Showing papers on "Keying published in 2012"

High-Efficiency Differential-Chaos-Shift-Keying Scheme for Chaos-Based Noncoherent Communication

Abstract: In this brief, a new noncoherent chaos-based communication scheme, named high-efficiency differential chaos shift keying (DCSK) (HE-DCSK), is proposed. By recycling each reference sample in DCSK, 2 bits of data can be carried in one data-modulated sample sequence, which offers our scheme double bandwidth efficiency and nonrepeated transmitted signal less prone to interception in comparison to DCSK. The bit-error performance of the proposed scheme is studied analytically based on Gaussian approximation for discrete-time implementations. Simulations in additive-white-Gaussian-noise channel are performed and compared with DCSK and correlation delay shift keying (CDSK) schemes. Results show that the bit-error rate performance of HE-DCSK can always outperform CDSK and be even better than DCSK with typical spreading factors and at reasonable Eb/No levels.

4-PAM for high-speed short-range optical communications

Abstract: In this work, we compare 4-pulse amplitude modulation and on-off keying modulation formats at high speed for short-range optical communication systems. The transmission system comprised a directly modulated vertical-cavity surface-emitting laser operating at a wavelength of 850 nm, an OM3+ multimode fiber link, and a photodetector detecting the intensity at the receiver end. The modulation formats were compared both at the same bit-rate and at the same symbol rate. The maximum bit-rate used was 25 Gbps. Propagation distances up to 600 m were investigated at 12.5 Gbps. All measurements were done in real time and without any equalization.

Design of a High-Data-Rate Differential Chaos-Shift Keying System

Abstract: In a differential chaos-shift keying (DCSK) system, the reference and information chaotic bearing signals are transmitted in two consecutive time slots and require the presence of delay components in the modulator and demodulator circuits. This system design requires a difficult-to-implement radio-frequency delay line that limits the data rate. The code-shifted DCSK (CS-DCSK) system proposes a solution for these problems by spreading the two chaotic slots by Walsh codes instead of using a time delay and sending them during the same time interval. In this brief, we extend the study of the CS-DCSK system, and we design two versions of a high-data-rate CS-DCSK system, which increase the data rate and can also perform in a multiuser case. The idea to achieve a high data rate is to get the information bits to share the same reference chaotic slot, where their separation is assured and maintained by different chaotic signals. In addition, this new design is not limited to a restricted number of Walsh codes such as CS-DCSK and provides from the properties of the chaotic signal in terms of security and good correlation properties. Finally, the performances of the systems are analyzed.

A Universal Space-Time Architecture for Multiple-Antenna Aided Systems

Abstract: In this tutorial, we first review the family of conventional multiple-antenna techniques, and then we provide a general overview of the recent concept of the powerful Multiple-Input Multiple-Output (MIMO) family based on a universal Space-Time Shift Keying (STSK) philosophy. When appropriately configured, the proposed STSK scheme has the potential of outperforming conventional MIMO arrangements.

Pilot-Symbols-Aided Carrier-Phase Recovery for 100-G PM-QPSK Digital Coherent Receivers

Abstract: A feedforward pilot-symbols-aided carrier-phase recovery scheme is described. The approach relies on pilot symbols that are time-division multiplexed with the transmitted data. In the scheme, an initial coarse estimation of the optical carrier phase, exploiting the knowledge of pilot symbols, is followed by a fine nondata-aided, or blind, estimation. The main advantage of the proposed solution is that of avoiding the phase- ambiguity problem after a cycle slip. The overhead and the impact on the performance of pilot symbols are investigated for long-haul transmission of 100-Gb/s polarization-multiplexed quadrature phase-shift keying wavelength-division-multiplexing signals in different scenarios. For homogeneous transmission, the proposed scheme outperforms blind carrier recovery with differential decoding.

