Showing papers on "Keying published in 2008"

High-Speed Visible Light Communications Using Multiple-Resonant Equalization

Abstract: White light-emitting diodes (LEDs) are becoming widespread in commercial lighting applications, and there are predictions that they will be in common use in domestic applications in the future. There is also growing interest in using these devices for both illumination and communications. One of the major challenges in visible light communications is the low modulation bandwidth (BW) available from devices, which is typically several megahertz. In this letter, we describe a link that uses 16 LEDs which are modulated using a resonant driving technique, creating an overall BW of 25 MHz. This is used to implement a 40-Mb/s nonreturn-to-zero on-off keying link which operates at low error rates, and also provides illumination at levels sufficient for a standard office environment.

Evaluation of Sensitivity of the Digital Coherent Receiver

Abstract: In this paper, we investigate the sensitivity of the digital coherent receiver both theoretically and experimentally. The receiver sensitivity close to the shot-noise limit is demonstrated in the 10-Gbit/s binary phase-shift keying system with the help of a low-noise optical preamplifier. We also introduce polarization diversity into our receiver. Maximal-ratio polarization combining in the digital domain makes the receiver sensitivity independent of the state of polarization of the incoming signal without power penalty.

UWB Direct Chaotic Communication Technology for Low-Rate WPAN Applications

Abstract: The goal of this paper is to describe the design of an ultrawideband (UWB) system that is optimized for low-complexity, low-power, low-cost, and low-rate wireless personal area network applications. To this aim, we propose a system based on novel direct chaotic communication (DCC) technology, in which a 2-GHz-wide chaotic signal is directly generated into the lower band of the UWB spectrum. Based on this system, two simple modulation schemes, namely, chaotic on-off keying and differential chaos-shift keying, are studied, and the performance of both noncoherent and differential-coherent transceiver architectures is evaluated. Various system design parameters and tradeoffs are discussed throughout the paper, including frequency band plans, data throughput, and system scalability. In particular, the frequency-division multiplexing technique is proposed as a low-cost alternative to achieving simultaneous operating piconets for short-distance applications. The average power consumption for various operating data rates and the technical feasibility of implementing the DCC system as a low-cost integrated circuit are also addressed. Finally, Monte Carlo simulations are performed based on the IEEE 802.15.4a standard channel models to evaluate the performance of the two modulation schemes. In general, both schemes experience little degradation under multipath environments due to the self-inherent wideband characteristic of the chaotic signal.

Short-range ultrasonic digital communications in air

Abstract: The use of ultrasound in air as a means of communicating digital signals is demonstrated. The work uses capacitive transducers with a useful bandwidth to transmit digitally coded signals across an air gap in the laboratory, using three of the common methods used in digital communications. These are on-off keying (OOK), binary frequency-shift keying (BFSK), and binary phase shift keying (BPSK). All three methods are simulated numerically using the available bandwidth of the transducer systems and are compared to results obtained experimentally. It is demonstrated that BPSK can be used to transmit signals with a low bit error rate.

Data transmission via multi-path channels using orthogonal multi-frequency signals with differential phase shift keying modulation

Abstract: A method and an apparatus relating to an OFDM data communications system where the sub-carriers are modulated using differential quadrature phase-shift keying (DQPSK). The multi-carrier transmitted signal is directly generated by means of summation of pre-computed sample points. As part of the multi-carrier signal generation, a signal for the guard interval is established. In an acoustic application of this approach, direct radiation of the sub-carrier approach is facilitated. Symbol synchronization in the receiver is based on signal correlation with the missed sub-carrier. Separation of the sub-carriers in the receiver by means of correlation of the received signal and reference signals that are derived from a table of pre-computed values. Optimal non-coherent processing of the sub-carriers without any phase tracking procedures is achieved.

