Pulse Amplitude Modulation

Combining pseudo random-modulation techniques with cavity enhanced spectroscopy allows the estimation of both optical path length and absorption while using a cw diode laser as the light source. Two pseudo-random modulation approaches are described, in each case combined with an off-axis cavity consisting of two cylindrical mirrors oriented to produce a dense pattern of cavity modes. In one approach, the amplitude of the laser is modulated; deconvolution results in an exponential ring-down decay curve. In the second approach, tone bursts that modulate the laser frequency are switched on and off with a pseudo-random code. Deconvolution yields the first derivative of an exponential whose amplitude is proportional to absorbance. With either approach the dynamic range of the transmitted intensity is much smaller than for a ring-down experiment, allowing high gain before the signal is digitized. Initial experimental results measuring carbon monoxide are presented, and the dependence of d...

In our previous work [1], we have analysed Multiuser Interference (MUI) by considering synchronous and asynchronous transmission under multiuser case for DS-CDMA based OFDM system. In [1] we have considered MUI at receiver from N-1 active users. In this paper we have examine MUI by considering packet based transmission with Impulse radio. In this situation MUI is generated due to collision of UWB pulses, which are used to define single bit under UWB transmission. This type of interference will take place in UWB based network due to organization of information bits into packets by higher layers. Here we have considered the TH-PAM and TH-PPM based Impulse radio systems for evaluating MUI.

The use of semiconductor amplifier in integrated transceivers increases sensitivity, but changes the noise statistics in pulse amplitude modulation (PAM) intensity modulation with direct detection. Using a straight-forward, mixed noise model, we optimize constellations for these systems with an autoencoderbased neural network (NN). We improve required signal-to-noise ratio (SNR) by 4 dB for amplified spontaneous emission (ASE)limited PAM4 and PAM8, without increasing system complexity. Performance can also be improved in O-band wavelength division multiplexing systems with semiconductor optical amplification and chromatic dispersion (CD). At 53 Gbaud, our simulations show we can extend the reach of PAM4 by 4 to 8 km when combining an optimized constellation with a NN decoder. We present an experimental validation of 4 dB improvement of an ASE-limited PAM4 back-to-back transmission at 60 Gbaud using an optimized constellation and a NN decoder.

To face the increased demand for bandwidth, cost-effectiveness and simplicity of future Ethernet data communications, a comparison between two different solutions based on directly-modulated VCSEL sources and Silicon Photonics technologies is carried out. Also by exploiting 4-PAM modulation, the transmission of 50-Gb/s and beyond capacity per channel is analyzed by means of BER performance. Applications for optical backplane, very short reach and in case of clientoptics networks and intra and inter massive data centers communications (up to 10 km) are taken into account. A comparative analysis based on the power consumption is also proposed.

In this paper, Pulse Position Modulation with Carrier (PPMWC) and its demodulator is presented. The scheme of proposed demodulator is based on the toggle circuit. The Pulse Position Modulation (PPM) signal is generated from the phase locked loop (PLL) circuit whereas the PPMWC signal is generated by summing the PPM signal and the PLL reference signal. In demodulation of the proposed scheme, the PPMWC signal is passed through the toggle circuit, resulting in the Pulse Width Modulation (PWM) signal. The output information is obtained by passing the PWM signal through the low pass filter. The obtained results from simulation and experiment agree well with the mathematical analysis.

In this paper, Pulse Position Modulation with Carrier (PPMWC) and its demodulator is presented. The scheme of proposed demodulator is based on the toggle circuit. The Pulse Position Modulation (PPM) signal is generated from the phase locked loop (PLL) circuit whereas the PPMWC signal is generated by summing the PPM signal and the PLL reference signal. In demodulation of the proposed scheme, the PPMWC signal is passed through the toggle circuit, resulting in the Pulse Width Modulation (PWM) signal. The output information is obtained by passing the PWM signal through the low pass filter. The obtained results from simulation and experiment agree well with the mathematical analysis.

