Raised Cosine Research Articles

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.

Time-Frequency Warped Waveforms for Well-Contained Massive Machine Type Communications

This paper proposes a novel time-frequency warped waveform for short symbols, massive machine-type communication (mMTC), and internet of things (IoT) applications. The waveform is composed of asymmetric raised cosine (RC) pulses to increase the signal containment in time and frequency domains. The waveform has low power tails in the time domain, hence better performance in the presence of delay spread and time offsets. The time-axis warping unitary transform is applied to control the waveform occupancy in time-frequency space and to compensate for the usage of high roll-off factor pulses at the symbol edges. The paper explains a step-by-step analysis for determining the roll-off factors profile and the warping functions. Gains are presented over the conventional Zero-tail Discrete Fourier Transform-spread-Orthogonal Frequency Division Multiplexing (ZT-DFT-s-OFDM), and Cyclic prefix (CP) DFT-s-OFDM schemes in the simulations section.

Low Complex Inter-Doppler Interference Mitigation for OTFS Systems via Global Receiver Windowing

Orthogonal time frequency space (OTFS) waveform has been considered as a potential candidate for affording a wide range of emerging communications and sensing applications in beyond 5G wireless technologies. OTFS takes advantage of both time and frequency selectivity of the doubly dispersive wireless environment, which has been considered as one of the limiting factors in classical wireless communication technologies. However, the performance of OTFS-based wireless systems is severely affected by fractional Doppler that arises due to inevitable and inherent characteristics of the wireless channel taps of not being always integer Doppler values in the delay-Doppler plane. Thus, this results in severe inter-Doppler interference (IDI) and a low channel sparsity in delay-Doppler (DD) domain. To this end, this work introduces a novel receiver (Rx) windowing technique to combat the impact of fractional Doppler on error performance of the OTFS-based transmission with practical pulse shaping filters at the transceiver. Specifically, we introduce a global cyclic prefix (CP) based raised cosine (RC) windowing at Rx in order to alleviate the effect of IDI on the received signal. To do so, the proposed scheme changes the pulse shape of the OTFS signal in DD domain that defines the IDI level and sparsity of the effective channel. Furthermore, we assess the performance of the proposed Rx windowed OTFS (RW-OTFS) scheme under various practical communication scenarios. The obtained numerical and simulation results validate the accuracy of the proposed IDI mitigator for OTFS systems in practical high-mobility scenarios.

Multicore raised cosine fibers for next generation space division multiplexing systems

Space division multiplexing (SDM) is a promising solution for improving the transmission capacity and increasing the spectral efficiency. SDM over few mode multicore fibers (FM-MCFs) is an attractive approach that observes increasing interest. In this work, after reviewing the basic guidelines for FM-MCFs design, we address, for the first time, the Raised Cosine (RC) profile to multicore fibers context. We optimize the single core RC profile in order to support exactly 6 linearly polarized (LP) modes with large effective mode area (min Aeff = 96 μm2), with low differential mode delay (DMD) (max DMD = 33 ps⧹km) and high intermodal separation (⩾2×10−4). Once achieved, we investigate the induced crosstalk between twin RC cores and twin trenched RC (TRC) cores. We then propose four 6 modes 7 cores RC⧹TRC fibers. Their crosstalk and their relative core multiplicity are analysed and compared with those reported in recently graded index-FM-MCFs. The selected designs could be promising candidates for short and medium haul interconnects.

Joint Range Estimation Using Single Carrier Burst Signals for Networked UAVs

The localization accuracy demand is ever growing in UAV communication networks. We propose a joint coarse and fine range estimation method using single carrier burst signals with two samples per symbol for UAV networks. The coarse estimation of our joint estimation method exploits multiple preamble symbols for flexible single-carrier frequency-domain equalization (SC-FDE) frame structures to calculate correlation metrics, which are insensitive to frequency offset due to the differential correlation operation. Then, we propose a fine range estimation method using only two samples per symbol with expectation relying on shaping or matched filter. Furthermore, we derive the performance bounds for the ranging system using both raised cosine (RC) and better than raised-cosine (BTRC) pulses. Finally, extensive simulations are conducted to validate the proposed method in terms of estimate bias and variance for different modulations, shaping filters, and fading channels. Our simulation results show that, the root mean square errors of proposed ranging method can reach the order of centimeter at medium-to-high signal-to-noise ratio (SNR) region, whereas the case using BTRC filter is capable of enhancing the ranging performance at low SNRs.

