Richa Bhatia

Comparative investigations of DWDM transmission system with PMD for different orthogonally modulated signals at 80Gb/s

Polarization mode dispersion PMD has become one of the major limiting factors for high-bit-rate optical transmission systems. This paper evaluates the performance of dense wavelength division multiplexed DWDM system with PMD at 80Gb/s in the presence of Kerr-nonlinear effects. Orthogonally modulated signals have been investigated and compared for tolerance against PMD in a DWDM transmission system with direct detection receivers. The optimized combinations of orthogonal polarization OP with carrier-suppressed return-to-zero CSRZ and CSRZ differential-phase-shift-keying signals are shown to improve PMD tolerance over high bit rates and long transmission lengths. Improved performance greater than 4dB is observed for CSRZ modulated signal with OP because of less channel cross talk and reduced power transfer between adjacent bits over different PMD values. The numerical results demonstrate that our proposed orthogonally modulated signals perform better with lesser complex direct detection receivers. Copyright

Performance evaluation of band-limited LPC vocoder and band-limited RELP vocoder in adaptive feedback cancellation

Feedback oscillation is one of the major problems faced by the hearing aid users. Adaptive feedback cancellation is used to suppress the feedback by using an adaptive filter to estimate the feedback path. However, this estimate is biased due to presence of high correlation between the original input signal and the loudspeaker input signal. Bias problem produces modeling error and can result in cancellation of the desired signal. Bias reduction can be obtained by using band-limited linear predictive coding based technique (BLPC) and band-limited residual excited linear predictive coding (BRELP) based technique. The paper compares performance of band-limited linear predictive coding based vocoder and band-limited residual excited linear predictive coding based vocoder in sound quality and bias reduction. The BLPC-AFC achieves more reduction in high-frequency correlation than BRELP-AFC. However, BRELP vocoder has a better output sound quality.

Effect of optimized alternate polarization on performance of N X 60-gb/s WDM transmission system

In this paper, simulation of 60-Gb/s alternate polarization of adjacent bits in a Wavelength Division Multiplexed (WDM) transmission link has been carried out for Return to Zero and differential phase shift keying modulation formats. Alternate Polarization Return to Zero (al-PRZ) system for 8, 16 and 32 channels has been analysed. The effect of variation of input power is observed in terms of Q value. It is found that Alternate Polarization Return to Zero (al-PRZ) suppresses the nonlinear effects at higher power levels of 22 dBm per channel and also improves the transmission length to 640km for a N X 60-Gb/s WDM system.

PAPR Reduction in OFDM System Using Hybrid OICF and Phase Rotation Scheme

Abstract Peak to average power ratio (PAPR) is one of the major limitations of orthogonal frequency division multiplexing (OFDM) systems because the higher PAPR induces the signal to get out of linear region of high power amplifier (HPA). In this article, a hybrid PAPR reduction scheme based on the combination of optimized iterative clipping and filtering (OICF) method and phase rotation is proposed. Using phase rotation, signal’s initial PAPR has been reduced by 14.23 dB and then OICF further reduces the final PAPR by 1.37 dB. Decreased PAPR will play an important role in reducing systems power consumption.

Performance evaluation of ROF communication link using DSB and SSB modulated signals compensated with parallel modulation scheme

This paper evaluates the performance of Radio over Fiber (ROF) communication link by compensating fiber chromatic dispersion(CD)using parallel electro-optic phase and intensity modulators for double-side-band (DSB) and single-side-band(SSB) modulated signals. Both the DSB and SSB modulated signals compensated with the same parallel modulation scheme, are investigated to compare their tolerance against CD induced power fading in ROF communication link. Comparative investigations are performed by loading a 9.5GHz RF signal with 2Gbps pseudorandom bit sequence and transmitting it over a 107km single mode fiber (SMF). The numerical results demonstrate that the parallel modulator based compensation scheme performs better resulting in wider eye opening. An improved performance with a BER of 10−60 is achieved with compensated SSB (CSSB) compared to a BER of 10—53 with compensated DSB (CDSB).

High speed broadband communication system for moving trains using Free Space Optics

The demand for the high speed broadband communication system is increasing on the moving trains, an alternative to the existing RF technology is the Free Space Optics (FSO) which is capable of providing data rates in Gbps. In recent past, the FSO system for moving trains has been proposed for 850nm wavelength. Considering the eye safety standards, the FSO system is investigated in this paper for 1550nm wavelength in which a single Base Station (BS) transmitter with a 25mW power can provide a data rate of 5Gbps for a coverage length of 180m. An improved performance with a BER of 10-71 when the train is nearest to the BS and 10-10 when the train is at the far end track at an extended range of 180m has been achieved.

Performance Evaluation of N × 80 Gb/s DWDM Optical System over SSMF for CSRZ-DPSK and RZ-DPSK Signals with Optimized Alternate Polarization

Abstract In this paper, the performance of N×80 Gb/s Dense Wavelength Division Multiplexed (DWDM) optical system is evaluated. Improved performance has been reported for CSRZ-DPSK signal with optimized alternate polarization (al-P), over 3120 km of SSMF using 80-km amplified spans in comparison to al-P RZ-DPSK. Investigations were conducted at 0.8 nm and 0.64 nm channel spacing. The results show that the CSRZ-DPSK signal with optimized al-P offers excellent performance for lower line width lasers. Orthogonal polarization and narrow spectrum of CSRZ-DPSK offer 5 dB improvement in quality factor for high-input power per channel with consistent performance over wider line widths.

Optimized alternate polarization and Four Wave Mixing in 60-Gb/s DWDM transmission system

In this paper, effect of Four-Wave Mixing has been described through simulation of 60-Gb/s alternate polarization of adjacent bits in a Dense Wavelength Division Multiplexed (DWDM) transmission link for Return to Zero and differential phase shift keying modulation formats. The optical spectra of alternate polarization return to zero (al-PRZ) system for 16 and 32 channels as well as different channel spacing have been analysed. It is found that alternate polarization return to zero (al-PRZ) shows better results than alternate polarization return to zero differential phase shift keying (al-P RZ-DPSK) format. For lower channel spacing of 60 GHz the performance deteriorates at lower power/channel of 15 dBm.