Algorithm elaboration of iterative processing of M-CPFSK signals in the ionospheric channel with selective interferences

摘要

In the report signal and code constructions (SCC) on the basis of continuous phase frequency shift key (CPFSK-64, CPFSK-256, CPFSK-1024) using low-speed turbo codes are provided. In the course of simulation program models of the modulator, demodulator, coder and decoder on a high-level language C++ were developed for application in system of simulation modeling of the digital communication systems Spectr-2. Codes were selected with the following code relations 5/16, 6/32, 7/64. The modulator and the demodulator has the user window from which it is supposed to select a type of modulation, modulation index and code rate. Sequences of synchronization was used during transmission of an information block in model of the system M-FSK of signal`s synchronization. By transmission of a sequence of synchronization, it is supposed to transfer the sectional M-sequences. When carrying out the analysis it was supposed to research SCC in Watterson's channel with additive white Gaussian noise, and in the presence of selective interferences. Built-in models of the generator of white Gaussian noise, model of the channel of a Waterson and measuring units for data output were used in the diagram of the program complex Spectr-2. In this paper, the signal occupied bandwidth of the channel 40000 kHz. Selective interferences made 25 percent from bandwidth of all signal. Processing of SKK includes an algorithm of normalization of output responses of filters for reduction of influence of selective interferences in case of detection and restoration of a signal. With growth of number of frequencies in CPFSK, there was a difficulty of processing of a signal in a receiving part. For the solution of this problem of using frequency shift-keying 256 is change of the reference generator in the demodulator, which makes calculation of values of a complex signal. It allowed to reduce the number of the operations calculated for 1 clock period of the system Spectr-2. However, for modulation of CPFSK-1024 it was required to completely, change digital processing of the accepted signal. The solution was found in application digital the filter of bank. As a prototype the filter with band pass range of 150 Hz and a band of a barrage of 300 Hz with suppression 70 dB was selected. The order of the filter prototype is 32768. Characteristics of bit error rate and frame error rate in different conditions were received because of simulation.