Barcode technology is slowly being replaced with transponder tags that have many benefits over barcodes. Four issues with transponder tags are battery life, power requirement, range of communication, and physical size. Microwave backscatter modulation (MBM) is used throughout industry to reduce the power requirement and size on the transponder tags while compromising range. Researchers and designers of current transponder tags typically utilize a passive carrier-present carrier-absent (CPCA) reflection of the reader's carrier wave, or their transponder design uses an active backscatter system with an amplifier and circular polarization modulation. This research project develops a communication system that mixes a reader's carrier wave with an intermediate frequency (IF) at the active Probe in order to improve isolation of the data signal in a high-clutter environment. The design and testing ofProbe and Reader concepts are discussed, and the advantages and weaknesses of each ...

By eliminating DSP/retimer functions, Linear Pluggable Optics modules offer reduced power, cost and latency. This paper explores the challenges associated with LPO system integration and examines industry progress towards achieving true plug-and-play functionality of LPO modules.

Conventional approaches of digital modulation schemes make use of amplitude, frequency and/or phase as modulation characteristic to transmit data. In this paper, we exploit circular polarization (CP) of the propagating electromagnetic carrier as modulation attribute which is a novel concept in digital communications. The requirement of antenna alignment to maximize received power is eliminated for CP signals and these are not affected by linearly polarized jamming signals. The work presents the concept of Circular Polarization Modulation for 2, 4 and 8 states of carrier and refers them as binary circular polarization modulation (BCPM), quaternary circular polarization modulation (QCPM) and 8-state circular polarization modulation (8CPM) respectively. Issues of modulation, demodulation, 3D symbol constellations and 3D propagating waveforms for the proposed modulation schemes are presented and analyzed in the presence of channel effects, and they are shown to have the same bit error performance in the presence of AWGN compared with conventional schemes while provide 3dB gain in the flat Rayleigh fading channel.

The transmission performance of 112 Gb/s hybrid multiband (HMB) carrier-less amplitude and phase (CAP)/quadrature amplitude modulation (QAM) system over a single mode fiber (SMF) is investigated. Analog squared root-raised cosine (SRRC) orthogonal shaping filters are used to implement the CAP signal that is used to modulate  the 1550 nm (or 1310 nm) continuous wave (CW) laser using Mach-Zehnder modulator. Simulation of HMB CAP-M/QAM-M schemes with M=16, 32, and 64 is performed and the results are compared with that of the corresponding 112 Gb/s single-band of the same scheme. The results show that increasing the roll-off factor r will improve the bit error rate (BER) performance of the system. The optical power required to achieve a BER of for CAP-16/QAM-16 system reduces by 0.75 and 1.88dBm for four-subband and single-band schemes, respectively, when r increases from 0 to 0.4. While the improvement in the laser transmitted optical power for 4-subband and single-band CAP-32/QAM-32 s...

This work describes the development and use of a multi-channel, programmable physiological stimulator. The device is intended for the detection of epileptic events and crisis prediction using encephalograms. The animals were followed by the kindling model. The system program accepts several inputs of stimulation parameters such as, pulse width, separation between pulses, pulse intensity and total number of pulses. The stimulator generates constant-current, bipolar pulses with a maximum amplitude of 5 mA and a resolution of 50μA. As regards voltage, the maximum amplitude is 150 V. The stimulator was constructed with a microcontroller (PIC18F4550), the latter version being controlled by a personal computer. Experiments of achieving the epileptic events were carried out on rats.

We experimentally demonstrate the photonic generation of symmetrical waveforms based on amplitude-only modulation in a fiber-based temporal pulse shaping (TPS) system. A rectangular waveform with a 3-dB width of 18.8 ps and a triangular waveform with a 3-dB width of 6.7 ps are experimentally generated.

