Pulse Amplitude Modulation Scheme Research Articles

SIPAM-4 scheme improves bit error rate performance in MISO X-ray communication system

X-ray communication (XCOM) technology, which uses X-ray as the carrier wave, is expected to solve the problem of reentry blackout region communication with its good penetration characteristics. In order to mitigate the effects of non-linear distortion of the gated X-ray tube (GMXT), the multiple-input single-output (MISO) technique has been introduced in XCOM systems. A pulse amplitude modulation scheme based on superimposed intensity (SIPAM) was proposed and achieved by configuring GMXTs with on/off keying modulation in MISO XCOM system. The feasibility of the proposed SIPAM scheme in XCOM was numerically investigated through Monte Carlo simulations. As the divergence angle of the GMXT increases, the optical power distribution tends to be more uniform in the receiving plane. It can greatly relax the requirements for link alignment. After that, we conduct a proof-of-concept experiment for the SIPAM with four levels (SIPAM-4) scheme by employing two GMXTs and an LYSO-SiPM-based X-ray detector. The experimental results show that when the bit error rate is within the forward error correction limit of 3.8 × 10−3, the SIPAM-4 scheme can reach a maximum communication rate of 1.20 Mbps, which is 20% higher than the conventional PAM-4 scheme. It can be included that the proposed MISO based the SIPAM-4 modulation scheme could improve the performance of the X-ray communication system.

Interband cascade technology for energy-efficient mid-infrared free-space communication

Space-to-ground high-speed transmission is of utmost importance for the development of a worldwide broadband network. Mid-infrared wavelengths offer numerous advantages for building such a system, spanning from low atmospheric attenuation to eye-safe operation and resistance to inclement weather conditions. We demonstrate a full interband cascade system for high-speed transmission around a wavelength of 4.18 µm. The low-power consumption of both the laser and the detector in combination with a large modulation bandwidth and sufficient output power makes this technology ideal for a free-space optical communication application. Our proof-of-concept experiment employs a radio-frequency optimized Fabry–Perot interband cascade laser and an interband cascade infrared photodetector based on a type-II InAs/GaSb superlattice. The bandwidth of the system is evaluated to be around 1.5 GHz. It allows us to achieve data rates of 12 Gbit/s with an on–off keying scheme and 14 Gbit/s with a 4-level pulse amplitude modulation scheme. The quality of the transmission is enhanced by conventional pre- and post-processing in order to be compatible with standard error-code correction.

Linearisation Method of DML-Based Transmitters for Optical Communications Part III: Pulse Amplitude Modulation

A new linearization method for optical transmitters based on directly modulated lasers (DMLs), named the Stretched A method, was proposed in Parts I and II of this work. Parts I and II presented the theoretical framework of the method for non-return-to-zero (NRZ) modulation and related detailed simulation and experimental results. Here, we extend the method to pulse amplitude modulation schemes (PAM). Focussing on 4-level PAM (PAM-4), we present the theoretical background and discuss implementation options. A simplified variation of the method for the generation of PAM signals with a significantly lower number of sub-currents is proposed. Simulation studies for PAM-4 transmission at 50 GBaud (100 Gb/s) and an experimental proof-of–principle demonstration at 16 GBaud (32 Gb/s) are reported based on 850 nm vertical-cavity surface-emitting lasers (VCSELs). For PAM-4, products of effective eye diagram areas ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\boldsymbol{PS}}$</tex-math></inline-formula> ) of 0.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> and 43 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> before and after applying the Stretched A method were measured, demonstrating an improvement ratio of ∼72. The sensitivity and tolerances of the method are analyzed using simulation and experiment.

