The Research Of The MIMO Non-Coherent Chaotic Spread-spectrum Communication Based On OFDM

With the development of modern wireless communication technology, we are constantly improving the reliability of the communication system, meanwhile we are more and more concern about its safety and security. As a pseudo random signal generated by the deterministic equation, chaotic signals have much advantages such as aperiodicity, unpredictability, noise-like characteristics, extremely sensitive to initial values, etc., while having a low power spectral density(PSD), large bandwidth, good concealment, low probability of interception(LPI) and interference immunity. These make chaotic digital communication wide prospects for development and application in military communications and LPI communications. Among different chaotic modulations, differential chaotic shift keying(DCSK) get extensive researches, since it does not need synchronization in receiver which makes it easy to implement, as well as its good noise performance and robustness.Combined with the core technology of the fourth generation mobile communication system-- MIMO technology and OFDM technologies, this paper propose a new chaotic communication system to improve the transmission efficiency and bit error rate(BER) performance of traditional DCSK system.1. In consideration of the poor performance of DCSK system under wireless fading channels, this paper uses MIMO technology to analyze the performance of MIMO-DCSK system under Nakagami-m fading channels. While three different BER calculation formulae are presented, including Gaussian approximation(GA) method based on the central limit theory(CLT), non-central F-distribution Exact BER calculation method based on data analysis, and closed-form approximation(CA) method based on moment generating function(MGF). The simulation results show that MIMO technology can efficiently enhance the transmission performance of DCSK system. The computation complexity of Exact BER formula is larger, while the closed-form BER formula was simplest. But the calculated curves obtained by the Exact BER formula is most consistent with the simulation curves, while the calculated curves obtained by the closed-form BER formula is most inconsistent.2. In order to improve the bandwidth efficiency and the power efficiency of DCSK system, this paper uses OFDM technology. To conquer the poor performance of CSK-OFDM system under multipath fading channels, we propose Multi-Carrier Chaotic Shift Keying(MC-CSK) system. Theoretical BER expressions of these two non-coherent chaotic spread communication systems based on OFDM are derived. Simulation results show that MC-CSK system can effectively improve the BER performance under multipath fading channels.3. In order to further improve the performance of MC-CSK system, we combine it with MIMO technology to analyze the performance of MIMO-MC-CSK system in Nakagami-m fading channels, and theoretical BER expressions are derived. The simulation results show that the performance of multi-antennas system is obviously superior to other non-coherent chaotic spread spectrum communication systems mentioned in this paper.4. The total design of MC-CSK system is proposed in this paper, where we choose CPCI general signal processing platform and the corresponding chips. The results of the fixed-point simulation show that the simulated curves of 16-bits and 8-bits quantization are much consistent with the floating-point simulation curves. With the decrease of the length of quantization, the deviation between two curves becomes lager, while a large deviation occurs when the length of quantization is 1 bit.