Almost perfect sequences applied for ionospheric oblique backscattering detection

Abstract

[1] Pseudorandom sequences are often used in radio systems; however, the nonzero out-of-phase autocorrelation of many binary sequences induces range sidelobes which significantly reduce the echo signal-to-noise ratio (SNR). In this paper, the use of almost perfect sequences, exhibiting zero out-of-phase autocorrelation except one value in the middle is examined with reference to common m sequences and perfect sequence. The ambiguity functions demonstrate that it is possible to use the almost perfect sequences for ranging without sidelobes and that their Doppler measurement performance is similar to m sequence of the same length. This is an important result for ionospheric oblique backscattering detection where the echoes are superposed and where range sidelobes can submerge the main lobes of weak signals. The 124-bit almost perfect sequence and the 127-bit m sequence are applied to the Wuhan Ionospheric Oblique Backscattering Sounding System for sequence testing. The test results have proven that the almost perfect sequence exhibits a higher echo SNR for the same detection conditions.

Design and Application of Wuhan Ionospheric Oblique Backscattering Sounding System with the Addition of an Antenna Array (WIOBSS-AA)

“…During the experiment, WIOBSS-AA periodically transmitted the phase-coded pulse train waveform and received the echoes during the pulse interval. The applied waveform parameters of the radio system were 39.0625 kHz pulse repetition rate, 20% duty cycle, and 511-bit pseudo-random code used as the modulating signal [ 28 , 29 ]. The range resolution was 3.84 km.…”

Development of backscatter sounding single‐site location system

“…The WIOBSS transmitted the pseudo‐random binary sequence modulated waves with 500 W peak power [12, 13]. The received waves will be filtered, pulse‐compressed and reprocessed, and then a clear ionogram can be obtained [14, 15].…”

Design and application of the digital multifunctional ionosonde

“…The application of the inter‐pulse phase coded waveform on the Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS) was successful [8, 9]. These periodic autocorrelation codes have very low sidelobes and a high mainlobe‐to‐sidelobe ratio [10, 11], and relevant content about the ionosondes has been reported [9, 12, 13]. With an increasing Doppler shift, the data process gain of the pulse autocorrelation will be decreased [14].…”