Spatial Pulse Position Modulation for Optical Communications

Abstract: This paper proposes a low complexity spatial modulation (SM) scheme that combines spatial shift keying (SSK) with pulse position modulation (PPM) for optical wireless communication systems. SM is a multi-transmitter technique for achieving increased data rate over the traditional on-off keying (OOK) and PPM signalling methods. Analysis of the error performance of the system in the presence of noise is presented and validated via simulations. There is a perfect agreement between the simulation and the theoretical analysis for the case of M = 2 bits/symbol and other values of M at symbol error rate (SER) of less than 10-2. At higher SER values the analytical prediction is about 1.2 dB more than that of the simulation. We also show the energy efficiency/bandwidth requirement trade-off involved when determining the system parameters such as the number of transmitters and the number of bits per symbol M. Using fewer transmitters improves the energy efficiency but requires more bandwidth. Moreover, the error performance of SPPM is dictated by both the individual channel gains of the multiple transmitters and the difference between these channel gains or path losses. Hence, distinct channel gains are a prerequisite in spatial modulation. An experimental set up to measure and show the dependence of the channel gains on the relative position of the transmitter to the receiver is also presented. These measured channel parameters are then used to evaluate the system error performance. The performance of the SPPM is also compared, in terms of energy and spectral efficiencies, with the classical SSK and repetition coded (RC) schemes in which the multiple transmitters are used to transmit the same data simultaneously. The results show the SPPM as a multi-transmitter signalling scheme that combines the energy efficiency of the PPM with the high spectral efficiency of the SSK.

Blind Digital Modulation Identification for Spatially-Correlated MIMO Systems

Abstract: Modulation type is one of the most important characteristics used in signal waveform identification and classification. Spatial correlation is a crucial factor for practical multiple-input multiple-output (MIMO) systems. This paper addresses the problem of blind digital modulation identification in spatially-correlated MIMO systems. The proposed algorithm is verified using higher order statistical moments and cumulants of the received signal. The purpose is to discriminate among different M-ary shift keying linear modulation schemes without any priori signal information. This study employs several MIMO techniques to identify the modulation with and without channel state information (CSI). The proposed classifier shows a high identification performance in acceptable signal-to-noise ratio (SNR) range.

Flexible and transparent all-graphene circuits for quaternary digital modulations

Abstract: In modern communication systems, modulation is a key function that embeds the baseband signal (information) into a carrier wave so that it can be successfully broadcasted through a medium such as air or cables. Here we report a flexible all-graphene modulator circuit with the capability of encoding a carrier signal with quaternary digital information. By exploiting the ambipolarity and the nonlinearity in a graphene transistor, we demonstrate two types of quaternary modulation schemes: quaternary amplitude-shift keying and quadrature phase-shift keying. Remarkably, both modulation schemes can be realized with just 1 and 2 all-graphene transistors, respectively, representing a drastic reduction in circuit complexity when compared with conventional modulators. In addition, the circuit is not only flexible but also highly transparent (~95% transmittance) owing to its all-graphene design with every component (channel, interconnects, load resistor and source/drain/gate electrodes) fabricated from graphene films. Signal modulation is a mechanism which embeds an information-carrying signal into a carrier wave to broadcast information and is essential for high-speed communication. Zhonget al. report a flexible, transparent all-graphene modulator circuit performing quaternary modulation schemes with only two transistors.

50-Gb/s silicon quadrature phase-shift keying modulator

Abstract: We report the first successful demonstration of quadrature phase-shift keying (QPSK) modulation using two nested silicon Mach-Zehnder modulators. 50-Gb/s QPSK signal is generated with only 2.7-dB optical signal-to-noise ratio penalties from the theoretical limit at a bit-error ratio of 10(-3). This result validates that silicon photonics could be a viable and powerful platform of photonic integrated circuits in coherent optical communications.

Constellation design for color-shift keying using interior point methods

Abstract: Color-shift keying (CSK) is a visible light modulation scheme that transmits data imperceptibly through the variation of output light color. In this work, a rigorous design framework for CSK constellations is presented based on interior point methods. A differentiable approximation to the CSK constellation design problem is presented which is compatible with commercial interior point optimization algorithms and is used to find locally optimal symbol sets. The benefits of the approach are that it can operate with a variety of peak and color-cross talk constraints (i.e., convex constraint regions), permits any desired operating color and is able to produce results for any size constellation. Design guidelines on tradeoffs between minimum distance and operating color as well a heuristic for handling larger constellations are also provided.

Blind Digital Modulation Identification forSpatially-Correlated MIMO Systems

Abstract: Modulation type is one of the most important characteristics used in signal waveform identification and classification. Spatial correlation is a crucial factor for practical multiple-input multiple-output (MIMO) systems. This paper addresses the problem of blind digital modulation identification in spatially-correlated MIMO systems. The proposed algorithm is verified using higher order statistical moments and cumulants of the received signal. The purpose is to discriminate among different M-ary shift keying linear modulation schemes without any priori signal information. This study employs several MIMO techniques to identify the modulation with and without channel state information (CSI). The proposed classifier shows a high identification performance in acceptable signal-to-noise ratio (SNR) range.

