Cosine Pulse Research Articles

Theoretical model and simulation of ship underwater radiated noise

Ship underwater radiated noise is one of the most important ocean ambient noise sources, and building a reasonable model for the ship underwater radiated noise is helpful for understanding the physical mechanism and reducing research cost of ship underwater radiated noise. The quasi-periodic random sound pulse sequence signals act well in explaining the rhythm and the power spectrum variation of the ship underwater radiated noise, and reveal that there are not any real sinusoidal components in ship radiated noise signals, which come from the non-linear transformation of the signals, and the analysis of some representative experimental data of ship radiated noise also supports this idea. Based on this, the explosion-type cosine pulses are used as the units of quasi-periodic random sound pulse sequences. This model can generate the power spectrum with a peak, and the peak location can change with ship velocity or ship type. The power spectrum variation characteristics of quasi-periodic random sound pulse sequences consisting of the explosion-type cosine pulses are in good agreement with the measured ship underwater radiated noise data, which shows that this model is of important practical value.

Physical Layer Network Coding With Spectrally Efficient Pulse Shapes

This letter investigates the use of spectrally efficient pulse shapes in a physical layer network coding (PNC) system. A multi-user detector is used in the form of a maximum likelihood sequence estimator that accounts for offsets in timing, amplitude and phase between the two incoming signals in the multiple-access phase of a PNC system. It is found that with root-raised cosine (RRC) pulses, the PNC system is much more sensitive to timing offset in terms of the performance of the receiver relative to when rectangular pulses are used. Simulation results confirm that it is necessary to keep the incoming signals aligned to within about 1/10th of a symbol interval to avoid substantial performance loss.

PROPOSAL OF NEW PULSE SHAPING METHOD FOR SIDE LOBES REDUCTION IN OFDM SYSTEM

In this paper, we propose a new pulse shaping method namely scale alpha for orthogonal frequency-division multiplexing (OFDM) system. The suggested pulse shape is designed and simulated using Matlab software. The results show that scale alpha has a better impulse response in both time and frequency domains with minimum side lobes compared to Franks, raised cosine, and double-jump pulses.

Enhancement of Neuromodulation with Novel Pulse Shapes Generated by Controllable Pulse Parameter Transcranial Magnetic Stimulation.

Standard repetitive transcranial magnetic stimulation (rTMS) devices generate bidirectional biphasic sinusoidal pulses that are energy efficient, but may be less effective than monophasic pulses that induce a more unidirectional electric field. To enable pulse shape optimization, we developed a controllable pulse parameter TMS (cTMS) device. We quantified changes in cortical excitability produced by conventional sinusoidal bidirectional pulses and by three rectangular-shaped cTMS pulses, one bidirectional and two unidirectional (in opposite directions), and compared their efficacy in modulating motor evoked potentials (MEPs) produced by stimulation of motor cortex. Thirteen healthy subjects completed four sessions of 1Hz rTMS of the left motor cortex. In each session, the rTMS electric field pulse had one of the four shapes. Excitability changes due to rTMS were measured by applying probe TMS pulses before and after rTMS, and comparing resultant MEP amplitudes. Separately, we measured the latency of the MEPs evoked by each of the four pulses. While the three cTMS pulses generated significant mean inhibitory effects in the subject group, the conventional biphasic cosine pulses did not. The strongest inhibition resulted from a rectangular unidirectional pulse with dominant induced current in the posterior-anterior direction. The MEP latency depended significantly on the pulse shape. The pulse shape is an important factor in rTMS-induced neuromodulation. The standard cosine biphasic pulse showed the smallest effect on cortical excitability, while the greatest inhibition was observed for an asymmetric, unidirectional, rectangular pulse. Differences in MEP latency across the various rTMS pulse shapes suggest activation of distinct subsets of cortical microcircuitry.

