Optimal binary phase codes and sidelobe-free decoding filters with application to incoherent scatter radar

Abstract. We present a novel approach for modulating radar transmissions in order to improve target range and Doppler estimation accuracy. This is achieved by using non-uniform baud lengths. With this method it is possible to increase subbaud range-resolution of phase coded radar measurements while maintaining a narrow transmission bandwidth. We first derive target backscatter amplitude estimation error covariance matrix for arbitrary targets when estimating backscatter in amplitude domain. We define target optimality and discuss different search strategies that can be used to find well performing transmission envelopes. We give several simulated examples of the method showing that fractional baudlength coding results in smaller estimation errors than conventional uniform baud length transmission codes when estimating the target backscatter amplitude at sub-baud range resolution. We also demonstrate the method in practice by analyzing the range resolved power of a low-altitude meteor trail echo that was measured using a fractional baud-length experiment with the EISCAT UHF system.

Section: Infinitely Extended Coherent Targetmentioning

confidence: 98%

Fractional baud-length coding

Vierinen¹

2011

“…This ratio for the case of a mismatched filter with an impulse response of λ mis (n) is given by (see Lehtinen et al (2004) for details)…”

Section: Snr Performance Comparison Of Adaptive and Mismatched Pulse mentioning

confidence: 99%

“…The present authors have carried out an exhaustive computer search of optimal binary phase code-mismatched filter pairs up to a code length of 25 and the advantages of eliminating the sidelobes in the analysis of an incoherent scatter measurement were demonstrated in practice by Lehtinen et al (2004) and the reference within. The present authors have also extended these kinds of investigations to aperiodic quadriphase codes Damtie et al (2008).…”

Section: Introductionmentioning

confidence: 99%

Comparison of the performance of different radar pulse compression techniques in an incoherent scatter radar measurement

Damtie

Lehtinen

2009

Self Cite

Abstract. Improving an estimate of an incoherent scatter radar signal is vital to provide reliable and unbiased information about the Earth's ionosphere. Thus optimizing the measurement spatial and temporal resolutions has attracted considerable attention. The optimization usually relies on employing different kinds of pulse compression filters in the analysis and a matched filter is perhaps the most widely used one. A mismatched filter has also been used in order to suppress the undesirable sidelobes that appear in the case of matched filtering. Moreover, recently an adaptive pulse compression method, which can be derived based on the minimum mean-square error estimate, has been proposed. In this paper we have investigated the performance of matched, mismatched and adaptive pulse compression methods in terms of the output signal-to-noise ratio (SNR) and the variance and bias of the estimator. This is done by using different types of optimal radar waveforms. It is shown that for the case of low SNR the signal degradation associated to an adaptive filtering is less than that of the mismatched filtering. The SNR loss of both matched and adaptive pulse compression techniques was found to be nearly the same for most of the investigated codes for the case of high SNR. We have shown that the adaptive filtering technique is a compromise between matched and mismatched filtering method when one evaluates its performance in terms of the variance and the bias of the estimator. All the three analysis methods were found to have the same performance when a sidelobe-free matched filter code is employed.

“…We have shown the R value defined in (Lehtinen et al, 2004) and (Damtie et al, 2002) to describe the close-to-perfectness of a code (or here a code set) on the panels of the second row for each lag profile. There we also print the minimum and maximum values of the Fourier side information curve, to make it easier to see how much it differs from a constant 1.…”

Section: Numerical Data Shown In the Panesmentioning

confidence: 99%

Fast comparison of IS radar code sequences for lag profile inversion

Lehtinen¹,

Virtanen

Vierinen³

2008

Self Cite

Abstract.A fast method for theoretically comparing the posteriori variances produced by different phase code sequences in incoherent scatter radar (ISR) experiments is introduced. Alternating codes of types 1 and 2 are known to be optimal for selected range resolutions, but the code sets are inconveniently long for many purposes like ground clutter estimation and in cases where coherent echoes from lower ionospheric layers are to be analyzed in addition to standard F-layer spectra.The method is used in practice for searching binary code quads that have estimation accuracy almost equal to that of much longer alternating code sets. Though the code sequences can consist of as few as four different transmission envelopes, the lag profile estimation variances are near to the theoretical minimum. Thus the short code sequence is equally good as a full cycle of alternating codes with the same pulse length and bit length. The short code groups cannot be directly decoded, but the decoding is done in connection with more computationally expensive lag profile inversion in data analysis.The actual code searches as well as the analysis and real data results from the found short code searches are explained in other papers sent to the same issue of this journal. We also discuss interesting subtle differences found between the different alternating codes by this method. We assume that thermal noise dominates the incoherent scatter signal.