جستجوی مقالات مرتبط با کلیدواژه « Non-orthogonal Multiple Access » در نشریات گروه « فنی و مهندسی »

The use of new physical layer security approaches such as intelligent reflective surfaces as well as the use of existing capabilities in the mobile network such as the participation of network users as network partners are solutions that can be very effective in the next generation of mobile telecommunications to improve and increase the total Secrecy Rate in the physical layer.The proposed solution for improving the secrecy rate of the transmitted signal in the physical layer performed by closed-form solution to the described system. In this paper, we analyzed a network consisting of a gNB, two users, an IRS and an eavesdropper in an environment full of obstacles. Using Simulations, we evaluate our solution mathematically and investigate the effect of the eavesdropper location on the total secrecy rate. Also, the analysis and simulation of secrecy rate for the proposed network is performed by taking into account practical network considerations such as changing the location of the Eavesdropper in the network. In addition, the impact of changing the number of elements of smart surface arrays has been analyzed. The numerical results reveal that increasing IRS elements can enhance the ergodic secrecy rate, the reason is that increasing of IRS elements can focuses the main beam of data signal on the first user which increase secrecy rate. Finally, we compare the performance of the OMA and NOMA techniques in the proposed system model. We show that the NOMA technique provides 50% more ergodic secrecy rate compared to the OMA technique.

In this paper, a downlink network with two users as transmitter and relay, respectively, and a central station as a receiver is considered. The aim is to determine the optimal coefficient of non-orthogonal signal symbols and the optimal power allocation in the source-relay in order to maximize the average total rate in a cooperative communication system using the non-orthogonal multiple access technique. To achieve these goals, the average total rate of the cooperative communication system with non-orthogonal multiple access with decode and forward relay in the independent Rayleigh channel was calculated. Then, in the first step, the optimization problem of the non-orthogonal symbols coefficient is mathematically expressed for each power allocation and a closed form solution is proposed. In the second step, the power allocation optimization for the source-relay was introduced and solved. Finally, the joint optimization problem of the non-orthogonal symbols coefficient and power allocation is investigated and an algorithm proposed for the joint optimization problem. The proposed algorithm shows that the joint optimization of the non-orthogonal symbols coefficient and power allocation achieve a higher average rate than the separate optimization of each of these parameters. Also, simulations and numerical results are presented to confirm the theoretical equation, where the simulations show the 3 dB gain for the optimized system using the proposed algorithm compared to the non-optimized system.

Mobile Edge computing is a new paradigm that allows users to combat the constraints of mobile devices For overcoming the long delay of cloud computing which decreases the quality of service, the users send their data to the server which is located at the edge of the network instead of sending a part of the program to a cloud server which is located in place far from the users. In this paper, a system which consists of a cell and several users is considered in which the network users to accomplish their computations request service from cloud and edge servers that are participating with each other. It is assumed that the users access the radio spectrum by a Non-orthogonal Multiple Access (NOMA) method and the queue theory is used for modeling the problem from the users and server sides. The main goal is to minimize the total users' energy consumption, the delay in users' receiving service, and the whole cost of using servers. The mathematical model of this problem would result in a multi-objective constraint non-convex optimization problem. SCA method is used to achieve the globally optimum solution. Through the simulation results, it is shown that by the applied assumptions in the proposed model, the amount of energy, delay and total cost of network is decreased around 50%.

In this paper we propose a new resource allocation framework for unmanned aerial vehicle (UAV)-based cooperative networks. In the considered network, three node exist: one transmitter and two receivers. In addition, we assume that a UAV is used in the network as a decode-and-forward (DF) relay. For the channel model, we only consider the path-loss. We assume that the information transmission is performed only when a line-of-sight (LoS) connection could be established between communicating parties. The UAV moves from the transmitter towards the receivers. UAV receives the information from the transmitter, and when it approaches to the receivers, it simultaneously transmits information intended for both the receivers using non-orthogonal multiple access (NOMA) technique. The resulting optimization problem is non-convex and hard to solve. To tackle the problem, we adopt the successive convex approximation (SCA) technique where the original problem is approximated by a convex problem which could be solved easily using existing optimization tools like CVX. Finally, the proposed framework is evaluated using simulation for different network parameters. Simulation results confirm the efficiency of the proposed scheme.