Research And Implementation Of Modulation And RAKE Receiver For Chaotic Spread-spectrum Communications

Modern warfare is an information-based and high-tech war. In future battlefield, electromagnetic environment will be quite complicated because of fierce struggle between counter-jamming and counter-jamming. Extensively using of electronic equipments, which with huge number, complexity system, variety and large power, not only make the electromagnetic signal in battlefield be quite intensive, but also make electromagnetic environment become more complicated. In this complex electromagnetic environment, signal submerged in various noises. how to find useful signal from intense electromagnetic interference become a critical problem. In addition, the wireless signals could be easily intercepted by the enemy in the process of transmission and furthermore probably cause confidential leak, so the battlefield not only need reliable communication, but also make sure that communication content are not leak.This paper based on the project of weak signal detection, we research normal modulation of the chaotic system and generalized RAKE receiver with the confidential nature of chaotic spread-spectrum code. On this basis, proposed two improved RAKE receivers and make the corresponding theoretical analysis and computer simulation. Both programs of two improved RAKE receivers are innovative points of this article (see Chapter5.1and5.2). The main content of this work and innovation are as follows.Firstly, it introduces the generation of spread spectrum communication system and chaotic sequences, and analyzes the cryptography characteristics of chaotic sequence. Compared with other spreading sequence, chaotic sequence has such particular characteristics as non-periodicity, unpredictability, being sensitive to and also dependent on initial value and etc. chaos sequence is hard to guess and copy, so it has very good secrecy.Secondly, DCSK modulation technology is studied in this paper, and it also analyzes bit error rate in DCSK modulation. Through some experiments analysis, bit error rate’s theoretical and practical values, it proves that DCSK is a kind of satisfactory modulation technology, which is not sensitive to the distortion of channel and transmission sampling function.Thirdly, it introduces RAKE reception technology, and analyzes the RAKE receiver’s performance in the chaotic sequence. Through mathematical analysis and experimental verification, it proves that under the same BER requirements, the more multi-path RAKE receiver has the higher input SNR the RAKE receiver requires. Namely, with the increase of multi-path, RAKE receiver’s performance becomes better. In addition, through experiment, we know that the energy transfer mainly concentrated in front paths, the branch behind which has less impact on the RAKE receiver as the increase of energy attenuation can be abandoned to simplify the circuit.Finally proposed two improved RAKE receives (Innovation of this paper). One is an improve RAKE receiver with DCSK modulation. Because of the characteristics of DCSK modulation, this type of rake receiver demodulation signal does not use local chaotic spreading codes. This receiver avoided the receiver spread spectrum signal with the local spreading code synchronization problem. The other is an improved RAKE receiver with delay adjustment, this receivers increases the accuracy of delay estimation and improve the local spreading code and spread spectrum signal synchronization accuracy and improve the BER performance of the RAKE receiver.