Single-carrier Frequency-division Multiplexing Research Articles

Enhanced performance of an indoor non-line-of-sight VLC system utilizing a multi-pixel photon counter and interleaved single-carrier FDM scheme

A non-line-of-sight (NLOS) visible light communication (VLC) system, utilizing a multi-pixel photon counter (MPPC) as the detector and interleaved single-carrier frequency division multiplexing (I-SC-FDM) scheme, was first proposed and experimentally investigated in this work. Specifically, the I-SC-FDM scheme exhibits a significantly lower peak-to-average power ratio (PAPR) than the original orthogonal frequency division multiplexing (OFDM) and widely used discrete Fourier transform spread (DFTs)-OFDM schemes, thereby necessitating a much lower power gain, which is greatly beneficial for indoor power-sensitive VLC systems. Meanwhile, the implementation of an MPPC with high sensitivity enables the detection of faintly scattered light and thus facilitates the possibility of omnidirectional optical transmission based on indoor NLOS links. Following this, an MPPC-based omnidirectional VLC system was developed and successfully achieved a net data rate up to 18 Mbps in a 3.6 m × 3 m × 3 m room, with a joint deployment of the I-SC-FDM scheme and hybrid time-frequency domain equalization (TFD-EQ) strategy. Such results can be viewed as an expansion of indoor VLC systems beyond line-of-sight (LOS) links and serve as a reference for the practical application of Light-Fidelity (LiFi) in future optical wireless access.

90-m/660-Mbps Underwater Wireless Optical Communication Enabled by Interleaved Single-Carrier FDM Scheme Combined With Sparse Weight-Initiated DNN Equalizer

In this paper, we first utilize the interleaved single-carrier frequency division multiplexing (I-SC-FDM) scheme with a novel sparse weight-initiated deep neural network (SWI-DNN) equalizer for underwater optical communication (UWOC) systems. In addition to the superior characteristics of I-SC-FDM over the original OFDM and localized SC-FDM (L-SC-FDM), such as lower peak-to-average power ratio (PAPR) and lower computational complexity, the implementation of a special sparse weight-initiated (SWI) structure can significantly reduce the necessary training epochs up to 10.3%, which enables the proposed SWI-DNN equalizer to outperform the traditional random weight-initiated DNN equalizer. Besides, further pruning operation can dramatically enhance the final sparsity of the SWI-DNN equalizer to 96.88% at the expense of an inappreciable performance penalty, thereby effectively saving occupied computing resources. Following this, a data rate of up to 660 Mbps over a 90-m underwater transmission can be achieved in a standard 50-m swimming pool, with a relatively low received optical power of -31.12 dBm (at the BER of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ). Such a data rate is 17.9% higher than that obtained with a common hybrid time-frequency domain (TFD) equalizer. Moreover, the computational complexity of the SWI-DNN equalizer after pruning operation is only 11.83% of that of the hybrid TFD equalizer and can still support a 625-Mbps transmission. This is the first time to employ I-SC-FDM combined with an SWI-DNN equalizer for long-distance high-speed UWOC transmission, and it can be highly beneficial to the cost-sensitive and power-sensitive systems in future deployment.

FBMC-Based Random Access Signal Design and Detection for LEO Base Stations

The integration of non-terrestrial networks into the 5G ecosystem is mainly driven by the possibility of provisioning service in remote areas. In this context, the advent of flying base stations at the low Earth orbit (LEO) will enable anywhere and anytime connectivity. To materialize this vision, it is of utmost importance to improve radio protocols with the aim of allowing direct satellite access. Bearing this aspect in mind, we present a new random access signal, which is based on the filter bank multicarrier (FBMC) waveform, and a computationally efficient detection scheme. The proposed solution outperforms the standardized access scheme based on single-carrier frequency division multiplexing (SC-FDM), by reducing out-of-band (OOB) emissions and reducing the missed detection probability in presence of very high carrier frequency offset (CFO), which is inherent to LEO satellite systems. The improvement is related to the fine frequency resolution of the detector and the use of pulse shaping techniques. Interestingly, the FBMC-based random access signal achieves a high level of commonality with 5G new radio, as the preamble generation method and the time-frequency allocation pattern can be kept unchanged. Concerning the practical implementation aspects, the complexity of the detector is similar in both SC-FDM and FBMC.