Suppression of four wave mixing effect in DWDM system

Abstract This article discusses the nonlinear effect, four-wave mixing (FWM), which lowers the performance of optical communication systems. The concept of orthogonal polarization was introduced to reduce the effects of FWM. Here, orthogonal polarization is used with various modulation techniques such as NRZ, RZ, GAUSSIAN and RAISED COSINE. Orthogonal polarization was found to reduce the effect of FWM more than round polarization. Weaknesses of the four wavelength mixes were analyzed for various levels of input power. The capacity of a four-wave mixing product (FWM) is assessed by an optical spectrum analyzer. System performance is analyzed in terms of quality factors and BER.

Identification of Nonlinear Dynamical System Based on Raised-Cosine Radial Basis Function Neural Networks

In this paper, we present and investigate a new type of radial basis function (RBF) neural networks mechanism using raised-cosine (RC) function to identify nonlinear dynamic system. In this design, the RBF neural networks mechanism utilizes RC function to replace Gaussian function, which is called RCRBF. An N-dimensional RC function has the constant interpolation property, which is benefit for the function approximating errors analysis in the neural networks. Based on multivariable RC function approximation theory, we develop how to select the updated parameters and the distance of adjacent nodes in lattice points. Therefore, the proposed networks can uniformly approximate nonlinear dynamical function. As persistency excitation (PE) plays an important part in neural networks learning system, how does PE condition behave in input sequences is formulated by RC function analysis. The weights updating and errors convergence are concluded by Lyapunov function analysis. To illustrate the effectiveness of the proposed RCRBF method, Van Der Pol and Rossler dynamical system are used as test examples, in comparison with GRBF mechanism. The results show that the proposed method has better accurate identification and approximating effect than that of GRBF mechanism.

Dual Pulse Shaping Transmission and Equalization for High-Speed Wideband Wireless Communication Systems

Analog-to-digital and digital-to-analog conversion devices for signals with very large bandwidth are not always available due to technical or cost issues. This limits the realization of very high data-rate digital communication systems. In this paper, we propose a dual pulse shaping (DPS) transmission scheme, which can achieve full Nyquist rate transmission with only a half of the sampling rate for each of the two data streams. Two classes of ideal complementary Nyquist pulses are formulated assuming raised-cosine (RC) pulse shaping. The condition for cross-symbol interference (CSI) free transmission is derived and validated for the proposed pulses. Structures of the DPS transmitter and receiver are described and low-complexity equalization techniques tailored to DPS are proposed. With DPS, a millimeter wave system with commercially available and affordable data conversion devices is exemplified for achieving high-speed low-cost wireless communications. Simulation results with two sets of practical dual spectral shaping pulses are provided. The results verify the effectiveness of the proposed scheme, with comparison to the benchmark conventional Nyquist pulse shaping system.

Performance of GFDM Systems Using Quadratic Programming Pulse Shaping Filter Design

Generalized Frequency Division Multiplexing (GFDM) has been considered as an attractive candidate to replace Orthogonal Frequency Division Multiplexing (OFDM) for the fifth generation (5G) mobile networks. GFDM system has better spectral characteristics compared to the OFDM system due to the use of properly selected pulse shaping filters. Non-causal ideal filters, such as the raised cosine (RC), are commonly used in the GFDM systems. In practical implementation, non-causal filters need to be truncated and shifted, which will increase the out-of-band (OOB) radiation of the signal and will introduce delay to the system. High OOB radiation will cause interferences between the adjacent channels, thus it should be minimized. This paper proposes to minimize the OOB radiation of the GFDM system using the designed pulse shaping filters. The pulse shaping filters are designed using the computationally efficient quadratic programming (QP) approach. Numerical results illustrate that OOB radiation level of the GFDM system is lower when the QP filters are used compared to the conventional RC filter. Further investigation shows that the use of the QP filters are efficient in increasing the high power amplifier (HPA) efficiency, improving the spectral efficiency, and reducing the BER at the receiver.