Low‐Complexity Digital Equalizers for High‐Speed Underwater Optical Wireless Communication

Hundreds of Megabit per second (Mb/s) data transmission over a moderate range (10m) underwater optical wireless channel is implemented with 4-level pulse amplitude modulation scheme using an off-the-shelf light-emitting diode as the optical source and digital equalizers. In particular, the channel nonlinear distortion from light-emitting diode is considered and a matched model is developed. To mitigate these distortions under various 4-level pulse amplitude modulation signal baud rates, the Bit error rate (BER) and Signal-to-noise ratio (SNR) performances of the pre-, post- and matched-equalizers are evaluated and compared. The digital matched-equalizer bank is shown and verified to offer the best BER/SNR performance for 4-level pulse amplitude modulation signal using more than 200 MBaud rate. With the proposed equalizer, we have recorded the highest data rate of 600Mb/s at 20% FEC limit over 10m free-space underwater link.

Improved optical camera communication systems using a freeform lens.

Optical camera communication (OCC) systems, which utilize image sensors embedded in commercial-off-the-shelf devices to detect time and spatial variations in light intensity for enabling data communications, have stirred up researchers' interest. Compared to a direct OCC system whose maximum data rate is strongly determined by the LED source size, a reflected OCC system can break that limitation since the camera captures the light rays reflecting off an observation plane (e.g., a wall) instead of those light rays directly emanated from the light source. However, the low signal-to-noise ratio caused by the non-uniform irradiance distribution produced by LED luminaire on the observation plane in current reflected OCC systems cannot be avoided, hence low complexity and accurate demodulation are hard to achieve. In this paper, we present a FreeOCC system, which employs a dedicatedly tailored freeform lens to precisely control the propagation of modulated light. A desired uniform rectangular illumination is produced on the observation plane by the freeform lens, yielding a uniform grayscale distribution within the received frame captured by the camera in the proposed FreeOCC system. Then, the received signal can be easily demodulated with high accuracy by a simple thresholding scheme. A prototype of the FreeOCC system demonstrates the high performance of the proposed system, and two pulse amplitude modulation schemes (4-order and 8-order) are performed. By using the freeform lens, the packet reception rate is increased by 35% and 32%, respectively; the bit error rate is decreased by 72% and 59%, respectively, at a transmission frequency of 5 kHz. The results clearly show that the FreeOCC system outperforms the common reflected OCC system.

In Vivo Motion Correction in Super-Resolution Imaging of Rat Kidneys.

Super-resolution (SR) imaging has the potential of visualizing the microvasculature down to the 10- [Formula: see text] level, but motion induced by breathing, heartbeats, and muscle contractions are often significantly above this level. This article, therefore, introduces a method for estimating tissue motion and compensating for this. The processing pipeline is described and validated using Field II simulations of an artificial kidney. In vivo measurements were conducted using a modified bk5000 research scanner (BK Medical, Herlev, Denmark) with a BK 9009 linear array probe employing a pulse amplitude modulation scheme. The left kidney of ten Sprague-Dawley rats was scanned during open laparotomy. A 1:10 diluted SonoVue contrast agent (Bracco, Milan, Italy) was injected through a jugular vein catheter at 100 [Formula: see text]/min. Motion was estimated using speckle tracking and decomposed into contributions from the heartbeats, breathing, and residual motion. The estimated peak motions and their precisions were: heart: axial- [Formula: see text] and lateral- [Formula: see text], breathing: axial- [Formula: see text] and lateral- [Formula: see text], and residual: axial-30 [Formula: see text] and lateral-90 [Formula: see text]. The motion corrected microbubble tracks yielded SR images of both bubble density and blood vector velocity. The estimation was, thus, sufficiently precise to correct shifts down to the 10- [Formula: see text] capillary level. Similar results were found in the other kidney measurements with a restoration of resolution for the small vessels demonstrating that motion correction in 2-D can enhance SR imaging quality.

Investigation of Ber Performances in Chaotic-Secured Optical Fiber Communication Systems using the 4-PAM Modulation Scheme

This paper presents a numerical simulation investigation on the bit error rate in a chaotic-secured fiber channel and a conventional fiber channel when propagating independently. The investigated communication system uses the pulse-amplitude modulation scheme (4-PAM) at the bit rate of 10 Gbps, the fiber length of 100 km, and the operation wavelength of 1550 nm. Our simulation results demonstrate both chaotic and non-chaotic transmission channels can well operate with the bit rate up to 20 Gbps with the BER smaller than 10-5 if dispersion and fiber loss issues are appropriately compensated without needing forwarderror-correction, showing high potential in physically secured optical fiber communication systems.

