Showing papers on "Keying published in 2010"

Capacity Limits of Optical Fiber Networks

Abstract: We describe a method to estimate the capacity limit of fiber-optic communication systems (or ?fiber channels?) based on information theory. This paper is divided into two parts. Part 1 reviews fundamental concepts of digital communications and information theory. We treat digitization and modulation followed by information theory for channels both without and with memory. We provide explicit relationships between the commonly used signal-to-noise ratio and the optical signal-to-noise ratio. We further evaluate the performance of modulation constellations such as quadrature-amplitude modulation, combinations of amplitude-shift keying and phase-shift keying, exotic constellations, and concentric rings for an additive white Gaussian noise channel using coherent detection. Part 2 is devoted specifically to the "fiber channel.'' We review the physical phenomena present in transmission over optical fiber networks, including sources of noise, the need for optical filtering in optically-routed networks, and, most critically, the presence of fiber Kerr nonlinearity. We describe various transmission scenarios and impairment mitigation techniques, and define a fiber channel deemed to be the most relevant for communication over optically-routed networks. We proceed to evaluate a capacity limit estimate for this fiber channel using ring constellations. Several scenarios are considered, including uniform and optimized ring constellations, different fiber dispersion maps, and varying transmission distances. We further present evidences that point to the physical origin of the fiber capacity limitations and provide a comparison of recent record experiments with our capacity limit estimation.

Coherent and Differential Space-Time Shift Keying: A Dispersion Matrix Approach

Abstract: Motivated by the recent concept of Spatial Modulation (SM), we propose a novel Space-Time Shift Keying (STSK) modulation scheme for Multiple-Input Multiple-Output (MIMO) communication systems, where the concept of SM is extended to include both the space and time dimensions, in order to provide a general shift-keying framework. More specifically, in the proposed STSK scheme one out of Q dispersion matrices is activated during each transmitted block, which enables us to strike a flexible diversity and multiplexing tradeoff. This is achieved by optimizing both the space-time block duration as well as the number of the dispersion matrices in addition to the number of transmit and receive antennas. We will demonstrate that the resultant equivalent system model does not impose any Inter-Channel Interference (ICI), and hence the employment of single-stream Maximum Likelihood (ML) detection becomes realistic at a low-complexity. Furthermore, we propose a Differential STSK (DSTSK) scheme, assisted by the Cayley unitary transform, which does not require any Channel State Information (CSI) at the receiver. Here, the usual error-doubling, caused by the differential decoding, gives rise to 3-dB performance penalty in comparison to Coherent STSK (CSTSK). Additionally, we introduce an enhanced CSTSK scheme, which avoids the requirement of Inter-Antenna Synchronization (IAS) between the RF chains associated with the transmit Antenna Elements (AEs) by imposing a certain constraint on the dispersion matrix design, where each column of the dispersion matrices includes only a single non-zero component. Moreover, according to the turbo-coding principle, the proposed CSTSK and DSTSK schemes are combined with multiple serially concatenated codes and an iterative bit-to-symbol soft-demapper. More specifically, the associated STSK parameters are optimized with the aid of Extrinsic Information Transfer (EXIT) charts, for the sake of achieving a near-capacity performance.

Indoor MIMO Optical Wireless Communication Using Spatial Modulation

Abstract: In this paper, a multiple-input multiple-output (MIMO) technique for indoor optical wireless (OW) communication is proposed. The technique is referred to as \emph{optical spatial modulation (OSM)}. The key concept is based on spatial modulation (SM). At any given time instant, only one transmitter is active and the others are inactive. A transmitter in space is considered as a spatial constellation point which is assigned a unique bit sequence. Consequently, transmitters are turned on and off depending on the incoming data bits, similar to the activation of constellation points in traditional digital modulation schemes. Hence, a data rate of the base two logarithm of the number of transmit units is achieved. The active transmitter radiates a certain intensity level at a particular time instant. At the receiver side, the optimal SM detector is slightly modified and used to estimate the spatial constellation point. The estimated spatial constellation point is used to arrive at the original bit stream via de-mapping. The upper bound bit-error-ratio (BER) of OSM is analyzed for a MIMO configuration consisting of four transmit units (light emitting diodes (LEDs)) and four receive units (photo diodes (PDs)) in a room. The BER performance is determined for different transmitter and receiver separation distances and different transmitter half power semiangles. It is shown that the proposed OSM technique achieves twice and four times the data rate as compared to OOK (on-off keying) and PPM (pulse-position modulation), respectively.