Channel Estimation and Peak‐to‐Average Power Ratio Analysis of Narrowband Internet of Things Uplink Systems

Narrowband Internet of Things (NB‐IoT) is a cellular based promising low‐power wide‐area network (LPWN) technology standardized by the 3rd Generation Partnership Project (3GPP) in release‐13 as a part of the future 5th Generation (5G) wireless communication systems. The main design target of NB‐IoT was to enhance radio coverage by repeating signal over an additional period of time for the ultralow‐end IoT devices that would be operated in extreme coverage environments. But the power efficiency of the low‐cost NB‐IoT user equipment (NB‐IoT UE) in the uplink is the major concern. Coverage improvement from signal repetitions depends on the channel estimation quality at extremely bad radio conditions. The typical operating signal‐to‐noise ratio (SNR) for NB‐IoT is expected to be much lower than the zero. In this paper, we have proposed two efficient narrowband demodulation reference signal (NDMRS)‐assisted channel estimation algorithms based on the conventional least squares (LS) and minimum mean square error (MMSE) estimation methods. The theoretical analysis and the link‐level performance of our proposed estimation methods are presented. Simulation results exhibit that the proposed methods provide better estimation precision compared to the traditional LS and MMSE methods at the low SNR situations. Furthermore, we have analyzed the raised‐cosine (RC) and square‐root‐raised cosine (RRC) pulse shaping to reduce peak‐to‐average power ratio (PAPR) as an uplink transmit filter. The PAPR values are evaluated through extensive computer simulations for both single‐tone and multi‐tone transmissions. Our evaluation results vindicate that the RRC pulse shaping with lower PAPR values is feasible to design of practical NB‐IoT uplink transmitter and increases power efficiency.

Trenched raised cosine FMF for differential mode delay management in next generation optical networks

Dispersion management in few mode fiber (FMF) technology is crucial to support the upcoming standard that reaches 400 Gbps and Terabit/s per wavelength. Recently in Chebaane et al. (2016), we defined two potential differential mode delay (DMD) management strategies, namely sawtooth and triangular. Moreover we proposed a novel parametric refractive index profile for FMF, referred as raised cosine (RC) profile. In this article, we improve and optimize the RC profile design by including additional shaping parameters, in order to obtain much more attractive dispersion characteristics. Our improved design enabled to obtain a zero DMD (z-DMD), strong positive DMD (p-DMD) and near-zero DMD (nz-DMD) for six-mode fiber, all appropriate for dispersion management in FMF system. In addition, we propose a positive DMD (p-DMD) fiber designs for both, four-mode fiber (4-FMF) and six-mode fiber (6-FMF), respectively, having particularly attractive dispersion characteristics.

Spectrum efficient power allocation schemes for OFDM cognitive radio with statistical interference constraints

In this paper, we study the power allocation problem for an orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) system. In a departure from the conventional power allocation schemes available in the literature for OFDM-based CR, we propose power allocation schemes that are augmented with spectral shaping. Active interference cancellation (AIC) is an effective spectral shaping technique for OFDM-based systems. Therefore, in particular, we propose AIC-based optimal and suboptimal power allocation schemes that aim to maximize the downlink transmission capacity of an OFDM-based CR system operating opportunistically within the licensed primary users (PUs) radio spectrum in an overlay approach. Since the CR transmitter may not have the perfect knowledge about the instantaneous channel quality between itself and the active PUs, the interference constraints imposed by each of the PUs are met in a statistical sense. We also study an optimal power allocation scheme that is augmented with raised cosine (RC) windowing-based spectral shaping. For a given power budget at the CR transmitter and the prescribed statistical interference constraints by the PUs, we demonstrate that although the on-the-run computational complexity of the proposed AIC-based optimal power allocation scheme is relatively higher, it may yield better transmission rate for the CR user compared to the RC windowing-based power allocation scheme. Further, the AIC-based suboptimal scheme has the least on-the-run computational complexity, and still may deliver performance that is comparable to that of the RC windowing-based power allocation scheme. The presented simulation results also show that both the AIC-based as well as the RC windowing-based power allocation schemes lead to significantly higher transmission rates for the CR user compared to the conventional (without any spectral shaping) optimal power allocation scheme.