Coherent Optical OFDM Transmitter Design Employing Predistortion

Abstract: In this letter, we analyze the transmitter design for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) employing predistortion. Digital clipping and digital predistortion processes are introduced to the radio frequency OFDM transmitter to compensate the nonlinearity effect introduced by the optical in-phase/quadrature modulator. We first provide a detailed description of signal processing involved in digital clipping and predistortion. We then carry out a numerical simulation to identify the performance dependence on clipping ratio, digital-to-analog converter (DAC) resolution, and modulation index. We find that for quadrature phase-shift keying modulation, 4-bit DAC resolution is sufficient for the CO-OFDM transmitter to incur only 0.3-dB penalty while maintaining the excess modulation insertion loss less than 6.0 dB. The performance improvement of the predistorted transmitter over nonpredistorted one is also discussed.

Optical Performance Monitoring of Phase-Modulated Signals Using Asynchronous Amplitude Histogram Analysis

Abstract: As optical networks continue to grow towards high capacity and high flexibility, new transmission technologies are being introduced. In order to maintain the quality of signal and control over network in the transparent domains, optical performance monitoring (OPM) systems are becoming a necessity. Phase modulation formats emerge as the solution of choice in transparent domains because of their sensitivity, spectral efficiency, and resilience to optical impairments. In this paper, we demonstrate a flexible OPM method for phase-modulated signals using asynchronous amplitude histogram analysis. We show numerically and experimentally the monitoring of optical signal-to-noise ratio (OSNR), chromatic dispersion (CD), and polarization-mode dispersion (PMD) for differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) signals. The OSNR can be measured within range of 20-35 dB and accumulated chromatic dispersion between 600 and 600 ps/nm. The asynchronous amplitude histogram monitoring method is proved to be a precise and versatile monitoring tool for high-capacity optical networks.

Handover Key Management and Re-authentication Problem Statement

Abstract: This document describes the Handover Keying (HOKEY) re-authentication problem statement. The current Extensible Authentication Protocol (EAP) keying framework is not designed to support re-authentication and handovers without re-executing an EAP method. This often causes unacceptable latency in various mobile wireless environments. This document details the problem and defines design goals for a generic mechanism to reuse derived EAP keying material for handover.

Performance of 40-Gb/s DPSK Demodulator in SOI-Technology

Abstract: A silicon-on-insulator delay interferometer manufactured in 4-mum rib waveguide technology is presented. The polarization-dependent frequency shift is tuned to a value as low as 0.4 GHz. Continuous-wave device performance and polarization-independent differential phase-shift keying demodulation performance in a 40-Gb/s testbed are demonstrated.

SBK: A Self-Configuring Framework for Bootstrapping Keys in Sensor Networks

Abstract: Key pre-distribution has been claimed to be the only viable approach for establishing shared keys between neighboring sensors after deployment for a typical sensor network. However, none of the proposed key pre-distribution schemes simultaneously achieves good performance in terms of scalability in network size, key-sharing probability between neighboring sensors, memory overhead for keying information storage, and resilience against node capture attacks. In this paper, we propose SBK, an in-situ self-configuring framework to bootstrap keys in large-scale sensor networks. SBK is fundamentally different compared to all key pre-distribution schemes. It requires no keying information pre-deployment. In SBK, sensors differentiate their roles as either service nodes or worker nodes after deployment. Service sensors construct key spaces, and distribute keying information in order for worker sensors to bootstrap pairwise keys. An improved scheme, iSBK, is also proposed to speed up the bootstrapping procedure. We conduct both theoretical analysis and simulation study to evaluate the performances of SBK and iSBK. To the best of our knowledge, SBK and iSBK are the only key establishment protocols that simultaneously achieve good performance in scalability, key-sharing probability, storage overhead, and resilience against node capture attacks.

Monolithic modulator and demodulator of differential quadrature phase-shift keying signals based on silicon microrings

Abstract: Silicon microring resonators are proposed to achieve ultrasmall differential quadrature phase-shift keying modulators and demodulators operated at 20 Gb/s, which may require a dramatically reduced chip size. The modulators are characterized in terms of the carrier transit time and misalignment of the driving signals, while the demodulation performance is analyzed in terms of the bandwidth and frequency detuning of the demodulator. A bit-error rate of <10(-9) is achieved using all microring-based devices in the back-to-back case.