Mitigation of Fiber Nonlinearity Using a Digital Coherent Receiver

Abstract: Coherent detection with receiver-based DSP has recently enabled the mitigation of fiber nonlinear effects. We investigate the performance benefits available from the backpropagation algorithm for polarization division multiplexed quadrature amplitude phase-shift keying (PDM-QPSK) and 16-state quadrature amplitude modulation (PDM-QAM16). The performance of the receiver using a digital backpropagation algorithm with varying nonlinear step size is characterized to determine an upper bound on the suppression of intrachannel nonlinearities in a single-channel system. The results show that for the system under investigation PDM-QPSK and PDM-QAM16 have maximum step sizes for optimal performance of 160 and 80 km, respectively. Whilst the optimal launch power is increased by 2 and 2.5 dB for PDM-QPSK and PDM-QAM16, respectively, the Q-factor is correspondingly increased by 1.6 and 1 dB, highlighting the importance of studying nonlinear compensation for higher level modulation formats.

The WHOI micromodem-2: A scalable system for acoustic communications and networking

Abstract: A successor to the WHOI Micromodem-1 underwater acoustic modem has recently been developed. The Micromodem-2 has the same compact form-factor as the Micromodem-1 and will support all of the existing applications for the Micromodem-1, as well as interoperate with the Micromodem-1. Existing acoustic communications protocols using phase-shift keying (PSK) as well as frequency-hopping frequency-shift keying (FH-FSK) are supported, as are navigation features including narrow-band and broadband long-baseline (LBL) navigation.

Inverse Source Coding for Dimming in Visible Light Communications Using NRZ-OOK on Reliable Links

Abstract: This letter proposes an inverse source coding scheme to mitigate the severe performance degradation caused by light dimming in visible light communications using on-off keying on reliable links. The proposed scheme meets the ratio of 0's to 1's for the dimming target, and transmission efficiency approaches the theoretical maximum, entropy. It outperforms the existing time-multiplexing scheme, and the difference in performance becomes larger the more the dimming target deviates from 50%. There might be several ways to implement inverse source coding and this letter presents an example utilizing Huffman coding.

Automatic modulation recognition using wavelet transform and neural networks in wireless systems

Abstract: Modulation type is one of the most important characteristics used in signal waveform identification. In this paper, an algorithm for automatic digital modulation recognition is proposed. The proposed algorithm is verified using higher-order statistical moments (HOM) of continuous wavelet transform (CWT) as a features set. A multilayer feed-forward neural network trained with resilient backpropagation learning algorithm is proposed as a classifier. The purpose is to discriminate among different M-ary shift keying modulation schemes and themodulation order without any priori signal information. Pre-processing and features subset selection using principal component analysis is used to reduce the network complexity and to improve the classifier's performance. The proposed algorithm is evaluated through confusion matrix and false recognition probability. The proposed classifier is shown to be capable of recognizing the modulation scheme with high accuracy over wide signal-to-noise ratio (SNR) range over both additive white Gaussian noise (AWGN) and different fading channels.

Coherent Optical Communications: Historical Perspectives and Future Directions

Abstract: Coherent optical fiber communications were studied extensively in the 1980s mainly because high sensitivity of coherent receivers could elongate the unrepeated transmission distance; however, their research and development have been interrupted for nearly 20 years behind the rapid progress in high-capacity wavelength-division multiplexed (WDM) systems using erbium-doped fiber amplifiers (EDFAs). In 2005, the demonstration of digital carrier phase estimation in coherent receivers has stimulated a widespread interest in coherent optical communications again. This is due to the fact that the digital coherent receiver enables us to employ a variety of spectrally efficient modulation formats such as M-ary phase-shift keying (PSK) and quadrature amplitude modulation (QAM) without relying upon a rather complicated optical phase-locked loop. In addition, since the phase information is preserved after detection, we can realize electrical post-processing functions such as compensation for chromatic dispersion and polarization-mode dispersion in the digital domain. These advantages of the born-again coherent receiver have enormous potential for innovating existing optical communication systems. In this chapter, after reviewing the 20-year history of coherent optical communication systems, we describe the principle of operation of coherent detection, the concept of the digital coherent receiver, and its performance evaluation. Finally, challenges for the future are summarized.

