Multiple-access interference (MAI) and beat noise (BN) are analyzed in asynchronous coherent time-spreading OCDMA
system according to the aperiodic cross-correlation function. Relationship between the mean intensity of aperiodic crosscorrelation
and MAI and BN is deduced. Considering the worst system performance, upper bound of BER performance
is evaluated by the maximum value of the mean intensity of aperiodic cross-correlation. For 511 length Gold sequence,
coherent time-spreading OCDMA system can support less than 5 interfering users in the worst performance.
Optical encoders/decoders based on fiber gratings are designed and fabricated. Experiment on one interference user
2.5Gb/s symbol overlapping optical fast frequency-hopping CDMA (SO-FFH OCDMA) system is demonstrated. Multiaccess
interference in SO-FFH OCDMA system is studied, and is compared with that of traditional FFH OCDMA
system. Experiment result shows that multi-access interference will degrade the system performance. With one
interference user, SO-FFH OCDMA can also decode data correctly at data bit rate 2.5Gb/s.
An analysis of the code parameters that are important to asynchronous coherent time-spreading OCDMA system is
presented. Relationship between the mean intensity of aperiodic cross-correlation and multiple-access interference
(MAI) and beat noise (BN) is deduced. Considering the mean system performance, MAI and BN can be calculated
directly from aperiodic auto-correlation function, and the aperiodic cross-correlation function is not needed. Hence, a
computational saving can be achieved For 511 length Gold sequence, coherent time-spreading OCDMA system can
support 12 interfering users for the mean performance.
The performance of normalized throughput in WDM+OCDMA is compared with that of MW OCDMA system after considering the effect of chromatic dispersion. Normalized throughput in MW OCDMA system will be reduced after considering the effect of chromatic dispersion. Both WDM+OCDMA and MW OCDMA systems have comparable performance of normalized throughput when traffic load is light. However, WDM+OCDMA system has better performance when traffic load is heavy. Furthermore, the peaked normalized throughput of WDM+OCDMA system is
larger than that of MW OCDMA system.
A scheme of WDM+OCDMA system employing optical hard-limiter(OHL) is proposed, and its performance of normalized throughput is analyzed. Upper bound of normalized throughput is obtained when all simultaneous users are equally allocated to different wavelength channels. Lower bound of normalized throughput is obtained when all simultaneous users are firstly allocated to same wavelength channels. Compared with the performance of WDM+OCDMA system without OHL, both upper bound and lower bound of normalized throughput in WDM+OCDMA system with OHL can be improved.
Estimating the number of simultaneous users on channel, optimum threshold value in multi-wavelength optical CDMA(MW OCDMA) is achieved according to maximum likelihood principle. When MW OCDMA system has large number of simultaneous users on channel, optimum threshold value will vary with the number of simultaneous users, and
the receiver will adjust the optimum threshold accordingly. Theoretical analysis and analogy simulation show that BER of MW OCDMA system will degrade greatly when employing the proposed optimum threshold value by maximum likelihood principle.
A new one-dimensional optical orthogonal codes named extend modified hyperbolic congruence codes(EMHC), is first constructed, and its performance is analyzed. Using EMHC for time spreading and prime codes (PC) for wavelength hopping, a new two-dimensional optical orthogonal codes named EMHC/PC is constructed. Then, the performance of EMHC/PC is analyzed, and is also compared with EQC/PC. It is shown that EMHC/PC has the same code cardinality and code length, but has better cyclic cross-correlation performance. Therefore, EMHC/PC can support more simultaneous users in optical CDMA networks.
Optical encoder and decoder devices based on fiber Bragg gratings is designed. An FFH-OCDMA system scheme is performed with the devices. Transmission of the system is demonstrated over 6.5km of G.652 fiber at data rate 622M bit/s and get the desired results.
The performance of normalized throughput in a hybrid WDMA-OCDMA system is studied. Effect of optical beat noise and dispersion on the normalized throughput is analyzed. The scheme of BCH channel coding is proposed to improve the performance of a hybrid WDMA-OCDMA system. Analysis result shows that the normalized throughput can be improved greatly when traffic load is medium. Furthermore, the maximum normalized throughput will increase for the BCH-coded hybrid WDMA-OCDMA system