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.

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].