A. K. M. Nazrul Islam

Analytical Evaluation of Bit Error Rate Performance of a Free-Space Optical Communication System with Receive Diversity Impaired by Pointing Error

Abstract Analysis is carried out to evaluate the conditional bit error rate conditioned on a given value of pointing error for a Free Space Optical (FSO) link with multiple receivers using Equal Gain Combining (EGC). The probability density function (pdf) of output signal to noise ratio (SNR) is also derived in presence of pointing error with EGC. The average BER of a SISO and SIMO FSO links are analytically evaluated by averaging the conditional BER over the pdf of the output SNR. The BER performance results are evaluated for several values of pointing jitter parameters and number of IM/DD receivers. The results show that, the FSO system suffers significant power penalty due to pointing error and can be reduced by increasing in the number of receivers at a given value of pointing error. The improvement of receiver sensitivity over SISO is about 4 dB and 9 dB when the number of photodetector is 2 and 4 at a BER of 10–10. It is also noticed that, system with receive diversity can tolerate higher value of pointing error at a given BER and transmit power.

Performance analysis of a free space optical link in the presence of pointing errors with space diversity

An analytical approach is presented to evaluate the bit error rate (BER) performance of an optical free space link considering the effect of pointing error. The analysis is presented to evaluate the BER with multiple photo detectors in the presence of pointing error. The results are evaluated at a bit rate of 10 Gbps for various system parameters. The receiver sensitivity with pointing error is evaluated for SISO and SIMO FSO links for various system parameters. It is noticed that SIMO FSO links can tolerate more pointing error compared to SISO.

Effect of Pointing Error on the BER Performance of an Optical CDMA FSO Link with SIK Receiver

Abstract An analytical approach is presented for an optical code division multiple access (OCDMA) system over free space optical (FSO) channel considering the effect of pointing error between the transmitter and the receiver. Analysis is carried out with an optical sequence inverse keying (SIK) correlator receiver with intensity modulation and direct detection (IM/DD) to find the bit error rate (BER) with pointing error. The results are evaluated numerically in terms of signal-to-noise plus multi-access interference (MAI) ratio, BER and power penalty due to pointing error. It is noticed that the OCDMA FSO system is highly affected by pointing error with significant power penalty at a BER of 10−6 and 10−9. For example, penalty at BER 10−9 is found to be 9 dB corresponding to normalized pointing error of 1.4 for 16 users with processing gain of 256 and is reduced to 6.9 dB when the processing gain is increased to 1,024.

Impact of timing jitter on the BER performance of an M-PPM free space optical link in presence of atmospheric turbulence

An analytical approach is presented to evaluate the impact of timing jitter on the Bit Error Rate (BER) performance of optical M-ary Pulse Position Modulation (M-PPM) Free Space Optical (FSO) link under the influence of atmospheric turbulence modelled by Log-normal distribution. The expression of the conditional BER for a given timing jitter is developed and the unconditional BER is found over the probability density function (pdf) of the timing jitter. The results are evaluated at a bit rate of 10 Gbps over weak turbulence for different M-PPM order. It is found that, there is a significant deterioration in BER performance with increase in timing jitter variance for a given M-PPM order. The system suffers penalty in receiver sensitivity at a given BER due to timing error. Further, it is noticed that higher order M-PPM system suffers less penalty than the lower order M-PPM system at a given bit rate and BER. The analysis may be useful for evaluating the impact of slot timing jitter for M-PPM FSO system with strong turbulence.

Effect of Pointing Error on BER Performance of a Multi-wavelength OCDMA FSO System with SIK Dual Detector Receiver

Abstract A novel analytical approach is presented to evaluate the bit error rate (BER) performance of a multi-wavelength optical code division multiple access (MW-OCDMA) free space optical (FSO) system using optical domain encoder and sequence inverse keying (SIK) balanced photodetector direct detection receiver taking the effect of pointing errors into considerations. The analysis is carried out to find the expression for the signal, multi-access interference (MAI) and crosstalk at the output of the SIK receiver in presence of pointing error. The BER performance results are evaluated for different values of standard deviation of pointing error, code length, number of simultaneous user and other system parameters. It is found that, MW-OCDMA system offers improved BER performance over single wavelength OCDMA FSO system. However, the performance of an MW-OCDMA system is degraded due to the effect of pointing error between the laser transmitter and optical receiver and the system suffers significant power penalty at a given BER of 10−9. The penalty is found to be 11.0 dB, 24.0 dB and 30 dB for jitter standard deviation of 1.3, 1.8 and 2.5 respectively when code length is 512 and number of user is 8 for number of wavelength 8. Further, the penalty can be greatly reduced by increasing the code length for a given number of user and number of wavelength.

BER performance analysis of a FSO OCDMA communication system with receive diversity using SIK dual photodetector receiver

An analytical approach is represented to evaluate the bit error rate (BER) performance results of an optical CDMA (OCDMA) free space optical (FSO) communication system with receive diversity using multiple photodiode dual-detect Sequence Inverse Keying (SIK) receiver. The analysis is presented to find the expression for the signal current and multi access interference (MAI) current at the output of an equal gain combiner (EGC) in presence of atmospheric channel effect, atmospheric turbulence and pointing error. The performance results in terms of BER are evaluated for different values of code lengths, number of receiver antennas, number of simultaneous user and the system parameters. It is found that, significant degradation in the receiver BER performance due to the atmospheric channel effect and in presence of pointing error can be substantially reduced by increasing the number of photodetectors. Further improvement in the receiver sensitivity can be obtained by increasing the optical code length for a given number of user at a given BER of 10−9. For example, at a BER of 10−9 and number of user K=16 sensitivity improvement due to receive diversity is found to be 2.15 dB, 2.35 dB, 2.6 dB corresponding to processing gain of 64, 256 and 512 respectively for number of photodetector receiver of 4.

Effect of weak atmospheric turbulence on the BER performance of an optical CDMA FSO link with Sequence Inverse Keying (SIK) balanced photodetector receiver

Analytical approach is presented to evaluate the effect of weak atmospheric turbulence on the bit error rate (BER) performance of an optical code division multiple access (OCDMA) free space optical (FSO) link using optical domain encoder and Sequence Inverse Keying (SIK) balanced photodetector receiver. The analysis is carried out to find the expression of the signal current and multi access interference (MAI) current at the output of the SIK receiver considering the effect of atmospheric turbulence of the channel. The conditional BER conditioned on a given atmospheric turbulence is evaluated and the average BER is obtained by averaging the conditional BER over the probability density function (pdf) of atmospheric turbulence. The results are evaluated for different code length, number of simultaneous users, turbulence variances and other system parameters. The performance of an OCDMA link is found to be highly degraded due to atmospheric scintillation and the power penalty due to turbulence effect is of the order of 2 to 10 dB depending on the turbulence variance. For example, power penalty is 3 dB to 10 dB at a BER of 10-9 for 12 numbers of users at 1 Gbps corresponding to turbulence variance 0.01 to 0.3 respectively. However, the penalty can be reduced significantly by increasing the processing gain.

BER performance of DS-CDMA system over a multipath Rayleigh fading channel considering path gain component and noise variance

The performance of DS-CDMA system is examined by the bit error rate (BER) performance of the system which is estimated by standard Gaussian approximation (SGA) with power control. The BER performance of multiple access system is studied over a fading channel such as frequency selective multipath Rayleigh fading channel. In this paper, the path gain component is considered as Rayleigh distribution and the effect of this path gain component and noise variance in BER performance of DS-CDMA system has been explained. In addition, optimum design parameters for a DS-CDMA system have been suggested.