A pulse amplitude modulation scheme based on in-line semiconductor optical amplifiers (SOAs) for optical soliton systems

&lt;p&gt;The objective of this work is to simulate a pulse amplitude modulation (PAM) scheme based on in-line semiconductor optical amplifiers for optical soliton systems. The max. power for soliton systems, based on various bits/symbol PAM modulation schemes after a fiber length of 100 km, is simulated and clarified. In addition to the max. Q factor for soliton systems, PAM modulation schemes with various in-line SOA injection currents and a fiber length of 100 km are also simulated and demonstrated in the results. The total electrical power after photo-detectors for soliton systems, based on PAM modulation schemes with various in-line SOA injection currents and a fiber length of 100 km, is also simulated and clarified in the results. The study emphasizes that the higher the SOA injection current, the higher the electrical power and the lower the Q factor that can be achieved in the soliton system.&lt;/p&gt;

Investigation of frequency dependent nonlinearity on pulse amplitude modulation in bandlimited visible light communications

In this work, the nonlinear behavior on pulse-amplitude-modulation (PAM) and their impact on the performance of RGB light-emitting-diodes (LED) based visible light communications (VLC) is presented. Particularly, how the limited source bandwidth affects the nonlinearity of fully modulated RGB LEDs is investigated. It is found that when symbol-rate is higher than the channel bandwidth the nonlinearity gradually diminishes. It causes the symbol-rate dependent nonlinearity. When applying PAM in VLC links, a pre-distortion method is often applied to compensate for the nonlinearity. Due to this symbol-rate dependency, however, the conventional pre-distortion method has a limitation on linearizing the non-linear VLC channel, especially in the case of applying various symbol-rates according to the channel condition. Although it can be adaptively compensated by nonlinear equalizers, their complexity is considerably high. In this work, the characteristics of multi-level PAM scheme in a band-limited nonlinear channel is presented. Also, the feasibility of a low complex but efficient pre-distortion method derived from monotonically decreasing characteristics of the frequency dependent nonlinearity is investigated.

VCSEL Array-Based Gigabit Free-Space Optical Femtocell Communication

We present an indoor free-space optical communication system to augment traditional short-range radio frequency wireless links. In this system, we integrated a high-frequency, high-current laser driver with an 850 nm wavelength, 500 mW vertical cavity surface emitting laser (VCSEL) array to transmit high speed optical signals with a large spatial coverage. The large current-bandwidth capability of the laser driver is enabled by a distributed current driver design utilizing three enhanced-mode pseudomorphic high electron mobility transistors. At the optical receiver end, a high-sensitivity avalanche photodiode is used to achieve high speed optical signal detection without any light concentrating optical device and is tolerant to angular deviation up to 27°. The communication link described in this article forms an optical femtocell with an area of 100 cm2 at a distance of three meters from the transmitter. A bit error rate of less than 10−4 is achieved throughout the optical femtocell in a normal in-door environment. On-off-keying and four-level pulse amplitude modulation schemes are both implemented with 1.25 Gb/s and 2 Gb/s data rate respectively, using the hardware described in this article. Additionally, the overall performance of this free-space optical link is evaluated in terms of viewing angle, distance range, and bit error rate.

