Yijin Pan

On consideration of content preference and sharing willingness in D2D assisted offloading

Device-to-device (D2D) assisted offloading heavily depends on the participation of human users. The content preference and sharing willingness of human users are two crucial factors in the D2D assisted offloading. In this paper, with consideration of these two factors, the optimal content pushing strategy is investigated by formulating an optimization problem to maximize the offloading gain measured by the offloaded traffic. Users are placed into groups according to their content preferences and share content with intergroup and intragroup users at different sharing probabilities. Although the optimization problem is nonconvex, the closed-form optimal solution for a special case is obtained, when the sharing probabilities for intergroup and intragroup users are the same. Furthermore, an alternative group optimization (AGO) algorithm is proposed to solve the general case of the optimization problem. Finally, simulation results are provided to demonstrate the offloading performance achieved by the optimal pushing strategy for the special case and AGO algorithm. An interesting conclusion drawn is that the group with the largest number of interested users is not necessarily given the highest pushing probability. It is more important to give high pushing probability to users with high sharing willingness.

Downlink Resource Allocation and Power Control for Device-to-Device Communication Underlaying Cellular Networks

This letter investigates the resource allocation and power control for both device-to-device (D2D) pairs and cellular users (CUs) in D2D communication underlaying single-cell cellular networks, where multiple D2D pairs can share the same resources with CUs. Our goal is to maximize the sum rate of D2D pairs subject to the rate requirements for all CUs and power requirements for both D2D pairs and the base station. We first give the optimal conditions for the resource allocation of D2D pairs and power control of CUs and then propose an iterative resource allocation and power control algorithm. Numerical results show that the proposed algorithm achieves higher sum rate of D2D pairs than the existing schemes.

On the Optimality of Power Allocation for NOMA Downlinks With Individual QoS Constraints

This letter investigates a power allocation problem in a downlink single-input single-output non-orthogonal multiple access (NOMA) system. Our goal is to maximize the sum rate of users subject to minimum user rate requirements. We rigorously prove the optimal user decoding order, and show that the sum rate maximization problem is convex, which guarantees the globally optimal solution. Numerical results validate the performance gain by the proposed NOMA compared with conventional schemes.

Iterative Receiver for Flip-OFDM in Optical Wireless Communication

To guarantee nonnegative signals in optical wireless communication systems, flipped orthogonal frequency division multiplexing (Flip-OFDM) transmits the positive and negative parts of the signal over two consecutive OFDM subframes (positive subframe and negative subfame, respectively). The conventional receiver for Flip-OFDM recovers the data by subtracting the negative subframe from the positive one. However, the signal analysis shows that the signals in the two subframes contain the information of the transmitted data and can be used together to decode the data. An iterative receiver is then proposed to improve the transmission performance of Flip-OFDM by exploiting the signals in both subframes. Simulation results show that the proposed iterative receiver provides significant signal-to-noise ratio gain over the conventional receiver. Moreover, the iterative receiver also outperforms the existing advanced receiver.

Energy-Efficient Resource Allocation in D2D Underlaid Cellular Uplinks

In this letter, we study the joint channel allocation and power control problem to maximize the energy efficiency (EE) of device-to-device (D2D) links in a D2D underlaid cellular network. Due to the location dispersion of D2D pairs and short-distance D2D transmission, it should be preferred that multiple D2D pairs can simultaneously share the resource with cellular users (CUs). To address the nonconvexity of the EE maximization problem, we divide the original problem into two subproblems and propose an iterative algorithm with low complexity to solve it. Simulation results show that the proposed algorithm converges rapidly and the EE of D2D links can be significantly improved compared with existing methods especially for an increasing number of CUs.

Power control and resource allocation for multi-cell OFDM networks

In this paper, we consider the problem of minimizing the total transmit power with power control and resource allocation in OFDM networks where mutual interference exists among cells. The signal-to-interference-and-noise-ratio (SINR) relation is interpreted by the load and power coupling model, where every resource is available for each user with a probability. These probability variables can be also named as load vector. To solve this problem, we develop one low-complexity distributed power control and resource allocation algorithm. Specially, each BS updates its load vector, power vector, rate vector information and broadcasts it to all other BSs. Having collected all the information, each BS calculates its own load vector, power vector and rate vector by solving a convex program and a linear program. Compared with the existing optimization algorithm, where each resource is allocated to at most one user in a period of time, our algorithm has lower computational complexity. Numerical results verify the effectiveness and convergence of our proposed algorithm.

Resource Allocation for D2D Communications Underlaying a NOMA-Based Cellular Network

This letter investigates the power control and channel assignment problem in device-to-device (D2D) communications underlaying a non-orthogonal multiple access (NOMA) cellular network. With the successive interference cancellation decoding order constraints, our target is to maximize the sum rate of D2D pairs while guaranteeing the minimum rate requirements of NOMA-based cellular users. Specifically, the optimal conditions for power control of cellular users on each subchannel are derived first. Then, based on these results, we propose a dual-based iterative algorithm to solve the resource allocation problem. Simulation results validate the superiority of proposed resource allocation algorithm over the existing orthogonal multiple access scheme.

Energy Minimization in Machine-to-Machine Systems with Energy Harvesting

In this paper, we investigate the sum energy minimization problem in an uplink machine-to- machine (M2M) system with energy harvesting. To solve this nonconvex sum energy minimization problem, we first transform it into an equivalent convex problem and provide the optimal condition of the original problem. Then, we propose a low- complexity iterative scheme, which yields the optimal solution. The complexity of the proposed scheme is also analyzed. Numerical results show that the proposed scheme can achieve good performance.

Energy-Efficient Optimization with Cell Load Coupling for OFDM Networks

In this paper, we consider the problem of maximizing the sum energy efficiency (EE) for LTE networks where the interferences occur between cells. Cell load, transmit rate and transmit power, where cell load demonstrates the average resource usage in a cell, are considered in the signal-to- interference-and-noise-ratio (SINR) model. Exploiting the properties of sum EE, we prove that operating at full load is optimal and provide a distributed power control algorithm. With all other powers fixed, we transform the original nonconvex optimization problem in fractional form into an equivalent optimization problem in subtractive form. In high SINR situation, the transformed problem in subtractive form is proved a convex problem. Numerical results demonstrate the remarkable improvements in terms of EE.

Cell load coupling with power control for LTE network planning

We consider the problem of optimization of sum cell load with the constraints of cell load coupling and power control in LTE network. Our system model characterizes the coupling relation between cell load and power, considering non-uniform traffic demand and interference between cells. Solving the problem involves optimization with fixed power, and optimization with power control. We prove the the convergence of fixed-point iteration, which is used in optimization with fixed power, and provide sufficient and necessary conditions for the feasibility of cell load coupling with power control. Numerical results illustrate that our proposed solutions are superior to the conventional power allocation schemes.