All-Optical Chromatic Dispersion Monitoring for Phase-Modulated Signals Utilizing Cross-Phase Modulation in a Highly Nonlinear Fiber

Abstract: We propose and experimentally demonstrate an all-optical chromatic dispersion (CD) monitoring technique for phase-modulated signals utilizing the cross-phase-modulation effect between the input signal and the inserted continuous-wave probe. The probe's optical spectrum changes with the accumulated CD on the input signal, indicating that the optical power variations can be measured for monitoring. The experimental results show that this technique can monitor up to 120 ps/nm of CD for a 40-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) transmission system, with the maximum measured optical power increment of 16.5 dB. The applicability of this monitoring technique to higher bit-rate phase-modulated signals, such as 80-Gb/s RZ differential quadrature phase-shift keying and 80-Gb/s polarization-multiplexed RZ-DPSK, is also investigated via simulation.

Closed-Form Expressions of the Exact Cramer-Rao Bound for Parameter Estimation of BPSK, MSK, or QPSK Waveforms

Abstract: This letter addresses the stochastic Cramer-Rao bound (CRB) pertaining to the joint estimation of the carrier frequency offset, the carrier phase and the noise and signal powers of binary phase-shift keying (BPSK), minimum shift keying (MSK), and quaternary phase-shift keying (QPSK) modulated signals corrupted by additive white circular Gaussian noise. Because the associated models are governed by simple Gaussian mixture distributions, an explicit expression of the Fisher information matrix is given and an explicit expression for the stochastic CRB of these four parameters are deduced. Specialized expressions for low and high SNR are presented as well. Finally, these expressions are related to the modified CRB and our proposed analytical expressions are numerically compared with the approximate expressions previously given in the literature.

Demonstration of an All-Optical OCDMA Encryption and Decryption System With Variable Two-Code Keying

Abstract: We demonstrate the first all-optical optical code-division multiple-access (OCDMA) encryption and decryption system with variable two-code keying. The nonlinear optical loop mirror (NOLM)-based exclusive or (xor) employed in encryption utilizes the shortest length silica-based nonlinear fiber element to date, enabling a compact architecture. Fiber Bragg grating arrays create wavelength-hopping time-spreading OCDMA codes from broadband pulses at output ports of the xor resulting in variable two-code keying, a code-switching modulation format characterized by a random alternation in bit representation and immunity to differential analysis unlike fixed two-code keying. The terahertz optical asymmetric demultiplexer employed in decryption shows mutual compatibility of nonlinear fiber-based and semiconductor optical amplifier-based NOLM configurations. Our architecture can potentially perform one-time pad encryption and decryption for unconditional security.

Blind detection of on-off keying for free-space optical communications

Abstract: We investigate blind detection, i.e. detection assuming the absence of instantaneous channel state information (CSI) and a statistical channel description at the receiver, of on-off keying (OOK) in a free-space optical (FSO) system. Using an observation window encompassing many consecutive independent bits, our blind detector capitalizes on the fact that the atmospheric turbulence is constant over the observation window and that the expected number of transmitted 1s and 0 s are equal. To improve receiver performance beyond that of the initial blind detector, we also consider the use of decision-aided threshold estimation and a second detection stage, respectively. Provided that a sufficiently large observation window is employed, simulation results indicate that the proposed receiver can attain performance comparable to that of the lower performance bound given by detection with CSI.

Robust Frequency Hopping for Interference and Fading Channels

Abstract: A robust frequency-hopping system with noncoherent detection, iterative turbo decoding and demodulation, and channel estimation is presented. The data modulation is the spectrally compact nonorthogonal continuous-phase frequency-shift keying, which strengthens the frequency-hopping system against multiple-access interference and multitone jamming. An analysis based on information theory provides the optimal values of the modulation index when there is a bandwidth constraint. The channel estimator, which is derived by applying the expectation- maximization algorithm, accommodates both frequency-selective fading and interference. Simulation experiments demonstrate the excellent system performance against both partial-band and multiple-access interference.

