International Journal Information and Communication Technology Research
Volume:5 Issue: 2, Spring 2013

Spatial diversity can be exploited by the use of cooperative communication technology. However, most of the well known cooperative protocols have some practical challenges. In this paper we introduce two disadvantages of several important cooperative diversity protocols including low spectral efficiency and requirement for perfect time and frequency synchronization of relay nodes. Then, a cooperative strategy is proposed that improves overall communication performance in comparison with non-cooperative protocols with high spectral efficiency and non synchronization problems. In this technique, we use a combination of superposition coding and network coding to achieve cooperative diversity in asymmetric wireless networks; hence the name superposition network coded cooperation (SNCC). The SNCC scheme is applied to a special but generalizable case of three users. In this case the receiver structure and error performance analysis of SNCC are presented. The results demonstrate performanceimprovement of wireless communication.

In this paper, the Filter-and-Forward strategy is developed for cooperative relays in Cognitive Radionetworks with underlay structure and frequency selective fading channels. A cost function is defined to minimize the required transmitting power of the relay networks and the secondary user. This is performed subject to keeping the power of noise and interferences at the primary receiver less than a predefined limit and an SINR above a given threshold. In this structure, a power control is also carried out on the secondary transmitter. Simulation results show that the proposed algorithm converges to an optimal solution based on the interior point method. The results show that compared to the Amplify-and-Forward strategy, we achieve a higher SINR threshold in the secondary receiver and need a lower transmitting power at the relays and secondary transmitter.

A deep spectrum sculpting is necessary to enable coexistence between a cognitive radio (CR) user and a licensed user which has low dynamic range and is susceptible to interferences. In this paper, we propose to use joint filter-bank based multicarrier system and cancellation carriers to guarantee an almost free out-of-band interference transmission and keep the quality of services of licensed adjacent bands unchanged. We investigate the performance of the proposed method with different well-known existing methods from viewpoints of the average level of out-ofband power, spectral efficiency, and computational complexity.

In this paper, we propose an optimization method to suitable locating minimum number of transmitterantennas to provide adequately signal coverage in a given indoor environment. This method is based on an integrated realized Ray-Tracing (RT) technique, so-called Ray-Tracing Engine (RTE), and Genetic Algorithm (GA). This integration provides an intelligent system in optimization process. To provide freedom in furniture placement each corner of every room contains a receiver. Therefore, we have a dense map of RSS distribution in propagation environment. According to Simulation results a full coverage using integrated RTE and GA is achieved through suitably locating three transmitters. Furthermore, GA avoids the time consuming process of antenna location finding in an exhaustive search method.

Rigorous mathematical Method of Moments (MoM) for analyzing various radiating spherical structures ispresented in this paper by using Dyadic Green's Functions (DGF) in conjunction with Mixed Potential Integral Equation (MPIE) formulation. With the aid of linear Rao-Wilton-Glisson (RWG) triangular basis functions and by converting spherical DGF to Cartesian DGF, a conformal dipole antenna over a Perfect Electric Conductor (PEC) sphere is analyzed. Mutual couplings between elements of a conformal dipole antenna array in an unbounded free space and over a conducting sphere are also investigated. Good agreement between the results obtained from the proposed method and asymptotic approximation as well as those of commercial simulator packages shows accuracy and high convergence speed of the presented method.

In this paper, a speaker-dependent speech enhancement is performed by using the codebooks. For thispurpose, making use of the STFT parameters, two codebooks are designed for speech and noise separately. In order to design the speech codebook, an adequate number of sentences of particular speakers are used. Utilizing an estimator based on a perceptually weighted distance function, we start searching within the codebooks to find the true indexes for each noisy frame. After finding the true indexes, we synthesize the enhanced speech by using the selected indexes of the speech codebook. As a modification, we suggest two methods to reduce the search time as follows: firstly, a new method for reduction of the codebook size is described. Secondly, by utilizing the relation between the spectral center-of-gravities of the speech, noise and noisy speech, the search area within the codebooks is effectively reduced. Simulation results show that the proposed method can enhance a noisy speech with low SNR. Moreover, since the proposed method is performed frame by frame and it does not use the previous frames of the noisy speech, therefore this method can enhance the noisy speech contaminated by a highly non-stationary noise.

In this paper, the distributed estimation in Wireless Sensor Network (WSN) using optimal task scheduling is looked upon. The main goal is to prolong network lifetime while the target parameter is estimated with desirable precision. The lifetime is defined as the number of rounds accomplished before network becomes nonfunctional. In order to prolong network lifetime, we determine the optimal number of active sensor nodes and the number of samples provided by each of them based on the degree of certainty (utilizing linear programming). Sensor observations from environment are quantized into messages and then directly forwarded to a fusion center where a final estimation is performed. Simulation results confirm that our optimal proposed algorithm has achieved significant efficiency when compared with other heuristic methods.