A new modulation scheme for 2-D OCDMA systems named multi-code modulation (MCM) is proposed in this paper. The key advantage of MCM over the conventional ones is the ability of mitigating simultaneously both multiple access interference and dispersion. We also propose to combine MCM with heterodyne detection, a powerful technique to relax optical beating interference, to obtain better performance. The numerical results show that the proposed system allows for lower bit error rate, lower required power, and higher user's bit rate than that of conventional ones using other modulation schemes such as on-off keying modulation, pulse amplitude modulation, and pulse position modulation.

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We experimentally demonstrate the photonic generation of symmetrical waveforms based on amplitude-only modulation in a fiber-based temporal pulse shaping (TPS) system. A rectangular waveform with a 3-dB width of 18.8 ps and a triangular waveform with a 3-dB width of 6.7 ps are experimentally generated.

We present a high-order UWB pulses generator based on a microwave photonic filter which provides a set of positive and negative samples by using the slicing of an incoherent optical source and the phase inversion in a Mach-Zehnder modulator. The simple scalability and high reconfigurability of the system permit a better accomplishment of the FCC requirements. Moreover, the proposed scheme permits an easy adaptation to pulse amplitude modulation, bi phase modulation, pulse shape modulation and pulse position modulation. The flexibility of the scheme for being adaptable to multilevel modulation formats permits to increase the transmission bit rate by using hybrid modulation formats.

We propose a decoy-pulse protocol for frequency-coded implementation of B92 quantum key distribution protocol. A direct extension of decoy-pulse method to frequency-coding scheme results in security loss as an eavesdropper can distinguish between signal and decoy pulses by measuring the carrier photon number without affecting other statistics. We overcome this problem by optimizing the ratio of carrier photon number of decoy-to-signal pulse to be as close to unity as possible. In our method the switching between signal and decoy pulses is achieved by changing the amplitude of RF signal as opposed to modulating the intensity of optical signal thus reducing system cost. We find an improvement by a factor of 100 approximately in the key generation rate using decoy-state protocol. We also study the effect of source fluctuation on key rate. Our simulation results show a key generation rate of 1.5×10 -4 /pulse for link lengths up to 70km. Finally, we discuss the optimum value of average photon number of signal pulse for a given key rate while also optimizing the carrier ratio.

-This paper presents a general frame work for computing the asymptotic error probability (i.e., at high average SNR's) of M-ary and binary signaling schemes over Rician and Rayleigh fading diversity channels. A general theorem (Theorem 1) relates the asymptotic error rate of multipath and multichannel receivers (over AWGN, IS1 free channels) to the multi-dimensional integral of the conditional error probability. Two other theorems are presented for the particular cases where the conditional error probability is a function of the sum of received SNR's (Theorem 2) or received amplitudes (Theorem 3). Theorems 2 and 3 are related for linear coherent systems, and closed form expressions are obtained for equal gain combining systems. Detection structures for typical diversity schemes (coherenffnoncoherent maximal ratio and equal gain combining, and quadratic noncoherent combining) are considered. We analyze the asymptotic error rates of some M-ary signaling schemes (MRSKMPAM with Kth order diversity and orthogonal signals with I< = 1 and with coherent and noncoherent detection). Binary signaling is also considered in our study. T tion systems over multipath or multichannel Rayleigh fading has been extensively studied in the literature [1]-[5], and Rician channels have also been considered [6], [7]. The complexity of the exact error rate expressions usually motivates a particularly important problem in practice, which is the asymptotical performance or asymptotic error rate evaluation at high average SNR's. This problem has been considered before by applying the limit theorems and/or some ad-hoc methods to the exact error rate expressions. Such methods resulted in some asymptotic error formulas for Rayleigh fading [4], [SI, while a similar analysis has not appeared for Rician Fading. However, a general approach for directly obtaining such asymptotic results for either channel type is not available.