Novel WDM-PON Architecture Based on a Spectrally Efficient IM-FSK Scheme Using DMLs and RSOAs

Abstract: This paper proposes a wavelength-division-multiplexing passive optical network architecture with colorless user terminals based on the use of a different modulation scheme for each way of communication. Narrow-frequency-shift keying (FSK) modulation obtained by direct modulation of a distributed feedback laser has been used for the downstream channel, and intensity modulation has been used for the upstream channel. The performance of a link based on this scheme has been assessed, with particular emphasis on the description of the narrow-FSK modulation technique and its range of applicability in terms of bit rates and power levels. The operation of the architecture is demonstrated by simultaneously transmitting Ethernet frames at 1.25 Gb/s (gigabit Ethernet) in both the upstream and downstream channels. Error rates for downstream and upstream channels show excellent performance for distances up to 50 km.

Generation and Transmission of Optical Carrier Suppressed-Optical Differential (Quadrature) Phase-Shift Keying (OCS-OD(Q)PSK) Signals in Radio Over Fiber Systems

Abstract: We propose and experimentally demonstrate generation of optical carrier suppressed-optical differential phase-shift keying (OCS-oDPSK) modulation format in radio-over-fiber (RoF) systems using one single-drive Mach-Zehnder modulator (MZM). This scheme realizes up-conversion of baseband data for downlink wireless service delivery, generation of remote local oscillator (LO) signal for down-conversion of uplink radio frequency (RF) signal, and remodulation of down-converted uplink data, thus lowering the cost of base stations (BSs) in full-duplex RoF systems. The proposed scheme is expected to be simple and compact due to the use of a single MZM. Furthermore, the OCS-oDPSK generation principle is extended to obtain an OCS-optical differential quadrature phase-shift keying (OCS-oDQPSK) signal by employing a dual-parallel MZM (DPMZM), which is useful to deliver multiple wireless services on the same RF carrier.

Blind Cooperative Diversity Using Distributed Space-Time Coding in Block Fading Channels

Abstract: Mobile users with single antennas can still take advantage of spatial diversity through cooperative space-time encoded transmission. In this paper, we consider a scheme in which a relay chooses to cooperate only if its source-relay channel is of an acceptable quality and we evaluate the usefulness of relaying when the source acts blindly and ignores the decision of the relays whether they may cooperate or not. In our study, we consider the regenerative relays in which the decisions to cooperate are based on a signal-to-noise ratio (SNR) threshold and consider the impact of the possible erroneously detected and transmitted data at the relays. We derive the end-to-end bit-error rate (BER) expression and its approximation for binary phase-shift keying modulation and look at two power allocation strategies between the source and the relays in order to minimize the end-to-end BER at the destination for high SNR. Some selected performance results show that computer simulations based results coincide well with our analytical results.

An Iterative Equalization and Decoding Approach for Underwater Acoustic Communication

Abstract: In this paper, we present an iterative approach for recovering information sent over a shallow underwater acoustic (UWA) communication channel. The procedure has three main tasks: estimation of channel model parameters (CMPs), channel equalization, and decoding. These tasks are performed cyclicly until the algorithm converges. Information bits are convolutionally encoded, punctured and permuted, mapped into quaternary phase-shift keying (QPSK) symbols, linearly modulated, and transmitted through a downward-refracting ocean waveguide. Training symbols are prepended to the transmitted sequence for initial estimation of CMPs. Our algorithm processes data from a single receive sensor. Data are received on a vertical array and the performance of the algorithm for each sensor in the array is examined. There is negligible Doppler spread in the received data. However, difference between transmitter and receiver clocks as well as slight motion of the receive array produce a nonnegligible compression of the received signals. Consequently, there is observable Doppler ldquoshift.rdquo Nonuniform resampling of the data produces time series we model as the output of a linear time-invariant system. Resampling and CMP estimation are done iteratively, in conjunction with equalization and decoding. The algorithm successfully processes the data to yield few or no information bit errors.