Noise analysis and massive MIMO modelling in VLC for 5G networks using EKF with SCFDM

Visible Light Communications (VLC) is the type of communication, which processes high-speed data transmission using the visible Light Emitting Diodes (LED). The VLC acts as an important supplementary that is used to define the hotspots for heterogeneous networks and plays an important role for 5G networks in wireless communications. However, performance of visible light systems is affected by various noises and Allan variance is used to analyze such noises in 5G networks. The Massive Multiple-Input and Multiple-Output (M-MIMO) technique is used for noise modeling which utilizes the mitigation circuit to find whether the noise is white noise, shot noise, random walk noises or typical noises. The existing Kalman Filter approach failed to attain the required bandwidth and higher spectral efficiency. Therefore, to achieve high data rates, the spectral efficient technologies such as Single Carrier Frequency Division Multiplexing (SCFDM) is performed in the research. The Allan Variance is utilized for analyzing the time-series that extracts the noise features of the data and the major noise is verified and considered by the M-MIMO technique. The present research uses the Extended Kalman Filter (EKF) which determines the observation models and the state transition that does not need linear functions to define the states. The proposed SCFDM was constructed based on the VLC for 5G networks that analyzes in terms of Bit Error Rate (BER) and Signal to Noise Ratio (SNR). The proposed SCFDM obtains a high SNR of 14% for the channels with white LED option when compared to the existing methods.

Dimming control scheme based on hybrid LACO-SCFDM for visible light communications

This paper proposes a hybrid layered asymmetrically clipped optical (HLACO) single-carrier frequency-division multiplexing (SCFDM) scheme for dimmable visible light communication. It designs a signal structure that combines layered asymmetrically clipped optical (LACO)-SCFDM and negative LACO-SCFDM in proportion for improving the inherent weaknesses of orthogonal frequency-division multiplexing (OFDM)-based dimmable schemes and further enhancing the system performance. Compared to the HLACO-OFDM-based dimming scheme, it obtains a lower bit error ratio and enables efficient communication over broader dimming range. Its spectral efficiency realizes 2.875 bit·s−1·Hz−1 within the dimming range of 30%–70%, and the attainable average spectral efficiency gains exceed at least 19.21% compared to other traditional dimmable schemes.

Effective PAPR reduction in SCFDM‐based massive MIMO system using binary crow search algorithm for visible light communication towards 5G networks

Presently, the single-carrier frequency division multiplexing (SCFDM)-based visible light communication (VLC) system is extensively implemented for secure and high-speed data transmission. However, the effect of additive white Gaussian noise in VLC with white light-emitting diode is high, due to a high peak to average power ratio (PAPR). To address this difficulty in 5G networks, two objectives were carried out in this research article. Initially, selective mapping (SLM) scheme was applied for PAPR reduction, because it considerably selects the effective phase rotation factors that help in the reduction of system complexity. Besides, binary crow search algorithm was used for sub-block partition optimisation in SLM for enhancing the convergence speed of the proposed SCFDM-based VLC system. In the experimental investigation, the proposed SCFDM-based VLC system was analysed in terms of complementary cumulative distribution function, bit error rate and signal-to-noise ratio by varying the equalisation techniques for 5G networks.

New Satellite Random Access Preamble Design Based on Pruned DFT-Spread FBMC

Next generation satellite payload technology is expected to provide digital processing capabilities. This will pave the way to regard satellites as flying base stations. However, the initial access procedure must be improved. In this work we focus on non-geostationary earth orbit (NGEO) satellite networks. In this scenario, the random access preamble signal and the detection must be robust to large carrier frequency offsets (CFOs). Towards this end, we investigate the adoption of the pruned discrete Fourier transform spread filter bank multicarrier waveform. The proposed design is suitable for the access scheme of forthcoming 5G-based NGEO satellite communications. The reason is twofold. First, it improves the spectral confinement with respect to the standard single-carrier frequency-division multiplexing (SC-FDM) waveform. Second, it achieves a high level of commonality with 5G new radio, by keeping unchanged the subcarrier spacing, the slot duration and the preamble sequence. Remarkably, the new design allows the straightforward application of non-coherent post detection integration (NCPDI) techniques, which divide the correlation in blocks. Numerical results show that the proposed solution reduces out-of-band emissions and the missed detection probability in presence of CFO, with respect to the conventional approach based on SC-FDM and preamble detection with full-length correlation.