Symbol Misalignment Estimation in Asynchronous Physical-Layer Network Coding

Symbol misalignment is inevitable in asynchronous physical-layer network coding (PNC) systems. It is paramount that such symbol misalignment is taken into account in PNC decoding for good performance. Thus, accurate estimation of symbol misalignment is crucial. This paper argues that, when Nyquist pulses (i.e., intersymbol-interference (ISI)-free pulses) are adopted, signal samples only need to be collected at baud rate for optimal symbol misalignment estimation. Based on this principle, we propose a highly accurate symbol misalignment estimation method with low complexity. Our method makes use of the constant amplitude zero autocorrelation sequence (Zadoff–Chu sequence (ZC sequence)). We derive a maximum-likelihood (ML) estimator for symbol misalignment based on the cross-correlation result of the ZC sequence. Unlike previous methods that employ oversampling, our estimation method requires only baud-rate sampling, thus having much lower complexity. Extensive simulations show that our method can accurately estimate both integral and fractional symbol misalignments using sinc pulse and raised-cosine (RC) pulse. The root-mean-square error (RMSE) of the estimation is below 10−2 (in unit of symbol duration) when the SNR is above 15, 18, and 21 dB for 127-, 63-, and 31-bit-length ZC sequences, respectively. Furthermore, our method, being an ML estimation method, has no error floor in the high-SNR regime, whereas the prior methods exhibit an error floor.

Comparative Performance of Modulation Formats using RAMAN-EDFA Hybrid Optical Amplifier in Fiber Optic Communication System

Abstract This paper presents the comparison of various modulation formats for 64×10 Gbps dense wavelength division multiplexing system using Raman–erbium-doped fiber amplifier optical amplifier with 100 GHz interval. We evaluate the suitability of various data formats like return-to-zero (RZ) raised cosine (RC), RZ rectangular (Rect), non-return-to-zero (NRZ) RC and NRZ-Rect for an optical transmission link. The results have been carried out by evaluating the value of quality factor, bit error rate (BER) and average opening of an eye. It is found that using NRZ-Rect data format, the signal can travel up to transmission length of 234 km with acceptable BER (1.10e−09) and Q-factor (15.57 dB), respectively. In addition, the effect of dispersion on various data formats has also been discussed. Further, we investigate the optical RZ pulse with variable duty cycle indicating the highest quality factor and optical output power for duty cycle 0.6 observed for the case of back-to-back system.

Proposed Raised Cosine FMF for Dispersion Management in Next-Generation Optical Networks

Spatial mode-division multiplexing (MDM) that exploits the emerging few-mode fiber (FMF) technology is one potential candidate for next-generation petabyte optical communication links. In this paper, we focus on the design issues and specifications of the next-generation FMF that will better enable future MDM networks. These systems suffer from two main optical fiber impairments: intermodal coupling and dispersion. In this paper, we focus on the dispersion management issues through an FMF optical link. We first define two potential differential mode group delay (DMD) management strategies, namely, sawtooth and triangular. Moreover, we propose and investigate a novel parametric refractive index profile few-mode fiber, referred to as raised cosine (RC) function, which has been extensively used in digital communication pulse shaping. We investigate the achievable DMD for a wide range of the RC shape parameter and identify the design values of a two-mode FMF fiber. We then improve the RC profile by including additional shaping parameters. This enabled us to develop one four-mode fiber (4-FMF) and one six-mode fiber (6-FMF) having particularly attractive dispersion characteristics for three kinds of FMF applications: nz-, p-, and n-DMD.

Digital signal processing techniques in Nyquist-WDM transmission systems

In single-carrier wavelength-division-multiplexing (WDM) systems, the spectral efficiency can be increased by reducing the channel spacing through digital signal processing (DSP). Two major issues of using tight filtering are crosstalk between channels and inter-symbol interference (ISI) within a channel. By fulfilling the Nyquist criterion, Nyquist spectral shaped WDM systems can achieve a narrow channel spacing close to the symbol rate (Rs) with negligible crosstalk and ISI. In principle, DSP can generate any signals with arbitrary waveforms and spectrum shapes. However, the complexity of DSP is limited by its cost and power consumption. It is necessary to optimize the DSP to achieve the required performance at a minimum complexity. In this paper, we investigated the use of digital finite impulse response (FIR) filters to generate Nyquist-WDM 16-ary quadrature amplitude modulation (16QAM) signals with the raised-cosine (RC) and root-raised-cosine (RRC) shape spectrum. The system performance of both the RC and RRC spectra are also examined. Moreover, we explored the various methods to reduce digital-to-analog-converter (DAC) sampling speed, such as using super Gaussian electrical filters (E-filter), and spectral pre-emphasis.

