Performance evaluation of optical DQPSK using saddle point approximation

Differential phase-shift keying (DPSK) has been widely implemented and developed in high-speed optical communication systems. The low error rate detection at high access rate is one of the considerable issues in practical engineering application. Balanced detection based on fiber Mach-Zehnder delay interferometer (MZDI) is the typical optical DPSK signal detecting method. It requires that the free spectrum range (FSR) of the MZDI equals the reciprocal of symbol period of the DPSK signal. For the reasons of ambient temperature variation and nonlinear phase noise, a dynamic frequency offset always exists between the FSR and the reciprocal of symbol period. That may introduce some optical signal-to-noise ratio (OSNR) costs and fault detections. Therefore, it is significant to inhibit the frequency offset on DPSK detection. In this paper, firstly, we discuss the effects of frequency offset on DPSK detection, and realize the conclusion that frequency offset is virtually equivalent to an additional phase difference between adjacent symbols. Secondly, through simulation, we analyze the feasibility of DPSK detection in the presence of a definite range of frequency offset, and present the quantitative computation of effective coverage, duty cycle, and optimal sampling time of symbol interference. Some issues which should be considered in practical implementation are also discussed. Finally, according to the relationship among phase difference, temperature and voltage, we propose a phase difference compensation scheme which can automatically adjust the voltage for optimal detections, and dynamically track the changing of ambient temperature and nonlinear phase noise. Furthermore, we ascertain the performance of the voltage requested for implementing the scheme. The scheme can be also developed to quadrature phase-shift keying (QPSK) and differential QPSK (DQPSK) modulation situations.

This paper presents recent progress toward the realization of ultrahigh-speed coherent optical transmission with a single-channel bit rate of more than 1 Tbit/s using ultrashort pulse technology and an advanced modulation format. We first describe Tbit/s optical time-division multiplexing (OTDM) transmission employing differential binary or quadrature phase shift keying. We present our recent demonstrations of single-polarization 640-Gb/s differential phase-shift keying and 1.28-Tb/s differential quadrature phase-shift keying transmissions over 525 km, which employ an ultrafast optical Fourier transformation technique. We then focus on coherent optical transmission using quadrature amplitude modulation (QAM) with a multiplicity of 512 that enables us to achieve an ultrahigh spectral efficiency of more than 10 b/s/Hz. Finally, we demonstrate a novel ultrahigh-speed, spectrally efficient coherent pulse transmission combining OTDM and QAM. A 400 Gb/s, 32 RZ/QAM signal was successfully transmitted over 225 km on a single carrier at 10 Gsymbol/s × 4-OTDM.

Wireless data transmission with binary phase-shift keying modulation encoded on a 92 GHz carrier is achieved using photonic components. A high-speed photodiode is used to convert the doubly-modulated optical signal to a modulated millimeter-wave carrier. A W-band Mach-Zehnder interferometer with a one-bit time delay is used to directly detect the differential phase-shift keyed millimeter-wave wireless signal without the use of a local oscillator. Field tests with antennas separated by 890 m demonstrate the ability to discriminate two phase states for differential binary phase shift keying (DBPSK) and four phase states for differential quadrature phase shift keying (DQPSK) at data rates of 2.3 Gb/s and 4.6 Gb/s, respectively.

Performance Analysis of Different Phase Shift Keying Modulation Schemes in Aeronautical Channels

A multi-tone code division multiple access (MT-CDMA) system with post-detection diversity combining is analyzed. The analysis is presented in terms of average bit error rate (BER). The modulator uses differential quadrature phase shift keying (DQPSK) signaling over a slowly Rician fading and frequency selective channel in the indoor environment. Here, the influence of the order of diversity and number of tones is studied for given bandwidth (BW), bit rate and transmitter power. The paper also compares the BER performance between differential binary phase shift keying (DBPSK) and DQPSK based MT-CDMA systems.

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.