Nyquist four-level pulse amplitude modulation scheme (PAM-4) based on hierarchical modulation in IM/DD-TDM PON with hybrid equalization

In order to achieve higher power margin in the intensity-modulation and direct detection (IM/DD) based time division multiplexed passive optical network (TDM-PON) system, at the optical line terminal (OLT) side, we propose to use a Nyquist pulse shaped four-level pulse amplitude modulation (PAM-4) by using the electric low pass filter(LPF). In addition, we apply the hierarchical modulation (HM) scheme by assigning of most-significant bits (MSBs) and the less-significant bits (LSBs) of the PAM-4 symbol to optical network units (ONUs) located at different link positions. In addition, an overlap frequency domain equalizer (OFDE) and a vestigial-side band (VSB) filter are used to mitigate the linear inter symbol interference (ISI) and power fading (both of which are incurred by chromatic dispersion (CD)), respectively. The system performance, i.e., bit error rate (BER) and receiver sensitivity for both MSB and LSB, are analyzed by varying different system configurations. Simulation results show that increasing the hierarchical power ratio, which determines the significance difference between the points in the Nyquist pulse shaped HM PAM-4 constellation diagram, can increase the MSB’s receiver sensitivity and reduce the LSB’s receiver sensitivity. Furthermore, it has been demonstrated that the electric low pass filter can reduce the system ISI. In addition, the effect of linear ISI and power fading can be migrated by utilizing OFDE and VSB filter, respectively.

New pulse amplitude modulation for fine tuning of memristor synapses

Nanoscale memristors can be used as synapses in brain-mimicking neuromorphic systems. Here, the fine tuning of memristor conductance is important in controlling the synapse weights precisely, because the coarse tuning of memristor synapses can cause a significant error in neuromorphic processing. In this paper, we propose a new Pulse Amplitude Modulation (PAM) method for the fine tuning of memristor conductance. The new PAM scheme is verified by the experimental measurement of real memristors, where the new PAM could reduce the pulse-to-pulse fluctuation in conductance change per pulse by 84.8%, compared to the previous linear PAM. For comparing the linear and new PAM schemes, they are tested in programming memristor synapses in the memristor-based Cellular Neural Networks (CNN). The simulation result confirms that the new-PAM-programmed CNN shows better quality of edge detection than the linear-PAM-programmed CNN.

Universal soft demapper for M-ary PAM with reduced complexity

In this paper, we propose an efficient soft demapper for M-ary pulse amplitude modulation (PAM) schemes. The proposed demapper estimates soft decision bit information (SDBI) for any M-ary PAM symbols using a universal type of hardware structure. The proposed method performs as well as the Max-log method, without any exhaustive search process. Instead, it maps a detected PAM symbol to a specific region, with only one constellation symbol to estimate the distance. In this way, the proposed method requires approximately one distance estimation per bit. We first derive the equations to estimate SDBI for a few Gray-mapped M-ary PAM schemes, and subsequently present compact universal equations applicable to any M-ary PAM scheme. The simulation results confirm that the proposed method produces exactly the same performance as the Max-log method with greatly reduced computational complexity.

Nyquist 4-ary pulse amplitude modulation scheme based on electrical Nyquist pulse shaping and fiber Bragg grating filter

Intensity modulation and direct detection signal are sensitive to power fading and nonlinear intersymbol interference (ISI) induced by modulator chirp, fiber dispersion, and square-law photo-detection. We propose and experimentally demonstrate a Nyquist 4-ary pulse amplitude modulation and direct detection scheme relying on pulse-shaping with an electrical filter and optical equalization with a vestigial-sideband (VSB) filter in the transmitter. The power fading could be eliminated by using the VSB filter. Compared with conventional 4-ary pulse amplitude modulation, the Nyquist signal has a stronger resistance to nonlinear ISI.

Solution refinement of wireless optical system model with multi-level modulation

Two optimisation models established for a wireless optical communication system based on the four-level pulse amplitude modulation scheme were recently reported. Both models were expressed in terms of multiple improper integrals. To improve the computational efficiency, the closed-form in terms of the incomplete gamma function is derived that is supported by most mathematical software packages, including MATLAB. The previously reported optimisation models are solved with the new method. The solutions are presented.