Inter-band interference suppression in multi-band OFDM-PON uplink transmission using window shaping

Abstract We propose window shaping based inter-band interference suppression technique in multi-band orthogonal frequency division multiple access (MB-OFDMA) based passive optical network (PON) system. Conventional MB-OFDMA and raised-cosine (RC) windowed MB-OFDMA were compared in QPSK transmission and adaptive modulation scenario. The effect of OFDM clipping ratio is analyzed, which is used to mitigate peak to average power ratio (PAPR) problem at the transmitter. Also, the MB-OFDMA based multiple access performance is investigated according to the different roll-off factor of RC window in terms of error vector magnitude (EVM) and effective bit rate. Compared with the conventional MB-OFDMA which is rectangular windowed, the RC-windowed MB-OFDMA shows better performance by suppressed sidelobe which leads to IBI. The maximum effective bit rate of 10 Gbps was achieved for 20 km transmission scenario at optimum roll-off factor, while it was 9 Gbps in the conventional MB-OFDMA transmission.

All Optical Wavelength Conversion of Nyquist-WDM Superchannels Using FWM in SOAs

In this paper, the performance of all-optical wavelength conversion (WC) of Nyquist-WDM superchannels is investigated for future implementation in optical networks. We consider advanced modulation formats of DQPSK and 16-QAM for the subchannel modulation format achieving raw bit rates of 448 and 896 Gb/s, respectively. We demonstrate through simulations the WC of Nyquist-WDM superchannel using degenerate and nondegenerate four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). We consider the effects of raised cosine (RC) and root raised cosine (RRC) signal pulse shaping within the wavelength conversion process. We find that the performance of the converted superchannel is severely impaired by crosstalk due to cross-gain modulation of the pump by the superchannel. Optimum performance of the converted superchannel is achieved by setting the detuning between the continuous-wave pump and the central wavelength of the superchannel to be around 200 GHz and using pumps of double the gain saturation power of the SOA with 23 dB pump to signal power ratio.

A New Linearly Combined Nyquist Pulses for PAPR Reduction in IFDMA

Single Carrier Frequency Division Multiple Access (SCFDMA) is proposed for uplink transmission of Long Term Evolution Advanced (LTE-A) due to its lower Peak to Average Power Ratio (PAPR) compared to Orthogonal Frequency Division Multiple Access (OFDMA). In this paper, a comparison is introduced between its two subcarrier mapping schemes, Localized-FDMA (LFDMA) and Interleaved-FDMA (IFDMA), in terms of PAPR. Moreover, the paper addresses the performance of SC-FDMA with Pulse Shaping (PS). Since conventional Raised Cosine (RC) PS introduces a trade-off between spectrum efficiency and low PAPR in IFDMA, the results show that some newly combined Nyquist pulses can reduce PAPR of IFDMA significantly while maintaining the same Bandwidth (BW) compared to conventional RC pulse.

Analysis of PAPR on DFT-OFDMA Systems

OFDM is a broadband wireless technology which supports data rates in excess of 100 Mbps. In addition to this, OFDM has some limitations as it requires strict frequency synchronization and low peak to average power ratio. So considering DFT-OFDMA, which performance in terms of PAPR, is equivalent to SC-FDMA. This paper represents the suitability of using OFDMA in the up-link for high-data-rate scenarios in local area by considering target performance metrics PAPR. The proposed design shows PAPR performance varies depending on the subcarrier allocation method. It has been also shown that performance of the PAPR by DFT-spreading technique with IFDMA and LFDMA, varying with roll-off factor α of the RC (Raised-Cosine) filter. Effect of the number of subcarriers on PAPR performance is also discussed in this paper.