Polynomial Pulses for Mitigating Fiber Nonlinearity in Coherent Optical Fiber Communications

Root polynomial (RP) pulses are considered for mitigating fiber nonlinearity for 128 Gb/s dual-polarization 8-ary quadrature-amplitude-modulation dense wavelength division multiplexed (DWDM) systems. RP pulses exhibit a fast asymptotic decay rate, low peak-to-average power ratio, and narrow pulse width. Consequently, they are tolerant toward intrachannel nonlinearity, digital-to-analog converter quantization effects, and timing recovery errors. In a nine-channel DWDM transmission experiment with a 25 GHz channel spacing and null-to-null modulated optical signal bandwidth of 25 GHz, the RP pulse shape yields a maximum distance of 4800 km, which extends the transmission distance by 300 km (length of the recirculating loop) relative to the root raised cosine pulse shape.

Distinguishing CPFSK from QAM and PSK Modulations

Digital modulation classification is important for many civilian as well as military applications. In this paper, we propose a simple and robust feature to distinguish continuous-phase FSK from QAM and PSK modulations. The feature is based on product of two consecutive signal values and on time averaging of imaginary part of the product. Conditional probability density functions of the feature given modulation type are determined. In order to overcome the complexity of calculating probability density functions, central limit theorem for strictly stationary m-dependent sequences is used to obtain Gaussian approximations. After calculating probability density functions, thresholds are determined based on minimization of total probability of misclassification. Since threshold-based results are valid for special cases requiring knowledge of some parameters, we resort to usage of support vector machines for classification, which require little training and no a priori information except for carrier frequency. Following that joint effects on the performance of carrier offset, fast fading, and non-synchronized sampling are studied in the presence of additive white Gaussian noise. For comparison purposes, rectangular pulse shape is used. To prove practical usefulness, not only the performance is analyzed for root-raised cosine pulses but also for quite less oversampling of symbols than what is found in other approaches. In the course of doing that, the performance is compared with wavelet-based feature that uses support vector machines for modulation separation.

ICI Alleviation in OFDM System Utilizing Scale Alpha Pulse Shaping

In this study, a new pulse shaping method namely scale alpha is proposed for mitigating Inter-Carrier Interference (ICI) effect in Orthogonal Frequency-Division Multiplexing (OFDM) system. The suggested pulse shape is designed and simulated using MATLAB software. Results show that the new pulse shape has lower ICI power and better impulse response performance than Franks, raised cosine and double-jump pulses

Simple Features for Separating CPFSK from QAM and PSK Modulations

In this letter we propose simple and robust features to distinguish continuous-phase frequency shift keying from quadrature amplitude modulation and phase shift keying modulations. The features are based on sample mean and sample variance of the imaginary part of the product of two consecutive complex signal values. Root raised cosine pulses are used to generate the linearly modulated signals. Support vector machines are employed to distinguish the signals. One benefit of using support vector machines is that it requires very few realizations for training. Moreover, no a priori information is required about carrier amplitude, carrier phase, carrier offset, symbol rate, pulse shape, initial symbol phase (timing offset) and channel impulse response. Effectiveness of the features and signal separation by support vector machines is tested by observing the joint effects of additive white Gaussian noise, carrier offset, lack of symbol and sampling synchronization, and either fast or slow fading. In the course of doing that, the proposed classifier is compared to the wavelet based classifier, equipped by support vector machines.

Experimental investigation on the nonlinear tolerance of root M-shaped pulse in spectrally efficient coherent transmissions.

We experimentally demonstrate improved intra-channel nonlinearity tolerance of the root M-shaped pulse (RMP) with respect to the root raised cosine (RRC) pulse in spectrally efficient 128 Gbit/s PDM-16QAM coherent transmission systems. In addition we evaluate the impact of dispersion map and fiber dispersion parameter on the intra-channel nonlinearity tolerance of the RRC pulse and the RMP via both simulation and experimentation. The RMP is shown to have a better nonlinear tolerance than the RRC pulse for most investigated scenarios except for links with zero residual dispersion percentage per span or the zero dispersion region of a fiber. Therefore, the RMP is suitable for extending the maximum reach of spectrally efficient coherent transmission systems in legacy links in addition to currently intensively studied standard single mode fiber (SSMF) based dispersion unmanaged links.