A Time-Domain Approach to Channel Estimation and Equalization for the SC-FDM System

Similar to orthogonal frequency division multiplexing receiver, the frequency-domain (FD) channel estimation (CE) and equalization are indispensable parts in the coherent single carrier frequency division multiplexing (SC-FDM) receiver. When the channel varies slowly, the FD processing is cost effective. For the applications with high mobility, the traditional implementation of the SC-FDM receiver causes significant performance degradation. In this paper, we propose to estimate time-varying pieces of channel taps for pilot symbols based on basis expansion model (BEM), and subsequently to reconstruct time-domain (TD) channel response for data symbols by utilizing the Slepian sequences-based piece-wise interpolation. Furthermore, two simplified schemes, i.e., the Slepian sequences-based multiple-point interpolation and the segmented BEM, are developed to reduce the computational complexity of the TD-CE. The Cramer-Rao lower bound (CRLB) of channel impulse response (CIR) estimation is also analyzed. In the light of the sparsity of TD channel gain matrix, we design an iterative least-squares QR decomposition algorithm to equalize the SC-FDM symbols. In the simulated SC-FDM system, when considering the carrier frequency of 5.9 GHz and the velocity of about 510 km/h, we observe that the traditional FD methods cause the demodulation failure, while the proposed TD processing schemes achieve ideal error-probability performance and preserve a relatively low complexity.

Hartley-Domain DD-FTN Algorithm for ACO-SCFDM in Optical-Wireless Communications

In this paper, we propose a Hartley-domain direct-detection faster-than-Nyquist (HD-DD-FTN) algorithm for asymmetrically clipped optical single-carrier frequency-division multiplexing (ACO-SCFDM) in optical-wireless communications (OWC). The HD-DD-FTN algorithm includes modified Hartley-domain equalization (HDE) and maximum likelihood sequence detection, which can simultaneously compensate serious high-frequency distortion and eliminate enhanced in-band noise for the bandwidth-limited OWC. Modified HDE can be implemented by real-valued operations, which is appropriate for dealing with real-valued signals. The simulation results show that ACO-SCFDM system using the HD-DD-FTN algorithm is more robust to inter-symbol interference than that using conventional HDE algorithm. Therefore, the bit error rate performance of the ACO-SCFDM system using HD-DD-FTN algorithm is better than that using the conventional HDE algorithm. In conclusion, the ACO-SCFDM system using the HD-DD-FTN algorithm shows great potential for bandwidth-limited OWC.

Low-PAPR interleaved single-carrier FDM scheme for optical wireless communications

As a potential complementary access technology for the 5G wireless systems, optical wireless communication (OWC) gains extensive attention for decades owing to its numerous advantages of broad license-free spectrum, immunity to electromagnetic interference and high-level privacy. However, two rigorous obstacles to achieve high data-rate OWC transmission are the severe nonlinear clipping of transmitter and high-frequency attenuation of OWC system. In this paper, we propose the first interleaved single-carrier frequency-division multiplexing (I-SC-FDM) scheme for OWC systems. Compared with orthogonal frequency-division multiplexing (OFDM), I-SC-FDM has a lower peak-to-average power ratio, which makes it more immune to the nonlinearity clipping in OWC systems. Meanwhile, for the bandwidth-limited OWC systems, I-SC-FDM has better performance on resistance to the serious high-frequency distortion. The simulation results indicate that, under the transmitter nonlinearity and optical-wireless diffuse fading channel, the maximum $$Q^2$$ of I-SC-FDM is about 3.44 dB and 3.14 dB higher than that of OFDM when 4-ary quadrature amplitude modulation (4-QAM) and 16-QAM are modulated, respectively. The results show the feasibility and advantages of I-SC-FDM for cost-sensitive OWC systems.

Spectral-Efficient L/E-ACO-SCFDM-Based Dimmable Visible Light Communication System

In this paper, we propose a dimmable visible light communication (VLC) system based on spectral-efficient layered/enhanced asymmetrically clipped optical single-carrier frequency-division multiplexing (L/E-ACO-SCFDM). L/E-ACO-SCFDM superimposes multi-layer ACO-SCFDMs occupying different subcarriers for enhancing the spectral efficiency of the system. Both the adjustable layer polarities and the low peak-to-average-power ratio property of ACO-SCFDM make it better suited to the linearity-limited VLC system. Meanwhile, L/E-ACO-SCFDM has the signal-to-noise ratio averaging advantage, which can effectively resist the high-frequency distortion caused by the bandwidth limitation of the VLC system. Based on the maximization of spectral efficiency of the system, the layer amplitudes, layer spectral efficiencies, and bias voltage are jointly optimized for providing the efficient communication under different illumination requirements. Benefiting from the numerous strengths, the proposed L/E-ACO-SCFDM-based dimming scheme can achieve at least 22.0% average spectral efficiency gain compared with several state-of-the-art OFDM-based dimming schemes within the same dimming range, which shows the great superiority for future practical applications of VLC.