Constellation design for color-shift keying using billiards algorithms

Abstract: Light-emitting diodes (LEDs) have the potential to replace traditional devices in a variety of lighting applications, offering the possibility of simultaneous modulation for communications. One modulation method, color-shift keying (CSK), has been recently proposed specifically for red/green/blue (RGB) LEDs. We examine the design of CSK signaling constellations for an additive white Gaussian noise channel, incorporating the common requirement that the RGB LED outputs a specific, possibly time-varying, perceived color. In particular, we equate this design problem to that of disk packing and employ modified billiards algorithms that rely on the “thermodynamic” settling of the disks to obtain constellation points with good minimum distance. Simulation results are presented that illustrate the design approach.

Scintillation effect on intensity modulated laser communication systems—a laboratory demonstration

Abstract: This paper shows the impact of atmospheric turbulence-induced fading on the symbol decision position in the on-off keying (OOK) and the binary phase shift keying (BPSK) subcarrier intensity modulated (SIM) laser communication link. Weak turbulence is simulated in the laboratory using a chamber equipped with heating elements and fans. We have shown that in atmospheric turbulence, it is advantageous to employ modulation schemes such as pulse time and subcarrier intensity modulations that do not directly impress data on the optical irradiance as is the case with the OOK. For the OOK-modulated laser communication system, atmospheric turbulence imposes complexity on the symbol decision subsystem and by extension places a limit on the achievable bit error rate (BER) performance.

Coherent state quantum key distribution with multi letter phase-shift keying

Abstract: We present a protocol for quantum key distribution using discrete modulation of coherent states of light. Information is encoded in the variable phase of coherent states which can be chosen from a regular discrete set ranging from binary to continuous modulation similar to phase-shift keying in classical communication. Information is decoded by simultaneous homodyne measurement of both quadratures and requires no active choice of basis. The protocol utilizes either direct or reverse reconciliation both with and without postselection. We analyze the security of the protocol and show how to enhance it by the optimal choice of all variable parameters of the quantum signal.

Large-Scale InP Transmitter PICs for PM-DQPSK Fiber Transmission Systems

Abstract: We report here the first demonstration of a large-scale monolithically integrated InP-based 10-channel 45.6-Gb/s per channel transmitter photonic integrated circuit employing polarization-multiplexed differential quadrature phase-shift keying modulation format.

System and method for generating graphical user interface

Abstract: An automated method for generating Graphical User Interfaces (GUI's) is illustrated in the context of a system for processing financial applications. In one embodiment, the GUI generator converts domain data representing over one thousand application types into an equal number of corresponding user screens. The interface may also be bi-directional, operating on user inputs to validate data or check for double keying.

Exact error rate analysis of equal gain and selection diversity for coherent free-space optical systems on strong turbulence channels

Abstract: Exact error rate performances are studied for coherent free-space optical communication systems under strong turbulence with diversity reception. Equal gain and selection diversity are considered as practical schemes to mitigate turbulence. The exact bit-error rate for binary phase-shift keying and outage probability are developed for equal gain diversity. Analytical expressions are obtained for the bit-error rate of differential phase-shift keying and asynchronous frequency-shift keying, as well as for outage probability using selection diversity. Furthermore, we provide the closed-form expressions of diversity order and coding gain with both diversity receptions. The analytical results are verified by computer simulations and are suitable for rapid error rates calculation.

Orthogonal chaotic vector shift keying in digital communications

Abstract: An orthogonal chaotic vector shift keying digital communication scheme is presented. The main characteristics of the scheme are increased data transmission rates with greatly improved robustness and an increase in security of communications links because of the structure of the scheme and the nature of the message bearer. Compared with some existing schemes, for example, quadrature chaos shift keying (QCSK) reported in the literature, the noise rejection is improved by an increase in the 'inter-symbolic separation'. Furthermore, a new method of characterising non-linear processing elements in complex communication schemes has been presented. Based on this, a simple modelling and evaluation method to determine the bit error rates of these schemes is derived. Various simulated results are presented to demonstrate these achievements.

A WDM-OFDM-PON architecture with centralized lightwave and PolSK-modulated multicast overlay

Abstract: We propose and demonstrate a novel wavelength-division-multiplexing orthogonal-frequency-division-multiplexing passive-optical-network (WDM-OFDM-PON) architecture with centralized lightwave sources and polarization shift keying (PolSK) multicast overlay. The 10-Gb/s 16QAM-OFDM point to point (P2P) signal, 2.5-Gb/s multicast PolSK signal and 2.5-Gb/s on-off keying (OOK) upstream signal are experimentally demonstrated. After transmission over 25km standard single mode fiber (SMF), 1.5dB crosstalk between the downstream signals is eliminated by employing a low pass electrical filter at the PolSK receiver. The power penalty of the upstream OOK signal at BER of 10−9 is less than 0.1dB.