A group of modulation schemes for adaptive modulation

Abstract: Adaptive modulation increases the throughput of a wireless network by adjusting the modulation scheme to the channel status. To have more capacity and more flexibility in using adaptive modulation, our research attempts to find a group of modulation schemes, which includes M-QAM where the number of signal points is not a power of 2, as well as non-squared QAM (or APSK: amplitude and phase-shift keying), so we can have n-bit modulation where n ranges fully from 1 to 6 including half-integer indices. Some recent research has shown that the gap between QPSK and 16-QAM, 16-QAM and 32-QAM, 32-QAM and 64-QAM can be filled smoothly by introducing 12-QAM, 24-QAM and 48-QAM. But the gap between QPSK (4-QAM) and 12-QAM is still an open problem. In this paper we insert 8-ary modulation schemes, and propose 6-ary modulation schemes. Simulation results show that our proposed group can fill smoothly the gap between QPSK and 12-QAM.

Digital Communications: Design for the Real World

Abstract: Preface. How to use the combined book and CD. 1 Background material. 1.1 Time/frequency representation of digital signals. 1.2 Trigonometric relationships. 1.3 Communications networks and signalling protocols. 1.4 Definition of terms. 2 Data transmission fundamentals. 2.1 Factors affecting system design. 2.2 Data transmission fundamentals. 2.3 Multi-level signalling (M-ary signalling). 2.4 Calculation of channel capacity. 3 Baseband data transmission. 3.1 Introduction. 3.2 Intersymbol interference (ISI). 3.3 Eye diagrams. 3.4 Raised cosine filtering. 3.5 Matched filtering. 3.6 Partial response signalling. 4 Sources and examples of channel degradation. 4.1 Introduction. 4.2 Gain, phase and group delay distortion. 4.3 Interference and noise. 4.4 The telephone channel. 4.5 The wireless channel. 5 Bandpass digital modulation. 5.1 Introduction. 5.2 Amplitude shift keying (ASK). 5.3 Frequency shift keying (FSK). 5.4 Phase shift keying (PSK). 5.5 Comparison of binary modulation schemes. 6 Multi-level digital modulation. 6.1 Introduction. 6.2 M-ary amplitude shift keying (M-ary ASK). 6.3 M-ary frequency shift keying (M-ary FSK). 6.4 M-ary phase shift keying (M-ary PSK). 6.5 Combined amplitude and phase keying. 6.6 Relative performance of multi-level bandpass modulation formats. 7 Coding theory and practice. 7.1 Source coding. 7.2 Channel coding. 7.3 Block coding. 7.4 Advanced block coding. 7.5 Convolutional coding. 7.6 Combined coding and modulation. 8 Multi-user digital modulation techniques. 8.1 Introduction. 8.2 Frequency division multiple access (FDMA). 8.3 Time division multiple access (TDMA). 8.4 Code division multiple access (CDMA). 8.5 Combined multiple access systems. Glossary. References. Index.

System and method for relative phase shift keying

Abstract: Disclosed are various embodiments of systems and methods for relative phase shift keying. In one embodiment, an analog waveform is converted to digital signals. A specified frequency range is isolated and the magnitudes of tones corresponding to a channel are measured. The relative phase of a subset of the tones having the greatest magnitude is measured and a relative phase component is generated. At least one symbol is associated with the subset of tones and the relative phase component.

A Comprehensive Study on Crosstalk Suppression Techniques in Fiber Optical Parametric Amplifier by Modulation Format

Abstract: With the presence of multiple-WDM input signals, ON-OFF keying (OOK)-modulated signals suffer from crosstalk in fiber optical parametric amplifier (OPA) due to cross-gain modulation (XGM) and four-wave mixing (FWM) effects. We demonstrated substantial crosstalk suppression in one-pump OPA by using return-zero differential phase-shift keying (RZ-DPSK) modulation format, which with its pattern-independent amplitude and subunity duty cycle would be effective in reducing the XGM and FWM effects significantly. By using the RZ-DPSK format, the power penalty was improved by at least 0.8 dB over RZ-OOK, non-RZ (NRZ)-DPSK, and NRZ-OOK formats with four 10 Gb/s channels, separated by 200 GHz spacing. With eight 10 Gb/s channels separated by 100 GHz spacing, a Q-factor penalty of the RZ-DPSK signal was reduced by 2.4 dB compared to RZ-OOK counterparts.