An Efficient SC-FDM Modulation Technique for a UAV Communication Link

Since the communication link of an unmanned aerial vehicle (UAV) and its reliability evaluation represent an arduous field, we have concentrated our work on this topic. The demand regarding the validity and reliability of the communication and data link of UAV is much higher since the environment of the modern battlefield is becoming more and more complex. Therefore, the communication channel between the vehicle and ground control station (GCS) should be secure and provide an efficient data link. In addition, similar to other types of communications, the data link of a UAV has several requirements such as long-range operation, high efficiency, reliability, and low latency. In order to achieve an efficient data link, we need to adopt a highly efficient modulation technique, which leads to an increase in the flight time of the UAV, data transmission rate, and the reliability of the communication link. For this purpose, we have investigated the single-carrier frequency division multiplexing (SC-FDM) modulation technique for a UAV communication system. The results obtained from the comparative study demonstrate that SC-FDM has better performance than the currently used modulation technique for a UAV communication link. We expect that our proposed approach can be a remarkable framework that will help drone manufacturers to establish an efficient UAV communication link and extend the flight duration of drones, especially those being used for search and rescue operations, military tasks, and delivery services.

Space-domain dimming control scheme based on SCFDM for visible light communications

Abstract In this paper, a space-domain dimming control scheme based on single-carrier frequency-division multiplexing (SD-SCFDM) is proposed for visible light communications (VLC). The SD-SCFDM scheme not only has the advantage of additional spatial dimming domain but inherits the strengths of SCFDM in resisting the clipping distortion and high-frequency attenuation, which can support the efficient communication under different illumination requirements. Considering the limited dynamic range of light emitting diode (LED) and bandwidth limitation in VLC system comprehensively, SD-SCFDM can achieve the communication with spectral efficiency of at least 1 bit/s/Hz higher than SD scheme based on orthogonal frequency-division multiplexing (SD-OFDM) in the whole dimming range. Additionally, the proposed SD-SCFDM has the low computational complexity of encoding. Meanwhile, for the proposed scheme with spectral efficiency of 2.5, 3 and 3.5 bit/s/Hz, the required number of LED chips in one lamp can be reduced by about 55.9%, 50% and 59% compared with its OFDM-based counterparts, respectively. In conclusion, the SD-SCFDM scheme shows the great potential and feasibility for future practical implementations of VLC.

Dimming Control Systems Based on Low-PAPR SCFDM for Visible Light Communications

In this paper, the efficient dimming control systems based on single-carrier frequency-division multiplexing (SCFDM) are proposed for visible light communications (VLC). By virtue of the strengths of the low peak-to-average power ratio and the inherent resistance to high-frequency distortion, the proposed SCFDM-based dimming control schemes are adaptive to the bandwidth-limited and linearity-limited VLC system, thus supporting the wide dimming range for different illumination requirements. Two SCFDM-based VLC systems with dimming control including asymmetrical hybrid optical SCFDM (AHO-SCFDM) and DC-biased optical SCFDM (DCO-SCFDM) are proposed. For AHO-SCFDM with spectral efficiency of 1.75 bit/s/Hz and DCO-SCFDM with spectral efficiency of 2 bit/s/Hz, the 20% wider dimming range can be achieved than their orthogonal frequency-division multiplexing (OFDM) based counterparts, respectively. Meanwhile, the two proposed schemes can also achieve 24.8% and 31.3% gains of average spectral efficiency under the same dimming range compared with their counterparts, respectively. For an overall analysis, SCFDM shows the feasibility and superiority for dimming control systems.

Optimized Layered/Enhanced ACO-SCFDM for Short-Reach Optical Interconnects

This letter is the first experimental demonstration of layered/enhanced asymmetrically clipped optical single-carrier frequency-division multiplexing (L/E-ACO-SCFDM) in short-reach optical interconnects. An optimized method is employed to significantly improve the performance of L/E-ACO-SCFDM. L/E-ACO-SCFDM has higher spectral efficiency than ACO-SCFDM, and it also has lower peak-to-average power ratio and computational complexity than L/E-ACO orthogonal frequency-division multiplexing (L/E-ACO-OFDM). In the experimental system, the low-cost electrical and optical devices are utilized, which induce serious high-frequency distortion caused by bandwidth limitation. Under the same spectral efficiency and net bit rate, the optimized L/E-ACO-SCFDM has about 4-dB and more than 3-dB receive sensitivity improvement at 7% forward error correction limit compared with the optimized L/E-ACO-OFDM and the optimized ACO-SCFDM, respectively. Therefore, L/E-ACO-SCFDM is a promising scheme for the future short-reach optical interconnects.

