Fast comparison of IS radar code sequences for lag profile inversion

Abstract

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.

Towards multi-purpose IS radar experiments

“…This way the estimation accuracy of the experiments is taken into account, but the analysis does not offer anything that could be directly used for comparisons with other experiments. Numerical studies of the variance behavior much similar to those presented in Lehtinen et al (2008) could be performed using lag profile inversion. This kind of analysis will be important when designing future experiments, but in this paper we settle on demonstrating that we are able to analyse the new experiments.…”

“…On the basis of Lehtinen et al (2008) we do know that the code sequences should perform well in a standard type of experiment with equal IPPs. In data analysis the lag profile variances offered by lag profile inversion are used in the parameter fit.…”

“…Though the inversion is possible with any phase code or a sequence of codes, the estimation accuracy of an experiment is much dependent on the codes used. When introducing the present lag profile inversion software , the possibility to search for efficient radar codes without taking care of the decoding properties was mentioned, but only alternating code (Lehtinen and Häggström, 1987) experiments were used to allow comparison between the two analysis methods. The lag profile inversion analysis of short code sequences has been earlier used at the EIS-CAT Svalbard radar by Lehtinen et al (2002).…”

Transmission code optimization method for incoherent scatter radar

“…The lags are assumed to be non-zero multiples of the baud length of the transmission code. Autocorrelation function estimation variance is presented more rigorously in the companion paper by Lehtinen et al (2008). The variance presented there also includes pulse-to-pulse and fractional lags, taking into account target post-integration as well.…”

Phase-coded pulse aperiodic transmitter coding

“…5. In the low-SNR evaluation, the variances presented in this paper are scaled very much in the same way as in Lehtinen et al (2008), where a unit variance was given to an experiment with perfect decoding properties. To allow a comparison between any two experiments with the same bit length in the phase coding, we are this time scaling the variances by the total duration of the full transmission cycle of the experiment.…”