This paper presents an analysis of the gated Gaussian impulsive noise and its effects on M -ary Quadrature Amplitude Modulation (M -QAM) schemes. In the approach, both amplitude variation and noisy pulse duration can be characterized as a modulation of the impulsive noise component by a discrete (binary or m-ary) random process. New exact expressions are presented for the probability density function, autocorrelation function and power spectral density of the noise, as well as for the bit error probability of M -QAM, considering the maximum a posteriori probability optimum receiver. An important aspect of the proposed approach is the fact that the discrete random process incorporates the main parameters of the impulsive noise, such as amplitude, duration, instants in which the noise is added and time intervals between instants in which the noise is added.

Coded modulation with probabilistic amplitude shaping (PAS) is considered for intensity modulation/direct detection channels with a transmitter peak-power constraint. PAS is used to map bits to a uniform PAM-6 distribution and outperforms PAM-8 for rates up to around 2.3 bits per channel use. PAM-6 with PAS also outperforms a cross-shaped QAM-32 constellation by up to 1 dB and 0.65 dB after bit-metric soft-and hard decoding, respectively. An alternative PAM-6 scheme based on a framed-cross-shaped QAM-32 constellation is proposed that shows similar gains.

Coded modulation with probabilistic amplitude shaping (PAS) is considered for intensity modulation/direct detection channels with a transmitter peak-power constraint. PAS is used to map bits to a uniform PAM-6 distribution and outperforms PAM-8 for rates up to around 2.3 bits per channel use. PAM-6 with PAS also outperforms a cross-shaped QAM-32 constellation by up to 1 dB and 0.65 dB after bit-metric soft-and hard decoding, respectively. An alternative PAM-6 scheme based on a framed-cross-shaped QAM-32 constellation is proposed that shows similar gains.

This paper presents the simple method optimization of one-dimensional M-ary Pulse Amplitude Modulation (M-PAM) constellations for the Additive White Gaussian Noise (AWGN) channels when the error probability is minimized under the power constraint. This method is independent of the distribution information source, and adapts the given source M-PAM signal constellation to transmission the AWGN channel.

This paper presents the simple method optimization of one-dimensional M-ary Pulse Amplitude Modulation (M-PAM) constellations for the Additive White Gaussian Noise (AWGN) channels when the error probability is minimized under the power constraint. This method is independent of the distribution information source, and adapts the given source M-PAM signal constellation to transmission the AWGN channel.

This paper illustrates the challenges imposed by the atmospheric channel on the design of a terrestrial laser communication link. The power loss due to scattering effect is described using the Kim/Kruse scattering model while the effect and the penalty imposed by atmospheric turbulence is highlighted by considering the bit error rate (BER) of an On-Off Keying modulated link in an optical Poisson channel. The power loss due to thick fog can measure over 100 dB/km while snow and rain result in much lower attenuation. We show that non-uniformity in the atmospheric temperature also contributes to performance deterioration due to scintillation effect. At a BER of 10 -4 , for a channel with a turbulence strength of >0.1, the penalty imposed by turbulence induced fading is over 20 photoelectron counts in order to achieve the same level of performance as a channel with no fading. The work reported here is part of the EU COST actions and EU projects..

The electronics producing a few nanoseconds long LED pulses tuneable in the amplitude and the optical system distributing the LED light to scintillators by a single optical fibre are described. The properties of the LED pulses are controlled by a computer connected via a CANbus to the controller on the board. We produced a prototype with 6 LED pulse drivers placed on a 4-layer PCB with dimension 250 x 147 mm2. The pulse width is constant and 3 ns long. Its amplitude can be tuned from zero to 1.2 A. The pulse frequency can be set in the range up to 100 kHz. The LED light is distributed by a 1 mm diameter optical fibre. On the length of 2 m the fibre has every 30 mm a notch which flashes light with homogeneity of \pm20%. The system is foreseen for calibration of silicon photomultipliers embedded in scintillation tiles.

