Super-Resolution Range and Velocity Estimations for SFA-OFDM Radar

Sparse frequency agile orthogonal frequency division multiplexing (SFA-OFDM) signal brings excellent performance to electronic counter-countermeasures (ECCM) and reduces the complexity of the radar system. However, frequency agility makes coherent processing a much more challenging task for the radar, which leads to the discontinuity of the echo phase in a coherent processing interval (CPI), so the fast Fourier transform (FFT)-based method is no longer a valid way to complete the coherent integration. To overcome this problem, we proposed a novel scheme to estimate both super-resolution range and velocity. The subcarriers of each pulse are firstly synthesized in time domain. Then, the range and velocity estimations for the SFA-OFDM radar are regarded as the parameter estimations of a linear array. Finally, both the super-resolution range and velocity are obtained by exploiting the multiple signal classification (MUSIC) algorithm. Simulation results are provided to demonstrate the effectiveness of the proposed method.

Democratisation of Business How More Democratic Business Structures Generate Innovation

Democratisation is a topic that is increasingly finding its way into the economic debate and is also becoming more and more of a trend within companies. The debates reveal various advantages and disadvantages of democratising companies. Within the various models of democratisation of companies, however, there seems to be a lack of coherent integration of the theoretical integration of this into the broad corporate structures – at least within business perspective. These often refer to orthodox theoretical foundations of hierarchical structures and corporate orientations, which in principle oppose and partly run counter to various forms of democratisation. In the present contribution, minimal conditions are to be worked out on the basis of democracy as cooperation and applied to the most elementary corporate structures. In such a coherent orientation and embedding, it can be shown that disadvantages of democratisation in the corporate context can be reduced and innovation and thus competitiveness can be promoted in a multidimensional way.

Signal-to-Noise Ratio Analyses of Spaceborne GNSS-Reflectometry from Galileo and BeiDou Satellites

In recent years, Global Navigation Satellite System Reflectometry (GNSS-R) technology has made considerable progress with the increasing of GNSS-R satellites in orbit, the improvements of GNSS-R data processing technology, and the expansion of its geophysical applications. Meanwhile, with the modernization and evolution of GNSS systems, more signal sources and signal modulation modes are available. The effective use of the signals at different frequencies or from new GNSS systems can improve the accuracy, reliability, and resolution of the GNSS-R data products. This paper analyses the signal-to-noise ratio (SNR) of the GNSS-R measurements from Galileo and BeiDou-3 (BDS-3) systems, which is one of the important indicators to measure the quality of GNSS-R data. The multi-GNSS (GPS, Galileo and BDS-3) complex waveform products generated from the raw intermediate frequency data from TechDemoSat-1 (TDS-1) satellite and Cyclone Global Navigation Satellite System (CYGNSS) constellation are used for such analyses. The SNR and normalized SNR (NSNR) of the reflected signals from Galileo and BDS-3 satellites are compared to these from GPS. Preliminary results show that the GNSS-R SNRs from Galileo and BDS-3 are ∼1–2 dB lower than the GNSS-R measurements from GPS, which could be due to the power of the transmitted power and the bandwidth of the receiver. In addition, the effect of coherent integration time on GNSS-R SNR is also assessed for different GNSS signals. It is shown that the SNR of the reflected signals can be improved by using longer coherent integration time (∼0.4–0.8 dB with 2 ms coherent integration and ∼0.6–1.2 dB with 4 ms coherent integration). In addition, it is also shown that the SNR can be improved more efficiently (∼0.2–0.4 dB) for reflected BDS-3 and Galileo signals than for GPS. These results can provide useful references for the design of future spaceborne GNSS-R instrument compatible with reflections from multi-GNSS constellations.

Cross-cultural realist interviews: An integration of the realist interview and cross-cultural qualitative research methods

Realist interviews are a data collection method used in realist evaluations. There is little available guidance for realist interviewing in cross-cultural contexts. Few published realist evaluations have included cross-cultural interviews, providing limited analyses of the cross-cultural application of realist methodology. This study integrated realist and cross-cultural qualitative methods in a realist evaluation of an Australian doula support program. The interviews were conducted with Arabic speaking clients of the program. The process included collaboration with a bicultural researcher, philosophically situating the study for methodologically coherent integration, bicultural review of the appropriateness of realist ‘how’ and ‘why’ questions, decisions about language translation and interpretation, pilot interviews, and co-facilitation of the interviews. Integration of the methods was feasible and valuable. This study may support other realist evaluators to give voice to people from culturally diverse groups, in a manner that is culturally safe, methodologically coherent and rigorous, and that produces trustworthy results.