Green Modulations in Energy-Constrained Wireless Sensor Networks

Abstract: Due to the unique characteristics of sensor devices, finding the energy-efficient modulation with a low-complexity implementation (refereed to as green modulation) poses significant challenges in the physical layer design of Wireless Sensor Networks (WSNs). Toward this goal, we present an in-depth analysis on the energy efficiency of various modulation schemes using realistic models in the IEEE 802.15.4 standard to find the optimum distance-based scheme in a WSN over Rayleigh and Rician fading channels with path-loss. We describe a proactive system model according to a flexible duty-cycling mechanism utilized in practical sensor apparatus. The present analysis includes the effect of the channel bandwidth and the active mode duration on the energy consumption of popular modulation designs. Path-loss exponent and DC-DC converter efficiency are also taken into consideration. In considering the energy efficiency and complexity, it is demonstrated that among various sinusoidal carrier-based modulations, the optimized Non-Coherent M-ary Frequency Shift Keying (NC-MFSK) is the most energy-efficient scheme in sparse WSNs for each value of the path-loss exponent, where the optimization is performed over the modulation parameters. In addition, we show that the On-Off Keying (OOK) displays a significant energy saving as compared to the optimized NC-MFSK in dense WSNs with small values of path-loss exponent.

Pilot-Assisted Decision-Aided Maximum-Likelihood Phase Estimation in Coherent Optical Phase-Modulated Systems With Nonlinear Phase Noise

Abstract: We proposed pilot-assisted (PA) decision-aided maximum-likelihood (DA ML) phase estimation for coherent optical M-ary phase-shift-keying systems. In a nonlinear-phase-noise channel with laser phase noise, the required launched power at bit-error-rate (BER) =10-4 using the proposed PA DA ML algorithm without differential encoding (DE) can be reduced by about 0.7 dB in quadrature phase-shift keying and eight-phase-shift keying systems, and about 0.4 dB in 16-quadrature amplitude modulation format, compared to their DE counterparts using DA ML.

Keying Material Exporters for Transport Layer Security (TLS)

Abstract: A number of protocols wish to leverage Transport Layer Security (TLS) to perform key establishment but then use some of the keying material for their own purposes. This document describes a general mechanism for allowing that.

Secure mobile ad hoc network

Abstract: Security in a mobile ad hoc network is maintained by using various forms of encryption, various encryption schemes, and various multi-phase keying techniques. In one configuration, an over the air, three-phase, re-keying technique is utilized to ensure that no authorized nodes are lost during re-keying and that nodes that are intended to be excluded from re-keying are excluded. In another configuration, an over the air, two-phase keying technique, is utilized to maintain backwards secrecy.

Optical performance monitoring of QPSK data channels by use of neural networks trained with parameters derived from asynchronous constellation diagrams

Abstract: We demonstrate a technique for performance monitoring of quadrature phase-shift keying data channels by simultaneously identifying optical signal-to-noise ratio (OSNR), chromatic dispersion (CD), and polarization-mode dispersion (PMD) using neural networks trained with parameters derived from asynchronous constellation diagrams. A correlation coefficient of 0.987 is reported for a set of testing data from a 40 Gbps return-to-zero, quadrature phase-shift keying (RZ-QPSK) system. The root-mean-square (RMS) errors are 0.77 dB for OSNR, 18.71 ps/nm for CD, and 1.17 ps for DGD.

On the performance of non-coherent transmission schemes with equal-gain combining in generalized Κ-fading

Abstract: The generalized κ-fading model, characterized by two parameters, κ and m, is a very versatile model and was recently shown to accurately capture the effects of composite shadowing and multipath fading in wireless communication systems. Furthermore, it can be used to model cascade multipath fading, which is relevant in, e.g., mobile-to-mobile communication scenarios. In this paper, we derive closed-form expressions for the bit error probability of two non-coherent transmission schemes over L diversity branches being subject to generalized κ-fading. Specifically, focus is on binary differential phase-shift keying (DPSK) and binary non-coherent frequency-shift keying (FSK) modulation with (post-detection) equal-gain combining at the receiver. We also discuss the extension of our results to M-ary modulation schemes. Considering both independent and correlated fading across the L branches, we derive expressions for the asymptotic diversity order, which reveal an interesting interplay between the two fading parameters κ and m. Moreover, we show that the diversity order of the considered non-coherent transmission schemes is the same as in the case of a coherent transmission scheme. Finally, numerical performance results are presented, and our analytical results are corroborated by means of Monte-Carlo simulations.

