Downloads & Free Reading Options - Results

This paper provides an accurate analysis of the performance of a random-carrier (RC) code-division multiple-access (CDMA) scheme recently introduced for use in high capacity optical networks. According to this scheme coherent optical techniques are employed to exploit the huge bandwidth of single-mode optical fibers and are coupled with spread spectrum direct sequence modulation in order to mitigate the interference from other signals due to the frequency overlap caused by the instability of the carrier frequency of the laser, or to the mistakes in the frequency coordination and assignment. The average bit error probability of this multiple-access scheme is evaluated by using the characteristic function of the other-user interference at the output of the matched optical filter. Both phase noise and thermal noise are taken into account in the computation. Time-synchronous as well as asynchronous systems are analyzed in this context. Binary phase shift keying (BPSK) and on-off-keying (OOK) data modulation schemes are considered. The analysis is valid for arbitrary values of the spreading gain and the number of interfering users. The performance evaluation of RC CDMA establishes the potential advantage in employing hybrids of wavelength division multiple access (WDMA) and CDMA to combat inter-carrier interference in dense WDMA systems.

The combination of 1D zero cross correlation (ZCC) and 1D Multi Diagonal (MD) results a new two dimensional hybrid called 2D ZCC/MD code for spectral/spatial OCDMA system. The proposed code aims to enhance the functional qualities of Optical Code Division Multiple Access (OCDMA) and to overcome the limitations of one dimensional codes. In this paper, 2D ZCC/MD is evaluated at data rate; 622Mbps.A comparison of the proposed 2D ZCC/MD code to 1D Random Diagonal (RD) and 1D Modified Double Weight (MDW) highlight that 2D ZCC/MDcan supporta large number of activeusers even at the higher user bit rate. Furthermore, in term of effective power 2D ZCC/MD can achieve lower effective power.

The effects of cross-correlation interference and intensity fading on the error rate performance of an optical code division multiple-access communication system are investigated. The system model is a multiaccess satellite repeater in which user separation is accomplished by direct sequence modulation. The analysis is for direct detection, optical polarization modulation systems. Generalized expressions for the conditional probability of error for the uplink and downlink channels are derived in terms of the number of active users, signal strength and the normalized cross-correlation between user codes. Numerical results are obtained for systems of two users, for both length 31 and 127 Gold codes. Analysis of a random sampling of the length 31 codes has shown that performance is significantly dependent on the magnitude of the normalized second moment of the cross-correlation between user codes. Further analysis showed that the error probability decreases with increasing code length. The multiuser capabilities of the uplink and downlink channels were shown to differ significantly.