Inter-satellite optical wireless communication system design and simulation

Abstract: An ultra-high bit-rate inter-satellite optical wireless communication (IsOWC) system is proposed in thisstudy. The system is designed and simulated up to the bit-rate of 400 Gbps. The proposed system is a non-diffused link or line-of-sight setup, which uses coherent optical quadrature phase-shift keying (QPSK) modulation technique. The performance of the system is analysed in terms of Q -factor, bit-error rate, eye opening and so on. The coverage distance observed with an input power level of 30 dBm for a bit-rate of 400, 160 and 100 Gbps are 4767, 7542 and 9532 km, respectively. Finally, the maximum bit-rate that can be communicated, for inter-satellite link at different orbits such as low-Earth orbit, medium-Earth orbit and geostationary Earth orbit are presented. To the best of the authors knowledge for the first time they have proposed a novel QPSK modulation technique for the design of IsOWC system for achieving higher coverage distance and data rate, which was not been addressed in any current or earlier publications.

Experimental demonstration of microring quadrature phase-shift keying modulators

Abstract: Advanced optical modulation formats are a key technology to increase the capacity of optical communication networks. Mach-Zehnder modulators are typically used to generate various modulation formats. Here, we report the first experimental demonstration of quadrature phase-shift keying (QPSK) modulation using compact microring modulators. Generation of 20 Gb/s QPSK signals is demonstrated with 30 μm radius silicon ring modulators with drive voltages of ~6 V. These compact QPSK modulators may be used in miniature optical transponders for high-capacity optical data links.

Effects of Channel Estimation on Spatial Modulation

Abstract: In this letter, we investigate the effects of training-based channel estimation on the achievable performance of the recent spatial modulation (SM) based multiple-input multiple-output (MIMO) scheme. This is motivated by the fact that the SM transmitter is constituted by a single radio-frequency (RF) branch and multiple antenna elements (AEs), hence simultaneous pilot transmissions from the AEs are impossible, unlike in the classic multiple-RF MIMO transmitters. Our simulation results demonstrate that the SM scheme's BER curve exhibits a performance penalty, while relying on realistic imperfect channel-estimation. In order to combat these limitations, we propose two single-RF arrangements, namely a reduced-complexity joint channel estimation and data detection aided SM scheme as well as a non-coherently detected single-RF space-time shift keying scheme dispensing with channel estimation.

PDM-DQPSK Silicon Receiver With Integrated Monitor and Minimum Number of Controls

Abstract: We demonstrate a novel polarization-division multiplexed differential quadrature phase-shift keying receiver. It has the minimum number of analog controls and an integrated polarization interference monitor for polarization tracking. It can theoretically tolerate polarization-dependent loss in the link. We achieve ~10 times tracking speed improvement, ~6-dB lower loss, and ~100 times lower average bit-error rate during most of the tracking over our previous work for 43-Gb/s PDM-DQPSK.

Mapping Selection and Code Construction for 2^m-ary Polar-Coded Modulation

Abstract: This paper proposes a mapping strategy and a code construction method for 2m-ary polar-coded modulation. In order to find a good mapping for a polar code in an efficient way, we reduce a search space for mapping patterns by exploiting the properties of its polarizing matrix. Once a mapping is selected, the set of unfrozen information bits to define a polar code is automatically determined. Numerical results show that our approach can provide a performance gain of about 0.3-0.5 dB over a conventional approach using random mapping and the polar code optimized for binary phase-shift keying (BPSK) modulation, when pulse-amplitude modulation (PAM) with Gray labelling is employed.

Demonstration of Record Sensitivities in Optically Preamplified Receivers by Combining PDM-QPSK and M-Ary Pulse-Position Modulation

Abstract: We present the principle, implementation, and performance of a recently introduced high-sensitivity modulation format based on the combined use of polarization-division-multiplexed quadrature phase-shift keying (PDM-QPSK, or PQ) and m-ary pulse-position modulation (m-PPM). This novel modulation format, termed PQ-mPPM, offers high receiver sensitivity in optically preamplified receivers. We study the sensitivity of the PQ-mPPM format both analytically and experimentally, and compare it to common modulation formats such as PDM-QPSK, m-PPM, differential phase-shift keying, and polarization-switched QPSK. The bandwidth expansion factor of this format is also discussed. A record sensitivity of 3.5 photons per bit at BER = 10-3 is experimentally demonstrated at 2.5 Gb/s with a novel pilot-assisted digital coherent-detection scheme, outperforming PDM-QPSK by about 3 dB.

