In current cellular systems, the performance of active users' devices at the cell edge suffers from the poor link quality. However, these connections also requires more resource blocks and transmission power. In order to reduce the number of resource blocks and transmission power, this paper discusses device to device communication in downlink and uplink cases of cellular communication systems. In order to optimize the connections of different network users, which means finding the best user’ s connection to a base station (minimum power consumption), which may be established through communication with other users or direct connection with the base station, and to minimize the total transmission power, different optimization methods such as gravitational search optimization, particle swarm optimization, genetic optimization algorithm and distributed strategy based on Q learning and softmax decision making methods are used. The numerical results show a power reduction of around 30 percent for these distributed communications with less computational complexity using the Q learning method compared to the case in which all users traditionally connect through the base station in a centralized way with high computational complexity.

The non-orthogonal access schemes are one of the multiple access techniques that are candidates to become an access technique for the next generation access radio. Power-domain non-orthogonal multiple-access (NOMA) is among these promising technologies. Improving the network capacity by providing massive connectivity through sharing the same spectral resources is the main advantage that this technique offers. The NOMA technique consists of exploiting the power domain which multiplex multiple users on the same resources applying a superposition coding then separating the multiplexed users at the receiver side. Due to the non-orthogonality access technique, the main disadvantage of NOMA is the presence of interferences between users. That is why this scheme is based on a successive interference cancelation (SIC) detector that separates the multiplexed signals at the receiver. In this paper, an embedded system is considered for designing and implementation of the power-NOMA For two users. The implementation is realized by employing a Zynq FPGA (Field programmable gate array) device through the Zybo-Z7 board using MATLAB/Simulink environment and Xilinx System Generator. The features offered by this device, hemps to consider the design of an uplink and a downlink scenario over Rayleigh fading channel in additive white Gaussian noise (AWGN) environment

Decoupling the uplink and downlink user association improves the throughput of heterogeneous networks (HetNets) and balances the traffic load of macro-and small-base stations. Recently, fiber-wireless HetNets (FiWi-HetNets) have been considered as viable solutions for access networks. To improve the accuracy of user association and resource allocation algorithms in FiWi-HetNets, the capacity limitation of various backhaul technologies must be considered. In this paper, we investigate the backhaul-aware decoupled uplink/downlink (UL/DL) user association, subcarrier allocation, and power control optimization problem in FiWi-HetNets. In our system model, fiber and millimeter wave (mmWave) links are used as backhaul of base stations, and the backhaul capacity limitation and minimum required transmission rate (R_min) are modeled in the optimization problem. As the formulated optimization problem is non-convex, we present a heuristic algorithm to divide the main problem into two sub-problems that are solved iteratively. The proposed algorithms are evaluated through exhaustive simulations. The results indicate that decoupling UL/DL user association improves the sum rate of FiWi-HetNets. Besides, we evaluate the effect of backhaul capacity limitation and R_min on the sum rate of FiWi-HetNets. The effect of upgrading fiber backhaul technology is also investigated to evaluate the role of fiber backhaul on the sum rate of the radio access network.

One of the major challenges in the heterogeneous networks, where different base stations with different capabilities serve users, is the access policy for establishing a communication link between the user and its serving node. To overcome this challenge in a heterogeneous network which also suffers from the backhaul constraint, a special kind of “ decoupled uplink and downlink access” policy is proposed in this paper, which let users to be served by different base stations in uplink and downlink communications. More precisely, in order to efficiently utilize the system resources, increase the users’ throughput, and guarantee the users’ fairness, a special load balancing association policy is considered in the uplink transmission and a problem which maximizes the weighted sum of users’ effective rates is solved. Simulation results show that using this association policy for the considered scenario, significantly improves the load balancing index, energy efficiency, and also users’ effective rate compared to the scenario which considers the criterion of the maximum received power of the downlink connection for both uplink and downlink transmissions. In addition we propose an algorithm which further improves the load balancing considering the backhaul constraint of the base stations and evaluate its efficiency.

Since there is no dierence between uplink and downlink subframes in the IEEE 802.16 mesh mode, both downlink and uplink tra cs are transmitted within a single time frame. Hence, in most scheduling methods, only one scheduling algorithm is used for both uplink and downlink tra c. However, because of the dierent characteristics of uplink and downlink tra c, dierent scheduling methods should be used for each of the tra c types. In this paper, we focus on the mesh centralized scheduling of downlink ow in the data subframe. After comprehensive analysis of the characteristics of downlink tra c, we propose a new algorithm, called Tra c-Aware Scheduling (TAS). In this algorithm, the downlink tra c distribution is tuned for maximum concurrent transmission rate. This goal is achieved by choosing dierent link selection criteria, such as maximum demandant sender, farthest receiver and least interfered path, based on the downlink tra c analysis results. The simulation results show that our algorithm outperforms existing methods in terms of scheduling length, link concurrency, and throughput (about 13.7% in average) for the downlink tra c. Moreover, the proposed algorithm is scalable. In particular, on average, 3% improvement is achieved in terms of scheduling length at higher tra c loads and in the number of nodes.