Experimental demonstration of a 10 Gb/s RSOA-based 16-QAM subcarrier multiplexed WDM PON

We experimentally demonstrate the performance of a 10 Gb/s subcarrier multiplexed (SCM) wavelength-division multiplexed (WDM) passive optical network (PON) using 2.5 Gbaud 16-QAM transmission signals. Digital signal processing (DSP) and square-root raised cosine (SRRC) pulse shaping enable both the uplink and downlink channels to achieve net spectral efficiencies up to 2.8 bit/s/Hz per channel using reflective semiconductor optical amplifier (RSOA)-based optical network units (ONUs) and economical 10 GHz intensity modulation and direct detection transceivers. We characterize the system's bit error rate (BER) performance over a 20 km single feeder PON with both remote continuous-wave (CW) seeding and full-duplex transmission scenarios, assuming standard forward error correction (FEC) codes.

A nonlinearity-tolerant frequency domain root M-shaped pulse for coherent optical communication systems

A new intersymbol interference (ISI)-free nonlinearity-tolerant frequency domain root M-shaped pulse (RMP) is derived for dispersion unmanaged coherent optical transmission systems. Beginning with the relationship between pulse shaping and intra-channel nonlinearity effects, we derive closed-form expressions for the proposed pulse. Experimental demonstrations reveal that by employing the proposed pulse at a roll-off factor of 1, the maximum transmission reach of a single-channel 56 Gb/s polarization-division-multiplexed quadrature phase-shift keying (PDM-QPSK) system can be extended by 33% and 17%, when compared to systems using a root raised cosine (RRC) pulse and a root optimized pulse (ROP), respectively. For a single-channel 128 Gb/s polarization-division-multiplexed 16-quadrature amplitude modulation (PDM-16QAM) system, the reach can be extended by 44% and 18%, respectively. Reach increases of 30% and 13% are also observed for a dense wavelength-division multiplexing (DWDM) 504 Gb/s PDM-QPSK transmission system. The tolerance to narrow filtering effect for the three pulses is experimentally studied as well.

Experimental Demonstration of a 10 Gb/s Subcarrier Multiplexed WDM PON

We experimentally demonstrate a 10 Gb/s bidirectional subcarrier multiplexed (SCM) wavelength-division multiplexed (WDM) passive optical network (PON). We use digital signal processing and square-root raised cosine pulse shaping techniques to generate M-ary quadrature amplitude modulation electrical signals for the downlink and uplink transmissions using simple intensity modulation and direct detection optoelectronics, and 10 GHz transceivers. The design includes spectral preemphasis and offset optical filtering to increase the effective bandwidth of a commercial 2.2 GHz reflective semiconductor optical amplifier based optical network unit. We realize symmetric 10 Gb/s transmission over a 20 km single feeder PON with optical line terminal launch powers from 1 to 9 dBm. We also demonstrate the ability of these SCM WDM PONs to withstand the effects of upstream impairments.

Molecular Dynamics in Strong Laser Fields: A New Algorithm for abInitio Classical Trajectories.

A new, more accurate Hessian-based predictor-corrector algorithm has been developed for simulating classical trajectories of molecules in intense laser fields. The first and second derivatives of the gradient with respect to the electric field are included in the both the predictor and the corrector steps for integrating trajectories. A Taylor expansion of the gradient is used as the surface for integrating the predictor step; a distance weighted interpolant of the gradient is employed for the corrector step. Test trajectories were calculated for HCO(+) in a continuous 10 μm, 2.9 × 10(14) W cm(-2) laser field and triplet allene dication in a 10 μm, 5.7 × 10(13) W cm(-2) four cycle cosine pulse. The first derivative of the gradient with respect to the electric field makes a significant contribution, while the second derivative makes a smaller contribution and can be neglected. To reduce the cost, the Hessian can be updated for several steps before being recalculated. The calculations indicate that a step size of Δt = 0.25 fs and 20 updates is efficient and reliable for these test systems.