The performance of burst-by-burst adaptive modulation is studied in conjunction with reduced complexity turbo equalization over a wideband multi-path Rayleigh fading channel. By employing the reduced complexity turbo equalizer, higher-order modulation modes such as 64-level Quadrature Amplitude Modulation (64-QAM) can be invoked, than upon using the conventional turbo equalizer. The structure of the reduced complexity turbo equalizer was also exploited in order to invoke an iterative least mean square channel estimator. Finally, the performance of the adaptive modulation scheme was compared to that of its constituent modulation modes and a signal-to-noise ratio gain of ½ ¼dB to ½ dB was recorded for the throughput range of 0.5 to 2.0 bits/symbol.

We demonstrate a reconfigurable optical transmitter of higher-order modulation formats including pulse-amplitudemodulation (PAM) signals and quadrature-amplitude-modulation (QAM) signals. We generated six different modulation formats by multiplexing 10 Gbit∕s on-off-keying (OOK) signals (10 Gbaud binary phase-shift keying, 4-PAM, 8-PAM quadrature phase-shift keying (QPSK), 16-QAM and 16-star-QAM with error-vector magnitudes (EVMs) of 8.1%, 7.5%, 7.8%, 8.2%, 7.2%, and 6.9%, respectively) and 80 Gbit∕s 16-QAM with an EVM of 8.5%, as well as 120 Gbit∕s 64-QAM with an EVM of 7.1%, using two or three 40 Gbit∕s QPSK signals, respectively. We also successfully transmitted the generated 16-QAM signals through a 100 km transmission line with negligible power penalty.

Next-generation high-speed passive optical network (HS-PON) transceivers supporting 25, 50 and 100 Gb/s are under the early stage of their standardization process. One key aspect of this process is the choice of the best modulation format. To this end, performance comparisons among several modulation formats against different physical constraints have been presented in literature and are still being carried out. In our contribution, we performed an exhaustive analysis on the impact of transceivers electrical frequency response shape on the performance of 2-levels pulse amplitude modulation (PAM-2), 4-levels PAM (PAM-4), electrical and optical duobinary modulation formats with adaptive equalizer at the receiver side. We show by means of numerical simulations that the specification of the typically used -3dB bandwidth is not sufficient, since also out-of-band electrical frequency response specifications (such as the -20dB bandwidth) has a huge impact on the performance of the analyzed modulation formats. The normalized graphs given at the end of the paper in terms of -3dB and -20 dB bandwidths can thus be useful for the design of the next generation of HS-PON transceivers.

— UWB is a new interesting technology for wireless communications. It can replace traditionally carrier-based radio transmission by pulse-based transmission using ultrawide band frequency but at a very low energy. An important aspect of research in this domain is to ...

Active control and cancellation of residual amplitude modulation (RAM) in phase modulation of an optical carrier is one of the key technologies for achieving the ultimate stability of a laser locked to an ultrastable optical cavity. Furthermore, such techniques are versatile tools in various frequency modulation-based spectroscopy applications. In this Letter we report a simple and robust approach to actively stabilize RAM in an optical phase modulation process. We employ a waveguide-based electro-optic modulator (EOM) to provide phase modulation and implement an active servo with both DC electric field and temperature feedback onto the EOM to cancel both the in-phase and quadrature components of the RAM. This technique allows RAM control on the parts-per-million level where RAM-induced frequency instability is comparable to or lower than the fundamental thermal noise limit of the best available optical cavities.

Combining pseudo random-modulation techniques with cavity enhanced spectroscopy allows the estimation of both optical path length and absorption while using a cw diode laser as the light source. Two pseudo-random modulation approaches are described, in each case combined with an off-axis cavity consisting of two cylindrical mirrors oriented to produce a dense pattern of cavity modes. In one approach, the amplitude of the laser is modulated; deconvolution results in an exponential ring-down decay curve. In the second approach, tone bursts that modulate the laser frequency are switched on and off with a pseudo-random code. Deconvolution yields the first derivative of an exponential whose amplitude is proportional to absorbance. With either approach the dynamic range of the transmitted intensity is much smaller than for a ring-down experiment, allowing high gain before the signal is digitized. Initial experimental results measuring carbon monoxide are presented, and the dependence of d...

