Simulation of Optical Spectrum Code Division Multiple Access in Fibre to the Home Access Network

Nowadays, the increasing number of end users accessing the Internet and taking advantage of today’s data transport capabilities has ignited an explosive demand for bandwidth. One of the next generation access systems that helps to improve this situation by pushing optical fibre closer to the home is called fibre-to-the-home (FTTH). FTTH offers virtually unlimited bandwidth to the subscriber with high splitting ratio, longer fibre span and provide the residential customers with bundled of high speed voice, data and video services. Generally, the study of FTTH access network by implementing Optical Spectrum Code Division Multiple Access (OSCDMA) technique was presented. This technique is one of the multiplexing schemes that recently have become popular among researchers because of its flexibility in allocating channels, ability to operate asynchronously, enhanced privacy and increased capacity in bursty nature networks. One of the considerations in designing OSCDMA systems is coding. So in this study, we proposed a new code namely Double Weight Code (DWC) with basic fixed weight of 2 that exists for every natural number. The DW codes possess ideal cross correlation properties, that are important characteristics in spectral encoding OCDMA system since these can eliminate multiple user interference and reduce noise. The performance of DW code against Hadamard code is compared through simulation by using OptiSystem version 2.2. There are two types of FTTH networks; point-to-point (P2P) and point-to-multipoint (P2MP) that have been designed for downstream application and both codes are being implemented inside the networks and the performance are characterized through Bit Error Rate (BER), eye opening and Q factor. It is found that DW code is better than Hadamard code for all simulation results at bit rates of 622 Mbps, 1.25 Gbps and 2.5 Gbps. The optimization configuration for P2P network with 16 users, with BER as good as 10-9 value is achieved at 38 km distance for 2.5 Gbps with transmission power set at 0 dBm. While for P2MP network, the other configurations value is still the same like P2P network but the changes only happen at the transmission side. A single light emitting diode (LED) has been used with total transmission power set to 16.4 dBm. The bit rate can only reach up to 1.25 Gbps with distance up to 20 km to get the minimal value of BER. However the results on P2MP network shows enhancements offered by erbium doped fibre amplifier (EDFA) provides longer fibre span, larger distribution to the end user and it is suitable to support high speed gigabit network.

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