enhances bandwidth efficiency compared to conventional GFDM. To design the optimal filter, we formulate an optimization problem that eliminates inband and adjacent subcarriers intrinsic interferences. We also provide analytical expressions for evaluating the system’s bit error rate (BER) and demonstrate the superiority of our optimized prototype filter over its current counterparts. To validate the design of the proposed prototype filter, we assess the noise enhancement factor (NEF). Our results indicate that our proposed filter improves system performance and reduces BER in GFDM systems.

Security analysis of encrypted audio based on elliptic curve and hybrid chaotic maps within GFDM modulator in 5G networks

Wireless communications face significant security challenges, so there is an ongoing necessity to develop an appropriate security strategy to protect data from eavesdroppers using cryptography based on chaos theory. Generalized frequency division multiplexing (GFDM) is a modern multicarrier waveform adaptable to 5G requirements, but its security issues have not been considered. Therefore, this paper proposed an efficient security technique within the GFDM modulator to protect the audio transmission against eavesdropping in 5G networks. The proposed GFDM is achieved by separating the subsymbols for the subcarrier into real and imaginary parts and combining them using a mixture of elliptic curve-linear congruential generator sequence (EC-LCG) with Ikeda and Tent maps, respectively. After that, the subsymbols of each subcarrier are permuted independently using the Duffing map. The effectiveness of the proposed approach to resist attacks was tested, and findings that were achieved are histogram, signal to noise ratio (SNR=-27.8068), spectral segment SNR (SSSNR=-34.9912), peak SNR (PSNR=0.9142), frequency weighted log spectral distance (dFWLOG=37.498), cepstral distance (dCD=9.0176), mean square error (MSE=0.82097), keyspace, and speed. These results show that the proposed model provides a high-security level, high speed in the encryption/decryption, large keyspace, and high sensitivity to the initial conditions.

Advanced lifting wavelet transform and V‐degree polynomial‐based channel estimation in MIMO‐GFDM

SummaryThe future generation of wireless communications systems uses the generalized frequency division multiplexing (GFDM) due to its viable candidate waveform to perform multiple user scheduling. It is a non‐orthogonal waveform susceptible to intercarrier and intersymbol interference (ISI); still, it offers flexible pulse shaping that enhances the efficiency of user scheduling. Here, to accomplish spatial diversity, the multiple‐input multiple‐output (MIMO) is incorporated with GFDM to enhance the performance; there is also an extra inter‐antenna interference problem that limits the model's performance. The issue concerning inter‐antenna interference can be resolved by adopting pilot‐based information transfer. The detection of a signal at the receiver based on the minimum mean square error has the issue of computational complexity while enhancing the estimation quality of a detector. Hence, a low‐complexity channel estimation technique is proposed in this research using the V‐degree polynomial‐based channel estimation technique, wherein the cubic order computation is reduced to square order. Also, the proposed adaptive pulse shaping technique, wherein the filter coefficient is optimized using the gazelle optimization algorithm (GOA) to provide optimal pulse shaping filter parameters by employing bit error rate (BER) as the objective function. The performance of a proposed V‐degree polynomial‐based channel estimation is analyzed based on various assessment measures like BER and MSE and acquired the minimal values of 5.75E‐05 and 2.07E‐05, respectively.

Unipolar GFDM With Dimming Support for Visible Light Communications

We propose and analyze a unipolar generalized frequency division multiplexing (GFDM) modulation scheme with dimming support for visible light communications (VLC). In the proposed method, the dimming level can be controlled at a transmitter using a single parameter that a receiver need not know. In addition, the dimming parameter can be adjusted by the transmitter at any time without affecting the quality of data transmissions. Expressions of the illumination percentage and the bit error rate (BER) are derived taking into account the dimming parameter, and validated through comparisons with simulation results. Using these expressions, it is possible to specify the dimming parameter at the transmitter based on the desired illumination percentage and estimate the corresponding BER for data transmissions. Numerical results indicate that, compared to adjusting the direct current (DC) bias for dimming control, the proposed method provides a wider dimming range subject to a constraint on the BER.

