Differential Phase-shift Keying Receiver Research Articles

Effect of Doppler shift on preamplifier DPSK receivers using balanced detection for optical satellite networks.

Optical satellite networks using laser intersatellite links are recognized as being capable of satisfying the increasing broadband communication demands. However, the Doppler shift due to relative movement between satellites must be taken into consideration. A convenient method that does not require complicated mathematical calculation is adopted to derive the relationship between the residual Doppler shift and the bit error rate (BER) for the balanced differential phase-shift keying (DPSK) detection system. It is shown that the DPSK receiver is sensitive to the residual Doppler shift; when the residual Doppler shift Δfres/Rb is 0.05, 0.10, and 0.15, the BER is reduced from a level of 10-17 to a level of 10-14, 10-11, and 10-6, respectively. The BER of a certain node pair under different link assignment schemes is calculated in a typical multi-hop LEO constellation. The results show that the communication BER of the same node pair is not only related to the step change of the Doppler but also related to the accumulation of the Doppler shift in the optical path. The results obtained here will be helpful in routing selection, link assignment, topology design, and system compensation.

Effect of partially coherent laser source on the performance of fiber-coupling DPSK receiver for optical communication

In practice, due to the reasons related to the laser device and the inevitable error of the processing technique, a laser source emitted from a communication terminal is represented by partially coherent laser source. The fiber-coupling efficiency and the incident optical power at the receiver aperture are affected by the source coherent parameter ζ through atmospheric turbulence. In this paper, the statistical distribution of both the fiber-coupling efficiency and the incident optical power are given, based on which the effect of the source coherent parameter ζ on the performance of fiber-coupling differential phase-shift keying (DPSK) receiver is systematically analyzed. The system fade margin, the average bit error rate (BER) and the power penalty are obtained in the presence of the degradation of the source coherent degree. The results manifest that the performance of fiber-coupling DPSK receiver system degrades drastically with increasing source coherent parameter ζ. The hope of this work is to improve the redundancy design of fiber-coupling DPSK receiver system.

Monolithic <inline-formula> <tex-math notation="LaTeX">$1\times 2$ </tex-math></inline-formula> MMI-Based 25-Gb/s SOI DPSK Demodulator Integrated With SiGe Photodetector

In this letter, the performance of a 25-Gb/s 1 × 2 multimode interference (MMI) coupler-based monolithic differential phase shift keying (DPSK) receiver integrated with Germanium (Ge) on silicon-on-insulator (SOI) photodetector (PD) is presented. Theoretical analysis suggests that the device exhibits more uniform extinction ratio over the C-band compared with a DPSK demodulator based on 2×2 MMI coupler. Electrical scattering parameters (S-parameters) investigated through component level simulation comparing the fabrication tolerance shows power penalty of 1.2 and 5 dB for unbalanced and balanced detection DPSK receiver, respectively. The SOI 1×2 MMI coupler-based unbalanced DPSK receiver has a sensitivity of 0.41 dBm at a bit error rate of 1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> without postelectrical amplification. The PD integrated single-end detectionbased receiver has a total footprint area of 0.39 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Impact of random angular jitter on fiber-coupled differential phase-shift keying receivers with Mach–Zehnder interferometer demodulation

In an optically preamplified differential phase-shift keying (DPSK) receiver with Mach&#x2013;Zehnder interferometer (MZI) demodulation, it is essential to couple free space light into a single-mode fiber, by which the received optical signal can be guided into the amplifier and MZI. Random angular jitter has a profound impact on fiber coupling efficiency, in that it would significantly deteriorate the receiver performance. In this paper, the average bit error rate (BER) of fiber-coupled DPSK receivers is obtained in the presence of random angular jitter. It is shown that the degradation is significant when the random angular jitter normalized by the mode field radius is larger than 0.3. We further analyze the impact of other factors, including central obstruction and optical filter transfer functions. Our results show that the super-Gaussian filter outperforms other filters and leads to lower average BER at a fixed optical signal-to-noise ratio. This work can be used to improve the design of fiber-coupled DPSK receivers.

Differential Phase-Shift Keying in Spatial Diversity Transmitters for Fade Mitigation

We investigate the use of differential phase-shift keying (DPSK) in multiwavelength spatial diversity transmitters for mitigation of atmospheric fading. By selecting the transmitter wavelengths to coincide with the transmission peaks of the delay-line interferometer in the receiver, the only modification required to a standard DPSK receiver is a wider optical filter. We examine the wavelength separation required to minimize penalties from beating between the wavelengths and find that a separation of twice the data rate is sufficient for a four-wavelength system with narrow filtering. We also demonstrate a reduction in scintillation loss for a four-wavelength DPSK system in a fading channel.