Genotype-inspired laser material processing: a new experimental approach and potential applications to protean materials

We have developed a new direct-write experimental technique that enables the delivery of preprogrammed laser pulse scripts to a substrate with high fidelity during patterning and motion sequences. The laser technique can be readily applied to fundamental investigations of complex laser–material interaction phenomena, and easily integrated into laser–material processing schemes for commercial and industrial applications. The laser direct-write technique has been crafted by association with the genome and genotype concepts, where predetermined and prescribed laser pulse scripts are synchronously linked with the tool path geometry, and each concatenated pulse sequence is intended to express a specific material attribute. This laser processing method is particularly well suited for protean or mutable materials that can be altered with extreme sensitivity by the application of high precision photon exposures. We envision that multifunctional materials can be altered on a localized scale to create integrated “devices” on a common substrate. The synchronized laser pulse amplitude modulation scheme and application to a candidate photosensitive glass ceramic are the focus of this paper.

PERFORMANCE ANALYSIS OF A NOVEL M-ARY CODE SELECTED DS-BPAM UWB COMMUNICATION SYSTEM

A novel M-ary direct sequence ultra wideband (UWB) communication system based on the selection of the direct sequence code is studied in this paper. The proposed M-ary code selected direct sequence bipolar pulse amplitude modulation scheme can achieve high bit rate without increasing the system bandwidth or changing the pulse shape. With the increase of the modulation level M, the system bit error rate will be improved even at lower signal to noise ratio per bit. The exact bit error probability is derived over the AWGN channel and correlation receivers. Both Monte-Carlo simulation and the theoretical analysis prove the efficiency of this M-ary UWB system.

MMSE multipath diversity combining for multi-access TH-UWB in the presence of NBI

The performance of asynchronous time-hopping ultra-wideband (TH-UWB) multiple access spread spectrum is analytically investigated in a UWB realistic multipath channel and in the presence of narrowband interference (NBI). In particular, an interference suppression receiver for TH-UWB wireless systems is proposed. It consists of selecting the first strongest multipath components using an appropriate Rake receiver with the path diversity combining being based on the minimum mean square error criterion. Pulse position modulation and pulse amplitude modulation schemes are considered. The expressions of the signal-to-interference and noise ratio at the output of the selective Rake combiner, the system multi-access data rate as well as the conditional bit error rate are also derived. The impact of different parameters, such as the number of selected dominant paths, the NBI power as well as the time hopping sequence code on the system performance are studied. Results reveal that the proposed receiver can almost completely eliminate the effect of NBI.

Linearisierung der primär nichtlinearen Modulationsart MSK - eine anschauliche Darstellung

MSK (minimum shift keying) is a binary digital modulation scheme leading to spectrally efficient modulated signals. A straightforward view of MSK is to consider this modulation scheme as continuous phase FSK (continuous phase frequency shift keying, CPFSK) which is a non-linear modulation scheme. It would be desirable to be able to regard MSK as a linear pulse amplitude modulation scheme (PAM). It then would be possible to exploit the advantages of linear modulation schemes in terms of signal generation by a transmitter and signal processing by a receiver

On the capacity of a twisted-wire pair: peak-power constraint

The capacity of a twisted-pair channel (TPC) with a peak-power constraint imposed on the transmitted signal is considered. Bounds on the capacity are evaluated for two models of the near-end crosstalk (NEXT). The NEXT is modeled either by a peak-limited signal governed by the same probability law characterizing the transmitted signal, or by a Gaussian process possessing the same power spectral density as that of the transmitted signal. White Gaussian noise is also present in addition to the NEXT interference. The important case of NEXT-dominated interference for which the bounds do not depend on the specific pulse-shape used, and therefore apply also for the optimized pulse amplitude modulation (PAM) scheme, is particularly examined. Optimized channel symbol rates and bounds on the number of information bits per channel symbol are evaluated using a certain PAM format and a suboptimal receiver. A comparison between optimally coded and uncoded PAM schemes is performed for the NEXT-dominated TPC. The results presented extend those reported in a previous work by I. Kalet and S. Shamai (see ibid., vol.38, p.379-83, Mar. 1990) on the capacity of a TPC in which a Gaussian model for both the transmitted and the NEXT signals is adopted and only an average power constraint on both signals is imposed. >