Semi-Blind Joint Channel Estimation and Data Detection for Space-Time Shift Keying Systems

Abstract: A low-complexity semi-blind joint channel estimation and data detection scheme is proposed for space-time shift keying (STSK) based multiple-input multiple-output systems. The minimum number of STSK training blocks, which is related to the number of transmitter antennas, is first utilized to provide a rough initial least square channel estimate (LSCE). Then low-complexity single-stream maximum likelihood (ML) data detection is carried out based on the initial LSCE and the detected data are employed to refine the decision-directed LSCE. It is demonstrated that a few iterations are sufficient to approach the optimal ML detection performance obtained with the perfect channel state information.

A new code family suitable for high-rate SAC OCDMA PONs applications

Abstract: In this paper, a new code family named partitioned partial prime (PPP) code is proposed for high-rate spectral amplitude code (SAC) optical code-division multiple-access (OCDMA) passive optical networks (PONs) applications. They are derived from the well-known prime codes (PCs) and a manner of partitioning technique. To minimize in-phase cross-correlation (IPCC), we employ the partial and padding schemes. In addition, the influences of both phase-induced intensity noise (PIIN) and shot noise are further mitigated by the partition and two-code keying (TCK) schemes. The PPP code family has the property of good code balance, flexible code length, and excellent orthogonality. The numerical results show that the proposed system using PPP codes can substantially accommodate a lot of maximum and simultaneous users with high-rate transmission and low bit error rate (BER).

100-GHz Wireless-Over-Fiber Links With Up to 16-Gb/s QPSK Modulation Using Optical Heterodyne Generation and Digital Coherent Detection

Abstract: In this letter, a novel technique for direct conversion of an optical baseband quadrature phase-shift keying (QPSK) signal to a millimeter-wave wireless signal and subsequent signal demodulation is reported. Optical heterodyne mixing of the optical baseband QPSK signal with a free-running unmodulated laser for the wireless signal generation is employed. To correct for the phase and frequency offset originating from the heterodyne mixing of the two free-running lasers, wireless signal demodulation based on optical coherent detection in combination with baseband digital signal processing is implemented. As a proof of concept, 5-Gb/s amplitude-shift keying and up to a 16-Gb/s QPSK wireless signal in the band of 75-110 GHz was generated and successfully demodulated. All-photonic millimeter-wave wireless signal generation and digital coherent detection at baud-rate are employed without complex optical phase-locked loop.

Polarization Demultiplexing by Independent Component Analysis

Abstract: Independent component analysis has been applied to polarization demultiplexing for coherent optical fiber communications. Polarization-multiplexed quadrature phase-shift keying and quadrature amplitude modulated signals were successfully demultiplexed by a tensor-based algorithm without using any knowledge of the modulation format.

Bidirectional communication techniques for wireless battery charging systems & portable consumer electronics

Abstract: Simultaneous power and signal transfer in a wireless/contactless system is an emerging technology for portable electronics. This paper aims at exploring simple and cost effective ways for such applications for a wide range of the portable consumer electronic devices such as mobile phones. Frequency-shift keying (FSK) and amplitude-shift keying (ASK) techniques for an inductive battery charging platform have been successfully implemented for simultaneous power and signal transfer in an 10W wireless charging system. The proposed techniques provide effective bidirectional communication between the charging platform and the loads and form the basis for load identification and battery monitoring in wireless charging system. Considerations of these methods for compatibility among a wide range of portable products are discussed.

Experimental investigation of the performance of different modulation techniques under controlled FSO turbulence channel

Abstract: This paper experimentally investigates and compares the performance of the free space optics system employing three different modulation schemes, on-off keying (OOK) with non-return-to-zero (NRZ) and return-to-zero (RZ) and the binary phase shift keying (BPSK) operating under the turbulent atmosphere. The received average signal is measured and used to characterize the strength of the turbulence. The experiment is performed with a temperature gradient of 4 degrees at a wind velocity of 4 m/s. The temperature gradient within the controlled channel results in turbulence of a log irradiance variance of 0.002, which is classified as a very weak turbulence. The received signal eye diagram and power histograms are presented and analyzed for performance evaluation of the selected modulation schemes in the weak turbulence model.