Research Of Sky Wave Interference Eliminating Method Based On Hybrid Multi-user Detection Technology

The marine radio navigation system is base on DS-CDMA frame, works in the MW & SW bands and uses the ground wave signals'time-lag to range and position. The system is with the characteristics of high positioning accuracy, large working area and good privacy. So it can be widely used in different domains of military and civil life.The marine radio navigation system is equipped with warship whose working environment is sea. As the main interference, sky wave brings in the form of MAI and near-far effect in the navigation receiver, which can affect the positioning accuracy seriously. The idiographic behave is that after certain distance propagation, the signal strength of sky wave will exceed the strength of ground wave apparently, it makes the receiver lock on the sky wave by error and the positioning result will deviate from the actual position. To solve this problem, this paper studies on the technology of multi user detection with the aim of eliminating the sky wave interference.Main contents of this paper are shown as following:Firstly, this paper analysis's the characters of medium and short wave channel deeply, and builds on the receiving signal math model. Based on this, it analyzes the influence of MAI and near-far effect brought by the sky wave, and shows that the sky wave signal is an atypical kind of fast time-varying signal who can interference positioning accuracy seriously and must be eliminated, which laid a preliminary foundation for the sky wave interference eliminating algorithm. Secondly, this paper illustrates the basic theory of traditional/ decor relation/MMSE/SIC/PIC multi-user detection methods, and carries out the simulations of all the multi-user detection methods. Simulation results show that:the typical multi-user detection methods need priori information too much, can not be used in the fast time-varying channel.To solve the defects of the typical multi-user detections, this paper study of the blind multi-user detection method, and then, improves the LMS, RLS algorithm with gradient step factor. The simulation results show that the new algorithm only needs the PN sequence of wanted signal, adapts the fast time-varying channel, but the improvement for BER is not obvious. So it can not be used in the system singly.Whereas this, the paper proposes a kind of hybrid multi-user detection in order to overcome the sky wave interfere, improve the system performance. First, this paper builds on the sky wave interference signal model. The detection is composed by two parts, one is the improving LMS module while another is the PIC module. Simulation results show that the hybrid algorithm's BER lows nearly four magnitudes than the traditional method, it can adapt the fast time-varying channel; and can be used in engineering practice as the solving scheme to eliminating the sky wave interference. At last, this paper achieves the key parts with C language and FPGA.To solve the problem that blind MUD can not eliminate sky wave interference effectively, this paper proposes a hybrid multi-user detection algorithm, simulation results show that the hybrid algorithm' BER lows three magnitude than LMS, it can adapt the fast time-varying channel; can be used in the engineering practice. At last, this paper achieves the key parts using C language and FPGA.