Higher spectral efficiency and greater data rate per channel are the most cost-effective strategies to meet the exponential demand of data traffic in the optical core network. Multilevel modulation formats being spectrally efficient enhance the transmission capacity by coding information in the amplitude, phase, polarization or a combination of all. This paper presents the design architecture of a 32-channel dense wavelength division multiplexed (DWDM) system, where each channel operates with multi-level phase modulation formats at 40 Gbps. The proposed design has been simulated for 50 GHz channel spacing to numerically compute the performance of both differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) modulation formats in such high-speed DWDM system. The transmission link is analyzed with perfect dispersion compensation and also with under-compensation scheme. The link performance in terms of quality factor (

Phase shift keying modulation approaches are widely used in the communication industry. Differential phase shift keying (DPSK) and Offset Quadrature phase shift keying (OQPSK) schemes are chosen to be investigated is multi environment channels, where both systems are designed using MATLAB Simulink and tested. Cross talk and unity of signals generated from DPSK and OQPSK are examined using Cross-correlation and auto-correlation, respectively. In this research a proposed system included improvement in bit error rate (BER) of both systems in the additive white Gaussian Noise (AWGN) channel, by using the convolutional and block codes, by increasing the ratio of energy in the specular component to the energy in the diffuse component (k) and the diversity order BER in the fading channels will be improved in both systems.

이 논문에서는 계층변조를 적용하는 AT-DMB (advanced terrestrial digital multimedia broadcasting) 시스템에 적용할 수 있는 블라인드등화 기법을 제시하고 그 성능을 살펴본다. AT-DMB 시스템은 기존 T-DMB의 DQPSK (differential quadrature phase-shift keying) 신호와 역방향 호환성을 보장하고 더 높은 데이터 전송률을 지원하기 위해 16-QAM (quadrature amplitude modulation) 계층변조 방식을 적용한다. 이 결과 SNR (signal to noise ratio)에 따라 기존 T-DMB 심볼과 추가된 심볼은 서로 다른 판정오율 (decision error rate)을 가진다. 따라서 판정한 신호로부터 채널을 추정할 때 판정오율이 낮은 선순위 심볼과 판정오율이 높은 후순위 심볼의 신뢰도에 따라 다른 가중치를 줌으로써 판정치의 전체적인 신뢰도를 향상시킬 수 있다. 이 논문에서는 계층변조에 따른 비트 오율(bit error rate) 성능의 악화정도를 분석하고, 모의실험을 통해 판정신호의 신뢰도에 따라 가중치를 주는 제안방식이 가중치를 주지 않은 경우에 비해 비트 오율 성능이 향상됨을 확인하였다. In this paper, we propose a blind equalization method for advanced terrestrial digital multimedia broadcasting (AT-DMB) systems which use hierarchical modulation. The AT-DMB system adopts hierarchical 16-ary quadrature amplitude modulation (16-QAM) to ensure backward-compatibly with the differential quadrature phase shift keying (DQPSK) signal of the legacy terrestrial digital multimedia broadcasting (T-DMB) systems and to support higher transmission rate. Due to the hierarchical modulation, the conventional T-DMB signal and the additional signal have different error rate at same signal to noise ratio (SNR). By weighting the decided symbols differently according to the reliability of the symbols, i.e., high priority symbol with low error rate and low priority symbol with high error rate, we can improve the channel estimation accuracy. In this paper, we analyze SNR loss by hierarchical modulation and confirm it through simulations. Moreover, through simulations, we verify that the proposed weighting method improve BER compared to the no-weighting method.