DGT-based pulse shaping filter for Generalized Frequency Division Multiplexing system

The future wireless communication systems belonging to the next generation will encounter many diverse demands, like the need for data rates that surpass the capabilities of fifth-generation networks, ultra-low power consumption to cater to battery-operated communication sensors, and extremely short response times essential for control applications. A unified physical layer waveform is envisaged to address these flexible requirements, introduced as Generalized Frequency Division Multiplexing (GFDM) for beyond 5G (B5G) communication systems. One of the important features of GFDM is the utilization of flexible pulse shaping filtering in the time domain, resulting in improved performance. In this paper, a pulse-shaping filter is designed for the GFDM system using discrete Gabor representation, discrete biorthogonality condition and Wigner distribution. An analytical expression for the analysis window is derived using the biorthogonality condition. Further, the performance of the GFDM system is analyzed in terms of out-of-band (OOB) radiation and symbol error rate (SER). The results are presented for the Quadrature Amplitude Modulation (QAM) scheme over Additive White Gaussian Noise (AWGN), Rayleigh, Nakagami-m, two wave with diffuse power (TWDP), and Nakagami-q fading channels. The detailed analysis shows that the OOB radiation and SER performance exhibit strong dependence on the choice of the pulse shaping filter.

Performance of GFDM system with channel estimation error over FTR mmWave channels for 5G and beyond communication

Millimeter-wave (mm-Wave) communication are the building block of the beyond 5G (B5G) generations. For mm-Wave communication, the fluctuating two-ray (FTR) fading channels serve as an appropriate model for the small-scale fading. Generalized frequency division multiplexing (GFDM) is envisioned as one of the potential candidate to fulfil the requirements of B5G communication systems. This paper presents the performance analysis of a GFDM system over the FTR fading environment. In this analysis, both GFDM and space–time coded (STC) GFDM system has been considered, and an exact closed-form expression of the average symbol error rate (ASER) is derived for the μ-QAM modulation technique under imperfect channel estimation condition. The simulation results demonstrate excellent agreement with the numerical results obtained for GFDM and STC-GFDM systems with different channel and system parameters such as m, Kf, Δ, TA, RA, ϱA2 and μ. An asymptotic analysis is also done for both systems.

Adaptive threshold for discrete fourier transform‐based channel estimation in generalized frequency division multiplexing system

AbstractEven though generalized frequency division multiplexing is an alternative waveform method expected to replace the orthogonal frequency division multiplexing in the future, its implementation must alleviate channel effects. Least‐squares (LS), a low‐complexity channel estimation technique, could be improved by using the discrete Fourier transform (DFT) without increasing complexity. Unlike the usage of the LS method, the DFT‐based method requires the receiver to know the channel impulse response (CIR) length, which is unknown. This study introduces a simple, yet effective, CIR length estimator by utilizing LS estimation. As the cyclic prefix (CP) length is commonly set to be longer than the CIR length, it is possible to search through the first samples if CP is larger than a threshold set using the remaining samples. An adaptive scale is also designed to lower the error probability of the estimation, and a simple signal‐to‐interference‐noise ratio estimation is also proposed by utilizing a sparse preamble to support the use of the scale. A software simulation is used to show the ability of the proposed system to estimate the CIR length. Due to shorter CIR length of rural area, the performance is slightly poorer compared to urban environment. Nevertheless, satisfactory performance is shown for both environments.

A Novel partial sequence technique based Chaotic biogeography optimization for PAPR reduction in generalized frequency division multiplexing waveform

For Orthogonal Frequency Division Multiplexing (OFDM) systems, the most significant problem is the peak-to-average power ratio. The utilisation of partial transmission sequence, often known as PTS, is an efficient method for reducing PAPR. When it comes to minimizing the peak-to-average power ratio (PAPR) in Orthogonal Frequency Division Multiplexing (OFDM) Systems, PTS is one of the most effective approaches that may be used. Due to the substantial data load, using peak-to-average power ratio in OFDM is challenging. The most crucial problem with OFDM is achieving better results by lowering PAPR. Provide a PTS in this research that is based on the Chaotic Biogeography Based Optimization (CBBO) algorithm to effectively address the high PAPR issue that exists in Generalized Frequency Division Multiplexing (GFDM) waveforms using Hermitian Symmetry property is used. The Hermitian symmetry is utilised in order to acquire a real-valued time-domain signal. Phase rotation factor combinations are carried out in an effective and optimal manner through the utilisation of an innovative combination of optimization techniques. In comparison to conventional optimization techniques, a new hybrid optimization offers quick convergence quality and minimal complexity. When compared to traditional PTS methods such traditional GFDM and OFDM-PTS, experimental results demonstrate that the suggested CBBO-PTS technique significantly improves on minimizing PAPR.

