V.N. Bondarenko – Dr.Sc. (Eng.), Professor, Departament «Radioelectronic systems», Engineering Physics and Radioelectronics Institute, Siberian Federal Universit (Krasnoyarsk)
T.V. Krasnov – Ph.D. (Eng.), Design Engineer, JSC «NPP «Radiosvyaz» (Krasnoyarsk)
V.F. Garifullin – Senior Lecturer, Engineering Physics and Radioelectronics Institute, Siberian Federal Universit (Krasnoyarsk)
P.V. Shtro – Research Engineer, Engineering Physics and Radioelectronics Institute, Siberian Federal Universit (Krasnoyarsk)
A.S. Dranishnikov– Student, Engineering Physics and Radioelectronics Institute, Siberian Federal Universit (Krasnoyarsk)
Correlation properties of noise-like signals commonly determine base parameters of wideband navigation system (accuracy, resolution capability, interference immunity). This paper shows mutual interference level increasing in code division multiple access wideband navigation system.
Mutual interferences level, characterized by a maximum and effective values of 2-dimension cross-correlation function of signals en-semble is determined, primarily by length of modulating pseudorandom sequence, used for noise-like signal generation. Code structure within length N >> 1 poorly influences on these level indicators (especially in the strip of Doppler frequency shifts). Even less at the level of VP is affected by the noise-like signal modulation (the form of quadrature videoband components). In the preferred method of broadband modulation (MSK) the shape of the main lobe of autocorrelation function is determined exclusively by clock frequency fT, and the sidelobe level of the module of the normalized autocorrelation function without additional data modulation equals 1/N (when using M-sequences and other optimal codes).
The effect of modulation of data on the correlation properties of the MSK signals is evaluated using normalized mutual correlation function. The results of calculation of normalized cross-correlation function of noise-like MSK signals with modulation data for codes of length N = 16383: 1) cyclic shifts of common maximum length sequence (consider a shift to m = 4096 elements); 2) common maximum length sequence with frequency shifts, a multiple of the element resolution frequency (consider a shift on 40 elements resolution frequency ΔF=1/Тп); 3) different maximum length sequences; 4) Kasami sequences.
As analisys result shows, the negative impact of additional data modulation on correlation properties of MSK-signals are expressed in the least when using the ensemble of cyclic shift of a maximum length sequence, that is common for all channels. It’s also shown, that partial frequency division of channels within acceptable limits in the middle-wave band has lower efficiency. In this case the structure of coding sequence and the form of quadrature videoband components has no influence. Two other ensembles (common maximum length sequence with frequency shifts and Kasami sequences) almost equivalent to the figure Rэ: about –42 dB. This is because the level of cross-correlation function of noise signals is determined primarily by the correlation properties of the codes used (which is equal to the length N differ little).