Estimating the Performance of Direct-Detection DPSK in Optical Networking Environments Using Eigenfunction Expansion Techniques

In-band crosstalk, due to multiple interferers, has been identified as one of the most severe impairments in optical transparent networks, especially in the ones with a large number of nodes and a high wavelength density. Due to its robustness to in-band crosstalk differential phase-shift keying (DPSK) emerges as an attractive modulation scheme to be used in such environments. This paper proposes a rigorous formulation to estimate the performance of direct-detection DPSK receivers using an eigenfunction expansion technique in the time domain. The method takes into account both the in-band crosstalk, due to an arbitrary number of interfering terms, and the amplified spontaneous emission noise and is able to deal with any combination of optical and electrical filter shapes. Using this method the accuracy of an approximation based on the wideband optical filtering assumption was evaluated and shown that the approximation, although not providing reliable results for the error probabilities, can be used with confidence to compute power penalties due to in-band crosstalk. Furthermore, the crosstalk tolerance of DPSK over on-off keying was quantified and shown that this tolerance is reduced when the number of interferers increases.

Dual Evanescently Coupled Waveguide Photodiodes with High Reliability for over 40-Gbps Optical Communication Systems

For over 40-Gbps optical communication systems, phase coded modulation formats, like differential phase shift keying (DPSK) and quadrature phase shift keying (QPSK), are very important for signal frequency efficiency and long-reach transmission. In such systems, differential receivers which regenerate phase signals are key components. Dual Photo Diodes (dual PDs) are key semiconductor devices which determine the receiver performance. Each PD of the dual PDs should realize high speed performance, high responsibility and high input power operation capability. Highly symmetrical characteristics between the two PDs should be also realized, thus the dual PDs are desired to be monolithically integrated to one chip. In this paper, we describe the design, fabrication, characteristics and reliability of monolithically integrated dual evanescently coupled waveguide photodiodes (EC-WG-PDs) for the purpose described above. The structure of the EC-WG-PDs offers the attractive advantages of high speed performance, high responsivity and high input power operation. Furthermore, their fabrication process is suitable for the integration of two PDs on one ship. First, the optimization was done for high products of 3-dB bandwidth and responsivity for 43-Gbps DPSK receivers. Excellent characteristics (50GHz bandwidth with a responsivity of 0.95A/W), and high reliability were demonstrated. The other type of optimization was done for ultra high speed operation up to 100-Gbps. The fabricated PDs exhibited the 3dB-bandwidth of 80GHz with a responsivity of 0.25A/W. Furthermore, 43-Gbps RZ-DPSK receivers including the dual EC-WG-PDs based on the former optimization and differential transimpedance amplifiers (TIAs) newly developed for the purpose were also presented. Clear and symmetrical eye openings were observed for both ports. The OSNR characteristics exhibited 14.3dB at a bit error rate of 10-3 that is able to be recovery with FEC. These performances are enough for practical use in 43-Gbps RZ-DPSK systems.

Multicanonical Monte Carlo Modeling of Wavelength Division Multiplexed Differential Phase Shift Keying Systems

Differential phase shift keying (DPSK) modulation is being considered as a possible candidate for future optical wavelength division multiplexed (WDM) transmission systems. In a single channel link, the balanced interferometric DPSK receiver exhibits increased tolerance against amplified spontaneous emitting (ASE) noise and fiber nonlinear effects. In this paper, a model is presented that can be used to estimate the performance of a multichannel DPSK system taking into account the influence of interchannel phenomena, namely cross-phase modulation (XPM) and four wave mixing (FWM), in the phase noise statistics. The model is based on an approximate solution of the fiber propagation equation and the multicanonical Monte Carlo (MCMC) method. It provides an efficient tool that can be used to investigate the influence of many link design parameters such as channel spacing, launch power, and fiber dispersion. The model is illustrated in the comparison of the performance of multichannel DPSK to on-off keying (OOK) systems. It is verified that, even in the presence of interchannel effects, DPSK modulation greatly enhances the system performance compared to OOK.

A DPSK Receiver With Enhanced CD Tolerance Through Optimized Demodulation and MLSE

We experimentally demonstrate that a differential phase-shift keying (DPSK) receiver employing a Mach-Zehnder delay interferometer (MZDI) with a bit delay of less than one bit combined with maximum likelihood sequence estimation can considerably enhance the tolerance to chromatic dispersion (CD). Furthermore, we analyze the impact of sampling phase and optimize the MZDI bit delay for 10.7-Gb/s nonreturn-to-zero (NRZ)-DPSK demodulation. Our investigation shows that a 4000-ps/nm CD tolerance at 2-dB penalty is feasible for 10.7-Gb/s NRZ-DPSK.