Error Rate of Subcarrier Intensity Modulations for Wireless Optical Communications

Abstract: Subcarrier intensity modulations are analyzed for the Gamma-Gamma turbulence channels. We study the error rate of a subcarrier intensity modulated wireless optical communication system employing phase-shift keying, differential phase-shift keying, and noncoherent frequency-shift keying. Closed-form error rate expressions are derived using a series expansion approach. Asymptotic error rate analysis and truncation error analysis are also presented. Our asymptotic analysis shows that the diversity order of the system and the signal-to-noise ratio penalty factors for noncoherent modulations depend only on the smaller channel parameter.

Bistatic backscatter radio for tag read-range extension

Abstract: This work examines the idea of dislocating the carrier transmission from the tag-modulated carrier reception, i.e. bi-static rather than mono-static backscatter radio. In that way, more than one carrier transmitters can be distributed in a given geographical area and illuminate a set of RF tags/sensors that modulate and scatter the received carrier towards a single software-defined receiver. The increased number of carrier transmitters and their distributed nature assists tags to be potentially located closer to one carrier transmitter and thus, improves the power of the scattered signals towards the receiver. Specifically, this work a) carefully derives near-optimal detectors for bi-static backscatter radio and on/off keying (OOK) tag modulation (which is widely used in commercial tags), b) analytically calculates their bit error rate (BER) performance, and c) experimentally tests them in practice with a custom bistatic backscatter radio link. As a collateral dividend, it is shown that the non-linear processing of the proposed receivers requires certain attention on the utilized tag design principles, commonly overlooked in the literature, validating recently reported theoretical results on the microwave domain.

Broadband Modulation Performance of 100-GHz EO Polymer MZMs

Abstract: We experimentally characterize the performance of 100-GHz electro-optical polymer Mach-Zehnder modulators in both dual-drive and single-drive versions using broadband modulation. For the dual-drive version, we measure bit-error rate (BER) at 80 Gbit/s for differential phase-shift keying (DPSK) and >; 90 Gbit/s for on-off keying (OOK). The eye diagrams of 100 Gbit/s OOK and S21 measurement of up to 110-GHz further indicate a response bandwidth of >;100 GHz. Tunable-chirp operation is also demonstrated by changing the phase and amplitude of each driving signal. For the single-drive version, a BER of 10-9 is achieved for both 100-Gbit/s OOK and DPSK signals without optical or electrical equalization. The single-drive version shows a 7-dB bandwidth of >; 110-GHz and a chirp factor of as low as -0.02.

Optical Performance Monitoring Using Artificial Neural Networks Trained With Empirical Moments of Asynchronously Sampled Signal Amplitudes

Abstract: We propose a low-cost technique for simultaneous and independent optical signal-to-noise ratio (OSNR), chromatic dispersion (CD), and polarization-mode dispersion (PMD) monitoring in 40/56-Gb/s return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) and 40-Gb/s RZ-DPSK systems, using artificial neural networks (ANN) trained with empirical moments of asynchronously sampled signal amplitudes. The proposed technique employs an extremely simple hardware and digital signal processing to enable multi-impairment monitoring at different data rates and for various modulation formats without necessitating hardware changes. Simulation results demonstrate wide dynamic ranges and good monitoring accuracies.

Optical Communication Using Subcarrier Intensity Modulation in Strong Atmospheric Turbulence

Abstract: Error rate performance of subcarrier intensity modulations is analyzed for optical wireless communications over strong atmospheric turbulence channels. We study the error rate of a subcarrier intensity modulated optical wireless communication system employing M -ary phase-shift keying, differential phase-shift keying, and noncoherent frequency-shift keying. Both K -distributed turbulence channel (strong) and negative exponential turbulence channel (saturated) are considered. Closed-form error rate expressions are derived using a series expansion of the modified Bessel function. Furthermore, the outage probability expressions are obtained for subcarrier intensity modulated optical wireless communication systems over the K-distributed turbulence and the negative exponential channels. Asymptotic error rate analysis and truncation error analysis are also presented. Our asymptotic analysis shows that differential phase-shift keying suffers a constant signal-to-noise ratio performance loss of 3.92 dB with respect to binary phase-shift keying under strong atmospheric turbulence conditions. The numerical results demonstrate that our series solutions are efficient and highly accurate.

Indoor optical wireless system dedicated to healthcare application in a hospital

Abstract: In this study, the authors deal with a wireless healthcare monitoring solution based on a secure technology in hospital context. Actually, radio frequency (RF) networks can present electromagnetic disturbances in hospital environments. The authors thus investigate an alternative solution based on infrared (IR) technology. As patient mobility is inevitable, they focus on mobile IR communications considering line-of-sight (LOS) propagation between the transmitter coupled with medical sensors and the receiver. The authors study different mobility scenarios, one in two dimensions (2D) for a fixed transmitter height and another in three dimensions (3D) by considering transmitter height variations. In each case, they analyse the distributions of channel gain state to find the statistical model of the mobile IR channel for a given distribution of the patient locations within the room (uniform or gaussian). By calculating the outage probability from statistical analysis, they investigate the impact of the mobility on data rates and quality of service needed for this application in the case of an on–off keying (OOK) modulation before concluding on the reliability of the studied mobile healthcare monitoring system.