Implementation of Pulse Shaping Techniques in OFDM System

Tremendous improvement has been made possible in wireless technology due to success of OFDM system which is a multi carrier modulation technique with capability to support high data rates. Despite its many advantages OFDM has failed against inter symbol interference (ISI), high sensitivity to Inter carrier interference (ICI), high peak to average power ratio (PAPR), phase noise and band limited channel. Hence the performance of an OFDM system is highly affected by the aforementioned undesired phenomenon. For this reason bandlimited system often employs pulse shaping techniques. In this paper pulse shaping of multi carrier signal is introduced by using various pulse shapes like Rectangular pulse (REC), Raised cosine pulse (RC), Better than raised cosine pulse (BTRC), Sinc power pulse (SP) and Improved sinc power pulse (ISP). The impulse responses and frequency spectrums have been evaluated and compared with system without using pulse shaping. Results obtained by simulation for OFDM system using pulse shaping and without using pulse shaping indicate that the performance of OFDM system with various pulse shapes is better than without using pulse shaping. Along with it can also be observed that among pulse shaping ISP exhibits better performance. Computer simulation has been done by using MATLAB 7.0 software.

Satellite Communications. SDPSK Modulator for Radiation Tolerant Satellite Modem / SDPSK Modulators Radiācijas Noturīgam Satelīta Modēmam

After a satellite has been launched, it is impossible to reprogram the hardware modulator. Therefore, a nanoRTU FPGA-based controller (AAC Microtec) in a modified modulation scheme may be programmed as a modem backend for softwaredefined radio (SDR) in the satellite communication system in order to adjust the balance of data rate vs. link reliability, enable coding or encryption system, change communication protocols, etc. For this purpose, a low-power radiation-tolerant reprogrammable satellite modem back-end has been realized for the satellite-to-Earth communication. This paper describes realization of a low data rate modulator based on a robust and reliable symmetric differential phase shift keying (SDPSK) modulation scheme combined with a raised cosine pulse shaping filter in nanoRTU, and presents results of its testing

Flat optical frequency comb generation and its application for optical waveform generation

We demonstrate the generation of a flat optical frequency comb (OFC) using an electro absorption modulator (EAM) and two cascaded phase modulators (PM). Compared with previous flat OFC generation schemes using a Mach–Zehnder modulator (MZM) for amplitude gating of the phase modulated light, an EAM creates much shorter time window for amplitude gating, and more flattened OFC spectrum is obtained using EAM as an amplitude gate. In our experiment, a very flat OFC having 11 lines within 3-dB bandwidth (3.8nm), and 40GHz comb line spacing is generated. Besides the excellent spectral flatness, the strong time-domain linear-chirp of the generated OFC can be simply compensated by a dispersion compensation fiber (DCF) link, which is preferred for optical waveform generation based on spectral manipulation. In this paper, we also demonstrate the OFC application for generation of several optical waveforms by manipulating the amplitude and phase of the comb lines. High repetition-rate optical cosine pulse, optical pulse burst, optical square and triangle pulses are successfully generated.

Bandlimited Intensity Modulation

In this paper, the design and analysis of a new bandwidth-efficient signaling method over the bandlimited intensity-modulated direct-detection (IM/DD) channel is presented. The channel can be modeled as a bandlimited channel with nonnegative input and additive white Gaussian noise (AWGN). Due to the nonnegativity constraint, standard methods for coherent bandlimited channels cannot be applied here. Previously established techniques for the IM/DD channel require bandwidth twice the required bandwidth over the conventional coherent channel. We propose a method to transmit without intersymbol interference in a bandwidth no larger than the bit rate. This is done by combining Nyquist or root-Nyquist pulses with a constant bias and using higher-order modulation formats. In fact, we can transmit with a bandwidth equal to that of coherent transmission. A trade-off between the required average optical power and the bandwidth is investigated. Depending on the bandwidth required, the most power-efficient transmission is obtained by the parametric linear pulse, the so-called "better than Nyquist" pulse, or the root-raised cosine pulse.

