A new flexible cross correlation (FCC) code for optical CDMA systems
Mohd Rashidi, Che Beson
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There are tremendous interest in applying code division multiple access (CDMA) techniques to fiber optic communication systems. This technique is one of the multiple access schemes that is becoming popular due to its channel allocation flexibility, asynchronously operation, enhanced privacy, and increased capacity in bursty networks. The performance of optical CDMA (OCDMA) systems are highly dependable on code designed properties. In this thesis, a new Flexible Cross Correlation (FCC) code for OCDMA system is designed, simulated and validated. The FCC code has numerous features such as unfixed cross correlation function with shortest code length, easy to build, and adaptability to accommodate variance number of users and weights. The FCC code is designed based on matrix combinatorial where the tridiagonal code matrix was adopted in developing the algorithm of this FCC code. This research examines the theoretical and simulation aspects in the case of incoherent signal from the broadband light source utilizing AND subtraction detection technique at the receiver side. The results revealed that the FCC code can accommodate 150 users, where FCC code offers 66%, 172%, 650% and 900% improvement as a contrast to 90, 55, 20 and 15 numbers of users for Dynamic Cyclic Shift (DCS), Modified Double Weight (MDW), Modified Frequency Hoping (MFH)and Hadamard codes, respectively, for a permissible bit error rate (BER) of 10−9. The FCC code indicates optical received power Psr of −25 dBm, thus, the detection system is more sensitive via utilizing FCC code. The performance of OCDMA codes were simulated using OptiSystem software from Optiwave TM. The performance of the systems were characterized by referring to the BER, bit rate, optical received power Psr and fiber length. The results shown that the FCC code performs adequately for 45 km as opposed to 21 km for MDW code within bit rate of 155 Mbps and BER of 10−9. In this work, AND subtraction detection technique is employed at the receiver end in order to reduce the receiver complexity, and improve the system performance in terms of distance and number of active users. It has been shown through theoretical and simulation results, the performance of the system with AND subtraction detection technique improved significantly. Based on the validation of theoretical and imulation results employing back-to-back (B2B) transmission, a receiver's power marginal of −36 dB is obtained at a bi rate of 155 Mbps and BER of 10−9 over 10 km fiber length.