Research On SAC Address Code And Two-dimensional Variable Weight Address Code In OCDMA System

Optical Code Division Multiple Access（OCDMA）is an optical spread spectrum communication technology that uses different address codes to distinguish user information and achieve random user access.OCDMA has important applications in secure communication,satellite communication,local area networks,and other fields.It can effectively improve the utilization and transmission capacity of optical fibers,and realize high-speed and high-capacity information transmission.In an OCDMA system,the address code is the basis for multi-user transmission.At the same time,factors such as the code length,code weight,and cross-correlation of the address code will have an important impact on the system’s performance.Address codes with excellent performance can improve the system’s data rate,anti-interference performance,and multi-user access capacity,thereby meeting higher communication needs.This article focuses on the design of address codes in OCDMA systems,analyzes the performance of code words,conducts system simulations and experimental verifications.The main work contents are as follows:1.A One-dimensional variable weight zero cross-correlation Latin square code（VW-ZLS）code was designed for use in spectral amplitude coding optical code division multiple access（SAC-OCDMA）systems.Based on standard Latin squares and variable-weight algorithms,this code can be used to construct both double-weight and multi-weight codes directly or through mapping techniques.The code has the advantages of diverse and simple construction,flexible weight selection,zero cross-correlation,and can provide multiple quality of service（Qo S）options.First,numerical simulations were conducted in Matlab,and the bit error rate formula derived from theoretical analysis of the VW-ZLS code was used to calculate the results.When the bit error rate is 10^-9,the code rate can reach 4.8Gbit/s,which is at least 0.5Gbit/s higher than other codes of the same type.Second,a 4-user simulation of the SAC-OCDMA system was performed using Opti System.Even at a data rate of 2Gbit/s and a transmission distance of 25km,clear eye diagrams were obtained and the bit error rate was no higher than 10^-9.2.A Two-dimensional equi-weight address code based on frequency domain/space domain,called the 2D multi-service optical orthogonal code（2D-MSOOC）,has been designed for SAC-OCDMA systems.The 2D-MSOOC extends the frequency and space domains of the one-dimensional multi-service（1D-MS）code,allowing for flexible selection of the number of users,while also having the advantages of small cross-correlation and large capacity.The error rate formula for the code is derived in this work and numerical simulations are conducted in Matlab.The results show that,at an error rate of 10^-9,2D-MSOOC can accommodate more users than similar codes,with a maximum of 148 users;it requires less effective power,as low as-18d Bm;and it supports faster code transmission.The 2D-MSOOC method is validated through a 4-user simulation using Opti System.When the user data rate is 1Gbit/s and transmitted via a star coupler,the error rate is approximately10^-18 and the Q factor is approximately 8.6,indicating good code performance.3.A Two-dimensional variable weight address code,quadratic congruence-hop codes/variable weight fixed right shift（QCHC/VW-FRS）code based on spectral/time for OCDMA systems is proposed.By combining spectral coding and time coding,QCHC is used as wavelength hopping sequence,and VW-FRS code is used as time spreading sequence,resulting in an address code with large capacity,flexible weight selection,and ability to provide multiple Qo S.The bit error rate formula is derived theoretically,and numerical simulations are performed in MATLAB.When considering only multi-access interference,the relationship between bit error rate and number of users,code length,code weight,and wavelength number is obtained,and the performance of QCHC/VW-FRS code is shown to be better than that of other similar codes.Furthermore,the OCDMA system is simulated with two users in Opti System.When the user data rate is 15Gbit/s and the transmission distance is 10 km,a clear and correct eye diagram can be obtained.The user with a code weight of 4 has an error rate that is two orders of magnitude lower than the user with a code weight of 3,indicating that the QCHC/VW-FRS code has the advantage of providing multiple Qo S.In addition,the experimental platform of the two-user 2D variable-weight OCDMA encoding and decoding system is verified in this work,and the experimental results show that the error rate of user 1 is 10^-9 and that of user 2 is 10^-8,and clear eye diagrams are obtained with the BERTWave tester.The QCHC/VW-FRS code has good performance.