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Performance analysis of an optical spectral amplitude-coding CDMA system

Wei Zou, Hooshang Ghafouri‐Shiraz, Cheng Tee Hiang, Edward Hartley Sargent

Published Jan 1, 2003• 0 citations
OpenAlex

Abstract

It has been proposed that arrived photon count at the photo-detector obeys negative binomial (NB) distribution when both the phase-induced intensity noise and Poisson-distributed photon arrival process are taken into account. In this paper, we analyze the performance of an optical spectral-amplitude-coding CDMA system based on this NB distribution. According to our knowledge, it is the first time that NB distribution is used in such kind of analysis. All previously published relevant papers have used Gaussian distribution in the calculation of bit error rates. We have also compared our analysis results with that from traditional Gaussian approximation. It has been shown that our analysis results are in good agreement with the Gaussion-approximated ones. When interference user number K=0, i.e. only the desired user is sending data, NB-distributionbased method gives a more precise performance estimation.

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It has been proposed that arrived photon count at the photo-detector obeys negative binomial (NB) distribution when both the phase-induced intensity noise and Poisson-distributed photon arrival process are taken into account. In this paper, we analyze the performance of an optical spectral-amplitude-coding CDMA system based on this NB distribution. According to our knowledge, it is the first time that NB distribution is used in such kind of analysis. All previously published relevant papers have used Gaussian distribution in the calculation of bit error rates. We have also compared our analysis results with that from traditional Gaussian approximation. It has been shown that our analysis results are in good agreement with the Gaussion-approximated ones. When interference user number K=0, i.e. only the desired user is sending data, NB-distributionbased method gives a more precise performance estimation.
It has been proposed that the arrived photon count obeys negative binomial (NB) distribution when a thermal optical source is used. In this letter, we have analyzed the bit-error rate (BER) of an optical spectral-amplitude-coding CDMA system using NB distribution. It has been shown that when the number of simultaneous users is small, the resultant BER is much lower than that calculated using Gaussian approximation. When the number of simultaneous users is large (for example N>19 when the effective power is -27 dBm), both NE distribution and Gaussian approximation give almost the same value for the BER of the system.
In this paper, performance analysis of conventional spectral amplitude coding (CSAC) with hybrid (HSAC) for OCDMA system is investigated in local area network (LAN) environment. The CSAC is built based on arithmetic sequence with simple algebraic ways. The HSAC technique is used in which spectral amplitude coding (SAC) combined with wavelength division multiplexing (WDM) to effectively reduce multiple access interference (MAI) and mitigate the influence of phase induced intensity noise (PIIN) arising in photodetecting process. The main idea is to construct the code sequences in SAC domain then repeat it diagonally in the wavelength domain as groups which maintains the same cardinality of a given code weight. Results show that HSAC outperforms CSAC when the number of active users is high due to its better correlation properties. It has been shown that the HSAC can suppress intensity noise effectively and improve the bandwidth utilization significantly up to 4.2 nm.
The performance of optical code-division multiple-access (CDMA) communication systems utilizing number-state light field is evaluated. Lossy direct detection optical channels are assumed. Both on-off keying (OOK) and pulse-position modulation (PPM) schemes are investigated. For OOK, the exact bit error rate is evaluated taking into account the effect of both multiple-user interference and transmission loss. Upper and lower bounds on the bit error probability for PPM-CDMA systems are derived under the above considerations. The effect of both background and thermal noise is neglected in the analysis. A comparison between the performance of the number- and coherent-state OOK/PPM-CDMA networks is also presented. The results demonstrate that the number-state system requires less than half the energy consumed by the coherent-state one in order to attain the same performance.>
The performance of optical code-division multiple-access (CDMA) communication systems utilizing number-state light field is evaluated. Lossy direct-detection optical channels are assumed. Both on-off keying (OOK) and pulse-position modulation (PPM) schemes are investigated. For OOK, the exact bit error rate is evaluated taking into account the effect of both multiple-user interference and transmission loss. Upper and lower bounds on the bit error probability for PPM-CDMA systems are derived under the above considerations. The effect of both background and thermal noise is neglected in our analysis. Performance comparison between the number-state and coherent-state OOK/PPM-CDMA networks is also presented. Our results demonstrate that the number-state system requires less than half the energy consumed by the coherent-state one in order to attain the same performance. Lower bounds on the maximum number of simultaneous users are derived for both number- and coherent-state PPM-CDMA systems with asymptotically zero error rate.>
Enhanced security has often been cited as an important benefit of optical code-division multiple-access (O-CDMA) signaling but has seldom been analyzed in detail. This paper presents a theoretical analysis of the degree of confidentiality that can be provided by spectral-phase-encoded O-CDMA. Two eavesdropping detector structures are presented that can theoretically break the confidentiality of spectral-phase-encoded signals by detecting the code words in use by a specific user. One of them, an optical beat detector, is quantitatively analyzed to determine the probability of correctly detecting user code words. The confidentiality of user signals is shown to be vulnerable to such a detector if an eavesdropper can isolate a single user signal with a sufficiently high signal-to-noise ratio (SNR). At lower SNRs, combining multiple bits is shown to dramatically increase the probability of an eavesdropper correctly detecting user code words; even for codes long enough to strain implementation capabilities (e.g., 2048 code elements), the probability of correct detection is shown to rise from negligibly low values to virtually 100% by the combining of less than 100 transmitted bits at the eavesdropper's receiver.