An Efficient Multiplexing Technique For 5G Wireless Network: Analysis and Selection

The 5G cellular communication technology is intended to base on the present Long-TermEvolution (LTE) 4G networks with adopted features. Features of low power consumption and theconstant power level should be the major requirement for an efficient channel allocation method. In thisresearch work, an analysis was performed on multiplexing techniques: Orthogonal Frequency DivisionMultiplexing (OFDM), Generalized Frequency Division Multiplexing (GFDM), Universal FilteredMulticarrier (UFMC) and Filter-Bank Multicarrier (FBMC). Smooth power level had been analyzedaccording to Power Spectral Density (PSD) function vs normalized frequency using AWGN channelmodel. The simulation was done by MATLAB 2019 Simulink software for OFDM and GFDM that werefurther compared to existing results of UFMC and FBMC multiplexing techniques. Calculated power forOFDM and GFDM were 32.1mW and 40.23 µW respectively. Comparative results showed the bettersmooth power spectrum, micro-watt power consumption and better hardware configuration for GFDM.That’s why GFDM channel allocation method selection is one step ahead for the next generationmultiplexing technique

GFDM Zero Forcing Equalizer for Large Doppler Shift in Correlated Double Ring Channel Models

The nature of wireless communication channels evolves throughout time. Depending on the channel model, wireless communication channels can also be affected by a number of key factors. In the Correlated Double Ring (CDR) wireless channel model, the channel gain parameters are affected by the movement of vehicles on the transmitter and receiver sides as well as the amount of scatterers surrounding the transmitter and receiver. When bits are transmitted across the CDR channel using a Generalized Frequency Division Multiplexing (GFDM) multi-carrier system, the received bit will be degraded as a result of Doppler shift and multipath. To circumvent this, we use a Zero Forcing (ZF) equalizer to correct the erroneous bits on the receive side. In this study, we simulate data bits transmitted via a CDR channel at various speeds, ranging from low speed to high speed, using a GFDM multicarrier system. The ZF equalization method that we propose to overcome the higher Doppler frequency on a high-speed CDR channel of 95 m/s with the scatterer of 8 has been demonstrated to increase Bit Error Rate (BER) performance in comparison to the emergence of a ZF equalization scheme. In order to counteract the vast number of up to 16 multipaths on CDR channels, the ZF equalization approach can improve the BER performance at 95 m/s when compared to when it is not employed. On the Rician CDR channel, the ZF equalization algorithm can efficiently overcome the highly significant Doppler effect and multipath fading.

Intelligent-Reflecting-Surface-Assisted GFDM Communication Systems

Demands for higher data rates is an inevitable fact. Therefore, the effect of the frequency selectivity and time variation of communication channels will be more significant. One effective technique to combat the doubly dispersive channels is generalized frequency division multiplexing (GFDM) scheme. Nevertheless, nonorthogonality of the used prototype filter can deteriorate the GFDM performance. On the other hand, intelligent reflecting surface (IRS) is a new revolutionary technology for future wireless networks. IRS can smartly reconfigure the propagation environment in order to improve the efficiency of the communication systems. In this article, IRS is applied in a GFDM communication system to enhance the system's performance. In this way, an IRS-assisted GFDM communication system model is proposed. The goal is to design the reflecting coefficients of the IRS such that the total noise power at a GFDM block is minimized. In order to obtain an effective solution, the optimization problem is converted to a quadratically constrained quadratic program (QCQP). The developed QCQP problem is convex, which can be solved by using an iterative algorithm. An analytical derivation of the maximum achievable rate (MAR) and bit error rate (BER) of the proposed IRS-assisted GFDM system is provided. Also, in simulations, the performance of the proposed method is compared with the conventional GFDM system in terms of MAR and BER. Simulation results confirm that using IRS by employing the proposed method dramatically improves the performance of a GFDM system.

Predistorter for Nonlinear Distortion Mitigation in GFDM Systems

Next-generation wireless systems use the non-orthogonal modulation technique known as generalized frequency division multiplexing (GFDM). The nonlinearity of the high-power amplifier (HPA) greatly affects the performance of the wireless system. Without phase distortion and only amplitude distortion in the GFDM system using HPA Model Rapp. The effects of nonlinear distortion that occur involve distortion of the amplitude, signal constellation distribution, and spectral distribution. There are two contributions to this paper. First, the impact of HPA Model Rapp's nonlinear distortion on the GFDM system in the AWGN (additive white Gaussian noise) and Rayleigh channels was investigated. The simplicity of this model is the reason it was picked and has an AM/AM (amplitude modulation/amplitude modulation) curve. Second, the linearization of HPA with the use of a predistorter method in GFDM systems has been proposed. The nonlinear distortion impact of HPA can be mitigated by this predistorter. This technique is implemented in the transmitter section. The system performance investigated is determined by a bit error rate (BER) analysis, a constellation diagram, and a spectrum analysis. HPA generates a 55 dB rise in out-of-band (OOB) in the signal spectrum. The HPA effect was successfully compensated for by a 55 dB decrease in the OOB value of the predistorter system.