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Performance Enhancement of Coherent Optical OFDM System Using LMS Algorithm

Bharti Manisha

Journal of Telecommunications and Information Technology

2020

nr 1

1--5

Instability of the local oscillator causes phase noise – a phenomenon that is a disadvantage and is considered to be a major obstacle in the functioning of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. An attempt has been made in this paper to reduce the eﬀects of common phase errors generated by phase noise. In this paper, a least mean square (LMS) based algorithm is proposed for estimation of phase noise. Using this proposed algorithm, the major problem of phase ambiguity caused by cycle slip is avoided and the bit error rate is greatly improved. Further, there is no requirement for modifying the frame structure of OFDM using this algorithm. A CO-OFDM system with the 8-PSK technique is used to implement the algorithm concerned. Furthermore, the algorithm, using the 8-PSK modulation technique, is analyzed and compared with the existing QPSK technique and with other algorithms. The investigations reveal that 8-PSK outperforms existing LMS algorithms using other techniques and signiﬁcantly reduces the bit error rate.

Implementation of C-PolSK Modulation in FSO Network and Analysis of its Atmospheric Performance

Chattopadhyay Diptangshu, Bharti Manisha

Journal of Telecommunications and Information Technology

2019

nr 4

43--49

Free Space Optical (FSO) communication is a quickly developing technology that is designed to handle high data rates while maintaining a good quality factor (Q-factor). Many novel techniques have been implemented to cope with atmospheric attenuating factors, such as fog and rain. Here, we have introduced circular polarization shift keying (C-PolSK) modulation to produce a stable and uniform light beam. The plane of polarized light keeps rotating along with the propagation vector, which helps reduce phase variations and cross-channel eﬀects. C-PolSK provides higher penetrating power and attenuation resistance over linear polarization shift keying (L-PolSK). Two diﬀerent C-PolSK models have been proposed and graphical comparisons, relying on such parameters as Q-factor, transmission distance and inputoutput power, have been made. The cases of moderate fog and rain attenuation are taken to verify the model’s eﬃciency. Polarized light is split into two orthogonal components and then modulated using the Mach-Zehnder modulator. One of the models also employs the principle of orthogonal diﬀerential phase shifting. Eye diagrams have been provided to verify the bit error rate (BER). The orthogonal diﬀerential phase shifted C-PolSK model proves to be the most suitable implementation prototype.