Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006ihy..worke..84d&link_type=abstract
2nd UN/NASA Workshop on International Heliophysical Year and Basic Space Science. Proceedings of the conference held 27 Novembe
Astronomy and Astrophysics
Astrophysics
Scientific paper
Binary phase codes have been often used in radar systems. The most widely known binary phase codes are Barker codes. Families of binary phase codes, which are called alternating codes, have been also discovered]. In a radar system, which employs a binary phase code, a matched filter is usually used to obtain a very high range resolution without decreasing the average transmitted power. However, matched filtering of a binary phase code gives unwanted sidelobes at the filter output. The amplitude of the sidelobes depends on the phase patterns of the binary phase code. Significant research effort has gone to search binary phase patterns that give smallest possible sidelobes. Most often peak-to-sidelobe ratio (PSR), integrated sidelobe ratio (TSR) and merit factor (F) are used as criterions to search for the best binary phase codes. The Barker codes have relatively high PSR. Other kind of binary phases with improved PSR have been found, including the 28-element code by Turyn] and the 40-element code by Lindner]. Although binary phase codes with maximum PSR can be satisfactory for some applications, in some cases removing the sidelobes reveals new and important information. Key showed that weighting networks to be placed after the standard matched filter can be designed, which reduces the sidelobes to an arbitrary low level. For any periodic digital signal with linearly independent cyclical shifts, lpatov] has showed that a filter can be constructed that suppresses to a zero level all the sidelobes. However, the filter has associated SNR losses when compared to the corresponding matched filter. Lpatov carried out a computer search for a binary periodic signal-filter pair with minimum possible SNR losses. The search includes all binary codes of length up to 30 elements. A different approach for eliminating the sidelobes in periodical binary phase codes by using mismatched filter have been published by Rohling and Plagg]. Exhaustive search for optimal aperiodic binary phase codes and mismatched filter pairs up to length of 25 has been carried out by Lehtinen. The benefits of eliminating sidelobes are also demonstrated in using real radar measurements. In this paper we present mismatched filtering of aperiodic binary phase codes. This is done without creating any sidelobes. A mismatched filter has small losses in SNR when compared with the corresponding matched filter. We have selected the best binary phase codes with length from 26 to 39. The best codes are the ones which have the smallest SNR losses in mismatched filtering when compared with the corresponding matched filtering. We have chosen one best code from each length and this means we have selected 14 different length best binary phase codes. These codes were chosen from a total number of 5.4972 x 1011 investigated codes. We have found these codes have nearly similar losses in SNR and it is about 15 percent. We did not find a binary phase code that outperforms the well-known 13-element Barker code, which has 4.8 percent SYR losses .
Damtie Baylie
Lehtinen Markku
Orispaa Mikko
Vierinen Juha
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