A Research And Verification Of The Key Techniques Of Continuously-variable Rate Direct-sequence Spread Spectrum Communication

With the rapid transmission of information, people have put forward more requirements in the Communication Function. As the existing bandwidth resources are on the decrease, in order to meet variable-rate data transmission, Variable-rate spread spectrum communication technology has become a hot topic for wireless communication in recent years.Therefore, this paper studies key techniques of continuously variable rate Direct Sequence Spread Spectrum Communication(DSSS). This paper proposes a spread spectrum technique by symbol processing and verifies the system performance of the matrix aided method against the common types of narrowband interference. We complete the demonstration and verification based on the u SDR platform. The work in this paper is organized as follows.Firstly, the paper designs a fractional times spread spectrum method. We investigate the existing two main schemes for multi-rate spread spectrum and compare the multi-code orthogonal SS scheme with variable-processing-gain one. This paper proposes a spread spectrum technique by symbol processing. Under the same channel bandwidth, we can continuously change the rate of information.Secondly, matrix aided method for narrowband interference suppression. We investigate the common types of narrowband interference and the Narrow Band Interference(for short, NBI) technology in DSSS system. This paper proposes a low complexity and strong interference suppression capability matrix aided method for narrowband interference suppression. This paper verifies the system performance of the matrix aided method against tone interference narrowband digital interference and Gaussian bandpass signal.Thirdly, the paper designs the overall data link scheme. According to the project requirements, this paper designs the overall data link and detailed designs the key technologies of the data link. The key technologies mainly include spread spectrum, digital frequency conversion, matrix aided method for narrowband interference suppression and acquisition and tracking technique. The performance simulation of the waveform are given on the Simulink, this paper tests the system performance of the matrix aided method against different types of interference when interference to signal ratio between 45 d B and 40 d B. The simulation results show that: in the condition of data rate of 10 Kbps, interference to signal ratio of 45 d B.Compared to the system without interference, the lost interference to signal ratio of DSSS system performance is less than 2 d B. In the condition of data rate of 10 Kbps, interference to signal ratio of 40 d B.Compared to the system without interference, the lost interference to signal ratio of DSSS system performance is less than 1.8 d B.Fourthly, the development of data link are complete on the graphical development tools System Generator. This paper detailed describes the implementation of the algorithm and process flow for each module of the transmitter and the receiver by the principle of top-down of FPGA. The paper demonstrates and verifies the time synchronization and bit error rate on the u SDR platform. The testing results show that: Compared to the system without interference, the lost interference to signal ratio of DSSS system performance is less than3 d B. This verifies the implementation scheme are rational and feasible.This paper proposes a spread spectrum technique by symbol processing, it has a good practicality in current DSSS systems, and it solves the problems of the conventional spread spectrum communication system which is limited to an integer multiple of the spreading gain. It provides a reference for the further exploration of spread spectrum communication.