Research On The Code Of Quasi-synchronous Optical Code Division Multiple Access System

With the development of the information society,the society is increasingly relying on the transmission of information.Optical fiber communication with high-speed large-capacity is gradually becoming the main mode of information transmission today.Optical Code Division Multiple Access(OCDMA)technology has gained a great of attention with regard to high security,anti-interference ability and all-optical processing.Quasi-synchronous OCDMA,compared with the synchronous OCDMA and asynchronous OCDMA,has a lot of advantages.For example,it has less complexity in hardware and allows users to flexibly access the system within a certain range.At the same time,it can eliminate multiple access interference and near-far effect in a certain range,which improves the performance of the system.One dimensional quasi-synchronous OCDMA has smaller code cardinality,and the number of users that the system can hold is very less.Based on NSFC “Research on physical layer security and optical coding for free space optical communication(61671306)”,and JCYJ “Research on key technologies of optical communication based on optical encoding physical layer security(20160328145357990)”,this paper makes a detailed analysis on the basis of two dimensional quasi-synchronous OCDMA.We propose a new construction method that can construct quasi-synchronous two dimensional address codes with different characteristics.Then,we construct a new two dimensional unipolar quasi-synchronous OCDMA address code and two kinds of two-dimensional bipolar quasi-synchronous OCDMA address codes.What's more,on the basis of theoretical analysis,the performances of these address codes are verified.The main work of this paper is as follows:1)The relationship between the correlation function of the two dimensional unipolar quasi-synchronous OCDMA address code and its corresponding two one dimensional sequence correlation functions is theoretically analyzed,and the relationship of their zero correlation zone(ZCZ)length.We propose a method constructing two dimensional unipolar quasi-synchronous OCDMA address codes with larger ZCZ by adopting ZCZ sequence and no hit zone sequence.It overcomes the shortcomings of the existing two-dimensional unipolaraddress code on ZCZ length,which is only equal to the corresponding one dimension sequence ZCZ length.Under the guidance of this method,we construct an address code whose code length is 156,code weight is 8,wavelength number is 8,cardinality is 4,ZCZ length is 32.2)As an improvement of the first work,we take use of the phase of the orthogonal bipolar sequence to control the phase of the pulse in the quasi-synchronous address code that has been constructed,and obtain a quasi-synchronous address code with a larger cardinality.The correlation performance of two-dimensional bipolar quasi-synchronous constructed by this method is theoretically analyzed.A address code with length being 156,code weight being 8,the number of wavelengths being 8,the cardinality being 32,the length of ZCZ being32 is constructed.Moreover,we use the ZCZ sequence,one coincidence sequence,and Walsh sequence to construct a two-dimensional bipolar quasi-synchronous address code.The address code length is 156,the code weight is 8,the number of wavelengths is 13,the ZCZ length is15,and the code word cardinality reaches 104.