Receiver sensitivity improvement using polarization-insensitive semiconductor optical amplifier

We investigate a semiconductor optical amplifier (SOA) preamplifier model by suitably choosing the material and device parameters for the SOA to reduce the amplified spontaneous emission (ASE) noise at low range of 22.3 µW with 0.1-mW input power for a PIN receiver. Our proposed SOA optical preamplifier is found to be more relaxed from the optical alignment and antireflection coating, eliminates the need for optical filter, and gives large tolerance for an input light wavelength of more than 100 nm. We also investigate the receiver sensitivity for different bit rates. We show that receiver sensitivity is –69.9 dBm at a bit error rate (BER) of 4.6×10–10 for 10 Gbit/s and for the 40 Gbit/s bit rate the improved receiver sensitivity is –19.2 dBm with a PIN receiver. We also observe a sensitivity of –40.5 dBm at 40 Gbit/s with a differential phase shift keying (DPSK) receiver. Further, the impact of amplified spontaneous emission power, gain variation with input light wavelength, and optical gain for the TE & TM modes with input power for the PIN & DPSK receivers is illustrated. We show that the optical gain of the SOA is polarization independent and remains constant at 30.06 dB up to gain saturation. We also show that the DPSK receiver suffers less from ASE noise. The variation of material loss, length, and bias current for our SOA preamplifier to optimize the receiver sensitivity is further illustrated.

Performance analysis of differential-phase-shift-keying optical receivers in the presence of in-band crosstalk noise

In-band crosstalk can pose important limitations in an all-optical wavelength-division-multiplexed (WDM) network. Recent studies have demonstrated that differential phase shift keying (DPSK), can tolerate higher in-band crosstalk-noise levels compared to amplitude shift keying (ASK). In this paper, the performance of a DPSK receiver, limited by in-band crosstalk noise, is studied theoretically. The model takes into account both the in-band crosstalk noise as well as the amplified-spontaneous-emission (ASE) noise of the optical amplifiers. The model is based on the evaluation of the moment-generating function (MGF) of the decision variable through which, the error probability (EP) can be calculated by applying the saddle point approximation. This provides a rigorous model for the evaluation of the EP of a DPSK receiver in the presence of ASE and in-band crosstalk noises. In the absence of the ASE noise, a closed-form formula for the EP is also given that is useful for estimating the error floor set by the in-band crosstalk noise.

Soft detection of multichip DPSK over the nonlinear fiber-optic channel

We analyze the performance of a recently proposed multichip differential phase-shift-keying (DPSK) format over the nonlinear fiber-optic channel. For a single wavelength nonlinear phase-noise-limited channel, a multichip DPSK receiver based on a three-chip observation can attain more than two orders of magnitude bit-error-rate reduction relative to a standard DPSK receiver, or equivalently /spl sim/1-dB improvement in Q-factor, significantly exceeding the 0.2-dB improvement achieved by the same format over a linear optical channel.

The impact of receiver imperfections on the Performance of optical direct-Detection DPSK

The goal of this paper is to analyze the effects of key receiver impairments on the performance of differential phase-shift keying (DPSK), like the responsivity imbalance between the two arms of the receiver balanced photodetector and the detuning of the asymmetric Mach-Zehnder filter. We extend to DPSK a semianalytical technique, based on the Karhunen-Loe/spl grave/ve series expansion, which can be used to obtain reliable performance results in the simulation of IM/DD optical systems. We show that the DPSK receiver imperfections may substantially decrease the sensitivity gain of DPSK over standard IM/DD systems. In particular, the performance turns out to be remarkably insensitive to the responsivity imbalance between the two arms of the receiver balanced photodetector but highly sensitive to the detuning of the asymmetric Mach-Zehnder filter. We also analyze the validity of the application of the Q parameter evaluation, which is extensively used in theory and simulation of intensity-modulation direct-detection (IM/DD) optical systems, to the study of the bit error rate performance of direct-detection DPSK optical systems, showing that its inaccuracy can be very large.

Noise statistics in optically preamplified differential phase-shift keying receivers with Mach-Zehnder interferometer demodulation.

We report an analysis of the noise statistics for an optically preamplified differential phase-shift keying (DPSK) receiver with balanced and single-port detections. It is found that identical signal-amplified spontaneous emission beating noise exists for bits 1 and 0 in DPSK balanced detection. It is also revealed that the bit error ratio (BER) of a DPSK receiver with balanced detection has no direct relation to the conventional Q factor. Moreover, an analytic BER expression for the DPSK balanced detection receiver is presented.