Self-coherent optical transport systems

Abstract: Publisher Summary This chapter is a comprehensive and in-depth treatment of self-coherent transmission systems, including theoretical considerations, receiver technologies, modulation formats, and adaptive equalization techniques. Self-coherent optical transmission based on differential phase-shift keying (DPSK) and direct detection has emerged as an attractive vehicle for supporting high-speed optical transport networks by offering lower requirements on optical signal-to-noise ratio (OSNR) and higher tolerance to system impairments such as fiber nonlinear effects and coherent crosstalk, as compared to traditional on-off keying (OOK)-based transmission. Multilevel DPSK formats such as differential quadrature phase-shift keying (DQPSK) additionally offer high spectral efficiency and high tolerance to chromatic dispersion (CD), polarization mode dispersion (PMD), and optical filtering. Various self-coherent modulation formats and their detection schemes are presented in this chapter. The most basic one is DBPSK, which can be generated by a single-waveguide phase modulator or a Mach–Zehnder Modulator (MZM) configured for phase modulation. There are two common types of modulators to effectively realize phase modulation. The single-waveguide phase modulator has the advantage of low loss, no need for bias control, and absence of modulator bandwidth limitation-induced signal amplitude fluctuations. Particularly, the digital self-coherent receiver and its potential capabilities in mitigating transmission impairments are discussed in the chapter. Self-coherent optical transport systems, promising many benefits not possible with traditional OOK-based systems, are expected to find a wide range of applications to meet the ever- increasing demand of capacity upgrade and cost reduction in future optical networks. Compared to traditional OOK, self-coherent optical modulation and detection schemes offer higher signal immunity to one or more of these impairments and are being used for many state-of-the-art optical transport systems.

Impact of Pump-Phase Modulation on FWM-Based Wavelength Conversion of D(Q)PSK Signals

Abstract: We investigate both theoretically and experimentally the impact of pump-phase modulation on differential phase shift keying (DPSK) and differential quadrature phase shift keying (DQPSK) signals in fiber-based parametric wavelength converters. It will be shown that the pump-phase modulation used to suppress stimulated Brillouin scattering introduces critical signal degradations and optical SNR penalties on DPSK signals, and more severe on DQPSK signals. Different modulation schemes will be theoretically investigated and the quantitative results are compared to system experiments. Finally, the theoretical results for a single conversion will be extended to multiple conversions to study the cascadability of the wavelength converter.

Performance analysis of a JTIDS/Link-16-type waveform transmitted over Nakagami fading channels with pulsed-noise interference

Abstract: The Joint Tactical Information Distribution System (JTIDS) is the communication terminal of Link-16. JTIDS is a hybrid direct sequence/frequency-hopping spread spectrum system and features Reed-Solomon codes for channel coding, cyclic code-shift keying for 32-ary symbol modulation, minimum-shift keying for chip modulation, symbol interleaving, chip sequence scrambling and random jittering for transmission security, and a double-pulse structure for diversity. Assuming that coherent chip demodulation is practical, we investigate the probability of symbol error of a JTIDS/Link-16-type waveform for both the single- and the double-pulse structure transmitted over a slow, flat Nakagami fading channel in the presence of pulsed-noise interference (PNI) in this paper. In general, the results show that the double-pulse structure always outperforms the single-pulse structure, whether the PNI is present or not and whether the channel is fading or not. Furthermore, barrage noise interference has the most effect in degrading performance when signal-to-interference ratio (SIR) is small. When SIR is large, PNI with a smaller fraction of time that interference is on causes the greatest degradation.

Enforcing the principle of least privilege for large tunnel-less VPNs

Abstract: Techniques for secure communication in a tunnel-less VPN are provided. A key server generates and provides, to each VPN gateway, different, yet mathematically-related keying material. A VPN gateway receives distinct keying material for each designated address block (e.g., subnet) behind the VPN gateway. In response to receiving a packet from one a source host whose address falls within one of the designated address blocks, the VPN gateway identifies the appropriate keying material. The VPN gateway determines an identifier for the address block that includes the destination address. The identifier and the identified keying material are used to generate a key. The VPN gateway encrypts the packet with the key and forwards the encrypted packet to the destination host.