One of the modern issues in SAR processing is the use of the OFDM waveform instead of the conventional LFM signal. OFDM is a digital modulation scheme in which some orthogonal sub carriers are used simultaneously dividing the available bandwidth into several narrowband and parallel sub channels. The advantages of using OFDM waveform for synthetic Aperture radar (SAR) imaging include enhanced resistance against jamming, lower Doppler ambiguity and the possibility of extracting phase background of the target on the basis of phase estimation of the OFDM sub carriers. In this paper, the basic relations of OFDM waveform generation was reviewed firstly, and then the form of imaging in the range and azimuth by using this signal in the form of RDA algorithm was described.

The role of waveform design is central to effective radar resource management for state-of-the art radar systems. The waveform shape employed by any radar system has always been a key factor in determining the performance and application. The design of radar waveform to minimize mean square error (MMSE) in estimating the target impulse response is based on power allocation using waterfilling. This paper shows the effect of various power control strategies in the MMSE performance of the waveform design. We find that the truncated power control strategy exhibits a good MMSE performance. The performance improvement results from the fact that with the truncated power control no power is wasted in poor quality modes.

Multilevel PWM waveforms can be decomposed into several multilevel PWM components. Phase-shifted carrier (PSC) is an efficient decomposition technique. In this paper, we have first demonstrated the equality of PSC and alternative phase opposition disposition techniques. Second, we have modified PSC to accommodate other disposition techniques. Third, we have investigated the effects of using asymmetrical carriers on the spectrum of the resulting PWM waveform. Fourth, we have proposed a logical algorithm for decomposing all types of multilevel PWM waveforms.

Cognitive Radar is a recently presented research topic, in which most efforts has been done for its conceptual description and the adaptive waveform design feature of these radars, while other aspects of additivity for optimum performance of cognitive radars has been ignored. In this paper, a framework for adaptive time resource management in Cognitive Radars is proposed. The main purpose of this paper is proposing an algorithm for time resource management, with incorporation of adaptive waveform design capability of cognitive radars, to enhance the radar performance for an efficient time resource usage. After developing the equations of radar time resource management using adaptive waveform design, an implementable algorithm is proposed for this purpose and its performance is simulated and analysed. The results show that the proposed algorithm resulted in more efficient time resource management compared to the existing ones.

Transmit waveform design is one of the most important problems in active sensing and communication systems. This problem, due to the complexity and non-convexity, has been always the main topic of many papers for the decades. However, still an optimal solution which guarantees a global minimum for this multi-variable optimization problem is not found. In this paper, we propose an attracting methodology to design transmit waveform of active sensing and communication systems with good auto-correlation properties. To this end, we tackle the non-convex optimization problem of Integrated Sidelobe Level (ISL) minimization with the unimodular constraint. Using the epigraph and Second Order Cone Programming (SOCP) approach, the in-hand non-convex optimization will resort to a Semi-Definite Programming (SDP). Then, we use Majorization-Minimization to deal with constraints and convert the obtained problem to a convex optimization problem. Finally, the obtained optimization problem is tackled using CVX toolbox. To obtain the code vectors from the extracted optimal code matrix, we use rank-one decomposition. The simulation and results indicate the powerfulness of the proposed algorithm in designing radar transmit sequences with unimodular constraint. We show the proposed algorithm can design long length sequences with a very small ISL values. The proposed framework further can be investigated for the future optimization problems, like Peak Side lobe Level (PSL) minimization.

For modeling the blast wave, its Green’s function must be solved first. Therefore, we use the Green’s function solution of explosive sources by Herman (1979). The study area was located around the gas pipes in high-speed rail project of Qom to Isfahan, from 50. o Eto51.0 o Eand 33.5 o N to 34.5 o N. In this study, we used the four-digit seismograph machines of type CMG-6TD. The seismograph machines were arranged around the blast site in such a way that the three-component seismic energy radiation patterns of the blast were recorded in the vertical, radial and transverse directions. Further, a component (the radial component) was always placed in the site of the explosion. The distance between two consecutive samples was determined to be 10 milliseconds. The purpose of this arrangement of seismic machines has been to determine the blast radiation pattern and the impact of maximum velocity of the particles resulting from the explosion on a gas pipe. To study changes of the velocity model in output waveforms, three independent files are prepared, including the velocity model parameters of the region and the physical parameters of the source. We will generate three different outputs and select the output which is more consistent with the real waveform. The process is repeated by increasing and decreasing the source depth by 0.5 m and the amount of explosive materials by 0.5 kg (to impact the energy released). Finally, the best model of waveform, in terms of the closeness to reality, will be determined as a result. After obtaining the waveforms from the modeling and matching with real waveforms, to compare the accuracy of the model waveform with the real waveform the following methods were used. In the first method, with the calculation of the maximum normal correlation amplitude between the two series of models and real data, the difference of the resulting numbers from unity indicates which waveform is better and more accurate in modeling. In this method, the smaller the number is, the higher is the matching of that model with the real data. In the second method, the values of the natural logarithm (Ln) of each waveform and their differences are calculated. The positive difference of the standard deviation of the resulting values from one is considered as a measure of error. According to the second method, a high amount of epicentral distance leads to more consistency between models and real data. This results in blasts recorded from the station No.4 to be clearly visible. Also, data from the station No.2 in both methods show the lowest percentage of errors. The effects of the three factors of velocity model, the source depth and the energy of explosion were studied. The results obtained can be summarized as follows. For the velocity model, by decreasing the body wave velocities by 0.5kms−1, the correlation between the waves amplitudes diminishes in such a way that the model wave amplitudes increases with respect to the real wave amplitudes, and vice versa. For the source depth, the source depth alteration is directly related to the amplitudes of the vertical component of the waves, so that a 0.5 m increase in depth cause the amplitude to increase and decrease in depth causes the amplitude to decrease. To study the effect of the amount of the energy released on waveform modeling, having epicentral distance and maximum wave amplitudes, the equivalent magnitude can be calculated in local scale (ml) and by changing that, the released energy can be indirectly incorporated in modeling.

One of the important challenges in the coastal altimetry is the contamination of the waveforms by non-oceanic effects. These effects, which have complex behavior, appear in different forms on the waveforms. Therefore, omitting or mitigating their effects is one of the important issues in preparing the precise time series of Sea Surface Height (SSH). So far, several statistical methods have been proposed by the altimetry experts, which can be classified into two categories: waveform modification and decontamination. The main difference between these two methods is related to detecting the erroneous gates of the waveforms in which the standard deviation of the residual waveform is used for modification, and the Root-Mean-Squared-Error (RMSE) of all of the residual waveforms of the echogram is used for decontamination. The residual waveform is obtained by subtracting a waveform from the reference waveform of the echogram. In this study, a comparison is made between the efficiency of each of these methods. Some novel ideas are also presented regarding the construction of the reference waveform and the methods for trimming the gates contaminated by non-ocean effects. The gate trimming is conducted by three methods, namely, weighted averaging of inverse distance, two-step weighted averaging, and the median of the adjacent powers around the erroneous gate. In the end, the trimmed waveforms are retracked by the spline retracker, and the time series of the SSH is compared with the tide-gauge data. This algorithm, which is evaluated on the three stations of Vinga, Onsala, and Halmstad on the coast of the Baltic Sea, on Jason-2 and Jason-3 data from passes 137, 68, and 213, provides a high-quality time series of the SSH 15 km away from the coastline. The comparisons between the SSH time series derived from the trimmed and raw waveforms reveal an improvement between 2. 5 to 23. 5% in unbiased RMSE and a maximum increase of 11% in the correlation coefficient.