This paper is devoted to an investigation of an exact average symbol error probability (SEP) for amplify and forward (AF) relaying in independent Nakagami‐m fading environments with a nonnegative integer plus one‐half m, which covers many actual scenarios, such as one‐side Gaussian distribution (m = 0.5). Using moment generating function approach, the closed‐form SEP is expressed in the form of Lauricella multivariate hypergeometric function. Four modulation modes are considered: rectangular quadrature amplitude modulation (QAM), M‐ary phase shift keying (MPSK), M‐ary differential phase shift keying (MDPSK), and π/4 differential quaternary phase shift keying (DQPSK). The result is very simple and general for a nonnegative integer plus one‐half m, which covers the same range as integer m. The tightness of theoretical analysis is confirmed by computer simulation results.

Abstract. In this paper an FPGA-based test system for high-speed transmission experiments with integrated photonic receivers is presented. Pseudorandom binary sequences are generated inside the FPGA and encoded as either differential quadrature phase shift keying (DQPSK) or quadrature phase shift keying (QPSK) signals. The DQPSK encoder uses a 64-fold parallel-prefix-layers architecture for real-time operation which allows for a maximum internal encoder data rate of 64 Gbit/s. Two-fold parallel data streams of I and Q signals suitable for driving an optical IQ-modulator can be transmitted and received by four 12.5 Gbit/s transceivers. Integrated bit error testers are used to determine bit error rates in real-time.

In digital communications, 90 or 180 degree phase ambiguity between the receiver and transmitter carrier is a serious problem for the coherent demodulation. To remove their phase ambiguity, differential quadrature phase shift keying (DQPSK) was proposed with the cost of a remarkable 2.4 dB performance degradation. Based on the iterative decoding (ID) scheme, an efficient joint convolutional code (CC)-coded DQPSK method is proposed to close the gap between quadrature phase shift keying (QPSK) and DQPSK. Using the extrinsic information transfer (EXIT) chart technique, we unveil that the low-complexity convolutional codes outperform the high-complexity Turbo codes for the ID scheme. Simulation results turn out that the proposed scheme can overcome the error-floor effect, and achieve almost 3.54 dB and 0.9 dB signal-to-noise ratio (SNR) gain compared with the non-iterative CC at 10−5 Bit Error Rate (BER)and iterative Turbo schemes at 10−7 BER, respectively.

SummaryOptical transmission networks (OTxNs) provide a cost‐effective solution towards ultrahigh data intercontinental transmission. However, nonlinear effects such as four‐wave mixing (FWM) and cross‐phase modulation (XPM) are the major performance limiting factors for OTxNs. This paper proposes the use of differential quadrature phase shift keying (DQPSK) modulation format and uneven channel spacings for dispersion compensation and investigates the nonlinear mitigation performance for a 32 channels ultradense wavelength division multiplexing (UDWDM) with data rate of up to 10 Gbps per channel. In addition, this paper presents an analysis on power budget and power penalties with a cost benefit analysis (CBA) for the proposed framework. The transmission link of the proposed UDWDM model is analyzed in terms of bit error rate (BER) for various lengths of optical fiber in long‐haul transmission, launch power, nonlinear effective area, and nonlinear refractive index. The analytical model is developed for mitigation of nonlinearity for the modeled UDWDM long‐haul and ultrahigh‐capacity system, beyond 1200‐km path span. The simulation results show systems advantages of having narrower spectrum than on‐off‐keying (OOK) modulation, significant tolerance to nonlinearities and low cost, compared with current OTxNs with 2.8‐dB optical signal‐to‐noise ratio (OSNR) improvement and successful mitigation of nonlinearities for as high launch powers as +4 dBm for such long distance transmission in dispersive channel.

In this paper, the performance of multiple-bit delay detection (MBDD) systems in optical differential phase shift keying (DPSK) is investigated. Assuming that the dominant noise in the system is originated by the optical amplifier and using Gaussian approximation, we present a closed form equation which predicts the overall bit-error-rate (BER) performance of the system as a function of the number of delay segments, optical signal-to-noise ratio (OSNR) at the receiver, and bandwidth of the optical bandpass filter. It is shown that with a large number of delay segments, the performance of MBDD system approaches to the performance of homodyne coherent detection.

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.