This paper presents an optical image encryption system based completely on amplitude modulation, phase modulation in the discrete Fourier transform and modified chaotic logistic map. Amplitude modulation and phase modulation are accomplished by the use of spatial light modulator (SLM). SLMs are normally used to control incident light in amplitude-best, phasebest or the mixture (amplitude-phase). The random amplitude modulation based on a chaotic Baker map is carried out in time domain, while the random phase modulation is accomplished in the frequency domain. In this paper, we proposed a technique to regulate and enhance protection in a chaotic logistic map method leading to increased variety of key space of the logistic map. This causes our encryption system to become exceptionally sturdy against brute pressure. An exhaustive analysis of the proposed encryption system is undergone and shows positive results in encryption metrics when compared to several different photo encryption techniques. The analysis demonstrates the highly valued security and immunity to noise of the photograph encryption. The proposed modified logistic map with amplitude and phase modulation is suitable for real-time application.

This paper deals with determination of the critical modulation frequency (CMF) for random amplitude and frequency changes in a sinusoidal signal . The CMF is defined as the smallest modulation frequency for which AM and FM detection thresholds , expressed as modulation indices, reach the same values. The random amplitude and frequency changes were produced by modulators which were sinusoidal waves with randomly changing amplitude from period to period. The results indicate that the CMF is an increasing function of the carrier frequency and the sound pressure level . It is also shown that thresholds for detecting modulation, when expressed as root-meansquare modulation index, do not depend on the character of the modulating signal , i.e. whether this signal is periodic or random. Further, the CMF is independent of the character of the modulating signal.

A just noticeable time delay (JNTD) between the onset of a single sinusoidal amplitude modulation (AM) and a complex modulation applied to the same carrier was measured in this study. The carrier was a 4-kHz tone and the modulator was a five-component multitone complex. In the first experiment, four of five components had constant frequencies, i.e. 160, 170, 180, 190 Hz and they were turned on synchronously (synchronous components) in the middle of the carrier duration. The frequency of the fifth component (asynchronous one) varied from 10 to 150 Hz and it was turned on earlier than the synchronous ones. In the second experiment, the asynchronous component was situated in the centre of the synchronous components' spectrum; its frequency was constant and equal to 100 Hz. The spectral separation between the asynchronous component and the synchronous ones of the modulator varied. The results, i.e. the just noticeable time delay between the onset of a single sinusoidal amplitude modulation and a complex modulation (or asynchrony threshold), are analogous to those obtained in the audible frequency domain. They can be interpreted on the basis of the auditory system model containing a bank of modulation filters. It seems that two separate mechanisms are responsible for the JNTD between the onset of the single component modulation and the complex modulation. The first one results from an interaction between all the components of a modulator passing a single modulation filter tuned to the frequency of the asynchronous component. This sort of interaction (or masking) was most effective when the spectral separation between the asynchronous component and the synchronous ones was the smallest one. With an increase in this separation, a significant decrease in the asynchrony thresholds was observed. The second mechanism determining the obtained asynchrony thresholds is based on the uncertainty principle: modulation filters with good frequency selectivity, i.e. filters tuned to low modulation rates, are characterised by a poor time resolution. Thus, in the case of the lowest frequencies of the asynchronous component the subjects' performance would be relatively poor even when there was a significant spectral interval between this component and the synchronous ones. As in the audible frequency domain, the pattern of the asynchronicity thresholds was related to the modulation filter bandwidth. The obtained results suggest the bandwidth of the modulation filters whose Q factor should be close to 1 or less.