Low-PAPR Layered/Enhanced ACO-SCFDM for Optical-Wireless Communications

In this letter, we propose layered/enhanced asymmetrically clipped optical single-carrier frequency-division multiplexing (L/E-ACO-SCFDM) for optical-wireless communications. L/E-ACO-SCFDM has a lower computational complexity and peak-to-average power ratio (PAPR) than L/E-ACO orthogonal frequency-division multiplexing (L/E-ACO-OFDM). The computational complexity of the simplified transmitter in L/E-ACO-SCFDM with $R$ layers is $(2-2/2^{R})O(N)$ , which is lower than the computational complexity of $(2-2/2^{R})O(N\text {log}_{2}N)$ in L/E-ACO-OFDM. At a complementary cumulative distribution function of $10^{-3}$ , the PAPR of L/E-ACO-SCFDM is approximately 4.2, 3.4, and 2.7 dB lower than that of L/E-ACO-OFDM for 2, 3, and 4 layers, respectively. The simulation results indicate that L/E-ACO-SCFDM has better performance than L/E-ACO-OFDM under the transmitter nonlinearity and multipath fading.

256-QAM Interleaved Single Carrier FDM for Short-Reach Optical Interconnects

In this letter, we experimentally demonstrated a 40-Gbit/s 256-quadrature amplitude modulation (256-QAM) interleaved single-carrier frequency-division multiplexing (I-SC-FDM) over 10-km standard single-mode fiber (SSMF) for optical interconnects. I-SC-FDM has lower peak-to-average power ratio and lower computational complexity of transmitter compared with orthogonal frequency division multiplex- ing (OFDM). High-level QAM can achieve high spectral efficiency; however, it is susceptible to both linear and nonlinear distortions. The frequency-domain one-tap equalizer and the time-domain decision-feedback equalizer with recursive least square and Volterra algorithm are jointly employed to eliminate the distortions for the 256-QAM I-SC-FDM. After 10-km SSMF, I-SC-FDM has better performance than localized SC-FDM and OFDM. Therefore, I-SC-FDM shows the potential for short-reach optical interconnects.

Interleaved single-carrier frequency-division multiplexing for optical interconnects.

In this paper, we propose a real-valued interleaved single-carrier frequency-division multiplexing (I-SC-FDM) scheme for intensity-modulation and direct-detection optical interconnects. By simplifying the encoding structure, the computational complexity can be reduced from Nlog2N complex multiplications to N complex multiplications. At the complementary cumulative distribution function of 10-2, a reduction of 10 dB and 7.5 dB for the peak-to-average power ratio (PAPR) of the I-SC-FDM is achieved than that of orthogonal frequency-division multiplexing modulated with QPSK and 16QAM, respectively, when the subcarrier number is set to 4096. We experimentally demonstrate the I-SC-FDM scheme for optical interconnects with data rates of 12 Gbit/s, 24 Gbit/s and 128 Gbit/s transmitted over 22.5-km, 22.5-km and 2.4-km standard single mode fiber, respectively. The I-SC-FDM scheme shows great potential for cost-sensitive and power-sensitive optical interconnects owing to its low computational complexity and low PAPR.

PAPR Reduction and Performance Improvement in OFDM Systems using WHT-based Schemes

Orthogonal frequency division multiplexing (OFDM) is a robust and reliable multicarrier modulation scheme that has proven to be adequate for broadband communications. It is widely used in broadcasting and broadband wireless and wireline systems. However, in scenarios where the communication devices are power-limited, such as mobile and satellite communications, OFDM has not been massively used or even not used at all. For instance, OFDM is used only in downlink of 4G networks, while the uplink uses single carrier frequency division multiplexing. One of the main culprits of this is the high peak to average power ratio (PAPR) of the OFDM signal. Reducing the PAPR of the OFDM signals is important for a large variety of application. Several PAPR reduction techniques for OFDM have been proposed recently.The aim of this paper is to present a tutorial about a set of algorithms based on Walsh-Hadamard transform (WHT) for reducing the PAPR of the OFDM symbols. We also propose a new technique, named selective mapping based on WHT without extended information (SLM-WHT-WEI), which does not convey the explicit information to the receiver. We will show that the approaches based on WHT can also improve the OFDM symbol error rate performance over frequency-selective channels. Different schemes based on the properties of the WHT are presented and compared, assuming linear and non-linear channels. The PAPR reduction performance analysis shows that the PAPR can be effectively reduced while good performance in terms of symbol error rate can be achieved even in severely constrained channel conditions.

Analysis of Carrier Frequency Offset Suppression Techniques in SC-FDMA Communication System

Single Carrier Frequency Division Multiplexing is a promising technique for high data rate uplink communication in 3GPP Long Term Evolution. It has a major advantage of low peak to average power ra...