Massive MIMO cellular networks, despite their ability to serve multiple users simultaneously, face a significant challenge due to pilot contamination. This paper presents an innovative two-stage algorithm to reduce this contamination and increase user data rates in both uplink and downlink. The key innovation of the proposed method lies in the intelligent integration of three techniques: Soft Pilot Reuse (SPR), optimal pilot sequence selection algorithm, and Weighted Graph Coloring (WGC). This combination simultaneously addresses three fundamental issues: contamination in SPR due to fixed thresholds, increased pilot overhead in WGC, and the problem of maximizing the data rate of the user with the lowest rate. The proposed algorithm operates in two stages. In the first stage, users are divided into center and edge groups, and optimal pilot sequences are determined based on their data rates. In the second stage, using the WGC algorithm and creating an Edge-Weighted Interference Graph (EWIG), pilot contamination is reduced based on the intensity of user interference. Simulation results show that this method significantly improves system performance compared to the best existing method (WGC). In the downlink, an 11 dB improvement in Signal-to-Interference-plus-Noise Ratio (SINR) and a 0.16 bps/Hz increase in average achievable rate are observed. In the uplink, a 2.4 dB improvement in SINR and a 0.46 bps/Hz increase in average achievable rate are achieved. In terms of computational complexity, the proposed method has lower complexity compared to the WGC scheme. Moreover, energy efficiency analysis confirms the superiority of the proposed method in both uplink and downlink scenarios.

In this paper, a wireless powered communication network (WPCN) is considered, in which the hybrid access point (HAP) and the users are equipped with multiple antennas. In the downlink phase, an energy HAP transfers the energy signal to the users and in the uplink phase, users apply the harvested energy to transfer their information to the HAP using spatial division multiple access (SDMA) technology. By considering the nonlinear behavior of energy harvester in system design and aiming to maximize the sum of the rates, we propose an optimal method for designing energy pre-coding matrices, user information pre-coding matrices, and time devoted to the downlink and uplink phases. For this purpose, we rewrite the problem as a convex optimization problem by appropriate change of variables and propose a method to solve it. The simulation results show that in practical scenarios, employing the nonlinear energy harvesting model in the system design could reduce the transmitted energy, increase and the sum rate of the users.

Millimeter wave (mW) communication is one of the key enabling technologies for meeting the vast data demand growth and bandwith scarcity. It offers higher bandwidth which resuls in higher capacity. To improve the user experience in the 5G communication, it is proposed to utilize the composition of microwave (μ, W) and mW networks. On the other hand, an ultra-dense network (UDN) has been envisioned as a promising network paradigm for spectrum efficiency (SE) enhancement. In this paper, the cellular network using TDD duplexing, consists of both mW and μ, W base stations. BSs and users are distributed in indoor and outdoor environments. Our aim is to calculate the spectral efficiency for both mW and μ, W sysyems, based on the BSs and users distribution. Moreover, the effect of BS density on spectral efficiency is evaluated. Finally, the problem of maximizing the downlink rate is formulated and solved as a linear optimization problem so that the minimum uplink rate is guaranted. The simulation results show that by servicing both mW and μ, W simultaneously on uplink and downlink, high SE can be achieved and with the help of optimal resources allocation, the network’, s perfomance is improved significantly.

In this research, performance analysis for the composition of non-orthogonal and orthogonal cellular digital television broadcasting is investigated. A downlink multi-carrier layered division multiplexing (LDM) superimposed with an evolved multimedia broadcast multicast service (eMBMS). We define two broadcast service providers (BSP), which offer different radio access technology (RAT). The BER and Sum-Rate efficiency are selected as our criteria. The proposed downlink composition framework can work without a subscriber identity module (SIM card) uplink and internet protocol (IP). Mathematical analysis, based on the exact closed-form expressions, is consistent with the theory of the proposed composition LDM/eMBMS. Evaluation and performance are done based on the Monte Carlo iterative methodology. The results show that the BER and Sum-Rate performance of a composition framework outperforms compared with LDM/eMBMS individually system.

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].