Digital audio watermarking is mainly used for ownership protection of digital audio. In this research, an audio watermarking method is presented which can be adopted in real-time situations due to its high speed in both embedding and detecting stages. This approach has a higher payload in comparison with similar recent approaches. In the proposed algorithm, which uses a time-domain synchronization, to embed the watermark, the audio signal is first split into a number of blocks. Then the watermark is embedded into the FFT components of audio signal with greater magnitudes. Unlike common audio watermarking methods that use the 1-bit embedding approach, in the proposed scheme, a 2-bit embedding approach is presented which doubles the embedding payload compared to a number of similar works. The evaluation results on different audio signals demonstrate that the new scheme is faster and more transparent compared to its counterparts. The presented watermarking is found robust enough against the common attacks like additive noise, MP3 compression, low pass filtering, re-sampling and re-quantization. Using FPGA implementation/evaluation, the time complexities of the major parts of the proposed algorithm are reported.

One of the satellite telecommunication services is the S&F service. In this article, the service characteristics are analyzed and the impact of them on the design parameters is explained. One of the challenges of telecommunication payload design is the mapping of service parameters to the technical requirements of payload components. First, analytical relationships between service parameters (the number of users, traffic, and delay) and technical requirements (network capacity and onboard memory) are presented. Then, the protocol stack and its parameters are selected with the aim of optimizing the power and network efficiency while considering the link conditions. By systematically identifying the service specification's impact on the design parameters and the design process, payload requirements in order to develop a network are easily extracted. One of the effective factors in the payload block diagram design is its reliability. The design of redundancy is proposed by considering the component's reliability and its function with the aim of achieving reliability and reducing fault propagation.

With the development of new information and communication technologies and the pervasive use of cyberspace, distributed denial of service (DDoS) attacks are a serious threat to online organizations. These attacks can have destructive effects, for example, on one of its effects can be in terms of the public face of the trademark and its revenue. A good way to deal with DDoS attacks is to save a signature for each attack. Today, most organizations and institutions, both national and military (military and law enforcement) face such attacks, so in this study, while trying to identify intrusion detection systems in the proposed method to produce the necessary signatures to explain. Using this method, any attack can be detected as soon as this signature is found in traffic. However, this process is not easy and the signature production process is usually time consuming and requires a lot of effort. To help solve this challenge of generating signature problems, in this research, we propose an automated method for generating data-based signatures for DDoS attacks. This study also examines the relationships between different data packets of the same attack. In fact, data packet-based digital signatures are used for attacks whose pattern and core are the same, with only minor differences in the structure of the attack. The research concludes with a proposal for a signature generation algorithm and its validation using applied tools.

This paper investigates the problem of controlling a team of quadrotors that cooperatively transport a common payload. The main contribution of this study is to propose a cooperative control algorithm based on a decentralized algorithm. This strategy is comprised of two main steps: the first one is calculating the basic control vectors for each quadrotor using Moore– Penrose theory aiming at cooperative transport of an object and the second one is combining these vectors with individual control vectors, which are obtained from a closed-loop non-linear robust controller. In this regard, a nonlinear robust controller is designed based on Second Order Sliding Mode (SOSMC) approach using Extended Kalman-Bucy Filter (EKBF) to estimate the unmeasured states which is capable of facing external disturbances. The distinctive features of this approach include robustness against model uncertainties along with high flexibility in designing the control parameters to have an optimal solution for the nonlinear dynamics of the system. Design of the controller is based on Lyapunov method which can provide the stability of the end-effecter during the tracking of the desired trajectory. Finally, simulation results are given to illustrate the effectiveness of the proposed method for the cooperative quadrotors to transport a common payload in various maneuvers.

Remote sensing using small spacecraft arising from multi-objective economic activity problems is getting more and more developed. These satellites require very accurate pointing to specific locations of interest, with high reliability and small latency. The space borne imaging systems always attempted to achieve the highest ground resolution possible with the available technology at the given time. Also mass, volume and power consumption of the spacecrafts and instruments followed the trend to miniaturization. But the most promising prospects for high resolution imaging with remote sensing satellites are connected with passive optical systems, especially push broom systems. In this paper optical system design process is described and different parameters of this process such as MTF, SNR, FOV, aperture diameter, stability and pointing, scanning schemes, detector selection, and target radiance are simulated and analyzed.

The purpose of this paper is designing a communications system and the required protocols for store and forward (S&F) payload of a LEO satellite. Considering users' dispersion in diverse places, split channel reservation multiple access (SRMA) technique, is applied through users to access the uplink channel. Different modulation methods are analyzed and PSK modulation and non-coherent FSK modulation are suggested for payload downlink and uplink, respectively. An error detection technique based on Reed-Solomon (255, 233) is used in the payload to improve the link performance and SR-ARQ approach is selected which is more efficient than other ARQ techniques. Moreover, communication protocols of the users' network, file transmitting to the satellite and file receiving from that along with their implementation are explained in terms of software. Finally, an appropriate hardware is proposed for this subsystem. Comparison of our design and the design strategy suggested in [4] show that onboard hardware complexity of current paper is less than [4]. Furthermore, our coding, modulation and protocol and Doppler compensation scenario is more efficient than [4].

In this paper, stray lights in optical system of remote sensing satellite camera is simulated. For this purpose, stray lights, sources of production and their destructive effects on the image quality is studied. Moreover, mechanisms to deal with these unwanted lights are presented. Then, the effect of optical housing and surface coatings on the performance of stray light in satellite camera, has been studied by the results of the simulation. Finally an optimal design includes a set of different techniques for improving the performance of the considered camera was selected. Simulation results show that by this method, at large angles, stray lights can be completely eliminated whereas at angles near the FOV, stray lights intensities can be very much reduced namely up to 100000 times of their original intensity without almost no serious disturbance in the camera’s field of view.

In this paper, a step-by-step laboratory procedure for performing a satellite's payload’s alignment measurement is presented. Four highly accurate theodolites are used along with two or more alignment corner cube to accurately extract the final attitude. Theodolites are arranged around the satellite in such a way that they have a clear direct view of the alignment cubes mounted on the payload and the satellite. Two theodolites should point to the payload’s alignment cube and the other two theodolites must point to the satellite’s alignment cube. Each theodolite must see at least one other theodolite, directly. Finally, by forming the coordinates systems of the payload and satellite in the theodolites coordinate system along with using the coordinate transfer matrices, the payload alignment correction matrix will be extracted in detail. The total method accuracy is within the order of few arcseconds.