Wide Dynamic Range 10-Gb/s DPSK Packet Receiver Using Optical-Limiting Amplifiers

We demonstrate a method to extend the dynamic range (DR) of 10-Gb/s differential phase-shift keying (DPSK) receivers in presence of burst-mode data. We achieve a DR of 25 dB by operating linear optical amplifiers in saturation and benefiting from fast optical-limiting amplification. A fixed decision threshold as enabled by DPSK receivers with balanced detection eliminates the need for guard times and removes inherent sensitivity penalty associated with the adaptive threshold as in conventional on-off keying receivers.

BER for optical heterodyne DPSK receivers using delay demodulation and integration detection

Previous work on the bit error rate (BER) performance of differential phase-shift keying (DPSK) including the effects of additive white Gaussian noise (AWGN) and phase noise has concentrated on the delay demodulator with narrow-band intermediate frequency (IF) bandpass filtering (BPF) and sampling detection. No similar analysis has yet been performed for the delay demodulator with wideband IF bandpass filtering and integration detection. Phase noise is an important consideration in coherent optical communication systems and the most widely accepted model is a Brownian motion process. A closed-form BER expression along with detailed Monte Carlo simulation results are presented for the DPSK delay demodulator with wideband IF bandpass filtering and integration detection filtering including phase noise effects using the Brownian motion model. Analytic expressions are also obtained for the moments of the phase noise component of the decision variable. Using these moments, estimates of the phase noise BER floor are produced. It is found that this receiver has noise performance comparable to receivers with narrowband IF bandpass filtering and sampling detectors for signal-to-noise ratio (SNR) and phase noise in the range of practical interest, but with potentially less degradation due to intersymbol interference (ISI).

A postdetection strategy for the reduction of error floors of optical DPSK receivers impaired by laser phase noise

A postdetection strategy for the performance enhancement of optical binary differential phase shift keying (DPSK) receivers impaired by phase noise is proposed and investigated. First, the bandwidth of integrate-and-dump (I&D) filters is increased so that multiple samples per symbol duration of the received signal are obtained. Previously, a scheme, hereafter referred to as fixed-window (FW) postdetection processing, was introduced. In this approach, the samples separated in time by a symbol time at the output of I&D filters are correlated. The decision circuitry, subsequently, provides a sum of the resulting signal over a symbol time to yield a decision variable. In the proposed scheme here, hereafter referred to as symmetrical expanding window (S-EW) postdetection processing scheme, samples that are centered about the signal transition point in a two-symbol signaling interval are correlated. Numerical results indicate that the S-EW scheme achieves an error floor that is significantly smaller than that of the its FW counterpart.

A systematic approach to the design and analysis of optimum DPSK receivers for generalized diversity communications over Rayleigh fading channels

A generalized diversity channel is introduced that models a variety of wireless communication systems that use time, frequency, multipath, and/or antenna diversity with various interbranch correlations between signaling waveforms and the fading and additive noise processes. In the context of this general model, a systematic approach to the design and analysis of optimum noncoherent differential phase-shift keying (DPSK) receivers is introduced. In particular, it is shown how the minimum error probability (MEP) and the generalized likelihood ratio tests (GLRT) can be applied to obtain optimal noncoherent combining rules. A comparative error-rate analysis of the GLRT and MEP detectors and an ad hoc equal-gain combiner is provided for binary signaling, and the suitability of the three schemes is determined as a function of fading characteristics. The asymptotic bit-error-rate analysis is undertaken for the MEP detector for slow and fast fading channels. An estimator-detector decomposition of the noncoherent MEP rule is obtained which allows an insightful comparative study of the fundamental limits of binary phase-shift keying and DPSK modulation-detection methods for both slow and fast fading. The results of this paper are also applicable to postdecorrelative receivers in multiuser channels.

A simple DPSK receiver with improved asymptotic performance over fast Rayleigh-fading channels

In this letter we present a simple receiver for differential phase shift keying (DPSK) signals transmitted over fast, frequency flat, fading channels, which is characterized by a very low asymptotic error probability. The system performance analysis is carried out for a 2-DPSK signal.

An adaptive maximum likelihood receiver for correlated Rayleigh-fading channels

The paper develops a receiver structure for random Gaussian signals in additive noise based on the classic maximum likelihood (M-L), estimator-correlator derivation of Kailath [1960], and applies it to differential phase shift keying (DPSK) on the correlated Rayleigh-fading channel. It is shown to lower the error floor found in the performance of conventional DPSK receivers by orders of magnitude. In addition, the maximum-likelihood procedure is shown to make uncorrelated symbol decisions. The performance of both conventional and optimal receivers, which require knowledge of the channel statistics, is examined analytically. A recursive, channel-adaptive version of the optimal receiver, utilizing decision feedback to estimate the channel statistics, is developed. Its simulated performance shows no penalty compared to theoretical calculations which require explicit knowledge of the channel statistics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>