The Spatiotemporal Chaotic Pseudorandom Sequences And Their Application

A pseudorandom sequence is a code sequence of 1's and 0's(-1's) whose correlation has properties similar to those of white noise. It is mainly used in cryptography and spread spectrum communication field. Spatiotemporal chaotic systems show chaotic behavior both in time and space domain. In communication field, especially in the generation of pseudorandom sequences, they have a very good prospect because of the pseudo-randomness, aperiodic, long-term unpredictability properties of the chaotic systems. The generation methods of spatiotemporal chaotic pseudorandom sequences and the application of the sequences are discussed in this paper, the main works are as following:(1) The pseudorandom sequences and one-dimensional chaotic pseudorandom sequences are summarized. On this basis, two novel methods to generate pseudorandom sequences are proposed:①Spatiotemporal chaos one-way coupled map lattices model has the invariant distribution property, the distribution of the system only related to the parameters of the system. A threshold value can be determined in accordance with the distribution, and the sequence can be generated. The threshold value also can be as a constant of the system.②Generating pseudorandom sequences based on the direction phase of chaotic systems. The sequences are gained by comparing the two consecutive state values of a single lattice in the OCML, when the system is in the state of fully developed turbulent mode. And using the Monte Carlo method to calculate the correlation, balanced and run-length qualities of the pseudorandom sequences which are generated above, compared these with the sequences generated by the traditional methods. The results show that the sequences generated by direction phase method have not an advantage over the traditional one, but the sequences generated based on the invariant distribution gain an advantage over, and these methods can generate more sequences than the traditional methods and have high efficiency.(2) On the MATLAB platforms, pseudorandom sequences generated by the above methods be used as spread spectrum codes, the Code Division Multiple Access (CDMA) spread spectrum communication system with multiple path,multiple access and add white Gaussian noise(AWGN) channel is constructed. With different spreading factor, different signal to noise ratio(SNR), different number of users, the anti-white noise interference, anti-Multiple Access Interference(MAI) and anti-Multiple Path Interference(MPI) capacity are simulated. The results show that the bit error rate(BER) of the system applying the sequences generated by direction phase is a little higher than that of m-sequences, the BER of the system which applies the sequences based on the invariant distribution is lower than that of m sequence, when the spreading factor relatively large. In practical CDMA communication system, spreading factor is relatively large.The formation methods of pseudorandom sequences and their application in CDMA communications discussed in this paper, make theoretical sense to some extent, and possess practical application value.