Performance improvement in an OFDM system with MBH combinational pulse shape

In this paper, the Modified Bartlett-Hanning (MBH) window family is used in an OFDM system to reduce the effect of frequency offset on both the parameters i.e., the inter-carrier interference (ICI) and bit error rate (BER). The performance metric of suggested OFDM model with several Nyquist pulse shapes, including rectangular, Bartlett, raised cosine (RC) and better than raised cosine (BTRC) pulse shapes are also evaluated. These pulse shapes are found as members of the MBH pulse shape family, exactly or equivalently. It is observed that the ICI, BER and signal to interference ratio (SIR) of the OFDM system with different MBH pulse shapes are better than BTRC, RC, Bartlett and rectangular pulse shapes. The MBH pulse shape family, where different pulses can be generated by taking numerous values of the pulse shape parameter '@b', is providing a consistent advantage over the BTRC pulse shape in terms of ICI and BER in the acceptable range of carrier frequency offset along with better spectral efficiency due to their improved side-lobe levels. The other pulse shapes e.g. second order continuous window (SOCW), phase modified sinc pulse (PMSP) and Frank@?s window are also compared with proposed pulse shapes and found that the MBH family pulse shapes are equally comparable in terms of performance metric used.

TD-CI Simulation of the Strong-Field Ionization of Polyenes

Ionization of ethylene, butadiene, hexatriene, and octatetraene by short, intense laser pulses was simulated using the time-dependent single-excitation configuration-interaction (TD-CIS) method and Klamroth's heuristic model for ionization (J. Chem. Phys.2009, 131, 114304). The calculations used the 6-31G(d,p) basis set augmented with up to three sets of diffuse sp functions on each heavy atom as well as the 6-311++G(2df,2pd) basis set. The simulations employed a seven-cycle cosine pulse (ω = 0.06 au, 760 nm) with intensities up to 3.5 × 10(14) W cm(-2) (E(max) = 0.10 au) directed along the vector connecting the end carbons of the linear polyenes. TD-CIS simulations for ionization were carried out as a function of the escape distance parameter, the field strength, the number of states, and the basis set size. With a distance parameter of 1 bohr, calculations with Klamroth's heuristic model reproduce the expected trend that the ionization rate increases as the molecular length increases. While the ionization rates are too high at low intensities, the ratios of ionization rates for ethylene, butadiene, hexatriene, and octatetraene are in good agreement with the ratios obtained from the ADK model. As compared to earlier work on the optical response of polyenes to intense laser pulses, ionization using Klamroth's model is less sensitive to the number of diffuse functions in the basis set, and only a fraction of the total possible CIS states are needed to model the strong field ionizations.

Effect of carrier frequency offset and symbol timing offset on the performance of FMT over time-frequency selective channels

This paper presents the effects of carrier frequency offset (CFO) and symbol timing offset (STO) in filtered multitone (FMT) systems over time and frequency selective multipath fading channels. The analysis is based on an FMT system using a square-root raised cosine pulse. The performance of FMT systems in the presence of CFO and STO over different fading channels are derived and compared with that of orthogonal frequency division multiplexing systems. The offsets degrade the performance of the FMT systems because they cause filter mismatch. The CFO changes the amplitude frequency characteristic of the receiver filter, while the STO changes the phase frequency characteristic of the receiver filter. The simulations are conducted over different fading channels. To achieve signal-to-interference ratio above 20 dB, over a flat static channel, the frequency offset relative to symbol duration must be less than 5% in the orthogonal frequency division multiplexing system, while the upper limit is 8% in the FMT system. The simulation results also show that the FMT system is less sensitive to CFO in time frequency selective channels. The signal-to-interference ratio expressions help predict the bit-error-rate performance of FMT with single tap subchannel equalization. The analysis also helps synchronization algorithm design after analyzing the synchronization offset effect in FMT systems under certain channel conditions. Copyright © 2012 John Wiley & Sons, Ltd.