Interperiod coherent integration of the received signal with a variable repetition period of the probing signal

Interperiod coherent integration of the received signal provides an increase in the signal-to-noise ratio and is simply implemented with a fixed repetition period of the probing signals. In practice, pulsed radars use a variable repetition period to protect against blind speeds. The algorithms of the interperiod coherent integration with a variable repetition period have been developed and their features have been revealed, which are advisable to take into account in the practical implementation in the radars. These features determine the complexity of the interperiod coherent integration algorithm, the radial velocity (Doppler frequency) survey interval and the spectrum features. An algorithm is developed with simultaneous interperiod coherent integration of the received signal and a single-delay clutter cancelation in the spectral domain in the case of variable repetition period of the probing signals. The quantitative indicators obtained by modeling are presented and a comparative analysis is carried out.

Improving the iGNSS-R Ocean Altimetric Precision Based on the Coherent Integration Time Optimization Model

Improving the altimetric precision under the requirement of ensuring the along-track resolution is of great significance to the application of iGNSS-R satellite ocean altimetry. The results obtained by using the empirical integration time need to be improved. Optimizing the integration time can suppress the noise interference from different sources to the greatest extent, thereby improving the altimetric precision. The inverse relationship between along-track resolution and signal integration time leads to the latter not being infinite. To obtain the optimal combination of integral parameters, this study first constructs an analytical model whose precision varies with coherent integration time. Second, the model is verified using airborne experimental data. The result shows that the average deviation between the model and the measured precision is about 0.16 m. The two are consistent. Third, we apply the model to obtain the optimal coherent integration time of the airborne experimental scenario. Compared with the empirical coherent integration parameters, the measured precision is improved by about 0.1 m. Fourth, the verified model is extrapolated to different spaceborne scenarios. Then, the optimal coherent integration time and the improvement of measured precision under various conditions are estimated. It was found that the optimal coherent integration time of the spaceborne scene is shorter than that of the airborne scene. Depending on the orbital altitude and the roughness of the sea surface, its value may also vary. Moreover, the model can significantly improve the precision for low signal-to-noise ratios. The coherent integration time optimization model proposed in this paper can enhance the altimetric precision. It would provide theoretical support for the signal optimization processing and sea surface height retrieval of iGNSS-R altimetry satellites with high precision and high along-track resolution in the future.

Modelling of the anti-tank guided missile scattering field and radar performance evaluation in terms of missile detection

The study presents the results achieved in an analysis of the variation of the level of an echo signal generated by the FGM-148 Javelin anti-tank missile, received by the active protection system radar with consideration given to the target attack flight profile. For our study, we use the results of modelling of the missile’s scattering field at frequencies of 1, 3, 6, and 10 GHz using the Altair FEKO CAD suite. According to estimated data, a radar using the frequency-modulated signal and operating at a medium radiation power of up to 1 W is able to detect a missile at a distance of at least 1,000 m. The results show that a combination of low power and a continuous broadband signal (100…150 MHz) along with coherent integration to units of seconds ensures concealed operations of the active protection system radar (estimated range of its radiation detection by a reconnaissance radar is not greater than 10 km).

Laboratory Demonstration of the Local Oscillator Concept for the Event Horizon Imager

Black hole imaging challenges the third-generation space VLBI, the Very Long Baseline Interferometry, to operate on a 500[Formula: see text]GHz band. The coherent integration time needed here is 450[Formula: see text]s though the available space oscillators cannot offer more than 10[Formula: see text]s. Self-calibration methods might solve this issue in an interferometer formed by three antenna/satellite systems, but the need for the third satellite increases the mission costs. A frequency transfer is of special interest to alleviate both performance and cost issues. A concept of two-way optical frequency transfer is examined to investigate its suitability to enable space-to-space interferometry, in particular, to image the “shadows” of black holes from space. The concept, promising on paper, has been demonstrated by tests. The laboratory test set-up is presented and the verification of the temporal stability using standard analysis tool as TimePod has been passed. The resulting Allan Deviation is dominated by the 1/[Formula: see text] phase noise trend since the frequency transfer timescale of interest is shorter than 0.2[Formula: see text]s. This trend continues into longer integration times, as proven by the longest tests spanning over a few hours. The Allan Deviation between derived 103.2[Formula: see text]GHz oscillators is [Formula: see text]/[Formula: see text] within 10[Formula: see text][Formula: see text][Formula: see text]s that degrades twice towards the longest delay of 0.2[Formula: see text]s. The worst case satisfies the requirement with a margin of 11 times. The obtained coherence in the range of 0.997[Formula: see text]0.9998 is beneficial for space VLBI at 557[Formula: see text]GHz. The result is of special interest to future science missions for black hole imaging from space.