Gigabit/s Photonic Generation, Modulation, and Transmission for a Reconfigurable Impulse Radio UWB Over Fiber System

Abstract: We propose and demonstrate a flexible and high-speed impulse radio ultrawideband (IR-UWB) over fiber system using various modulation schemes. Two kinds of fully Federal Communication Commission (FCC) compliant UWB pulses are produced, which is based on the incoherent summation of multiple monocycle pulses with inverse polarities, proper time delays, and different weights. Theoretically, their spectral power efficiency can achieve 33.9% and 47.4%, respectively, which is much higher than that of the conventional monocycle and doublet pulses. A good agreement between the theoretical and experimental results for the generation of designed UWB pulses is also observed. Moreover, electrically reconfigurable multiple modulation formats such as on-off keying (OOK) modulation, binary phase shift keying (BPSK) modulation, pulse shape modulation (PSM), and pulse position modulation (PPM) are implemented experimentally. Furthermore, the UWB signals with OOK, BPSK, and PPM are transmitted over a combined wired (single-mode fiber) and wireless link. The transmission performance of the newly generated UWB pulses is then evaluated by electrical spectra, eye diagrams, and bit-error-rate measurements. For all the modulation formats, a forward-error-correction (FEC)-limit error-free operation is obtained, and the power penalties of transmission are less than 1 dB.

2 Tbit/s free-space data transmission on two orthogonal orbital-angular-momentum beams each carrying 25 WDM channels

Abstract: We demonstrate a 2 Tbit/s free-space data link using two orthogonal orbital angular momentum beams each carrying 25 different wavelength-division-multiplexing channels. We measure the performance for different modulation formats, including directly detected 40 Gbit/s nonreturn-to-zero (NRZ) differential phase-shift keying, 40 Gbit/s NRZ on-off keying, and coherently-detected 10 Gbaud NRZ quadrature phase-shift keying, and achieve low bit error rates with penalties less than 5 dB.

Binary-input non-line-of-sight solar-blind UV channels: Modeling, capacity and coding

Abstract: There has been recent interest in establishing non-line-of-sight links in the solar-blind ultraviolet region for outdoor optical wireless communications. This paper presents a novel channel model combining both photon propagation and detection statistics. The channel capacity with binary inputs is numerically computed for on-off keying and 4-pulse-position modulation (4-PPM) at different baud rates. To approach the capacity, error control coding is applied and a message passing decoding technique is outlined. Simulation results for a running example through the paper indicate that, at a given power, there is an optimum transmitted baud rate that maximizes the achievable data rate on such links. With the application of proper coding techniques, it is demonstrated that a near fifty-fold increase in rate over previous reported designs for this channel is feasible.

Design of APSK Constellations for Coherent Optical Channels with Nonlinear Phase Noise

Abstract: We study the design of amplitude phase-shift keying (APSK) constellations for a coherent fiber-optical communication system where nonlinear phase noise (NLPN) is the main system impairment. APSK constellations can be regarded as a union of phase-shift keying (PSK) signal sets with different amplitude levels. A practical two-stage (TS) detection scheme is analyzed, which performs close to optimal detection for high enough input power. We optimize APSK constellations with 4, 8, and 16 points in terms of symbol error probability (SEP) under TS detection for several combinations of input power and fiber length. For 16 points, performance gains of 3.2 dB can be achieved at a SEP of 10-2 compared to 16-QAM by choosing an optimized APSK constellation. We also demonstrate that in the presence of severe nonlinear distortions, it may become beneficial to sacrifice a constellation point or an entire constellation ring to reduce the average SEP. Finally, we discuss the problem of selecting a good binary labeling for the found constellations.

11-Gbps 80-km transmission performance of zero-chirp silicon Mach-Zehnder modulator

Abstract: Zero-chirp operation of silicon Mach-Zehnder modulator is achieved in 11.1-Gbps on-off keying and 22.3-Gbps binary phase-shift keying. Low-dispersion-penalty transmission up to 80 km is proved in 11.3-Gbps bit-error-rate measurement for the zero-chirp silicon modulator with performance comparable with a commercialised lithium-niobate modulator.