Modelling of an Optical Coherent QPSK Transmission System PART-I

2018

The always increasing amount of internet traffic in optical networks led to the need of using efficient modulation formats. Conventional on-off-keyed (OOK) signals have been extensively employed in optical communication systems. However, OOK modulation is inadequate for transmission of 40 Gbit/s per channel, or higher, bit rates (Winzer & Essiambre, 2006) mainly because of its reduced robustness to fiber nonlinearity, chromatic dispersion and optical filtering at such bit rates. In order to overcome such impairments, several advanced modulation formats received particular attention in the last few years. Some of these modulation formats still carry the information in the amplitude of the signal. However, they also modulate the phase of the signal to increase its robustness to transmission impairments. Some examples of such modulation formats are duobinary and alternate mark inversion. The most promising modulation formats for future optical networks make use of the phase of the sign...

Advances in Lasers and Electro Optics, 2010

OFC/NFOEC 2008 - 2008 Conference on Optical Fiber Communication/National Fiber Optic Engineers Conference, 2008

The feasibility of long-haul transmission using differential quadrature phase shift keying (DQPSK) modulation is discussed. We focus in particular on the trade-off between spectral efficiency and reach in optical transmission systems using DQPSK modulation.

Indonesian Journal of Electrical Engineering and Computer Science, 2022

This paper presents an orthogonal frequency division multiplexing (OFDM) for a long-haul optical transmission system with high-rate transferability to alleviate dispersion effects. In addition, we suggest combining polarization division multiplexing (PDM) with coherent OFDM (CO-OFDM) to increase spectral efficiency (SE). Based on OptiSystem (2021) version 18.0" software package, a 100 Gbps single-channel PDM-CO-OFDM transmission system is investigated using different modulation formats; bipolar phase keying (BPSK), quadrature phase shift keying (QPSK), Eight-Phase-Shift Keying modulators (8-PSK), and quadrature amplitude modulation (16-QAM). A 60 km span of standard single-mode fiber (SSMF) cable is employed in this investigation. The system's performance and spectral efficiency have been evaluated by comparing against the different modulation schemes. The outcomes that were got show that the BPSK modulation scheme has the longest transmission distance and requires a lesser level of optical signal to noise ratio (OSNR) at the receiver side. Concerning spectral efficiency, 16-QAM outperforms the others. Farther, the impact of employing ultra-low loss and large effective area fiber in reducing loss and nonlinear effects in the optical channel for 16-QAM modulation formats is examined. The result found that the system with advanced fiber has superior performance than the SSMF. The bit error rate (BER) of 0.033 (20% concatenated forward error correction (FEC) threshold) is used as a baseline.

Optical coherent Quadrature Phase Shift Keying (QPSK) transmissions can double the data rate of existing intensity modulation and direct detection (IM/DD) systems [Noe]. Coherent receivers have superior sensitivity and the transmission impairments (chromatic dispersion, polarization mode dispersion, noise) can be compensated in electronic domain at low speed [Pfau]. This paper models an optical coherent QPSK transmission system with Additive White Gaussian Noise (AWGN) and laser phase noise. The paper discusses low pass filtering methods with different filtering algorithms that reduce the effects of AWGN and laser phase noise [Noe, Pfau].

2014 16th International Conference on Transparent Optical Networks (ICTON), 2014

A hybrid 2 slots binary phase shift keying-on off keying (hybrid 2BPSK-OOK) scheme is proposed as a new modulation technique to improve the performance of both conventional binary phase shift keying (BPSK) and on-off (OOK) modulation techniques in optical fiber communications systems. In conventional BPSK scheme, a consecutive stream of low power BPSK symbols are transmitted, while in the proposed scheme, a less number of high power BPSK symbols are transmitted in a two slot hybrid frame and their positions are exploited to transmit more bits. That is, the transmitted information is carried in both the positions and phases of the transmitted pulses. The transmission characteristics, transmitter and receiver block diagram, bandwidthutilization, and optimal decoding for the proposed scheme are all studied in this paper. An upper bound on the bit-error rate is obtained for the proposed scheme and is compared to that of the traditional schemes under the same energy per bit constraint. Our results reveal that, for both moderate and high signal-to-noise ratios, the proposed hybrid scheme achieves much lower levels of bit-error rates than that of ordinary coherent-and directdetected OOK schemes. However, at all energy per bit levels, the proposed scheme achieves less performance than that of ordinary BPSK. In addition, the proposed modulation scheme achieves much higher bandwidthutilization efficiencies as compared to that of ordinary schemes. Keywords: binary phase shift keying modulation (BPSK), bit-error rate, hybrid modulations, on-off keying (OOK), optical fiber communications, symbol-error rate.

bzu.edu.pk

Two-channel phase shift keying (PSK) optical communication using a single laser light source has been investigated with the help of Michelson Interferometer for encoding signals and homodyne technique was used for decoding signals. Light from the laser source was divided into three parts out of which two parts were used to carry two signals independently and the third part was used as a reference signal for decoding both signals. All of the three parts of light waves were originated from the same laser source but transmitted with different planes of polarization. In this system, on the receiving end, these three light-waves were recombined in sets of two signals with the reference signal that decodes the two light-wave signals independently.

European Transactions on Telecommunications, 2008

We report on the occurrence of unequal bit error probability in a coherent quadrature phase shift keying (QPSK) fiber-optic system. The bit error rates (BER) of two QPSK bits are derived individually based on the developed system model, and they turn out to differ by more than an order of magnitude for a phase modulator based transmitter. The phenomenon, previously unreported, arises because such a transmitter introduces a controlled form of inter-symbol-interference (ISI), and the receiver low-pass filters affect this ISI differently for the two bits. The optimum bandwidth of the receiver low-pass filter is obtained from the analytic derivation, which is about 0.7 times the symbol rate. We propose two simple system modifications, one in the transmitter and one in the receiver, to compensate for the phenomenon and equalize the two BER's. Those modifications improve the system performance by about 2 dB without adding any extra hardware.

Coherent optical fiber communications for data rates of 100 Gbit/s and beyond have recently been studied extensively because high sensitivity of coherent receivers could extend the transmission distance. Spectrally efficient modulation techniques such as M-ary phase shift keying (PSK) can be employed for coherent optical links. The integration of mul-ti-level modulation formats based on coherent technologies with wavelength-division multiplexed (WDM) systems is vital to meet the aggregate bandwidth demand. This paper reviews coherent quadrature PSK (QPSK) systems to scale the network capacity and maximum reach of coherent optical communication systems to accommodate traffic growth.